Adding upstream version 7.0.14-dfsg.upstream/7.0.14-dfsg

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 11182 insertions, 0 deletions

diff --git a/src/VBox/Main/src-server/MediumImpl.cpp b/src/VBox/Main/src-server/MediumImpl.cpp
new file mode 100644
index 00000000..abcdd910
--- /dev/null
+++ b/src/VBox/Main/src-server/MediumImpl.cpp
@@ -0,0 +1,11182 @@
+/* $Id: MediumImpl.cpp $ */
+/** @file
+ * VirtualBox COM class implementation
+ */
+
+/*
+ * Copyright (C) 2008-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_MAIN_MEDIUM
+#include "MediumImpl.h"
+#include "MediumIOImpl.h"
+#include "TokenImpl.h"
+#include "ProgressImpl.h"
+#include "SystemPropertiesImpl.h"
+#include "VirtualBoxImpl.h"
+#include "ExtPackManagerImpl.h"
+
+#include "AutoCaller.h"
+#include "Global.h"
+#include "LoggingNew.h"
+#include "ThreadTask.h"
+#include "VBox/com/MultiResult.h"
+#include "VBox/com/ErrorInfo.h"
+
+#include <VBox/err.h>
+#include <VBox/settings.h>
+
+#include <iprt/param.h>
+#include <iprt/path.h>
+#include <iprt/file.h>
+#include <iprt/cpp/utils.h>
+#include <iprt/memsafer.h>
+#include <iprt/base64.h>
+#include <iprt/vfs.h>
+#include <iprt/fsvfs.h>
+
+#include <VBox/vd.h>
+
+#include <algorithm>
+#include <list>
+#include <set>
+#include <map>
+
+
+typedef std::list<Guid> GuidList;
+
+
+#ifdef VBOX_WITH_EXTPACK
+static const char g_szVDPlugin[] = "VDPluginCrypt";
+#endif
+
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Medium data definition
+//
+////////////////////////////////////////////////////////////////////////////////
+#if __cplusplus < 201700 && RT_GNUC_PREREQ(11,0) /* gcc/libstdc++ 12.1.1 errors out here because unary_function is deprecated */
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+#endif
+
+struct SnapshotRef
+{
+    /** Equality predicate for stdc++. */
+    struct EqualsTo
+#if __cplusplus < 201700 /* deprecated in C++11, removed in C++17. */
+        : public std::unary_function <SnapshotRef, bool>
+#endif
+    {
+        explicit EqualsTo(const Guid &aSnapshotId) : snapshotId(aSnapshotId) {}
+
+#if __cplusplus < 201700 /* deprecated in C++11, removed in C++17. */
+        bool operator()(const argument_type &aThat) const
+#else
+        bool operator()(const SnapshotRef &aThat) const
+#endif
+        {
+            return aThat.snapshotId == snapshotId;
+        }
+
+        const Guid snapshotId;
+    };
+
+    SnapshotRef(const Guid &aSnapshotId,
+                const int &aRefCnt = 1)
+        : snapshotId(aSnapshotId),
+          iRefCnt(aRefCnt) {}
+
+    Guid snapshotId;
+    /*
+     * The number of attachments of the medium in the same snapshot.
+     * Used for MediumType_Readonly. It is always equal to 1 for other types.
+     * Usual int is used because any changes in the BackRef are guarded by
+     * AutoWriteLock.
+     */
+    int  iRefCnt;
+};
+
+/** Describes how a machine refers to this medium. */
+struct BackRef
+{
+    /** Equality predicate for stdc++. */
+    struct EqualsTo
+#if __cplusplus < 201700 /* deprecated in C++11, removed in C++17. */
+        : public std::unary_function <BackRef, bool>
+#endif
+    {
+        explicit EqualsTo(const Guid &aMachineId) : machineId(aMachineId) {}
+
+#if __cplusplus < 201700 /* deprecated in C++11, removed in C++17. */
+        bool operator()(const argument_type &aThat) const
+#else
+        bool operator()(const BackRef &aThat) const
+#endif
+        {
+            return aThat.machineId == machineId;
+        }
+
+        const Guid machineId;
+    };
+
+    BackRef(const Guid &aMachineId,
+            const Guid &aSnapshotId = Guid::Empty)
+        : machineId(aMachineId),
+          iRefCnt(1),
+          fInCurState(aSnapshotId.isZero())
+    {
+        if (aSnapshotId.isValid() && !aSnapshotId.isZero())
+            llSnapshotIds.push_back(SnapshotRef(aSnapshotId));
+    }
+
+    Guid machineId;
+    /*
+     * The number of attachments of the medium in the same machine.
+     * Used for MediumType_Readonly. It is always equal to 1 for other types.
+     * Usual int is used because any changes in the BackRef are guarded by
+     * AutoWriteLock.
+     */
+    int iRefCnt;
+    bool fInCurState : 1;
+    std::list<SnapshotRef> llSnapshotIds;
+};
+
+typedef std::list<BackRef> BackRefList;
+
+#if __cplusplus < 201700 && RT_GNUC_PREREQ(11,0)
+# pragma GCC diagnostic pop
+#endif
+
+
+struct Medium::Data
+{
+    Data()
+        : pVirtualBox(NULL),
+          state(MediumState_NotCreated),
+          variant(MediumVariant_Standard),
+          size(0),
+          readers(0),
+          preLockState(MediumState_NotCreated),
+          queryInfoSem(LOCKCLASS_MEDIUMQUERY),
+          queryInfoRunning(false),
+          type(MediumType_Normal),
+          devType(DeviceType_HardDisk),
+          logicalSize(0),
+          hddOpenMode(OpenReadWrite),
+          autoReset(false),
+          hostDrive(false),
+          implicit(false),
+          fClosing(false),
+          uOpenFlagsDef(VD_OPEN_FLAGS_IGNORE_FLUSH),
+          numCreateDiffTasks(0),
+          vdDiskIfaces(NULL),
+          vdImageIfaces(NULL),
+          fMoveThisMedium(false)
+    { }
+
+    /** weak VirtualBox parent */
+    VirtualBox * const pVirtualBox;
+
+    // pParent and llChildren are protected by VirtualBox::i_getMediaTreeLockHandle()
+    ComObjPtr<Medium> pParent;
+    MediaList llChildren;           // to add a child, just call push_back; to remove
+                                    // a child, call child->deparent() which does a lookup
+
+    GuidList llRegistryIDs;         // media registries in which this medium is listed
+
+    const Guid id;
+    Utf8Str strDescription;
+    MediumState_T state;
+    MediumVariant_T variant;
+    Utf8Str strLocationFull;
+    uint64_t size;
+    Utf8Str strLastAccessError;
+
+    BackRefList backRefs;
+
+    size_t readers;
+    MediumState_T preLockState;
+
+    /** Special synchronization for operations which must wait for
+     * Medium::i_queryInfo in another thread to complete. Using a SemRW is
+     * not quite ideal, but at least it is subject to the lock validator,
+     * unlike the SemEventMulti which we had here for many years. Catching
+     * possible deadlocks is more important than a tiny bit of efficiency. */
+    RWLockHandle queryInfoSem;
+    bool queryInfoRunning : 1;
+
+    const Utf8Str strFormat;
+    ComObjPtr<MediumFormat> formatObj;
+
+    MediumType_T type;
+    DeviceType_T devType;
+    uint64_t logicalSize;
+
+    HDDOpenMode hddOpenMode;
+
+    bool autoReset : 1;
+
+    /** New UUID to be set on the next Medium::i_queryInfo call. */
+    const Guid uuidImage;
+    /** New parent UUID to be set on the next Medium::i_queryInfo call. */
+    const Guid uuidParentImage;
+
+/** @todo r=bird: the boolean bitfields are pointless if they're not grouped! */
+    bool hostDrive : 1;
+
+    settings::StringsMap mapProperties;
+
+    bool implicit : 1;
+    /** Flag whether the medium is in the process of being closed. */
+    bool fClosing: 1;
+
+    /** Default flags passed to VDOpen(). */
+    unsigned uOpenFlagsDef;
+
+    uint32_t numCreateDiffTasks;
+
+    Utf8Str vdError;        /*< Error remembered by the VD error callback. */
+
+    VDINTERFACEERROR vdIfError;
+
+    VDINTERFACECONFIG vdIfConfig;
+
+    /** The handle to the default VD TCP/IP interface. */
+    VDIFINST          hTcpNetInst;
+
+    PVDINTERFACE vdDiskIfaces;
+    PVDINTERFACE vdImageIfaces;
+
+    /** Flag if the medium is going to move to a new
+     *  location. */
+    bool fMoveThisMedium;
+    /** new location path  */
+    Utf8Str strNewLocationFull;
+};
+
+typedef struct VDSOCKETINT
+{
+    /** Socket handle. */
+    RTSOCKET hSocket;
+} VDSOCKETINT, *PVDSOCKETINT;
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Globals
+//
+////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Medium::Task class for asynchronous operations.
+ *
+ * @note Instances of this class must be created using new() because the
+ *       task thread function will delete them when the task is complete.
+ *
+ * @note The constructor of this class adds a caller on the managed Medium
+ *       object which is automatically released upon destruction.
+ */
+class Medium::Task : public ThreadTask
+{
+public:
+    Task(Medium *aMedium, Progress *aProgress, bool fNotifyAboutChanges = true)
+        : ThreadTask("Medium::Task"),
+          mVDOperationIfaces(NULL),
+          mMedium(aMedium),
+          mMediumCaller(aMedium),
+          mProgress(aProgress),
+          mVirtualBoxCaller(NULL),
+          mNotifyAboutChanges(fNotifyAboutChanges)
+    {
+        AssertReturnVoidStmt(aMedium, mHrc = E_FAIL);
+        mHrc = mMediumCaller.hrc();
+        if (FAILED(mHrc))
+            return;
+
+        /* Get strong VirtualBox reference, see below. */
+        VirtualBox *pVirtualBox = aMedium->m->pVirtualBox;
+        mVirtualBox = pVirtualBox;
+        mVirtualBoxCaller.attach(pVirtualBox);
+        mHrc = mVirtualBoxCaller.hrc();
+        if (FAILED(mHrc))
+            return;
+
+        /* Set up a per-operation progress interface, can be used freely (for
+         * binary operations you can use it either on the source or target). */
+        if (mProgress)
+        {
+            mVDIfProgress.pfnProgress = aProgress->i_vdProgressCallback;
+            int vrc = VDInterfaceAdd(&mVDIfProgress.Core,
+                                     "Medium::Task::vdInterfaceProgress",
+                                     VDINTERFACETYPE_PROGRESS,
+                                     mProgress,
+                                     sizeof(mVDIfProgress),
+                                     &mVDOperationIfaces);
+            AssertRC(vrc);
+            if (RT_FAILURE(vrc))
+                mHrc = E_FAIL;
+        }
+    }
+
+    // Make all destructors virtual. Just in case.
+    virtual ~Task()
+    {
+        /* send the notification of completion.*/
+        if (   isAsync()
+            && !mProgress.isNull())
+            mProgress->i_notifyComplete(mHrc);
+    }
+
+    HRESULT hrc() const { return mHrc; }
+    bool isOk() const { return SUCCEEDED(hrc()); }
+    bool NotifyAboutChanges() const { return mNotifyAboutChanges; }
+
+    const ComPtr<Progress>& GetProgressObject() const {return mProgress;}
+
+    /**
+     * Runs Medium::Task::executeTask() on the current thread
+     * instead of creating a new one.
+     */
+    HRESULT runNow()
+    {
+        LogFlowFuncEnter();
+
+        mHrc = executeTask();
+
+        LogFlowFunc(("hrc=%Rhrc\n", mHrc));
+        LogFlowFuncLeave();
+        return mHrc;
+    }
+
+    /**
+     * Implementation code for the "create base" task.
+     * Used as function for execution from a standalone thread.
+     */
+    void handler()
+    {
+        LogFlowFuncEnter();
+        try
+        {
+            mHrc = executeTask(); /* (destructor picks up mHrc, see above) */
+            LogFlowFunc(("hrc=%Rhrc\n", mHrc));
+        }
+        catch (...)
+        {
+            LogRel(("Some exception in the function Medium::Task:handler()\n"));
+        }
+
+        LogFlowFuncLeave();
+    }
+
+    PVDINTERFACE mVDOperationIfaces;
+
+    const ComObjPtr<Medium> mMedium;
+    AutoCaller mMediumCaller;
+
+protected:
+    HRESULT mHrc;
+
+private:
+    virtual HRESULT executeTask() = 0;
+
+    const ComObjPtr<Progress> mProgress;
+
+    VDINTERFACEPROGRESS mVDIfProgress;
+
+    /* Must have a strong VirtualBox reference during a task otherwise the
+     * reference count might drop to 0 while a task is still running. This
+     * would result in weird behavior, including deadlocks due to uninit and
+     * locking order issues. The deadlock often is not detectable because the
+     * uninit uses event semaphores which sabotages deadlock detection. */
+    ComObjPtr<VirtualBox> mVirtualBox;
+    AutoCaller mVirtualBoxCaller;
+    bool mNotifyAboutChanges;
+};
+
+class Medium::CreateBaseTask : public Medium::Task
+{
+public:
+    CreateBaseTask(Medium *aMedium,
+                   Progress *aProgress,
+                   uint64_t aSize,
+                   MediumVariant_T aVariant,
+                   bool fNotifyAboutChanges = true)
+        : Medium::Task(aMedium, aProgress, fNotifyAboutChanges),
+          mSize(aSize),
+          mVariant(aVariant)
+    {
+        m_strTaskName = "createBase";
+    }
+
+    uint64_t mSize;
+    MediumVariant_T mVariant;
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskCreateBaseHandler(*this);
+    }
+};
+
+class Medium::CreateDiffTask : public Medium::Task
+{
+public:
+    CreateDiffTask(Medium *aMedium,
+                   Progress *aProgress,
+                   Medium *aTarget,
+                   MediumVariant_T aVariant,
+                   MediumLockList *aMediumLockList,
+                   bool fKeepMediumLockList = false,
+                   bool fNotifyAboutChanges = true)
+        : Medium::Task(aMedium, aProgress, fNotifyAboutChanges),
+          mpMediumLockList(aMediumLockList),
+          mTarget(aTarget),
+          mVariant(aVariant),
+          mTargetCaller(aTarget),
+          mfKeepMediumLockList(fKeepMediumLockList)
+    {
+        AssertReturnVoidStmt(aTarget != NULL, mHrc = E_FAIL);
+        mHrc = mTargetCaller.hrc();
+        if (FAILED(mHrc))
+            return;
+        m_strTaskName = "createDiff";
+    }
+
+    ~CreateDiffTask()
+    {
+        if (!mfKeepMediumLockList && mpMediumLockList)
+            delete mpMediumLockList;
+    }
+
+    MediumLockList *mpMediumLockList;
+
+    const ComObjPtr<Medium> mTarget;
+    MediumVariant_T mVariant;
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskCreateDiffHandler(*this);
+    }
+
+    AutoCaller mTargetCaller;
+    bool mfKeepMediumLockList;
+};
+
+class Medium::CloneTask : public Medium::Task
+{
+public:
+    CloneTask(Medium *aMedium,
+              Progress *aProgress,
+              Medium *aTarget,
+              MediumVariant_T aVariant,
+              Medium *aParent,
+              uint32_t idxSrcImageSame,
+              uint32_t idxDstImageSame,
+              MediumLockList *aSourceMediumLockList,
+              MediumLockList *aTargetMediumLockList,
+              bool fKeepSourceMediumLockList = false,
+              bool fKeepTargetMediumLockList = false,
+              bool fNotifyAboutChanges = true,
+              uint64_t aTargetLogicalSize = 0)
+        : Medium::Task(aMedium, aProgress, fNotifyAboutChanges),
+          mTarget(aTarget),
+          mParent(aParent),
+          mTargetLogicalSize(aTargetLogicalSize),
+          mpSourceMediumLockList(aSourceMediumLockList),
+          mpTargetMediumLockList(aTargetMediumLockList),
+          mVariant(aVariant),
+          midxSrcImageSame(idxSrcImageSame),
+          midxDstImageSame(idxDstImageSame),
+          mTargetCaller(aTarget),
+          mParentCaller(aParent),
+          mfKeepSourceMediumLockList(fKeepSourceMediumLockList),
+          mfKeepTargetMediumLockList(fKeepTargetMediumLockList)
+    {
+        AssertReturnVoidStmt(aTarget != NULL, mHrc = E_FAIL);
+        mHrc = mTargetCaller.hrc();
+        if (FAILED(mHrc))
+            return;
+        /* aParent may be NULL */
+        mHrc = mParentCaller.hrc();
+        if (FAILED(mHrc))
+            return;
+        AssertReturnVoidStmt(aSourceMediumLockList != NULL, mHrc = E_FAIL);
+        AssertReturnVoidStmt(aTargetMediumLockList != NULL, mHrc = E_FAIL);
+        m_strTaskName = "createClone";
+    }
+
+    ~CloneTask()
+    {
+        if (!mfKeepSourceMediumLockList && mpSourceMediumLockList)
+            delete mpSourceMediumLockList;
+        if (!mfKeepTargetMediumLockList && mpTargetMediumLockList)
+            delete mpTargetMediumLockList;
+    }
+
+    const ComObjPtr<Medium> mTarget;
+    const ComObjPtr<Medium> mParent;
+    uint64_t mTargetLogicalSize;
+    MediumLockList *mpSourceMediumLockList;
+    MediumLockList *mpTargetMediumLockList;
+    MediumVariant_T mVariant;
+    uint32_t midxSrcImageSame;
+    uint32_t midxDstImageSame;
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskCloneHandler(*this);
+    }
+
+    AutoCaller mTargetCaller;
+    AutoCaller mParentCaller;
+    bool mfKeepSourceMediumLockList;
+    bool mfKeepTargetMediumLockList;
+};
+
+class Medium::MoveTask : public Medium::Task
+{
+public:
+    MoveTask(Medium *aMedium,
+              Progress *aProgress,
+              MediumVariant_T aVariant,
+              MediumLockList *aMediumLockList,
+              bool fKeepMediumLockList = false,
+              bool fNotifyAboutChanges = true)
+        : Medium::Task(aMedium, aProgress, fNotifyAboutChanges),
+          mpMediumLockList(aMediumLockList),
+          mVariant(aVariant),
+          mfKeepMediumLockList(fKeepMediumLockList)
+    {
+        AssertReturnVoidStmt(aMediumLockList != NULL, mHrc = E_FAIL);
+        m_strTaskName = "createMove";
+    }
+
+    ~MoveTask()
+    {
+        if (!mfKeepMediumLockList && mpMediumLockList)
+            delete mpMediumLockList;
+    }
+
+    MediumLockList *mpMediumLockList;
+    MediumVariant_T mVariant;
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskMoveHandler(*this);
+    }
+
+    bool mfKeepMediumLockList;
+};
+
+class Medium::CompactTask : public Medium::Task
+{
+public:
+    CompactTask(Medium *aMedium,
+                Progress *aProgress,
+                MediumLockList *aMediumLockList,
+                bool fKeepMediumLockList = false,
+                bool fNotifyAboutChanges = true)
+        : Medium::Task(aMedium, aProgress, fNotifyAboutChanges),
+          mpMediumLockList(aMediumLockList),
+          mfKeepMediumLockList(fKeepMediumLockList)
+    {
+        AssertReturnVoidStmt(aMediumLockList != NULL, mHrc = E_FAIL);
+        m_strTaskName = "createCompact";
+    }
+
+    ~CompactTask()
+    {
+        if (!mfKeepMediumLockList && mpMediumLockList)
+            delete mpMediumLockList;
+    }
+
+    MediumLockList *mpMediumLockList;
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskCompactHandler(*this);
+    }
+
+    bool mfKeepMediumLockList;
+};
+
+class Medium::ResizeTask : public Medium::Task
+{
+public:
+    ResizeTask(Medium *aMedium,
+               uint64_t aSize,
+               Progress *aProgress,
+               MediumLockList *aMediumLockList,
+               bool fKeepMediumLockList = false,
+               bool fNotifyAboutChanges = true)
+        : Medium::Task(aMedium, aProgress, fNotifyAboutChanges),
+          mSize(aSize),
+          mpMediumLockList(aMediumLockList),
+          mfKeepMediumLockList(fKeepMediumLockList)
+    {
+        AssertReturnVoidStmt(aMediumLockList != NULL, mHrc = E_FAIL);
+        m_strTaskName = "createResize";
+    }
+
+    ~ResizeTask()
+    {
+        if (!mfKeepMediumLockList && mpMediumLockList)
+            delete mpMediumLockList;
+    }
+
+    uint64_t        mSize;
+    MediumLockList *mpMediumLockList;
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskResizeHandler(*this);
+    }
+
+    bool mfKeepMediumLockList;
+};
+
+class Medium::ResetTask : public Medium::Task
+{
+public:
+    ResetTask(Medium *aMedium,
+              Progress *aProgress,
+              MediumLockList *aMediumLockList,
+              bool fKeepMediumLockList = false,
+              bool fNotifyAboutChanges = true)
+        : Medium::Task(aMedium, aProgress, fNotifyAboutChanges),
+          mpMediumLockList(aMediumLockList),
+          mfKeepMediumLockList(fKeepMediumLockList)
+    {
+        m_strTaskName = "createReset";
+    }
+
+    ~ResetTask()
+    {
+        if (!mfKeepMediumLockList && mpMediumLockList)
+            delete mpMediumLockList;
+    }
+
+    MediumLockList *mpMediumLockList;
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskResetHandler(*this);
+    }
+
+    bool mfKeepMediumLockList;
+};
+
+class Medium::DeleteTask : public Medium::Task
+{
+public:
+    DeleteTask(Medium *aMedium,
+               Progress *aProgress,
+               MediumLockList *aMediumLockList,
+               bool fKeepMediumLockList = false,
+               bool fNotifyAboutChanges = true)
+        : Medium::Task(aMedium, aProgress, fNotifyAboutChanges),
+          mpMediumLockList(aMediumLockList),
+          mfKeepMediumLockList(fKeepMediumLockList)
+    {
+        m_strTaskName = "createDelete";
+    }
+
+    ~DeleteTask()
+    {
+        if (!mfKeepMediumLockList && mpMediumLockList)
+            delete mpMediumLockList;
+    }
+
+    MediumLockList *mpMediumLockList;
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskDeleteHandler(*this);
+    }
+
+    bool mfKeepMediumLockList;
+};
+
+class Medium::MergeTask : public Medium::Task
+{
+public:
+    MergeTask(Medium *aMedium,
+              Medium *aTarget,
+              bool fMergeForward,
+              Medium *aParentForTarget,
+              MediumLockList *aChildrenToReparent,
+              Progress *aProgress,
+              MediumLockList *aMediumLockList,
+              bool fKeepMediumLockList = false,
+              bool fNotifyAboutChanges = true)
+        : Medium::Task(aMedium, aProgress, fNotifyAboutChanges),
+          mTarget(aTarget),
+          mfMergeForward(fMergeForward),
+          mParentForTarget(aParentForTarget),
+          mpChildrenToReparent(aChildrenToReparent),
+          mpMediumLockList(aMediumLockList),
+          mTargetCaller(aTarget),
+          mParentForTargetCaller(aParentForTarget),
+          mfKeepMediumLockList(fKeepMediumLockList)
+    {
+        AssertReturnVoidStmt(aMediumLockList != NULL, mHrc = E_FAIL);
+        m_strTaskName = "createMerge";
+    }
+
+    ~MergeTask()
+    {
+        if (!mfKeepMediumLockList && mpMediumLockList)
+            delete mpMediumLockList;
+        if (mpChildrenToReparent)
+            delete mpChildrenToReparent;
+    }
+
+    const ComObjPtr<Medium> mTarget;
+    bool mfMergeForward;
+    /* When mpChildrenToReparent is null then mParentForTarget is non-null and
+     * vice versa. In other words: they are used in different cases. */
+    const ComObjPtr<Medium> mParentForTarget;
+    MediumLockList *mpChildrenToReparent;
+    MediumLockList *mpMediumLockList;
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskMergeHandler(*this);
+    }
+
+    AutoCaller mTargetCaller;
+    AutoCaller mParentForTargetCaller;
+    bool mfKeepMediumLockList;
+};
+
+class Medium::ImportTask : public Medium::Task
+{
+public:
+    ImportTask(Medium *aMedium,
+               Progress *aProgress,
+               const char *aFilename,
+               MediumFormat *aFormat,
+               MediumVariant_T aVariant,
+               RTVFSIOSTREAM aVfsIosSrc,
+               Medium *aParent,
+               MediumLockList *aTargetMediumLockList,
+               bool fKeepTargetMediumLockList = false,
+               bool fNotifyAboutChanges = true)
+        : Medium::Task(aMedium, aProgress, fNotifyAboutChanges),
+          mFilename(aFilename),
+          mFormat(aFormat),
+          mVariant(aVariant),
+          mParent(aParent),
+          mpTargetMediumLockList(aTargetMediumLockList),
+          mpVfsIoIf(NULL),
+          mParentCaller(aParent),
+          mfKeepTargetMediumLockList(fKeepTargetMediumLockList)
+    {
+        AssertReturnVoidStmt(aTargetMediumLockList != NULL, mHrc = E_FAIL);
+        /* aParent may be NULL */
+        mHrc = mParentCaller.hrc();
+        if (FAILED(mHrc))
+            return;
+
+        mVDImageIfaces = aMedium->m->vdImageIfaces;
+
+        int vrc = VDIfCreateFromVfsStream(aVfsIosSrc, RTFILE_O_READ, &mpVfsIoIf);
+        AssertRCReturnVoidStmt(vrc, mHrc = E_FAIL);
+
+        vrc = VDInterfaceAdd(&mpVfsIoIf->Core, "Medium::ImportTaskVfsIos",
+                             VDINTERFACETYPE_IO, mpVfsIoIf,
+                             sizeof(VDINTERFACEIO), &mVDImageIfaces);
+        AssertRCReturnVoidStmt(vrc, mHrc = E_FAIL);
+        m_strTaskName = "createImport";
+    }
+
+    ~ImportTask()
+    {
+        if (!mfKeepTargetMediumLockList && mpTargetMediumLockList)
+            delete mpTargetMediumLockList;
+        if (mpVfsIoIf)
+        {
+            VDIfDestroyFromVfsStream(mpVfsIoIf);
+            mpVfsIoIf = NULL;
+        }
+    }
+
+    Utf8Str mFilename;
+    ComObjPtr<MediumFormat> mFormat;
+    MediumVariant_T mVariant;
+    const ComObjPtr<Medium> mParent;
+    MediumLockList *mpTargetMediumLockList;
+    PVDINTERFACE mVDImageIfaces;
+    PVDINTERFACEIO mpVfsIoIf; /**< Pointer to the VFS I/O stream to VD I/O interface wrapper. */
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskImportHandler(*this);
+    }
+
+    AutoCaller mParentCaller;
+    bool mfKeepTargetMediumLockList;
+};
+
+class Medium::EncryptTask : public Medium::Task
+{
+public:
+    EncryptTask(Medium *aMedium,
+                const com::Utf8Str &strNewPassword,
+                const com::Utf8Str &strCurrentPassword,
+                const com::Utf8Str &strCipher,
+                const com::Utf8Str &strNewPasswordId,
+                Progress *aProgress,
+                MediumLockList *aMediumLockList)
+        : Medium::Task(aMedium, aProgress, false),
+          mstrNewPassword(strNewPassword),
+          mstrCurrentPassword(strCurrentPassword),
+          mstrCipher(strCipher),
+          mstrNewPasswordId(strNewPasswordId),
+          mpMediumLockList(aMediumLockList)
+    {
+        AssertReturnVoidStmt(aMediumLockList != NULL, mHrc = E_FAIL);
+        /* aParent may be NULL */
+        mHrc = mParentCaller.hrc();
+        if (FAILED(mHrc))
+            return;
+
+        mVDImageIfaces = aMedium->m->vdImageIfaces;
+        m_strTaskName = "createEncrypt";
+    }
+
+    ~EncryptTask()
+    {
+        if (mstrNewPassword.length())
+            RTMemWipeThoroughly(mstrNewPassword.mutableRaw(), mstrNewPassword.length(), 10 /* cPasses */);
+        if (mstrCurrentPassword.length())
+            RTMemWipeThoroughly(mstrCurrentPassword.mutableRaw(), mstrCurrentPassword.length(), 10 /* cPasses */);
+
+        /* Keep any errors which might be set when deleting the lock list. */
+        ErrorInfoKeeper eik;
+        delete mpMediumLockList;
+    }
+
+    Utf8Str mstrNewPassword;
+    Utf8Str mstrCurrentPassword;
+    Utf8Str mstrCipher;
+    Utf8Str mstrNewPasswordId;
+    MediumLockList *mpMediumLockList;
+    PVDINTERFACE    mVDImageIfaces;
+
+private:
+    HRESULT executeTask()
+    {
+        return mMedium->i_taskEncryptHandler(*this);
+    }
+
+    AutoCaller mParentCaller;
+};
+
+
+
+/**
+ * Converts the Medium device type to the VD type.
+ */
+static const char *getVDTypeName(VDTYPE enmType)
+{
+    switch (enmType)
+    {
+        case VDTYPE_HDD:                return "HDD";
+        case VDTYPE_OPTICAL_DISC:       return "DVD";
+        case VDTYPE_FLOPPY:             return "floppy";
+        case VDTYPE_INVALID:            return "invalid";
+        default:
+            AssertFailedReturn("unknown");
+    }
+}
+
+/**
+ * Converts the Medium device type to the VD type.
+ */
+static const char *getDeviceTypeName(DeviceType_T enmType)
+{
+    switch (enmType)
+    {
+        case DeviceType_HardDisk:       return "HDD";
+        case DeviceType_DVD:            return "DVD";
+        case DeviceType_Floppy:         return "floppy";
+        case DeviceType_Null:           return "null";
+        case DeviceType_Network:        return "network";
+        case DeviceType_USB:            return "USB";
+        case DeviceType_SharedFolder:   return "shared folder";
+        case DeviceType_Graphics3D:     return "graphics 3d";
+        default:
+            AssertFailedReturn("unknown");
+    }
+}
+
+
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Medium constructor / destructor
+//
+////////////////////////////////////////////////////////////////////////////////
+
+DEFINE_EMPTY_CTOR_DTOR(Medium)
+
+HRESULT Medium::FinalConstruct()
+{
+    m = new Data;
+
+    /* Initialize the callbacks of the VD error interface */
+    m->vdIfError.pfnError = i_vdErrorCall;
+    m->vdIfError.pfnMessage = NULL;
+
+    /* Initialize the callbacks of the VD config interface */
+    m->vdIfConfig.pfnAreKeysValid = i_vdConfigAreKeysValid;
+    m->vdIfConfig.pfnQuerySize = i_vdConfigQuerySize;
+    m->vdIfConfig.pfnQuery = i_vdConfigQuery;
+    m->vdIfConfig.pfnUpdate = i_vdConfigUpdate;
+    m->vdIfConfig.pfnQueryBytes = NULL;
+
+    /* Initialize the per-disk interface chain (could be done more globally,
+     * but it's not wasting much time or space so it's not worth it). */
+    int vrc;
+    vrc = VDInterfaceAdd(&m->vdIfError.Core,
+                         "Medium::vdInterfaceError",
+                         VDINTERFACETYPE_ERROR, this,
+                         sizeof(VDINTERFACEERROR), &m->vdDiskIfaces);
+    AssertRCReturn(vrc, E_FAIL);
+
+    /* Initialize the per-image interface chain */
+    vrc = VDInterfaceAdd(&m->vdIfConfig.Core,
+                         "Medium::vdInterfaceConfig",
+                         VDINTERFACETYPE_CONFIG, this,
+                         sizeof(VDINTERFACECONFIG), &m->vdImageIfaces);
+    AssertRCReturn(vrc, E_FAIL);
+
+    /* Initialize the callbacks of the VD TCP interface (we always use the host
+     * IP stack for now) */
+    vrc = VDIfTcpNetInstDefaultCreate(&m->hTcpNetInst, &m->vdImageIfaces);
+    AssertRCReturn(vrc, E_FAIL);
+
+    return BaseFinalConstruct();
+}
+
+void Medium::FinalRelease()
+{
+    uninit();
+
+    VDIfTcpNetInstDefaultDestroy(m->hTcpNetInst);
+    delete m;
+
+    BaseFinalRelease();
+}
+
+/**
+ * Initializes an empty hard disk object without creating or opening an associated
+ * storage unit.
+ *
+ * This gets called by VirtualBox::CreateMedium() in which case uuidMachineRegistry
+ * is empty since starting with VirtualBox 4.0, we no longer add opened media to a
+ * registry automatically (this is deferred until the medium is attached to a machine).
+ *
+ * This also gets called when VirtualBox creates diff images; in this case uuidMachineRegistry
+ * is set to the registry of the parent image to make sure they all end up in the same
+ * file.
+ *
+ * For hard disks that don't have the MediumFormatCapabilities_CreateFixed or
+ * MediumFormatCapabilities_CreateDynamic capability (and therefore cannot be created or deleted
+ * with the means of VirtualBox) the associated storage unit is assumed to be
+ * ready for use so the state of the hard disk object will be set to Created.
+ *
+ * @param aVirtualBox   VirtualBox object.
+ * @param aFormat
+ * @param aLocation     Storage unit location.
+ * @param uuidMachineRegistry The registry to which this medium should be added
+ *                            (global registry UUID or machine UUID or empty if none).
+ * @param aDeviceType   Device Type.
+ */
+HRESULT Medium::init(VirtualBox *aVirtualBox,
+                     const Utf8Str &aFormat,
+                     const Utf8Str &aLocation,
+                     const Guid &uuidMachineRegistry,
+                     const DeviceType_T aDeviceType)
+{
+    AssertReturn(aVirtualBox != NULL, E_FAIL);
+    AssertReturn(!aFormat.isEmpty(), E_FAIL);
+
+    /* Enclose the state transition NotReady->InInit->Ready */
+    AutoInitSpan autoInitSpan(this);
+    AssertReturn(autoInitSpan.isOk(), E_FAIL);
+
+    HRESULT hrc = S_OK;
+
+    unconst(m->pVirtualBox) = aVirtualBox;
+
+    if (uuidMachineRegistry.isValid() && !uuidMachineRegistry.isZero())
+        m->llRegistryIDs.push_back(uuidMachineRegistry);
+
+    /* no storage yet */
+    m->state = MediumState_NotCreated;
+
+    /* cannot be a host drive */
+    m->hostDrive = false;
+
+    m->devType = aDeviceType;
+
+    /* No storage unit is created yet, no need to call Medium::i_queryInfo */
+
+    hrc = i_setFormat(aFormat);
+    if (FAILED(hrc)) return hrc;
+
+    hrc = i_setLocation(aLocation);
+    if (FAILED(hrc)) return hrc;
+
+    if (!(m->formatObj->i_getCapabilities() & (  MediumFormatCapabilities_CreateFixed
+                                               | MediumFormatCapabilities_CreateDynamic
+                                               | MediumFormatCapabilities_File))
+       )
+    {
+        /* Storage for media of this format can neither be explicitly
+         * created by VirtualBox nor deleted, so we place the medium to
+         * Inaccessible state here and also add it to the registry. The
+         * state means that one has to use RefreshState() to update the
+         * medium format specific fields. */
+        m->state = MediumState_Inaccessible;
+        // create new UUID
+        unconst(m->id).create();
+
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+        ComObjPtr<Medium> pMedium;
+
+        /*
+         * Check whether the UUID is taken already and create a new one
+         * if required.
+         * Try this only a limited amount of times in case the PRNG is broken
+         * in some way to prevent an endless loop.
+         */
+        for (unsigned i = 0; i < 5; i++)
+        {
+            bool fInUse;
+
+            fInUse = m->pVirtualBox->i_isMediaUuidInUse(m->id, aDeviceType);
+            if (fInUse)
+            {
+                // create new UUID
+                unconst(m->id).create();
+            }
+            else
+                break;
+        }
+
+        hrc = m->pVirtualBox->i_registerMedium(this, &pMedium, treeLock);
+        Assert(this == pMedium || FAILED(hrc));
+    }
+
+    /* Confirm a successful initialization when it's the case */
+    if (SUCCEEDED(hrc))
+        autoInitSpan.setSucceeded();
+
+    return hrc;
+}
+
+/**
+ * Initializes the medium object by opening the storage unit at the specified
+ * location. The enOpenMode parameter defines whether the medium will be opened
+ * read/write or read-only.
+ *
+ * This gets called by VirtualBox::OpenMedium() and also by
+ * Machine::AttachDevice() and createImplicitDiffs() when new diff
+ * images are created.
+ *
+ * There is no registry for this case since starting with VirtualBox 4.0, we
+ * no longer add opened media to a registry automatically (this is deferred
+ * until the medium is attached to a machine).
+ *
+ * For hard disks, the UUID, format and the parent of this medium will be
+ * determined when reading the medium storage unit. For DVD and floppy images,
+ * which have no UUIDs in their storage units, new UUIDs are created.
+ * If the detected or set parent is not known to VirtualBox, then this method
+ * will fail.
+ *
+ * @param aVirtualBox   VirtualBox object.
+ * @param aLocation     Storage unit location.
+ * @param enOpenMode    Whether to open the medium read/write or read-only.
+ * @param fForceNewUuid Whether a new UUID should be set to avoid duplicates.
+ * @param aDeviceType   Device type of medium.
+ */
+HRESULT Medium::init(VirtualBox *aVirtualBox,
+                     const Utf8Str &aLocation,
+                     HDDOpenMode enOpenMode,
+                     bool fForceNewUuid,
+                     DeviceType_T aDeviceType)
+{
+    AssertReturn(aVirtualBox, E_INVALIDARG);
+    AssertReturn(!aLocation.isEmpty(), E_INVALIDARG);
+
+    HRESULT hrc = S_OK;
+
+    {
+        /* Enclose the state transition NotReady->InInit->Ready */
+        AutoInitSpan autoInitSpan(this);
+        AssertReturn(autoInitSpan.isOk(), E_FAIL);
+
+        unconst(m->pVirtualBox) = aVirtualBox;
+
+        /* there must be a storage unit */
+        m->state = MediumState_Created;
+
+        /* remember device type for correct unregistering later */
+        m->devType = aDeviceType;
+
+        /* cannot be a host drive */
+        m->hostDrive = false;
+
+        /* remember the open mode (defaults to ReadWrite) */
+        m->hddOpenMode = enOpenMode;
+
+        if (aDeviceType == DeviceType_DVD)
+            m->type = MediumType_Readonly;
+        else if (aDeviceType == DeviceType_Floppy)
+            m->type = MediumType_Writethrough;
+
+        hrc = i_setLocation(aLocation);
+        if (FAILED(hrc)) return hrc;
+
+        /* get all the information about the medium from the storage unit */
+        if (fForceNewUuid)
+            unconst(m->uuidImage).create();
+
+        m->state = MediumState_Inaccessible;
+        m->strLastAccessError = tr("Accessibility check was not yet performed");
+
+        /* Confirm a successful initialization before the call to i_queryInfo.
+         * Otherwise we can end up with a AutoCaller deadlock because the
+         * medium becomes visible but is not marked as initialized. Causes
+         * locking trouble (e.g. trying to save media registries) which is
+         * hard to solve. */
+        autoInitSpan.setSucceeded();
+    }
+
+    /* we're normal code from now on, no longer init */
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc()))
+        return autoCaller.hrc();
+
+    /* need to call i_queryInfo immediately to correctly place the medium in
+     * the respective media tree and update other information such as uuid */
+    hrc = i_queryInfo(fForceNewUuid /* fSetImageId */, false /* fSetParentId */, autoCaller);
+    if (SUCCEEDED(hrc))
+    {
+        AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        /* if the storage unit is not accessible, it's not acceptable for the
+         * newly opened media so convert this into an error */
+        if (m->state == MediumState_Inaccessible)
+        {
+            Assert(!m->strLastAccessError.isEmpty());
+            hrc = setError(E_FAIL, "%s", m->strLastAccessError.c_str());
+            alock.release();
+            autoCaller.release();
+            uninit();
+        }
+        else
+        {
+            AssertStmt(!m->id.isZero(),
+                       alock.release(); autoCaller.release(); uninit(); return E_FAIL);
+
+            /* storage format must be detected by Medium::i_queryInfo if the
+             * medium is accessible */
+            AssertStmt(!m->strFormat.isEmpty(),
+                       alock.release(); autoCaller.release(); uninit(); return E_FAIL);
+        }
+    }
+    else
+    {
+        /* opening this image failed, mark the object as dead */
+        autoCaller.release();
+        uninit();
+    }
+
+    return hrc;
+}
+
+/**
+ * Initializes the medium object by loading its data from the given settings
+ * node. The medium will always be opened read/write.
+ *
+ * In this case, since we're loading from a registry, uuidMachineRegistry is
+ * always set: it's either the global registry UUID or a machine UUID when
+ * loading from a per-machine registry.
+ *
+ * @param aParent       Parent medium disk or NULL for a root (base) medium.
+ * @param aDeviceType   Device type of the medium.
+ * @param uuidMachineRegistry The registry to which this medium should be
+ *                            added (global registry UUID or machine UUID).
+ * @param data          Configuration settings.
+ * @param strMachineFolder The machine folder with which to resolve relative paths;
+ *                         if empty, then we use the VirtualBox home directory
+ *
+ * @note Locks the medium tree for writing.
+ */
+HRESULT Medium::initOne(Medium *aParent,
+                        DeviceType_T aDeviceType,
+                        const Guid &uuidMachineRegistry,
+                        const Utf8Str &strMachineFolder,
+                        const settings::Medium &data)
+{
+    HRESULT hrc;
+
+    if (uuidMachineRegistry.isValid() && !uuidMachineRegistry.isZero())
+        m->llRegistryIDs.push_back(uuidMachineRegistry);
+
+    /* register with VirtualBox/parent early, since uninit() will
+     * unconditionally unregister on failure */
+    if (aParent)
+    {
+        // differencing medium: add to parent
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+        // no need to check maximum depth as settings reading did it
+        i_setParent(aParent);
+    }
+
+    /* see below why we don't call Medium::i_queryInfo (and therefore treat
+     * the medium as inaccessible for now */
+    m->state = MediumState_Inaccessible;
+    m->strLastAccessError = tr("Accessibility check was not yet performed");
+
+    /* required */
+    unconst(m->id) = data.uuid;
+
+    /* assume not a host drive */
+    m->hostDrive = false;
+
+    /* optional */
+    m->strDescription = data.strDescription;
+
+    /* required */
+    if (aDeviceType == DeviceType_HardDisk)
+    {
+        AssertReturn(!data.strFormat.isEmpty(), E_FAIL);
+        hrc = i_setFormat(data.strFormat);
+        if (FAILED(hrc)) return hrc;
+    }
+    else
+    {
+        /// @todo handle host drive settings here as well?
+        if (!data.strFormat.isEmpty())
+            hrc = i_setFormat(data.strFormat);
+        else
+            hrc = i_setFormat("RAW");
+        if (FAILED(hrc)) return hrc;
+    }
+
+    /* optional, only for diffs, default is false; we can only auto-reset
+     * diff media so they must have a parent */
+    if (aParent != NULL)
+        m->autoReset = data.fAutoReset;
+    else
+        m->autoReset = false;
+
+    /* properties (after setting the format as it populates the map). Note that
+     * if some properties are not supported but present in the settings file,
+     * they will still be read and accessible (for possible backward
+     * compatibility; we can also clean them up from the XML upon next
+     * XML format version change if we wish) */
+    for (settings::StringsMap::const_iterator it = data.properties.begin();
+         it != data.properties.end();
+         ++it)
+    {
+        const Utf8Str &name = it->first;
+        const Utf8Str &value = it->second;
+        m->mapProperties[name] = value;
+    }
+
+    /* try to decrypt an optional iSCSI initiator secret */
+    settings::StringsMap::const_iterator itCph = data.properties.find("InitiatorSecretEncrypted");
+    if (   itCph != data.properties.end()
+        && !itCph->second.isEmpty())
+    {
+        Utf8Str strPlaintext;
+        int vrc = m->pVirtualBox->i_decryptSetting(&strPlaintext, itCph->second);
+        if (RT_SUCCESS(vrc))
+            m->mapProperties["InitiatorSecret"] = strPlaintext;
+    }
+
+    Utf8Str strFull;
+    if (m->formatObj->i_getCapabilities() & MediumFormatCapabilities_File)
+    {
+        // compose full path of the medium, if it's not fully qualified...
+        // slightly convoluted logic here. If the caller has given us a
+        // machine folder, then a relative path will be relative to that:
+        if (    !strMachineFolder.isEmpty()
+             && !RTPathStartsWithRoot(data.strLocation.c_str())
+           )
+        {
+            strFull = strMachineFolder;
+            strFull += RTPATH_SLASH;
+            strFull += data.strLocation;
+        }
+        else
+        {
+            // Otherwise use the old VirtualBox "make absolute path" logic:
+            int vrc = m->pVirtualBox->i_calculateFullPath(data.strLocation, strFull);
+            if (RT_FAILURE(vrc))
+                return Global::vboxStatusCodeToCOM(vrc);
+        }
+    }
+    else
+        strFull = data.strLocation;
+
+    hrc = i_setLocation(strFull);
+    if (FAILED(hrc)) return hrc;
+
+    if (aDeviceType == DeviceType_HardDisk)
+    {
+        /* type is only for base hard disks */
+        if (m->pParent.isNull())
+            m->type = data.hdType;
+    }
+    else if (aDeviceType == DeviceType_DVD)
+        m->type = MediumType_Readonly;
+    else
+        m->type = MediumType_Writethrough;
+
+    /* remember device type for correct unregistering later */
+    m->devType = aDeviceType;
+
+    LogFlowThisFunc(("m->strLocationFull='%s', m->strFormat=%s, m->id={%RTuuid}\n",
+                     m->strLocationFull.c_str(), m->strFormat.c_str(), m->id.raw()));
+
+    return S_OK;
+}
+
+/**
+ * Initializes and registers the medium object and its children by loading its
+ * data from the given settings node. The medium will always be opened
+ * read/write.
+ *
+ * @todo r=bird: What's that stuff about 'always be opened read/write'?
+ *
+ * In this case, since we're loading from a registry, uuidMachineRegistry is
+ * always set: it's either the global registry UUID or a machine UUID when
+ * loading from a per-machine registry.
+ *
+ * The only caller is currently VirtualBox::initMedia().
+ *
+ * @param aVirtualBox   VirtualBox object.
+ * @param aDeviceType   Device type of the medium.
+ * @param uuidMachineRegistry The registry to which this medium should be added
+ *                      (global registry UUID or machine UUID).
+ * @param strMachineFolder The machine folder with which to resolve relative
+ *                      paths; if empty, then we use the VirtualBox home directory
+ * @param data          Configuration settings.
+ * @param mediaTreeLock Autolock.
+ * @param uIdsForNotify List to be updated with newly registered media.
+ *
+ * @note Assumes that the medium tree lock is held for writing. May release
+ * and lock it again. At the end it is always held.
+ */
+/* static */
+HRESULT Medium::initFromSettings(VirtualBox *aVirtualBox,
+                                 DeviceType_T aDeviceType,
+                                 const Guid &uuidMachineRegistry,
+                                 const Utf8Str &strMachineFolder,
+                                 const settings::Medium &data,
+                                 AutoWriteLock &mediaTreeLock,
+                                 std::list<std::pair<Guid, DeviceType_T> > &uIdsForNotify)
+{
+    Assert(aVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+    AssertReturn(aVirtualBox, E_INVALIDARG);
+
+    HRESULT hrc = S_OK;
+
+    MediaList llMediaTocleanup;
+
+    std::list<const settings::Medium *> llSettingsTodo;
+    llSettingsTodo.push_back(&data);
+    MediaList llParentsTodo;
+    llParentsTodo.push_back(NULL);
+
+    while (!llSettingsTodo.empty())
+    {
+        const settings::Medium *current = llSettingsTodo.front();
+        llSettingsTodo.pop_front();
+        ComObjPtr<Medium> pParent = llParentsTodo.front();
+        llParentsTodo.pop_front();
+
+        bool fReleasedMediaTreeLock = false;
+        ComObjPtr<Medium> pMedium;
+        hrc = pMedium.createObject();
+        if (FAILED(hrc))
+            break;
+        ComObjPtr<Medium> pActualMedium(pMedium);
+
+        {
+            AutoInitSpan autoInitSpan(pMedium);
+            AssertBreakStmt(autoInitSpan.isOk(), hrc = E_FAIL);
+
+            unconst(pMedium->m->pVirtualBox) = aVirtualBox;
+            hrc = pMedium->initOne(pParent, aDeviceType, uuidMachineRegistry, strMachineFolder, *current);
+            if (FAILED(hrc))
+                break;
+            hrc = aVirtualBox->i_registerMedium(pActualMedium, &pActualMedium, mediaTreeLock, true /*fCalledFromMediumInit*/);
+            if (SUCCEEDED(hrc) && pActualMedium == pMedium)
+            {
+                /* It is a truly new medium, remember details for cleanup. */
+                autoInitSpan.setSucceeded();
+                llMediaTocleanup.push_front(pMedium);
+            }
+            else
+            {
+                /* Since the newly created medium was replaced by an already
+                 * known one when merging medium trees, we can immediately mark
+                 * it as failed. */
+                autoInitSpan.setFailed();
+                mediaTreeLock.release();
+                fReleasedMediaTreeLock = true;
+            }
+        }
+        if (fReleasedMediaTreeLock)
+        {
+            /* With the InitSpan out of the way it's safe to let the refcount
+             * drop to 0 without causing uninit trouble. */
+            pMedium.setNull();
+            mediaTreeLock.acquire();
+
+            if (FAILED(hrc))
+                break;
+        }
+
+        /* create all children */
+        std::list<settings::Medium>::const_iterator itBegin = current->llChildren.begin();
+        std::list<settings::Medium>::const_iterator itEnd = current->llChildren.end();
+        for (std::list<settings::Medium>::const_iterator it = itBegin; it != itEnd; ++it)
+        {
+            llSettingsTodo.push_back(&*it);
+            llParentsTodo.push_back(pActualMedium);
+        }
+    }
+
+    if (SUCCEEDED(hrc))
+    {
+        /* Check for consistency. */
+        Assert(llSettingsTodo.size() == 0);
+        Assert(llParentsTodo.size() == 0);
+        /* Create the list of notifications, parent first. */
+        for (MediaList::const_reverse_iterator it = llMediaTocleanup.rbegin(); it != llMediaTocleanup.rend(); ++it)
+        {
+            ComObjPtr<Medium> pMedium = *it;
+            AutoCaller mediumCaller(pMedium);
+            if (mediumCaller.isOk())
+            {
+                const Guid &id = pMedium->i_getId();
+                uIdsForNotify.push_back(std::pair<Guid, DeviceType_T>(id, aDeviceType));
+            }
+        }
+    }
+    else
+    {
+        /* Forget state of the settings processing. */
+        llSettingsTodo.clear();
+        llParentsTodo.clear();
+        /* Unregister all accumulated medium objects in the right order (last
+         * created to first created, avoiding config leftovers). */
+        MediaList::const_iterator itBegin = llMediaTocleanup.begin();
+        MediaList::const_iterator itEnd = llMediaTocleanup.end();
+        for (MediaList::const_iterator it = itBegin; it != itEnd; ++it)
+        {
+            ComObjPtr<Medium> pMedium = *it;
+            pMedium->i_unregisterWithVirtualBox();
+        }
+        /* Forget the only references to all newly created medium objects,
+         * triggering freeing (uninit happened in unregistering above). */
+        mediaTreeLock.release();
+        llMediaTocleanup.clear();
+        mediaTreeLock.acquire();
+    }
+
+    return hrc;
+}
+
+/**
+ * Initializes the medium object by providing the host drive information.
+ * Not used for anything but the host floppy/host DVD case.
+ *
+ * There is no registry for this case.
+ *
+ * @param aVirtualBox   VirtualBox object.
+ * @param aDeviceType   Device type of the medium.
+ * @param aLocation     Location of the host drive.
+ * @param aDescription  Comment for this host drive.
+ *
+ * @note Locks VirtualBox lock for writing.
+ */
+HRESULT Medium::init(VirtualBox *aVirtualBox,
+                     DeviceType_T aDeviceType,
+                     const Utf8Str &aLocation,
+                     const Utf8Str &aDescription /* = Utf8Str::Empty */)
+{
+    ComAssertRet(aDeviceType == DeviceType_DVD || aDeviceType == DeviceType_Floppy, E_INVALIDARG);
+    ComAssertRet(!aLocation.isEmpty(), E_INVALIDARG);
+
+    /* Enclose the state transition NotReady->InInit->Ready */
+    AutoInitSpan autoInitSpan(this);
+    AssertReturn(autoInitSpan.isOk(), E_FAIL);
+
+    unconst(m->pVirtualBox) = aVirtualBox;
+
+    // We do not store host drives in VirtualBox.xml or anywhere else, so if we want
+    // host drives to be identifiable by UUID and not give the drive a different UUID
+    // every time VirtualBox starts, we need to fake a reproducible UUID here:
+    RTUUID uuid;
+    RTUuidClear(&uuid);
+    if (aDeviceType == DeviceType_DVD)
+        memcpy(&uuid.au8[0], "DVD", 3);
+    else
+        memcpy(&uuid.au8[0], "FD", 2);
+    /* use device name, adjusted to the end of uuid, shortened if necessary */
+    size_t lenLocation = aLocation.length();
+    if (lenLocation > 12)
+        memcpy(&uuid.au8[4], aLocation.c_str() + (lenLocation - 12), 12);
+    else
+        memcpy(&uuid.au8[4 + 12 - lenLocation], aLocation.c_str(), lenLocation);
+    unconst(m->id) = uuid;
+
+    if (aDeviceType == DeviceType_DVD)
+        m->type = MediumType_Readonly;
+    else
+        m->type = MediumType_Writethrough;
+    m->devType = aDeviceType;
+    m->state = MediumState_Created;
+    m->hostDrive = true;
+    HRESULT hrc = i_setFormat("RAW");
+    if (FAILED(hrc)) return hrc;
+    hrc = i_setLocation(aLocation);
+    if (FAILED(hrc)) return hrc;
+    m->strDescription = aDescription;
+
+    autoInitSpan.setSucceeded();
+    return S_OK;
+}
+
+/**
+ * Uninitializes the instance.
+ *
+ * Called either from FinalRelease() or by the parent when it gets destroyed.
+ *
+ * @note All children of this medium get uninitialized, too, in a stack
+ *       friendly manner.
+ */
+void Medium::uninit()
+{
+    /* It is possible that some previous/concurrent uninit has already cleared
+     * the pVirtualBox reference, and in this case we don't need to continue.
+     * Normally this would be handled through the AutoUninitSpan magic, however
+     * this cannot be done at this point as the media tree must be locked
+     * before reaching the AutoUninitSpan, otherwise deadlocks can happen.
+     *
+     * NOTE: The tree lock is higher priority than the medium caller and medium
+     * object locks, i.e. the medium caller may have to be released and be
+     * re-acquired in the right place later. See Medium::getParent() for sample
+     * code how to do this safely. */
+    VirtualBox *pVirtualBox = m->pVirtualBox;
+    if (!pVirtualBox)
+        return;
+
+    /* Caller must not hold the object (checked below) or media tree lock. */
+    Assert(!pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+
+    AutoWriteLock treeLock(pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+    /* Must use a list without refcounting help since "this" might already have
+     * reached 0, and then the refcount must not be increased again since it
+     * would otherwise trigger a double free. For all other list entries this
+     * needs manual refcount updating, to make sure the refcount for children
+     * does not drop to 0 too early. */
+    std::list<Medium *> llMediaTodo;
+    llMediaTodo.push_back(this);
+
+    while (!llMediaTodo.empty())
+    {
+        Medium *pMedium = llMediaTodo.front();
+        llMediaTodo.pop_front();
+
+        /* Enclose the state transition Ready->InUninit->NotReady */
+        AutoUninitSpan autoUninitSpan(pMedium);
+        if (autoUninitSpan.uninitDone())
+        {
+            if (pMedium != this)
+                pMedium->Release();
+            continue;
+        }
+
+        Assert(!pMedium->isWriteLockOnCurrentThread());
+#ifdef DEBUG
+        if (!pMedium->m->backRefs.empty())
+            pMedium->i_dumpBackRefs();
+#endif
+        Assert(pMedium->m->backRefs.empty());
+
+        pMedium->m->formatObj.setNull();
+
+        if (pMedium->m->state == MediumState_Deleting)
+        {
+            /* This medium has been already deleted (directly or as part of a
+             * merge).  Reparenting has already been done. */
+            Assert(pMedium->m->pParent.isNull());
+            Assert(pMedium->m->llChildren.empty());
+            if (pMedium != this)
+                pMedium->Release();
+            continue;
+        }
+
+        //Assert(!pMedium->m->pParent);
+        /** @todo r=klaus Should not be necessary, since the caller should be
+         * doing the deparenting. No time right now to test everything. */
+        if (pMedium == this && pMedium->m->pParent)
+            pMedium->i_deparent();
+
+        /* Process all children */
+        MediaList::const_iterator itBegin = pMedium->m->llChildren.begin();
+        MediaList::const_iterator itEnd = pMedium->m->llChildren.end();
+        for (MediaList::const_iterator it = itBegin; it != itEnd; ++it)
+        {
+            Medium *pChild = *it;
+            pChild->m->pParent.setNull();
+            pChild->AddRef();
+            llMediaTodo.push_back(pChild);
+        }
+
+        /* Children information obsolete, will be processed anyway. */
+        pMedium->m->llChildren.clear();
+
+        unconst(pMedium->m->pVirtualBox) = NULL;
+
+        if (pMedium != this)
+            pMedium->Release();
+
+        autoUninitSpan.setSucceeded();
+    }
+}
+
+/**
+ * Internal helper that removes "this" from the list of children of its
+ * parent. Used in uninit() and other places when reparenting is necessary.
+ *
+ * The caller must hold the medium tree lock!
+ */
+void Medium::i_deparent()
+{
+    MediaList &llParent = m->pParent->m->llChildren;
+    for (MediaList::iterator it = llParent.begin();
+         it != llParent.end();
+         ++it)
+    {
+        Medium *pParentsChild = *it;
+        if (this == pParentsChild)
+        {
+            llParent.erase(it);
+            break;
+        }
+    }
+    m->pParent.setNull();
+}
+
+/**
+ * Internal helper that removes "this" from the list of children of its
+ * parent. Used in uninit() and other places when reparenting is necessary.
+ *
+ * The caller must hold the medium tree lock!
+ */
+void Medium::i_setParent(const ComObjPtr<Medium> &pParent)
+{
+    m->pParent = pParent;
+    if (pParent)
+        pParent->m->llChildren.push_back(this);
+}
+
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// IMedium public methods
+//
+////////////////////////////////////////////////////////////////////////////////
+
+HRESULT Medium::getId(com::Guid &aId)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    aId = m->id;
+
+    return S_OK;
+}
+
+HRESULT Medium::getDescription(AutoCaller &autoCaller, com::Utf8Str &aDescription)
+{
+    NOREF(autoCaller);
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    aDescription = m->strDescription;
+
+    return S_OK;
+}
+
+HRESULT Medium::setDescription(AutoCaller &autoCaller, const com::Utf8Str &aDescription)
+{
+    /// @todo update m->strDescription and save the global registry (and local
+    /// registries of portable VMs referring to this medium), this will also
+    /// require to add the mRegistered flag to data
+
+    HRESULT hrc = S_OK;
+
+    MediumLockList *pMediumLockList(new MediumLockList());
+
+    try
+    {
+        autoCaller.release();
+
+        // to avoid redundant locking, which just takes a time, just call required functions.
+        // the error will be just stored and will be reported after locks will be acquired again
+
+        const char *pszError = NULL;
+
+
+        /* Build the lock list. */
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                     this /* pToLockWrite */,
+                                     true /* fMediumLockWriteAll */,
+                                     NULL,
+                                     *pMediumLockList);
+        if (FAILED(hrc))
+            pszError = tr("Failed to create medium lock list for '%s'");
+        else
+        {
+            hrc = pMediumLockList->Lock();
+            if (FAILED(hrc))
+                pszError = tr("Failed to lock media '%s'");
+        }
+
+        // locking: we need the tree lock first because we access parent pointers
+        // and we need to write-lock the media involved
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+        autoCaller.add();
+        AssertComRCThrowRC(autoCaller.hrc());
+
+        AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        if (FAILED(hrc))
+            throw setError(hrc, pszError, i_getLocationFull().c_str());
+
+        /* Set a new description */
+        m->strDescription = aDescription;
+
+        // save the settings
+        alock.release();
+        autoCaller.release();
+        treeLock.release();
+        i_markRegistriesModified();
+        m->pVirtualBox->i_saveModifiedRegistries();
+        m->pVirtualBox->i_onMediumConfigChanged(this);
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    delete pMediumLockList;
+
+    return hrc;
+}
+
+HRESULT Medium::getState(MediumState_T *aState)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+    *aState = m->state;
+
+    return S_OK;
+}
+
+HRESULT Medium::getVariant(std::vector<MediumVariant_T> &aVariant)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    const size_t cBits = sizeof(MediumVariant_T) * 8;
+    aVariant.resize(cBits);
+    for (size_t i = 0; i < cBits; ++i)
+        aVariant[i] = (MediumVariant_T)(m->variant & RT_BIT(i));
+
+    return S_OK;
+}
+
+HRESULT Medium::getLocation(com::Utf8Str &aLocation)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    aLocation = m->strLocationFull;
+
+    return S_OK;
+}
+
+HRESULT Medium::getName(com::Utf8Str &aName)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    aName = i_getName();
+
+    return S_OK;
+}
+
+HRESULT Medium::getDeviceType(DeviceType_T *aDeviceType)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aDeviceType = m->devType;
+
+    return S_OK;
+}
+
+HRESULT Medium::getHostDrive(BOOL *aHostDrive)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aHostDrive = m->hostDrive;
+
+    return S_OK;
+}
+
+HRESULT Medium::getSize(LONG64 *aSize)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aSize = (LONG64)m->size;
+
+    return S_OK;
+}
+
+HRESULT Medium::getFormat(com::Utf8Str &aFormat)
+{
+    /* no need to lock, m->strFormat is const */
+
+    aFormat = m->strFormat;
+    return S_OK;
+}
+
+HRESULT Medium::getMediumFormat(ComPtr<IMediumFormat> &aMediumFormat)
+{
+    /* no need to lock, m->formatObj is const */
+    m->formatObj.queryInterfaceTo(aMediumFormat.asOutParam());
+
+    return S_OK;
+}
+
+HRESULT Medium::getType(AutoCaller &autoCaller, MediumType_T *aType)
+{
+    NOREF(autoCaller);
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aType = m->type;
+
+    return S_OK;
+}
+
+HRESULT Medium::setType(AutoCaller &autoCaller, MediumType_T aType)
+{
+    autoCaller.release();
+
+    /* It is possible that some previous/concurrent uninit has already cleared
+     * the pVirtualBox reference, see #uninit(). */
+    ComObjPtr<VirtualBox> pVirtualBox(m->pVirtualBox);
+
+    // we access m->pParent
+    AutoReadLock treeLock(!pVirtualBox.isNull() ? &pVirtualBox->i_getMediaTreeLockHandle() : NULL COMMA_LOCKVAL_SRC_POS);
+
+    autoCaller.add();
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    AutoWriteLock mlock(this COMMA_LOCKVAL_SRC_POS);
+
+    /* Wait for a concurrently running Medium::i_queryInfo to complete. */
+    while (m->queryInfoRunning)
+    {
+        mlock.release();
+        autoCaller.release();
+        treeLock.release();
+        /* Must not hold the media tree lock, as Medium::i_queryInfo needs
+         * this lock and thus we would run into a deadlock here. */
+        Assert(!m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+        /* must not hold the object lock now */
+        Assert(!isWriteLockOnCurrentThread());
+        {
+            AutoReadLock qlock(m->queryInfoSem COMMA_LOCKVAL_SRC_POS);
+        }
+        treeLock.acquire();
+        autoCaller.add();
+        if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+        mlock.acquire();
+    }
+
+    switch (m->state)
+    {
+        case MediumState_Created:
+        case MediumState_Inaccessible:
+            break;
+        default:
+            return i_setStateError();
+    }
+
+    if (m->type == aType)
+    {
+        /* Nothing to do */
+        return S_OK;
+    }
+
+    DeviceType_T devType = i_getDeviceType();
+    // DVD media can only be readonly.
+    if (devType == DeviceType_DVD && aType != MediumType_Readonly)
+        return setError(VBOX_E_INVALID_OBJECT_STATE,
+                        tr("Cannot change the type of DVD medium '%s'"),
+                        m->strLocationFull.c_str());
+    // Floppy media can only be writethrough or readonly.
+    if (   devType == DeviceType_Floppy
+        && aType != MediumType_Writethrough
+        && aType != MediumType_Readonly)
+        return setError(VBOX_E_INVALID_OBJECT_STATE,
+                        tr("Cannot change the type of floppy medium '%s'"),
+                        m->strLocationFull.c_str());
+
+    /* cannot change the type of a differencing medium */
+    if (m->pParent)
+        return setError(VBOX_E_INVALID_OBJECT_STATE,
+                        tr("Cannot change the type of medium '%s' because it is a differencing medium"),
+                        m->strLocationFull.c_str());
+
+    /* Cannot change the type of a medium being in use by more than one VM.
+     * If the change is to Immutable or MultiAttach then it must not be
+     * directly attached to any VM, otherwise the assumptions about indirect
+     * attachment elsewhere are violated and the VM becomes inaccessible.
+     * Attaching an immutable medium triggers the diff creation, and this is
+     * vital for the correct operation. */
+    if (   m->backRefs.size() > 1
+        || (   (   aType == MediumType_Immutable
+                || aType == MediumType_MultiAttach)
+            && m->backRefs.size() > 0))
+        return setError(VBOX_E_INVALID_OBJECT_STATE,
+                        tr("Cannot change the type of medium '%s' because it is attached to %d virtual machines",
+                           "", m->backRefs.size()),
+                        m->strLocationFull.c_str(), m->backRefs.size());
+
+    switch (aType)
+    {
+        case MediumType_Normal:
+        case MediumType_Immutable:
+        case MediumType_MultiAttach:
+        {
+            /* normal can be easily converted to immutable and vice versa even
+             * if they have children as long as they are not attached to any
+             * machine themselves */
+            break;
+        }
+        case MediumType_Writethrough:
+        case MediumType_Shareable:
+        case MediumType_Readonly:
+        {
+            /* cannot change to writethrough, shareable or readonly
+             * if there are children */
+            if (i_getChildren().size() != 0)
+                return setError(VBOX_E_OBJECT_IN_USE,
+                                tr("Cannot change type for medium '%s' since it has %d child media", "", i_getChildren().size()),
+                                m->strLocationFull.c_str(), i_getChildren().size());
+            if (aType == MediumType_Shareable)
+            {
+                MediumVariant_T variant = i_getVariant();
+                if (!(variant & MediumVariant_Fixed))
+                    return setError(VBOX_E_INVALID_OBJECT_STATE,
+                                    tr("Cannot change type for medium '%s' to 'Shareable' since it is a dynamic medium storage unit"),
+                                    m->strLocationFull.c_str());
+            }
+            else if (aType == MediumType_Readonly && devType == DeviceType_HardDisk)
+            {
+                // Readonly hard disks are not allowed, this medium type is reserved for
+                // DVDs and floppy images at the moment. Later we might allow readonly hard
+                // disks, but that's extremely unusual and many guest OSes will have trouble.
+                return setError(VBOX_E_INVALID_OBJECT_STATE,
+                                tr("Cannot change type for medium '%s' to 'Readonly' since it is a hard disk"),
+                                m->strLocationFull.c_str());
+            }
+            break;
+        }
+        default:
+            AssertFailedReturn(E_FAIL);
+    }
+
+    if (aType == MediumType_MultiAttach)
+    {
+        // This type is new with VirtualBox 4.0 and therefore requires settings
+        // version 1.11 in the settings backend. Unfortunately it is not enough to do
+        // the usual routine in MachineConfigFile::bumpSettingsVersionIfNeeded() for
+        // two reasons: The medium type is a property of the media registry tree, which
+        // can reside in the global config file (for pre-4.0 media); we would therefore
+        // possibly need to bump the global config version. We don't want to do that though
+        // because that might make downgrading to pre-4.0 impossible.
+        // As a result, we can only use these two new types if the medium is NOT in the
+        // global registry:
+        const Guid &uuidGlobalRegistry = m->pVirtualBox->i_getGlobalRegistryId();
+        if (i_isInRegistry(uuidGlobalRegistry))
+            return setError(VBOX_E_INVALID_OBJECT_STATE,
+                            tr("Cannot change type for medium '%s': the media type 'MultiAttach' can only be used "
+                               "on media registered with a machine that was created with VirtualBox 4.0 or later"),
+                            m->strLocationFull.c_str());
+    }
+
+    m->type = aType;
+
+    // save the settings
+    mlock.release();
+    autoCaller.release();
+    treeLock.release();
+    i_markRegistriesModified();
+    m->pVirtualBox->i_saveModifiedRegistries();
+    m->pVirtualBox->i_onMediumConfigChanged(this);
+
+    return S_OK;
+}
+
+HRESULT Medium::getAllowedTypes(std::vector<MediumType_T> &aAllowedTypes)
+{
+    NOREF(aAllowedTypes);
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    ReturnComNotImplemented();
+}
+
+HRESULT Medium::getParent(AutoCaller &autoCaller, ComPtr<IMedium> &aParent)
+{
+    autoCaller.release();
+
+    /* It is possible that some previous/concurrent uninit has already cleared
+     * the pVirtualBox reference, see #uninit(). */
+    ComObjPtr<VirtualBox> pVirtualBox(m->pVirtualBox);
+
+    /* we access m->pParent */
+    AutoReadLock treeLock(!pVirtualBox.isNull() ? &pVirtualBox->i_getMediaTreeLockHandle() : NULL COMMA_LOCKVAL_SRC_POS);
+
+    autoCaller.add();
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    m->pParent.queryInterfaceTo(aParent.asOutParam());
+
+    return S_OK;
+}
+
+HRESULT Medium::getChildren(AutoCaller &autoCaller, std::vector<ComPtr<IMedium> > &aChildren)
+{
+    autoCaller.release();
+
+    /* It is possible that some previous/concurrent uninit has already cleared
+     * the pVirtualBox reference, see #uninit(). */
+    ComObjPtr<VirtualBox> pVirtualBox(m->pVirtualBox);
+
+    /* we access children */
+    AutoReadLock treeLock(!pVirtualBox.isNull() ? &pVirtualBox->i_getMediaTreeLockHandle() : NULL COMMA_LOCKVAL_SRC_POS);
+
+    autoCaller.add();
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    MediaList children(this->i_getChildren());
+    aChildren.resize(children.size());
+    size_t i = 0;
+    for (MediaList::const_iterator it =  children.begin(); it != children.end(); ++it, ++i)
+        (*it).queryInterfaceTo(aChildren[i].asOutParam());
+    return S_OK;
+}
+
+HRESULT Medium::getBase(AutoCaller &autoCaller, ComPtr<IMedium> &aBase)
+{
+    autoCaller.release();
+
+    /* i_getBase() will do callers/locking */
+    i_getBase().queryInterfaceTo(aBase.asOutParam());
+
+    return S_OK;
+}
+
+HRESULT Medium::getReadOnly(AutoCaller &autoCaller, BOOL *aReadOnly)
+{
+    autoCaller.release();
+
+    /* isReadOnly() will do locking */
+    *aReadOnly = i_isReadOnly();
+
+    return S_OK;
+}
+
+HRESULT Medium::getLogicalSize(LONG64 *aLogicalSize)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aLogicalSize = (LONG64)m->logicalSize;
+
+    return S_OK;
+}
+
+HRESULT Medium::getAutoReset(BOOL *aAutoReset)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    if (m->pParent.isNull())
+        *aAutoReset = FALSE;
+    else
+        *aAutoReset = m->autoReset;
+
+    return S_OK;
+}
+
+HRESULT Medium::setAutoReset(BOOL aAutoReset)
+{
+    AutoWriteLock mlock(this COMMA_LOCKVAL_SRC_POS);
+
+    if (m->pParent.isNull())
+        return setError(VBOX_E_NOT_SUPPORTED,
+                        tr("Medium '%s' is not differencing"),
+                        m->strLocationFull.c_str());
+
+    if (m->autoReset != !!aAutoReset)
+    {
+        m->autoReset = !!aAutoReset;
+
+        // save the settings
+        mlock.release();
+        i_markRegistriesModified();
+        m->pVirtualBox->i_saveModifiedRegistries();
+        m->pVirtualBox->i_onMediumConfigChanged(this);
+    }
+
+    return S_OK;
+}
+
+HRESULT Medium::getLastAccessError(com::Utf8Str &aLastAccessError)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    aLastAccessError = m->strLastAccessError;
+
+    return S_OK;
+}
+
+HRESULT Medium::getMachineIds(std::vector<com::Guid> &aMachineIds)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    if (m->backRefs.size() != 0)
+    {
+        BackRefList brlist(m->backRefs);
+        aMachineIds.resize(brlist.size());
+        size_t i = 0;
+        for (BackRefList::const_iterator it = brlist.begin(); it != brlist.end(); ++it, ++i)
+             aMachineIds[i] = it->machineId;
+    }
+
+    return S_OK;
+}
+
+HRESULT Medium::setIds(AutoCaller &autoCaller,
+                       BOOL aSetImageId,
+                       const com::Guid &aImageId,
+                       BOOL aSetParentId,
+                       const com::Guid &aParentId)
+{
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    /* Wait for a concurrently running Medium::i_queryInfo to complete. */
+    if (m->queryInfoRunning)
+    {
+        /* Must not hold the media tree lock, as Medium::i_queryInfo needs this
+         * lock and thus we would run into a deadlock here. */
+        Assert(!m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+        while (m->queryInfoRunning)
+        {
+            alock.release();
+            /* must not hold the object lock now */
+            Assert(!isWriteLockOnCurrentThread());
+            {
+                AutoReadLock qlock(m->queryInfoSem COMMA_LOCKVAL_SRC_POS);
+            }
+            alock.acquire();
+        }
+    }
+
+    switch (m->state)
+    {
+        case MediumState_Created:
+            break;
+        default:
+            return i_setStateError();
+    }
+
+    Guid imageId, parentId;
+    if (aSetImageId)
+    {
+        if (aImageId.isZero())
+            imageId.create();
+        else
+        {
+            imageId = aImageId;
+            if (!imageId.isValid())
+                return setError(E_INVALIDARG, tr("Argument %s is invalid"), "aImageId");
+        }
+    }
+    if (aSetParentId)
+    {
+        if (aParentId.isZero())
+            parentId.create();
+        else
+            parentId = aParentId;
+    }
+
+    const Guid uPrevImage = m->uuidImage;
+    unconst(m->uuidImage) = imageId;
+    ComObjPtr<Medium> pPrevParent = i_getParent();
+    unconst(m->uuidParentImage) = parentId;
+
+    // must not hold any locks before calling Medium::i_queryInfo
+    alock.release();
+
+    HRESULT hrc = i_queryInfo(!!aSetImageId /* fSetImageId */,
+                              !!aSetParentId /* fSetParentId */,
+                              autoCaller);
+
+    AutoReadLock arlock(this COMMA_LOCKVAL_SRC_POS);
+    const Guid uCurrImage = m->uuidImage;
+    ComObjPtr<Medium> pCurrParent = i_getParent();
+    arlock.release();
+
+    if (SUCCEEDED(hrc))
+    {
+        if (uCurrImage != uPrevImage)
+            m->pVirtualBox->i_onMediumConfigChanged(this);
+        if (pPrevParent != pCurrParent)
+        {
+            if (pPrevParent)
+                m->pVirtualBox->i_onMediumConfigChanged(pPrevParent);
+            if (pCurrParent)
+                m->pVirtualBox->i_onMediumConfigChanged(pCurrParent);
+        }
+    }
+
+    return hrc;
+}
+
+HRESULT Medium::refreshState(AutoCaller &autoCaller, MediumState_T *aState)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    HRESULT hrc = S_OK;
+
+    switch (m->state)
+    {
+        case MediumState_Created:
+        case MediumState_Inaccessible:
+        case MediumState_LockedRead:
+        {
+            // must not hold any locks before calling Medium::i_queryInfo
+            alock.release();
+
+            hrc = i_queryInfo(false /* fSetImageId */, false /* fSetParentId */, autoCaller);
+
+            alock.acquire();
+            break;
+        }
+        default:
+            break;
+    }
+
+    *aState = m->state;
+
+    return hrc;
+}
+
+HRESULT Medium::getSnapshotIds(const com::Guid &aMachineId,
+                               std::vector<com::Guid> &aSnapshotIds)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    for (BackRefList::const_iterator it = m->backRefs.begin();
+         it != m->backRefs.end(); ++it)
+    {
+        if (it->machineId == aMachineId)
+        {
+            size_t size = it->llSnapshotIds.size();
+
+            /* if the medium is attached to the machine in the current state, we
+             * return its ID as the first element of the array */
+            if (it->fInCurState)
+                ++size;
+
+            if (size > 0)
+            {
+                aSnapshotIds.resize(size);
+
+                size_t j = 0;
+                if (it->fInCurState)
+                    aSnapshotIds[j++] = it->machineId.toUtf16();
+
+                for(std::list<SnapshotRef>::const_iterator jt = it->llSnapshotIds.begin(); jt != it->llSnapshotIds.end(); ++jt, ++j)
+                    aSnapshotIds[j] = jt->snapshotId;
+            }
+
+            break;
+        }
+    }
+
+    return S_OK;
+}
+
+HRESULT Medium::lockRead(ComPtr<IToken> &aToken)
+{
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    /* Wait for a concurrently running Medium::i_queryInfo to complete. */
+    if (m->queryInfoRunning)
+    {
+        /* Must not hold the media tree lock, as Medium::i_queryInfo needs this
+         * lock and thus we would run into a deadlock here. */
+        Assert(!m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+        while (m->queryInfoRunning)
+        {
+            alock.release();
+            /* must not hold the object lock now */
+            Assert(!isWriteLockOnCurrentThread());
+            {
+                AutoReadLock qlock(m->queryInfoSem COMMA_LOCKVAL_SRC_POS);
+            }
+            alock.acquire();
+        }
+    }
+
+    HRESULT hrc = S_OK;
+
+    switch (m->state)
+    {
+        case MediumState_Created:
+        case MediumState_Inaccessible:
+        case MediumState_LockedRead:
+        {
+            ++m->readers;
+
+            ComAssertMsgBreak(m->readers != 0, (tr("Counter overflow")), hrc = E_FAIL);
+
+            /* Remember pre-lock state */
+            if (m->state != MediumState_LockedRead)
+                m->preLockState = m->state;
+
+            LogFlowThisFunc(("Okay - prev state=%d readers=%d\n", m->state, m->readers));
+            m->state = MediumState_LockedRead;
+
+            ComObjPtr<MediumLockToken> pToken;
+            hrc = pToken.createObject();
+            if (SUCCEEDED(hrc))
+                hrc = pToken->init(this, false /* fWrite */);
+            if (FAILED(hrc))
+            {
+                --m->readers;
+                if (m->readers == 0)
+                    m->state = m->preLockState;
+                return hrc;
+            }
+
+            pToken.queryInterfaceTo(aToken.asOutParam());
+            break;
+        }
+        default:
+        {
+            LogFlowThisFunc(("Failing - state=%d\n", m->state));
+            hrc = i_setStateError();
+            break;
+        }
+    }
+
+    return hrc;
+}
+
+/**
+ * @note @a aState may be NULL if the state value is not needed (only for
+ *       in-process calls).
+ */
+HRESULT Medium::i_unlockRead(MediumState_T *aState)
+{
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    HRESULT hrc = S_OK;
+
+    switch (m->state)
+    {
+        case MediumState_LockedRead:
+        {
+            ComAssertMsgBreak(m->readers != 0, (tr("Counter underflow")), hrc = E_FAIL);
+            --m->readers;
+
+            /* Reset the state after the last reader */
+            if (m->readers == 0)
+            {
+                m->state = m->preLockState;
+                /* There are cases where we inject the deleting state into
+                 * a medium locked for reading. Make sure #unmarkForDeletion()
+                 * gets the right state afterwards. */
+                if (m->preLockState == MediumState_Deleting)
+                    m->preLockState = MediumState_Created;
+            }
+
+            LogFlowThisFunc(("new state=%d\n", m->state));
+            break;
+        }
+        default:
+        {
+            LogFlowThisFunc(("Failing - state=%d\n", m->state));
+            hrc = setError(VBOX_E_INVALID_OBJECT_STATE, tr("Medium '%s' is not locked for reading"), m->strLocationFull.c_str());
+            break;
+        }
+    }
+
+    /* return the current state after */
+    if (aState)
+        *aState = m->state;
+
+    return hrc;
+}
+HRESULT Medium::lockWrite(ComPtr<IToken> &aToken)
+{
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    /* Wait for a concurrently running Medium::i_queryInfo to complete. */
+    if (m->queryInfoRunning)
+    {
+        /* Must not hold the media tree lock, as Medium::i_queryInfo needs this
+         * lock and thus we would run into a deadlock here. */
+        Assert(!m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+        while (m->queryInfoRunning)
+        {
+            alock.release();
+            /* must not hold the object lock now */
+            Assert(!isWriteLockOnCurrentThread());
+            {
+                AutoReadLock qlock(m->queryInfoSem COMMA_LOCKVAL_SRC_POS);
+            }
+            alock.acquire();
+        }
+    }
+
+    HRESULT hrc = S_OK;
+
+    switch (m->state)
+    {
+        case MediumState_Created:
+        case MediumState_Inaccessible:
+        {
+            m->preLockState = m->state;
+
+            LogFlowThisFunc(("Okay - prev state=%d locationFull=%s\n", m->state, i_getLocationFull().c_str()));
+            m->state = MediumState_LockedWrite;
+
+            ComObjPtr<MediumLockToken> pToken;
+            hrc = pToken.createObject();
+            if (SUCCEEDED(hrc))
+                hrc = pToken->init(this, true /* fWrite */);
+            if (FAILED(hrc))
+            {
+                m->state = m->preLockState;
+                return hrc;
+            }
+
+            pToken.queryInterfaceTo(aToken.asOutParam());
+            break;
+        }
+        default:
+        {
+            LogFlowThisFunc(("Failing - state=%d locationFull=%s\n", m->state, i_getLocationFull().c_str()));
+            hrc = i_setStateError();
+            break;
+        }
+    }
+
+    return hrc;
+}
+
+/**
+ * @note @a aState may be NULL if the state value is not needed (only for
+ *       in-process calls).
+ */
+HRESULT Medium::i_unlockWrite(MediumState_T *aState)
+{
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    HRESULT hrc = S_OK;
+
+    switch (m->state)
+    {
+        case MediumState_LockedWrite:
+        {
+            m->state = m->preLockState;
+            /* There are cases where we inject the deleting state into
+             * a medium locked for writing. Make sure #unmarkForDeletion()
+             * gets the right state afterwards. */
+            if (m->preLockState == MediumState_Deleting)
+                m->preLockState = MediumState_Created;
+            LogFlowThisFunc(("new state=%d locationFull=%s\n", m->state, i_getLocationFull().c_str()));
+            break;
+        }
+        default:
+        {
+            LogFlowThisFunc(("Failing - state=%d locationFull=%s\n", m->state, i_getLocationFull().c_str()));
+            hrc = setError(VBOX_E_INVALID_OBJECT_STATE, tr("Medium '%s' is not locked for writing"), m->strLocationFull.c_str());
+            break;
+        }
+    }
+
+    /* return the current state after */
+    if (aState)
+        *aState = m->state;
+
+    return hrc;
+}
+
+HRESULT Medium::close(AutoCaller &aAutoCaller)
+{
+    // make a copy of VirtualBox pointer which gets nulled by uninit()
+    ComObjPtr<VirtualBox> pVirtualBox(m->pVirtualBox);
+
+    Guid uId = i_getId();
+    DeviceType_T devType = i_getDeviceType();
+    MultiResult mrc = i_close(aAutoCaller);
+
+    pVirtualBox->i_saveModifiedRegistries();
+
+    if (SUCCEEDED(mrc) && uId.isValid() && !uId.isZero())
+        pVirtualBox->i_onMediumRegistered(uId, devType, FALSE);
+
+    return mrc;
+}
+
+HRESULT Medium::getProperty(const com::Utf8Str &aName,
+                            com::Utf8Str &aValue)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    settings::StringsMap::const_iterator it = m->mapProperties.find(aName);
+    if (it == m->mapProperties.end())
+    {
+        if (!aName.startsWith("Special/"))
+            return setError(VBOX_E_OBJECT_NOT_FOUND,
+                            tr("Property '%s' does not exist"), aName.c_str());
+        else
+            /* be more silent here */
+            return VBOX_E_OBJECT_NOT_FOUND;
+    }
+
+    aValue = it->second;
+
+    return S_OK;
+}
+
+HRESULT Medium::setProperty(const com::Utf8Str &aName,
+                            const com::Utf8Str &aValue)
+{
+    AutoWriteLock mlock(this COMMA_LOCKVAL_SRC_POS);
+
+    /* Wait for a concurrently running Medium::i_queryInfo to complete. */
+    if (m->queryInfoRunning)
+    {
+        /* Must not hold the media tree lock, as Medium::i_queryInfo needs this
+         * lock and thus we would run into a deadlock here. */
+        Assert(!m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+        while (m->queryInfoRunning)
+        {
+            mlock.release();
+            /* must not hold the object lock now */
+            Assert(!isWriteLockOnCurrentThread());
+            {
+                AutoReadLock qlock(m->queryInfoSem COMMA_LOCKVAL_SRC_POS);
+            }
+            mlock.acquire();
+        }
+    }
+
+    switch (m->state)
+    {
+        case MediumState_NotCreated:
+        case MediumState_Created:
+        case MediumState_Inaccessible:
+            break;
+        default:
+            return i_setStateError();
+    }
+
+    settings::StringsMap::iterator it = m->mapProperties.find(aName);
+    if (   !aName.startsWith("Special/")
+        && !i_isPropertyForFilter(aName))
+    {
+        if (it == m->mapProperties.end())
+            return setError(VBOX_E_OBJECT_NOT_FOUND,
+                            tr("Property '%s' does not exist"),
+                            aName.c_str());
+        it->second = aValue;
+    }
+    else
+    {
+        if (it == m->mapProperties.end())
+        {
+            if (!aValue.isEmpty())
+                m->mapProperties[aName] = aValue;
+        }
+        else
+        {
+            if (!aValue.isEmpty())
+                it->second = aValue;
+            else
+                m->mapProperties.erase(it);
+        }
+    }
+
+    // save the settings
+    mlock.release();
+    i_markRegistriesModified();
+    m->pVirtualBox->i_saveModifiedRegistries();
+    m->pVirtualBox->i_onMediumConfigChanged(this);
+
+    return S_OK;
+}
+
+HRESULT Medium::getProperties(const com::Utf8Str &aNames,
+                              std::vector<com::Utf8Str> &aReturnNames,
+                              std::vector<com::Utf8Str> &aReturnValues)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    /// @todo make use of aNames according to the documentation
+    NOREF(aNames);
+
+    aReturnNames.resize(m->mapProperties.size());
+    aReturnValues.resize(m->mapProperties.size());
+    size_t i = 0;
+    for (settings::StringsMap::const_iterator it = m->mapProperties.begin();
+         it != m->mapProperties.end();
+         ++it, ++i)
+    {
+        aReturnNames[i] = it->first;
+        aReturnValues[i] = it->second;
+    }
+    return S_OK;
+}
+
+HRESULT Medium::setProperties(const std::vector<com::Utf8Str> &aNames,
+                              const std::vector<com::Utf8Str> &aValues)
+{
+    AutoWriteLock mlock(this COMMA_LOCKVAL_SRC_POS);
+
+    /* first pass: validate names */
+    for (size_t i = 0;
+         i < aNames.size();
+         ++i)
+    {
+        Utf8Str strName(aNames[i]);
+        if (   !strName.startsWith("Special/")
+            && !i_isPropertyForFilter(strName)
+            && m->mapProperties.find(strName) == m->mapProperties.end())
+            return setError(VBOX_E_OBJECT_NOT_FOUND,
+                            tr("Property '%s' does not exist"), strName.c_str());
+    }
+
+    /* second pass: assign */
+    for (size_t i = 0;
+         i < aNames.size();
+         ++i)
+    {
+        Utf8Str strName(aNames[i]);
+        Utf8Str strValue(aValues[i]);
+        settings::StringsMap::iterator it = m->mapProperties.find(strName);
+        if (   !strName.startsWith("Special/")
+            && !i_isPropertyForFilter(strName))
+        {
+            AssertReturn(it != m->mapProperties.end(), E_FAIL);
+            it->second = strValue;
+        }
+        else
+        {
+            if (it == m->mapProperties.end())
+            {
+                if (!strValue.isEmpty())
+                    m->mapProperties[strName] = strValue;
+            }
+            else
+            {
+                if (!strValue.isEmpty())
+                    it->second = strValue;
+                else
+                    m->mapProperties.erase(it);
+            }
+        }
+    }
+
+    // save the settings
+    mlock.release();
+    i_markRegistriesModified();
+    m->pVirtualBox->i_saveModifiedRegistries();
+    m->pVirtualBox->i_onMediumConfigChanged(this);
+
+    return S_OK;
+}
+
+HRESULT Medium::createBaseStorage(LONG64 aLogicalSize,
+                                  const std::vector<MediumVariant_T> &aVariant,
+                                  ComPtr<IProgress> &aProgress)
+{
+    if (aLogicalSize < 0)
+        return setError(E_INVALIDARG, tr("The medium size argument (%lld) is negative"), aLogicalSize);
+
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        ULONG mediumVariantFlags = 0;
+
+        if (aVariant.size())
+        {
+            for (size_t i = 0; i < aVariant.size(); i++)
+                mediumVariantFlags |= (ULONG)aVariant[i];
+        }
+
+        mediumVariantFlags &= ((unsigned)~MediumVariant_Diff);
+
+        if (    !(mediumVariantFlags & MediumVariant_Fixed)
+            &&  !(m->formatObj->i_getCapabilities() & MediumFormatCapabilities_CreateDynamic))
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Medium format '%s' does not support dynamic storage creation"),
+                           m->strFormat.c_str());
+
+        if (    (mediumVariantFlags & MediumVariant_Fixed)
+            &&  !(m->formatObj->i_getCapabilities() & MediumFormatCapabilities_CreateFixed))
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Medium format '%s' does not support fixed storage creation"),
+                           m->strFormat.c_str());
+
+        if (    (mediumVariantFlags & MediumVariant_Formatted)
+            &&  i_getDeviceType() != DeviceType_Floppy)
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Medium variant 'formatted' applies to floppy images only"));
+
+        if (m->state != MediumState_NotCreated)
+            throw i_setStateError();
+
+        pProgress.createObject();
+        hrc = pProgress->init(m->pVirtualBox,
+                              static_cast<IMedium*>(this),
+                              mediumVariantFlags & MediumVariant_Fixed
+                              ? BstrFmt(tr("Creating fixed medium storage unit '%s'"), m->strLocationFull.c_str()).raw()
+                              : BstrFmt(tr("Creating dynamic medium storage unit '%s'"), m->strLocationFull.c_str()).raw(),
+                              TRUE /* aCancelable */);
+        if (FAILED(hrc))
+            throw hrc;
+
+        /* setup task object to carry out the operation asynchronously */
+        pTask = new Medium::CreateBaseTask(this, pProgress, (uint64_t)aLogicalSize,
+                                           (MediumVariant_T)mediumVariantFlags);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+
+        m->state = MediumState_Creating;
+    }
+    catch (HRESULT hrcXcpt)
+    {
+        hrc = hrcXcpt;
+    }
+
+    if (SUCCEEDED(hrc))
+    {
+        hrc = pTask->createThread();
+        pTask = NULL;
+
+        if (SUCCEEDED(hrc))
+            pProgress.queryInterfaceTo(aProgress.asOutParam());
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    return hrc;
+}
+
+HRESULT Medium::deleteStorage(ComPtr<IProgress> &aProgress)
+{
+    ComObjPtr<Progress> pProgress;
+
+    MultiResult mrc = i_deleteStorage(&pProgress,
+                                      false /* aWait */,
+                                      true /* aNotify */);
+    /* Must save the registries in any case, since an entry was removed. */
+    m->pVirtualBox->i_saveModifiedRegistries();
+
+    if (SUCCEEDED(mrc))
+        pProgress.queryInterfaceTo(aProgress.asOutParam());
+
+    return mrc;
+}
+
+HRESULT Medium::createDiffStorage(AutoCaller &autoCaller,
+                                  const ComPtr<IMedium> &aTarget,
+                                  const std::vector<MediumVariant_T> &aVariant,
+                                  ComPtr<IProgress> &aProgress)
+{
+    IMedium *aT = aTarget;
+    ComObjPtr<Medium> diff = static_cast<Medium*>(aT);
+
+    autoCaller.release();
+
+    /* It is possible that some previous/concurrent uninit has already cleared
+     * the pVirtualBox reference, see #uninit(). */
+    ComObjPtr<VirtualBox> pVirtualBox(m->pVirtualBox);
+
+    // we access m->pParent
+    AutoReadLock treeLock(!pVirtualBox.isNull() ? &pVirtualBox->i_getMediaTreeLockHandle() : NULL COMMA_LOCKVAL_SRC_POS);
+
+    autoCaller.add();
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    AutoMultiWriteLock2 alock(this, diff COMMA_LOCKVAL_SRC_POS);
+
+    if (m->type == MediumType_Writethrough)
+        return setError(VBOX_E_INVALID_OBJECT_STATE,
+                        tr("Medium type of '%s' is Writethrough"),
+                        m->strLocationFull.c_str());
+    else if (m->type == MediumType_Shareable)
+        return setError(VBOX_E_INVALID_OBJECT_STATE,
+                        tr("Medium type of '%s' is Shareable"),
+                        m->strLocationFull.c_str());
+    else if (m->type == MediumType_Readonly)
+        return setError(VBOX_E_INVALID_OBJECT_STATE,
+                        tr("Medium type of '%s' is Readonly"),
+                        m->strLocationFull.c_str());
+
+    /* Apply the normal locking logic to the entire chain. */
+    MediumLockList *pMediumLockList(new MediumLockList());
+    alock.release();
+    autoCaller.release();
+    treeLock.release();
+    HRESULT hrc = diff->i_createMediumLockList(true /* fFailIfInaccessible */,
+                                               diff /* pToLockWrite */,
+                                               false /* fMediumLockWriteAll */,
+                                               this,
+                                               *pMediumLockList);
+    treeLock.acquire();
+    autoCaller.add();
+    if (FAILED(autoCaller.hrc()))
+        hrc = autoCaller.hrc();
+    alock.acquire();
+    if (FAILED(hrc))
+    {
+        delete pMediumLockList;
+        return hrc;
+    }
+
+    alock.release();
+    autoCaller.release();
+    treeLock.release();
+    hrc = pMediumLockList->Lock();
+    treeLock.acquire();
+    autoCaller.add();
+    if (FAILED(autoCaller.hrc()))
+        hrc = autoCaller.hrc();
+    alock.acquire();
+    if (FAILED(hrc))
+    {
+        delete pMediumLockList;
+
+        return setError(hrc, tr("Could not lock medium when creating diff '%s'"),
+                        diff->i_getLocationFull().c_str());
+    }
+
+    Guid parentMachineRegistry;
+    if (i_getFirstRegistryMachineId(parentMachineRegistry))
+    {
+        /* since this medium has been just created it isn't associated yet */
+        diff->m->llRegistryIDs.push_back(parentMachineRegistry);
+        alock.release();
+        autoCaller.release();
+        treeLock.release();
+        diff->i_markRegistriesModified();
+        treeLock.acquire();
+        autoCaller.add();
+        alock.acquire();
+    }
+
+    alock.release();
+    autoCaller.release();
+    treeLock.release();
+
+    ComObjPtr<Progress> pProgress;
+
+    ULONG mediumVariantFlags = 0;
+
+    if (aVariant.size())
+    {
+        for (size_t i = 0; i < aVariant.size(); i++)
+            mediumVariantFlags |= (ULONG)aVariant[i];
+    }
+
+    if (mediumVariantFlags & MediumVariant_Formatted)
+    {
+        delete pMediumLockList;
+        return setError(VBOX_E_NOT_SUPPORTED,
+                        tr("Medium variant 'formatted' applies to floppy images only"));
+    }
+
+    hrc = i_createDiffStorage(diff, (MediumVariant_T)mediumVariantFlags, pMediumLockList,
+                              &pProgress, false /* aWait */, true /* aNotify */);
+    if (FAILED(hrc))
+        delete pMediumLockList;
+    else
+        pProgress.queryInterfaceTo(aProgress.asOutParam());
+
+    return hrc;
+}
+
+HRESULT Medium::mergeTo(const ComPtr<IMedium> &aTarget,
+                        ComPtr<IProgress> &aProgress)
+{
+    IMedium *aT = aTarget;
+
+    ComAssertRet(aT != this, E_INVALIDARG);
+
+    ComObjPtr<Medium> pTarget = static_cast<Medium*>(aT);
+
+    bool fMergeForward = false;
+    ComObjPtr<Medium> pParentForTarget;
+    MediumLockList *pChildrenToReparent = NULL;
+    MediumLockList *pMediumLockList = NULL;
+
+    HRESULT hrc = i_prepareMergeTo(pTarget, NULL, NULL, true, fMergeForward,
+                                   pParentForTarget, pChildrenToReparent, pMediumLockList);
+    if (FAILED(hrc)) return hrc;
+
+    ComObjPtr<Progress> pProgress;
+
+    hrc = i_mergeTo(pTarget, fMergeForward, pParentForTarget, pChildrenToReparent,
+                    pMediumLockList, &pProgress, false /* aWait */, true /* aNotify */);
+    if (FAILED(hrc))
+        i_cancelMergeTo(pChildrenToReparent, pMediumLockList);
+    else
+        pProgress.queryInterfaceTo(aProgress.asOutParam());
+
+    return hrc;
+}
+
+HRESULT Medium::cloneToBase(const ComPtr<IMedium> &aTarget,
+                            const std::vector<MediumVariant_T> &aVariant,
+                            ComPtr<IProgress> &aProgress)
+{
+     return cloneTo(aTarget, aVariant, NULL, aProgress);
+}
+
+HRESULT Medium::cloneTo(const ComPtr<IMedium> &aTarget,
+                        const std::vector<MediumVariant_T> &aVariant,
+                        const ComPtr<IMedium> &aParent,
+                        ComPtr<IProgress> &aProgress)
+{
+    /** @todo r=jack: Remove redundancy. Call Medium::resizeAndCloneTo. */
+
+    /** @todo r=klaus The code below needs to be double checked with regard
+     * to lock order violations, it probably causes lock order issues related
+     * to the AutoCaller usage. */
+    ComAssertRet(aTarget != this, E_INVALIDARG);
+
+    IMedium *aT = aTarget;
+    ComObjPtr<Medium> pTarget = static_cast<Medium*>(aT);
+    ComObjPtr<Medium> pParent;
+    if (aParent)
+    {
+        IMedium *aP = aParent;
+        pParent = static_cast<Medium*>(aP);
+    }
+
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        // locking: we need the tree lock first because we access parent pointers
+        // and we need to write-lock the media involved
+        uint32_t    cHandles    = 3;
+        LockHandle* pHandles[4] = { &m->pVirtualBox->i_getMediaTreeLockHandle(),
+                                    this->lockHandle(),
+                                    pTarget->lockHandle() };
+        /* Only add parent to the lock if it is not null */
+        if (!pParent.isNull())
+            pHandles[cHandles++] = pParent->lockHandle();
+        AutoWriteLock alock(cHandles,
+                            pHandles
+                            COMMA_LOCKVAL_SRC_POS);
+
+        if (    pTarget->m->state != MediumState_NotCreated
+            &&  pTarget->m->state != MediumState_Created)
+            throw pTarget->i_setStateError();
+
+        /* Build the source lock list. */
+        MediumLockList *pSourceMediumLockList(new MediumLockList());
+        alock.release();
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                     NULL /* pToLockWrite */,
+                                     false /* fMediumLockWriteAll */,
+                                     NULL,
+                                     *pSourceMediumLockList);
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            throw hrc;
+        }
+
+        /* Build the target lock list (including the to-be parent chain). */
+        MediumLockList *pTargetMediumLockList(new MediumLockList());
+        alock.release();
+        hrc = pTarget->i_createMediumLockList(true /* fFailIfInaccessible */,
+                                              pTarget /* pToLockWrite */,
+                                              false /* fMediumLockWriteAll */,
+                                              pParent,
+                                              *pTargetMediumLockList);
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw hrc;
+        }
+
+        alock.release();
+        hrc = pSourceMediumLockList->Lock();
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock source media '%s'"),
+                           i_getLocationFull().c_str());
+        }
+        alock.release();
+        hrc = pTargetMediumLockList->Lock();
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock target media '%s'"),
+                           pTarget->i_getLocationFull().c_str());
+        }
+
+        pProgress.createObject();
+        hrc = pProgress->init(m->pVirtualBox,
+                              static_cast <IMedium *>(this),
+                              BstrFmt(tr("Creating clone medium '%s'"), pTarget->m->strLocationFull.c_str()).raw(),
+                              TRUE /* aCancelable */);
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw hrc;
+        }
+
+        ULONG mediumVariantFlags = 0;
+
+        if (aVariant.size())
+        {
+            for (size_t i = 0; i < aVariant.size(); i++)
+                mediumVariantFlags |= (ULONG)aVariant[i];
+        }
+
+        if (mediumVariantFlags & MediumVariant_Formatted)
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Medium variant 'formatted' applies to floppy images only"));
+        }
+
+        /* setup task object to carry out the operation asynchronously */
+        pTask = new Medium::CloneTask(this, pProgress, pTarget,
+                                      (MediumVariant_T)mediumVariantFlags,
+                                      pParent, UINT32_MAX, UINT32_MAX,
+                                      pSourceMediumLockList, pTargetMediumLockList);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+
+        if (pTarget->m->state == MediumState_NotCreated)
+            pTarget->m->state = MediumState_Creating;
+    }
+    catch (HRESULT hrcXcpt)
+    {
+        hrc = hrcXcpt;
+    }
+
+    if (SUCCEEDED(hrc))
+    {
+        hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc))
+            pProgress.queryInterfaceTo(aProgress.asOutParam());
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    return hrc;
+}
+
+/**
+ * This is a helper function that combines the functionality of
+ * Medium::cloneTo() and Medium::resize(). The target medium will take the
+ * contents of the calling medium.
+ *
+ * @param aTarget           Medium to resize and clone to
+ * @param aLogicalSize      Desired size for targer medium
+ * @param aVariant
+ * @param aParent
+ * @param aProgress
+ * @return HRESULT
+ */
+HRESULT Medium::resizeAndCloneTo(const ComPtr<IMedium> &aTarget,
+                                 LONG64 aLogicalSize,
+                                 const std::vector<MediumVariant_T> &aVariant,
+                                 const ComPtr<IMedium> &aParent,
+                                 ComPtr<IProgress> &aProgress)
+{
+    /* Check for valid args */
+    ComAssertRet(aTarget != this, E_INVALIDARG);
+    CheckComArgExpr(aLogicalSize, aLogicalSize >= 0);
+
+    /* Convert args to usable/needed types */
+    IMedium *aT = aTarget;
+    ComObjPtr<Medium> pTarget = static_cast<Medium*>(aT);
+    ComObjPtr<Medium> pParent;
+    if (aParent)
+    {
+        IMedium *aP = aParent;
+        pParent = static_cast<Medium*>(aP);
+    }
+
+    /* Set up variables. Fetch needed data in lockable blocks */
+    HRESULT hrc = S_OK;
+    Medium::Task *pTask = NULL;
+
+    Utf8Str strSourceName;
+    {
+        AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+        strSourceName = i_getName();
+    }
+
+    uint64_t uTargetExistingSize = 0;
+    Utf8Str strTargetName;
+    {
+        AutoReadLock alock(pTarget COMMA_LOCKVAL_SRC_POS);
+        uTargetExistingSize = pTarget->i_getLogicalSize();
+        strTargetName = pTarget->i_getName();
+    }
+
+    /* Set up internal multi-subprocess progress object */
+    ComObjPtr<Progress> pProgress;
+    pProgress.createObject();
+    hrc = pProgress->init(m->pVirtualBox,
+                          static_cast<IMedium*>(this),
+                          BstrFmt(tr("Resizing medium and cloning into it")).raw(),
+                          TRUE, /* aCancelable */
+                          2, /* Number of opearations */
+                          BstrFmt(tr("Resizing medium before clone")).raw()
+                          );
+    if (FAILED(hrc))
+        return hrc;
+
+    /* If target does not exist, handle resize. */
+    if (pTarget->m->state != MediumState_NotCreated && aLogicalSize > 0)
+    {
+        if ((LONG64)uTargetExistingSize != aLogicalSize) {
+            if (!i_isMediumFormatFile())
+            {
+                hrc = setError(VBOX_E_NOT_SUPPORTED,
+                               tr("Sizes of '%s' and '%s' are different and medium format does not support resing"),
+                               strSourceName.c_str(), strTargetName.c_str());
+                return hrc;
+            }
+
+            /**
+             * Need to lock the target medium as i_resize does do so
+             * automatically.
+             */
+
+            ComPtr<IToken> pToken;
+            hrc = pTarget->LockWrite(pToken.asOutParam());
+
+            if (FAILED(hrc)) return hrc;
+
+            /**
+             * Have to make own lock list, because "resize" method resizes only
+             * last image in the lock chain.
+             */
+
+            MediumLockList* pMediumLockListForResize = new MediumLockList();
+            pMediumLockListForResize->Append(pTarget, pTarget->m->state == MediumState_LockedWrite);
+
+            hrc = pMediumLockListForResize->Lock(true /* fSkipOverLockedMedia */);
+            if (FAILED(hrc))
+            {
+                AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+                hrc = setError(hrc,
+                               tr("Failed to lock the medium '%s' to resize before merge"),
+                               strTargetName.c_str());
+                delete pMediumLockListForResize;
+                return hrc;
+            }
+
+
+            hrc = pTarget->i_resize((uint64_t)aLogicalSize, pMediumLockListForResize, &pProgress, true, false);
+            if (FAILED(hrc))
+            {
+                /* No need to setError becasue i_resize and i_taskResizeHandler handle this automatically. */
+                AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+                delete pMediumLockListForResize;
+                return hrc;
+            }
+
+            delete pMediumLockListForResize;
+
+            pTarget->m->logicalSize = (uint64_t)aLogicalSize;
+
+            pToken->Abandon();
+            pToken.setNull();
+        }
+    }
+
+    /* Report progress to supplied progress argument */
+    if (SUCCEEDED(hrc))
+    {
+        pProgress.queryInterfaceTo(aProgress.asOutParam());
+    }
+
+    try
+    {
+        // locking: we need the tree lock first because we access parent pointers
+        // and we need to write-lock the media involved
+        uint32_t    cHandles    = 3;
+        LockHandle* pHandles[4] = { &m->pVirtualBox->i_getMediaTreeLockHandle(),
+                                    this->lockHandle(),
+                                    pTarget->lockHandle() };
+        /* Only add parent to the lock if it is not null */
+        if (!pParent.isNull())
+            pHandles[cHandles++] = pParent->lockHandle();
+        AutoWriteLock alock(cHandles,
+                            pHandles
+                            COMMA_LOCKVAL_SRC_POS);
+
+        if (    pTarget->m->state != MediumState_NotCreated
+            &&  pTarget->m->state != MediumState_Created)
+            throw pTarget->i_setStateError();
+
+        /* Build the source lock list. */
+        MediumLockList *pSourceMediumLockList(new MediumLockList());
+        alock.release();
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                     NULL /* pToLockWrite */,
+                                     false /* fMediumLockWriteAll */,
+                                     NULL,
+                                     *pSourceMediumLockList);
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            throw hrc;
+        }
+
+        /* Build the target lock list (including the to-be parent chain). */
+        MediumLockList *pTargetMediumLockList(new MediumLockList());
+        alock.release();
+        hrc = pTarget->i_createMediumLockList(true /* fFailIfInaccessible */,
+                                              pTarget /* pToLockWrite */,
+                                              false /* fMediumLockWriteAll */,
+                                              pParent,
+                                              *pTargetMediumLockList);
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw hrc;
+        }
+
+        alock.release();
+        hrc = pSourceMediumLockList->Lock();
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock source media '%s'"),
+                           i_getLocationFull().c_str());
+        }
+        alock.release();
+        hrc = pTargetMediumLockList->Lock();
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock target media '%s'"),
+                           pTarget->i_getLocationFull().c_str());
+        }
+
+        ULONG mediumVariantFlags = 0;
+
+        if (aVariant.size())
+        {
+            for (size_t i = 0; i < aVariant.size(); i++)
+                mediumVariantFlags |= (ULONG)aVariant[i];
+        }
+
+        if (mediumVariantFlags & MediumVariant_Formatted)
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Medium variant 'formatted' applies to floppy images only"));
+        }
+
+        if (pTarget->m->state != MediumState_NotCreated || aLogicalSize == 0)
+        {
+            /* setup task object to carry out the operation asynchronously */
+            pTask = new Medium::CloneTask(this, pProgress, pTarget,
+                                          (MediumVariant_T)mediumVariantFlags,
+                                          pParent, UINT32_MAX, UINT32_MAX,
+                                          pSourceMediumLockList, pTargetMediumLockList,
+                                          false, false, true, 0);
+        }
+        else
+        {
+            /* setup task object to carry out the operation asynchronously */
+            pTask = new Medium::CloneTask(this, pProgress, pTarget,
+                                          (MediumVariant_T)mediumVariantFlags,
+                                          pParent, UINT32_MAX, UINT32_MAX,
+                                          pSourceMediumLockList, pTargetMediumLockList,
+                                          false, false, true, (uint64_t)aLogicalSize);
+        }
+
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+
+        if (pTarget->m->state == MediumState_NotCreated)
+            pTarget->m->state = MediumState_Creating;
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc))
+            pProgress.queryInterfaceTo(aProgress.asOutParam());
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    return hrc;
+}
+
+HRESULT Medium::moveTo(AutoCaller &autoCaller, const com::Utf8Str &aLocation, ComPtr<IProgress> &aProgress)
+{
+    ComObjPtr<Medium> pParent;
+    ComObjPtr<Progress> pProgress;
+    HRESULT hrc = S_OK;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+    /// @todo NEWMEDIA for file names, add the default extension if no extension
+    /// is present (using the information from the VD backend which also implies
+    /// that one more parameter should be passed to moveTo() requesting
+    /// that functionality since it is only allowed when called from this method
+
+    /// @todo NEWMEDIA rename the file and set m->location on success, then save
+    /// the global registry (and local registries of portable VMs referring to
+    /// this medium), this will also require to add the mRegistered flag to data
+
+        autoCaller.release();
+
+        // locking: we need the tree lock first because we access parent pointers
+        // and we need to write-lock the media involved
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+        autoCaller.add();
+        AssertComRCThrowRC(autoCaller.hrc());
+
+        AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        /* play with locations */
+        {
+            /* get source path and filename */
+            Utf8Str sourcePath = i_getLocationFull();
+            Utf8Str sourceFName = i_getName();
+
+            if (aLocation.isEmpty())
+            {
+                hrc = setErrorVrc(VERR_PATH_ZERO_LENGTH,
+                                  tr("Medium '%s' can't be moved. Destination path is empty."),
+                                  i_getLocationFull().c_str());
+                throw hrc;
+            }
+
+            /* extract destination path and filename */
+            Utf8Str destPath(aLocation);
+            Utf8Str destFName(destPath);
+            destFName.stripPath();
+
+            if (destFName.isNotEmpty() && !RTPathHasSuffix(destFName.c_str()))
+            {
+                /*
+                 * The target path has no filename: Either "/path/to/new/location" or
+                 * just "newname" (no trailing backslash or there is no filename extension).
+                 */
+                if (destPath.equals(destFName))
+                {
+                    /* new path contains only "newname", no path, no extension */
+                    destFName.append(RTPathSuffix(sourceFName.c_str()));
+                    destPath = destFName;
+                }
+                else
+                {
+                    /* new path looks like "/path/to/new/location" */
+                    destFName.setNull();
+                    destPath.append(RTPATH_SLASH);
+                }
+            }
+
+            if (destFName.isEmpty())
+            {
+                /* No target name */
+                destPath.append(sourceFName);
+            }
+            else
+            {
+                if (destPath.equals(destFName))
+                {
+                    /*
+                     * The target path contains of only a filename without a directory.
+                     * Move the medium within the source directory to the new name
+                     * (actually rename operation).
+                     * Scratches sourcePath!
+                     */
+                    destPath = sourcePath.stripFilename().append(RTPATH_SLASH).append(destFName);
+                }
+
+                const char *pszSuffix = RTPathSuffix(sourceFName.c_str());
+
+                /* Suffix is empty and one is deduced from the medium format */
+                if (pszSuffix == NULL)
+                {
+                    Utf8Str strExt = i_getFormat();
+                    if (strExt.compare("RAW", Utf8Str::CaseInsensitive) == 0)
+                    {
+                        DeviceType_T devType = i_getDeviceType();
+                        switch (devType)
+                        {
+                            case DeviceType_DVD:
+                                strExt = "iso";
+                                break;
+                            case DeviceType_Floppy:
+                                strExt = "img";
+                                break;
+                            default:
+                                hrc = setErrorVrc(VERR_NOT_A_FILE, /** @todo r=bird: Mixing status codes again. */
+                                                  tr("Medium '%s' has RAW type. \"Move\" operation isn't supported for this type."),
+                                                  i_getLocationFull().c_str());
+                                throw hrc;
+                        }
+                    }
+                    else if (strExt.compare("Parallels", Utf8Str::CaseInsensitive) == 0)
+                    {
+                        strExt = "hdd";
+                    }
+
+                    /* Set the target extension like on the source. Any conversions are prohibited */
+                    strExt.toLower();
+                    destPath.stripSuffix().append('.').append(strExt);
+                }
+                else
+                    destPath.stripSuffix().append(pszSuffix);
+            }
+
+            /* Simple check for existence */
+            if (RTFileExists(destPath.c_str()))
+                throw setError(VBOX_E_FILE_ERROR,
+                               tr("The given path '%s' is an existing file. Delete or rename this file."),
+                               destPath.c_str());
+
+            if (!i_isMediumFormatFile())
+                throw setErrorVrc(VERR_NOT_A_FILE,
+                                  tr("Medium '%s' isn't a file object. \"Move\" operation isn't supported."),
+                                  i_getLocationFull().c_str());
+            /* Path must be absolute */
+            if (!RTPathStartsWithRoot(destPath.c_str()))
+                throw setError(VBOX_E_FILE_ERROR,
+                               tr("The given path '%s' is not fully qualified"),
+                               destPath.c_str());
+            /* Check path for a new file object */
+            hrc = VirtualBox::i_ensureFilePathExists(destPath, true);
+            if (FAILED(hrc))
+                throw hrc;
+
+            /* Set needed variables for "moving" procedure. It'll be used later in separate thread task */
+            hrc = i_preparationForMoving(destPath);
+            if (FAILED(hrc))
+                throw setErrorVrc(VERR_NO_CHANGE,
+                                  tr("Medium '%s' is already in the correct location"),
+                                  i_getLocationFull().c_str());
+        }
+
+        /* Check VMs which have this medium attached to*/
+        std::vector<com::Guid> aMachineIds;
+        hrc = getMachineIds(aMachineIds);
+        std::vector<com::Guid>::const_iterator currMachineID = aMachineIds.begin();
+        std::vector<com::Guid>::const_iterator lastMachineID = aMachineIds.end();
+
+        while (currMachineID != lastMachineID)
+        {
+            Guid id(*currMachineID);
+            ComObjPtr<Machine> aMachine;
+
+            alock.release();
+            autoCaller.release();
+            treeLock.release();
+            hrc = m->pVirtualBox->i_findMachine(id, false, true, &aMachine);
+            treeLock.acquire();
+            autoCaller.add();
+            AssertComRCThrowRC(autoCaller.hrc());
+            alock.acquire();
+
+            if (SUCCEEDED(hrc))
+            {
+                ComObjPtr<SessionMachine> sm;
+                ComPtr<IInternalSessionControl> ctl;
+
+                alock.release();
+                autoCaller.release();
+                treeLock.release();
+                bool ses = aMachine->i_isSessionOpenVM(sm, &ctl);
+                treeLock.acquire();
+                autoCaller.add();
+                AssertComRCThrowRC(autoCaller.hrc());
+                alock.acquire();
+
+                if (ses)
+                    throw setError(VBOX_E_INVALID_VM_STATE,
+                                   tr("At least the VM '%s' to whom this medium '%s' attached has currently an opened session. Stop all VMs before relocating this medium"),
+                                   id.toString().c_str(), i_getLocationFull().c_str());
+            }
+            ++currMachineID;
+        }
+
+        /* Build the source lock list. */
+        MediumLockList *pMediumLockList(new MediumLockList());
+        alock.release();
+        autoCaller.release();
+        treeLock.release();
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                     this /* pToLockWrite */,
+                                     true /* fMediumLockWriteAll */,
+                                     NULL,
+                                     *pMediumLockList);
+        treeLock.acquire();
+        autoCaller.add();
+        AssertComRCThrowRC(autoCaller.hrc());
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw setError(hrc, tr("Failed to create medium lock list for '%s'"), i_getLocationFull().c_str());
+        }
+        alock.release();
+        autoCaller.release();
+        treeLock.release();
+        hrc = pMediumLockList->Lock();
+        treeLock.acquire();
+        autoCaller.add();
+        AssertComRCThrowRC(autoCaller.hrc());
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw setError(hrc, tr("Failed to lock media '%s'"), i_getLocationFull().c_str());
+        }
+
+        pProgress.createObject();
+        hrc = pProgress->init(m->pVirtualBox,
+                              static_cast <IMedium *>(this),
+                              BstrFmt(tr("Moving medium '%s'"), m->strLocationFull.c_str()).raw(),
+                              TRUE /* aCancelable */);
+
+        /* Do the disk moving. */
+        if (SUCCEEDED(hrc))
+        {
+            ULONG mediumVariantFlags = i_getVariant();
+
+            /* setup task object to carry out the operation asynchronously */
+            pTask = new Medium::MoveTask(this, pProgress,
+                                         (MediumVariant_T)mediumVariantFlags,
+                                         pMediumLockList);
+            hrc = pTask->hrc();
+            AssertComRC(hrc);
+            if (FAILED(hrc))
+                throw hrc;
+        }
+
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc))
+            pProgress.queryInterfaceTo(aProgress.asOutParam());
+    }
+    else
+    {
+        if (pTask)
+            delete pTask;
+    }
+
+    return hrc;
+}
+
+HRESULT Medium::setLocation(const com::Utf8Str &aLocation)
+{
+    HRESULT hrc = S_OK;
+
+    try
+    {
+        // locking: we need the tree lock first because we access parent pointers
+        // and we need to write-lock the media involved
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+        AutoCaller autoCaller(this);
+        AssertComRCThrowRC(autoCaller.hrc());
+
+        AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        Utf8Str destPath(aLocation);
+
+        // some check for file based medium
+        if (i_isMediumFormatFile())
+        {
+            /* Path must be absolute */
+            if (!RTPathStartsWithRoot(destPath.c_str()))
+                throw setError(VBOX_E_FILE_ERROR, tr("The given path '%s' is not fully qualified"), destPath.c_str());
+
+            /* Simple check for existence */
+            if (!RTFileExists(destPath.c_str()))
+                throw setError(VBOX_E_FILE_ERROR,
+                               tr("The given path '%s' is not an existing file. New location is invalid."),
+                               destPath.c_str());
+        }
+
+        /* Check VMs which have this medium attached to*/
+        std::vector<com::Guid> aMachineIds;
+        hrc = getMachineIds(aMachineIds);
+
+        // switch locks only if there are machines with this medium attached
+        if (!aMachineIds.empty())
+        {
+            std::vector<com::Guid>::const_iterator currMachineID = aMachineIds.begin();
+            std::vector<com::Guid>::const_iterator lastMachineID = aMachineIds.end();
+
+            alock.release();
+            autoCaller.release();
+            treeLock.release();
+
+            while (currMachineID != lastMachineID)
+            {
+                Guid id(*currMachineID);
+                ComObjPtr<Machine> aMachine;
+                hrc = m->pVirtualBox->i_findMachine(id, false, true, &aMachine);
+                if (SUCCEEDED(hrc))
+                {
+                    ComObjPtr<SessionMachine> sm;
+                    ComPtr<IInternalSessionControl> ctl;
+
+                    bool ses = aMachine->i_isSessionOpenVM(sm, &ctl);
+                    if (ses)
+                    {
+                        treeLock.acquire();
+                        autoCaller.add();
+                        AssertComRCThrowRC(autoCaller.hrc());
+                        alock.acquire();
+
+                        throw setError(VBOX_E_INVALID_VM_STATE,
+                                       tr("At least the VM '%s' to whom this medium '%s' attached has currently an opened session. Stop all VMs before set location for this medium"),
+                                       id.toString().c_str(),
+                                       i_getLocationFull().c_str());
+                    }
+                }
+                ++currMachineID;
+            }
+
+            treeLock.acquire();
+            autoCaller.add();
+            AssertComRCThrowRC(autoCaller.hrc());
+            alock.acquire();
+        }
+
+        m->strLocationFull = destPath;
+
+        // save the settings
+        alock.release();
+        autoCaller.release();
+        treeLock.release();
+
+        i_markRegistriesModified();
+        m->pVirtualBox->i_saveModifiedRegistries();
+
+        MediumState_T mediumState;
+        refreshState(autoCaller, &mediumState);
+        m->pVirtualBox->i_onMediumConfigChanged(this);
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    return hrc;
+}
+
+HRESULT Medium::compact(ComPtr<IProgress> &aProgress)
+{
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        /* Build the medium lock list. */
+        MediumLockList *pMediumLockList(new MediumLockList());
+        alock.release();
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */ ,
+                                     this /* pToLockWrite */,
+                                     false /* fMediumLockWriteAll */,
+                                     NULL,
+                                     *pMediumLockList);
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw hrc;
+        }
+
+        alock.release();
+        hrc = pMediumLockList->Lock();
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock media when compacting '%s'"),
+                           i_getLocationFull().c_str());
+        }
+
+        pProgress.createObject();
+        hrc = pProgress->init(m->pVirtualBox,
+                              static_cast <IMedium *>(this),
+                              BstrFmt(tr("Compacting medium '%s'"), m->strLocationFull.c_str()).raw(),
+                              TRUE /* aCancelable */);
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw hrc;
+        }
+
+        /* setup task object to carry out the operation asynchronously */
+        pTask = new Medium::CompactTask(this, pProgress, pMediumLockList);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc))
+            pProgress.queryInterfaceTo(aProgress.asOutParam());
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    return hrc;
+}
+
+HRESULT Medium::resize(LONG64 aLogicalSize,
+                       ComPtr<IProgress> &aProgress)
+{
+    CheckComArgExpr(aLogicalSize, aLogicalSize > 0);
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+
+    /* Build the medium lock list. */
+    MediumLockList *pMediumLockList(new MediumLockList());
+
+    try
+    {
+        const char *pszError = NULL;
+
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */ ,
+                                     this /* pToLockWrite */,
+                                     false /* fMediumLockWriteAll */,
+                                     NULL,
+                                     *pMediumLockList);
+        if (FAILED(hrc))
+            pszError = tr("Failed to create medium lock list when resizing '%s'");
+        else
+        {
+            hrc = pMediumLockList->Lock();
+            if (FAILED(hrc))
+                pszError = tr("Failed to lock media when resizing '%s'");
+        }
+
+
+        AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        if (FAILED(hrc))
+        {
+            throw setError(hrc, pszError, i_getLocationFull().c_str());
+        }
+
+        pProgress.createObject();
+        hrc = pProgress->init(m->pVirtualBox,
+                              static_cast <IMedium *>(this),
+                              BstrFmt(tr("Resizing medium '%s'"), m->strLocationFull.c_str()).raw(),
+                              TRUE /* aCancelable */);
+        if (FAILED(hrc))
+        {
+            throw hrc;
+        }
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+        hrc = i_resize((uint64_t)aLogicalSize, pMediumLockList, &pProgress, false /* aWait */, true /* aNotify */);
+
+    if (SUCCEEDED(hrc))
+        pProgress.queryInterfaceTo(aProgress.asOutParam());
+    else
+        delete pMediumLockList;
+
+    return hrc;
+}
+
+HRESULT Medium::reset(AutoCaller &autoCaller, ComPtr<IProgress> &aProgress)
+{
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        autoCaller.release();
+
+        /* It is possible that some previous/concurrent uninit has already
+         * cleared the pVirtualBox reference, see #uninit(). */
+        ComObjPtr<VirtualBox> pVirtualBox(m->pVirtualBox);
+
+        /* i_canClose() needs the tree lock */
+        AutoMultiWriteLock2 multilock(!pVirtualBox.isNull() ? &pVirtualBox->i_getMediaTreeLockHandle() : NULL,
+                                      this->lockHandle()
+                                      COMMA_LOCKVAL_SRC_POS);
+
+        autoCaller.add();
+        if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+        LogFlowThisFunc(("ENTER for medium %s\n", m->strLocationFull.c_str()));
+
+        if (m->pParent.isNull())
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Medium type of '%s' is not differencing"),
+                           m->strLocationFull.c_str());
+
+        hrc = i_canClose();
+        if (FAILED(hrc))
+            throw hrc;
+
+        /* Build the medium lock list. */
+        MediumLockList *pMediumLockList(new MediumLockList());
+        multilock.release();
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                     this /* pToLockWrite */,
+                                     false /* fMediumLockWriteAll */,
+                                     NULL,
+                                     *pMediumLockList);
+        multilock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw hrc;
+        }
+
+        multilock.release();
+        hrc = pMediumLockList->Lock();
+        multilock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock media when resetting '%s'"),
+                           i_getLocationFull().c_str());
+        }
+
+        pProgress.createObject();
+        hrc = pProgress->init(m->pVirtualBox,
+                              static_cast<IMedium*>(this),
+                              BstrFmt(tr("Resetting differencing medium '%s'"), m->strLocationFull.c_str()).raw(),
+                              FALSE /* aCancelable */);
+        if (FAILED(hrc))
+            throw hrc;
+
+        /* setup task object to carry out the operation asynchronously */
+        pTask = new Medium::ResetTask(this, pProgress, pMediumLockList);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc))
+            pProgress.queryInterfaceTo(aProgress.asOutParam());
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    LogFlowThisFunc(("LEAVE, hrc=%Rhrc\n", hrc));
+
+    return hrc;
+}
+
+HRESULT Medium::changeEncryption(const com::Utf8Str &aCurrentPassword, const com::Utf8Str &aCipher,
+                                 const com::Utf8Str &aNewPassword, const com::Utf8Str &aNewPasswordId,
+                                 ComPtr<IProgress> &aProgress)
+{
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        DeviceType_T devType = i_getDeviceType();
+        /* Cannot encrypt DVD or floppy images so far. */
+        if (   devType == DeviceType_DVD
+            || devType == DeviceType_Floppy)
+            return setError(VBOX_E_INVALID_OBJECT_STATE,
+                            tr("Cannot encrypt DVD or Floppy medium '%s'"),
+                            m->strLocationFull.c_str());
+
+        /* Cannot encrypt media which are attached to more than one virtual machine. */
+        if (m->backRefs.size() > 1)
+            return setError(VBOX_E_INVALID_OBJECT_STATE,
+                            tr("Cannot encrypt medium '%s' because it is attached to %d virtual machines", "", m->backRefs.size()),
+                            m->strLocationFull.c_str(), m->backRefs.size());
+
+        if (i_getChildren().size() != 0)
+            return setError(VBOX_E_INVALID_OBJECT_STATE,
+                            tr("Cannot encrypt medium '%s' because it has %d children", "", i_getChildren().size()),
+                            m->strLocationFull.c_str(), i_getChildren().size());
+
+        /* Build the medium lock list. */
+        MediumLockList *pMediumLockList(new MediumLockList());
+        alock.release();
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */ ,
+                                     this /* pToLockWrite */,
+                                     true /* fMediumLockAllWrite */,
+                                     NULL,
+                                     *pMediumLockList);
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw hrc;
+        }
+
+        alock.release();
+        hrc = pMediumLockList->Lock();
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock media for encryption '%s'"),
+                           i_getLocationFull().c_str());
+        }
+
+        /*
+         * Check all media in the chain to not contain any branches or references to
+         * other virtual machines, we support encrypting only a list of differencing media at the moment.
+         */
+        MediumLockList::Base::const_iterator mediumListBegin = pMediumLockList->GetBegin();
+        MediumLockList::Base::const_iterator mediumListEnd = pMediumLockList->GetEnd();
+        for (MediumLockList::Base::const_iterator it = mediumListBegin;
+             it != mediumListEnd;
+             ++it)
+        {
+            const MediumLock &mediumLock = *it;
+            const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+            AutoReadLock mediumReadLock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+            Assert(pMedium->m->state == MediumState_LockedWrite);
+
+            if (pMedium->m->backRefs.size() > 1)
+            {
+                hrc = setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Cannot encrypt medium '%s' because it is attached to %d virtual machines", "",
+                                  pMedium->m->backRefs.size()),
+                               pMedium->m->strLocationFull.c_str(), pMedium->m->backRefs.size());
+                break;
+            }
+            else if (pMedium->i_getChildren().size() > 1)
+            {
+                hrc = setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Cannot encrypt medium '%s' because it has %d children", "", pMedium->i_getChildren().size()),
+                               pMedium->m->strLocationFull.c_str(), pMedium->i_getChildren().size());
+                break;
+            }
+        }
+
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw hrc;
+        }
+
+        const char *pszAction = tr("Encrypting medium");
+        if (   aCurrentPassword.isNotEmpty()
+            && aCipher.isEmpty())
+            pszAction = tr("Decrypting medium");
+
+        pProgress.createObject();
+        hrc = pProgress->init(m->pVirtualBox,
+                              static_cast <IMedium *>(this),
+                              BstrFmt("%s '%s'", pszAction, m->strLocationFull.c_str()).raw(),
+                              TRUE /* aCancelable */);
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw hrc;
+        }
+
+        /* setup task object to carry out the operation asynchronously */
+        pTask = new Medium::EncryptTask(this, aNewPassword, aCurrentPassword,
+                                        aCipher, aNewPasswordId, pProgress, pMediumLockList);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc))
+            pProgress.queryInterfaceTo(aProgress.asOutParam());
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    return hrc;
+}
+
+HRESULT Medium::getEncryptionSettings(AutoCaller &autoCaller, com::Utf8Str &aCipher, com::Utf8Str &aPasswordId)
+{
+#ifndef VBOX_WITH_EXTPACK
+    RT_NOREF(aCipher, aPasswordId);
+#endif
+    HRESULT hrc = S_OK;
+
+    try
+    {
+        autoCaller.release();
+        ComObjPtr<Medium> pBase = i_getBase();
+        autoCaller.add();
+        if (FAILED(autoCaller.hrc()))
+            throw hrc;
+        AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        /* Check whether encryption is configured for this medium. */
+        settings::StringsMap::iterator it = pBase->m->mapProperties.find("CRYPT/KeyStore");
+        if (it == pBase->m->mapProperties.end())
+            throw VBOX_E_NOT_SUPPORTED;
+
+# ifdef VBOX_WITH_EXTPACK
+        ExtPackManager *pExtPackManager = m->pVirtualBox->i_getExtPackManager();
+        if (pExtPackManager->i_isExtPackUsable(ORACLE_PUEL_EXTPACK_NAME))
+        {
+            /* Load the plugin */
+            Utf8Str strPlugin;
+            hrc = pExtPackManager->i_getLibraryPathForExtPack(g_szVDPlugin, ORACLE_PUEL_EXTPACK_NAME, &strPlugin);
+            if (SUCCEEDED(hrc))
+            {
+                int vrc = VDPluginLoadFromFilename(strPlugin.c_str());
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_NOT_SUPPORTED, vrc,
+                                       tr("Retrieving encryption settings of the image failed because the encryption plugin could not be loaded (%s)"),
+                                       i_vdError(vrc).c_str());
+            }
+            else
+                throw setError(VBOX_E_NOT_SUPPORTED,
+                               tr("Encryption is not supported because the extension pack '%s' is missing the encryption plugin (old extension pack installed?)"),
+                               ORACLE_PUEL_EXTPACK_NAME);
+        }
+        else
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Encryption is not supported because the extension pack '%s' is missing"),
+                           ORACLE_PUEL_EXTPACK_NAME);
+
+        PVDISK pDisk = NULL;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &pDisk);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        MediumCryptoFilterSettings CryptoSettings;
+
+        i_taskEncryptSettingsSetup(&CryptoSettings, NULL, it->second.c_str(), NULL, false /* fCreateKeyStore */);
+        vrc = VDFilterAdd(pDisk, "CRYPT", VD_FILTER_FLAGS_READ | VD_FILTER_FLAGS_INFO, CryptoSettings.vdFilterIfaces);
+        if (RT_FAILURE(vrc))
+            throw setErrorBoth(VBOX_E_INVALID_OBJECT_STATE, vrc,
+                               tr("Failed to load the encryption filter: %s"),
+                               i_vdError(vrc).c_str());
+
+        it = pBase->m->mapProperties.find("CRYPT/KeyId");
+        if (it == pBase->m->mapProperties.end())
+            throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                           tr("Image is configured for encryption but doesn't has a KeyId set"));
+
+        aPasswordId = it->second.c_str();
+        aCipher = CryptoSettings.pszCipherReturned;
+        RTStrFree(CryptoSettings.pszCipherReturned);
+
+        VDDestroy(pDisk);
+# else
+        throw setError(VBOX_E_NOT_SUPPORTED,
+                       tr("Encryption is not supported because extension pack support is not built in"));
+# endif
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    return hrc;
+}
+
+HRESULT Medium::checkEncryptionPassword(const com::Utf8Str &aPassword)
+{
+    HRESULT hrc = S_OK;
+
+    try
+    {
+        ComObjPtr<Medium> pBase = i_getBase();
+        AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        settings::StringsMap::iterator it = pBase->m->mapProperties.find("CRYPT/KeyStore");
+        if (it == pBase->m->mapProperties.end())
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("The image is not configured for encryption"));
+
+        if (aPassword.isEmpty())
+            throw setError(E_INVALIDARG,
+                           tr("The given password must not be empty"));
+
+# ifdef VBOX_WITH_EXTPACK
+        ExtPackManager *pExtPackManager = m->pVirtualBox->i_getExtPackManager();
+        if (pExtPackManager->i_isExtPackUsable(ORACLE_PUEL_EXTPACK_NAME))
+        {
+            /* Load the plugin */
+            Utf8Str strPlugin;
+            hrc = pExtPackManager->i_getLibraryPathForExtPack(g_szVDPlugin, ORACLE_PUEL_EXTPACK_NAME, &strPlugin);
+            if (SUCCEEDED(hrc))
+            {
+                int vrc = VDPluginLoadFromFilename(strPlugin.c_str());
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_NOT_SUPPORTED, vrc,
+                                       tr("Retrieving encryption settings of the image failed because the encryption plugin could not be loaded (%s)"),
+                                       i_vdError(vrc).c_str());
+            }
+            else
+                throw setError(VBOX_E_NOT_SUPPORTED,
+                               tr("Encryption is not supported because the extension pack '%s' is missing the encryption plugin (old extension pack installed?)"),
+                               ORACLE_PUEL_EXTPACK_NAME);
+        }
+        else
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Encryption is not supported because the extension pack '%s' is missing"),
+                           ORACLE_PUEL_EXTPACK_NAME);
+
+        PVDISK pDisk = NULL;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &pDisk);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        MediumCryptoFilterSettings CryptoSettings;
+
+        i_taskEncryptSettingsSetup(&CryptoSettings, NULL, it->second.c_str(), aPassword.c_str(),
+                                   false /* fCreateKeyStore */);
+        vrc = VDFilterAdd(pDisk, "CRYPT", VD_FILTER_FLAGS_READ, CryptoSettings.vdFilterIfaces);
+        if (vrc == VERR_VD_PASSWORD_INCORRECT)
+            throw setError(VBOX_E_PASSWORD_INCORRECT,
+                           tr("The given password is incorrect"));
+        else if (RT_FAILURE(vrc))
+            throw setErrorBoth(VBOX_E_INVALID_OBJECT_STATE, vrc,
+                               tr("Failed to load the encryption filter: %s"),
+                               i_vdError(vrc).c_str());
+
+        VDDestroy(pDisk);
+# else
+        throw setError(VBOX_E_NOT_SUPPORTED,
+                       tr("Encryption is not supported because extension pack support is not built in"));
+# endif
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    return hrc;
+}
+
+HRESULT Medium::openForIO(BOOL aWritable, com::Utf8Str const &aPassword, ComPtr<IMediumIO> &aMediumIO)
+{
+    /*
+     * Input validation.
+     */
+    if (aWritable && i_isReadOnly())
+        return setError(E_ACCESSDENIED, tr("Write access denied: read-only"));
+
+    com::Utf8Str const strKeyId = i_getKeyId();
+    if (strKeyId.isEmpty() && aPassword.isNotEmpty())
+        return setError(E_INVALIDARG, tr("Password given for unencrypted medium"));
+    if (strKeyId.isNotEmpty() && aPassword.isEmpty())
+        return setError(E_INVALIDARG, tr("Password needed for encrypted medium"));
+
+    /*
+     * Create IO object and return it.
+     */
+    ComObjPtr<MediumIO> ptrIO;
+    HRESULT hrc = ptrIO.createObject();
+    if (SUCCEEDED(hrc))
+    {
+        hrc = ptrIO->initForMedium(this, m->pVirtualBox, aWritable != FALSE, strKeyId, aPassword);
+        if (SUCCEEDED(hrc))
+            ptrIO.queryInterfaceTo(aMediumIO.asOutParam());
+    }
+    return hrc;
+}
+
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Medium public internal methods
+//
+////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Internal method to return the medium's parent medium. Must have caller + locking!
+ * @return
+ */
+const ComObjPtr<Medium>& Medium::i_getParent() const
+{
+    return m->pParent;
+}
+
+/**
+ * Internal method to return the medium's list of child media. Must have caller + locking!
+ * @return
+ */
+const MediaList& Medium::i_getChildren() const
+{
+    return m->llChildren;
+}
+
+/**
+ * Internal method to return the medium's GUID. Must have caller + locking!
+ * @return
+ */
+const Guid& Medium::i_getId() const
+{
+    return m->id;
+}
+
+/**
+ * Internal method to return the medium's state. Must have caller + locking!
+ * @return
+ */
+MediumState_T Medium::i_getState() const
+{
+    return m->state;
+}
+
+/**
+ * Internal method to return the medium's variant. Must have caller + locking!
+ * @return
+ */
+MediumVariant_T Medium::i_getVariant() const
+{
+    return m->variant;
+}
+
+/**
+ * Internal method which returns true if this medium represents a host drive.
+ * @return
+ */
+bool Medium::i_isHostDrive() const
+{
+    return m->hostDrive;
+}
+
+/**
+ * Internal method which returns true if this medium is in the process of being closed.
+ * @return
+ */
+bool Medium::i_isClosing() const
+{
+    return m->fClosing;
+}
+
+/**
+ * Internal method to return the medium's full location. Must have caller + locking!
+ * @return
+ */
+const Utf8Str& Medium::i_getLocationFull() const
+{
+    return m->strLocationFull;
+}
+
+/**
+ * Internal method to return the medium's format string. Must have caller + locking!
+ * @return
+ */
+const Utf8Str& Medium::i_getFormat() const
+{
+    return m->strFormat;
+}
+
+/**
+ * Internal method to return the medium's format object. Must have caller + locking!
+ * @return
+ */
+const ComObjPtr<MediumFormat>& Medium::i_getMediumFormat() const
+{
+    return m->formatObj;
+}
+
+/**
+ * Internal method that returns true if the medium is represented by a file on the host disk
+ * (and not iSCSI or something).
+ * @return
+ */
+bool Medium::i_isMediumFormatFile() const
+{
+    if (    m->formatObj
+         && (m->formatObj->i_getCapabilities() & MediumFormatCapabilities_File)
+       )
+        return true;
+    return false;
+}
+
+/**
+ * Internal method to return the medium's size. Must have caller + locking!
+ * @return
+ */
+uint64_t Medium::i_getSize() const
+{
+    return m->size;
+}
+
+/**
+ * Internal method to return the medium's size. Must have caller + locking!
+ * @return
+ */
+uint64_t Medium::i_getLogicalSize() const
+{
+    return m->logicalSize;
+}
+
+/**
+ * Returns the medium device type. Must have caller + locking!
+ * @return
+ */
+DeviceType_T Medium::i_getDeviceType() const
+{
+    return m->devType;
+}
+
+/**
+ * Returns the medium type. Must have caller + locking!
+ * @return
+ */
+MediumType_T Medium::i_getType() const
+{
+    return m->type;
+}
+
+/**
+ * Returns a short version of the location attribute.
+ *
+ * @note Must be called from under this object's read or write lock.
+ */
+Utf8Str Medium::i_getName()
+{
+    Utf8Str name = RTPathFilename(m->strLocationFull.c_str());
+    return name;
+}
+
+/**
+ * Same as i_addRegistry() except that we don't check the object state, making
+ * it safe to call with initFromSettings() on the call stack.
+ */
+bool Medium::i_addRegistryNoCallerCheck(const Guid &id)
+{
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    bool fAdd = true;
+
+    // hard disks cannot be in more than one registry
+    if (   m->devType == DeviceType_HardDisk
+        && m->llRegistryIDs.size() > 0)
+        fAdd = false;
+
+    // no need to add the UUID twice
+    if (fAdd)
+    {
+        for (GuidList::const_iterator it = m->llRegistryIDs.begin();
+             it != m->llRegistryIDs.end();
+             ++it)
+        {
+            if ((*it) == id)
+            {
+                fAdd = false;
+                break;
+            }
+        }
+    }
+
+    if (fAdd)
+        m->llRegistryIDs.push_back(id);
+
+    return fAdd;
+}
+
+/**
+ * This adds the given UUID to the list of media registries in which this
+ * medium should be registered. The UUID can either be a machine UUID,
+ * to add a machine registry, or the global registry UUID as returned by
+ * VirtualBox::getGlobalRegistryId().
+ *
+ * Note that for hard disks, this method does nothing if the medium is
+ * already in another registry to avoid having hard disks in more than
+ * one registry, which causes trouble with keeping diff images in sync.
+ * See getFirstRegistryMachineId() for details.
+ *
+ * @param id
+ * @return true if the registry was added; false if the given id was already on the list.
+ */
+bool Medium::i_addRegistry(const Guid &id)
+{
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc()))
+        return false;
+    return i_addRegistryNoCallerCheck(id);
+}
+
+/**
+ * This adds the given UUID to the list of media registries in which this
+ * medium should be registered. The UUID can either be a machine UUID,
+ * to add a machine registry, or the global registry UUID as returned by
+ * VirtualBox::getGlobalRegistryId(). Thisis applied to all children.
+ *
+ * Note that for hard disks, this method does nothing if the medium is
+ * already in another registry to avoid having hard disks in more than
+ * one registry, which causes trouble with keeping diff images in sync.
+ * See getFirstRegistryMachineId() for details.
+ *
+ * @note the caller must hold the media tree lock for reading.
+ *
+ * @param id
+ * @return true if the registry was added; false if the given id was already on the list.
+ */
+bool Medium::i_addRegistryAll(const Guid &id)
+{
+    MediaList llMediaTodo;
+    llMediaTodo.push_back(this);
+
+    bool fAdd = false;
+
+    while (!llMediaTodo.empty())
+    {
+        ComObjPtr<Medium> pMedium = llMediaTodo.front();
+        llMediaTodo.pop_front();
+
+        AutoCaller mediumCaller(pMedium);
+        if (FAILED(mediumCaller.hrc())) continue;
+
+        fAdd |= pMedium->i_addRegistryNoCallerCheck(id);
+
+        // protected by the medium tree lock held by our original caller
+        MediaList::const_iterator itBegin = pMedium->i_getChildren().begin();
+        MediaList::const_iterator itEnd = pMedium->i_getChildren().end();
+        for (MediaList::const_iterator it = itBegin; it != itEnd; ++it)
+            llMediaTodo.push_back(*it);
+    }
+
+    return fAdd;
+}
+
+/**
+ * Removes the given UUID from the list of media registry UUIDs of this medium.
+ *
+ * @param id
+ * @return true if the UUID was found or false if not.
+ */
+bool Medium::i_removeRegistry(const Guid &id)
+{
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc()))
+        return false;
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    bool fRemove = false;
+
+    /// @todo r=klaus eliminate this code, replace it by using find.
+    for (GuidList::iterator it = m->llRegistryIDs.begin();
+         it != m->llRegistryIDs.end();
+         ++it)
+    {
+        if ((*it) == id)
+        {
+            // getting away with this as the iterator isn't used after
+            m->llRegistryIDs.erase(it);
+            fRemove = true;
+            break;
+        }
+    }
+
+    return fRemove;
+}
+
+/**
+ * Removes the given UUID from the list of media registry UUIDs, for this
+ * medium and all its children.
+ *
+ * @note the caller must hold the media tree lock for reading.
+ *
+ * @param id
+ * @return true if the UUID was found or false if not.
+ */
+bool Medium::i_removeRegistryAll(const Guid &id)
+{
+    MediaList llMediaTodo;
+    llMediaTodo.push_back(this);
+
+    bool fRemove = false;
+
+    while (!llMediaTodo.empty())
+    {
+        ComObjPtr<Medium> pMedium = llMediaTodo.front();
+        llMediaTodo.pop_front();
+
+        AutoCaller mediumCaller(pMedium);
+        if (FAILED(mediumCaller.hrc())) continue;
+
+        fRemove |= pMedium->i_removeRegistry(id);
+
+        // protected by the medium tree lock held by our original caller
+        MediaList::const_iterator itBegin = pMedium->i_getChildren().begin();
+        MediaList::const_iterator itEnd = pMedium->i_getChildren().end();
+        for (MediaList::const_iterator it = itBegin; it != itEnd; ++it)
+            llMediaTodo.push_back(*it);
+    }
+
+    return fRemove;
+}
+
+/**
+ * Returns true if id is in the list of media registries for this medium.
+ *
+ * Must have caller + read locking!
+ *
+ * @param id
+ * @return
+ */
+bool Medium::i_isInRegistry(const Guid &id)
+{
+    /// @todo r=klaus eliminate this code, replace it by using find.
+    for (GuidList::const_iterator it = m->llRegistryIDs.begin();
+         it != m->llRegistryIDs.end();
+         ++it)
+    {
+        if (*it == id)
+            return true;
+    }
+
+    return false;
+}
+
+/**
+ * Internal method to return the medium's first registry machine (i.e. the machine in whose
+ * machine XML this medium is listed).
+ *
+ * Every attached medium must now (4.0) reside in at least one media registry, which is identified
+ * by a UUID. This is either a machine UUID if the machine is from 4.0 or newer, in which case
+ * machines have their own media registries, or it is the pseudo-UUID of the VirtualBox
+ * object if the machine is old and still needs the global registry in VirtualBox.xml.
+ *
+ * By definition, hard disks may only be in one media registry, in which all its children
+ * will be stored as well. Otherwise we run into problems with having keep multiple registries
+ * in sync. (This is the "cloned VM" case in which VM1 may link to the disks of VM2; in this
+ * case, only VM2's registry is used for the disk in question.)
+ *
+ * If there is no medium registry, particularly if the medium has not been attached yet, this
+ * does not modify uuid and returns false.
+ *
+ * ISOs and RAWs, by contrast, can be in more than one repository to make things easier for
+ * the user.
+ *
+ * Must have caller + locking!
+ *
+ * @param uuid Receives first registry machine UUID, if available.
+ * @return true if uuid was set.
+ */
+bool Medium::i_getFirstRegistryMachineId(Guid &uuid) const
+{
+    if (m->llRegistryIDs.size())
+    {
+        uuid = m->llRegistryIDs.front();
+        return true;
+    }
+    return false;
+}
+
+/**
+ * Marks all the registries in which this medium is registered as modified.
+ */
+void Medium::i_markRegistriesModified()
+{
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc())) return;
+
+    // Get local copy, as keeping the lock over VirtualBox::markRegistryModified
+    // causes trouble with the lock order
+    GuidList llRegistryIDs;
+    {
+        AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+        llRegistryIDs = m->llRegistryIDs;
+    }
+
+    autoCaller.release();
+
+    /* Save the error information now, the implicit restore when this goes
+     * out of scope will throw away spurious additional errors created below. */
+    ErrorInfoKeeper eik;
+    for (GuidList::const_iterator it = llRegistryIDs.begin();
+         it != llRegistryIDs.end();
+         ++it)
+    {
+        m->pVirtualBox->i_markRegistryModified(*it);
+    }
+}
+
+/**
+ * Adds the given machine and optionally the snapshot to the list of the objects
+ * this medium is attached to.
+ *
+ * @param aMachineId    Machine ID.
+ * @param aSnapshotId   Snapshot ID; when non-empty, adds a snapshot attachment.
+ */
+HRESULT Medium::i_addBackReference(const Guid &aMachineId,
+                                   const Guid &aSnapshotId /*= Guid::Empty*/)
+{
+    AssertReturn(aMachineId.isValid(), E_FAIL);
+
+    LogFlowThisFunc(("ENTER, aMachineId: {%RTuuid}, aSnapshotId: {%RTuuid}\n", aMachineId.raw(), aSnapshotId.raw()));
+
+    AutoCaller autoCaller(this);
+    AssertComRCReturnRC(autoCaller.hrc());
+
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    switch (m->state)
+    {
+        case MediumState_Created:
+        case MediumState_Inaccessible:
+        case MediumState_LockedRead:
+        case MediumState_LockedWrite:
+            break;
+
+        default:
+            return i_setStateError();
+    }
+
+    if (m->numCreateDiffTasks > 0)
+        return setError(VBOX_E_OBJECT_IN_USE,
+                        tr("Cannot attach medium '%s' {%RTuuid}: %u differencing child media are being created", "",
+                           m->numCreateDiffTasks),
+                        m->strLocationFull.c_str(),
+                        m->id.raw(),
+                        m->numCreateDiffTasks);
+
+    BackRefList::iterator it = std::find_if(m->backRefs.begin(),
+                                            m->backRefs.end(),
+                                            BackRef::EqualsTo(aMachineId));
+    if (it == m->backRefs.end())
+    {
+        BackRef ref(aMachineId, aSnapshotId);
+        m->backRefs.push_back(ref);
+
+        return S_OK;
+    }
+    bool fDvd = false;
+    {
+        AutoReadLock arlock(this COMMA_LOCKVAL_SRC_POS);
+        /*
+         *  Check the medium is DVD and readonly. It's for the case if DVD
+         *  will be able to be writable sometime in the future.
+         */
+        fDvd = m->type == MediumType_Readonly && m->devType == DeviceType_DVD;
+    }
+
+    // if the caller has not supplied a snapshot ID, then we're attaching
+    // to a machine a medium which represents the machine's current state,
+    // so set the flag
+
+    if (aSnapshotId.isZero())
+    {
+        // Allow DVD having MediumType_Readonly to be attached twice.
+        // (the medium already had been added to back reference)
+        if (fDvd)
+        {
+            it->iRefCnt++;
+            return S_OK;
+        }
+
+        /* sanity: no duplicate attachments */
+        if (it->fInCurState)
+            return setError(VBOX_E_OBJECT_IN_USE,
+                            tr("Cannot attach medium '%s' {%RTuuid}: medium is already associated with the current state of machine uuid {%RTuuid}!"),
+                            m->strLocationFull.c_str(),
+                            m->id.raw(),
+                            aMachineId.raw());
+        it->fInCurState = true;
+
+        return S_OK;
+    }
+
+    // otherwise: a snapshot medium is being attached
+
+    /* sanity: no duplicate attachments */
+    for (std::list<SnapshotRef>::iterator jt = it->llSnapshotIds.begin();
+         jt != it->llSnapshotIds.end();
+         ++jt)
+    {
+        const Guid &idOldSnapshot = jt->snapshotId;
+
+        if (idOldSnapshot == aSnapshotId)
+        {
+            if (fDvd)
+            {
+                jt->iRefCnt++;
+                return S_OK;
+            }
+#ifdef DEBUG
+            i_dumpBackRefs();
+#endif
+            return setError(VBOX_E_OBJECT_IN_USE,
+                            tr("Cannot attach medium '%s' {%RTuuid} from snapshot '%RTuuid': medium is already in use by this snapshot!"),
+                            m->strLocationFull.c_str(),
+                            m->id.raw(),
+                            aSnapshotId.raw());
+        }
+    }
+
+    it->llSnapshotIds.push_back(SnapshotRef(aSnapshotId));
+    // Do not touch fInCurState, as the image may be attached to the current
+    // state *and* a snapshot, otherwise we lose the current state association!
+
+    LogFlowThisFuncLeave();
+
+    return S_OK;
+}
+
+/**
+ * Removes the given machine and optionally the snapshot from the list of the
+ * objects this medium is attached to.
+ *
+ * @param aMachineId    Machine ID.
+ * @param aSnapshotId   Snapshot ID; when non-empty, removes the snapshot
+ *                      attachment.
+ */
+HRESULT Medium::i_removeBackReference(const Guid &aMachineId,
+                                      const Guid &aSnapshotId /*= Guid::Empty*/)
+{
+    AssertReturn(aMachineId.isValid(), E_FAIL);
+
+    AutoCaller autoCaller(this);
+    AssertComRCReturnRC(autoCaller.hrc());
+
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    BackRefList::iterator it =
+        std::find_if(m->backRefs.begin(), m->backRefs.end(),
+                     BackRef::EqualsTo(aMachineId));
+    AssertReturn(it != m->backRefs.end(), E_FAIL);
+
+    if (aSnapshotId.isZero())
+    {
+        it->iRefCnt--;
+        if (it->iRefCnt > 0)
+            return S_OK;
+
+        /* remove the current state attachment */
+        it->fInCurState = false;
+    }
+    else
+    {
+        /* remove the snapshot attachment */
+        std::list<SnapshotRef>::iterator jt =
+                std::find_if(it->llSnapshotIds.begin(),
+                             it->llSnapshotIds.end(),
+                             SnapshotRef::EqualsTo(aSnapshotId));
+
+        AssertReturn(jt != it->llSnapshotIds.end(), E_FAIL);
+
+        jt->iRefCnt--;
+        if (jt->iRefCnt > 0)
+            return S_OK;
+
+        it->llSnapshotIds.erase(jt);
+    }
+
+    /* if the backref becomes empty, remove it */
+    if (it->fInCurState == false && it->llSnapshotIds.size() == 0)
+        m->backRefs.erase(it);
+
+    return S_OK;
+}
+
+/**
+ * Internal method to return the medium's list of backrefs. Must have caller + locking!
+ * @return
+ */
+const Guid* Medium::i_getFirstMachineBackrefId() const
+{
+    if (!m->backRefs.size())
+        return NULL;
+
+    return &m->backRefs.front().machineId;
+}
+
+/**
+ * Internal method which returns a machine that either this medium or one of its children
+ * is attached to. This is used for finding a replacement media registry when an existing
+ * media registry is about to be deleted in VirtualBox::unregisterMachine().
+ *
+ * Must have caller + locking, *and* caller must hold the media tree lock!
+ * @param aId   Id to ignore when looking for backrefs.
+ * @return
+ */
+const Guid* Medium::i_getAnyMachineBackref(const Guid &aId) const
+{
+    std::list<const Medium *> llMediaTodo;
+    llMediaTodo.push_back(this);
+
+    while (!llMediaTodo.empty())
+    {
+        const Medium *pMedium = llMediaTodo.front();
+        llMediaTodo.pop_front();
+
+        if (pMedium->m->backRefs.size())
+        {
+            if (pMedium->m->backRefs.front().machineId != aId)
+                return &pMedium->m->backRefs.front().machineId;
+            if (pMedium->m->backRefs.size() > 1)
+            {
+                BackRefList::const_iterator it = pMedium->m->backRefs.begin();
+                ++it;
+                return &it->machineId;
+            }
+        }
+
+        MediaList::const_iterator itBegin = pMedium->i_getChildren().begin();
+        MediaList::const_iterator itEnd = pMedium->i_getChildren().end();
+        for (MediaList::const_iterator it = itBegin; it != itEnd; ++it)
+            llMediaTodo.push_back(*it);
+    }
+
+    return NULL;
+}
+
+const Guid* Medium::i_getFirstMachineBackrefSnapshotId() const
+{
+    if (!m->backRefs.size())
+        return NULL;
+
+    const BackRef &ref = m->backRefs.front();
+    if (ref.llSnapshotIds.empty())
+        return NULL;
+
+    return &ref.llSnapshotIds.front().snapshotId;
+}
+
+size_t Medium::i_getMachineBackRefCount() const
+{
+    return m->backRefs.size();
+}
+
+#ifdef DEBUG
+/**
+ * Debugging helper that gets called after VirtualBox initialization that writes all
+ * machine backreferences to the debug log.
+ */
+void Medium::i_dumpBackRefs()
+{
+    AutoCaller autoCaller(this);
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    LogFlowThisFunc(("Dumping backrefs for medium '%s':\n", m->strLocationFull.c_str()));
+
+    for (BackRefList::iterator it2 = m->backRefs.begin();
+         it2 != m->backRefs.end();
+         ++it2)
+    {
+        const BackRef &ref = *it2;
+        LogFlowThisFunc(("  Backref from machine {%RTuuid} (fInCurState: %d, iRefCnt: %d)\n", ref.machineId.raw(), ref.fInCurState, ref.iRefCnt));
+
+        for (std::list<SnapshotRef>::const_iterator jt2 = it2->llSnapshotIds.begin();
+             jt2 != it2->llSnapshotIds.end();
+             ++jt2)
+        {
+            const Guid &id = jt2->snapshotId;
+            LogFlowThisFunc(("  Backref from snapshot {%RTuuid} (iRefCnt = %d)\n", id.raw(), jt2->iRefCnt));
+        }
+    }
+}
+#endif
+
+/**
+ * Checks if the given change of \a aOldPath to \a aNewPath affects the location
+ * of this media and updates it if necessary to reflect the new location.
+ *
+ * @param strOldPath  Old path (full).
+ * @param strNewPath  New path (full).
+ *
+ * @note Locks this object for writing.
+ */
+HRESULT Medium::i_updatePath(const Utf8Str &strOldPath, const Utf8Str &strNewPath)
+{
+    AssertReturn(!strOldPath.isEmpty(), E_FAIL);
+    AssertReturn(!strNewPath.isEmpty(), E_FAIL);
+
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    LogFlowThisFunc(("locationFull.before='%s'\n", m->strLocationFull.c_str()));
+
+    const char *pcszMediumPath = m->strLocationFull.c_str();
+
+    if (RTPathStartsWith(pcszMediumPath, strOldPath.c_str()))
+    {
+        Utf8Str newPath(strNewPath);
+        newPath.append(pcszMediumPath + strOldPath.length());
+        unconst(m->strLocationFull) = newPath;
+
+        m->pVirtualBox->i_onMediumConfigChanged(this);
+
+        LogFlowThisFunc(("locationFull.after='%s'\n", m->strLocationFull.c_str()));
+        // we changed something
+        return S_OK;
+    }
+
+    // no change was necessary, signal error which the caller needs to interpret
+    return VBOX_E_FILE_ERROR;
+}
+
+/**
+ * Returns the base medium of the media chain this medium is part of.
+ *
+ * The base medium is found by walking up the parent-child relationship axis.
+ * If the medium doesn't have a parent (i.e. it's a base medium), it
+ * returns itself in response to this method.
+ *
+ * @param aLevel    Where to store the number of ancestors of this medium
+ *                  (zero for the base), may be @c NULL.
+ *
+ * @note Locks medium tree for reading.
+ */
+ComObjPtr<Medium> Medium::i_getBase(uint32_t *aLevel /*= NULL*/)
+{
+    ComObjPtr<Medium> pBase;
+
+    /* it is possible that some previous/concurrent uninit has already cleared
+     * the pVirtualBox reference, and in this case we don't need to continue */
+    ComObjPtr<VirtualBox> pVirtualBox(m->pVirtualBox);
+    if (!pVirtualBox)
+        return pBase;
+
+    /* we access m->pParent */
+    AutoReadLock treeLock(pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+    AutoCaller autoCaller(this);
+    AssertReturn(autoCaller.isOk(), pBase);
+
+    pBase = this;
+    uint32_t level = 0;
+
+    if (m->pParent)
+    {
+        for (;;)
+        {
+            AutoCaller baseCaller(pBase);
+            AssertReturn(baseCaller.isOk(), pBase);
+
+            if (pBase->m->pParent.isNull())
+                break;
+
+            pBase = pBase->m->pParent;
+            ++level;
+        }
+    }
+
+    if (aLevel != NULL)
+        *aLevel = level;
+
+    return pBase;
+}
+
+/**
+ * Returns the depth of this medium in the media chain.
+ *
+ * @note Locks medium tree for reading.
+ */
+uint32_t Medium::i_getDepth()
+{
+    /* it is possible that some previous/concurrent uninit has already cleared
+     * the pVirtualBox reference, and in this case we don't need to continue */
+    ComObjPtr<VirtualBox> pVirtualBox(m->pVirtualBox);
+    if (!pVirtualBox)
+        return 1;
+
+    /* we access m->pParent */
+    AutoReadLock treeLock(pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+    uint32_t cDepth = 0;
+    ComObjPtr<Medium> pMedium(this);
+    while (!pMedium.isNull())
+    {
+        AutoCaller autoCaller(this);
+        AssertReturn(autoCaller.isOk(), cDepth + 1);
+
+        pMedium = pMedium->m->pParent;
+        cDepth++;
+    }
+
+    return cDepth;
+}
+
+/**
+ * Returns @c true if this medium cannot be modified because it has
+ * dependents (children) or is part of the snapshot. Related to the medium
+ * type and posterity, not to the current media state.
+ *
+ * @note Locks this object and medium tree for reading.
+ */
+bool Medium::i_isReadOnly()
+{
+    /* it is possible that some previous/concurrent uninit has already cleared
+     * the pVirtualBox reference, and in this case we don't need to continue */
+    ComObjPtr<VirtualBox> pVirtualBox(m->pVirtualBox);
+    if (!pVirtualBox)
+        return false;
+
+    /* we access children */
+    AutoReadLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+    AutoCaller autoCaller(this);
+    AssertComRCReturn(autoCaller.hrc(), false);
+
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    switch (m->type)
+    {
+        case MediumType_Normal:
+        {
+            if (i_getChildren().size() != 0)
+                return true;
+
+            for (BackRefList::const_iterator it = m->backRefs.begin();
+                 it != m->backRefs.end(); ++it)
+                if (it->llSnapshotIds.size() != 0)
+                    return true;
+
+            if (m->variant & MediumVariant_VmdkStreamOptimized)
+                return true;
+
+            return false;
+        }
+        case MediumType_Immutable:
+        case MediumType_MultiAttach:
+            return true;
+        case MediumType_Writethrough:
+        case MediumType_Shareable:
+        case MediumType_Readonly: /* explicit readonly media has no diffs */
+            return false;
+        default:
+            break;
+    }
+
+    AssertFailedReturn(false);
+}
+
+/**
+ * Internal method to update the medium's id. Must have caller + locking!
+ */
+void Medium::i_updateId(const Guid &id)
+{
+    unconst(m->id) = id;
+}
+
+/**
+ * Saves the settings of one medium.
+ *
+ * @note Caller MUST take care of the medium tree lock and caller.
+ *
+ * @param data      Settings struct to be updated.
+ * @param strHardDiskFolder Folder for which paths should be relative.
+ */
+void Medium::i_saveSettingsOne(settings::Medium &data, const Utf8Str &strHardDiskFolder)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    data.uuid = m->id;
+
+    // make path relative if needed
+    if (    !strHardDiskFolder.isEmpty()
+         && RTPathStartsWith(m->strLocationFull.c_str(), strHardDiskFolder.c_str())
+       )
+        data.strLocation = m->strLocationFull.substr(strHardDiskFolder.length() + 1);
+    else
+        data.strLocation = m->strLocationFull;
+    data.strFormat = m->strFormat;
+
+    /* optional, only for diffs, default is false */
+    if (m->pParent)
+        data.fAutoReset = m->autoReset;
+    else
+        data.fAutoReset = false;
+
+    /* optional */
+    data.strDescription = m->strDescription;
+
+    /* optional properties */
+    data.properties.clear();
+
+    /* handle iSCSI initiator secrets transparently */
+    bool fHaveInitiatorSecretEncrypted = false;
+    Utf8Str strCiphertext;
+    settings::StringsMap::const_iterator itPln = m->mapProperties.find("InitiatorSecret");
+    if (   itPln != m->mapProperties.end()
+        && !itPln->second.isEmpty())
+    {
+        /* Encrypt the plain secret. If that does not work (i.e. no or wrong settings key
+         * specified), just use the encrypted secret (if there is any). */
+        int vrc = m->pVirtualBox->i_encryptSetting(itPln->second, &strCiphertext);
+        if (RT_SUCCESS(vrc))
+            fHaveInitiatorSecretEncrypted = true;
+    }
+    for (settings::StringsMap::const_iterator it = m->mapProperties.begin();
+         it != m->mapProperties.end();
+         ++it)
+    {
+        /* only save properties that have non-default values */
+        if (!it->second.isEmpty())
+        {
+            const Utf8Str &name = it->first;
+            const Utf8Str &value = it->second;
+            bool fCreateOnly = false;
+            for (MediumFormat::PropertyArray::const_iterator itf = m->formatObj->i_getProperties().begin();
+                 itf != m->formatObj->i_getProperties().end();
+                 ++itf)
+            {
+                if (   itf->strName.equals(name)
+                    && (itf->flags & VD_CFGKEY_CREATEONLY))
+                {
+                    fCreateOnly = true;
+                    break;
+                }
+            }
+            if (!fCreateOnly)
+                /* do NOT store the plain InitiatorSecret */
+                if (   !fHaveInitiatorSecretEncrypted
+                    || !name.equals("InitiatorSecret"))
+                    data.properties[name] = value;
+        }
+    }
+    if (fHaveInitiatorSecretEncrypted)
+        data.properties["InitiatorSecretEncrypted"] = strCiphertext;
+
+    /* only for base media */
+    if (m->pParent.isNull())
+        data.hdType = m->type;
+}
+
+/**
+ * Saves medium data by putting it into the provided data structure.
+ * The settings of all children is saved, too.
+ *
+ * @param data      Settings struct to be updated.
+ * @param strHardDiskFolder Folder for which paths should be relative.
+ *
+ * @note Locks this object, medium tree and children for reading.
+ */
+HRESULT Medium::i_saveSettings(settings::Medium &data,
+                               const Utf8Str &strHardDiskFolder)
+{
+    /* we access m->pParent */
+    AutoReadLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    MediaList llMediaTodo;
+    llMediaTodo.push_back(this);
+    std::list<settings::Medium *> llSettingsTodo;
+    llSettingsTodo.push_back(&data);
+
+    while (!llMediaTodo.empty())
+    {
+        ComObjPtr<Medium> pMedium = llMediaTodo.front();
+        llMediaTodo.pop_front();
+        settings::Medium *current = llSettingsTodo.front();
+        llSettingsTodo.pop_front();
+
+        AutoCaller mediumCaller(pMedium);
+        if (FAILED(mediumCaller.hrc())) return mediumCaller.hrc();
+
+        pMedium->i_saveSettingsOne(*current, strHardDiskFolder);
+
+        /* save all children */
+        MediaList::const_iterator itBegin = pMedium->i_getChildren().begin();
+        MediaList::const_iterator itEnd = pMedium->i_getChildren().end();
+        for (MediaList::const_iterator it = itBegin; it != itEnd; ++it)
+        {
+            llMediaTodo.push_back(*it);
+            current->llChildren.push_back(settings::Medium::Empty);
+            llSettingsTodo.push_back(&current->llChildren.back());
+        }
+    }
+
+    return S_OK;
+}
+
+/**
+ * Constructs a medium lock list for this medium. The lock is not taken.
+ *
+ * @note Caller MUST NOT hold the media tree or medium lock.
+ *
+ * @param fFailIfInaccessible If true, this fails with an error if a medium is inaccessible. If false,
+ *          inaccessible media are silently skipped and not locked (i.e. their state remains "Inaccessible");
+ *          this is necessary for a VM's removable media VM startup for which we do not want to fail.
+ * @param pToLockWrite         If not NULL, associate a write lock with this medium object.
+ * @param fMediumLockWriteAll  Whether to associate a write lock to all other media too.
+ * @param pToBeParent          Medium which will become the parent of this medium.
+ * @param mediumLockList       Where to store the resulting list.
+ */
+HRESULT Medium::i_createMediumLockList(bool fFailIfInaccessible,
+                                       Medium *pToLockWrite,
+                                       bool fMediumLockWriteAll,
+                                       Medium *pToBeParent,
+                                       MediumLockList &mediumLockList)
+{
+    /** @todo r=klaus this needs to be reworked, as the code below uses
+     * i_getParent without holding the tree lock, and changing this is
+     * a significant amount of effort. */
+    Assert(!m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+    Assert(!isWriteLockOnCurrentThread());
+
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    HRESULT hrc = S_OK;
+
+    /* paranoid sanity checking if the medium has a to-be parent medium */
+    if (pToBeParent)
+    {
+        AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+        ComAssertRet(i_getParent().isNull(), E_FAIL);
+        ComAssertRet(i_getChildren().size() == 0, E_FAIL);
+    }
+
+    ErrorInfoKeeper eik;
+    MultiResult mrc(S_OK);
+
+    ComObjPtr<Medium> pMedium = this;
+    while (!pMedium.isNull())
+    {
+        AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+        /* Accessibility check must be first, otherwise locking interferes
+         * with getting the medium state. Lock lists are not created for
+         * fun, and thus getting the medium status is no luxury. */
+        MediumState_T mediumState = pMedium->i_getState();
+        if (mediumState == MediumState_Inaccessible)
+        {
+            alock.release();
+            hrc = pMedium->i_queryInfo(false /* fSetImageId */, false /* fSetParentId */, autoCaller);
+            alock.acquire();
+            if (FAILED(hrc)) return hrc;
+
+            mediumState = pMedium->i_getState();
+            if (mediumState == MediumState_Inaccessible)
+            {
+                // ignore inaccessible ISO media and silently return S_OK,
+                // otherwise VM startup (esp. restore) may fail without good reason
+                if (!fFailIfInaccessible)
+                    return S_OK;
+
+                // otherwise report an error
+                Bstr error;
+                hrc = pMedium->COMGETTER(LastAccessError)(error.asOutParam());
+                if (FAILED(hrc)) return hrc;
+
+                /* collect multiple errors */
+                eik.restore();
+                Assert(!error.isEmpty());
+                mrc = setError(E_FAIL,
+                               "%ls",
+                               error.raw());
+                    // error message will be something like
+                    // "Could not open the medium ... VD: error VERR_FILE_NOT_FOUND opening image file ... (VERR_FILE_NOT_FOUND).
+                eik.fetch();
+            }
+        }
+
+        if (pMedium == pToLockWrite)
+            mediumLockList.Prepend(pMedium, true);
+        else
+            mediumLockList.Prepend(pMedium, fMediumLockWriteAll);
+
+        pMedium = pMedium->i_getParent();
+        if (pMedium.isNull() && pToBeParent)
+        {
+            pMedium = pToBeParent;
+            pToBeParent = NULL;
+        }
+    }
+
+    return mrc;
+}
+
+/**
+ * Creates a new differencing storage unit using the format of the given target
+ * medium and the location. Note that @c aTarget must be NotCreated.
+ *
+ * The @a aMediumLockList parameter contains the associated medium lock list,
+ * which must be in locked state. If @a aWait is @c true then the caller is
+ * responsible for unlocking.
+ *
+ * If @a aProgress is not NULL but the object it points to is @c null then a
+ * new progress object will be created and assigned to @a *aProgress on
+ * success, otherwise the existing progress object is used. If @a aProgress is
+ * NULL, then no progress object is created/used at all.
+ *
+ * When @a aWait is @c false, this method will create a thread to perform the
+ * create operation asynchronously and will return immediately. Otherwise, it
+ * will perform the operation on the calling thread and will not return to the
+ * caller until the operation is completed. Note that @a aProgress cannot be
+ * NULL when @a aWait is @c false (this method will assert in this case).
+ *
+ * @param aTarget           Target medium.
+ * @param aVariant          Precise medium variant to create.
+ * @param aMediumLockList   List of media which should be locked.
+ * @param aProgress         Where to find/store a Progress object to track
+ *                          operation completion.
+ * @param aWait             @c true if this method should block instead of
+ *                          creating an asynchronous thread.
+ * @param aNotify           Notify about media for which metadata is changed
+ *                          during execution of the function.
+ *
+ * @note Locks this object and @a aTarget for writing.
+ */
+HRESULT Medium::i_createDiffStorage(ComObjPtr<Medium> &aTarget,
+                                    MediumVariant_T aVariant,
+                                    MediumLockList *aMediumLockList,
+                                    ComObjPtr<Progress> *aProgress,
+                                    bool aWait,
+                                    bool aNotify)
+{
+    AssertReturn(!aTarget.isNull(), E_FAIL);
+    AssertReturn(aMediumLockList, E_FAIL);
+    AssertReturn(aProgress != NULL || aWait == true, E_FAIL);
+
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    AutoCaller targetCaller(aTarget);
+    if (FAILED(targetCaller.hrc())) return targetCaller.hrc();
+
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        AutoMultiWriteLock2 alock(this, aTarget COMMA_LOCKVAL_SRC_POS);
+
+        ComAssertThrow(   m->type != MediumType_Writethrough
+                       && m->type != MediumType_Shareable
+                       && m->type != MediumType_Readonly, E_FAIL);
+        ComAssertThrow(m->state == MediumState_LockedRead, E_FAIL);
+
+        if (aTarget->m->state != MediumState_NotCreated)
+            throw aTarget->i_setStateError();
+
+        /* Check that the medium is not attached to the current state of
+         * any VM referring to it. */
+        for (BackRefList::const_iterator it = m->backRefs.begin();
+             it != m->backRefs.end();
+             ++it)
+        {
+            if (it->fInCurState)
+            {
+                /* Note: when a VM snapshot is being taken, all normal media
+                 * attached to the VM in the current state will be, as an
+                 * exception, also associated with the snapshot which is about
+                 * to create (see SnapshotMachine::init()) before deassociating
+                 * them from the current state (which takes place only on
+                 * success in Machine::fixupHardDisks()), so that the size of
+                 * snapshotIds will be 1 in this case. The extra condition is
+                 * used to filter out this legal situation. */
+                if (it->llSnapshotIds.size() == 0)
+                    throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                                   tr("Medium '%s' is attached to a virtual machine with UUID {%RTuuid}. No differencing media based on it may be created until it is detached"),
+                                   m->strLocationFull.c_str(), it->machineId.raw());
+
+                Assert(it->llSnapshotIds.size() == 1);
+            }
+        }
+
+        if (aProgress != NULL)
+        {
+            /* use the existing progress object... */
+            pProgress = *aProgress;
+
+            /* ...but create a new one if it is null */
+            if (pProgress.isNull())
+            {
+                pProgress.createObject();
+                hrc = pProgress->init(m->pVirtualBox,
+                                      static_cast<IMedium*>(this),
+                                      BstrFmt(tr("Creating differencing medium storage unit '%s'"),
+                                              aTarget->m->strLocationFull.c_str()).raw(),
+                                      TRUE /* aCancelable */);
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+        }
+
+        /* setup task object to carry out the operation sync/async */
+        pTask = new Medium::CreateDiffTask(this, pProgress, aTarget, aVariant,
+                                           aMediumLockList,
+                                           aWait /* fKeepMediumLockList */,
+                                           aNotify);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+             throw hrc;
+
+        /* register a task (it will deregister itself when done) */
+        ++m->numCreateDiffTasks;
+        Assert(m->numCreateDiffTasks != 0); /* overflow? */
+
+        aTarget->m->state = MediumState_Creating;
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        if (aWait)
+        {
+            hrc = pTask->runNow();
+            delete pTask;
+        }
+        else
+            hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc) && aProgress != NULL)
+            *aProgress = pProgress;
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    return hrc;
+}
+
+/**
+ * Returns a preferred format for differencing media.
+ */
+Utf8Str Medium::i_getPreferredDiffFormat()
+{
+    AutoCaller autoCaller(this);
+    AssertComRCReturn(autoCaller.hrc(), Utf8Str::Empty);
+
+    /* check that our own format supports diffs */
+    if (!(m->formatObj->i_getCapabilities() & MediumFormatCapabilities_Differencing))
+    {
+        /* use the default format if not */
+        Utf8Str tmp;
+        m->pVirtualBox->i_getDefaultHardDiskFormat(tmp);
+        return tmp;
+    }
+
+    /* m->strFormat is const, no need to lock */
+    return m->strFormat;
+}
+
+/**
+ * Returns a preferred variant for differencing media.
+ */
+MediumVariant_T Medium::i_getPreferredDiffVariant()
+{
+    AutoCaller autoCaller(this);
+    AssertComRCReturn(autoCaller.hrc(), MediumVariant_Standard);
+
+    /* check that our own format supports diffs */
+    if (!(m->formatObj->i_getCapabilities() & MediumFormatCapabilities_Differencing))
+        return MediumVariant_Standard;
+
+    /* m->variant is const, no need to lock */
+    ULONG mediumVariantFlags = (ULONG)m->variant;
+    mediumVariantFlags &= ~(ULONG)(MediumVariant_Fixed | MediumVariant_VmdkStreamOptimized | MediumVariant_VmdkESX | MediumVariant_VmdkRawDisk);
+    mediumVariantFlags |= MediumVariant_Diff;
+    return (MediumVariant_T)mediumVariantFlags;
+}
+
+/**
+ * Implementation for the public Medium::Close() with the exception of calling
+ * VirtualBox::saveRegistries(), in case someone wants to call this for several
+ * media.
+ *
+ * After this returns with success, uninit() has been called on the medium, and
+ * the object is no longer usable ("not ready" state).
+ *
+ * @param autoCaller AutoCaller instance which must have been created on the caller's
+ *                              stack for this medium. This gets released hereupon
+ *                              which the Medium instance gets uninitialized.
+ * @return
+ */
+HRESULT Medium::i_close(AutoCaller &autoCaller)
+{
+    // must temporarily drop the caller, need the tree lock first
+    autoCaller.release();
+
+    // we're accessing parent/child and backrefs, so lock the tree first, then ourselves
+    AutoMultiWriteLock2 multilock(&m->pVirtualBox->i_getMediaTreeLockHandle(),
+                                  this->lockHandle()
+                                  COMMA_LOCKVAL_SRC_POS);
+
+    autoCaller.add();
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    /* Wait for a concurrently running Medium::i_queryInfo to complete. */
+    while (m->queryInfoRunning)
+    {
+        autoCaller.release();
+        multilock.release();
+        /* Must not hold the media tree lock, as Medium::i_queryInfo needs
+         * this lock and thus we would run into a deadlock here. */
+        Assert(!m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+        /* must not hold the object lock now */
+        Assert(!isWriteLockOnCurrentThread());
+        {
+            AutoReadLock qlock(m->queryInfoSem COMMA_LOCKVAL_SRC_POS);
+        }
+        multilock.acquire();
+        autoCaller.add();
+        if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+    }
+
+    LogFlowFunc(("ENTER for %s\n", i_getLocationFull().c_str()));
+
+    bool wasCreated = true;
+
+    switch (m->state)
+    {
+        case MediumState_NotCreated:
+            wasCreated = false;
+            break;
+        case MediumState_Created:
+        case MediumState_Inaccessible:
+            break;
+        default:
+            return i_setStateError();
+    }
+
+    if (m->fClosing)
+        return setError(VBOX_E_OBJECT_IN_USE,
+                        tr("Medium '%s' cannot be closed because it is already in the process of being closed", ""),
+                        m->strLocationFull.c_str());
+
+    if (m->backRefs.size() != 0)
+        return setError(VBOX_E_OBJECT_IN_USE,
+                        tr("Medium '%s' cannot be closed because it is still attached to %d virtual machines", "",
+                           m->backRefs.size()),
+                        m->strLocationFull.c_str(), m->backRefs.size());
+
+    // perform extra media-dependent close checks
+    HRESULT hrc = i_canClose();
+    if (FAILED(hrc)) return hrc;
+
+    m->fClosing = true;
+
+    if (wasCreated)
+    {
+        // remove from the list of known media before performing actual
+        // uninitialization (to keep the media registry consistent on
+        // failure to do so)
+        hrc = i_unregisterWithVirtualBox();
+        if (FAILED(hrc)) return hrc;
+
+        multilock.release();
+        // Release the AutoCaller now, as otherwise uninit() will simply hang.
+        // Needs to be done before mark the registries as modified and saving
+        // the registry, as otherwise there may be a deadlock with someone else
+        // closing this object while we're in i_saveModifiedRegistries(), which
+        // needs the media tree lock, which the other thread holds until after
+        // uninit() below.
+        autoCaller.release();
+        i_markRegistriesModified();
+        m->pVirtualBox->i_saveModifiedRegistries();
+    }
+    else
+    {
+        multilock.release();
+        // release the AutoCaller, as otherwise uninit() will simply hang
+        autoCaller.release();
+    }
+
+    uninit();
+
+    LogFlowFuncLeave();
+
+    return hrc;
+}
+
+/**
+ * Deletes the medium storage unit.
+ *
+ * If @a aProgress is not NULL but the object it points to is @c null then a new
+ * progress object will be created and assigned to @a *aProgress on success,
+ * otherwise the existing progress object is used. If Progress is NULL, then no
+ * progress object is created/used at all.
+ *
+ * When @a aWait is @c false, this method will create a thread to perform the
+ * delete operation asynchronously and will return immediately. Otherwise, it
+ * will perform the operation on the calling thread and will not return to the
+ * caller until the operation is completed. Note that @a aProgress cannot be
+ * NULL when @a aWait is @c false (this method will assert in this case).
+ *
+ * @param aProgress     Where to find/store a Progress object to track operation
+ *                      completion.
+ * @param aWait         @c true if this method should block instead of creating
+ *                      an asynchronous thread.
+ * @param aNotify       Notify about media for which metadata is changed
+ *                      during execution of the function.
+ *
+ * @note Locks mVirtualBox and this object for writing. Locks medium tree for
+ *       writing.
+ */
+HRESULT Medium::i_deleteStorage(ComObjPtr<Progress> *aProgress,
+                                bool aWait, bool aNotify)
+{
+    AssertReturn(aProgress != NULL || aWait == true, E_FAIL);
+
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        /* we're accessing the media tree, and i_canClose() needs it too */
+        AutoWriteLock treelock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+        AutoCaller autoCaller(this);
+        AssertComRCThrowRC(autoCaller.hrc());
+
+        AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+        LogFlowThisFunc(("aWait=%RTbool locationFull=%s\n", aWait, i_getLocationFull().c_str() ));
+
+        if (    !(m->formatObj->i_getCapabilities() & (  MediumFormatCapabilities_CreateDynamic
+                                                       | MediumFormatCapabilities_CreateFixed)))
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Medium format '%s' does not support storage deletion"),
+                           m->strFormat.c_str());
+
+        /* Wait for a concurrently running Medium::i_queryInfo to complete. */
+        /** @todo r=klaus would be great if this could be moved to the async
+         * part of the operation as it can take quite a while */
+        while (m->queryInfoRunning)
+        {
+            alock.release();
+            autoCaller.release();
+            treelock.release();
+            /* Must not hold the media tree lock or the object lock, as
+             * Medium::i_queryInfo needs this lock and thus we would run
+             * into a deadlock here. */
+            Assert(!m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+            Assert(!isWriteLockOnCurrentThread());
+            {
+                AutoReadLock qlock(m->queryInfoSem COMMA_LOCKVAL_SRC_POS);
+            }
+            treelock.acquire();
+            autoCaller.add();
+            AssertComRCThrowRC(autoCaller.hrc());
+            alock.acquire();
+        }
+
+        /* Note that we are fine with Inaccessible state too: a) for symmetry
+         * with create calls and b) because it doesn't really harm to try, if
+         * it is really inaccessible, the delete operation will fail anyway.
+         * Accepting Inaccessible state is especially important because all
+         * registered media are initially Inaccessible upon VBoxSVC startup
+         * until COMGETTER(RefreshState) is called. Accept Deleting state
+         * because some callers need to put the medium in this state early
+         * to prevent races. */
+        switch (m->state)
+        {
+            case MediumState_Created:
+            case MediumState_Deleting:
+            case MediumState_Inaccessible:
+                break;
+            default:
+                throw i_setStateError();
+        }
+
+        if (m->backRefs.size() != 0)
+        {
+            Utf8Str strMachines;
+            for (BackRefList::const_iterator it = m->backRefs.begin();
+                it != m->backRefs.end();
+                ++it)
+            {
+                const BackRef &b = *it;
+                if (strMachines.length())
+                    strMachines.append(", ");
+                strMachines.append(b.machineId.toString().c_str());
+            }
+#ifdef DEBUG
+            i_dumpBackRefs();
+#endif
+            throw setError(VBOX_E_OBJECT_IN_USE,
+                           tr("Cannot delete storage: medium '%s' is still attached to the following %d virtual machine(s): %s",
+                              "", m->backRefs.size()),
+                           m->strLocationFull.c_str(),
+                           m->backRefs.size(),
+                           strMachines.c_str());
+        }
+
+        hrc = i_canClose();
+        if (FAILED(hrc))
+            throw hrc;
+
+        /* go to Deleting state, so that the medium is not actually locked */
+        if (m->state != MediumState_Deleting)
+        {
+            hrc = i_markForDeletion();
+            if (FAILED(hrc))
+                throw hrc;
+        }
+
+        /* Build the medium lock list. */
+        MediumLockList *pMediumLockList(new MediumLockList());
+        alock.release();
+        autoCaller.release();
+        treelock.release();
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                     this /* pToLockWrite */,
+                                     false /* fMediumLockWriteAll */,
+                                     NULL,
+                                     *pMediumLockList);
+        treelock.acquire();
+        autoCaller.add();
+        AssertComRCThrowRC(autoCaller.hrc());
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw hrc;
+        }
+
+        alock.release();
+        autoCaller.release();
+        treelock.release();
+        hrc = pMediumLockList->Lock();
+        treelock.acquire();
+        autoCaller.add();
+        AssertComRCThrowRC(autoCaller.hrc());
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock media when deleting '%s'"),
+                           i_getLocationFull().c_str());
+        }
+
+        /* try to remove from the list of known media before performing
+         * actual deletion (we favor the consistency of the media registry
+         * which would have been broken if unregisterWithVirtualBox() failed
+         * after we successfully deleted the storage) */
+        hrc = i_unregisterWithVirtualBox();
+        if (FAILED(hrc))
+            throw hrc;
+        // no longer need lock
+        alock.release();
+        autoCaller.release();
+        treelock.release();
+        i_markRegistriesModified();
+
+        if (aProgress != NULL)
+        {
+            /* use the existing progress object... */
+            pProgress = *aProgress;
+
+            /* ...but create a new one if it is null */
+            if (pProgress.isNull())
+            {
+                pProgress.createObject();
+                hrc = pProgress->init(m->pVirtualBox,
+                                      static_cast<IMedium*>(this),
+                                      BstrFmt(tr("Deleting medium storage unit '%s'"), m->strLocationFull.c_str()).raw(),
+                                      FALSE /* aCancelable */);
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+        }
+
+        /* setup task object to carry out the operation sync/async */
+        pTask = new Medium::DeleteTask(this, pProgress, pMediumLockList, false, aNotify);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        if (aWait)
+        {
+            hrc = pTask->runNow();
+            delete pTask;
+        }
+        else
+            hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc) && aProgress != NULL)
+            *aProgress = pProgress;
+    }
+    else
+    {
+        if (pTask)
+            delete pTask;
+
+        /* Undo deleting state if necessary. */
+        AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+        /* Make sure that any error signalled by unmarkForDeletion() is not
+         * ending up in the error list (if the caller uses MultiResult). It
+         * usually is spurious, as in most cases the medium hasn't been marked
+         * for deletion when the error was thrown above. */
+        ErrorInfoKeeper eik;
+        i_unmarkForDeletion();
+    }
+
+    return hrc;
+}
+
+/**
+ * Mark a medium for deletion.
+ *
+ * @note Caller must hold the write lock on this medium!
+ */
+HRESULT Medium::i_markForDeletion()
+{
+    ComAssertRet(isWriteLockOnCurrentThread(), E_FAIL);
+    switch (m->state)
+    {
+        case MediumState_Created:
+        case MediumState_Inaccessible:
+            m->preLockState = m->state;
+            m->state = MediumState_Deleting;
+            return S_OK;
+        default:
+            return i_setStateError();
+    }
+}
+
+/**
+ * Removes the "mark for deletion".
+ *
+ * @note Caller must hold the write lock on this medium!
+ */
+HRESULT Medium::i_unmarkForDeletion()
+{
+    ComAssertRet(isWriteLockOnCurrentThread(), E_FAIL);
+    switch (m->state)
+    {
+        case MediumState_Deleting:
+            m->state = m->preLockState;
+            return S_OK;
+        default:
+            return i_setStateError();
+    }
+}
+
+/**
+ * Mark a medium for deletion which is in locked state.
+ *
+ * @note Caller must hold the write lock on this medium!
+ */
+HRESULT Medium::i_markLockedForDeletion()
+{
+    ComAssertRet(isWriteLockOnCurrentThread(), E_FAIL);
+    if (   (   m->state == MediumState_LockedRead
+            || m->state == MediumState_LockedWrite)
+        && m->preLockState == MediumState_Created)
+    {
+        m->preLockState = MediumState_Deleting;
+        return S_OK;
+    }
+    else
+        return i_setStateError();
+}
+
+/**
+ * Removes the "mark for deletion" for a medium in locked state.
+ *
+ * @note Caller must hold the write lock on this medium!
+ */
+HRESULT Medium::i_unmarkLockedForDeletion()
+{
+    ComAssertRet(isWriteLockOnCurrentThread(), E_FAIL);
+    if (   (   m->state == MediumState_LockedRead
+            || m->state == MediumState_LockedWrite)
+        && m->preLockState == MediumState_Deleting)
+    {
+        m->preLockState = MediumState_Created;
+        return S_OK;
+    }
+    else
+        return i_setStateError();
+}
+
+/**
+ * Queries the preferred merge direction from this to the other medium, i.e.
+ * the one which requires the least amount of I/O and therefore time and
+ * disk consumption.
+ *
+ * @returns Status code.
+ * @retval  E_FAIL in case determining the merge direction fails for some reason,
+ *          for example if getting the size of the media fails. There is no
+ *          error set though and the caller is free to continue to find out
+ *          what was going wrong later. Leaves fMergeForward unset.
+ * @retval  VBOX_E_INVALID_OBJECT_STATE if both media are not related to each other
+ *          An error is set.
+ * @param pOther           The other medium to merge with.
+ * @param fMergeForward    Resulting preferred merge direction (out).
+ */
+HRESULT Medium::i_queryPreferredMergeDirection(const ComObjPtr<Medium> &pOther,
+                                               bool &fMergeForward)
+{
+    AssertReturn(pOther != NULL, E_FAIL);
+    AssertReturn(pOther != this, E_FAIL);
+
+    HRESULT hrc = S_OK;
+    bool fThisParent = false; /**<< Flag whether this medium is the parent of pOther. */
+
+    try
+    {
+        // locking: we need the tree lock first because we access parent pointers
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+        AutoCaller autoCaller(this);
+        AssertComRCThrowRC(autoCaller.hrc());
+
+        AutoCaller otherCaller(pOther);
+        AssertComRCThrowRC(otherCaller.hrc());
+
+        /* more sanity checking and figuring out the current merge direction */
+        ComObjPtr<Medium> pMedium = i_getParent();
+        while (!pMedium.isNull() && pMedium != pOther)
+            pMedium = pMedium->i_getParent();
+        if (pMedium == pOther)
+            fThisParent = false;
+        else
+        {
+            pMedium = pOther->i_getParent();
+            while (!pMedium.isNull() && pMedium != this)
+                pMedium = pMedium->i_getParent();
+            if (pMedium == this)
+                fThisParent = true;
+            else
+            {
+                Utf8Str tgtLoc;
+                {
+                    AutoReadLock alock(pOther COMMA_LOCKVAL_SRC_POS);
+                    tgtLoc = pOther->i_getLocationFull();
+                }
+
+                AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Media '%s' and '%s' are unrelated"),
+                               m->strLocationFull.c_str(), tgtLoc.c_str());
+            }
+        }
+
+        /*
+         * Figure out the preferred merge direction. The current way is to
+         * get the current sizes of file based images and select the merge
+         * direction depending on the size.
+         *
+         * Can't use the VD API to get current size here as the media might
+         * be write locked by a running VM. Resort to RTFileQuerySize().
+         */
+        int vrc = VINF_SUCCESS;
+        uint64_t cbMediumThis = 0;
+        uint64_t cbMediumOther = 0;
+
+        if (i_isMediumFormatFile() && pOther->i_isMediumFormatFile())
+        {
+            vrc = RTFileQuerySizeByPath(this->i_getLocationFull().c_str(), &cbMediumThis);
+            if (RT_SUCCESS(vrc))
+            {
+                vrc = RTFileQuerySizeByPath(pOther->i_getLocationFull().c_str(),
+                                      &cbMediumOther);
+            }
+
+            if (RT_FAILURE(vrc))
+                hrc = E_FAIL;
+            else
+            {
+                /*
+                 * Check which merge direction might be more optimal.
+                 * This method is not bullet proof of course as there might
+                 * be overlapping blocks in the images so the file size is
+                 * not the best indicator but it is good enough for our purpose
+                 * and everything else is too complicated, especially when the
+                 * media are used by a running VM.
+                 */
+
+                uint32_t mediumVariants =  MediumVariant_Fixed | MediumVariant_VmdkStreamOptimized;
+                uint32_t mediumCaps = MediumFormatCapabilities_CreateDynamic | MediumFormatCapabilities_File;
+
+                bool fDynamicOther  = pOther->i_getMediumFormat()->i_getCapabilities() & mediumCaps
+                                   && pOther->i_getVariant() & ~mediumVariants;
+                bool fDynamicThis   = i_getMediumFormat()->i_getCapabilities() & mediumCaps
+                                   && i_getVariant() & ~mediumVariants;
+                bool fMergeIntoThis = (fDynamicThis && !fDynamicOther)
+                                   || (fDynamicThis == fDynamicOther && cbMediumThis > cbMediumOther);
+                fMergeForward = fMergeIntoThis != fThisParent;
+            }
+        }
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    return hrc;
+}
+
+/**
+ * Prepares this (source) medium, target medium and all intermediate media
+ * for the merge operation.
+ *
+ * This method is to be called prior to calling the #mergeTo() to perform
+ * necessary consistency checks and place involved media to appropriate
+ * states. If #mergeTo() is not called or fails, the state modifications
+ * performed by this method must be undone by #i_cancelMergeTo().
+ *
+ * See #mergeTo() for more information about merging.
+ *
+ * @param pTarget       Target medium.
+ * @param aMachineId    Allowed machine attachment. NULL means do not check.
+ * @param aSnapshotId   Allowed snapshot attachment. NULL or empty UUID means
+ *                      do not check.
+ * @param fLockMedia    Flag whether to lock the medium lock list or not.
+ *                      If set to false and the medium lock list locking fails
+ *                      later you must call #i_cancelMergeTo().
+ * @param fMergeForward Resulting merge direction (out).
+ * @param pParentForTarget New parent for target medium after merge (out).
+ * @param aChildrenToReparent Medium lock list containing all children of the
+ *                      source which will have to be reparented to the target
+ *                      after merge (out).
+ * @param aMediumLockList Medium locking information (out).
+ *
+ * @note Locks medium tree for reading. Locks this object, aTarget and all
+ *       intermediate media for writing.
+ */
+HRESULT Medium::i_prepareMergeTo(const ComObjPtr<Medium> &pTarget,
+                                 const Guid *aMachineId,
+                                 const Guid *aSnapshotId,
+                                 bool fLockMedia,
+                                 bool &fMergeForward,
+                                 ComObjPtr<Medium> &pParentForTarget,
+                                 MediumLockList * &aChildrenToReparent,
+                                 MediumLockList * &aMediumLockList)
+{
+    AssertReturn(pTarget != NULL, E_FAIL);
+    AssertReturn(pTarget != this, E_FAIL);
+
+    HRESULT hrc = S_OK;
+    fMergeForward = false;
+    pParentForTarget.setNull();
+    Assert(aChildrenToReparent == NULL);
+    aChildrenToReparent = NULL;
+    Assert(aMediumLockList == NULL);
+    aMediumLockList = NULL;
+
+    try
+    {
+        // locking: we need the tree lock first because we access parent pointers
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+        AutoCaller autoCaller(this);
+        AssertComRCThrowRC(autoCaller.hrc());
+
+        AutoCaller targetCaller(pTarget);
+        AssertComRCThrowRC(targetCaller.hrc());
+
+        /* more sanity checking and figuring out the merge direction */
+        ComObjPtr<Medium> pMedium = i_getParent();
+        while (!pMedium.isNull() && pMedium != pTarget)
+            pMedium = pMedium->i_getParent();
+        if (pMedium == pTarget)
+            fMergeForward = false;
+        else
+        {
+            pMedium = pTarget->i_getParent();
+            while (!pMedium.isNull() && pMedium != this)
+                pMedium = pMedium->i_getParent();
+            if (pMedium == this)
+                fMergeForward = true;
+            else
+            {
+                Utf8Str tgtLoc;
+                {
+                    AutoReadLock alock(pTarget COMMA_LOCKVAL_SRC_POS);
+                    tgtLoc = pTarget->i_getLocationFull();
+                }
+
+                AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Media '%s' and '%s' are unrelated"),
+                               m->strLocationFull.c_str(), tgtLoc.c_str());
+            }
+        }
+
+        /* Build the lock list. */
+        aMediumLockList = new MediumLockList();
+        targetCaller.release();
+        autoCaller.release();
+        treeLock.release();
+        if (fMergeForward)
+            hrc = pTarget->i_createMediumLockList(true /* fFailIfInaccessible */,
+                                                  pTarget /* pToLockWrite */,
+                                                  false /* fMediumLockWriteAll */,
+                                                  NULL,
+                                                  *aMediumLockList);
+        else
+            hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                         pTarget /* pToLockWrite */,
+                                         false /* fMediumLockWriteAll */,
+                                         NULL,
+                                         *aMediumLockList);
+        treeLock.acquire();
+        autoCaller.add();
+        AssertComRCThrowRC(autoCaller.hrc());
+        targetCaller.add();
+        AssertComRCThrowRC(targetCaller.hrc());
+        if (FAILED(hrc))
+            throw hrc;
+
+        /* Sanity checking, must be after lock list creation as it depends on
+         * valid medium states. The medium objects must be accessible. Only
+         * do this if immediate locking is requested, otherwise it fails when
+         * we construct a medium lock list for an already running VM. Snapshot
+         * deletion uses this to simplify its life. */
+        if (fLockMedia)
+        {
+            {
+                AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+                if (m->state != MediumState_Created)
+                    throw i_setStateError();
+            }
+            {
+                AutoReadLock alock(pTarget COMMA_LOCKVAL_SRC_POS);
+                if (pTarget->m->state != MediumState_Created)
+                    throw pTarget->i_setStateError();
+            }
+        }
+
+        /* check medium attachment and other sanity conditions */
+        if (fMergeForward)
+        {
+            AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+            if (i_getChildren().size() > 1)
+            {
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Medium '%s' involved in the merge operation has more than one child medium (%d)"),
+                               m->strLocationFull.c_str(), i_getChildren().size());
+            }
+            /* One backreference is only allowed if the machine ID is not empty
+             * and it matches the machine the medium is attached to (including
+             * the snapshot ID if not empty). */
+            if (   m->backRefs.size() != 0
+                && (   !aMachineId
+                    || m->backRefs.size() != 1
+                    || aMachineId->isZero()
+                    || *i_getFirstMachineBackrefId() != *aMachineId
+                    || (   (!aSnapshotId || !aSnapshotId->isZero())
+                        && *i_getFirstMachineBackrefSnapshotId() != *aSnapshotId)))
+                throw setError(VBOX_E_OBJECT_IN_USE,
+                               tr("Medium '%s' is attached to %d virtual machines", "", m->backRefs.size()),
+                               m->strLocationFull.c_str(), m->backRefs.size());
+            if (m->type == MediumType_Immutable)
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Medium '%s' is immutable"),
+                               m->strLocationFull.c_str());
+            if (m->type == MediumType_MultiAttach)
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Medium '%s' is multi-attach"),
+                               m->strLocationFull.c_str());
+        }
+        else
+        {
+            AutoReadLock alock(pTarget COMMA_LOCKVAL_SRC_POS);
+            if (pTarget->i_getChildren().size() > 1)
+            {
+                throw setError(VBOX_E_OBJECT_IN_USE,
+                               tr("Medium '%s' involved in the merge operation has more than one child medium (%d)"),
+                               pTarget->m->strLocationFull.c_str(),
+                               pTarget->i_getChildren().size());
+            }
+            if (pTarget->m->type == MediumType_Immutable)
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Medium '%s' is immutable"),
+                               pTarget->m->strLocationFull.c_str());
+            if (pTarget->m->type == MediumType_MultiAttach)
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Medium '%s' is multi-attach"),
+                               pTarget->m->strLocationFull.c_str());
+        }
+        ComObjPtr<Medium> pLast(fMergeForward ? (Medium *)pTarget : this);
+        ComObjPtr<Medium> pLastIntermediate = pLast->i_getParent();
+        for (pLast = pLastIntermediate;
+             !pLast.isNull() && pLast != pTarget && pLast != this;
+             pLast = pLast->i_getParent())
+        {
+            AutoReadLock alock(pLast COMMA_LOCKVAL_SRC_POS);
+            if (pLast->i_getChildren().size() > 1)
+            {
+                throw setError(VBOX_E_OBJECT_IN_USE,
+                               tr("Medium '%s' involved in the merge operation has more than one child medium (%d)"),
+                               pLast->m->strLocationFull.c_str(),
+                               pLast->i_getChildren().size());
+            }
+            if (pLast->m->backRefs.size() != 0)
+                throw setError(VBOX_E_OBJECT_IN_USE,
+                               tr("Medium '%s' is attached to %d virtual machines", "", pLast->m->backRefs.size()),
+                               pLast->m->strLocationFull.c_str(),
+                               pLast->m->backRefs.size());
+
+        }
+
+        /* Update medium states appropriately */
+        {
+            AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+            if (m->state == MediumState_Created)
+            {
+                hrc = i_markForDeletion();
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+            else
+            {
+                if (fLockMedia)
+                    throw i_setStateError();
+                else if (   m->state == MediumState_LockedWrite
+                         || m->state == MediumState_LockedRead)
+                {
+                    /* Either mark it for deletion in locked state or allow
+                     * others to have done so. */
+                    if (m->preLockState == MediumState_Created)
+                        i_markLockedForDeletion();
+                    else if (m->preLockState != MediumState_Deleting)
+                        throw i_setStateError();
+                }
+                else
+                    throw i_setStateError();
+            }
+        }
+
+        if (fMergeForward)
+        {
+            /* we will need parent to reparent target */
+            pParentForTarget = i_getParent();
+        }
+        else
+        {
+            /* we will need to reparent children of the source */
+            aChildrenToReparent = new MediumLockList();
+            for (MediaList::const_iterator it = i_getChildren().begin();
+                 it != i_getChildren().end();
+                 ++it)
+            {
+                pMedium = *it;
+                aChildrenToReparent->Append(pMedium, true /* fLockWrite */);
+            }
+            if (fLockMedia && aChildrenToReparent)
+            {
+                targetCaller.release();
+                autoCaller.release();
+                treeLock.release();
+                hrc = aChildrenToReparent->Lock();
+                treeLock.acquire();
+                autoCaller.add();
+                AssertComRCThrowRC(autoCaller.hrc());
+                targetCaller.add();
+                AssertComRCThrowRC(targetCaller.hrc());
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+        }
+        for (pLast = pLastIntermediate;
+             !pLast.isNull() && pLast != pTarget && pLast != this;
+             pLast = pLast->i_getParent())
+        {
+            AutoWriteLock alock(pLast COMMA_LOCKVAL_SRC_POS);
+            if (pLast->m->state == MediumState_Created)
+            {
+                hrc = pLast->i_markForDeletion();
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+            else
+                throw pLast->i_setStateError();
+        }
+
+        /* Tweak the lock list in the backward merge case, as the target
+         * isn't marked to be locked for writing yet. */
+        if (!fMergeForward)
+        {
+            MediumLockList::Base::iterator lockListBegin =
+                aMediumLockList->GetBegin();
+            MediumLockList::Base::iterator lockListEnd =
+                aMediumLockList->GetEnd();
+            ++lockListEnd;
+            for (MediumLockList::Base::iterator it = lockListBegin;
+                 it != lockListEnd;
+                 ++it)
+            {
+                MediumLock &mediumLock = *it;
+                if (mediumLock.GetMedium() == pTarget)
+                {
+                    HRESULT hrc2 = mediumLock.UpdateLock(true);
+                    AssertComRC(hrc2);
+                    break;
+                }
+            }
+        }
+
+        if (fLockMedia)
+        {
+            targetCaller.release();
+            autoCaller.release();
+            treeLock.release();
+            hrc = aMediumLockList->Lock();
+            treeLock.acquire();
+            autoCaller.add();
+            AssertComRCThrowRC(autoCaller.hrc());
+            targetCaller.add();
+            AssertComRCThrowRC(targetCaller.hrc());
+            if (FAILED(hrc))
+            {
+                AutoReadLock alock(pTarget COMMA_LOCKVAL_SRC_POS);
+                throw setError(hrc,
+                               tr("Failed to lock media when merging to '%s'"),
+                               pTarget->i_getLocationFull().c_str());
+            }
+        }
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (FAILED(hrc))
+    {
+        if (aMediumLockList)
+        {
+            delete aMediumLockList;
+            aMediumLockList = NULL;
+        }
+        if (aChildrenToReparent)
+        {
+            delete aChildrenToReparent;
+            aChildrenToReparent = NULL;
+        }
+    }
+
+    return hrc;
+}
+
+/**
+ * Merges this medium to the specified medium which must be either its
+ * direct ancestor or descendant.
+ *
+ * Given this medium is SOURCE and the specified medium is TARGET, we will
+ * get two variants of the merge operation:
+ *
+ *                forward merge
+ *                ------------------------->
+ *  [Extra] <- SOURCE <- Intermediate <- TARGET
+ *  Any        Del       Del             LockWr
+ *
+ *
+ *                            backward merge
+ *                <-------------------------
+ *             TARGET <- Intermediate <- SOURCE <- [Extra]
+ *             LockWr    Del             Del       LockWr
+ *
+ * Each diagram shows the involved media on the media chain where
+ * SOURCE and TARGET belong. Under each medium there is a state value which
+ * the medium must have at a time of the mergeTo() call.
+ *
+ * The media in the square braces may be absent (e.g. when the forward
+ * operation takes place and SOURCE is the base medium, or when the backward
+ * merge operation takes place and TARGET is the last child in the chain) but if
+ * they present they are involved too as shown.
+ *
+ * Neither the source medium nor intermediate media may be attached to
+ * any VM directly or in the snapshot, otherwise this method will assert.
+ *
+ * The #i_prepareMergeTo() method must be called prior to this method to place
+ * all involved to necessary states and perform other consistency checks.
+ *
+ * If @a aWait is @c true then this method will perform the operation on the
+ * calling thread and will not return to the caller until the operation is
+ * completed. When this method succeeds, all intermediate medium objects in
+ * the chain will be uninitialized, the state of the target medium (and all
+ * involved extra media) will be restored. @a aMediumLockList will not be
+ * deleted, whether the operation is successful or not. The caller has to do
+ * this if appropriate. Note that this (source) medium is not uninitialized
+ * because of possible AutoCaller instances held by the caller of this method
+ * on the current thread. It's therefore the responsibility of the caller to
+ * call Medium::uninit() after releasing all callers.
+ *
+ * If @a aWait is @c false then this method will create a thread to perform the
+ * operation asynchronously and will return immediately. If the operation
+ * succeeds, the thread will uninitialize the source medium object and all
+ * intermediate medium objects in the chain, reset the state of the target
+ * medium (and all involved extra media) and delete @a aMediumLockList.
+ * If the operation fails, the thread will only reset the states of all
+ * involved media and delete @a aMediumLockList.
+ *
+ * When this method fails (regardless of the @a aWait mode), it is a caller's
+ * responsibility to undo state changes and delete @a aMediumLockList using
+ * #i_cancelMergeTo().
+ *
+ * If @a aProgress is not NULL but the object it points to is @c null then a new
+ * progress object will be created and assigned to @a *aProgress on success,
+ * otherwise the existing progress object is used. If Progress is NULL, then no
+ * progress object is created/used at all. Note that @a aProgress cannot be
+ * NULL when @a aWait is @c false (this method will assert in this case).
+ *
+ * @param pTarget       Target medium.
+ * @param fMergeForward Merge direction.
+ * @param pParentForTarget New parent for target medium after merge.
+ * @param aChildrenToReparent List of children of the source which will have
+ *                      to be reparented to the target after merge.
+ * @param aMediumLockList Medium locking information.
+ * @param aProgress     Where to find/store a Progress object to track operation
+ *                      completion.
+ * @param aWait         @c true if this method should block instead of creating
+ *                      an asynchronous thread.
+ * @param aNotify       Notify about media for which metadata is changed
+ *                      during execution of the function.
+ *
+ * @note Locks the tree lock for writing. Locks the media from the chain
+ *       for writing.
+ */
+HRESULT Medium::i_mergeTo(const ComObjPtr<Medium> &pTarget,
+                          bool fMergeForward,
+                          const ComObjPtr<Medium> &pParentForTarget,
+                          MediumLockList *aChildrenToReparent,
+                          MediumLockList *aMediumLockList,
+                          ComObjPtr<Progress> *aProgress,
+                          bool aWait, bool aNotify)
+{
+    AssertReturn(pTarget != NULL, E_FAIL);
+    AssertReturn(pTarget != this, E_FAIL);
+    AssertReturn(aMediumLockList != NULL, E_FAIL);
+    AssertReturn(aProgress != NULL || aWait == true, E_FAIL);
+
+    AutoCaller autoCaller(this);
+    AssertComRCReturnRC(autoCaller.hrc());
+
+    AutoCaller targetCaller(pTarget);
+    AssertComRCReturnRC(targetCaller.hrc());
+
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        if (aProgress != NULL)
+        {
+            /* use the existing progress object... */
+            pProgress = *aProgress;
+
+            /* ...but create a new one if it is null */
+            if (pProgress.isNull())
+            {
+                Utf8Str tgtName;
+                {
+                    AutoReadLock alock(pTarget COMMA_LOCKVAL_SRC_POS);
+                    tgtName = pTarget->i_getName();
+                }
+
+                AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+                pProgress.createObject();
+                hrc = pProgress->init(m->pVirtualBox,
+                                      static_cast<IMedium*>(this),
+                                      BstrFmt(tr("Merging medium '%s' to '%s'"),
+                                              i_getName().c_str(),
+                                              tgtName.c_str()).raw(),
+                                      TRUE, /* aCancelable */
+                                      2, /* Number of opearations */
+                                      BstrFmt(tr("Resizing medium '%s' before merge"),
+                                              tgtName.c_str()).raw()
+                                      );
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+        }
+
+        /* setup task object to carry out the operation sync/async */
+        pTask = new Medium::MergeTask(this, pTarget, fMergeForward,
+                                      pParentForTarget, aChildrenToReparent,
+                                      pProgress, aMediumLockList,
+                                      aWait /* fKeepMediumLockList */,
+                                      aNotify);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        if (aWait)
+        {
+            hrc = pTask->runNow();
+            delete pTask;
+        }
+        else
+            hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc) && aProgress != NULL)
+            *aProgress = pProgress;
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    return hrc;
+}
+
+/**
+ * Undoes what #i_prepareMergeTo() did. Must be called if #mergeTo() is not
+ * called or fails. Frees memory occupied by @a aMediumLockList and unlocks
+ * the medium objects in @a aChildrenToReparent.
+ *
+ * @param aChildrenToReparent List of children of the source which will have
+ *                      to be reparented to the target after merge.
+ * @param aMediumLockList Medium locking information.
+ *
+ * @note Locks the tree lock for writing. Locks the media from the chain
+ *       for writing.
+ */
+void Medium::i_cancelMergeTo(MediumLockList *aChildrenToReparent,
+                             MediumLockList *aMediumLockList)
+{
+    AutoCaller autoCaller(this);
+    AssertComRCReturnVoid(autoCaller.hrc());
+
+    AssertReturnVoid(aMediumLockList != NULL);
+
+    /* Revert media marked for deletion to previous state. */
+    MediumLockList::Base::const_iterator mediumListBegin =
+        aMediumLockList->GetBegin();
+    MediumLockList::Base::const_iterator mediumListEnd =
+        aMediumLockList->GetEnd();
+    for (MediumLockList::Base::const_iterator it = mediumListBegin;
+         it != mediumListEnd;
+         ++it)
+    {
+        const MediumLock &mediumLock = *it;
+        const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+        AutoWriteLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+        if (pMedium->m->state == MediumState_Deleting)
+        {
+            HRESULT hrc = pMedium->i_unmarkForDeletion();
+            AssertComRC(hrc);
+        }
+        else if (   (   pMedium->m->state == MediumState_LockedWrite
+                     || pMedium->m->state == MediumState_LockedRead)
+                 && pMedium->m->preLockState == MediumState_Deleting)
+        {
+            HRESULT hrc = pMedium->i_unmarkLockedForDeletion();
+            AssertComRC(hrc);
+        }
+    }
+
+    /* the destructor will do the work */
+    delete aMediumLockList;
+
+    /* unlock the children which had to be reparented, the destructor will do
+     * the work */
+    if (aChildrenToReparent)
+        delete aChildrenToReparent;
+}
+
+/**
+ * Resizes the media.
+ *
+ * If @a aWait is @c true then this method will perform the operation on the
+ * calling thread and will not return to the caller until the operation is
+ * completed. When this method succeeds, the state of the target medium (and all
+ * involved extra media) will be restored. @a aMediumLockList will not be
+ * deleted, whether the operation is successful or not. The caller has to do
+ * this if appropriate.
+ *
+ * If @a aWait is @c false then this method will create a thread to perform the
+ * operation asynchronously and will return immediately. The thread will reset
+ * the state of the target medium (and all involved extra media) and delete
+ * @a aMediumLockList.
+ *
+ * When this method fails (regardless of the @a aWait mode), it is a caller's
+ * responsibility to undo state changes and delete @a aMediumLockList.
+ *
+ * If @a aProgress is not NULL but the object it points to is @c null then a new
+ * progress object will be created and assigned to @a *aProgress on success,
+ * otherwise the existing progress object is used. If Progress is NULL, then no
+ * progress object is created/used at all. Note that @a aProgress cannot be
+ * NULL when @a aWait is @c false (this method will assert in this case).
+ *
+ * @param aLogicalSize  New nominal capacity of the medium in bytes.
+ * @param aMediumLockList Medium locking information.
+ * @param aProgress     Where to find/store a Progress object to track operation
+ *                      completion.
+ * @param aWait         @c true if this method should block instead of creating
+ *                      an asynchronous thread.
+ * @param aNotify       Notify about media for which metadata is changed
+ *                      during execution of the function.
+ *
+ * @note Locks the media from the chain for writing.
+ */
+
+HRESULT Medium::i_resize(uint64_t aLogicalSize,
+                         MediumLockList *aMediumLockList,
+                         ComObjPtr<Progress> *aProgress,
+                         bool aWait,
+                         bool aNotify)
+{
+    AssertReturn(aMediumLockList != NULL, E_FAIL);
+    AssertReturn(aProgress != NULL || aWait == true, E_FAIL);
+
+    AutoCaller autoCaller(this);
+    AssertComRCReturnRC(autoCaller.hrc());
+
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        if (aProgress != NULL)
+        {
+            /* use the existing progress object... */
+            pProgress = *aProgress;
+
+            /* ...but create a new one if it is null */
+            if (pProgress.isNull())
+            {
+                AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+                pProgress.createObject();
+                hrc = pProgress->init(m->pVirtualBox,
+                                      static_cast <IMedium *>(this),
+                                      BstrFmt(tr("Resizing medium '%s'"), m->strLocationFull.c_str()).raw(),
+                                      TRUE /* aCancelable */);
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+        }
+
+        /* setup task object to carry out the operation asynchronously */
+        pTask = new Medium::ResizeTask(this,
+                                       aLogicalSize,
+                                       pProgress,
+                                       aMediumLockList,
+                                       aWait /* fKeepMediumLockList */,
+                                       aNotify);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        if (aWait)
+        {
+            hrc = pTask->runNow();
+            delete pTask;
+        }
+        else
+            hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc) && aProgress != NULL)
+            *aProgress = pProgress;
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    return hrc;
+}
+
+/**
+ * Fix the parent UUID of all children to point to this medium as their
+ * parent.
+ */
+HRESULT Medium::i_fixParentUuidOfChildren(MediumLockList *pChildrenToReparent)
+{
+    /** @todo r=klaus The code below needs to be double checked with regard
+     * to lock order violations, it probably causes lock order issues related
+     * to the AutoCaller usage. Likewise the code using this method seems
+     * problematic. */
+    Assert(!isWriteLockOnCurrentThread());
+    Assert(!m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+    MediumLockList mediumLockList;
+    HRESULT hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                         NULL /* pToLockWrite */,
+                                         false /* fMediumLockWriteAll */,
+                                         this,
+                                         mediumLockList);
+    AssertComRCReturnRC(hrc);
+
+    try
+    {
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        try
+        {
+            MediumLockList::Base::iterator lockListBegin =
+                mediumLockList.GetBegin();
+            MediumLockList::Base::iterator lockListEnd =
+                mediumLockList.GetEnd();
+            for (MediumLockList::Base::iterator it = lockListBegin;
+                 it != lockListEnd;
+                 ++it)
+            {
+                MediumLock &mediumLock = *it;
+                const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+                AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                // open the medium
+                vrc = VDOpen(hdd,
+                             pMedium->m->strFormat.c_str(),
+                             pMedium->m->strLocationFull.c_str(),
+                             VD_OPEN_FLAGS_READONLY | m->uOpenFlagsDef,
+                             pMedium->m->vdImageIfaces);
+                if (RT_FAILURE(vrc))
+                    throw vrc;
+            }
+
+            MediumLockList::Base::iterator childrenBegin = pChildrenToReparent->GetBegin();
+            MediumLockList::Base::iterator childrenEnd = pChildrenToReparent->GetEnd();
+            for (MediumLockList::Base::iterator it = childrenBegin;
+                 it != childrenEnd;
+                 ++it)
+            {
+                Medium *pMedium = it->GetMedium();
+                /* VD_OPEN_FLAGS_INFO since UUID is wrong yet */
+                vrc = VDOpen(hdd,
+                             pMedium->m->strFormat.c_str(),
+                             pMedium->m->strLocationFull.c_str(),
+                             VD_OPEN_FLAGS_INFO | m->uOpenFlagsDef,
+                             pMedium->m->vdImageIfaces);
+                if (RT_FAILURE(vrc))
+                    throw vrc;
+
+                vrc = VDSetParentUuid(hdd, VD_LAST_IMAGE, m->id.raw());
+                if (RT_FAILURE(vrc))
+                    throw vrc;
+
+                vrc = VDClose(hdd, false /* fDelete */);
+                if (RT_FAILURE(vrc))
+                    throw vrc;
+            }
+        }
+        catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+        catch (int vrcXcpt)
+        {
+            hrc = setErrorBoth(E_FAIL, vrcXcpt,
+                               tr("Could not update medium UUID references to parent '%s' (%s)"),
+                               m->strLocationFull.c_str(),
+                               i_vdError(vrcXcpt).c_str());
+        }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    return hrc;
+}
+
+/**
+ *
+ * @note    Similar code exists in i_taskExportHandler.
+ */
+HRESULT Medium::i_addRawToFss(const char *aFilename, SecretKeyStore *pKeyStore, RTVFSFSSTREAM hVfsFssDst,
+                              const ComObjPtr<Progress> &aProgress, bool fSparse)
+{
+    AutoCaller autoCaller(this);
+    HRESULT hrc = autoCaller.hrc();
+    if (SUCCEEDED(hrc))
+    {
+        /*
+         * Get a readonly hdd for this medium.
+         */
+        MediumCryptoFilterSettings      CryptoSettingsRead;
+        MediumLockList                  SourceMediumLockList;
+        PVDISK                          pHdd;
+        hrc = i_openForIO(false /*fWritable*/, pKeyStore, &pHdd, &SourceMediumLockList, &CryptoSettingsRead);
+        if (SUCCEEDED(hrc))
+        {
+            /*
+             * Create a VFS file interface to the HDD and attach a progress wrapper
+             * that monitors the progress reading of the raw image.  The image will
+             * be read twice if hVfsFssDst does sparse processing.
+             */
+            RTVFSFILE hVfsFileDisk = NIL_RTVFSFILE;
+            int vrc = VDCreateVfsFileFromDisk(pHdd, 0 /*fFlags*/, &hVfsFileDisk);
+            if (RT_SUCCESS(vrc))
+            {
+                RTVFSFILE hVfsFileProgress = NIL_RTVFSFILE;
+                vrc = RTVfsCreateProgressForFile(hVfsFileDisk, aProgress->i_iprtProgressCallback, &*aProgress,
+                                                 RTVFSPROGRESS_F_CANCELABLE | RTVFSPROGRESS_F_FORWARD_SEEK_AS_READ,
+                                                 VDGetSize(pHdd, VD_LAST_IMAGE) * (fSparse ? 2 : 1) /*cbExpectedRead*/,
+                                                 0 /*cbExpectedWritten*/, &hVfsFileProgress);
+                RTVfsFileRelease(hVfsFileDisk);
+                if (RT_SUCCESS(vrc))
+                {
+                    RTVFSOBJ hVfsObj = RTVfsObjFromFile(hVfsFileProgress);
+                    RTVfsFileRelease(hVfsFileProgress);
+
+                    vrc = RTVfsFsStrmAdd(hVfsFssDst, aFilename, hVfsObj, 0 /*fFlags*/);
+                    RTVfsObjRelease(hVfsObj);
+                    if (RT_FAILURE(vrc))
+                        hrc = setErrorBoth(VBOX_E_FILE_ERROR, vrc, tr("Failed to add '%s' to output (%Rrc)"), aFilename, vrc);
+                }
+                else
+                    hrc = setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("RTVfsCreateProgressForFile failed when processing '%s' (%Rrc)"), aFilename, vrc);
+            }
+            else
+                hrc = setErrorBoth(VBOX_E_FILE_ERROR, vrc, tr("VDCreateVfsFileFromDisk failed for '%s' (%Rrc)"), aFilename, vrc);
+            VDDestroy(pHdd);
+        }
+    }
+    return hrc;
+}
+
+/**
+ * Used by IAppliance to export disk images.
+ *
+ * @param aFilename         Filename to create (UTF8).
+ * @param aFormat           Medium format for creating @a aFilename.
+ * @param aVariant          Which exact image format variant to use for the
+ *                          destination image.
+ * @param pKeyStore         The optional key store for decrypting the data for
+ *                          encrypted media during the export.
+ * @param hVfsIosDst        The destination I/O stream object.
+ * @param aProgress         Progress object to use.
+ * @return
+ *
+ * @note The source format is defined by the Medium instance.
+ */
+HRESULT Medium::i_exportFile(const char *aFilename,
+                             const ComObjPtr<MediumFormat> &aFormat,
+                             MediumVariant_T aVariant,
+                             SecretKeyStore *pKeyStore,
+                             RTVFSIOSTREAM hVfsIosDst,
+                             const ComObjPtr<Progress> &aProgress)
+{
+    AssertPtrReturn(aFilename, E_INVALIDARG);
+    AssertReturn(aFormat.isNotNull(), E_INVALIDARG);
+    AssertReturn(aProgress.isNotNull(), E_INVALIDARG);
+
+    AutoCaller autoCaller(this);
+    HRESULT hrc = autoCaller.hrc();
+    if (SUCCEEDED(hrc))
+    {
+        /*
+         * Setup VD interfaces.
+         */
+        PVDINTERFACE   pVDImageIfaces = m->vdImageIfaces;
+        PVDINTERFACEIO pVfsIoIf;
+        int vrc = VDIfCreateFromVfsStream(hVfsIosDst, RTFILE_O_WRITE, &pVfsIoIf);
+        if (RT_SUCCESS(vrc))
+        {
+            vrc = VDInterfaceAdd(&pVfsIoIf->Core, "Medium::ExportTaskVfsIos", VDINTERFACETYPE_IO,
+                                 pVfsIoIf, sizeof(VDINTERFACEIO), &pVDImageIfaces);
+            if (RT_SUCCESS(vrc))
+            {
+                /*
+                 * Get a readonly hdd for this medium (source).
+                 */
+                MediumCryptoFilterSettings      CryptoSettingsRead;
+                MediumLockList                  SourceMediumLockList;
+                PVDISK                          pSrcHdd;
+                hrc = i_openForIO(false /*fWritable*/, pKeyStore, &pSrcHdd, &SourceMediumLockList, &CryptoSettingsRead);
+                if (SUCCEEDED(hrc))
+                {
+                    /*
+                     * Create the target medium.
+                     */
+                    Utf8Str strDstFormat(aFormat->i_getId());
+
+                    /* ensure the target directory exists */
+                    uint64_t fDstCapabilities = aFormat->i_getCapabilities();
+                    if (fDstCapabilities & MediumFormatCapabilities_File)
+                    {
+                        Utf8Str strDstLocation(aFilename);
+                        hrc = VirtualBox::i_ensureFilePathExists(strDstLocation.c_str(),
+                                                                 !(aVariant & MediumVariant_NoCreateDir) /* fCreate */);
+                    }
+                    if (SUCCEEDED(hrc))
+                    {
+                        PVDISK pDstHdd;
+                        vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &pDstHdd);
+                        if (RT_SUCCESS(vrc))
+                        {
+                            /*
+                             * Create an interface for getting progress callbacks.
+                             */
+                            VDINTERFACEPROGRESS ProgressIf = VDINTERFACEPROGRESS_INITALIZER(aProgress->i_vdProgressCallback);
+                            PVDINTERFACE        pProgress = NULL;
+                            vrc = VDInterfaceAdd(&ProgressIf.Core, "export-progress", VDINTERFACETYPE_PROGRESS,
+                                                 &*aProgress, sizeof(ProgressIf), &pProgress);
+                            AssertRC(vrc);
+
+                            /*
+                             * Do the exporting.
+                             */
+                            vrc = VDCopy(pSrcHdd,
+                                         VD_LAST_IMAGE,
+                                         pDstHdd,
+                                         strDstFormat.c_str(),
+                                         aFilename,
+                                         false /* fMoveByRename */,
+                                         0 /* cbSize */,
+                                         aVariant & ~(MediumVariant_NoCreateDir | MediumVariant_Formatted | MediumVariant_VmdkESX | MediumVariant_VmdkRawDisk),
+                                         NULL /* pDstUuid */,
+                                         VD_OPEN_FLAGS_NORMAL | VD_OPEN_FLAGS_SEQUENTIAL,
+                                         pProgress,
+                                         pVDImageIfaces,
+                                         NULL);
+                            if (RT_SUCCESS(vrc))
+                                hrc = S_OK;
+                            else
+                                hrc = setErrorBoth(VBOX_E_FILE_ERROR, vrc, tr("Could not create the exported medium '%s'%s"),
+                                                   aFilename, i_vdError(vrc).c_str());
+                            VDDestroy(pDstHdd);
+                        }
+                        else
+                            hrc = setErrorVrc(vrc);
+                    }
+                }
+                VDDestroy(pSrcHdd);
+            }
+            else
+                hrc = setErrorVrc(vrc, "VDInterfaceAdd -> %Rrc", vrc);
+            VDIfDestroyFromVfsStream(pVfsIoIf);
+        }
+        else
+            hrc = setErrorVrc(vrc, "VDIfCreateFromVfsStream -> %Rrc", vrc);
+    }
+    return hrc;
+}
+
+/**
+ * Used by IAppliance to import disk images.
+ *
+ * @param aFilename             Filename to read (UTF8).
+ * @param aFormat               Medium format for reading @a aFilename.
+ * @param aVariant              Which exact image format variant to use
+ *                              for the destination image.
+ * @param aVfsIosSrc            Handle to the source I/O stream.
+ * @param aParent               Parent medium. May be NULL.
+ * @param aProgress             Progress object to use.
+ * @param aNotify               Notify about media for which metadata is changed
+ *                              during execution of the function.
+ * @return
+ * @note The destination format is defined by the Medium instance.
+ *
+ * @todo The only consumer of this method (Appliance::i_importOneDiskImage) is
+ *       already on a worker thread, so perhaps consider bypassing the thread
+ *       here and run in the task synchronously?  VBoxSVC has enough threads as
+ *       it is...
+ */
+HRESULT Medium::i_importFile(const char *aFilename,
+                             const ComObjPtr<MediumFormat> &aFormat,
+                             MediumVariant_T aVariant,
+                             RTVFSIOSTREAM aVfsIosSrc,
+                             const ComObjPtr<Medium> &aParent,
+                             const ComObjPtr<Progress> &aProgress,
+                             bool aNotify)
+{
+    /** @todo r=klaus The code below needs to be double checked with regard
+     * to lock order violations, it probably causes lock order issues related
+     * to the AutoCaller usage. */
+    AssertPtrReturn(aFilename, E_INVALIDARG);
+    AssertReturn(!aFormat.isNull(), E_INVALIDARG);
+    AssertReturn(!aProgress.isNull(), E_INVALIDARG);
+
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    HRESULT hrc = S_OK;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        // locking: we need the tree lock first because we access parent pointers
+        // and we need to write-lock the media involved
+        uint32_t    cHandles    = 2;
+        LockHandle* pHandles[3] = { &m->pVirtualBox->i_getMediaTreeLockHandle(),
+                                    this->lockHandle() };
+        /* Only add parent to the lock if it is not null */
+        if (!aParent.isNull())
+            pHandles[cHandles++] = aParent->lockHandle();
+        AutoWriteLock alock(cHandles,
+                            pHandles
+                            COMMA_LOCKVAL_SRC_POS);
+
+        if (   m->state != MediumState_NotCreated
+            && m->state != MediumState_Created)
+            throw i_setStateError();
+
+        /* Build the target lock list. */
+        MediumLockList *pTargetMediumLockList(new MediumLockList());
+        alock.release();
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                     this /* pToLockWrite */,
+                                     false /* fMediumLockWriteAll */,
+                                     aParent,
+                                     *pTargetMediumLockList);
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pTargetMediumLockList;
+            throw hrc;
+        }
+
+        alock.release();
+        hrc = pTargetMediumLockList->Lock();
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pTargetMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock target media '%s'"),
+                           i_getLocationFull().c_str());
+        }
+
+        /* setup task object to carry out the operation asynchronously */
+        pTask = new Medium::ImportTask(this, aProgress, aFilename, aFormat, aVariant,
+                                       aVfsIosSrc, aParent, pTargetMediumLockList, false, aNotify);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+
+        if (m->state == MediumState_NotCreated)
+            m->state = MediumState_Creating;
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        hrc = pTask->createThread();
+        pTask = NULL;
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    return hrc;
+}
+
+/**
+ * Internal version of the public CloneTo API which allows to enable certain
+ * optimizations to improve speed during VM cloning.
+ *
+ * @param aTarget            Target medium
+ * @param aVariant           Which exact image format variant to use
+ *                           for the destination image.
+ * @param aParent            Parent medium. May be NULL.
+ * @param aProgress          Progress object to use.
+ * @param idxSrcImageSame    The last image in the source chain which has the
+ *                           same content as the given image in the destination
+ *                           chain. Use UINT32_MAX to disable this optimization.
+ * @param idxDstImageSame    The last image in the destination chain which has the
+ *                           same content as the given image in the source chain.
+ *                           Use UINT32_MAX to disable this optimization.
+ * @param aNotify            Notify about media for which metadata is changed
+ *                           during execution of the function.
+ * @return
+ */
+HRESULT Medium::i_cloneToEx(const ComObjPtr<Medium> &aTarget, MediumVariant_T aVariant,
+                            const ComObjPtr<Medium> &aParent, IProgress **aProgress,
+                            uint32_t idxSrcImageSame, uint32_t idxDstImageSame, bool aNotify)
+{
+    /** @todo r=klaus The code below needs to be double checked with regard
+     * to lock order violations, it probably causes lock order issues related
+     * to the AutoCaller usage. */
+    CheckComArgNotNull(aTarget);
+    CheckComArgOutPointerValid(aProgress);
+    ComAssertRet(aTarget != this, E_INVALIDARG);
+
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    HRESULT hrc = S_OK;
+    ComObjPtr<Progress> pProgress;
+    Medium::Task *pTask = NULL;
+
+    try
+    {
+        // locking: we need the tree lock first because we access parent pointers
+        // and we need to write-lock the media involved
+        uint32_t    cHandles    = 3;
+        LockHandle* pHandles[4] = { &m->pVirtualBox->i_getMediaTreeLockHandle(),
+                                    this->lockHandle(),
+                                    aTarget->lockHandle() };
+        /* Only add parent to the lock if it is not null */
+        if (!aParent.isNull())
+            pHandles[cHandles++] = aParent->lockHandle();
+        AutoWriteLock alock(cHandles,
+                            pHandles
+                            COMMA_LOCKVAL_SRC_POS);
+
+        if (    aTarget->m->state != MediumState_NotCreated
+            &&  aTarget->m->state != MediumState_Created)
+            throw aTarget->i_setStateError();
+
+        /* Build the source lock list. */
+        MediumLockList *pSourceMediumLockList(new MediumLockList());
+        alock.release();
+        hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                    NULL /* pToLockWrite */,
+                                    false /* fMediumLockWriteAll */,
+                                    NULL,
+                                    *pSourceMediumLockList);
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            throw hrc;
+        }
+
+        /* Build the target lock list (including the to-be parent chain). */
+        MediumLockList *pTargetMediumLockList(new MediumLockList());
+        alock.release();
+        hrc = aTarget->i_createMediumLockList(true /* fFailIfInaccessible */,
+                                              aTarget /* pToLockWrite */,
+                                              false /* fMediumLockWriteAll */,
+                                              aParent,
+                                              *pTargetMediumLockList);
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw hrc;
+        }
+
+        alock.release();
+        hrc = pSourceMediumLockList->Lock();
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock source media '%s'"),
+                           i_getLocationFull().c_str());
+        }
+        alock.release();
+        hrc = pTargetMediumLockList->Lock();
+        alock.acquire();
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw setError(hrc,
+                           tr("Failed to lock target media '%s'"),
+                           aTarget->i_getLocationFull().c_str());
+        }
+
+        pProgress.createObject();
+        hrc = pProgress->init(m->pVirtualBox,
+                              static_cast <IMedium *>(this),
+                              BstrFmt(tr("Creating clone medium '%s'"), aTarget->m->strLocationFull.c_str()).raw(),
+                              TRUE /* aCancelable */);
+        if (FAILED(hrc))
+        {
+            delete pSourceMediumLockList;
+            delete pTargetMediumLockList;
+            throw hrc;
+        }
+
+        /* setup task object to carry out the operation asynchronously */
+        pTask = new Medium::CloneTask(this, pProgress, aTarget, aVariant,
+                                      aParent, idxSrcImageSame,
+                                      idxDstImageSame, pSourceMediumLockList,
+                                      pTargetMediumLockList, false, false, aNotify);
+        hrc = pTask->hrc();
+        AssertComRC(hrc);
+        if (FAILED(hrc))
+            throw hrc;
+
+        if (aTarget->m->state == MediumState_NotCreated)
+            aTarget->m->state = MediumState_Creating;
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        hrc = pTask->createThread();
+        pTask = NULL;
+        if (SUCCEEDED(hrc))
+            pProgress.queryInterfaceTo(aProgress);
+    }
+    else if (pTask != NULL)
+        delete pTask;
+
+    return hrc;
+}
+
+/**
+ * Returns the key identifier for this medium if encryption is configured.
+ *
+ * @returns Key identifier or empty string if no encryption is configured.
+ */
+const Utf8Str& Medium::i_getKeyId()
+{
+    ComObjPtr<Medium> pBase = i_getBase();
+
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    settings::StringsMap::const_iterator it = pBase->m->mapProperties.find("CRYPT/KeyId");
+    if (it == pBase->m->mapProperties.end())
+        return Utf8Str::Empty;
+
+    return it->second;
+}
+
+
+/**
+ * Returns all filter related properties.
+ *
+ * @returns COM status code.
+ * @param   aReturnNames    Where to store the properties names on success.
+ * @param   aReturnValues   Where to store the properties values on success.
+ */
+HRESULT Medium::i_getFilterProperties(std::vector<com::Utf8Str> &aReturnNames,
+                                      std::vector<com::Utf8Str> &aReturnValues)
+{
+    std::vector<com::Utf8Str> aPropNames;
+    std::vector<com::Utf8Str> aPropValues;
+    HRESULT hrc = getProperties(Utf8Str(""), aPropNames, aPropValues);
+
+    if (SUCCEEDED(hrc))
+    {
+        unsigned cReturnSize = 0;
+        aReturnNames.resize(0);
+        aReturnValues.resize(0);
+        for (unsigned idx = 0; idx < aPropNames.size(); idx++)
+        {
+            if (i_isPropertyForFilter(aPropNames[idx]))
+            {
+                aReturnNames.resize(cReturnSize + 1);
+                aReturnValues.resize(cReturnSize + 1);
+                aReturnNames[cReturnSize] = aPropNames[idx];
+                aReturnValues[cReturnSize] = aPropValues[idx];
+                cReturnSize++;
+            }
+        }
+    }
+
+    return hrc;
+}
+
+/**
+ * Preparation to move this medium to a new location
+ *
+ * @param aLocation Location of the storage unit. If the location is a FS-path,
+ *                  then it can be relative to the VirtualBox home directory.
+ *
+ * @note Must be called from under this object's write lock.
+ */
+HRESULT Medium::i_preparationForMoving(const Utf8Str &aLocation)
+{
+    HRESULT hrc = E_FAIL;
+
+    if (i_getLocationFull() != aLocation)
+    {
+        m->strNewLocationFull = aLocation;
+        m->fMoveThisMedium = true;
+        hrc = S_OK;
+    }
+
+    return hrc;
+}
+
+/**
+ * Checking whether current operation "moving" or not
+ */
+bool Medium::i_isMoveOperation(const ComObjPtr<Medium> &aTarget) const
+{
+    RT_NOREF(aTarget);
+    return m->fMoveThisMedium;
+}
+
+bool Medium::i_resetMoveOperationData()
+{
+    m->strNewLocationFull.setNull();
+    m->fMoveThisMedium = false;
+    return true;
+}
+
+Utf8Str Medium::i_getNewLocationForMoving() const
+{
+    if (m->fMoveThisMedium == true)
+        return m->strNewLocationFull;
+    else
+        return Utf8Str();
+}
+////////////////////////////////////////////////////////////////////////////////
+//
+// Private methods
+//
+////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Queries information from the medium.
+ *
+ * As a result of this call, the accessibility state and data members such as
+ * size and description will be updated with the current information.
+ *
+ * @note This method may block during a system I/O call that checks storage
+ *       accessibility.
+ *
+ * @note Caller MUST NOT hold the media tree or medium lock.
+ *
+ * @note Locks m->pParent for reading. Locks this object for writing.
+ *
+ * @param fSetImageId   Whether to reset the UUID contained in the image file
+ *                      to the UUID in the medium instance data (see SetIDs())
+ * @param fSetParentId  Whether to reset the parent UUID contained in the image
+ *                      file to the parent UUID in the medium instance data (see
+ *                      SetIDs())
+ * @param autoCaller
+ * @return
+ */
+HRESULT Medium::i_queryInfo(bool fSetImageId, bool fSetParentId, AutoCaller &autoCaller)
+{
+    Assert(!isWriteLockOnCurrentThread());
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    if (   (   m->state != MediumState_Created
+            && m->state != MediumState_Inaccessible
+            && m->state != MediumState_LockedRead)
+        || m->fClosing)
+        return E_FAIL;
+
+    HRESULT hrc = S_OK;
+
+    int vrc = VINF_SUCCESS;
+
+    /* check if a blocking i_queryInfo() call is in progress on some other thread,
+     * and wait for it to finish if so instead of querying data ourselves */
+    if (m->queryInfoRunning)
+    {
+        Assert(   m->state == MediumState_LockedRead
+               || m->state == MediumState_LockedWrite);
+
+        while (m->queryInfoRunning)
+        {
+            alock.release();
+            /* must not hold the object lock now */
+            Assert(!isWriteLockOnCurrentThread());
+            {
+                AutoReadLock qlock(m->queryInfoSem COMMA_LOCKVAL_SRC_POS);
+            }
+            alock.acquire();
+        }
+
+        return S_OK;
+    }
+
+    bool success = false;
+    Utf8Str lastAccessError;
+
+    /* are we dealing with a new medium constructed using the existing
+     * location? */
+    bool isImport = m->id.isZero();
+    unsigned uOpenFlags = VD_OPEN_FLAGS_INFO;
+
+    /* Note that we don't use VD_OPEN_FLAGS_READONLY when opening new
+     * media because that would prevent necessary modifications
+     * when opening media of some third-party formats for the first
+     * time in VirtualBox (such as VMDK for which VDOpen() needs to
+     * generate an UUID if it is missing) */
+    if (    m->hddOpenMode == OpenReadOnly
+         || m->type == MediumType_Readonly
+         || (!isImport && !fSetImageId && !fSetParentId)
+       )
+        uOpenFlags |= VD_OPEN_FLAGS_READONLY;
+
+    /* Open shareable medium with the appropriate flags */
+    if (m->type == MediumType_Shareable)
+        uOpenFlags |= VD_OPEN_FLAGS_SHAREABLE;
+
+    /* Lock the medium, which makes the behavior much more consistent, must be
+     * done before dropping the object lock and setting queryInfoRunning. */
+    ComPtr<IToken> pToken;
+    if (uOpenFlags & (VD_OPEN_FLAGS_READONLY | VD_OPEN_FLAGS_SHAREABLE))
+        hrc = LockRead(pToken.asOutParam());
+    else
+        hrc = LockWrite(pToken.asOutParam());
+    if (FAILED(hrc)) return hrc;
+
+    /* Copies of the input state fields which are not read-only,
+     * as we're dropping the lock. CAUTION: be extremely careful what
+     * you do with the contents of this medium object, as you will
+     * create races if there are concurrent changes. */
+    Utf8Str format(m->strFormat);
+    Utf8Str location(m->strLocationFull);
+    ComObjPtr<MediumFormat> formatObj = m->formatObj;
+
+    /* "Output" values which can't be set because the lock isn't held
+     * at the time the values are determined. */
+    Guid mediumId = m->id;
+    uint64_t mediumSize = 0;
+    uint64_t mediumLogicalSize = 0;
+
+    /* Flag whether a base image has a non-zero parent UUID and thus
+     * need repairing after it was closed again. */
+    bool fRepairImageZeroParentUuid = false;
+
+    ComObjPtr<VirtualBox> pVirtualBox = m->pVirtualBox;
+
+    /* must be set before leaving the object lock the first time */
+    m->queryInfoRunning = true;
+
+    /* must leave object lock now, because a lock from a higher lock class
+     * is needed and also a lengthy operation is coming */
+    alock.release();
+    autoCaller.release();
+
+    /* Note that taking the queryInfoSem after leaving the object lock above
+     * can lead to short spinning of the loops waiting for i_queryInfo() to
+     * complete. This is unavoidable since the other order causes a lock order
+     * violation: here it would be requesting the object lock (at the beginning
+     * of the method), then queryInfoSem, and below the other way round. */
+    AutoWriteLock qlock(m->queryInfoSem COMMA_LOCKVAL_SRC_POS);
+
+    /* take the opportunity to have a media tree lock, released initially */
+    Assert(!isWriteLockOnCurrentThread());
+    Assert(!pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+    AutoWriteLock treeLock(pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+    treeLock.release();
+
+    /* re-take the caller, but not the object lock, to keep uninit away */
+    autoCaller.add();
+    if (FAILED(autoCaller.hrc()))
+    {
+        m->queryInfoRunning = false;
+        return autoCaller.hrc();
+    }
+
+    try
+    {
+        /* skip accessibility checks for host drives */
+        if (m->hostDrive)
+        {
+            success = true;
+            throw S_OK;
+        }
+
+        PVDISK hdd;
+        vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        try
+        {
+            /** @todo This kind of opening of media is assuming that diff
+             * media can be opened as base media. Should be documented that
+             * it must work for all medium format backends. */
+            vrc = VDOpen(hdd,
+                         format.c_str(),
+                         location.c_str(),
+                         uOpenFlags | m->uOpenFlagsDef,
+                         m->vdImageIfaces);
+            if (RT_FAILURE(vrc))
+            {
+                lastAccessError = Utf8StrFmt(tr("Could not open the medium '%s'%s"),
+                                             location.c_str(), i_vdError(vrc).c_str());
+                throw S_OK;
+            }
+
+            if (formatObj->i_getCapabilities() & MediumFormatCapabilities_Uuid)
+            {
+                /* Modify the UUIDs if necessary. The associated fields are
+                 * not modified by other code, so no need to copy. */
+                if (fSetImageId)
+                {
+                    alock.acquire();
+                    vrc = VDSetUuid(hdd, 0, m->uuidImage.raw());
+                    alock.release();
+                    if (RT_FAILURE(vrc))
+                    {
+                        lastAccessError = Utf8StrFmt(tr("Could not update the UUID of medium '%s'%s"),
+                                         location.c_str(), i_vdError(vrc).c_str());
+                        throw S_OK;
+                    }
+                    mediumId = m->uuidImage;
+                }
+                if (fSetParentId)
+                {
+                    alock.acquire();
+                    vrc = VDSetParentUuid(hdd, 0, m->uuidParentImage.raw());
+                    alock.release();
+                    if (RT_FAILURE(vrc))
+                    {
+                        lastAccessError = Utf8StrFmt(tr("Could not update the parent UUID of medium '%s'%s"),
+                                         location.c_str(), i_vdError(vrc).c_str());
+                        throw S_OK;
+                    }
+                }
+                /* zap the information, these are no long-term members */
+                alock.acquire();
+                unconst(m->uuidImage).clear();
+                unconst(m->uuidParentImage).clear();
+                alock.release();
+
+                /* check the UUID */
+                RTUUID uuid;
+                vrc = VDGetUuid(hdd, 0, &uuid);
+                ComAssertRCThrow(vrc, E_FAIL);
+
+                if (isImport)
+                {
+                    mediumId = uuid;
+
+                    if (mediumId.isZero() && (m->hddOpenMode == OpenReadOnly))
+                        // only when importing a VDMK that has no UUID, create one in memory
+                        mediumId.create();
+                }
+                else
+                {
+                    Assert(!mediumId.isZero());
+
+                    if (mediumId != uuid)
+                    {
+                        /** @todo r=klaus this always refers to VirtualBox.xml as the medium registry, even for new VMs */
+                        lastAccessError = Utf8StrFmt(
+                                tr("UUID {%RTuuid} of the medium '%s' does not match the value {%RTuuid} stored in the media registry ('%s')"),
+                                &uuid,
+                                location.c_str(),
+                                mediumId.raw(),
+                                pVirtualBox->i_settingsFilePath().c_str());
+                        throw S_OK;
+                    }
+                }
+            }
+            else
+            {
+                /* the backend does not support storing UUIDs within the
+                 * underlying storage so use what we store in XML */
+
+                if (fSetImageId)
+                {
+                    /* set the UUID if an API client wants to change it */
+                    alock.acquire();
+                    mediumId = m->uuidImage;
+                    alock.release();
+                }
+                else if (isImport)
+                {
+                    /* generate an UUID for an imported UUID-less medium */
+                    mediumId.create();
+                }
+            }
+
+            /* set the image uuid before the below parent uuid handling code
+             * might place it somewhere in the media tree, so that the medium
+             * UUID is valid at this point */
+            alock.acquire();
+            if (isImport || fSetImageId)
+                unconst(m->id) = mediumId;
+            alock.release();
+
+            /* get the medium variant */
+            unsigned uImageFlags;
+            vrc = VDGetImageFlags(hdd, 0, &uImageFlags);
+            ComAssertRCThrow(vrc, E_FAIL);
+            alock.acquire();
+            m->variant = (MediumVariant_T)uImageFlags;
+            alock.release();
+
+            /* check/get the parent uuid and update corresponding state */
+            if (uImageFlags & VD_IMAGE_FLAGS_DIFF)
+            {
+                RTUUID parentId;
+                vrc = VDGetParentUuid(hdd, 0, &parentId);
+                ComAssertRCThrow(vrc, E_FAIL);
+
+                /* streamOptimized VMDK images are only accepted as base
+                 * images, as this allows automatic repair of OVF appliances.
+                 * Since such images don't support random writes they will not
+                 * be created for diff images. Only an overly smart user might
+                 * manually create this case. Too bad for him. */
+                if (   (isImport || fSetParentId)
+                    && !(uImageFlags & VD_VMDK_IMAGE_FLAGS_STREAM_OPTIMIZED))
+                {
+                    /* the parent must be known to us. Note that we freely
+                     * call locking methods of mVirtualBox and parent, as all
+                     * relevant locks must be already held. There may be no
+                     * concurrent access to the just opened medium on other
+                     * threads yet (and init() will fail if this method reports
+                     * MediumState_Inaccessible) */
+
+                    ComObjPtr<Medium> pParent;
+                    if (RTUuidIsNull(&parentId))
+                        hrc = VBOX_E_OBJECT_NOT_FOUND;
+                    else
+                        hrc = pVirtualBox->i_findHardDiskById(Guid(parentId), false /* aSetError */, &pParent);
+                    if (FAILED(hrc))
+                    {
+                        if (fSetImageId && !fSetParentId)
+                        {
+                            /* If the image UUID gets changed for an existing
+                             * image then the parent UUID can be stale. In such
+                             * cases clear the parent information. The parent
+                             * information may/will be re-set later if the
+                             * API client wants to adjust a complete medium
+                             * hierarchy one by one. */
+                            hrc = S_OK;
+                            alock.acquire();
+                            RTUuidClear(&parentId);
+                            vrc = VDSetParentUuid(hdd, 0, &parentId);
+                            alock.release();
+                            ComAssertRCThrow(vrc, E_FAIL);
+                        }
+                        else
+                        {
+                            lastAccessError = Utf8StrFmt(tr("Parent medium with UUID {%RTuuid} of the medium '%s' is not found in the media registry ('%s')"),
+                                                         &parentId, location.c_str(),
+                                                         pVirtualBox->i_settingsFilePath().c_str());
+                            throw S_OK;
+                        }
+                    }
+
+                    /* must drop the caller before taking the tree lock */
+                    autoCaller.release();
+                    /* we set m->pParent & children() */
+                    treeLock.acquire();
+                    autoCaller.add();
+                    if (FAILED(autoCaller.hrc()))
+                        throw autoCaller.hrc();
+
+                    if (m->pParent)
+                        i_deparent();
+
+                    if (!pParent.isNull())
+                        if (pParent->i_getDepth() >= SETTINGS_MEDIUM_DEPTH_MAX)
+                        {
+                            AutoReadLock plock(pParent COMMA_LOCKVAL_SRC_POS);
+                            throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                                           tr("Cannot open differencing image for medium '%s', because it exceeds the medium tree depth limit. Please merge some images which you no longer need"),
+                                           pParent->m->strLocationFull.c_str());
+                        }
+                    i_setParent(pParent);
+
+                    treeLock.release();
+                }
+                else
+                {
+                    /* must drop the caller before taking the tree lock */
+                    autoCaller.release();
+                    /* we access m->pParent */
+                    treeLock.acquire();
+                    autoCaller.add();
+                    if (FAILED(autoCaller.hrc()))
+                        throw autoCaller.hrc();
+
+                    /* check that parent UUIDs match. Note that there's no need
+                     * for the parent's AutoCaller (our lifetime is bound to
+                     * it) */
+
+                    if (m->pParent.isNull())
+                    {
+                        /* Due to a bug in VDCopy() in VirtualBox 3.0.0-3.0.14
+                         * and 3.1.0-3.1.8 there are base images out there
+                         * which have a non-zero parent UUID. No point in
+                         * complaining about them, instead automatically
+                         * repair the problem. Later we can bring back the
+                         * error message, but we should wait until really
+                         * most users have repaired their images, either with
+                         * VBoxFixHdd or this way. */
+#if 1
+                        fRepairImageZeroParentUuid = true;
+#else /* 0 */
+                        lastAccessError = Utf8StrFmt(
+                                tr("Medium type of '%s' is differencing but it is not associated with any parent medium in the media registry ('%s')"),
+                                location.c_str(),
+                                pVirtualBox->settingsFilePath().c_str());
+                        treeLock.release();
+                        throw S_OK;
+#endif /* 0 */
+                    }
+
+                    {
+                        autoCaller.release();
+                        AutoReadLock parentLock(m->pParent COMMA_LOCKVAL_SRC_POS);
+                        autoCaller.add();
+                        if (FAILED(autoCaller.hrc()))
+                            throw autoCaller.hrc();
+
+                        if (   !fRepairImageZeroParentUuid
+                            && m->pParent->i_getState() != MediumState_Inaccessible
+                            && m->pParent->i_getId() != parentId)
+                        {
+                            /** @todo r=klaus this always refers to VirtualBox.xml as the medium registry, even for new VMs */
+                            lastAccessError = Utf8StrFmt(
+                                    tr("Parent UUID {%RTuuid} of the medium '%s' does not match UUID {%RTuuid} of its parent medium stored in the media registry ('%s')"),
+                                    &parentId, location.c_str(),
+                                    m->pParent->i_getId().raw(),
+                                    pVirtualBox->i_settingsFilePath().c_str());
+                            parentLock.release();
+                            treeLock.release();
+                            throw S_OK;
+                        }
+                    }
+
+                    /// @todo NEWMEDIA what to do if the parent is not
+                    /// accessible while the diff is? Probably nothing. The
+                    /// real code will detect the mismatch anyway.
+
+                    treeLock.release();
+                }
+            }
+
+            mediumSize = VDGetFileSize(hdd, 0);
+            mediumLogicalSize = VDGetSize(hdd, 0);
+
+            success = true;
+        }
+        catch (HRESULT hrcXcpt)
+        {
+            hrc = hrcXcpt;
+        }
+
+        vrc = VDDestroy(hdd);
+        if (RT_FAILURE(vrc))
+        {
+            lastAccessError.printf(tr("Could not update and close the medium '%s'%s"),
+                                   location.c_str(), i_vdError(vrc).c_str());
+            success = false;
+            throw S_OK;
+        }
+    }
+    catch (HRESULT hrcXcpt)
+    {
+        hrc = hrcXcpt;
+    }
+
+    autoCaller.release();
+    treeLock.acquire();
+    autoCaller.add();
+    if (FAILED(autoCaller.hrc()))
+    {
+        m->queryInfoRunning = false;
+        return autoCaller.hrc();
+    }
+    alock.acquire();
+
+    if (success)
+    {
+        m->size = mediumSize;
+        m->logicalSize = mediumLogicalSize;
+        m->strLastAccessError.setNull();
+    }
+    else
+    {
+        m->strLastAccessError = lastAccessError;
+        Log1WarningFunc(("'%s' is not accessible (error='%s', hrc=%Rhrc, vrc=%Rrc)\n",
+                         location.c_str(), m->strLastAccessError.c_str(), hrc, vrc));
+    }
+
+    /* Set the proper state according to the result of the check */
+    if (success)
+        m->preLockState = MediumState_Created;
+    else
+        m->preLockState = MediumState_Inaccessible;
+
+    /* unblock anyone waiting for the i_queryInfo results */
+    qlock.release();
+    m->queryInfoRunning = false;
+
+    pToken->Abandon();
+    pToken.setNull();
+
+    if (FAILED(hrc))
+        return hrc;
+
+    /* If this is a base image which incorrectly has a parent UUID set,
+     * repair the image now by zeroing the parent UUID. This is only done
+     * when we have structural information from a config file, on import
+     * this is not possible. If someone would accidentally call openMedium
+     * with a diff image before the base is registered this would destroy
+     * the diff. Not acceptable. */
+    do
+    {
+        if (fRepairImageZeroParentUuid)
+        {
+            hrc = LockWrite(pToken.asOutParam());
+            if (FAILED(hrc))
+                break;
+
+            alock.release();
+
+            try
+            {
+                PVDISK hdd;
+                vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+                ComAssertRCThrow(vrc, E_FAIL);
+
+                try
+                {
+                    vrc = VDOpen(hdd,
+                                 format.c_str(),
+                                 location.c_str(),
+                                 (uOpenFlags & ~VD_OPEN_FLAGS_READONLY) | m->uOpenFlagsDef,
+                                 m->vdImageIfaces);
+                    if (RT_FAILURE(vrc))
+                        throw S_OK;
+
+                    RTUUID zeroParentUuid;
+                    RTUuidClear(&zeroParentUuid);
+                    vrc = VDSetParentUuid(hdd, 0, &zeroParentUuid);
+                    ComAssertRCThrow(vrc, E_FAIL);
+                }
+                catch (HRESULT hrcXcpt)
+                {
+                    hrc = hrcXcpt;
+                }
+
+                VDDestroy(hdd);
+            }
+            catch (HRESULT hrcXcpt)
+            {
+                hrc = hrcXcpt;
+            }
+
+            pToken->Abandon();
+            pToken.setNull();
+            if (FAILED(hrc))
+                break;
+        }
+    } while(0);
+
+    return hrc;
+}
+
+/**
+ * Performs extra checks if the medium can be closed and returns S_OK in
+ * this case. Otherwise, returns a respective error message. Called by
+ * Close() under the medium tree lock and the medium lock.
+ *
+ * @note Also reused by Medium::Reset().
+ *
+ * @note Caller must hold the media tree write lock!
+ */
+HRESULT Medium::i_canClose()
+{
+    Assert(m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+
+    if (i_getChildren().size() != 0)
+        return setError(VBOX_E_OBJECT_IN_USE,
+                        tr("Cannot close medium '%s' because it has %d child media", "", i_getChildren().size()),
+                        m->strLocationFull.c_str(), i_getChildren().size());
+
+    return S_OK;
+}
+
+/**
+ * Unregisters this medium with mVirtualBox. Called by close() under the medium tree lock.
+ *
+ * @note Caller must have locked the media tree lock for writing!
+ */
+HRESULT Medium::i_unregisterWithVirtualBox()
+{
+    /* Note that we need to de-associate ourselves from the parent to let
+     * VirtualBox::i_unregisterMedium() properly save the registry */
+
+    /* we modify m->pParent and access children */
+    Assert(m->pVirtualBox->i_getMediaTreeLockHandle().isWriteLockOnCurrentThread());
+
+    Medium *pParentBackup = m->pParent;
+    AssertReturn(i_getChildren().size() == 0, E_FAIL);
+    if (m->pParent)
+        i_deparent();
+
+    HRESULT hrc = m->pVirtualBox->i_unregisterMedium(this);
+    if (FAILED(hrc))
+    {
+        if (pParentBackup)
+        {
+            // re-associate with the parent as we are still relatives in the registry
+            i_setParent(pParentBackup);
+        }
+    }
+
+    return hrc;
+}
+
+/**
+ * Like SetProperty but do not trigger a settings store. Only for internal use!
+ */
+HRESULT Medium::i_setPropertyDirect(const Utf8Str &aName, const Utf8Str &aValue)
+{
+    AutoCaller autoCaller(this);
+    if (FAILED(autoCaller.hrc())) return autoCaller.hrc();
+
+    AutoWriteLock mlock(this COMMA_LOCKVAL_SRC_POS);
+
+    switch (m->state)
+    {
+        case MediumState_Created:
+        case MediumState_Inaccessible:
+            break;
+        default:
+            return i_setStateError();
+    }
+
+    m->mapProperties[aName] = aValue;
+
+    return S_OK;
+}
+
+/**
+ * Sets the extended error info according to the current media state.
+ *
+ * @note Must be called from under this object's write or read lock.
+ */
+HRESULT Medium::i_setStateError()
+{
+    HRESULT hrc;
+
+    switch (m->state)
+    {
+        case MediumState_NotCreated:
+            hrc = setError(VBOX_E_INVALID_OBJECT_STATE,
+                           tr("Storage for the medium '%s' is not created"),
+                           m->strLocationFull.c_str());
+            break;
+        case MediumState_Created:
+            hrc = setError(VBOX_E_INVALID_OBJECT_STATE,
+                           tr("Storage for the medium '%s' is already created"),
+                           m->strLocationFull.c_str());
+            break;
+        case MediumState_LockedRead:
+            hrc = setError(VBOX_E_INVALID_OBJECT_STATE,
+                           tr("Medium '%s' is locked for reading by another task"),
+                           m->strLocationFull.c_str());
+            break;
+        case MediumState_LockedWrite:
+            hrc = setError(VBOX_E_INVALID_OBJECT_STATE,
+                           tr("Medium '%s' is locked for writing by another task"),
+                           m->strLocationFull.c_str());
+            break;
+        case MediumState_Inaccessible:
+            /* be in sync with Console::powerUpThread() */
+            if (!m->strLastAccessError.isEmpty())
+                hrc = setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Medium '%s' is not accessible. %s"),
+                               m->strLocationFull.c_str(), m->strLastAccessError.c_str());
+            else
+                hrc = setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Medium '%s' is not accessible"),
+                               m->strLocationFull.c_str());
+            break;
+        case MediumState_Creating:
+            hrc = setError(VBOX_E_INVALID_OBJECT_STATE,
+                           tr("Storage for the medium '%s' is being created"),
+                           m->strLocationFull.c_str());
+            break;
+        case MediumState_Deleting:
+            hrc = setError(VBOX_E_INVALID_OBJECT_STATE,
+                           tr("Storage for the medium '%s' is being deleted"),
+                           m->strLocationFull.c_str());
+            break;
+        default:
+            AssertFailed();
+            hrc = E_FAIL;
+            break;
+    }
+
+    return hrc;
+}
+
+/**
+ * Sets the value of m->strLocationFull. The given location must be a fully
+ * qualified path; relative paths are not supported here.
+ *
+ * As a special exception, if the specified location is a file path that ends with '/'
+ * then the file name part will be generated by this method automatically in the format
+ * '{\<uuid\>}.\<ext\>' where \<uuid\> is a fresh UUID that this method will generate
+ * and assign to this medium, and \<ext\> is the default extension for this
+ * medium's storage format. Note that this procedure requires the media state to
+ * be NotCreated and will return a failure otherwise.
+ *
+ * @param aLocation Location of the storage unit. If the location is a FS-path,
+ *                  then it can be relative to the VirtualBox home directory.
+ * @param aFormat   Optional fallback format if it is an import and the format
+ *                  cannot be determined.
+ *
+ * @note Must be called from under this object's write lock.
+ */
+HRESULT Medium::i_setLocation(const Utf8Str &aLocation,
+                              const Utf8Str &aFormat /* = Utf8Str::Empty */)
+{
+    AssertReturn(!aLocation.isEmpty(), E_FAIL);
+
+    AutoCaller autoCaller(this);
+    AssertComRCReturnRC(autoCaller.hrc());
+
+    /* formatObj may be null only when initializing from an existing path and
+     * no format is known yet */
+    AssertReturn(    (!m->strFormat.isEmpty() && !m->formatObj.isNull())
+                  || (    getObjectState().getState() == ObjectState::InInit
+                       && m->state != MediumState_NotCreated
+                       && m->id.isZero()
+                       && m->strFormat.isEmpty()
+                       && m->formatObj.isNull()),
+                 E_FAIL);
+
+    /* are we dealing with a new medium constructed using the existing
+     * location? */
+    bool isImport = m->strFormat.isEmpty();
+
+    if (   isImport
+        || (   (m->formatObj->i_getCapabilities() & MediumFormatCapabilities_File)
+            && !m->hostDrive))
+    {
+        Guid id;
+
+        Utf8Str locationFull(aLocation);
+
+        if (m->state == MediumState_NotCreated)
+        {
+            /* must be a file (formatObj must be already known) */
+            Assert(m->formatObj->i_getCapabilities() & MediumFormatCapabilities_File);
+
+            if (RTPathFilename(aLocation.c_str()) == NULL)
+            {
+                /* no file name is given (either an empty string or ends with a
+                 * slash), generate a new UUID + file name if the state allows
+                 * this */
+
+                ComAssertMsgRet(!m->formatObj->i_getFileExtensions().empty(),
+                                (tr("Must be at least one extension if it is MediumFormatCapabilities_File\n")),
+                                E_FAIL);
+
+                Utf8Str strExt = m->formatObj->i_getFileExtensions().front();
+                ComAssertMsgRet(!strExt.isEmpty(),
+                                (tr("Default extension must not be empty\n")),
+                                E_FAIL);
+
+                id.create();
+
+                locationFull = Utf8StrFmt("%s{%RTuuid}.%s",
+                                          aLocation.c_str(), id.raw(), strExt.c_str());
+            }
+        }
+
+        // we must always have full paths now (if it refers to a file)
+        if (   (   m->formatObj.isNull()
+                || m->formatObj->i_getCapabilities() & MediumFormatCapabilities_File)
+            && !RTPathStartsWithRoot(locationFull.c_str()))
+            return setError(VBOX_E_FILE_ERROR,
+                            tr("The given path '%s' is not fully qualified"),
+                            locationFull.c_str());
+
+        /* detect the backend from the storage unit if importing */
+        if (isImport)
+        {
+            VDTYPE const enmDesiredType = i_convertDeviceType();
+            VDTYPE enmType = VDTYPE_INVALID;
+            char *backendName = NULL;
+
+            /* is it a file? */
+            RTFILE hFile;
+            int vrc = RTFileOpen(&hFile, locationFull.c_str(), RTFILE_O_READ | RTFILE_O_OPEN | RTFILE_O_DENY_NONE);
+            if (RT_SUCCESS(vrc))
+            {
+                RTFileClose(hFile);
+                vrc = VDGetFormat(NULL /* pVDIfsDisk */, NULL /* pVDIfsImage */,
+                                  locationFull.c_str(), enmDesiredType, &backendName, &enmType);
+            }
+            else if (   vrc != VERR_FILE_NOT_FOUND
+                     && vrc != VERR_PATH_NOT_FOUND
+                     && vrc != VERR_ACCESS_DENIED
+                     && locationFull != aLocation)
+            {
+                /* assume it's not a file, restore the original location */
+                locationFull = aLocation;
+                vrc = VDGetFormat(NULL /* pVDIfsDisk */, NULL /* pVDIfsImage */,
+                                  locationFull.c_str(), enmDesiredType, &backendName, &enmType);
+            }
+
+            if (RT_FAILURE(vrc))
+            {
+                if (vrc == VERR_ACCESS_DENIED)
+                    return setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                        tr("Permission problem accessing the file for the medium '%s' (%Rrc)"),
+                                        locationFull.c_str(), vrc);
+                if (vrc == VERR_FILE_NOT_FOUND || vrc == VERR_PATH_NOT_FOUND)
+                    return setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                        tr("Could not find file for the medium '%s' (%Rrc)"),
+                                        locationFull.c_str(), vrc);
+                if (aFormat.isEmpty())
+                    return setErrorBoth(VBOX_E_IPRT_ERROR, vrc,
+                                        tr("Could not get the storage format of the medium '%s' (%Rrc)"),
+                                        locationFull.c_str(), vrc);
+                HRESULT hrc = i_setFormat(aFormat);
+                /* setFormat() must not fail since we've just used the backend so
+                         * the format object must be there */
+                AssertComRCReturnRC(hrc);
+            }
+            else if (   enmType == VDTYPE_INVALID
+                     || m->devType != i_convertToDeviceType(enmType))
+            {
+                /*
+                 * The user tried to use a image as a device which is not supported
+                 * by the backend.
+                 */
+                RTStrFree(backendName);
+                return setError(E_FAIL,
+                                tr("The medium '%s' can't be used as the requested device type (%s, detected %s)"),
+                                locationFull.c_str(), getDeviceTypeName(m->devType), getVDTypeName(enmType));
+            }
+            else
+            {
+                ComAssertRet(backendName != NULL && *backendName != '\0', E_FAIL);
+
+                HRESULT hrc = i_setFormat(backendName);
+                RTStrFree(backendName);
+
+                /* setFormat() must not fail since we've just used the backend so
+                 * the format object must be there */
+                AssertComRCReturnRC(hrc);
+            }
+        }
+
+        m->strLocationFull = locationFull;
+
+        /* is it still a file? */
+        if (    (m->formatObj->i_getCapabilities() & MediumFormatCapabilities_File)
+             && (m->state == MediumState_NotCreated)
+           )
+            /* assign a new UUID (this UUID will be used when calling
+             * VDCreateBase/VDCreateDiff as a wanted UUID). Note that we
+             * also do that if we didn't generate it to make sure it is
+             * either generated by us or reset to null */
+            unconst(m->id) = id;
+    }
+    else
+        m->strLocationFull = aLocation;
+
+    return S_OK;
+}
+
+/**
+ * Checks that the format ID is valid and sets it on success.
+ *
+ * Note that this method will caller-reference the format object on success!
+ * This reference must be released somewhere to let the MediumFormat object be
+ * uninitialized.
+ *
+ * @note Must be called from under this object's write lock.
+ */
+HRESULT Medium::i_setFormat(const Utf8Str &aFormat)
+{
+    /* get the format object first */
+    {
+        SystemProperties *pSysProps = m->pVirtualBox->i_getSystemProperties();
+        AutoReadLock propsLock(pSysProps COMMA_LOCKVAL_SRC_POS);
+
+        unconst(m->formatObj) = pSysProps->i_mediumFormat(aFormat);
+        if (m->formatObj.isNull())
+            return setError(E_INVALIDARG,
+                            tr("Invalid medium storage format '%s'"),
+                            aFormat.c_str());
+
+        /* get properties (preinsert them as keys in the map). Note that the
+         * map doesn't grow over the object life time since the set of
+         * properties is meant to be constant. */
+
+        Assert(m->mapProperties.empty());
+
+        for (MediumFormat::PropertyArray::const_iterator it = m->formatObj->i_getProperties().begin();
+             it != m->formatObj->i_getProperties().end();
+             ++it)
+        {
+            m->mapProperties.insert(std::make_pair(it->strName, Utf8Str::Empty));
+        }
+    }
+
+    unconst(m->strFormat) = aFormat;
+
+    return S_OK;
+}
+
+/**
+ * Converts the Medium device type to the VD type.
+ */
+VDTYPE Medium::i_convertDeviceType()
+{
+    VDTYPE enmType;
+
+    switch (m->devType)
+    {
+        case DeviceType_HardDisk:
+            enmType = VDTYPE_HDD;
+            break;
+        case DeviceType_DVD:
+            enmType = VDTYPE_OPTICAL_DISC;
+            break;
+        case DeviceType_Floppy:
+            enmType = VDTYPE_FLOPPY;
+            break;
+        default:
+            ComAssertFailedRet(VDTYPE_INVALID);
+    }
+
+    return enmType;
+}
+
+/**
+ * Converts from the VD type to the medium type.
+ */
+DeviceType_T Medium::i_convertToDeviceType(VDTYPE enmType)
+{
+    DeviceType_T devType;
+
+    switch (enmType)
+    {
+        case VDTYPE_HDD:
+            devType = DeviceType_HardDisk;
+            break;
+        case VDTYPE_OPTICAL_DISC:
+            devType = DeviceType_DVD;
+            break;
+        case VDTYPE_FLOPPY:
+            devType = DeviceType_Floppy;
+            break;
+        default:
+            ComAssertFailedRet(DeviceType_Null);
+    }
+
+    return devType;
+}
+
+/**
+ * Internal method which checks whether a property name is for a filter plugin.
+ */
+bool Medium::i_isPropertyForFilter(const com::Utf8Str &aName)
+{
+    /* If the name contains "/" use the part before as a filter name and lookup the filter. */
+    size_t offSlash;
+    if ((offSlash = aName.find("/", 0)) != aName.npos)
+    {
+        com::Utf8Str strFilter;
+        com::Utf8Str strKey;
+
+        HRESULT hrc = strFilter.assignEx(aName, 0, offSlash);
+        if (FAILED(hrc))
+            return false;
+
+        hrc = strKey.assignEx(aName, offSlash + 1, aName.length() - offSlash - 1); /* Skip slash */
+        if (FAILED(hrc))
+            return false;
+
+        VDFILTERINFO FilterInfo;
+        int vrc = VDFilterInfoOne(strFilter.c_str(), &FilterInfo);
+        if (RT_SUCCESS(vrc))
+        {
+            /* Check that the property exists. */
+            PCVDCONFIGINFO paConfig = FilterInfo.paConfigInfo;
+            while (paConfig->pszKey)
+            {
+                if (strKey.equals(paConfig->pszKey))
+                    return true;
+                paConfig++;
+            }
+        }
+    }
+
+    return false;
+}
+
+/**
+ * Returns the last error message collected by the i_vdErrorCall callback and
+ * resets it.
+ *
+ * The error message is returned prepended with a dot and a space, like this:
+ * <code>
+ *   ". <error_text> (%Rrc)"
+ * </code>
+ * to make it easily appendable to a more general error message. The @c %Rrc
+ * format string is given @a aVRC as an argument.
+ *
+ * If there is no last error message collected by i_vdErrorCall or if it is a
+ * null or empty string, then this function returns the following text:
+ * <code>
+ *   " (%Rrc)"
+ * </code>
+ *
+ * @note Doesn't do any object locking; it is assumed that the caller makes sure
+ *       the callback isn't called by more than one thread at a time.
+ *
+ * @param aVRC  VBox error code to use when no error message is provided.
+ */
+Utf8Str Medium::i_vdError(int aVRC)
+{
+    Utf8Str error;
+
+    if (m->vdError.isEmpty())
+        error.printf(" (%Rrc)", aVRC);
+    else
+        error.printf(".\n%s", m->vdError.c_str());
+
+    m->vdError.setNull();
+
+    return error;
+}
+
+/**
+ * Error message callback.
+ *
+ * Puts the reported error message to the m->vdError field.
+ *
+ * @note Doesn't do any object locking; it is assumed that the caller makes sure
+ *       the callback isn't called by more than one thread at a time.
+ *
+ * @param   pvUser          The opaque data passed on container creation.
+ * @param   vrc             The VBox error code.
+ * @param   SRC_POS         Use RT_SRC_POS.
+ * @param   pszFormat       Error message format string.
+ * @param   va              Error message arguments.
+ */
+/*static*/
+DECLCALLBACK(void) Medium::i_vdErrorCall(void *pvUser, int vrc, RT_SRC_POS_DECL,
+                                         const char *pszFormat, va_list va)
+{
+    NOREF(pszFile); NOREF(iLine); NOREF(pszFunction); /* RT_SRC_POS_DECL */
+
+    Medium *that = static_cast<Medium*>(pvUser);
+    AssertReturnVoid(that != NULL);
+
+    va_list vaCopy; /* For gcc */
+    va_copy(vaCopy, va);
+    if (that->m->vdError.isEmpty())
+        that->m->vdError.printf("%N (%Rrc)", pszFormat, &vaCopy, vrc);
+    else
+        that->m->vdError.appendPrintf(".\n%N (%Rrc)", pszFormat, &vaCopy, vrc);
+    va_end(vaCopy);
+}
+
+/* static */
+DECLCALLBACK(bool) Medium::i_vdConfigAreKeysValid(void *pvUser,
+                                                  const char * /* pszzValid */)
+{
+    Medium *that = static_cast<Medium*>(pvUser);
+    AssertReturn(that != NULL, false);
+
+    /* we always return true since the only keys we have are those found in
+     * VDBACKENDINFO */
+    return true;
+}
+
+/* static */
+DECLCALLBACK(int) Medium::i_vdConfigQuerySize(void *pvUser,
+                                              const char *pszName,
+                                              size_t *pcbValue)
+{
+    AssertPtrReturn(pcbValue, VERR_INVALID_POINTER);
+
+    Medium *that = static_cast<Medium*>(pvUser);
+    AssertReturn(that != NULL, VERR_GENERAL_FAILURE);
+
+    settings::StringsMap::const_iterator it = that->m->mapProperties.find(Utf8Str(pszName));
+    if (it == that->m->mapProperties.end())
+        return VERR_CFGM_VALUE_NOT_FOUND;
+
+    /* we interpret null values as "no value" in Medium */
+    if (it->second.isEmpty())
+        return VERR_CFGM_VALUE_NOT_FOUND;
+
+    *pcbValue = it->second.length() + 1 /* include terminator */;
+
+    return VINF_SUCCESS;
+}
+
+/* static */
+DECLCALLBACK(int) Medium::i_vdConfigQuery(void *pvUser,
+                                          const char *pszName,
+                                          char *pszValue,
+                                          size_t cchValue)
+{
+    AssertPtrReturn(pszValue, VERR_INVALID_POINTER);
+
+    Medium *that = static_cast<Medium*>(pvUser);
+    AssertReturn(that != NULL, VERR_GENERAL_FAILURE);
+
+    settings::StringsMap::const_iterator it = that->m->mapProperties.find(Utf8Str(pszName));
+    if (it == that->m->mapProperties.end())
+        return VERR_CFGM_VALUE_NOT_FOUND;
+
+    /* we interpret null values as "no value" in Medium */
+    if (it->second.isEmpty())
+        return VERR_CFGM_VALUE_NOT_FOUND;
+
+    const Utf8Str &value = it->second;
+    if (value.length() >= cchValue)
+        return VERR_CFGM_NOT_ENOUGH_SPACE;
+
+    memcpy(pszValue, value.c_str(), value.length() + 1);
+
+    return VINF_SUCCESS;
+}
+
+DECLCALLBACK(bool) Medium::i_vdCryptoConfigAreKeysValid(void *pvUser, const char *pszzValid)
+{
+    /* Just return always true here. */
+    NOREF(pvUser);
+    NOREF(pszzValid);
+    return true;
+}
+
+DECLCALLBACK(int) Medium::i_vdCryptoConfigQuerySize(void *pvUser, const char *pszName, size_t *pcbValue)
+{
+    MediumCryptoFilterSettings *pSettings = (MediumCryptoFilterSettings *)pvUser;
+    AssertPtrReturn(pSettings, VERR_GENERAL_FAILURE);
+    AssertPtrReturn(pcbValue, VERR_INVALID_POINTER);
+
+    size_t cbValue = 0;
+    if (!strcmp(pszName, "Algorithm"))
+        cbValue = strlen(pSettings->pszCipher) + 1;
+    else if (!strcmp(pszName, "KeyId"))
+        cbValue = sizeof("irrelevant");
+    else if (!strcmp(pszName, "KeyStore"))
+    {
+        if (!pSettings->pszKeyStoreLoad)
+            return VERR_CFGM_VALUE_NOT_FOUND;
+        cbValue = strlen(pSettings->pszKeyStoreLoad) + 1;
+    }
+    else if (!strcmp(pszName, "CreateKeyStore"))
+        cbValue = 2; /* Single digit + terminator. */
+    else
+        return VERR_CFGM_VALUE_NOT_FOUND;
+
+    *pcbValue = cbValue + 1 /* include terminator */;
+
+    return VINF_SUCCESS;
+}
+
+DECLCALLBACK(int) Medium::i_vdCryptoConfigQuery(void *pvUser, const char *pszName,
+                                                char *pszValue, size_t cchValue)
+{
+    MediumCryptoFilterSettings *pSettings = (MediumCryptoFilterSettings *)pvUser;
+    AssertPtrReturn(pSettings, VERR_GENERAL_FAILURE);
+    AssertPtrReturn(pszValue, VERR_INVALID_POINTER);
+
+    const char *psz = NULL;
+    if (!strcmp(pszName, "Algorithm"))
+        psz = pSettings->pszCipher;
+    else if (!strcmp(pszName, "KeyId"))
+        psz = "irrelevant";
+    else if (!strcmp(pszName, "KeyStore"))
+        psz = pSettings->pszKeyStoreLoad;
+    else if (!strcmp(pszName, "CreateKeyStore"))
+    {
+        if (pSettings->fCreateKeyStore)
+            psz = "1";
+        else
+            psz = "0";
+    }
+    else
+        return VERR_CFGM_VALUE_NOT_FOUND;
+
+    size_t cch = strlen(psz);
+    if (cch >= cchValue)
+        return VERR_CFGM_NOT_ENOUGH_SPACE;
+
+    memcpy(pszValue, psz, cch + 1);
+    return VINF_SUCCESS;
+}
+
+DECLCALLBACK(int) Medium::i_vdConfigUpdate(void *pvUser,
+                                           bool fCreate,
+                                           const char *pszName,
+                                           const char *pszValue)
+{
+    Medium *that = (Medium *)pvUser;
+
+    // Detect if this runs inside i_queryInfo() on the current thread.
+    // Skip if not. Check does not need synchronization.
+    if (!that->m || !that->m->queryInfoRunning || !that->m->queryInfoSem.isWriteLockOnCurrentThread())
+        return VINF_SUCCESS;
+
+    // It's guaranteed that this code is executing inside Medium::i_queryInfo,
+    // can assume it took care of synchronization.
+    int rv = VINF_SUCCESS;
+    Utf8Str strName(pszName);
+    settings::StringsMap::const_iterator it = that->m->mapProperties.find(strName);
+    if (it == that->m->mapProperties.end() && !fCreate)
+        rv = VERR_CFGM_VALUE_NOT_FOUND;
+    else
+        that->m->mapProperties[strName] = Utf8Str(pszValue);
+    return rv;
+}
+
+DECLCALLBACK(int) Medium::i_vdCryptoKeyRetain(void *pvUser, const char *pszId,
+                                              const uint8_t **ppbKey, size_t *pcbKey)
+{
+    MediumCryptoFilterSettings *pSettings = (MediumCryptoFilterSettings *)pvUser;
+    NOREF(pszId);
+    NOREF(ppbKey);
+    NOREF(pcbKey);
+    AssertPtrReturn(pSettings, VERR_GENERAL_FAILURE);
+    AssertMsgFailedReturn(("This method should not be called here!\n"), VERR_INVALID_STATE);
+}
+
+DECLCALLBACK(int) Medium::i_vdCryptoKeyRelease(void *pvUser, const char *pszId)
+{
+    MediumCryptoFilterSettings *pSettings = (MediumCryptoFilterSettings *)pvUser;
+    NOREF(pszId);
+    AssertPtrReturn(pSettings, VERR_GENERAL_FAILURE);
+    AssertMsgFailedReturn(("This method should not be called here!\n"), VERR_INVALID_STATE);
+}
+
+DECLCALLBACK(int) Medium::i_vdCryptoKeyStorePasswordRetain(void *pvUser, const char *pszId, const char **ppszPassword)
+{
+    MediumCryptoFilterSettings *pSettings = (MediumCryptoFilterSettings *)pvUser;
+    AssertPtrReturn(pSettings, VERR_GENERAL_FAILURE);
+
+    NOREF(pszId);
+    *ppszPassword = pSettings->pszPassword;
+    return VINF_SUCCESS;
+}
+
+DECLCALLBACK(int) Medium::i_vdCryptoKeyStorePasswordRelease(void *pvUser, const char *pszId)
+{
+    MediumCryptoFilterSettings *pSettings = (MediumCryptoFilterSettings *)pvUser;
+    AssertPtrReturn(pSettings, VERR_GENERAL_FAILURE);
+    NOREF(pszId);
+    return VINF_SUCCESS;
+}
+
+DECLCALLBACK(int) Medium::i_vdCryptoKeyStoreSave(void *pvUser, const void *pvKeyStore, size_t cbKeyStore)
+{
+    MediumCryptoFilterSettings *pSettings = (MediumCryptoFilterSettings *)pvUser;
+    AssertPtrReturn(pSettings, VERR_GENERAL_FAILURE);
+
+    pSettings->pszKeyStore = (char *)RTMemAllocZ(cbKeyStore);
+    if (!pSettings->pszKeyStore)
+        return VERR_NO_MEMORY;
+
+    memcpy(pSettings->pszKeyStore, pvKeyStore, cbKeyStore);
+    return VINF_SUCCESS;
+}
+
+DECLCALLBACK(int) Medium::i_vdCryptoKeyStoreReturnParameters(void *pvUser, const char *pszCipher,
+                                                             const uint8_t *pbDek, size_t cbDek)
+{
+    MediumCryptoFilterSettings *pSettings = (MediumCryptoFilterSettings *)pvUser;
+    AssertPtrReturn(pSettings, VERR_GENERAL_FAILURE);
+
+    pSettings->pszCipherReturned = RTStrDup(pszCipher);
+    pSettings->pbDek             = pbDek;
+    pSettings->cbDek             = cbDek;
+
+    return pSettings->pszCipherReturned ? VINF_SUCCESS : VERR_NO_MEMORY;
+}
+
+/**
+ * Creates a VDISK instance for this medium.
+ *
+ * @note    Caller should not hold any medium related locks as this method will
+ *          acquire the medium lock for writing and others (VirtualBox).
+ *
+ * @returns COM status code.
+ * @param   fWritable               Whether to return a writable VDISK instance
+ *                                  (true) or a read-only one (false).
+ * @param   pKeyStore               The key store.
+ * @param   ppHdd                   Where to return the pointer to the VDISK on
+ *                                  success.
+ * @param   pMediumLockList         The lock list to populate and lock.  Caller
+ *                                  is responsible for calling the destructor or
+ *                                  MediumLockList::Clear() after destroying
+ *                                  @a *ppHdd
+ * @param   pCryptoSettings         The crypto settings to use for setting up
+ *                                  decryption/encryption of the VDISK.  This object
+ *                                  must be alive until the VDISK is destroyed!
+ */
+HRESULT Medium::i_openForIO(bool fWritable, SecretKeyStore *pKeyStore, PVDISK *ppHdd, MediumLockList *pMediumLockList,
+                            MediumCryptoFilterSettings *pCryptoSettings)
+{
+    /*
+     * Create the media lock list and lock the media.
+     */
+    HRESULT hrc = i_createMediumLockList(true /* fFailIfInaccessible */,
+                                         fWritable ? this : NULL /* pToLockWrite */,
+                                         false /* fMediumLockWriteAll */,
+                                         NULL,
+                                         *pMediumLockList);
+    if (SUCCEEDED(hrc))
+        hrc = pMediumLockList->Lock();
+    if (FAILED(hrc))
+        return hrc;
+
+    /*
+     * Get the base medium before write locking this medium.
+     */
+    ComObjPtr<Medium> pBase = i_getBase();
+    AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+    /*
+     * Create the VDISK instance.
+     */
+    PVDISK pHdd;
+    int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &pHdd);
+    AssertRCReturn(vrc, E_FAIL);
+
+    /*
+     * Goto avoidance using try/catch/throw(HRESULT).
+     */
+    try
+    {
+        settings::StringsMap::iterator itKeyStore = pBase->m->mapProperties.find("CRYPT/KeyStore");
+        if (itKeyStore != pBase->m->mapProperties.end())
+        {
+#ifdef VBOX_WITH_EXTPACK
+            settings::StringsMap::iterator itKeyId = pBase->m->mapProperties.find("CRYPT/KeyId");
+
+            ExtPackManager *pExtPackManager = m->pVirtualBox->i_getExtPackManager();
+            if (pExtPackManager->i_isExtPackUsable(ORACLE_PUEL_EXTPACK_NAME))
+            {
+                /* Load the plugin */
+                Utf8Str strPlugin;
+                hrc = pExtPackManager->i_getLibraryPathForExtPack(g_szVDPlugin, ORACLE_PUEL_EXTPACK_NAME, &strPlugin);
+                if (SUCCEEDED(hrc))
+                {
+                    vrc = VDPluginLoadFromFilename(strPlugin.c_str());
+                    if (RT_FAILURE(vrc))
+                        throw setErrorBoth(VBOX_E_NOT_SUPPORTED, vrc,
+                                           tr("Retrieving encryption settings of the image failed because the encryption plugin could not be loaded (%s)"),
+                                           i_vdError(vrc).c_str());
+                }
+                else
+                    throw setError(VBOX_E_NOT_SUPPORTED,
+                                   tr("Encryption is not supported because the extension pack '%s' is missing the encryption plugin (old extension pack installed?)"),
+                                   ORACLE_PUEL_EXTPACK_NAME);
+            }
+            else
+                throw setError(VBOX_E_NOT_SUPPORTED,
+                               tr("Encryption is not supported because the extension pack '%s' is missing"),
+                               ORACLE_PUEL_EXTPACK_NAME);
+
+            if (itKeyId == pBase->m->mapProperties.end())
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Image '%s' is configured for encryption but doesn't has a key identifier set"),
+                               pBase->m->strLocationFull.c_str());
+
+            /* Find the proper secret key in the key store. */
+            if (!pKeyStore)
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Image '%s' is configured for encryption but there is no key store to retrieve the password from"),
+                               pBase->m->strLocationFull.c_str());
+
+            SecretKey *pKey = NULL;
+            vrc = pKeyStore->retainSecretKey(itKeyId->second, &pKey);
+            if (RT_FAILURE(vrc))
+                throw setErrorBoth(VBOX_E_INVALID_OBJECT_STATE, vrc,
+                                   tr("Failed to retrieve the secret key with ID \"%s\" from the store (%Rrc)"),
+                                   itKeyId->second.c_str(), vrc);
+
+            i_taskEncryptSettingsSetup(pCryptoSettings, NULL, itKeyStore->second.c_str(), (const char *)pKey->getKeyBuffer(),
+                                       false /* fCreateKeyStore */);
+            vrc = VDFilterAdd(pHdd, "CRYPT", VD_FILTER_FLAGS_DEFAULT, pCryptoSettings->vdFilterIfaces);
+            pKeyStore->releaseSecretKey(itKeyId->second);
+            if (vrc == VERR_VD_PASSWORD_INCORRECT)
+                throw setErrorBoth(VBOX_E_PASSWORD_INCORRECT, vrc, tr("The password to decrypt the image is incorrect"));
+            if (RT_FAILURE(vrc))
+                throw setErrorBoth(VBOX_E_INVALID_OBJECT_STATE, vrc, tr("Failed to load the decryption filter: %s"),
+                                   i_vdError(vrc).c_str());
+#else
+            RT_NOREF(pKeyStore, pCryptoSettings);
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Encryption is not supported because extension pack support is not built in"));
+#endif /* VBOX_WITH_EXTPACK */
+        }
+
+        /*
+         * Open all media in the source chain.
+         */
+        MediumLockList::Base::const_iterator sourceListBegin = pMediumLockList->GetBegin();
+        MediumLockList::Base::const_iterator sourceListEnd   = pMediumLockList->GetEnd();
+        MediumLockList::Base::const_iterator mediumListLast  = sourceListEnd;
+        --mediumListLast;
+
+        for (MediumLockList::Base::const_iterator it = sourceListBegin; it != sourceListEnd; ++it)
+        {
+            const MediumLock &mediumLock = *it;
+            const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+            AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+            /* sanity check */
+            Assert(pMedium->m->state == (fWritable && it == mediumListLast ? MediumState_LockedWrite : MediumState_LockedRead));
+
+            /* Open all media in read-only mode. */
+            vrc = VDOpen(pHdd,
+                         pMedium->m->strFormat.c_str(),
+                         pMedium->m->strLocationFull.c_str(),
+                         m->uOpenFlagsDef | (fWritable && it == mediumListLast ? VD_OPEN_FLAGS_NORMAL : VD_OPEN_FLAGS_READONLY),
+                         pMedium->m->vdImageIfaces);
+            if (RT_FAILURE(vrc))
+                throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                   tr("Could not open the medium storage unit '%s'%s"),
+                                   pMedium->m->strLocationFull.c_str(),
+                                   i_vdError(vrc).c_str());
+        }
+
+        Assert(m->state == (fWritable ? MediumState_LockedWrite : MediumState_LockedRead));
+
+        /*
+         * Done!
+         */
+        *ppHdd = pHdd;
+        return S_OK;
+    }
+    catch (HRESULT hrc2)
+    {
+        hrc = hrc2;
+    }
+
+    VDDestroy(pHdd);
+    return hrc;
+
+}
+
+/**
+ * Implementation code for the "create base" task.
+ *
+ * This only gets started from Medium::CreateBaseStorage() and always runs
+ * asynchronously. As a result, we always save the VirtualBox.xml file when
+ * we're done here.
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskCreateBaseHandler(Medium::CreateBaseTask &task)
+{
+    /** @todo r=klaus The code below needs to be double checked with regard
+     * to lock order violations, it probably causes lock order issues related
+     * to the AutoCaller usage. */
+    HRESULT hrc = S_OK;
+
+    /* these parameters we need after creation */
+    uint64_t size = 0, logicalSize = 0;
+    MediumVariant_T variant = MediumVariant_Standard;
+    bool fGenerateUuid = false;
+
+    try
+    {
+        AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+        /* The object may request a specific UUID (through a special form of
+        * the moveTo() argument). Otherwise we have to generate it */
+        Guid id = m->id;
+
+        fGenerateUuid = id.isZero();
+        if (fGenerateUuid)
+        {
+            id.create();
+            /* VirtualBox::i_registerMedium() will need UUID */
+            unconst(m->id) = id;
+        }
+
+        Utf8Str format(m->strFormat);
+        Utf8Str location(m->strLocationFull);
+        uint64_t capabilities = m->formatObj->i_getCapabilities();
+        ComAssertThrow(capabilities & (  MediumFormatCapabilities_CreateFixed
+                                       | MediumFormatCapabilities_CreateDynamic), E_FAIL);
+        Assert(m->state == MediumState_Creating);
+
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        /* unlock before the potentially lengthy operation */
+        thisLock.release();
+
+        try
+        {
+            /* ensure the directory exists */
+            if (capabilities & MediumFormatCapabilities_File)
+            {
+                hrc = VirtualBox::i_ensureFilePathExists(location, !(task.mVariant & MediumVariant_NoCreateDir) /* fCreate */);
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+
+            VDGEOMETRY geo = { 0, 0, 0 }; /* auto-detect */
+
+            vrc = VDCreateBase(hdd,
+                               format.c_str(),
+                               location.c_str(),
+                               task.mSize,
+                               task.mVariant & ~(MediumVariant_NoCreateDir | MediumVariant_Formatted),
+                               NULL,
+                               &geo,
+                               &geo,
+                               id.raw(),
+                               VD_OPEN_FLAGS_NORMAL | m->uOpenFlagsDef,
+                               m->vdImageIfaces,
+                               task.mVDOperationIfaces);
+            if (RT_FAILURE(vrc))
+            {
+                if (vrc == VERR_VD_INVALID_TYPE)
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Parameters for creating the medium storage unit '%s' are invalid%s"),
+                                       location.c_str(), i_vdError(vrc).c_str());
+                else
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not create the medium storage unit '%s'%s"),
+                                       location.c_str(), i_vdError(vrc).c_str());
+            }
+
+            if (task.mVariant & MediumVariant_Formatted)
+            {
+                RTVFSFILE hVfsFile;
+                vrc = VDCreateVfsFileFromDisk(hdd, 0 /*fFlags*/, &hVfsFile);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc, tr("Opening medium storage unit '%s' failed%s"),
+                                       location.c_str(), i_vdError(vrc).c_str());
+                RTERRINFOSTATIC ErrInfo;
+                vrc = RTFsFatVolFormat(hVfsFile, 0 /* offVol */, 0 /* cbVol */, RTFSFATVOL_FMT_F_FULL,
+                                       0 /* cbSector */, 0 /* cbSectorPerCluster */, RTFSFATTYPE_INVALID,
+                                       0 /* cHeads */, 0 /* cSectorsPerTrack*/, 0 /* bMedia */,
+                                       0 /* cRootDirEntries */, 0 /* cHiddenSectors */,
+                                       RTErrInfoInitStatic(&ErrInfo));
+                RTVfsFileRelease(hVfsFile);
+                if (RT_FAILURE(vrc) && RTErrInfoIsSet(&ErrInfo.Core))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc, tr("Formatting medium storage unit '%s' failed: %s"),
+                                       location.c_str(), ErrInfo.Core.pszMsg);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc, tr("Formatting medium storage unit '%s' failed%s"),
+                                       location.c_str(), i_vdError(vrc).c_str());
+            }
+
+            size = VDGetFileSize(hdd, 0);
+            logicalSize = VDGetSize(hdd, 0);
+            unsigned uImageFlags;
+            vrc = VDGetImageFlags(hdd, 0, &uImageFlags);
+            if (RT_SUCCESS(vrc))
+                variant = (MediumVariant_T)uImageFlags;
+        }
+        catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        /* register with mVirtualBox as the last step and move to
+         * Created state only on success (leaving an orphan file is
+         * better than breaking media registry consistency) */
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+        ComObjPtr<Medium> pMedium;
+        hrc = m->pVirtualBox->i_registerMedium(this, &pMedium, treeLock);
+        Assert(pMedium == NULL || this == pMedium);
+    }
+
+    // re-acquire the lock before changing state
+    AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+    if (SUCCEEDED(hrc))
+    {
+        m->state = MediumState_Created;
+
+        m->size = size;
+        m->logicalSize = logicalSize;
+        m->variant = variant;
+
+        thisLock.release();
+        i_markRegistriesModified();
+        if (task.isAsync())
+        {
+            // in asynchronous mode, save settings now
+            m->pVirtualBox->i_saveModifiedRegistries();
+        }
+    }
+    else
+    {
+        /* back to NotCreated on failure */
+        m->state = MediumState_NotCreated;
+
+        /* reset UUID to prevent it from being reused next time */
+        if (fGenerateUuid)
+            unconst(m->id).clear();
+    }
+
+    if (task.NotifyAboutChanges() && SUCCEEDED(hrc))
+    {
+        m->pVirtualBox->i_onMediumConfigChanged(this);
+        m->pVirtualBox->i_onMediumRegistered(m->id, m->devType, TRUE);
+    }
+
+    return hrc;
+}
+
+/**
+ * Implementation code for the "create diff" task.
+ *
+ * This task always gets started from Medium::createDiffStorage() and can run
+ * synchronously or asynchronously depending on the "wait" parameter passed to
+ * that function. If we run synchronously, the caller expects the medium
+ * registry modification to be set before returning; otherwise (in asynchronous
+ * mode), we save the settings ourselves.
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskCreateDiffHandler(Medium::CreateDiffTask &task)
+{
+    /** @todo r=klaus The code below needs to be double checked with regard
+     * to lock order violations, it probably causes lock order issues related
+     * to the AutoCaller usage. */
+    HRESULT hrcTmp = S_OK;
+
+    const ComObjPtr<Medium> &pTarget = task.mTarget;
+
+    uint64_t size = 0, logicalSize = 0;
+    MediumVariant_T variant = MediumVariant_Standard;
+    bool fGenerateUuid = false;
+
+    try
+    {
+        if (i_getDepth() >= SETTINGS_MEDIUM_DEPTH_MAX)
+        {
+            AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+            throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                           tr("Cannot create differencing image for medium '%s', because it exceeds the medium tree depth limit. Please merge some images which you no longer need"),
+                           m->strLocationFull.c_str());
+        }
+
+        /* Lock both in {parent,child} order. */
+        AutoMultiWriteLock2 mediaLock(this, pTarget COMMA_LOCKVAL_SRC_POS);
+
+        /* The object may request a specific UUID (through a special form of
+         * the moveTo() argument). Otherwise we have to generate it */
+        Guid targetId = pTarget->m->id;
+
+        fGenerateUuid = targetId.isZero();
+        if (fGenerateUuid)
+        {
+            targetId.create();
+            /* VirtualBox::i_registerMedium() will need UUID */
+            unconst(pTarget->m->id) = targetId;
+        }
+
+        Guid id = m->id;
+
+        Utf8Str targetFormat(pTarget->m->strFormat);
+        Utf8Str targetLocation(pTarget->m->strLocationFull);
+        uint64_t capabilities = pTarget->m->formatObj->i_getCapabilities();
+        ComAssertThrow(capabilities & MediumFormatCapabilities_CreateDynamic, E_FAIL);
+
+        Assert(pTarget->m->state == MediumState_Creating);
+        Assert(m->state == MediumState_LockedRead);
+
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        /* the two media are now protected by their non-default states;
+         * unlock the media before the potentially lengthy operation */
+        mediaLock.release();
+
+        try
+        {
+            /* Open all media in the target chain but the last. */
+            MediumLockList::Base::const_iterator targetListBegin =
+                task.mpMediumLockList->GetBegin();
+            MediumLockList::Base::const_iterator targetListEnd =
+                task.mpMediumLockList->GetEnd();
+            for (MediumLockList::Base::const_iterator it = targetListBegin;
+                 it != targetListEnd;
+                 ++it)
+            {
+                const MediumLock &mediumLock = *it;
+                const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+
+                AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                /* Skip over the target diff medium */
+                if (pMedium->m->state == MediumState_Creating)
+                    continue;
+
+                /* sanity check */
+                Assert(pMedium->m->state == MediumState_LockedRead);
+
+                /* Open all media in appropriate mode. */
+                vrc = VDOpen(hdd,
+                             pMedium->m->strFormat.c_str(),
+                             pMedium->m->strLocationFull.c_str(),
+                             VD_OPEN_FLAGS_READONLY | VD_OPEN_FLAGS_INFO | m->uOpenFlagsDef,
+                             pMedium->m->vdImageIfaces);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not open the medium storage unit '%s'%s"),
+                                       pMedium->m->strLocationFull.c_str(),
+                                       i_vdError(vrc).c_str());
+            }
+
+            /* ensure the target directory exists */
+            if (capabilities & MediumFormatCapabilities_File)
+            {
+                HRESULT hrc = VirtualBox::i_ensureFilePathExists(targetLocation,
+                                                                 !(task.mVariant & MediumVariant_NoCreateDir) /* fCreate */);
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+
+            vrc = VDCreateDiff(hdd,
+                               targetFormat.c_str(),
+                               targetLocation.c_str(),
+                                 (task.mVariant & ~(MediumVariant_NoCreateDir | MediumVariant_Formatted | MediumVariant_VmdkESX | MediumVariant_VmdkRawDisk))
+                               | VD_IMAGE_FLAGS_DIFF,
+                               NULL,
+                               targetId.raw(),
+                               id.raw(),
+                               VD_OPEN_FLAGS_NORMAL | m->uOpenFlagsDef,
+                               pTarget->m->vdImageIfaces,
+                               task.mVDOperationIfaces);
+            if (RT_FAILURE(vrc))
+            {
+                if (vrc == VERR_VD_INVALID_TYPE)
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Parameters for creating the differencing medium storage unit '%s' are invalid%s"),
+                                       targetLocation.c_str(), i_vdError(vrc).c_str());
+                else
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not create the differencing medium storage unit '%s'%s"),
+                                       targetLocation.c_str(), i_vdError(vrc).c_str());
+            }
+
+            size = VDGetFileSize(hdd, VD_LAST_IMAGE);
+            logicalSize = VDGetSize(hdd, VD_LAST_IMAGE);
+            unsigned uImageFlags;
+            vrc = VDGetImageFlags(hdd, 0, &uImageFlags);
+            if (RT_SUCCESS(vrc))
+                variant = (MediumVariant_T)uImageFlags;
+        }
+        catch (HRESULT hrcXcpt) { hrcTmp = hrcXcpt; }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrcTmp = hrcXcpt; }
+
+    MultiResult mrc(hrcTmp);
+
+    if (SUCCEEDED(mrc))
+    {
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+        Assert(pTarget->m->pParent.isNull());
+
+        /* associate child with the parent, maximum depth was checked above */
+        pTarget->i_setParent(this);
+
+        /* diffs for immutable media are auto-reset by default */
+        bool fAutoReset;
+        {
+            ComObjPtr<Medium> pBase = i_getBase();
+            AutoReadLock block(pBase COMMA_LOCKVAL_SRC_POS);
+            fAutoReset = (pBase->m->type == MediumType_Immutable);
+        }
+        {
+            AutoWriteLock tlock(pTarget COMMA_LOCKVAL_SRC_POS);
+            pTarget->m->autoReset = fAutoReset;
+        }
+
+        /* register with mVirtualBox as the last step and move to
+         * Created state only on success (leaving an orphan file is
+         * better than breaking media registry consistency) */
+        ComObjPtr<Medium> pMedium;
+        mrc = m->pVirtualBox->i_registerMedium(pTarget, &pMedium, treeLock);
+        Assert(pTarget == pMedium);
+
+        if (FAILED(mrc))
+            /* break the parent association on failure to register */
+            i_deparent();
+    }
+
+    AutoMultiWriteLock2 mediaLock(this, pTarget COMMA_LOCKVAL_SRC_POS);
+
+    if (SUCCEEDED(mrc))
+    {
+        pTarget->m->state = MediumState_Created;
+
+        pTarget->m->size = size;
+        pTarget->m->logicalSize = logicalSize;
+        pTarget->m->variant = variant;
+    }
+    else
+    {
+        /* back to NotCreated on failure */
+        pTarget->m->state = MediumState_NotCreated;
+
+        pTarget->m->autoReset = false;
+
+        /* reset UUID to prevent it from being reused next time */
+        if (fGenerateUuid)
+            unconst(pTarget->m->id).clear();
+    }
+
+    // deregister the task registered in createDiffStorage()
+    Assert(m->numCreateDiffTasks != 0);
+    --m->numCreateDiffTasks;
+
+    mediaLock.release();
+    i_markRegistriesModified();
+    if (task.isAsync())
+    {
+        // in asynchronous mode, save settings now
+        m->pVirtualBox->i_saveModifiedRegistries();
+    }
+
+    /* Note that in sync mode, it's the caller's responsibility to
+     * unlock the medium. */
+
+    if (task.NotifyAboutChanges() && SUCCEEDED(mrc))
+    {
+        m->pVirtualBox->i_onMediumConfigChanged(this);
+        m->pVirtualBox->i_onMediumRegistered(m->id, m->devType, TRUE);
+    }
+
+    return mrc;
+}
+
+/**
+ * Implementation code for the "merge" task.
+ *
+ * This task always gets started from Medium::mergeTo() and can run
+ * synchronously or asynchronously depending on the "wait" parameter passed to
+ * that function. If we run synchronously, the caller expects the medium
+ * registry modification to be set before returning; otherwise (in asynchronous
+ * mode), we save the settings ourselves.
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskMergeHandler(Medium::MergeTask &task)
+{
+    /** @todo r=klaus The code below needs to be double checked with regard
+     * to lock order violations, it probably causes lock order issues related
+     * to the AutoCaller usage. */
+    HRESULT hrcTmp = S_OK;
+
+    const ComObjPtr<Medium> &pTarget = task.mTarget;
+
+    try
+    {
+        if (!task.mParentForTarget.isNull())
+            if (task.mParentForTarget->i_getDepth() >= SETTINGS_MEDIUM_DEPTH_MAX)
+            {
+                AutoReadLock plock(task.mParentForTarget COMMA_LOCKVAL_SRC_POS);
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Cannot merge image for medium '%s', because it exceeds the medium tree depth limit. Please merge some images which you no longer need"),
+                               task.mParentForTarget->m->strLocationFull.c_str());
+            }
+
+        // Resize target to source size, if possible. Otherwise throw an error.
+        // It's offline resizing. Online resizing will be called in the
+        // SessionMachine::onlineMergeMedium.
+
+        uint64_t sourceSize = 0;
+        Utf8Str sourceName;
+        {
+            AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+            sourceSize = i_getLogicalSize();
+            sourceName = i_getName();
+        }
+        uint64_t targetSize = 0;
+        Utf8Str targetName;
+        {
+            AutoReadLock alock(pTarget COMMA_LOCKVAL_SRC_POS);
+            targetSize = pTarget->i_getLogicalSize();
+            targetName = pTarget->i_getName();
+        }
+
+        //reducing vm disks are not implemented yet
+        if (sourceSize > targetSize)
+        {
+            if (i_isMediumFormatFile())
+            {
+                /// @todo r=klaus Can this use the standard code for creating a medium lock list?
+                // Have to make own lock list, because "resize" method resizes the last image
+                // in the lock chain only. The lock chain is already in the task.mpMediumLockList,
+                // so just make new lock list based on it, with the right last medium. The own
+                // lock list skips double locking and therefore does not affect the general lock
+                // state after the "resize" method.
+                MediumLockList* pMediumLockListForResize = new MediumLockList();
+
+                for (MediumLockList::Base::iterator it = task.mpMediumLockList->GetBegin();
+                     it != task.mpMediumLockList->GetEnd();
+                     ++it)
+                {
+                    ComObjPtr<Medium> pMedium = it->GetMedium();
+                    pMediumLockListForResize->Append(pMedium, pMedium->m->state == MediumState_LockedWrite);
+                    if (pMedium == pTarget)
+                        break;
+                }
+
+                // just to switch internal state of the lock list to avoid errors during list deletion,
+                // because all media in the list already locked by task.mpMediumLockList
+                HRESULT hrc = pMediumLockListForResize->Lock(true /* fSkipOverLockedMedia */);
+                if (FAILED(hrc))
+                {
+                    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+                    delete pMediumLockListForResize;
+                    throw  setError(hrc,
+                                    tr("Failed to lock the medium '%s' to resize before merge"),
+                                    targetName.c_str());
+                }
+
+                ComObjPtr<Progress> pProgress(task.GetProgressObject());
+                hrc = pTarget->i_resize(sourceSize, pMediumLockListForResize, &pProgress, true, false);
+                if (FAILED(hrc))
+                {
+                    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+                    delete pMediumLockListForResize;
+                    throw setError(hrc,
+                                   tr("Failed to set size of '%s' to size of '%s'"),
+                                   targetName.c_str(), sourceName.c_str());
+                }
+                delete pMediumLockListForResize;
+            }
+            else
+            {
+                AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+                throw setError(VBOX_E_NOT_SUPPORTED,
+                               tr("Sizes of '%s' and '%s' are different and medium format does not support resing"),
+                               sourceName.c_str(), targetName.c_str());
+            }
+        }
+
+        task.GetProgressObject()->SetNextOperation(BstrFmt(tr("Merging medium '%s' to '%s'"),
+                                                           i_getName().c_str(),
+                                                           targetName.c_str()).raw(),
+                                                   1);
+
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        try
+        {
+            // Similar code appears in SessionMachine::onlineMergeMedium, so
+            // if you make any changes below check whether they are applicable
+            // in that context as well.
+
+            unsigned uTargetIdx = VD_LAST_IMAGE;
+            unsigned uSourceIdx = VD_LAST_IMAGE;
+            /* Open all media in the chain. */
+            MediumLockList::Base::iterator lockListBegin =
+                task.mpMediumLockList->GetBegin();
+            MediumLockList::Base::iterator lockListEnd =
+                task.mpMediumLockList->GetEnd();
+            unsigned i = 0;
+            for (MediumLockList::Base::iterator it = lockListBegin;
+                 it != lockListEnd;
+                 ++it)
+            {
+                MediumLock &mediumLock = *it;
+                const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+
+                if (pMedium == this)
+                    uSourceIdx = i;
+                else if (pMedium == pTarget)
+                    uTargetIdx = i;
+
+                AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                /*
+                 * complex sanity (sane complexity)
+                 *
+                 * The current medium must be in the Deleting (medium is merged)
+                 * or LockedRead (parent medium) state if it is not the target.
+                 * If it is the target it must be in the LockedWrite state.
+                 */
+                Assert(   (   pMedium != pTarget
+                           && (   pMedium->m->state == MediumState_Deleting
+                               || pMedium->m->state == MediumState_LockedRead))
+                       || (   pMedium == pTarget
+                           && pMedium->m->state == MediumState_LockedWrite));
+                /*
+                 * Medium must be the target, in the LockedRead state
+                 * or Deleting state where it is not allowed to be attached
+                 * to a virtual machine.
+                 */
+                Assert(   pMedium == pTarget
+                       || pMedium->m->state == MediumState_LockedRead
+                       || (   pMedium->m->backRefs.size() == 0
+                           && pMedium->m->state == MediumState_Deleting));
+                /* The source medium must be in Deleting state. */
+                Assert(  pMedium != this
+                       || pMedium->m->state == MediumState_Deleting);
+
+                unsigned uOpenFlags = VD_OPEN_FLAGS_NORMAL;
+
+                if (   pMedium->m->state == MediumState_LockedRead
+                    || pMedium->m->state == MediumState_Deleting)
+                    uOpenFlags = VD_OPEN_FLAGS_READONLY;
+                if (pMedium->m->type == MediumType_Shareable)
+                    uOpenFlags |= VD_OPEN_FLAGS_SHAREABLE;
+
+                /* Open the medium */
+                vrc = VDOpen(hdd,
+                             pMedium->m->strFormat.c_str(),
+                             pMedium->m->strLocationFull.c_str(),
+                             uOpenFlags | m->uOpenFlagsDef,
+                             pMedium->m->vdImageIfaces);
+                if (RT_FAILURE(vrc))
+                    throw vrc;
+
+                i++;
+            }
+
+            ComAssertThrow(   uSourceIdx != VD_LAST_IMAGE
+                           && uTargetIdx != VD_LAST_IMAGE, E_FAIL);
+
+            vrc = VDMerge(hdd, uSourceIdx, uTargetIdx,
+                          task.mVDOperationIfaces);
+            if (RT_FAILURE(vrc))
+                throw vrc;
+
+            /* update parent UUIDs */
+            if (!task.mfMergeForward)
+            {
+                /* we need to update UUIDs of all source's children
+                 * which cannot be part of the container at once so
+                 * add each one in there individually */
+                if (task.mpChildrenToReparent)
+                {
+                    MediumLockList::Base::iterator childrenBegin = task.mpChildrenToReparent->GetBegin();
+                    MediumLockList::Base::iterator childrenEnd = task.mpChildrenToReparent->GetEnd();
+                    for (MediumLockList::Base::iterator it = childrenBegin;
+                         it != childrenEnd;
+                         ++it)
+                    {
+                        Medium *pMedium = it->GetMedium();
+                        /* VD_OPEN_FLAGS_INFO since UUID is wrong yet */
+                        vrc = VDOpen(hdd,
+                                     pMedium->m->strFormat.c_str(),
+                                     pMedium->m->strLocationFull.c_str(),
+                                     VD_OPEN_FLAGS_INFO | m->uOpenFlagsDef,
+                                     pMedium->m->vdImageIfaces);
+                        if (RT_FAILURE(vrc))
+                            throw vrc;
+
+                        vrc = VDSetParentUuid(hdd, VD_LAST_IMAGE,
+                                              pTarget->m->id.raw());
+                        if (RT_FAILURE(vrc))
+                            throw vrc;
+
+                        vrc = VDClose(hdd, false /* fDelete */);
+                        if (RT_FAILURE(vrc))
+                            throw vrc;
+                    }
+                }
+            }
+        }
+        catch (HRESULT hrcXcpt) { hrcTmp = hrcXcpt; }
+        catch (int aVRC)
+        {
+            hrcTmp = setErrorBoth(VBOX_E_FILE_ERROR, aVRC,
+                                  tr("Could not merge the medium '%s' to '%s'%s"),
+                                  m->strLocationFull.c_str(),
+                                  pTarget->m->strLocationFull.c_str(),
+                                  i_vdError(aVRC).c_str());
+        }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrcTmp = hrcXcpt; }
+
+    ErrorInfoKeeper eik;
+    MultiResult mrc(hrcTmp);
+    HRESULT hrc2;
+
+    std::set<ComObjPtr<Medium> > pMediaForNotify;
+    std::map<Guid, DeviceType_T> uIdsForNotify;
+
+    if (SUCCEEDED(mrc))
+    {
+        /* all media but the target were successfully deleted by
+         * VDMerge; reparent the last one and uninitialize deleted media. */
+
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+        if (task.mfMergeForward)
+        {
+            /* first, unregister the target since it may become a base
+             * medium which needs re-registration */
+            hrc2 = m->pVirtualBox->i_unregisterMedium(pTarget);
+            AssertComRC(hrc2);
+
+            /* then, reparent it and disconnect the deleted branch at both ends
+             * (chain->parent() is source's parent). Depth check above. */
+            pTarget->i_deparent();
+            pTarget->i_setParent(task.mParentForTarget);
+            if (task.mParentForTarget)
+            {
+                i_deparent();
+                if (task.NotifyAboutChanges())
+                    pMediaForNotify.insert(task.mParentForTarget);
+            }
+
+            /* then, register again */
+            ComObjPtr<Medium> pMedium;
+            hrc2 = m->pVirtualBox->i_registerMedium(pTarget, &pMedium, treeLock);
+            AssertComRC(hrc2);
+        }
+        else
+        {
+            Assert(pTarget->i_getChildren().size() == 1);
+            Medium *targetChild = pTarget->i_getChildren().front();
+
+            /* disconnect the deleted branch at the elder end */
+            targetChild->i_deparent();
+
+            /* reparent source's children and disconnect the deleted
+             * branch at the younger end */
+            if (task.mpChildrenToReparent)
+            {
+                /* obey {parent,child} lock order */
+                AutoWriteLock sourceLock(this COMMA_LOCKVAL_SRC_POS);
+
+                MediumLockList::Base::iterator childrenBegin = task.mpChildrenToReparent->GetBegin();
+                MediumLockList::Base::iterator childrenEnd = task.mpChildrenToReparent->GetEnd();
+                for (MediumLockList::Base::iterator it = childrenBegin;
+                     it != childrenEnd;
+                     ++it)
+                {
+                    Medium *pMedium = it->GetMedium();
+                    AutoWriteLock childLock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                    pMedium->i_deparent();  // removes pMedium from source
+                    // no depth check, reduces depth
+                    pMedium->i_setParent(pTarget);
+
+                    if (task.NotifyAboutChanges())
+                        pMediaForNotify.insert(pMedium);
+                }
+            }
+            pMediaForNotify.insert(pTarget);
+        }
+
+        /* unregister and uninitialize all media removed by the merge */
+        MediumLockList::Base::iterator lockListBegin =
+            task.mpMediumLockList->GetBegin();
+        MediumLockList::Base::iterator lockListEnd =
+            task.mpMediumLockList->GetEnd();
+        for (MediumLockList::Base::iterator it = lockListBegin;
+             it != lockListEnd;
+             )
+        {
+            MediumLock &mediumLock = *it;
+            /* Create a real copy of the medium pointer, as the medium
+             * lock deletion below would invalidate the referenced object. */
+            const ComObjPtr<Medium> pMedium = mediumLock.GetMedium();
+
+            /* The target and all media not merged (readonly) are skipped */
+            if (   pMedium == pTarget
+                || pMedium->m->state == MediumState_LockedRead)
+            {
+                ++it;
+                continue;
+            }
+
+            uIdsForNotify[pMedium->i_getId()] = pMedium->i_getDeviceType();
+            hrc2 = pMedium->m->pVirtualBox->i_unregisterMedium(pMedium);
+            AssertComRC(hrc2);
+
+            /* now, uninitialize the deleted medium (note that
+             * due to the Deleting state, uninit() will not touch
+             * the parent-child relationship so we need to
+             * uninitialize each disk individually) */
+
+            /* note that the operation initiator medium (which is
+             * normally also the source medium) is a special case
+             * -- there is one more caller added by Task to it which
+             * we must release. Also, if we are in sync mode, the
+             * caller may still hold an AutoCaller instance for it
+             * and therefore we cannot uninit() it (it's therefore
+             * the caller's responsibility) */
+            if (pMedium == this)
+            {
+                Assert(i_getChildren().size() == 0);
+                Assert(m->backRefs.size() == 0);
+                task.mMediumCaller.release();
+            }
+
+            /* Delete the medium lock list entry, which also releases the
+             * caller added by MergeChain before uninit() and updates the
+             * iterator to point to the right place. */
+            hrc2 = task.mpMediumLockList->RemoveByIterator(it);
+            AssertComRC(hrc2);
+
+            if (task.isAsync() || pMedium != this)
+            {
+                treeLock.release();
+                pMedium->uninit();
+                treeLock.acquire();
+            }
+        }
+    }
+
+    i_markRegistriesModified();
+    if (task.isAsync())
+    {
+        // in asynchronous mode, save settings now
+        eik.restore();
+        m->pVirtualBox->i_saveModifiedRegistries();
+        eik.fetch();
+    }
+
+    if (FAILED(mrc))
+    {
+        /* Here we come if either VDMerge() failed (in which case we
+         * assume that it tried to do everything to make a further
+         * retry possible -- e.g. not deleted intermediate media
+         * and so on) or VirtualBox::saveRegistries() failed (where we
+         * should have the original tree but with intermediate storage
+         * units deleted by VDMerge()). We have to only restore states
+         * (through the MergeChain dtor) unless we are run synchronously
+         * in which case it's the responsibility of the caller as stated
+         * in the mergeTo() docs. The latter also implies that we
+         * don't own the merge chain, so release it in this case. */
+        if (task.isAsync())
+            i_cancelMergeTo(task.mpChildrenToReparent, task.mpMediumLockList);
+    }
+    else if (task.NotifyAboutChanges())
+    {
+        for (std::set<ComObjPtr<Medium> >::const_iterator it = pMediaForNotify.begin();
+             it != pMediaForNotify.end();
+             ++it)
+        {
+            if (it->isNotNull())
+                m->pVirtualBox->i_onMediumConfigChanged(*it);
+        }
+        for (std::map<Guid, DeviceType_T>::const_iterator it = uIdsForNotify.begin();
+             it != uIdsForNotify.end();
+             ++it)
+        {
+            m->pVirtualBox->i_onMediumRegistered(it->first, it->second, FALSE);
+        }
+    }
+
+    return mrc;
+}
+
+/**
+ * Implementation code for the "clone" task.
+ *
+ * This only gets started from Medium::CloneTo() and always runs asynchronously.
+ * As a result, we always save the VirtualBox.xml file when we're done here.
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskCloneHandler(Medium::CloneTask &task)
+{
+    /** @todo r=klaus The code below needs to be double checked with regard
+     * to lock order violations, it probably causes lock order issues related
+     * to the AutoCaller usage. */
+    HRESULT hrcTmp = S_OK;
+
+    const ComObjPtr<Medium> &pTarget = task.mTarget;
+    const ComObjPtr<Medium> &pParent = task.mParent;
+
+    bool fCreatingTarget = false;
+
+    uint64_t size = 0, logicalSize = 0;
+    MediumVariant_T variant = MediumVariant_Standard;
+    bool fGenerateUuid = false;
+
+    try
+    {
+        if (!pParent.isNull())
+        {
+
+            if (pParent->i_getDepth() >= SETTINGS_MEDIUM_DEPTH_MAX)
+            {
+                AutoReadLock plock(pParent COMMA_LOCKVAL_SRC_POS);
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Cannot clone image for medium '%s', because it exceeds the medium tree depth limit. Please merge some images which you no longer need"),
+                               pParent->m->strLocationFull.c_str());
+            }
+        }
+
+        /* Lock all in {parent,child} order. The lock is also used as a
+         * signal from the task initiator (which releases it only after
+         * RTThreadCreate()) that we can start the job. */
+        AutoMultiWriteLock3 thisLock(this, pTarget, pParent COMMA_LOCKVAL_SRC_POS);
+
+        fCreatingTarget = pTarget->m->state == MediumState_Creating;
+
+        /* The object may request a specific UUID (through a special form of
+         * the moveTo() argument). Otherwise we have to generate it */
+        Guid targetId = pTarget->m->id;
+
+        fGenerateUuid = targetId.isZero();
+        if (fGenerateUuid)
+        {
+            targetId.create();
+            /* VirtualBox::registerMedium() will need UUID */
+            unconst(pTarget->m->id) = targetId;
+        }
+
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        try
+        {
+            /* Open all media in the source chain. */
+            MediumLockList::Base::const_iterator sourceListBegin =
+                task.mpSourceMediumLockList->GetBegin();
+            MediumLockList::Base::const_iterator sourceListEnd =
+                task.mpSourceMediumLockList->GetEnd();
+            for (MediumLockList::Base::const_iterator it = sourceListBegin;
+                 it != sourceListEnd;
+                 ++it)
+            {
+                const MediumLock &mediumLock = *it;
+                const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+                AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                /* sanity check */
+                Assert(pMedium->m->state == MediumState_LockedRead);
+
+                /** Open all media in read-only mode. */
+                vrc = VDOpen(hdd,
+                             pMedium->m->strFormat.c_str(),
+                             pMedium->m->strLocationFull.c_str(),
+                             VD_OPEN_FLAGS_READONLY | m->uOpenFlagsDef,
+                             pMedium->m->vdImageIfaces);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not open the medium storage unit '%s'%s"),
+                                       pMedium->m->strLocationFull.c_str(),
+                                       i_vdError(vrc).c_str());
+            }
+
+            Utf8Str targetFormat(pTarget->m->strFormat);
+            Utf8Str targetLocation(pTarget->m->strLocationFull);
+            uint64_t capabilities = pTarget->m->formatObj->i_getCapabilities();
+
+            Assert(   pTarget->m->state == MediumState_Creating
+                   || pTarget->m->state == MediumState_LockedWrite);
+            Assert(m->state == MediumState_LockedRead);
+            Assert(   pParent.isNull()
+                   || pParent->m->state == MediumState_LockedRead);
+
+            /* unlock before the potentially lengthy operation */
+            thisLock.release();
+
+            /* ensure the target directory exists */
+            if (capabilities & MediumFormatCapabilities_File)
+            {
+                HRESULT hrc = VirtualBox::i_ensureFilePathExists(targetLocation,
+                                                                 !(task.mVariant & MediumVariant_NoCreateDir) /* fCreate */);
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+
+            PVDISK targetHdd;
+            vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &targetHdd);
+            ComAssertRCThrow(vrc, E_FAIL);
+
+            try
+            {
+                /* Open all media in the target chain. */
+                MediumLockList::Base::const_iterator targetListBegin =
+                    task.mpTargetMediumLockList->GetBegin();
+                MediumLockList::Base::const_iterator targetListEnd =
+                    task.mpTargetMediumLockList->GetEnd();
+                for (MediumLockList::Base::const_iterator it = targetListBegin;
+                     it != targetListEnd;
+                     ++it)
+                {
+                    const MediumLock &mediumLock = *it;
+                    const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+
+                    /* If the target medium is not created yet there's no
+                     * reason to open it. */
+                    if (pMedium == pTarget && fCreatingTarget)
+                        continue;
+
+                    AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                    /* sanity check */
+                    Assert(    pMedium->m->state == MediumState_LockedRead
+                            || pMedium->m->state == MediumState_LockedWrite);
+
+                    unsigned uOpenFlags = VD_OPEN_FLAGS_NORMAL;
+                    if (pMedium->m->state != MediumState_LockedWrite)
+                        uOpenFlags = VD_OPEN_FLAGS_READONLY;
+                    if (pMedium->m->type == MediumType_Shareable)
+                        uOpenFlags |= VD_OPEN_FLAGS_SHAREABLE;
+
+                    /* Open all media in appropriate mode. */
+                    vrc = VDOpen(targetHdd,
+                                 pMedium->m->strFormat.c_str(),
+                                 pMedium->m->strLocationFull.c_str(),
+                                 uOpenFlags | m->uOpenFlagsDef,
+                                 pMedium->m->vdImageIfaces);
+                    if (RT_FAILURE(vrc))
+                        throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                           tr("Could not open the medium storage unit '%s'%s"),
+                                           pMedium->m->strLocationFull.c_str(),
+                                           i_vdError(vrc).c_str());
+                }
+
+                /* target isn't locked, but no changing data is accessed */
+                if (task.midxSrcImageSame == UINT32_MAX)
+                {
+                    vrc = VDCopy(hdd,
+                                 VD_LAST_IMAGE,
+                                 targetHdd,
+                                 targetFormat.c_str(),
+                                 (fCreatingTarget) ? targetLocation.c_str() : (char *)NULL,
+                                 false /* fMoveByRename */,
+                                 task.mTargetLogicalSize /* cbSize */,
+                                 task.mVariant & ~(MediumVariant_NoCreateDir | MediumVariant_Formatted | MediumVariant_VmdkESX | MediumVariant_VmdkRawDisk),
+                                 targetId.raw(),
+                                 VD_OPEN_FLAGS_NORMAL | m->uOpenFlagsDef,
+                                 NULL /* pVDIfsOperation */,
+                                 pTarget->m->vdImageIfaces,
+                                 task.mVDOperationIfaces);
+                }
+                else
+                {
+                    vrc = VDCopyEx(hdd,
+                                   VD_LAST_IMAGE,
+                                   targetHdd,
+                                   targetFormat.c_str(),
+                                   (fCreatingTarget) ? targetLocation.c_str() : (char *)NULL,
+                                   false /* fMoveByRename */,
+                                   task.mTargetLogicalSize /* cbSize */,
+                                   task.midxSrcImageSame,
+                                   task.midxDstImageSame,
+                                   task.mVariant & ~(MediumVariant_NoCreateDir | MediumVariant_Formatted | MediumVariant_VmdkESX | MediumVariant_VmdkRawDisk),
+                                   targetId.raw(),
+                                   VD_OPEN_FLAGS_NORMAL | m->uOpenFlagsDef,
+                                   NULL /* pVDIfsOperation */,
+                                   pTarget->m->vdImageIfaces,
+                                   task.mVDOperationIfaces);
+                }
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not create the clone medium '%s'%s"),
+                                       targetLocation.c_str(), i_vdError(vrc).c_str());
+
+                size = VDGetFileSize(targetHdd, VD_LAST_IMAGE);
+                logicalSize = VDGetSize(targetHdd, VD_LAST_IMAGE);
+                unsigned uImageFlags;
+                vrc = VDGetImageFlags(targetHdd, 0, &uImageFlags);
+                if (RT_SUCCESS(vrc))
+                    variant = (MediumVariant_T)uImageFlags;
+            }
+            catch (HRESULT hrcXcpt) { hrcTmp = hrcXcpt; }
+
+            VDDestroy(targetHdd);
+        }
+        catch (HRESULT hrcXcpt) { hrcTmp = hrcXcpt; }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrcTmp = hrcXcpt; }
+
+    ErrorInfoKeeper eik;
+    MultiResult mrc(hrcTmp);
+
+    /* Only do the parent changes for newly created media. */
+    if (SUCCEEDED(mrc) && fCreatingTarget)
+    {
+        /* we set m->pParent & children() */
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+        Assert(pTarget->m->pParent.isNull());
+
+        if (pParent)
+        {
+            /* Associate the clone with the parent and deassociate
+             * from VirtualBox. Depth check above. */
+            pTarget->i_setParent(pParent);
+
+            /* register with mVirtualBox as the last step and move to
+             * Created state only on success (leaving an orphan file is
+             * better than breaking media registry consistency) */
+            eik.restore();
+            ComObjPtr<Medium> pMedium;
+            mrc = pParent->m->pVirtualBox->i_registerMedium(pTarget, &pMedium,
+                                                            treeLock);
+            Assert(   FAILED(mrc)
+                   || pTarget == pMedium);
+            eik.fetch();
+
+            if (FAILED(mrc))
+                /* break parent association on failure to register */
+                pTarget->i_deparent();     // removes target from parent
+        }
+        else
+        {
+            /* just register  */
+            eik.restore();
+            ComObjPtr<Medium> pMedium;
+            mrc = m->pVirtualBox->i_registerMedium(pTarget, &pMedium,
+                                                   treeLock);
+            Assert(   FAILED(mrc)
+                   || pTarget == pMedium);
+            eik.fetch();
+        }
+    }
+
+    if (fCreatingTarget)
+    {
+        AutoWriteLock mLock(pTarget COMMA_LOCKVAL_SRC_POS);
+
+        if (SUCCEEDED(mrc))
+        {
+            pTarget->m->state = MediumState_Created;
+
+            pTarget->m->size = size;
+            pTarget->m->logicalSize = logicalSize;
+            pTarget->m->variant = variant;
+        }
+        else
+        {
+            /* back to NotCreated on failure */
+            pTarget->m->state = MediumState_NotCreated;
+
+            /* reset UUID to prevent it from being reused next time */
+            if (fGenerateUuid)
+                unconst(pTarget->m->id).clear();
+        }
+    }
+
+    /* Copy any filter related settings over to the target. */
+    if (SUCCEEDED(mrc))
+    {
+        /* Copy any filter related settings over. */
+        ComObjPtr<Medium> pBase = i_getBase();
+        ComObjPtr<Medium> pTargetBase = pTarget->i_getBase();
+        std::vector<com::Utf8Str> aFilterPropNames;
+        std::vector<com::Utf8Str> aFilterPropValues;
+        mrc = pBase->i_getFilterProperties(aFilterPropNames, aFilterPropValues);
+        if (SUCCEEDED(mrc))
+        {
+            /* Go through the properties and add them to the target medium. */
+            for (unsigned idx = 0; idx < aFilterPropNames.size(); idx++)
+            {
+                mrc = pTargetBase->i_setPropertyDirect(aFilterPropNames[idx], aFilterPropValues[idx]);
+                if (FAILED(mrc)) break;
+            }
+
+            // now, at the end of this task (always asynchronous), save the settings
+            if (SUCCEEDED(mrc))
+            {
+                // save the settings
+                i_markRegistriesModified();
+                /* collect multiple errors */
+                eik.restore();
+                m->pVirtualBox->i_saveModifiedRegistries();
+                eik.fetch();
+
+                if (task.NotifyAboutChanges())
+                {
+                    if (!fCreatingTarget)
+                    {
+                        if (!aFilterPropNames.empty())
+                            m->pVirtualBox->i_onMediumConfigChanged(pTargetBase);
+                        if (pParent)
+                            m->pVirtualBox->i_onMediumConfigChanged(pParent);
+                    }
+                    else
+                    {
+                        m->pVirtualBox->i_onMediumRegistered(pTarget->i_getId(), pTarget->i_getDeviceType(), TRUE);
+                    }
+                }
+            }
+        }
+    }
+
+    /* Everything is explicitly unlocked when the task exits,
+     * as the task destruction also destroys the source chain. */
+
+    /* Make sure the source chain is released early. It could happen
+     * that we get a deadlock in Appliance::Import when Medium::Close
+     * is called & the source chain is released at the same time. */
+    task.mpSourceMediumLockList->Clear();
+
+    return mrc;
+}
+
+/**
+ * Implementation code for the "move" task.
+ *
+ * This only gets started from Medium::MoveTo() and always
+ * runs asynchronously.
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskMoveHandler(Medium::MoveTask &task)
+{
+    LogFlowFuncEnter();
+    HRESULT hrcOut = S_OK;
+
+    /* pTarget is equal "this" in our case */
+    const ComObjPtr<Medium> &pTarget = task.mMedium;
+
+    uint64_t size = 0; NOREF(size);
+    uint64_t logicalSize = 0; NOREF(logicalSize);
+    MediumVariant_T variant = MediumVariant_Standard; NOREF(variant);
+
+    /*
+     * it's exactly moving, not cloning
+     */
+    if (!i_isMoveOperation(pTarget))
+    {
+        LogFlowFunc(("LEAVE: hrc=VBOX_E_FILE_ERROR (early)\n"));
+        return setError(VBOX_E_FILE_ERROR,
+                        tr("Wrong preconditions for moving the medium %s"),
+                        pTarget->m->strLocationFull.c_str());
+    }
+
+    try
+    {
+        /* Lock all in {parent,child} order. The lock is also used as a
+         * signal from the task initiator (which releases it only after
+         * RTThreadCreate()) that we can start the job. */
+
+        AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        try
+        {
+            /* Open all media in the source chain. */
+            MediumLockList::Base::const_iterator sourceListBegin =
+                task.mpMediumLockList->GetBegin();
+            MediumLockList::Base::const_iterator sourceListEnd =
+                task.mpMediumLockList->GetEnd();
+            for (MediumLockList::Base::const_iterator it = sourceListBegin;
+                 it != sourceListEnd;
+                 ++it)
+            {
+                const MediumLock &mediumLock = *it;
+                const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+                AutoWriteLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                /* sanity check */
+                Assert(pMedium->m->state == MediumState_LockedWrite);
+
+                vrc = VDOpen(hdd,
+                             pMedium->m->strFormat.c_str(),
+                             pMedium->m->strLocationFull.c_str(),
+                             VD_OPEN_FLAGS_NORMAL,
+                             pMedium->m->vdImageIfaces);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not open the medium storage unit '%s'%s"),
+                                       pMedium->m->strLocationFull.c_str(),
+                                       i_vdError(vrc).c_str());
+            }
+
+            /* we can directly use pTarget->m->"variables" but for better reading we use local copies */
+            Guid targetId = pTarget->m->id;
+            Utf8Str targetFormat(pTarget->m->strFormat);
+            uint64_t targetCapabilities = pTarget->m->formatObj->i_getCapabilities();
+
+            /*
+             * change target location
+             * m->strNewLocationFull has been set already together with m->fMoveThisMedium in
+             * i_preparationForMoving()
+             */
+            Utf8Str targetLocation = i_getNewLocationForMoving();
+
+            /* unlock before the potentially lengthy operation */
+            thisLock.release();
+
+            /* ensure the target directory exists */
+            if (targetCapabilities & MediumFormatCapabilities_File)
+            {
+                HRESULT hrc = VirtualBox::i_ensureFilePathExists(targetLocation,
+                                                                 !(task.mVariant & MediumVariant_NoCreateDir) /* fCreate */);
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+
+            try
+            {
+                vrc = VDCopy(hdd,
+                             VD_LAST_IMAGE,
+                             hdd,
+                             targetFormat.c_str(),
+                             targetLocation.c_str(),
+                             true /* fMoveByRename */,
+                             0 /* cbSize */,
+                             VD_IMAGE_FLAGS_NONE,
+                             targetId.raw(),
+                             VD_OPEN_FLAGS_NORMAL,
+                             NULL /* pVDIfsOperation */,
+                             pTarget->m->vdImageIfaces,
+                             task.mVDOperationIfaces);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not move medium '%s'%s"),
+                                       targetLocation.c_str(), i_vdError(vrc).c_str());
+                size = VDGetFileSize(hdd, VD_LAST_IMAGE);
+                logicalSize = VDGetSize(hdd, VD_LAST_IMAGE);
+                unsigned uImageFlags;
+                vrc = VDGetImageFlags(hdd, 0, &uImageFlags);
+                if (RT_SUCCESS(vrc))
+                    variant = (MediumVariant_T)uImageFlags;
+
+                /*
+                 * set current location, because VDCopy\VDCopyEx doesn't do it.
+                 * also reset moving flag
+                 */
+                i_resetMoveOperationData();
+                m->strLocationFull = targetLocation;
+
+            }
+            catch (HRESULT hrcXcpt) { hrcOut = hrcXcpt; }
+
+        }
+        catch (HRESULT hrcXcpt) { hrcOut = hrcXcpt; }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrcOut = hrcXcpt; }
+
+    ErrorInfoKeeper eik;
+    MultiResult mrc(hrcOut);
+
+    // now, at the end of this task (always asynchronous), save the settings
+    if (SUCCEEDED(mrc))
+    {
+        // save the settings
+        i_markRegistriesModified();
+        /* collect multiple errors */
+        eik.restore();
+        m->pVirtualBox->i_saveModifiedRegistries();
+        eik.fetch();
+    }
+
+    /* Everything is explicitly unlocked when the task exits,
+     * as the task destruction also destroys the source chain. */
+
+    task.mpMediumLockList->Clear();
+
+    if (task.NotifyAboutChanges() && SUCCEEDED(mrc))
+        m->pVirtualBox->i_onMediumConfigChanged(this);
+
+    LogFlowFunc(("LEAVE: mrc=%Rhrc\n", (HRESULT)mrc));
+    return mrc;
+}
+
+/**
+ * Implementation code for the "delete" task.
+ *
+ * This task always gets started from Medium::deleteStorage() and can run
+ * synchronously or asynchronously depending on the "wait" parameter passed to
+ * that function.
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskDeleteHandler(Medium::DeleteTask &task)
+{
+    NOREF(task);
+    HRESULT hrc = S_OK;
+
+    try
+    {
+        /* The lock is also used as a signal from the task initiator (which
+         * releases it only after RTThreadCreate()) that we can start the job */
+        AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        Utf8Str format(m->strFormat);
+        Utf8Str location(m->strLocationFull);
+
+        /* unlock before the potentially lengthy operation */
+        Assert(m->state == MediumState_Deleting);
+        thisLock.release();
+
+        try
+        {
+            vrc = VDOpen(hdd,
+                         format.c_str(),
+                         location.c_str(),
+                         VD_OPEN_FLAGS_READONLY | VD_OPEN_FLAGS_INFO | m->uOpenFlagsDef,
+                         m->vdImageIfaces);
+            if (RT_SUCCESS(vrc))
+                vrc = VDClose(hdd, true /* fDelete */);
+
+            if (RT_FAILURE(vrc) && vrc != VERR_FILE_NOT_FOUND)
+                throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                   tr("Could not delete the medium storage unit '%s'%s"),
+                                   location.c_str(), i_vdError(vrc).c_str());
+
+        }
+        catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+    /* go to the NotCreated state even on failure since the storage
+     * may have been already partially deleted and cannot be used any
+     * more. One will be able to manually re-open the storage if really
+     * needed to re-register it. */
+    m->state = MediumState_NotCreated;
+
+    /* Reset UUID to prevent Create* from reusing it again */
+    com::Guid uOldId = m->id;
+    unconst(m->id).clear();
+
+    if (task.NotifyAboutChanges() && SUCCEEDED(hrc))
+    {
+        if (m->pParent.isNotNull())
+            m->pVirtualBox->i_onMediumConfigChanged(m->pParent);
+        m->pVirtualBox->i_onMediumRegistered(uOldId, m->devType, FALSE);
+    }
+
+    return hrc;
+}
+
+/**
+ * Implementation code for the "reset" task.
+ *
+ * This always gets started asynchronously from Medium::Reset().
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskResetHandler(Medium::ResetTask &task)
+{
+    HRESULT hrc = S_OK;
+
+    uint64_t size = 0, logicalSize = 0;
+    MediumVariant_T variant = MediumVariant_Standard;
+
+    try
+    {
+        /* The lock is also used as a signal from the task initiator (which
+         * releases it only after RTThreadCreate()) that we can start the job */
+        AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+        /// @todo Below we use a pair of delete/create operations to reset
+        /// the diff contents but the most efficient way will of course be
+        /// to add a VDResetDiff() API call
+
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        Guid id = m->id;
+        Utf8Str format(m->strFormat);
+        Utf8Str location(m->strLocationFull);
+
+        Medium *pParent = m->pParent;
+        Guid parentId = pParent->m->id;
+        Utf8Str parentFormat(pParent->m->strFormat);
+        Utf8Str parentLocation(pParent->m->strLocationFull);
+
+        Assert(m->state == MediumState_LockedWrite);
+
+        /* unlock before the potentially lengthy operation */
+        thisLock.release();
+
+        try
+        {
+            /* Open all media in the target chain but the last. */
+            MediumLockList::Base::const_iterator targetListBegin =
+                task.mpMediumLockList->GetBegin();
+            MediumLockList::Base::const_iterator targetListEnd =
+                task.mpMediumLockList->GetEnd();
+            for (MediumLockList::Base::const_iterator it = targetListBegin;
+                 it != targetListEnd;
+                 ++it)
+            {
+                const MediumLock &mediumLock = *it;
+                const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+
+                AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                /* sanity check, "this" is checked above */
+                Assert(   pMedium == this
+                       || pMedium->m->state == MediumState_LockedRead);
+
+                /* Open all media in appropriate mode. */
+                vrc = VDOpen(hdd,
+                             pMedium->m->strFormat.c_str(),
+                             pMedium->m->strLocationFull.c_str(),
+                             VD_OPEN_FLAGS_READONLY | m->uOpenFlagsDef,
+                             pMedium->m->vdImageIfaces);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not open the medium storage unit '%s'%s"),
+                                       pMedium->m->strLocationFull.c_str(),
+                                       i_vdError(vrc).c_str());
+
+                /* Done when we hit the media which should be reset */
+                if (pMedium == this)
+                    break;
+            }
+
+            /* first, delete the storage unit */
+            vrc = VDClose(hdd, true /* fDelete */);
+            if (RT_FAILURE(vrc))
+                throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                   tr("Could not delete the medium storage unit '%s'%s"),
+                                   location.c_str(), i_vdError(vrc).c_str());
+
+            /* next, create it again */
+            vrc = VDOpen(hdd,
+                         parentFormat.c_str(),
+                         parentLocation.c_str(),
+                         VD_OPEN_FLAGS_READONLY | VD_OPEN_FLAGS_INFO | m->uOpenFlagsDef,
+                         m->vdImageIfaces);
+            if (RT_FAILURE(vrc))
+                throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                   tr("Could not open the medium storage unit '%s'%s"),
+                                   parentLocation.c_str(), i_vdError(vrc).c_str());
+
+            vrc = VDCreateDiff(hdd,
+                               format.c_str(),
+                               location.c_str(),
+                               /// @todo use the same medium variant as before
+                               VD_IMAGE_FLAGS_NONE,
+                               NULL,
+                               id.raw(),
+                               parentId.raw(),
+                               VD_OPEN_FLAGS_NORMAL,
+                               m->vdImageIfaces,
+                               task.mVDOperationIfaces);
+            if (RT_FAILURE(vrc))
+            {
+                if (vrc == VERR_VD_INVALID_TYPE)
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Parameters for creating the differencing medium storage unit '%s' are invalid%s"),
+                                       location.c_str(), i_vdError(vrc).c_str());
+                else
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not create the differencing medium storage unit '%s'%s"),
+                                       location.c_str(), i_vdError(vrc).c_str());
+            }
+
+            size = VDGetFileSize(hdd, VD_LAST_IMAGE);
+            logicalSize = VDGetSize(hdd, VD_LAST_IMAGE);
+            unsigned uImageFlags;
+            vrc = VDGetImageFlags(hdd, 0, &uImageFlags);
+            if (RT_SUCCESS(vrc))
+                variant = (MediumVariant_T)uImageFlags;
+        }
+        catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+    m->size = size;
+    m->logicalSize = logicalSize;
+    m->variant = variant;
+
+    if (task.NotifyAboutChanges() && SUCCEEDED(hrc))
+        m->pVirtualBox->i_onMediumConfigChanged(this);
+
+    /* Everything is explicitly unlocked when the task exits,
+     * as the task destruction also destroys the media chain. */
+
+    return hrc;
+}
+
+/**
+ * Implementation code for the "compact" task.
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskCompactHandler(Medium::CompactTask &task)
+{
+    HRESULT hrc = S_OK;
+
+    /* Lock all in {parent,child} order. The lock is also used as a
+     * signal from the task initiator (which releases it only after
+     * RTThreadCreate()) that we can start the job. */
+    AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+    try
+    {
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        try
+        {
+            /* Open all media in the chain. */
+            MediumLockList::Base::const_iterator mediumListBegin =
+                task.mpMediumLockList->GetBegin();
+            MediumLockList::Base::const_iterator mediumListEnd =
+                task.mpMediumLockList->GetEnd();
+            MediumLockList::Base::const_iterator mediumListLast =
+                mediumListEnd;
+            --mediumListLast;
+            for (MediumLockList::Base::const_iterator it = mediumListBegin;
+                 it != mediumListEnd;
+                 ++it)
+            {
+                const MediumLock &mediumLock = *it;
+                const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+                AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                /* sanity check */
+                if (it == mediumListLast)
+                    Assert(pMedium->m->state == MediumState_LockedWrite);
+                else
+                    Assert(pMedium->m->state == MediumState_LockedRead);
+
+                /* Open all media but last in read-only mode. Do not handle
+                 * shareable media, as compaction and sharing are mutually
+                 * exclusive. */
+                vrc = VDOpen(hdd,
+                             pMedium->m->strFormat.c_str(),
+                             pMedium->m->strLocationFull.c_str(),
+                             m->uOpenFlagsDef | (it == mediumListLast ? VD_OPEN_FLAGS_NORMAL : VD_OPEN_FLAGS_READONLY),
+                             pMedium->m->vdImageIfaces);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not open the medium storage unit '%s'%s"),
+                                       pMedium->m->strLocationFull.c_str(),
+                                       i_vdError(vrc).c_str());
+            }
+
+            Assert(m->state == MediumState_LockedWrite);
+
+            Utf8Str location(m->strLocationFull);
+
+            /* unlock before the potentially lengthy operation */
+            thisLock.release();
+
+            vrc = VDCompact(hdd, VD_LAST_IMAGE, task.mVDOperationIfaces);
+            if (RT_FAILURE(vrc))
+            {
+                if (vrc == VERR_NOT_SUPPORTED)
+                    throw setErrorBoth(VBOX_E_NOT_SUPPORTED, vrc,
+                                       tr("Compacting is not yet supported for medium '%s'"),
+                                       location.c_str());
+                else if (vrc == VERR_NOT_IMPLEMENTED)
+                    throw setErrorBoth(E_NOTIMPL, vrc,
+                                       tr("Compacting is not implemented, medium '%s'"),
+                                       location.c_str());
+                else
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not compact medium '%s'%s"),
+                                       location.c_str(),
+                                       i_vdError(vrc).c_str());
+            }
+        }
+        catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (task.NotifyAboutChanges() && SUCCEEDED(hrc))
+        m->pVirtualBox->i_onMediumConfigChanged(this);
+
+    /* Everything is explicitly unlocked when the task exits,
+     * as the task destruction also destroys the media chain. */
+
+    return hrc;
+}
+
+/**
+ * Implementation code for the "resize" task.
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskResizeHandler(Medium::ResizeTask &task)
+{
+    HRESULT hrc = S_OK;
+
+    uint64_t size = 0, logicalSize = 0;
+
+    try
+    {
+        /* The lock is also used as a signal from the task initiator (which
+         * releases it only after RTThreadCreate()) that we can start the job */
+        AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        try
+        {
+            /* Open all media in the chain. */
+            MediumLockList::Base::const_iterator mediumListBegin =
+                task.mpMediumLockList->GetBegin();
+            MediumLockList::Base::const_iterator mediumListEnd =
+                task.mpMediumLockList->GetEnd();
+            MediumLockList::Base::const_iterator mediumListLast =
+                mediumListEnd;
+            --mediumListLast;
+            for (MediumLockList::Base::const_iterator it = mediumListBegin;
+                 it != mediumListEnd;
+                 ++it)
+            {
+                const MediumLock &mediumLock = *it;
+                const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+                AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                /* sanity check */
+                if (it == mediumListLast)
+                    Assert(pMedium->m->state == MediumState_LockedWrite);
+                else
+                    Assert(pMedium->m->state == MediumState_LockedRead ||
+                           // Allow resize the target image during mergeTo in case
+                           // of direction from parent to child because all intermediate
+                           // images are marked to MediumState_Deleting and will be
+                           // destroyed after successful merge
+                           pMedium->m->state == MediumState_Deleting);
+
+                /* Open all media but last in read-only mode. Do not handle
+                 * shareable media, as compaction and sharing are mutually
+                 * exclusive. */
+                vrc = VDOpen(hdd,
+                             pMedium->m->strFormat.c_str(),
+                             pMedium->m->strLocationFull.c_str(),
+                             m->uOpenFlagsDef | (it == mediumListLast ? VD_OPEN_FLAGS_NORMAL : VD_OPEN_FLAGS_READONLY),
+                             pMedium->m->vdImageIfaces);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not open the medium storage unit '%s'%s"),
+                                       pMedium->m->strLocationFull.c_str(),
+                                       i_vdError(vrc).c_str());
+            }
+
+            Assert(m->state == MediumState_LockedWrite);
+
+            Utf8Str location(m->strLocationFull);
+
+            /* unlock before the potentially lengthy operation */
+            thisLock.release();
+
+            VDGEOMETRY geo = {0, 0, 0}; /* auto */
+            vrc = VDResize(hdd, task.mSize, &geo, &geo, task.mVDOperationIfaces);
+            if (RT_FAILURE(vrc))
+            {
+                if (vrc == VERR_VD_SHRINK_NOT_SUPPORTED)
+                    throw setErrorBoth(VBOX_E_NOT_SUPPORTED, vrc,
+                                       tr("Shrinking is not yet supported for medium '%s'"),
+                                       location.c_str());
+                if (vrc == VERR_NOT_SUPPORTED)
+                    throw setErrorBoth(VBOX_E_NOT_SUPPORTED, vrc,
+                                       tr("Resizing to new size %llu is not yet supported for medium '%s'"),
+                                       task.mSize, location.c_str());
+                else if (vrc == VERR_NOT_IMPLEMENTED)
+                    throw setErrorBoth(E_NOTIMPL, vrc,
+                                       tr("Resizing is not implemented, medium '%s'"),
+                                       location.c_str());
+                else
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not resize medium '%s'%s"),
+                                       location.c_str(),
+                                       i_vdError(vrc).c_str());
+            }
+            size = VDGetFileSize(hdd, VD_LAST_IMAGE);
+            logicalSize = VDGetSize(hdd, VD_LAST_IMAGE);
+        }
+        catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    if (SUCCEEDED(hrc))
+    {
+        AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+        m->size = size;
+        m->logicalSize = logicalSize;
+
+        if (task.NotifyAboutChanges())
+            m->pVirtualBox->i_onMediumConfigChanged(this);
+    }
+
+    /* Everything is explicitly unlocked when the task exits,
+     * as the task destruction also destroys the media chain. */
+
+    return hrc;
+}
+
+/**
+ * Implementation code for the "import" task.
+ *
+ * This only gets started from Medium::importFile() and always runs
+ * asynchronously. It potentially touches the media registry, so we
+ * always save the VirtualBox.xml file when we're done here.
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskImportHandler(Medium::ImportTask &task)
+{
+    /** @todo r=klaus The code below needs to be double checked with regard
+     * to lock order violations, it probably causes lock order issues related
+     * to the AutoCaller usage. */
+    HRESULT hrcTmp = S_OK;
+
+    const ComObjPtr<Medium> &pParent = task.mParent;
+
+    bool fCreatingTarget = false;
+
+    uint64_t size = 0, logicalSize = 0;
+    MediumVariant_T variant = MediumVariant_Standard;
+    bool fGenerateUuid = false;
+
+    try
+    {
+        if (!pParent.isNull())
+            if (pParent->i_getDepth() >= SETTINGS_MEDIUM_DEPTH_MAX)
+            {
+                AutoReadLock plock(pParent COMMA_LOCKVAL_SRC_POS);
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("Cannot import image for medium '%s', because it exceeds the medium tree depth limit. Please merge some images which you no longer need"),
+                               pParent->m->strLocationFull.c_str());
+            }
+
+        /* Lock all in {parent,child} order. The lock is also used as a
+         * signal from the task initiator (which releases it only after
+         * RTThreadCreate()) that we can start the job. */
+        AutoMultiWriteLock2 thisLock(this, pParent COMMA_LOCKVAL_SRC_POS);
+
+        fCreatingTarget = m->state == MediumState_Creating;
+
+        /* The object may request a specific UUID (through a special form of
+         * the moveTo() argument). Otherwise we have to generate it */
+        Guid targetId = m->id;
+
+        fGenerateUuid = targetId.isZero();
+        if (fGenerateUuid)
+        {
+            targetId.create();
+            /* VirtualBox::i_registerMedium() will need UUID */
+            unconst(m->id) = targetId;
+        }
+
+
+        PVDISK hdd;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &hdd);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        try
+        {
+            /* Open source medium. */
+            vrc = VDOpen(hdd,
+                         task.mFormat->i_getId().c_str(),
+                         task.mFilename.c_str(),
+                         VD_OPEN_FLAGS_READONLY | VD_OPEN_FLAGS_SEQUENTIAL | m->uOpenFlagsDef,
+                         task.mVDImageIfaces);
+            if (RT_FAILURE(vrc))
+                throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                   tr("Could not open the medium storage unit '%s'%s"),
+                                   task.mFilename.c_str(),
+                                   i_vdError(vrc).c_str());
+
+            Utf8Str targetFormat(m->strFormat);
+            Utf8Str targetLocation(m->strLocationFull);
+            uint64_t capabilities = task.mFormat->i_getCapabilities();
+
+            Assert(   m->state == MediumState_Creating
+                   || m->state == MediumState_LockedWrite);
+            Assert(   pParent.isNull()
+                   || pParent->m->state == MediumState_LockedRead);
+
+            /* unlock before the potentially lengthy operation */
+            thisLock.release();
+
+            /* ensure the target directory exists */
+            if (capabilities & MediumFormatCapabilities_File)
+            {
+                HRESULT hrc = VirtualBox::i_ensureFilePathExists(targetLocation,
+                                                                 !(task.mVariant & MediumVariant_NoCreateDir) /* fCreate */);
+                if (FAILED(hrc))
+                    throw hrc;
+            }
+
+            PVDISK targetHdd;
+            vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &targetHdd);
+            ComAssertRCThrow(vrc, E_FAIL);
+
+            try
+            {
+                /* Open all media in the target chain. */
+                MediumLockList::Base::const_iterator targetListBegin =
+                    task.mpTargetMediumLockList->GetBegin();
+                MediumLockList::Base::const_iterator targetListEnd =
+                    task.mpTargetMediumLockList->GetEnd();
+                for (MediumLockList::Base::const_iterator it = targetListBegin;
+                     it != targetListEnd;
+                     ++it)
+                {
+                    const MediumLock &mediumLock = *it;
+                    const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+
+                    /* If the target medium is not created yet there's no
+                     * reason to open it. */
+                    if (pMedium == this && fCreatingTarget)
+                        continue;
+
+                    AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                    /* sanity check */
+                    Assert(    pMedium->m->state == MediumState_LockedRead
+                            || pMedium->m->state == MediumState_LockedWrite);
+
+                    unsigned uOpenFlags = VD_OPEN_FLAGS_NORMAL;
+                    if (pMedium->m->state != MediumState_LockedWrite)
+                        uOpenFlags = VD_OPEN_FLAGS_READONLY;
+                    if (pMedium->m->type == MediumType_Shareable)
+                        uOpenFlags |= VD_OPEN_FLAGS_SHAREABLE;
+
+                    /* Open all media in appropriate mode. */
+                    vrc = VDOpen(targetHdd,
+                                 pMedium->m->strFormat.c_str(),
+                                 pMedium->m->strLocationFull.c_str(),
+                                 uOpenFlags | m->uOpenFlagsDef,
+                                 pMedium->m->vdImageIfaces);
+                    if (RT_FAILURE(vrc))
+                        throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                           tr("Could not open the medium storage unit '%s'%s"),
+                                           pMedium->m->strLocationFull.c_str(),
+                                           i_vdError(vrc).c_str());
+                }
+
+                vrc = VDCopy(hdd,
+                             VD_LAST_IMAGE,
+                             targetHdd,
+                             targetFormat.c_str(),
+                             (fCreatingTarget) ? targetLocation.c_str() : (char *)NULL,
+                             false /* fMoveByRename */,
+                             0 /* cbSize */,
+                             task.mVariant & ~(MediumVariant_NoCreateDir | MediumVariant_Formatted | MediumVariant_VmdkESX | MediumVariant_VmdkRawDisk),
+                             targetId.raw(),
+                             VD_OPEN_FLAGS_NORMAL,
+                             NULL /* pVDIfsOperation */,
+                             m->vdImageIfaces,
+                             task.mVDOperationIfaces);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not create the imported medium '%s'%s"),
+                                       targetLocation.c_str(), i_vdError(vrc).c_str());
+
+                size = VDGetFileSize(targetHdd, VD_LAST_IMAGE);
+                logicalSize = VDGetSize(targetHdd, VD_LAST_IMAGE);
+                unsigned uImageFlags;
+                vrc = VDGetImageFlags(targetHdd, 0, &uImageFlags);
+                if (RT_SUCCESS(vrc))
+                    variant = (MediumVariant_T)uImageFlags;
+            }
+            catch (HRESULT hrcXcpt) { hrcTmp = hrcXcpt; }
+
+            VDDestroy(targetHdd);
+        }
+        catch (HRESULT hrcXcpt) { hrcTmp = hrcXcpt; }
+
+        VDDestroy(hdd);
+    }
+    catch (HRESULT hrcXcpt) { hrcTmp = hrcXcpt; }
+
+    ErrorInfoKeeper eik;
+    MultiResult mrc(hrcTmp);
+
+    /* Only do the parent changes for newly created media. */
+    if (SUCCEEDED(mrc) && fCreatingTarget)
+    {
+        /* we set m->pParent & children() */
+        AutoWriteLock treeLock(m->pVirtualBox->i_getMediaTreeLockHandle() COMMA_LOCKVAL_SRC_POS);
+
+        Assert(m->pParent.isNull());
+
+        if (pParent)
+        {
+            /* Associate the imported medium with the parent and deassociate
+             * from VirtualBox. Depth check above. */
+            i_setParent(pParent);
+
+            /* register with mVirtualBox as the last step and move to
+             * Created state only on success (leaving an orphan file is
+             * better than breaking media registry consistency) */
+            eik.restore();
+            ComObjPtr<Medium> pMedium;
+            mrc = pParent->m->pVirtualBox->i_registerMedium(this, &pMedium,
+                                                            treeLock);
+            Assert(this == pMedium);
+            eik.fetch();
+
+            if (FAILED(mrc))
+                /* break parent association on failure to register */
+                this->i_deparent();     // removes target from parent
+        }
+        else
+        {
+            /* just register  */
+            eik.restore();
+            ComObjPtr<Medium> pMedium;
+            mrc = m->pVirtualBox->i_registerMedium(this, &pMedium, treeLock);
+            Assert(this == pMedium);
+            eik.fetch();
+        }
+    }
+
+    if (fCreatingTarget)
+    {
+        AutoWriteLock mLock(this COMMA_LOCKVAL_SRC_POS);
+
+        if (SUCCEEDED(mrc))
+        {
+            m->state = MediumState_Created;
+
+            m->size = size;
+            m->logicalSize = logicalSize;
+            m->variant = variant;
+        }
+        else
+        {
+            /* back to NotCreated on failure */
+            m->state = MediumState_NotCreated;
+
+            /* reset UUID to prevent it from being reused next time */
+            if (fGenerateUuid)
+                unconst(m->id).clear();
+        }
+    }
+
+    // now, at the end of this task (always asynchronous), save the settings
+    {
+        // save the settings
+        i_markRegistriesModified();
+        /* collect multiple errors */
+        eik.restore();
+        m->pVirtualBox->i_saveModifiedRegistries();
+        eik.fetch();
+    }
+
+    /* Everything is explicitly unlocked when the task exits,
+     * as the task destruction also destroys the target chain. */
+
+    /* Make sure the target chain is released early, otherwise it can
+     * lead to deadlocks with concurrent IAppliance activities. */
+    task.mpTargetMediumLockList->Clear();
+
+    if (task.NotifyAboutChanges() && SUCCEEDED(mrc))
+    {
+        if (pParent)
+            m->pVirtualBox->i_onMediumConfigChanged(pParent);
+        if (fCreatingTarget)
+            m->pVirtualBox->i_onMediumConfigChanged(this);
+        else
+            m->pVirtualBox->i_onMediumRegistered(m->id, m->devType, TRUE);
+    }
+
+    return mrc;
+}
+
+/**
+ * Sets up the encryption settings for a filter.
+ */
+void Medium::i_taskEncryptSettingsSetup(MediumCryptoFilterSettings *pSettings, const char *pszCipher,
+                                        const char *pszKeyStore, const char *pszPassword,
+                                        bool fCreateKeyStore)
+{
+    pSettings->pszCipher       = pszCipher;
+    pSettings->pszPassword     = pszPassword;
+    pSettings->pszKeyStoreLoad = pszKeyStore;
+    pSettings->fCreateKeyStore = fCreateKeyStore;
+    pSettings->pbDek           = NULL;
+    pSettings->cbDek           = 0;
+    pSettings->vdFilterIfaces  = NULL;
+
+    pSettings->vdIfCfg.pfnAreKeysValid = i_vdCryptoConfigAreKeysValid;
+    pSettings->vdIfCfg.pfnQuerySize    = i_vdCryptoConfigQuerySize;
+    pSettings->vdIfCfg.pfnQuery        = i_vdCryptoConfigQuery;
+    pSettings->vdIfCfg.pfnQueryBytes   = NULL;
+
+    pSettings->vdIfCrypto.pfnKeyRetain                = i_vdCryptoKeyRetain;
+    pSettings->vdIfCrypto.pfnKeyRelease               = i_vdCryptoKeyRelease;
+    pSettings->vdIfCrypto.pfnKeyStorePasswordRetain   = i_vdCryptoKeyStorePasswordRetain;
+    pSettings->vdIfCrypto.pfnKeyStorePasswordRelease  = i_vdCryptoKeyStorePasswordRelease;
+    pSettings->vdIfCrypto.pfnKeyStoreSave             = i_vdCryptoKeyStoreSave;
+    pSettings->vdIfCrypto.pfnKeyStoreReturnParameters = i_vdCryptoKeyStoreReturnParameters;
+
+    int vrc = VDInterfaceAdd(&pSettings->vdIfCfg.Core,
+                             "Medium::vdInterfaceCfgCrypto",
+                             VDINTERFACETYPE_CONFIG, pSettings,
+                             sizeof(VDINTERFACECONFIG), &pSettings->vdFilterIfaces);
+    AssertRC(vrc);
+
+    vrc = VDInterfaceAdd(&pSettings->vdIfCrypto.Core,
+                         "Medium::vdInterfaceCrypto",
+                         VDINTERFACETYPE_CRYPTO, pSettings,
+                         sizeof(VDINTERFACECRYPTO), &pSettings->vdFilterIfaces);
+    AssertRC(vrc);
+}
+
+/**
+ * Implementation code for the "encrypt" task.
+ *
+ * @param task
+ * @return
+ */
+HRESULT Medium::i_taskEncryptHandler(Medium::EncryptTask &task)
+{
+# ifndef VBOX_WITH_EXTPACK
+    RT_NOREF(task);
+# endif
+    HRESULT hrc = S_OK;
+
+    /* Lock all in {parent,child} order. The lock is also used as a
+     * signal from the task initiator (which releases it only after
+     * RTThreadCreate()) that we can start the job. */
+    ComObjPtr<Medium> pBase = i_getBase();
+    AutoWriteLock thisLock(this COMMA_LOCKVAL_SRC_POS);
+
+    try
+    {
+# ifdef VBOX_WITH_EXTPACK
+        ExtPackManager *pExtPackManager = m->pVirtualBox->i_getExtPackManager();
+        if (pExtPackManager->i_isExtPackUsable(ORACLE_PUEL_EXTPACK_NAME))
+        {
+            /* Load the plugin */
+            Utf8Str strPlugin;
+            hrc = pExtPackManager->i_getLibraryPathForExtPack(g_szVDPlugin, ORACLE_PUEL_EXTPACK_NAME, &strPlugin);
+            if (SUCCEEDED(hrc))
+            {
+                int vrc = VDPluginLoadFromFilename(strPlugin.c_str());
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_NOT_SUPPORTED, vrc,
+                                       tr("Encrypting the image failed because the encryption plugin could not be loaded (%s)"),
+                                       i_vdError(vrc).c_str());
+            }
+            else
+                throw setError(VBOX_E_NOT_SUPPORTED,
+                               tr("Encryption is not supported because the extension pack '%s' is missing the encryption plugin (old extension pack installed?)"),
+                               ORACLE_PUEL_EXTPACK_NAME);
+        }
+        else
+            throw setError(VBOX_E_NOT_SUPPORTED,
+                           tr("Encryption is not supported because the extension pack '%s' is missing"),
+                           ORACLE_PUEL_EXTPACK_NAME);
+
+        PVDISK pDisk = NULL;
+        int vrc = VDCreate(m->vdDiskIfaces, i_convertDeviceType(), &pDisk);
+        ComAssertRCThrow(vrc, E_FAIL);
+
+        MediumCryptoFilterSettings CryptoSettingsRead;
+        MediumCryptoFilterSettings CryptoSettingsWrite;
+
+        void *pvBuf = NULL;
+        const char *pszPasswordNew = NULL;
+        try
+        {
+            /* Set up disk encryption filters. */
+            if (task.mstrCurrentPassword.isEmpty())
+            {
+                /*
+                 * Query whether the medium property indicating that encryption is
+                 * configured is existing.
+                 */
+                settings::StringsMap::iterator it = pBase->m->mapProperties.find("CRYPT/KeyStore");
+                if (it != pBase->m->mapProperties.end())
+                    throw setError(VBOX_E_PASSWORD_INCORRECT,
+                                   tr("The password given for the encrypted image is incorrect"));
+            }
+            else
+            {
+                settings::StringsMap::iterator it = pBase->m->mapProperties.find("CRYPT/KeyStore");
+                if (it == pBase->m->mapProperties.end())
+                    throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                                   tr("The image is not configured for encryption"));
+
+                i_taskEncryptSettingsSetup(&CryptoSettingsRead, NULL, it->second.c_str(), task.mstrCurrentPassword.c_str(),
+                                           false /* fCreateKeyStore */);
+                vrc = VDFilterAdd(pDisk, "CRYPT", VD_FILTER_FLAGS_READ, CryptoSettingsRead.vdFilterIfaces);
+                if (vrc == VERR_VD_PASSWORD_INCORRECT)
+                    throw setError(VBOX_E_PASSWORD_INCORRECT,
+                                   tr("The password to decrypt the image is incorrect"));
+                else if (RT_FAILURE(vrc))
+                    throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                                   tr("Failed to load the decryption filter: %s"),
+                                   i_vdError(vrc).c_str());
+            }
+
+            if (task.mstrCipher.isNotEmpty())
+            {
+                if (   task.mstrNewPassword.isEmpty()
+                    && task.mstrNewPasswordId.isEmpty()
+                    && task.mstrCurrentPassword.isNotEmpty())
+                {
+                    /* An empty password and password ID will default to the current password. */
+                    pszPasswordNew = task.mstrCurrentPassword.c_str();
+                }
+                else if (task.mstrNewPassword.isEmpty())
+                    throw setError(VBOX_E_OBJECT_NOT_FOUND,
+                                   tr("A password must be given for the image encryption"));
+                else if (task.mstrNewPasswordId.isEmpty())
+                    throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                                   tr("A valid identifier for the password must be given"));
+                else
+                    pszPasswordNew = task.mstrNewPassword.c_str();
+
+                i_taskEncryptSettingsSetup(&CryptoSettingsWrite, task.mstrCipher.c_str(), NULL,
+                                           pszPasswordNew, true /* fCreateKeyStore */);
+                vrc = VDFilterAdd(pDisk, "CRYPT", VD_FILTER_FLAGS_WRITE, CryptoSettingsWrite.vdFilterIfaces);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_INVALID_OBJECT_STATE, vrc,
+                                       tr("Failed to load the encryption filter: %s"),
+                                       i_vdError(vrc).c_str());
+            }
+            else if (task.mstrNewPasswordId.isNotEmpty() || task.mstrNewPassword.isNotEmpty())
+                throw setError(VBOX_E_INVALID_OBJECT_STATE,
+                               tr("The password and password identifier must be empty if the output should be unencrypted"));
+
+            /* Open all media in the chain. */
+            MediumLockList::Base::const_iterator mediumListBegin =
+                task.mpMediumLockList->GetBegin();
+            MediumLockList::Base::const_iterator mediumListEnd =
+                task.mpMediumLockList->GetEnd();
+            MediumLockList::Base::const_iterator mediumListLast =
+                mediumListEnd;
+            --mediumListLast;
+            for (MediumLockList::Base::const_iterator it = mediumListBegin;
+                 it != mediumListEnd;
+                 ++it)
+            {
+                const MediumLock &mediumLock = *it;
+                const ComObjPtr<Medium> &pMedium = mediumLock.GetMedium();
+                AutoReadLock alock(pMedium COMMA_LOCKVAL_SRC_POS);
+
+                Assert(pMedium->m->state == MediumState_LockedWrite);
+
+                /* Open all media but last in read-only mode. Do not handle
+                 * shareable media, as compaction and sharing are mutually
+                 * exclusive. */
+                vrc = VDOpen(pDisk,
+                             pMedium->m->strFormat.c_str(),
+                             pMedium->m->strLocationFull.c_str(),
+                             m->uOpenFlagsDef | (it == mediumListLast ? VD_OPEN_FLAGS_NORMAL : VD_OPEN_FLAGS_READONLY),
+                             pMedium->m->vdImageIfaces);
+                if (RT_FAILURE(vrc))
+                    throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                       tr("Could not open the medium storage unit '%s'%s"),
+                                       pMedium->m->strLocationFull.c_str(),
+                                       i_vdError(vrc).c_str());
+            }
+
+            Assert(m->state == MediumState_LockedWrite);
+
+            Utf8Str location(m->strLocationFull);
+
+            /* unlock before the potentially lengthy operation */
+            thisLock.release();
+
+            vrc = VDPrepareWithFilters(pDisk, task.mVDOperationIfaces);
+            if (RT_FAILURE(vrc))
+                throw setErrorBoth(VBOX_E_FILE_ERROR, vrc,
+                                   tr("Could not prepare disk images for encryption (%Rrc): %s"),
+                                   vrc, i_vdError(vrc).c_str());
+
+            thisLock.acquire();
+            /* If everything went well set the new key store. */
+            settings::StringsMap::iterator it = pBase->m->mapProperties.find("CRYPT/KeyStore");
+            if (it != pBase->m->mapProperties.end())
+                pBase->m->mapProperties.erase(it);
+
+            /* Delete KeyId if encryption is removed or the password did change. */
+            if (   task.mstrNewPasswordId.isNotEmpty()
+                || task.mstrCipher.isEmpty())
+            {
+                it = pBase->m->mapProperties.find("CRYPT/KeyId");
+                if (it != pBase->m->mapProperties.end())
+                    pBase->m->mapProperties.erase(it);
+            }
+
+            if (CryptoSettingsWrite.pszKeyStore)
+            {
+                pBase->m->mapProperties["CRYPT/KeyStore"] = Utf8Str(CryptoSettingsWrite.pszKeyStore);
+                if (task.mstrNewPasswordId.isNotEmpty())
+                    pBase->m->mapProperties["CRYPT/KeyId"] = task.mstrNewPasswordId;
+            }
+
+            if (CryptoSettingsRead.pszCipherReturned)
+                RTStrFree(CryptoSettingsRead.pszCipherReturned);
+
+            if (CryptoSettingsWrite.pszCipherReturned)
+                RTStrFree(CryptoSettingsWrite.pszCipherReturned);
+
+            thisLock.release();
+            pBase->i_markRegistriesModified();
+            m->pVirtualBox->i_saveModifiedRegistries();
+        }
+        catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+        if (pvBuf)
+            RTMemFree(pvBuf);
+
+        VDDestroy(pDisk);
+# else
+        throw setError(VBOX_E_NOT_SUPPORTED,
+                       tr("Encryption is not supported because extension pack support is not built in"));
+# endif
+    }
+    catch (HRESULT hrcXcpt) { hrc = hrcXcpt; }
+
+    /* Everything is explicitly unlocked when the task exits,
+     * as the task destruction also destroys the media chain. */
+
+    return hrc;
+}
+
+/* vi: set tabstop=4 shiftwidth=4 expandtab: */