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, 2596 insertions, 0 deletions

diff --git a/src/VBox/Main/src-server/HostUSBDeviceImpl.cpp b/src/VBox/Main/src-server/HostUSBDeviceImpl.cpp
new file mode 100644
index 00000000..a6c612a5
--- /dev/null
+++ b/src/VBox/Main/src-server/HostUSBDeviceImpl.cpp
@@ -0,0 +1,2596 @@
+/* $Id: HostUSBDeviceImpl.cpp $ */
+/** @file
+ * VirtualBox IHostUSBDevice COM interface implementation.
+ */
+
+/*
+ * Copyright (C) 2005-2023 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_HOSTUSBDEVICE
+#include <iprt/types.h> /* for UINT64_C */
+
+#include "HostUSBDeviceImpl.h"
+#include "MachineImpl.h"
+#include "HostImpl.h"
+#include "VirtualBoxErrorInfoImpl.h"
+#include "USBProxyBackend.h"
+#include "USBIdDatabase.h"
+#include "LoggingNew.h"
+
+#include "AutoCaller.h"
+
+#include <VBox/err.h>
+#include <iprt/cpp/utils.h>
+
+// constructor / destructor
+/////////////////////////////////////////////////////////////////////////////
+
+DEFINE_EMPTY_CTOR_DTOR(HostUSBDevice)
+
+HRESULT HostUSBDevice::FinalConstruct()
+{
+    mUSBProxyBackend = NULL;
+    mUsb = NULL;
+
+    return BaseFinalConstruct();
+}
+
+void HostUSBDevice::FinalRelease()
+{
+    uninit();
+    BaseFinalRelease();
+}
+
+// public initializer/uninitializer for internal purposes only
+/////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Initializes the USB device object.
+ *
+ * @returns COM result indicator
+ * @param   aUsb                Pointer to the usb device structure for which the object is to be a wrapper.
+ *                              This structure is now fully owned by the HostUSBDevice object and will be
+ *                              freed when it is destructed.
+ * @param   aUSBProxyBackend    Pointer to the USB Proxy Backend object owning the device.
+ */
+HRESULT HostUSBDevice::init(PUSBDEVICE aUsb, USBProxyBackend *aUSBProxyBackend)
+{
+    ComAssertRet(aUsb, E_INVALIDARG);
+
+    /* Enclose the state transition NotReady->InInit->Ready */
+    AutoInitSpan autoInitSpan(this);
+    AssertReturn(autoInitSpan.isOk(), E_FAIL);
+
+    /*
+     * We need a unique ID for this VBoxSVC session.
+     * The UUID isn't stored anywhere.
+     */
+    unconst(mId).create();
+
+    /*
+     * Set the initial device state.
+     */
+    AssertMsgReturn(   aUsb->enmState >= USBDEVICESTATE_UNSUPPORTED
+                    && aUsb->enmState <  USBDEVICESTATE_USED_BY_GUEST, /* used-by-guest is not a legal initial state. */
+                    ("%d\n", aUsb->enmState), E_FAIL);
+    mUniState = (HostUSBDeviceState)aUsb->enmState;
+    mUniSubState = kHostUSBDeviceSubState_Default;
+    mPendingUniState = kHostUSBDeviceState_Invalid;
+    mPrevUniState = mUniState;
+    mIsPhysicallyDetached = false;
+
+    /* Other data members */
+    mUSBProxyBackend = aUSBProxyBackend;
+    mUsb = aUsb;
+
+    /* Set the name. */
+    mNameObj = i_getName();
+    mName = mNameObj.c_str();
+
+    /* Confirm the successful initialization */
+    autoInitSpan.setSucceeded();
+
+    return S_OK;
+}
+
+/**
+ *  Uninitializes the instance and sets the ready flag to FALSE.
+ *  Called either from FinalRelease() or by the parent when it gets destroyed.
+ */
+void HostUSBDevice::uninit()
+{
+    /* Enclose the state transition Ready->InUninit->NotReady */
+    AutoUninitSpan autoUninitSpan(this);
+    if (autoUninitSpan.uninitDone())
+        return;
+
+    if (mUsb != NULL)
+    {
+        USBProxyBackend::freeDevice(mUsb);
+        mUsb = NULL;
+    }
+
+    mUSBProxyBackend = NULL;
+    mUniState = kHostUSBDeviceState_Invalid;
+}
+
+// Wrapped IUSBDevice properties
+/////////////////////////////////////////////////////////////////////////////
+HRESULT HostUSBDevice::getId(com::Guid &aId)
+{
+    /* mId is constant during life time, no need to lock */
+    aId = mId;
+
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getVendorId(USHORT *aVendorId)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aVendorId = mUsb->idVendor;
+
+    return S_OK;
+}
+
+HRESULT HostUSBDevice::getProductId(USHORT *aProductId)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aProductId = mUsb->idProduct;
+
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getRevision(USHORT *aRevision)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aRevision = mUsb->bcdDevice;
+
+    return S_OK;
+}
+
+HRESULT HostUSBDevice::getManufacturer(com::Utf8Str &aManufacturer)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    aManufacturer = mUsb->pszManufacturer;
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getProduct(com::Utf8Str &aProduct)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    aProduct = mUsb->pszProduct;
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getSerialNumber(com::Utf8Str &aSerialNumber)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    aSerialNumber = mUsb->pszSerialNumber;
+
+    return S_OK;
+}
+
+HRESULT HostUSBDevice::getAddress(com::Utf8Str &aAddress)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+    aAddress = mUsb->pszAddress;
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getPort(USHORT *aPort)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aPort = mUsb->bPort;
+
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getPortPath(com::Utf8Str &aPortPath)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    aPortPath = mUsb->pszPortPath;
+
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getVersion(USHORT *aVersion)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aVersion = (USHORT)(mUsb->bcdUSB >> 8);
+
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getSpeed(USBConnectionSpeed_T *aSpeed)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    /* If the speed is unknown (which it shouldn't be), make a guess
+     * which will be correct for USB 1 and 3 devices, but may be wrong
+     * for USB 2.0 devices
+     */
+    switch (mUsb->enmSpeed)
+    {
+        case USBDEVICESPEED_LOW:        *aSpeed = USBConnectionSpeed_Low;       break;
+        case USBDEVICESPEED_FULL:       *aSpeed = USBConnectionSpeed_Full;      break;
+        case USBDEVICESPEED_HIGH:       *aSpeed = USBConnectionSpeed_High;      break;
+        case USBDEVICESPEED_SUPER:      *aSpeed = USBConnectionSpeed_Super;     break;
+//        case USBDEVICESPEED_SUPERPLUS:  *aSpeed = USBConnectionSpeed_SuperPlus; break;
+        default:
+            switch (mUsb->bcdUSB >> 8)
+            {
+                case 3:     *aSpeed = USBConnectionSpeed_Super; break;
+                case 2:     *aSpeed = USBConnectionSpeed_High;  break;
+                default:    *aSpeed = USBConnectionSpeed_Full;
+            }
+    }
+
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getPortVersion(USHORT *aPortVersion)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+    /* Port version is 2 (EHCI) if and only if the device runs at high speed;
+     * if speed is unknown, fall back to the old and inaccurate method.
+     */
+    if (mUsb->enmSpeed == USBDEVICESPEED_UNKNOWN)
+        *aPortVersion = (USHORT)(mUsb->bcdUSB >> 8);
+    else
+    {
+        switch (mUsb->enmSpeed)
+        {
+            case USBDEVICESPEED_SUPER:
+                *aPortVersion = 3;
+                break;
+            case USBDEVICESPEED_HIGH:
+                *aPortVersion = 2;
+                break;
+            case USBDEVICESPEED_FULL:
+            case USBDEVICESPEED_LOW:
+            case USBDEVICESPEED_VARIABLE:
+                *aPortVersion = 1;
+                break;
+            default:
+                AssertMsgFailed(("Invalid USB speed: %d\n", mUsb->enmSpeed));
+                *aPortVersion = 1;
+        }
+    }
+
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getRemote(BOOL *aRemote)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aRemote = FALSE;
+
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getState(USBDeviceState_T *aState)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    *aState = i_canonicalState();
+
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getBackend(com::Utf8Str &aBackend)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    aBackend = mUsb->pszBackend;
+
+    return S_OK;
+}
+
+
+HRESULT HostUSBDevice::getDeviceInfo(std::vector<com::Utf8Str> &aInfo)
+{
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    com::Utf8Str strManufacturer;
+    com::Utf8Str strProduct;
+
+    if (mUsb->pszManufacturer && *mUsb->pszManufacturer)
+        strManufacturer = mUsb->pszManufacturer;
+    else
+        strManufacturer = USBIdDatabase::findVendor(mUsb->idVendor);
+
+    if (mUsb->pszProduct && *mUsb->pszProduct)
+        strProduct = mUsb->pszProduct;
+    else
+        strProduct = USBIdDatabase::findProduct(mUsb->idVendor, mUsb->idProduct);
+
+    aInfo.resize(2);
+    aInfo[0] = strManufacturer;
+    aInfo[1] = strProduct;
+
+    return S_OK;
+}
+
+// public methods only for internal purposes
+////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * @note Locks this object for reading.
+ */
+com::Utf8Str HostUSBDevice::i_getName()
+{
+    Utf8Str name;
+
+    AutoCaller autoCaller(this);
+    AssertComRCReturn(autoCaller.hrc(), name);
+
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    bool haveManufacturer = mUsb->pszManufacturer && *mUsb->pszManufacturer;
+    bool haveProduct = mUsb->pszProduct && *mUsb->pszProduct;
+    if (haveManufacturer && haveProduct)
+        name = Utf8StrFmt("%s %s", mUsb->pszManufacturer, mUsb->pszProduct);
+    else
+    {
+        Utf8Str strProduct;
+        Utf8Str strVendor = USBIdDatabase::findVendorAndProduct(mUsb->idVendor, mUsb->idProduct, &strProduct);
+        if (   (strVendor.isNotEmpty() || haveManufacturer)
+            && (strProduct.isNotEmpty() || haveProduct))
+            name = Utf8StrFmt("%s %s", haveManufacturer ? mUsb->pszManufacturer
+                                                        : strVendor.c_str(),
+                                       haveProduct ? mUsb->pszProduct
+                                                   : strProduct.c_str());
+        else
+        {
+            LogRel(("USB: Unknown USB device detected (idVendor: 0x%04x, idProduct: 0x%04x)\n",
+                    mUsb->idVendor, mUsb->idProduct));
+            if (strVendor.isNotEmpty())
+                name = strVendor;
+            else
+            {
+                Assert(strProduct.isEmpty());
+                name = "<unknown>";
+            }
+        }
+    }
+
+    return name;
+}
+
+/**
+ * Requests the USB proxy service capture the device (from the host)
+ * and attach it to a VM.
+ *
+ * As a convenience, this method will operate like attachToVM() if the device
+ * is already held by the proxy. Note that it will then perform IPC to the VM
+ * process, which means it will temporarily release all locks. (Is this a good idea?)
+ *
+ * @param   aMachine         Machine this device should be attach to.
+ * @param   aSetError        Whether to set full error message or not to bother.
+ * @param   aCaptureFilename The filename to capture the USB traffic to.
+ * @param   aMaskedIfs       The interfaces to hide from the guest.
+ *
+ * @returns Status indicating whether it was successfully captured and/or attached.
+ * @retval  S_OK on success.
+ * @retval  E_UNEXPECTED if the device state doesn't permit for any attaching.
+ * @retval  E_* as appropriate.
+ */
+HRESULT HostUSBDevice::i_requestCaptureForVM(SessionMachine *aMachine, bool aSetError,
+                                             const com::Utf8Str &aCaptureFilename, ULONG aMaskedIfs /* = 0*/)
+{
+    /*
+     * Validate preconditions and input.
+     */
+    AssertReturn(aMachine, E_INVALIDARG);
+    AssertReturn(!isWriteLockOnCurrentThread(), E_FAIL);
+    AssertReturn(!aMachine->isWriteLockOnCurrentThread(), E_FAIL);
+
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+    LogFlowThisFunc(("{%s} aMachine=%p aMaskedIfs=%#x\n", mName, aMachine, aMaskedIfs));
+
+    if (aSetError)
+    {
+        if (mUniState == kHostUSBDeviceState_Unsupported)
+            return setError(E_INVALIDARG,
+                            tr("USB device '%s' with UUID {%RTuuid} cannot be accessed by guest computers"),
+                            mName, mId.raw());
+        if (mUniState == kHostUSBDeviceState_UsedByHost)
+            return setError(E_INVALIDARG,
+                            tr("USB device '%s' with UUID {%RTuuid} is being exclusively used by the host computer"),
+                            mName, mId.raw());
+        if (mUniState == kHostUSBDeviceState_UsedByVM)
+        {
+            /* Machine::name() requires a read lock */
+            alock.release();
+            AutoReadLock machLock(mMachine COMMA_LOCKVAL_SRC_POS);
+            return setError(E_INVALIDARG,
+                            tr("USB device '%s' with UUID {%RTuuid} is already captured by the virtual machine '%s'"),
+                            mName, mId.raw(), mMachine->i_getName().c_str());
+        }
+        if (mUniState >= kHostUSBDeviceState_FirstTransitional)
+            return setError(E_INVALIDARG,
+                            tr("USB device '%s' with UUID {%RTuuid} is busy with a previous request. Please try again later"),
+                             mName, mId.raw());
+        if (    mUniState != kHostUSBDeviceState_Unused
+            &&  mUniState != kHostUSBDeviceState_HeldByProxy
+            &&  mUniState != kHostUSBDeviceState_Capturable)
+            return setError(E_INVALIDARG,
+                            tr("USB device '%s' with UUID {%RTuuid} is not in the right state for capturing (%s)"),
+                            mName, mId.raw(), i_getStateName());
+    }
+
+    AssertReturn(   mUniState == kHostUSBDeviceState_HeldByProxy
+                 || mUniState == kHostUSBDeviceState_Unused
+                 || mUniState == kHostUSBDeviceState_Capturable,
+                 E_UNEXPECTED);
+    Assert(mMachine.isNull());
+
+    /*
+     * If it's already held by the proxy, we'll simply call
+     * attachToVM synchronously.
+     */
+    if (mUniState == kHostUSBDeviceState_HeldByProxy)
+    {
+        alock.release();
+        HRESULT hrc = i_attachToVM(aMachine, aCaptureFilename, aMaskedIfs);
+        return hrc;
+    }
+
+    /*
+     * Need to capture the device before it can be used.
+     *
+     * The device will be attached to the VM by the USB proxy service thread
+     * when the request succeeds (i.e. asynchronously).
+     */
+    LogFlowThisFunc(("{%s} capturing the device.\n", mName));
+    if (mUSBProxyBackend->i_isDevReEnumerationRequired())
+        i_setState(kHostUSBDeviceState_Capturing, kHostUSBDeviceState_UsedByVM, kHostUSBDeviceSubState_AwaitingDetach);
+    else
+        i_setState(kHostUSBDeviceState_Capturing, kHostUSBDeviceState_UsedByVM);
+
+    mMachine = aMachine;
+    mMaskedIfs = aMaskedIfs;
+    mCaptureFilename = aCaptureFilename;
+    alock.release();
+    int vrc = mUSBProxyBackend->captureDevice(this);
+    if (RT_FAILURE(vrc))
+    {
+        alock.acquire();
+        i_failTransition(kHostUSBDeviceState_Invalid);
+        mMachine.setNull();
+        if (vrc == VERR_SHARING_VIOLATION)
+            return setErrorBoth(E_FAIL, vrc,
+                                tr("USB device '%s' with UUID {%RTuuid} is in use by someone else"),
+                                mName, mId.raw());
+        return E_FAIL;
+    }
+
+    return S_OK;
+}
+
+/**
+ * Attempts to attach the USB device to a VM.
+ *
+ * The device must be in the HeldByProxy state or about to exit the
+ * Capturing state.
+ *
+ * This method will make an IPC to the VM process and do the actual
+ * attaching. While in the IPC locks will be abandond.
+ *
+ * @returns Status indicating whether it was successfully attached or not.
+ * @retval  S_OK on success.
+ * @retval  E_UNEXPECTED if the device state doesn't permit for any attaching.
+ * @retval  E_* as appropriate.
+ *
+ * @param   aMachine        Machine this device should be attach to.
+ * @param   aCaptureFilename Filename to capture the USB traffic to.
+ * @param   aMaskedIfs      The interfaces to hide from the guest.
+ */
+HRESULT HostUSBDevice::i_attachToVM(SessionMachine *aMachine, const com::Utf8Str &aCaptureFilename,
+                                    ULONG aMaskedIfs /* = 0*/)
+{
+    AssertReturn(!isWriteLockOnCurrentThread(), E_FAIL);
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+    /*
+     * Validate and update the state.
+     */
+    AssertReturn(   mUniState == kHostUSBDeviceState_Capturing
+                 || mUniState == kHostUSBDeviceState_HeldByProxy
+                 || mUniState == kHostUSBDeviceState_AttachingToVM,
+                 E_UNEXPECTED);
+    i_setState(kHostUSBDeviceState_AttachingToVM, kHostUSBDeviceState_UsedByVM);
+
+    /*
+     * The VM process will query the object, so grab a reference to ourselves and release the locks.
+     */
+    ComPtr<IUSBDevice> d = this;
+
+    /*
+     * Call the VM process (IPC) and request it to attach the device.
+     *
+     * There are many reasons for this to fail, so, as a consequence we don't
+     * assert the return code as it will crash the daemon and annoy the heck
+     * out of people.
+     */
+    LogFlowThisFunc(("{%s} Calling machine->onUSBDeviceAttach()...\n", mName));
+    alock.release();
+    HRESULT hrc = aMachine->i_onUSBDeviceAttach(d, NULL, aMaskedIfs, aCaptureFilename);
+    LogFlowThisFunc(("{%s} Done machine->onUSBDeviceAttach()=%08X\n", mName, hrc));
+
+    /*
+     * As we re-acquire the lock, we'll have to check if the device was
+     * physically detached while we were busy.
+     */
+    alock.acquire();
+
+    if (SUCCEEDED(hrc))
+    {
+        mMachine = aMachine;
+        if (!mIsPhysicallyDetached)
+            i_setState(kHostUSBDeviceState_UsedByVM);
+        else
+        {
+            alock.release();
+            i_detachFromVM(kHostUSBDeviceState_PhysDetached);
+            hrc = E_UNEXPECTED;
+        }
+    }
+    else
+    {
+        mMachine.setNull();
+        if (!mIsPhysicallyDetached)
+        {
+            i_setState(kHostUSBDeviceState_HeldByProxy);
+            if (hrc == E_UNEXPECTED)
+                hrc = E_FAIL; /* No confusion. */
+        }
+        else
+        {
+            alock.release();
+            i_onPhysicalDetachedInternal();
+            hrc = E_UNEXPECTED;
+        }
+    }
+    return hrc;
+}
+
+
+/**
+ * Detaches the device from the VM.
+ *
+ * This is used for a special scenario in attachToVM() and from
+ * onPhysicalDetachedInternal().
+ *
+ * @param   aFinalState     The final state (PhysDetached).
+ */
+void HostUSBDevice::i_detachFromVM(HostUSBDeviceState aFinalState)
+{
+    NOREF(aFinalState);
+
+    /*
+     * Assert preconditions.
+     */
+    Assert(aFinalState == kHostUSBDeviceState_PhysDetached);
+    AssertReturnVoid(!isWriteLockOnCurrentThread());
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+    Assert(   mUniState == kHostUSBDeviceState_AttachingToVM
+           || mUniState == kHostUSBDeviceState_UsedByVM);
+    Assert(!mMachine.isNull());
+
+    /*
+     * Change the state and abandon the locks. The VM may query
+     * data and we don't want to deadlock - the state protects us,
+     * so, it's not a bit issue here.
+     */
+    i_setState(kHostUSBDeviceState_PhysDetachingFromVM, kHostUSBDeviceState_PhysDetached);
+
+    /*
+     * Call the VM process (IPC) and request it to detach the device.
+     *
+     * There are many reasons for this to fail, so, as a consequence we don't
+     * assert the return code as it will crash the daemon and annoy the heck
+     * out of people.
+     */
+    alock.release();
+    LogFlowThisFunc(("{%s} Calling machine->onUSBDeviceDetach()...\n", mName));
+    HRESULT hrc = mMachine->i_onUSBDeviceDetach(mId.toUtf16().raw(), NULL);
+    LogFlowThisFunc(("{%s} Done machine->onUSBDeviceDetach()=%Rhrc\n", mName, hrc));
+    NOREF(hrc);
+
+    /*
+     * Re-acquire the locks and complete the transition.
+     */
+    alock.acquire();
+    i_advanceTransition();
+}
+
+/**
+ * Called when the VM process to inform us about the device being
+ * detached from it.
+ *
+ * This is NOT called when we detach the device via onUSBDeviceDetach.
+ *
+ *
+ * @param[in]   aMachine    The machine making the request.
+ *                          This must be the machine this device is currently attached to.
+ * @param[in]   aDone       When set to false, the VM just informs us that it's about
+ *                          to detach this device but hasn't done it just yet.
+ *                          When set to true, the VM informs us that it has completed
+ *                          the detaching of this device.
+ * @param[out]  aRunFilters Whether to run filters.
+ * @param[in]   aAbnormal   Set if we're cleaning up after a crashed VM.
+ *
+ * @returns S_OK on success, and E_UNEXPECTED if the device isn't in the right state.
+ *
+ * @note    Must be called from under the object write lock.
+ */
+HRESULT HostUSBDevice::i_onDetachFromVM(SessionMachine *aMachine, bool aDone, bool *aRunFilters, bool aAbnormal /*= true*/)
+{
+    LogFlowThisFunc(("{%s} state=%s aDone=%RTbool aAbnormal=%RTbool\n", mName, i_getStateName(), aDone, aAbnormal));
+
+    /*
+     * Validate preconditions.
+     */
+    AssertPtrReturn(aRunFilters, E_INVALIDARG);
+    AssertReturn(isWriteLockOnCurrentThread(), E_FAIL);
+    if (!aDone)
+    {
+        if (mUniState != kHostUSBDeviceState_UsedByVM)
+            return setError(E_INVALIDARG,
+                            tr("USB device '%s' with UUID {%RTuuid} is busy (state '%s'). Please try again later"),
+                            mName, mId.raw(), i_getStateName());
+    }
+    else
+        AssertMsgReturn(    mUniState == kHostUSBDeviceState_DetachingFromVM /** @todo capturing for VM
+                                                                                 ends up here on termination. */
+                        ||  (mUniState == kHostUSBDeviceState_UsedByVM && aAbnormal),
+                        ("{%s} %s\n", mName, i_getStateName()), E_UNEXPECTED);
+    AssertMsgReturn((mMachine == aMachine), ("%p != %p\n", (void *)mMachine, aMachine), E_FAIL);
+
+    /*
+     * Change the state.
+     */
+    if (!aDone)
+    {
+        *aRunFilters = i_startTransition(kHostUSBDeviceState_DetachingFromVM, kHostUSBDeviceState_HeldByProxy);
+        /* PORTME: This might require host specific changes if you re-enumerate the device. */
+    }
+    else if (aAbnormal && mUniState == kHostUSBDeviceState_UsedByVM)
+    {
+        /* Fast forward thru the DetachingFromVM state and on to HeldByProxy. */
+        /** @todo need to update the state machine to handle crashed VMs. */
+        i_startTransition(kHostUSBDeviceState_DetachingFromVM, kHostUSBDeviceState_HeldByProxy);
+        *aRunFilters = i_advanceTransition();
+        mMachine.setNull();
+        /* PORTME: ditto / trouble if you depend on the VM process to do anything. */
+    }
+    else
+    {
+        /* normal completion. */
+        Assert(mUniSubState == kHostUSBDeviceSubState_Default); /* PORTME: ditto */
+        *aRunFilters = i_advanceTransition();
+        mMachine.setNull();
+    }
+
+    return S_OK;
+}
+
+/**
+ * Requests the USB proxy service to release the device back to the host.
+ *
+ * This method will ignore (not assert) calls for devices that already
+ * belong to the host because it simplifies the usage a bit.
+ *
+ * @returns COM status code.
+ * @retval  S_OK on success.
+ * @retval  E_UNEXPECTED on bad state.
+ * @retval  E_* as appropriate.
+ *
+ * @note Must be called without holding the object lock.
+ */
+HRESULT HostUSBDevice::i_requestReleaseToHost()
+{
+    /*
+     * Validate preconditions.
+     */
+    AssertReturn(!isWriteLockOnCurrentThread(), E_FAIL);
+    Assert(mMachine.isNull());
+
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+    LogFlowThisFunc(("{%s}\n", mName));
+    if (    mUniState == kHostUSBDeviceState_Unused
+        ||  mUniState == kHostUSBDeviceState_Capturable)
+        return S_OK;
+    AssertMsgReturn(mUniState == kHostUSBDeviceState_HeldByProxy, ("{%s} %s\n", mName, i_getStateName()), E_UNEXPECTED);
+
+    /*
+     * Try release it.
+     */
+    if (mUSBProxyBackend->i_isDevReEnumerationRequired())
+        i_startTransition(kHostUSBDeviceState_ReleasingToHost, kHostUSBDeviceState_Unused, kHostUSBDeviceSubState_AwaitingDetach);
+    else
+        i_startTransition(kHostUSBDeviceState_ReleasingToHost, kHostUSBDeviceState_Unused);
+
+    alock.release();
+    int vrc = mUSBProxyBackend->releaseDevice(this);
+    if (RT_FAILURE(vrc))
+    {
+        alock.acquire();
+        i_failTransition(kHostUSBDeviceState_Invalid);
+        return E_FAIL;
+    }
+    return S_OK;
+}
+
+/**
+ * Requests the USB proxy service to capture and hold the device.
+ *
+ * The device must be owned by the host at the time of the call. But for
+ * the callers convenience, calling this method on a device that is already
+ * being held will success without any assertions.
+ *
+ * @returns COM status code.
+ * @retval  S_OK on success.
+ * @retval  E_UNEXPECTED on bad state.
+ * @retval  E_* as appropriate.
+ *
+ * @note Must be called without holding the object lock.
+ */
+HRESULT HostUSBDevice::i_requestHold()
+{
+    /*
+     * Validate preconditions.
+     */
+    AssertReturn(!isWriteLockOnCurrentThread(), E_FAIL);
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+    LogFlowThisFunc(("{%s}\n", mName));
+    AssertMsgReturn(   mUniState == kHostUSBDeviceState_Unused
+                    || mUniState == kHostUSBDeviceState_Capturable
+                    || mUniState == kHostUSBDeviceState_HeldByProxy,
+                    ("{%s} %s\n", mName, i_getStateName()),
+                    E_UNEXPECTED);
+
+    Assert(mMachine.isNull());
+    mMachine.setNull();
+
+    if (mUniState == kHostUSBDeviceState_HeldByProxy)
+        return S_OK;
+
+    /*
+     * Do the job.
+     */
+    if (mUSBProxyBackend->i_isDevReEnumerationRequired())
+        i_startTransition(kHostUSBDeviceState_Capturing, kHostUSBDeviceState_HeldByProxy, kHostUSBDeviceSubState_AwaitingDetach);
+    else
+        i_startTransition(kHostUSBDeviceState_Capturing, kHostUSBDeviceState_HeldByProxy);
+
+    alock.release();
+    int vrc = mUSBProxyBackend->captureDevice(this);
+    if (RT_FAILURE(vrc))
+    {
+        alock.acquire();
+        i_failTransition(kHostUSBDeviceState_Invalid);
+        return E_FAIL;
+    }
+    return S_OK;
+}
+
+
+/**
+ * Check a detach detected by the USB Proxy Service to see if
+ * it's a real one or just a logical following a re-enumeration.
+ *
+ * This will work the internal sub state of the device and do time
+ * outs, so it does more than just querying data!
+ *
+ * @returns true if it was actually detached, false if it's just a re-enumeration.
+ */
+bool HostUSBDevice::i_wasActuallyDetached()
+{
+    /*
+     * This only applies to the detach and re-attach states.
+     */
+    switch (mUniState)
+    {
+        case kHostUSBDeviceState_Capturing:
+        case kHostUSBDeviceState_ReleasingToHost:
+        case kHostUSBDeviceState_AttachingToVM:
+        case kHostUSBDeviceState_DetachingFromVM:
+            switch (mUniSubState)
+            {
+                /*
+                 * If we're awaiting a detach, the this has now occurred
+                 * and the state should be advanced.
+                 */
+                case kHostUSBDeviceSubState_AwaitingDetach:
+                    i_advanceTransition();
+                    return false; /* not physically detached. */
+
+                /*
+                 * Check for timeouts.
+                 */
+                case kHostUSBDeviceSubState_AwaitingReAttach:
+                {
+#ifndef RT_OS_WINDOWS /* check the implementation details here. */
+                    uint64_t elapsedNanoseconds = RTTimeNanoTS() - mLastStateChangeTS;
+                    if (elapsedNanoseconds > UINT64_C(60000000000)) /* 60 seconds */
+                    {
+                        LogRel(("USB: Async operation timed out for device %s (state: %s)\n", mName, i_getStateName()));
+                        i_failTransition(kHostUSBDeviceState_PhysDetached);
+                    }
+#endif
+                    return false; /* not physically detached. */
+                }
+
+                /* not applicable.*/
+                case kHostUSBDeviceSubState_Default:
+                    break;
+            }
+            break;
+
+        /* not applicable. */
+        case kHostUSBDeviceState_Unsupported:
+        case kHostUSBDeviceState_UsedByHost:
+        case kHostUSBDeviceState_Capturable:
+        case kHostUSBDeviceState_Unused:
+        case kHostUSBDeviceState_HeldByProxy:
+        case kHostUSBDeviceState_UsedByVM:
+        case kHostUSBDeviceState_PhysDetachingFromVM:
+        case kHostUSBDeviceState_PhysDetached:
+            break;
+
+        default:
+            AssertLogRelMsgFailed(("this=%p %s\n", this, i_getStateName()));
+            break;
+    }
+
+    /* It was detached. */
+    return true;
+}
+
+/**
+ * Notification from the USB Proxy that the device was physically detached.
+ *
+ * If a transition is pending, mIsPhysicallyDetached will be set and
+ * handled when the transition advances forward.
+ *
+ * Otherwise the device will be detached from any VM currently using it - this
+ * involves IPC and will temporarily abandon locks - and all the device data
+ * reset.
+ */
+void HostUSBDevice::i_onPhysicalDetached()
+{
+    AssertReturnVoid(!isWriteLockOnCurrentThread());
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+    LogFlowThisFunc(("{%s}\n", mName));
+
+    mIsPhysicallyDetached = true;
+    if (mUniState < kHostUSBDeviceState_FirstTransitional)
+    {
+        alock.release();
+        i_onPhysicalDetachedInternal();
+    }
+}
+
+
+/**
+ * Do the physical detach work for a device in a stable state or
+ * at a transition state change.
+ *
+ * See onPhysicalDetach() for details.
+ */
+void HostUSBDevice::i_onPhysicalDetachedInternal()
+{
+    AssertReturnVoid(!isWriteLockOnCurrentThread());
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+    LogFlowThisFunc(("{%s}\n", mName));
+    Assert(mIsPhysicallyDetached);
+
+    /*
+     * Do we need to detach it from the VM first?
+     */
+    if (    !mMachine.isNull()
+        &&  (   mUniState == kHostUSBDeviceState_UsedByVM
+             || mUniState == kHostUSBDeviceState_AttachingToVM))
+    {
+        alock.release();
+        i_detachFromVM(kHostUSBDeviceState_PhysDetached);
+        alock.acquire();
+    }
+    else
+        AssertMsg(mMachine.isNull(), ("%s\n", i_getStateName()));
+
+    /*
+     * Reset the data and enter the final state.
+     */
+    mMachine.setNull();
+    i_setState(kHostUSBDeviceState_PhysDetached);
+}
+
+
+/**
+ *  Returns true if this device matches the given filter data.
+ *
+ *  @note It is assumed, that the filter data owner is appropriately
+ *        locked before calling this method.
+ *
+ *  @note
+ *      This method MUST correlate with
+ *      USBController::hasMatchingFilter (IUSBDevice *)
+ *      in the sense of the device matching logic.
+ *
+ *  @note Locks this object for reading.
+ */
+bool HostUSBDevice::i_isMatch(const USBDeviceFilter::BackupableUSBDeviceFilterData &aData)
+{
+    AutoCaller autoCaller(this);
+    AssertComRCReturn(autoCaller.hrc(), false);
+
+    AutoReadLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    if (!aData.mData.fActive)
+        return false;
+
+    if (!aData.mRemote.isMatch(FALSE))
+        return false;
+
+    if (!USBFilterMatchDevice(&aData.mUSBFilter, mUsb))
+        return false;
+
+    /* Don't match busy devices with a 100% wildcard filter - this will
+       later become a filter prop (ring-3 only). */
+    if (    mUsb->enmState == USBDEVICESTATE_USED_BY_HOST_CAPTURABLE
+        &&  !USBFilterHasAnySubstatialCriteria(&aData.mUSBFilter))
+        return false;
+
+    LogFlowThisFunc(("returns true\n"));
+    return true;
+}
+
+/**
+ * Compares this device with a USBDEVICE and decides if the match or which comes first.
+ *
+ * This will take into account device re-attaching and omit the bits
+ * that may change during a device re-enumeration.
+ *
+ * @param   aDev2   Device 2.
+ *
+ * @returns < 0 if this should come before aDev2.
+ * @returns   0 if this and aDev2 are equal.
+ * @returns > 0 if this should come after aDev2.
+ *
+ * @note Must be called from under the object write lock.
+ */
+int HostUSBDevice::i_compare(PCUSBDEVICE aDev2)
+{
+    AssertReturn(isWriteLockOnCurrentThread(), -1);
+    //Log3(("%Rfn: %p {%s}\n", __PRETTY_FUNCTION__, this, mName));
+    return i_compare(mUsb, aDev2,
+                        mUniSubState == kHostUSBDeviceSubState_AwaitingDetach /* (In case we don't get the detach notice.) */
+                     || mUniSubState == kHostUSBDeviceSubState_AwaitingReAttach);
+}
+
+/**
+ * Compares two USBDEVICE structures and decides if the match or which comes first.
+ *
+ * @param   aDev1               Device 1.
+ * @param   aDev2               Device 2.
+ * @param   aIsAwaitingReAttach Whether to omit bits that will change in a device
+ *                              re-enumeration (true) or not (false).
+ *
+ * @returns < 0 if aDev1 should come before aDev2.
+ * @returns   0 if aDev1 and aDev2 are equal.
+ * @returns > 0 if aDev1 should come after aDev2.
+ */
+/*static*/
+int HostUSBDevice::i_compare(PCUSBDEVICE aDev1, PCUSBDEVICE aDev2, bool aIsAwaitingReAttach /*= false */)
+{
+    /* Comparing devices from different backends doesn't make any sense and should not happen. */
+    AssertReturn(!strcmp(aDev1->pszBackend, aDev2->pszBackend), -1);
+
+    /*
+     * Things that stays the same everywhere.
+     *
+     * The more uniquely these properties identifies a device the less the chance
+     * that we mix similar devices during re-enumeration. Bus+port would help
+     * provide ~99.8% accuracy if the host can provide those attributes.
+     */
+    int iDiff = aDev1->idVendor - aDev2->idVendor;
+    if (iDiff)
+        return iDiff;
+
+    iDiff = aDev1->idProduct - aDev2->idProduct;
+    if (iDiff)
+        return iDiff;
+
+    iDiff = aDev1->bcdDevice - aDev2->bcdDevice;
+    if (iDiff)
+    {
+        //Log3(("compare: bcdDevice: %#x != %#x\n", aDev1->bcdDevice, aDev2->bcdDevice));
+        return iDiff;
+    }
+
+#ifdef RT_OS_WINDOWS /* the string query may fail on windows during replugging, ignore serial mismatch if this is the case. */
+    if (    aDev1->u64SerialHash != aDev2->u64SerialHash
+        &&  (   !aIsAwaitingReAttach
+             || (aDev2->pszSerialNumber && *aDev2->pszSerialNumber)
+             || (aDev2->pszManufacturer && *aDev2->pszManufacturer)
+             || (aDev2->pszProduct      && *aDev2->pszProduct))
+       )
+#else
+    if (aDev1->u64SerialHash != aDev2->u64SerialHash)
+#endif
+    {
+        //Log3(("compare: u64SerialHash: %#llx != %#llx\n", aDev1->u64SerialHash, aDev2->u64SerialHash));
+        return aDev1->u64SerialHash < aDev2->u64SerialHash ? -1 : 1;
+    }
+
+    /* The hub/bus + port should help a lot in a re-attach situation. */
+#ifdef RT_OS_WINDOWS
+    /* The hub name makes only sense for the host backend. */
+    if (   !strcmp(aDev1->pszBackend, "host")
+        && aDev1->pszHubName
+        && aDev2->pszHubName)
+    {
+        iDiff = strcmp(aDev1->pszHubName, aDev2->pszHubName);
+        if (iDiff)
+        {
+            //Log3(("compare: HubName: %s != %s\n", aDev1->pszHubName, aDev2->pszHubName));
+            return iDiff;
+        }
+    }
+#else
+    iDiff = aDev1->bBus - aDev2->bBus;
+    if (iDiff)
+    {
+        //Log3(("compare: bBus: %#x != %#x\n", aDev1->bBus, aDev2->bBus));
+        return iDiff;
+    }
+#endif
+
+    iDiff = aDev1->bPort - aDev2->bPort;    /* shouldn't change anywhere and help pinpoint it very accurately. */
+    if (iDiff)
+    {
+        //Log3(("compare: bPort: %#x != %#x\n", aDev1->bPort, aDev2->bPort));
+        return iDiff;
+    }
+
+    /*
+     * Things that usually doesn't stay the same when re-enumerating
+     * a device. The fewer things in the category the better chance
+     * that we avoid messing up when more than one device of the same
+     * kind is attached.
+     */
+    if (aIsAwaitingReAttach)
+    {
+        //Log3(("aDev1=%p == aDev2=%p\n", aDev1, aDev2));
+        return 0;
+    }
+    /* device number always changes. */
+    return strcmp(aDev1->pszAddress, aDev2->pszAddress);
+}
+
+/**
+ *  Updates the state of the device.
+ *
+ *  If this method returns @c true, Host::onUSBDeviceStateChanged() will be
+ *  called to process the state change (complete the state change request,
+ *  inform the VM process etc.).
+ *
+ *  If this method returns @c false, it is assumed that the given state change
+ *  is "minor": it doesn't require any further action other than update the
+ *  mState field with the actual state value.
+ *
+ *  Regardless of the return value, this method always takes ownership of the
+ *  new USBDEVICE structure passed in and updates the pNext and pPrev fiends in
+ *  it using the values of the old structure.
+ *
+ * @param[in]   aDev            The current device state as seen by the proxy backend.
+ * @param[out]  aRunFilters     Whether the state change should be accompanied by
+ *                              running filters on the device.
+ * @param[out]  aIgnoreMachine  Machine to ignore when running filters.
+ *
+ * @returns Whether the Host object should be bothered with this state change.
+ *
+ * @todo    Just do everything here, that is, call filter runners and everything that
+ *          works by state change. Using 3 return codes/parameters is just plain ugly.
+ */
+bool HostUSBDevice::i_updateState(PCUSBDEVICE aDev, bool *aRunFilters, SessionMachine **aIgnoreMachine)
+{
+    *aRunFilters = false;
+    *aIgnoreMachine = NULL;
+
+    /*
+     * Locking.
+     */
+    AssertReturn(!isWriteLockOnCurrentThread(), false);
+    AutoCaller autoCaller(this);
+    AssertComRCReturn(autoCaller.hrc(), false);
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+
+    /*
+     * Replace the existing structure by the new one.
+     */
+    const USBDEVICESTATE enmOldState = mUsb->enmState; NOREF(enmOldState);
+    if (mUsb != aDev)
+    {
+#if defined(RT_OS_WINDOWS)
+        /* we used this logic of string comparison in HostUSBDevice::compare
+         * now we need to preserve strings from the old device if the new device has zero strings
+         * this ensures the device is correctly matched later on
+         * otherwise we may end up with a phantom misconfigured device instance */
+        if ((mUniSubState == kHostUSBDeviceSubState_AwaitingDetach /* (In case we don't get the detach notice.) */
+                   || mUniSubState == kHostUSBDeviceSubState_AwaitingReAttach)
+               && (!aDev->pszSerialNumber || !*aDev->pszSerialNumber)
+               && (!aDev->pszManufacturer || !*aDev->pszManufacturer)
+               && (!aDev->pszProduct      || !*aDev->pszProduct))
+        {
+            aDev->u64SerialHash = mUsb->u64SerialHash;
+
+            if (mUsb->pszSerialNumber && *mUsb->pszSerialNumber)
+            {
+                if (aDev->pszSerialNumber)
+                    RTStrFree((char *)aDev->pszSerialNumber);
+
+                /* since we're going to free old device later on,
+                 * we can just assign the string from it to the new device
+                 * and zero up the string filed for the old device */
+                aDev->pszSerialNumber = mUsb->pszSerialNumber;
+                mUsb->pszSerialNumber = NULL;
+            }
+
+            if (mUsb->pszManufacturer && *mUsb->pszManufacturer)
+            {
+                if (aDev->pszManufacturer)
+                    RTStrFree((char *)aDev->pszManufacturer);
+
+                /* since we're going to free old device later on,
+                 * we can just assign the string from it to the new device
+                 * and zero up the string filed for the old device */
+                aDev->pszManufacturer = mUsb->pszManufacturer;
+                mUsb->pszManufacturer = NULL;
+            }
+
+            if (mUsb->pszProduct && *mUsb->pszProduct)
+            {
+                if (aDev->pszProduct)
+                    RTStrFree((char *)aDev->pszProduct);
+
+                /* since we're going to free old device later on,
+                 * we can just assign the string from it to the new device
+                 * and zero up the string filed for the old device */
+                aDev->pszProduct = mUsb->pszProduct;
+                mUsb->pszProduct = NULL;
+            }
+        }
+#endif
+        aDev->pNext = mUsb->pNext;
+        aDev->pPrev = mUsb->pPrev;
+        USBProxyBackend::freeDevice(mUsb);
+        mUsb = aDev;
+    }
+
+/*
+ * Defined on hosts where we have a driver that keeps proper device states.
+ */
+# if defined(RT_OS_LINUX) || defined(RT_OS_DARWIN)
+#  define HOSTUSBDEVICE_FUZZY_STATE 1
+# else
+#  undef  HOSTUSBDEVICE_FUZZY_STATE
+# endif
+    /*
+     * For some hosts we'll have to be pretty careful here because
+     * they don't always have a clue what is going on. This is
+     * particularly true on linux and solaris, while windows and
+     * darwin generally knows a bit more.
+     */
+    bool fIsImportant = false;
+    if (enmOldState != mUsb->enmState)
+    {
+        LogFlowThisFunc(("%p {%s} %s\n", this, mName, i_getStateName()));
+        switch (mUsb->enmState)
+        {
+            /*
+             * Little fuzziness here, except where we fake capture.
+             */
+            case USBDEVICESTATE_USED_BY_HOST:
+                switch (mUniState)
+                {
+                    /* Host drivers installed, that's fine. */
+                    case kHostUSBDeviceState_Capturable:
+                    case kHostUSBDeviceState_Unused:
+                        LogThisFunc(("{%s} %s -> %s\n", mName, i_getStateName(), i_stateName(kHostUSBDeviceState_UsedByHost)));
+                        *aRunFilters = i_setState(kHostUSBDeviceState_UsedByHost);
+                        break;
+                    case kHostUSBDeviceState_UsedByHost:
+                        break;
+
+                    /* Can only mean that we've failed capturing it. */
+                    case kHostUSBDeviceState_Capturing:
+                        LogThisFunc(("{%s} capture failed! (#1)\n", mName));
+                        mUSBProxyBackend->captureDeviceCompleted(this, false /* aSuccess */);
+                        *aRunFilters = i_failTransition(kHostUSBDeviceState_UsedByHost);
+                        mMachine.setNull();
+                        break;
+
+                    /* Guess we've successfully released it. */
+                    case kHostUSBDeviceState_ReleasingToHost:
+                        LogThisFunc(("{%s} %s -> %s\n", mName, i_getStateName(), i_stateName(kHostUSBDeviceState_UsedByHost)));
+                        mUSBProxyBackend->releaseDeviceCompleted(this, true /* aSuccess */);
+                        *aRunFilters = i_setState(kHostUSBDeviceState_UsedByHost);
+                        break;
+
+                    /* These are IPC states and should be left alone. */
+                    case kHostUSBDeviceState_AttachingToVM:
+                    case kHostUSBDeviceState_DetachingFromVM:
+                    case kHostUSBDeviceState_PhysDetachingFromVM:
+                        LogThisFunc(("{%s} %s - changed to USED_BY_HOST...\n", mName, i_getStateName()));
+                        break;
+
+#ifdef HOSTUSBDEVICE_FUZZY_STATE
+                    /* Fake: We can't prevent anyone from grabbing it. */
+                    case kHostUSBDeviceState_HeldByProxy:
+                        LogThisFunc(("{%s} %s -> %s!\n", mName, i_getStateName(), i_stateName(kHostUSBDeviceState_UsedByHost)));
+                        *aRunFilters = i_setState(kHostUSBDeviceState_UsedByHost);
+                        break;
+                    //case kHostUSBDeviceState_UsedByVM:
+                    //    /** @todo needs to be detached from the VM. */
+                    //    break;
+#endif
+                    /* Not supposed to happen... */
+#ifndef HOSTUSBDEVICE_FUZZY_STATE
+                    case kHostUSBDeviceState_HeldByProxy:
+#endif
+                    case kHostUSBDeviceState_UsedByVM:
+                    case kHostUSBDeviceState_PhysDetached:
+                    case kHostUSBDeviceState_Unsupported:
+                    default:
+                        AssertMsgFailed(("{%s} %s\n", mName, i_getStateName()));
+                        break;
+                }
+                break;
+
+            /*
+             * It changed to capturable. Fuzzy hosts might easily
+             * confuse UsedByVM with this one.
+             */
+            case USBDEVICESTATE_USED_BY_HOST_CAPTURABLE:
+                switch (mUniState)
+                {
+                    /* No change. */
+#ifdef HOSTUSBDEVICE_FUZZY_STATE
+                    case kHostUSBDeviceState_HeldByProxy:
+                    case kHostUSBDeviceState_UsedByVM:
+#endif
+                    case kHostUSBDeviceState_Capturable:
+                        break;
+
+                    /* Changed! */
+                    case kHostUSBDeviceState_UsedByHost:
+                        fIsImportant = true;
+                        RT_FALL_THRU();
+                    case kHostUSBDeviceState_Unused:
+                        LogThisFunc(("{%s} %s -> %s\n", mName, i_getStateName(), i_stateName(kHostUSBDeviceState_Capturable)));
+                        *aRunFilters = i_setState(kHostUSBDeviceState_Capturable);
+                        break;
+
+                    /* Can only mean that we've failed capturing it. */
+                    case kHostUSBDeviceState_Capturing:
+                        LogThisFunc(("{%s} capture failed! (#2)\n", mName));
+                        mUSBProxyBackend->captureDeviceCompleted(this, false /* aSuccess */);
+                        *aRunFilters = i_failTransition(kHostUSBDeviceState_Capturable);
+                        mMachine.setNull();
+                        break;
+
+                    /* Guess we've successfully released it. */
+                    case kHostUSBDeviceState_ReleasingToHost:
+                        LogThisFunc(("{%s} %s -> %s\n", mName, i_getStateName(), i_stateName(kHostUSBDeviceState_Capturable)));
+                        mUSBProxyBackend->releaseDeviceCompleted(this, true /* aSuccess */);
+                        *aRunFilters = i_setState(kHostUSBDeviceState_Capturable);
+                        break;
+
+                    /* These are IPC states and should be left alone. */
+                    case kHostUSBDeviceState_AttachingToVM:
+                    case kHostUSBDeviceState_DetachingFromVM:
+                    case kHostUSBDeviceState_PhysDetachingFromVM:
+                        LogThisFunc(("{%s} %s - changed to USED_BY_HOST_CAPTURABLE...\n", mName, i_getStateName()));
+                        break;
+
+                    /* Not supposed to happen*/
+#ifndef HOSTUSBDEVICE_FUZZY_STATE
+                    case kHostUSBDeviceState_HeldByProxy:
+                    case kHostUSBDeviceState_UsedByVM:
+#endif
+                    case kHostUSBDeviceState_Unsupported:
+                    case kHostUSBDeviceState_PhysDetached:
+                    default:
+                        AssertMsgFailed(("{%s} %s\n", mName, i_getStateName()));
+                        break;
+                }
+                break;
+
+
+            /*
+             * It changed to capturable. Fuzzy hosts might easily
+             * confuse UsedByVM and HeldByProxy with this one.
+             */
+            case USBDEVICESTATE_UNUSED:
+                switch (mUniState)
+                {
+                    /* No change. */
+#ifdef HOSTUSBDEVICE_FUZZY_STATE
+                    case kHostUSBDeviceState_HeldByProxy:
+                    case kHostUSBDeviceState_UsedByVM:
+#endif
+                    case kHostUSBDeviceState_Unused:
+                        break;
+
+                    /* Changed! */
+                    case kHostUSBDeviceState_UsedByHost:
+                    case kHostUSBDeviceState_Capturable:
+                        fIsImportant = true;
+                        LogThisFunc(("{%s} %s -> %s\n", mName, i_getStateName(), i_stateName(kHostUSBDeviceState_Unused)));
+                        *aRunFilters = i_setState(kHostUSBDeviceState_Unused);
+                        break;
+
+                    /* Can mean that we've failed capturing it, but on windows it is the detach signal. */
+                    case kHostUSBDeviceState_Capturing:
+#if defined(RT_OS_WINDOWS)
+                        if (mUniSubState == kHostUSBDeviceSubState_AwaitingDetach)
+                        {
+                            LogThisFunc(("{%s} capture advancing thru UNUSED...\n", mName));
+                            *aRunFilters = i_advanceTransition();
+                        }
+                        else
+#endif
+                        {
+                            LogThisFunc(("{%s} capture failed! (#3)\n", mName));
+                            mUSBProxyBackend->captureDeviceCompleted(this, false /* aSuccess */);
+                            *aRunFilters = i_failTransition(kHostUSBDeviceState_Unused);
+                            mMachine.setNull();
+                        }
+                        break;
+
+                    /* Guess we've successfully released it. */
+                    case kHostUSBDeviceState_ReleasingToHost:
+                        LogThisFunc(("{%s} %s -> %s\n", mName, i_getStateName(), i_stateName(kHostUSBDeviceState_Unused)));
+                        mUSBProxyBackend->releaseDeviceCompleted(this, true /* aSuccess */);
+                        *aRunFilters = i_setState(kHostUSBDeviceState_Unused);
+                        break;
+
+                    /* These are IPC states and should be left alone. */
+                    case kHostUSBDeviceState_AttachingToVM:
+                    case kHostUSBDeviceState_DetachingFromVM:
+                    case kHostUSBDeviceState_PhysDetachingFromVM:
+                        LogThisFunc(("{%s} %s - changed to UNUSED...\n", mName, i_getStateName()));
+                        break;
+
+                    /* Not supposed to happen*/
+#ifndef HOSTUSBDEVICE_FUZZY_STATE
+                    case kHostUSBDeviceState_HeldByProxy:
+                    case kHostUSBDeviceState_UsedByVM:
+#endif
+                    case kHostUSBDeviceState_Unsupported:
+                    case kHostUSBDeviceState_PhysDetached:
+                    default:
+                        AssertMsgFailed(("{%s} %s\n", mName, i_getStateName()));
+                        break;
+                }
+                break;
+
+            /*
+             * This is pretty straight forward, except that everyone
+             * might sometimes confuse this and the UsedByVM state.
+             */
+            case USBDEVICESTATE_HELD_BY_PROXY:
+                switch (mUniState)
+                {
+                    /* No change. */
+                    case kHostUSBDeviceState_HeldByProxy:
+                        break;
+                    case kHostUSBDeviceState_UsedByVM:
+                        LogThisFunc(("{%s} %s - changed to HELD_BY_PROXY...\n", mName, i_getStateName()));
+                        break;
+
+                    /* Guess we've successfully captured it. */
+                    case kHostUSBDeviceState_Capturing:
+                        LogThisFunc(("{%s} capture succeeded!\n", mName));
+                        mUSBProxyBackend->captureDeviceCompleted(this, true /* aSuccess */);
+                        *aRunFilters = i_advanceTransition(true /* fast forward thru re-attach */);
+
+                        /* Take action if we're supposed to attach it to a VM. */
+                        if (mUniState == kHostUSBDeviceState_AttachingToVM)
+                        {
+                            alock.release();
+                            i_attachToVM(mMachine, mCaptureFilename, mMaskedIfs);
+                            alock.acquire();
+                        }
+                        break;
+
+                    /* Can only mean that we've failed capturing it. */
+                    case kHostUSBDeviceState_ReleasingToHost:
+                        LogThisFunc(("{%s} %s failed!\n", mName, i_getStateName()));
+                        mUSBProxyBackend->releaseDeviceCompleted(this, false /* aSuccess */);
+                        *aRunFilters = i_setState(kHostUSBDeviceState_HeldByProxy);
+                        break;
+
+                    /* These are IPC states and should be left alone. */
+                    case kHostUSBDeviceState_AttachingToVM:
+                    case kHostUSBDeviceState_DetachingFromVM:
+                    case kHostUSBDeviceState_PhysDetachingFromVM:
+                        LogThisFunc(("{%s} %s - changed to HELD_BY_PROXY...\n", mName, i_getStateName()));
+                        break;
+
+                    /* Not supposed to happen. */
+                    case kHostUSBDeviceState_Unsupported:
+                    case kHostUSBDeviceState_UsedByHost:
+                    case kHostUSBDeviceState_Capturable:
+                    case kHostUSBDeviceState_Unused:
+                    case kHostUSBDeviceState_PhysDetached:
+                    default:
+                        AssertMsgFailed(("{%s} %s\n", mName, i_getStateName()));
+                        break;
+                }
+                break;
+
+            /*
+             * This is very straight forward and only Darwin implements it.
+             */
+            case USBDEVICESTATE_USED_BY_GUEST:
+                switch (mUniState)
+                {
+                    /* No change. */
+                    case kHostUSBDeviceState_HeldByProxy:
+                        LogThisFunc(("{%s} %s - changed to USED_BY_GUEST...\n", mName, i_getStateName()));
+                        break;
+                    case kHostUSBDeviceState_UsedByVM:
+                        break;
+
+                    /* These are IPC states and should be left alone. */
+                    case kHostUSBDeviceState_AttachingToVM:
+                    case kHostUSBDeviceState_DetachingFromVM:
+                    case kHostUSBDeviceState_PhysDetachingFromVM:
+                        LogThisFunc(("{%s} %s - changed to USED_BY_GUEST...\n", mName, i_getStateName()));
+                        break;
+
+                    /* Not supposed to happen. */
+                    case kHostUSBDeviceState_Unsupported:
+                    case kHostUSBDeviceState_Capturable:
+                    case kHostUSBDeviceState_Unused:
+                    case kHostUSBDeviceState_UsedByHost:
+                    case kHostUSBDeviceState_PhysDetached:
+                    case kHostUSBDeviceState_ReleasingToHost:
+                    case kHostUSBDeviceState_Capturing:
+                    default:
+                        AssertMsgFailed(("{%s} %s\n", mName, i_getStateName()));
+                        break;
+                }
+                break;
+
+            /*
+             * This is not supposed to happen and indicates a bug in the backend!
+             */
+            case USBDEVICESTATE_UNSUPPORTED:
+                AssertMsgFailed(("enmOldState=%d {%s} %s\n", enmOldState, mName, i_getStateName()));
+                break;
+            default:
+                AssertMsgFailed(("enmState=%d {%s} %s\n", mUsb->enmState, mName, i_getStateName()));
+                break;
+        }
+    }
+    else if (   mUniSubState == kHostUSBDeviceSubState_AwaitingDetach
+             && i_hasAsyncOperationTimedOut())
+    {
+        LogRel(("USB: timeout in %s for {%RTuuid} / {%s}\n", i_getStateName(), mId.raw(), mName));
+        *aRunFilters = i_failTransition(kHostUSBDeviceState_Invalid);
+        fIsImportant = true;
+    }
+    else
+    {
+        LogFlowThisFunc(("%p {%s} %s - no change %d\n", this, mName, i_getStateName(), enmOldState));
+        /** @todo might have to handle some stuff here too if we cannot make the release/capture
+         *  handling deal with that above ... */
+    }
+
+    return fIsImportant;
+}
+
+
+/**
+ * Updates the state of the device, checking for cases which we fake.
+ *
+ * See HostUSBDevice::updateState() for details.
+ *
+ * @param[in]   aDev            See HostUSBDevice::updateState().
+ * @param[out]  aRunFilters     See HostUSBDevice::updateState()
+ * @param[out]  aIgnoreMachine  See HostUSBDevice::updateState()
+ *
+ * @returns See HostUSBDevice::updateState()
+ */
+bool HostUSBDevice::i_updateStateFake(PCUSBDEVICE aDev, bool *aRunFilters, SessionMachine **aIgnoreMachine)
+{
+    Assert(!isWriteLockOnCurrentThread());
+    AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
+    const HostUSBDeviceState enmState = mUniState;
+    switch (enmState)
+    {
+        case kHostUSBDeviceState_Capturing:
+        case kHostUSBDeviceState_ReleasingToHost:
+        {
+            *aIgnoreMachine = mUniState == kHostUSBDeviceState_ReleasingToHost ? mMachine : NULL;
+            *aRunFilters = i_advanceTransition();
+            LogThisFunc(("{%s} %s\n", mName, i_getStateName()));
+
+            if (mUsb != aDev)
+            {
+                aDev->pNext = mUsb->pNext;
+                aDev->pPrev = mUsb->pPrev;
+                USBProxyBackend::freeDevice(mUsb);
+                mUsb = aDev;
+            }
+
+            /* call the completion method */
+            if (enmState == kHostUSBDeviceState_Capturing)
+                mUSBProxyBackend->captureDeviceCompleted(this, true /* aSuccess */);
+            else
+                mUSBProxyBackend->releaseDeviceCompleted(this, true /* aSuccess */);
+
+            /* Take action if we're supposed to attach it to a VM. */
+            if (mUniState == kHostUSBDeviceState_AttachingToVM)
+            {
+                alock.release();
+                i_attachToVM(mMachine, mCaptureFilename, mMaskedIfs);
+            }
+            return true;
+        }
+
+        default:
+            alock.release();
+            return i_updateState(aDev, aRunFilters, aIgnoreMachine);
+    }
+}
+
+
+/**
+ * Checks if there is a pending asynchronous operation and whether
+ * it has timed out or not.
+ *
+ * @returns true on timeout, false if not.
+ *
+ * @note    Caller must have read or write locked the object before calling.
+ */
+bool HostUSBDevice::i_hasAsyncOperationTimedOut() const
+{
+    switch (mUniSubState)
+    {
+#ifndef RT_OS_WINDOWS /* no timeouts on windows yet since I don't have all the details here... */
+        case kHostUSBDeviceSubState_AwaitingDetach:
+        case kHostUSBDeviceSubState_AwaitingReAttach:
+        {
+            uint64_t elapsedNanoseconds = RTTimeNanoTS() - mLastStateChangeTS;
+            return elapsedNanoseconds > UINT64_C(60000000000); /* 60 seconds */  /* PORTME */
+        }
+#endif
+        default:
+            return false;
+    }
+}
+
+
+/**
+ * Translate the state into
+ *
+ * @returns
+ * @param   aState
+ * @param   aSubState
+ * @param   aPendingState
+ */
+/*static*/ const char *HostUSBDevice::i_stateName(HostUSBDeviceState aState,
+                                                  HostUSBDeviceState aPendingState /*= kHostUSBDeviceState_Invalid*/,
+                                                  HostUSBDeviceSubState aSubState /*= kHostUSBDeviceSubState_Default*/)
+{
+    switch (aState)
+    {
+        case kHostUSBDeviceState_Unsupported:
+            AssertReturn(aPendingState == kHostUSBDeviceState_Invalid, "Unsupported{bad}");
+            AssertReturn(aSubState == kHostUSBDeviceSubState_Default, "Unsupported[bad]");
+            return "Unsupported";
+
+        case kHostUSBDeviceState_UsedByHost:
+            AssertReturn(aPendingState == kHostUSBDeviceState_Invalid, "UsedByHost{bad}");
+            AssertReturn(aSubState == kHostUSBDeviceSubState_Default, "UsedByHost[bad]");
+            return "UsedByHost";
+
+        case kHostUSBDeviceState_Capturable:
+            AssertReturn(aPendingState == kHostUSBDeviceState_Invalid, "Capturable{bad}");
+            AssertReturn(aSubState == kHostUSBDeviceSubState_Default, "Capturable[bad]");
+            return "Capturable";
+
+        case kHostUSBDeviceState_Unused:
+            AssertReturn(aPendingState == kHostUSBDeviceState_Invalid, "Unused{bad}");
+            AssertReturn(aSubState == kHostUSBDeviceSubState_Default, "Unused[bad]");
+            return "Unused";
+
+        case kHostUSBDeviceState_HeldByProxy:
+            AssertReturn(aPendingState == kHostUSBDeviceState_Invalid, "HeldByProxy{bad}");
+            AssertReturn(aSubState == kHostUSBDeviceSubState_Default, "HeldByProxy[bad]");
+            return "HeldByProxy";
+
+        case kHostUSBDeviceState_UsedByVM:
+            AssertReturn(aPendingState == kHostUSBDeviceState_Invalid, "UsedByVM{bad}");
+            AssertReturn(aSubState == kHostUSBDeviceSubState_Default, "UsedByVM[bad]");
+            return "UsedByVM";
+
+        case kHostUSBDeviceState_PhysDetached:
+            AssertReturn(aPendingState == kHostUSBDeviceState_Invalid, "PhysDetached{bad}");
+            AssertReturn(aSubState == kHostUSBDeviceSubState_Default, "PhysDetached[bad]");
+            return "PhysDetached";
+
+        case kHostUSBDeviceState_Capturing:
+            switch (aPendingState)
+            {
+                case kHostUSBDeviceState_UsedByVM:
+                    switch (aSubState)
+                    {
+                        case kHostUSBDeviceSubState_Default:
+                            return "CapturingForVM";
+                        case kHostUSBDeviceSubState_AwaitingDetach:
+                            return "CapturingForVM[Detach]";
+                        case kHostUSBDeviceSubState_AwaitingReAttach:
+                            return "CapturingForVM[Attach]";
+                        default:
+                            AssertFailedReturn("CapturingForVM[bad]");
+                    }
+                    break;
+
+                case kHostUSBDeviceState_HeldByProxy:
+                    switch (aSubState)
+                    {
+                        case kHostUSBDeviceSubState_Default:
+                            return "CapturingForProxy";
+                        case kHostUSBDeviceSubState_AwaitingDetach:
+                            return "CapturingForProxy[Detach]";
+                        case kHostUSBDeviceSubState_AwaitingReAttach:
+                            return "CapturingForProxy[Attach]";
+                        default:
+                            AssertFailedReturn("CapturingForProxy[bad]");
+                    }
+                    break;
+
+                default:
+                    AssertFailedReturn("Capturing{bad}");
+            }
+            break;
+
+        case kHostUSBDeviceState_ReleasingToHost:
+            switch (aPendingState)
+            {
+                case kHostUSBDeviceState_Unused:
+                    switch (aSubState)
+                    {
+                        case kHostUSBDeviceSubState_Default:
+                            return "ReleasingToHost";
+                        case kHostUSBDeviceSubState_AwaitingDetach:
+                            return "ReleasingToHost[Detach]";
+                        case kHostUSBDeviceSubState_AwaitingReAttach:
+                            return "ReleasingToHost[Attach]";
+                        default:
+                            AssertFailedReturn("ReleasingToHost[bad]");
+                    }
+                    break;
+                default:
+                    AssertFailedReturn("ReleasingToHost{bad}");
+            }
+            break;
+
+        case kHostUSBDeviceState_DetachingFromVM:
+            switch (aPendingState)
+            {
+                case kHostUSBDeviceState_HeldByProxy:
+                    switch (aSubState)
+                    {
+                        case kHostUSBDeviceSubState_Default:
+                            return "DetatchingFromVM>Proxy";
+                        case kHostUSBDeviceSubState_AwaitingDetach:
+                            return "DetatchingFromVM>Proxy[Detach]";
+                        case kHostUSBDeviceSubState_AwaitingReAttach:
+                            return "DetatchingFromVM>Proxy[Attach]";
+                        default:
+                            AssertFailedReturn("DetatchingFromVM>Proxy[bad]");
+                    }
+                    break;
+
+                case kHostUSBDeviceState_Unused:
+                    switch (aSubState)
+                    {
+                        case kHostUSBDeviceSubState_Default:
+                            return "DetachingFromVM>Host";
+                        case kHostUSBDeviceSubState_AwaitingDetach:
+                            return "DetachingFromVM>Host[Detach]";
+                        case kHostUSBDeviceSubState_AwaitingReAttach:
+                            return "DetachingFromVM>Host[Attach]";
+                        default:
+                            AssertFailedReturn("DetachingFromVM>Host[bad]");
+                    }
+                    break;
+
+                default:
+                    AssertFailedReturn("DetachingFromVM{bad}");
+            }
+            break;
+
+        case kHostUSBDeviceState_AttachingToVM:
+            switch (aPendingState)
+            {
+                case kHostUSBDeviceState_UsedByVM:
+                    switch (aSubState)
+                    {
+                        case kHostUSBDeviceSubState_Default:
+                            return "AttachingToVM";
+                        case kHostUSBDeviceSubState_AwaitingDetach:
+                            return "AttachingToVM[Detach]";
+                        case kHostUSBDeviceSubState_AwaitingReAttach:
+                            return "AttachingToVM[Attach]";
+                        default:
+                            AssertFailedReturn("AttachingToVM[bad]");
+                    }
+                    break;
+
+                default:
+                    AssertFailedReturn("AttachingToVM{bad}");
+            }
+            break;
+
+
+        case kHostUSBDeviceState_PhysDetachingFromVM:
+            switch (aPendingState)
+            {
+                case kHostUSBDeviceState_PhysDetached:
+                    switch (aSubState)
+                    {
+                        case kHostUSBDeviceSubState_Default:
+                            return "PhysDetachingFromVM";
+                        default:
+                            AssertFailedReturn("AttachingToVM[bad]");
+                    }
+                    break;
+
+                default:
+                    AssertFailedReturn("AttachingToVM{bad}");
+            }
+            break;
+
+        default:
+            AssertFailedReturn("BadState");
+
+    }
+    /* not reached */
+}
+
+/**
+ * Set the device state.
+ *
+ * This method will verify that the state transition is a legal one
+ * according to the statemachine. It will also take care of the
+ * associated house keeping and determine if filters needs to be applied.
+ *
+ * @param   aNewState           The new state.
+ * @param   aNewPendingState    The final state of a transition when applicable.
+ * @param   aNewSubState        The new sub-state when applicable.
+ *
+ * @returns true if filters should be applied to the device, false if not.
+ *
+ * @note    The caller must own the write lock for this object.
+ */
+bool HostUSBDevice::i_setState(HostUSBDeviceState aNewState,
+                               HostUSBDeviceState aNewPendingState /*= kHostUSBDeviceState_Invalid*/,
+                               HostUSBDeviceSubState aNewSubState /*= kHostUSBDeviceSubState_Default*/)
+{
+    Assert(isWriteLockOnCurrentThread());
+    Assert(    aNewSubState == kHostUSBDeviceSubState_Default
+           ||  aNewSubState == kHostUSBDeviceSubState_AwaitingDetach
+           ||  aNewSubState == kHostUSBDeviceSubState_AwaitingReAttach);
+
+    /*
+     * If the state is unchanged, then don't bother going
+     * thru the validation and setting. This saves a bit of code.
+     */
+    if (   aNewState == mUniState
+        && aNewPendingState == mPendingUniState
+        && aNewSubState == mUniSubState)
+        return false;
+
+    /*
+     * Welcome to the switch orgies!
+     * You're welcome to check out the ones in startTransition(),
+     * advanceTransition(), failTransition() and i_getStateName() too. Enjoy!
+     */
+
+    bool fFilters = false;
+    HostUSBDeviceState NewPrevState = mUniState;
+    switch (mUniState)
+    {
+        /*
+         * Not much can be done with a device in this state.
+         */
+        case kHostUSBDeviceState_Unsupported:
+            switch (aNewState)
+            {
+                case kHostUSBDeviceState_PhysDetached:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+        /*
+         * Only the host OS (or the user) can make changes
+         * that'll make a device get out of this state.
+         */
+        case kHostUSBDeviceState_UsedByHost:
+            switch (aNewState)
+            {
+                case kHostUSBDeviceState_Capturable:
+                case kHostUSBDeviceState_Unused:
+                    fFilters = true;
+                    RT_FALL_THRU();
+                case kHostUSBDeviceState_PhysDetached:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+        /*
+         * Now it gets interesting.
+         */
+        case kHostUSBDeviceState_Capturable:
+            switch (aNewState)
+            {
+                /* Host changes. */
+                case kHostUSBDeviceState_Unused:
+                    fFilters = true; /* Wildcard only... */
+                    RT_FALL_THRU();
+                case kHostUSBDeviceState_UsedByHost:
+                case kHostUSBDeviceState_PhysDetached:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+
+                /* VBox actions */
+                case kHostUSBDeviceState_Capturing:
+                    switch (aNewPendingState)
+                    {
+                        case kHostUSBDeviceState_HeldByProxy:
+                        case kHostUSBDeviceState_UsedByVM:
+                            break;
+                        default:
+                            AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                         i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+                    }
+                    break;
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_Unused:
+            switch (aNewState)
+            {
+                /* Host changes. */
+                case kHostUSBDeviceState_PhysDetached:
+                case kHostUSBDeviceState_UsedByHost:
+                case kHostUSBDeviceState_Capturable:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+
+                /* VBox actions */
+                case kHostUSBDeviceState_Capturing:
+                    switch (aNewPendingState)
+                    {
+                        case kHostUSBDeviceState_HeldByProxy:
+                        case kHostUSBDeviceState_UsedByVM:
+                            break;
+                        default:
+                            AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                         i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+                    }
+                    break;
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+        /*
+         * VBox owns this device now, what's next...
+         */
+        case kHostUSBDeviceState_HeldByProxy:
+            switch (aNewState)
+            {
+                /* Host changes. */
+                case kHostUSBDeviceState_PhysDetached:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+
+                /* VBox actions */
+                case kHostUSBDeviceState_AttachingToVM:
+                    switch (aNewPendingState)
+                    {
+                        case kHostUSBDeviceState_UsedByVM:
+                            break;
+                        default:
+                            AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                         i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+                    }
+                    break;
+                case kHostUSBDeviceState_ReleasingToHost:
+                    switch (aNewPendingState)
+                    {
+                        case kHostUSBDeviceState_Unused: /* Only this! */
+                            break;
+                        default:
+                            AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                         i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+                    }
+                    break;
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+
+        case kHostUSBDeviceState_UsedByVM:
+            switch (aNewState)
+            {
+                /* Host changes. */
+                case kHostUSBDeviceState_PhysDetachingFromVM:
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    Assert(aNewPendingState == kHostUSBDeviceState_PhysDetached);
+                    break;
+
+                /* VBox actions */
+                case kHostUSBDeviceState_DetachingFromVM:
+                    switch (aNewPendingState)
+                    {
+                        case kHostUSBDeviceState_HeldByProxy:
+                        case kHostUSBDeviceState_Unused: /* Only this! */
+                            break;
+                        default:
+                            AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                         i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+                    }
+                    break;
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+        /*
+         * The final state.
+         */
+        case kHostUSBDeviceState_PhysDetached:
+            switch (mUniState)
+            {
+                case kHostUSBDeviceState_Unsupported:
+                case kHostUSBDeviceState_UsedByHost:
+                case kHostUSBDeviceState_Capturable:
+                case kHostUSBDeviceState_Unused:
+                case kHostUSBDeviceState_HeldByProxy:
+                case kHostUSBDeviceState_PhysDetachingFromVM:
+                case kHostUSBDeviceState_DetachingFromVM: // ??
+                case kHostUSBDeviceState_Capturing:
+                case kHostUSBDeviceState_ReleasingToHost:
+                    break;
+
+                case kHostUSBDeviceState_AttachingToVM: // ??
+                case kHostUSBDeviceState_UsedByVM:
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+
+        /*
+         * The transitional states.
+         */
+        case kHostUSBDeviceState_Capturing:
+            NewPrevState = mPrevUniState;
+            switch (aNewState)
+            {
+                /* Sub state advance. */
+                case kHostUSBDeviceState_Capturing:
+                    switch (aNewSubState)
+                    {
+                        case kHostUSBDeviceSubState_AwaitingReAttach:
+                            Assert(mUniSubState == kHostUSBDeviceSubState_AwaitingDetach);
+                            Assert(aNewPendingState == mPendingUniState);
+                            break;
+                        default:
+                            AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+                    }
+                    break;
+
+                /* Host/User/Failure. */
+                case kHostUSBDeviceState_PhysDetached:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+                case kHostUSBDeviceState_UsedByHost:
+                case kHostUSBDeviceState_Capturable:
+                case kHostUSBDeviceState_Unused:
+                    Assert(aNewState == mPrevUniState); /** @todo This is kind of wrong, see i_failTransition. */
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+
+                /* VBox */
+                case kHostUSBDeviceState_HeldByProxy:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    Assert(   mPendingUniState == kHostUSBDeviceState_HeldByProxy
+                           || mPendingUniState == kHostUSBDeviceState_UsedByVM /* <- failure */ );
+                    break;
+                case kHostUSBDeviceState_AttachingToVM:
+                    Assert(aNewPendingState == kHostUSBDeviceState_UsedByVM);
+                    NewPrevState = kHostUSBDeviceState_HeldByProxy;
+                    break;
+
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_ReleasingToHost:
+            Assert(mPrevUniState == kHostUSBDeviceState_HeldByProxy);
+            NewPrevState = mPrevUniState;
+            switch (aNewState)
+            {
+                /* Sub state advance. */
+                case kHostUSBDeviceState_ReleasingToHost:
+                    switch (aNewSubState)
+                    {
+                        case kHostUSBDeviceSubState_AwaitingReAttach:
+                            Assert(mUniSubState == kHostUSBDeviceSubState_AwaitingDetach);
+                            Assert(aNewPendingState == mPendingUniState);
+                            break;
+                        default:
+                            AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+                    }
+                    break;
+
+                /* Host/Failure. */
+                case kHostUSBDeviceState_PhysDetached:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+                case kHostUSBDeviceState_HeldByProxy:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    Assert(mPendingUniState == kHostUSBDeviceState_Unused);
+                    break;
+
+                /* Success */
+                case kHostUSBDeviceState_UsedByHost:
+                case kHostUSBDeviceState_Capturable:
+                case kHostUSBDeviceState_Unused:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    Assert(mPendingUniState == kHostUSBDeviceState_Unused);
+                    break;
+
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_AttachingToVM:
+            Assert(mPrevUniState == kHostUSBDeviceState_HeldByProxy);
+            NewPrevState = mPrevUniState;
+            switch (aNewState)
+            {
+                /* Host/Failure. */
+                case kHostUSBDeviceState_PhysDetachingFromVM:
+                    Assert(aNewPendingState == kHostUSBDeviceState_PhysDetached);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+                case kHostUSBDeviceState_HeldByProxy:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    Assert(mPendingUniState == kHostUSBDeviceState_UsedByVM);
+                    break;
+
+                /* Success */
+                case kHostUSBDeviceState_UsedByVM:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    Assert(mPendingUniState == kHostUSBDeviceState_UsedByVM);
+                    break;
+
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_DetachingFromVM:
+            Assert(mPrevUniState == kHostUSBDeviceState_UsedByVM);
+            NewPrevState = mPrevUniState;
+            switch (aNewState)
+            {
+                /* Host/Failure. */
+                case kHostUSBDeviceState_PhysDetached: //??
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+                case kHostUSBDeviceState_PhysDetachingFromVM:
+                    Assert(aNewPendingState == kHostUSBDeviceState_PhysDetached);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+
+                /* Success */
+                case kHostUSBDeviceState_HeldByProxy:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    Assert(mPendingUniState == kHostUSBDeviceState_HeldByProxy);
+                    fFilters = true;
+                    break;
+
+                case kHostUSBDeviceState_ReleasingToHost:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    Assert(mPendingUniState == kHostUSBDeviceState_Unused);
+                    NewPrevState = kHostUSBDeviceState_HeldByProxy;
+                    break;
+
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_PhysDetachingFromVM:
+            Assert(   mPrevUniState == kHostUSBDeviceState_DetachingFromVM
+                   || mPrevUniState == kHostUSBDeviceState_AttachingToVM
+                   || mPrevUniState == kHostUSBDeviceState_UsedByVM);
+            NewPrevState = mPrevUniState; /* preserving it is more useful. */
+            switch (aNewState)
+            {
+                case kHostUSBDeviceState_PhysDetached:
+                    Assert(aNewPendingState == kHostUSBDeviceState_Invalid);
+                    Assert(aNewSubState == kHostUSBDeviceSubState_Default);
+                    break;
+                default:
+                    AssertLogRelMsgFailedReturn(("this=%p %s -X-> %s\n", this, i_getStateName(),
+                                                 i_stateName(aNewState, aNewPendingState, aNewSubState)), false);
+            }
+            break;
+
+        default:
+            AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+    }
+
+    /*
+     * Make the state change.
+     */
+    if (NewPrevState != mPrevUniState)
+        LogFlowThisFunc(("%s -> %s (prev: %s -> %s) [%s]\n",
+                         i_getStateName(), i_stateName(aNewState, aNewPendingState, aNewSubState),
+                         i_stateName(mPrevUniState), i_stateName(NewPrevState), mName));
+    else
+        LogFlowThisFunc(("%s -> %s (prev: %s) [%s]\n",
+                         i_getStateName(), i_stateName(aNewState, aNewPendingState, aNewSubState),
+                         i_stateName(NewPrevState), mName));
+    mPrevUniState = NewPrevState;
+    mUniState = aNewState;
+    mUniSubState = aNewSubState;
+    mPendingUniState = aNewPendingState;
+    mLastStateChangeTS = RTTimeNanoTS();
+
+    return fFilters;
+}
+
+
+/**
+ * A convenience for entering a transitional state.
+
+ * @param   aNewState       The new state (transitional).
+ * @param   aFinalState     The final state of the transition (non-transitional).
+ * @param   aNewSubState    The new sub-state when applicable.
+ *
+ * @returns Always false because filters are never applied for the start of a transition.
+ *
+ * @note    The caller must own the write lock for this object.
+ */
+bool HostUSBDevice::i_startTransition(HostUSBDeviceState aNewState, HostUSBDeviceState aFinalState,
+                                      HostUSBDeviceSubState aNewSubState /*= kHostUSBDeviceSubState_Default*/)
+{
+    AssertReturn(isWriteLockOnCurrentThread(), false);
+    /*
+     * A quick prevalidation thing. Not really necessary since setState
+     * verifies this too, but it's very easy here.
+     */
+    switch (mUniState)
+    {
+        case kHostUSBDeviceState_Unsupported:
+        case kHostUSBDeviceState_UsedByHost:
+        case kHostUSBDeviceState_Capturable:
+        case kHostUSBDeviceState_Unused:
+        case kHostUSBDeviceState_HeldByProxy:
+        case kHostUSBDeviceState_UsedByVM:
+            break;
+
+        case kHostUSBDeviceState_DetachingFromVM:
+        case kHostUSBDeviceState_Capturing:
+        case kHostUSBDeviceState_ReleasingToHost:
+        case kHostUSBDeviceState_AttachingToVM:
+        case kHostUSBDeviceState_PhysDetachingFromVM:
+            AssertMsgFailedReturn(("this=%p %s is a transitional state.\n", this, i_getStateName()), false);
+
+        case kHostUSBDeviceState_PhysDetached:
+        default:
+            AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+    }
+
+    return i_setState(aNewState, aFinalState, aNewSubState);
+}
+
+
+/**
+ * A convenience for advancing a transitional state forward.
+ *
+ * @param   aSkipReAttach   Fast forwards thru the re-attach substate if
+ *                          applicable.
+ *
+ * @returns true if filters should be applied to the device, false if not.
+ *
+ * @note    The caller must own the write lock for this object.
+ */
+bool HostUSBDevice::i_advanceTransition(bool aSkipReAttach /* = false */)
+{
+    AssertReturn(isWriteLockOnCurrentThread(), false);
+    HostUSBDeviceState enmPending = mPendingUniState;
+    HostUSBDeviceSubState enmSub = mUniSubState;
+    HostUSBDeviceState enmState = mUniState;
+    switch (enmState)
+    {
+        case kHostUSBDeviceState_Capturing:
+            switch (enmSub)
+            {
+                case kHostUSBDeviceSubState_AwaitingDetach:
+                    enmSub = kHostUSBDeviceSubState_AwaitingReAttach;
+                    break;
+                case kHostUSBDeviceSubState_AwaitingReAttach:
+                    enmSub = kHostUSBDeviceSubState_Default;
+                    RT_FALL_THRU();
+                case kHostUSBDeviceSubState_Default:
+                    switch (enmPending)
+                    {
+                        case kHostUSBDeviceState_UsedByVM:
+                            enmState = kHostUSBDeviceState_AttachingToVM;
+                            break;
+                        case kHostUSBDeviceState_HeldByProxy:
+                            enmState = enmPending;
+                            enmPending = kHostUSBDeviceState_Invalid;
+                            break;
+                        default:
+                            AssertMsgFailedReturn(("this=%p invalid pending state %d: %s\n",
+                                                   this, enmPending, i_getStateName()), false);
+                    }
+                    break;
+                default:
+                    AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_ReleasingToHost:
+            switch (enmSub)
+            {
+                case kHostUSBDeviceSubState_AwaitingDetach:
+                    enmSub = kHostUSBDeviceSubState_AwaitingReAttach;
+                    break;
+                case kHostUSBDeviceSubState_AwaitingReAttach:
+                    enmSub = kHostUSBDeviceSubState_Default;
+                    RT_FALL_THRU();
+                case kHostUSBDeviceSubState_Default:
+                    switch (enmPending)
+                    {
+                        /* Use Unused here since it implies that filters has been applied
+                           and will make sure they aren't applied if the final state really
+                           is Capturable. */
+                        case kHostUSBDeviceState_Unused:
+                            enmState = enmPending;
+                            enmPending = kHostUSBDeviceState_Invalid;
+                            break;
+                        default:
+                            AssertMsgFailedReturn(("this=%p invalid pending state %d: %s\n",
+                                                   this, enmPending, i_getStateName()), false);
+                    }
+                    break;
+                default:
+                    AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_AttachingToVM:
+            switch (enmSub)
+            {
+                case kHostUSBDeviceSubState_AwaitingDetach:
+                    enmSub = kHostUSBDeviceSubState_AwaitingReAttach;
+                    break;
+                case kHostUSBDeviceSubState_AwaitingReAttach:
+                    enmSub = kHostUSBDeviceSubState_Default;
+                    RT_FALL_THRU();
+                case kHostUSBDeviceSubState_Default:
+                    switch (enmPending)
+                    {
+                        case kHostUSBDeviceState_UsedByVM:
+                            enmState = enmPending;
+                            enmPending = kHostUSBDeviceState_Invalid;
+                            break;
+                        default:
+                            AssertMsgFailedReturn(("this=%p invalid pending state %d: %s\n",
+                                                   this, enmPending, i_getStateName()), false);
+                    }
+                    break;
+                default:
+                    AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_DetachingFromVM:
+            switch (enmSub)
+            {
+                case kHostUSBDeviceSubState_AwaitingDetach:
+                    enmSub = kHostUSBDeviceSubState_AwaitingReAttach;
+                    break;
+                case kHostUSBDeviceSubState_AwaitingReAttach:
+                    enmSub = kHostUSBDeviceSubState_Default;
+                    RT_FALL_THRU();
+                case kHostUSBDeviceSubState_Default:
+                    switch (enmPending)
+                    {
+                        case kHostUSBDeviceState_HeldByProxy:
+                            enmState = enmPending;
+                            enmPending = kHostUSBDeviceState_Invalid;
+                            break;
+                        case kHostUSBDeviceState_Unused:
+                            enmState = kHostUSBDeviceState_ReleasingToHost;
+                            break;
+                        default:
+                            AssertMsgFailedReturn(("this=%p invalid pending state %d: %s\n",
+                                                   this, enmPending, i_getStateName()), false);
+                    }
+                    break;
+                default:
+                    AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_PhysDetachingFromVM:
+            switch (enmSub)
+            {
+                case kHostUSBDeviceSubState_Default:
+                    switch (enmPending)
+                    {
+                        case kHostUSBDeviceState_PhysDetached:
+                            enmState = enmPending;
+                            enmPending = kHostUSBDeviceState_Invalid;
+                            break;
+                        default:
+                            AssertMsgFailedReturn(("this=%p invalid pending state %d: %s\n",
+                                                   this, enmPending, i_getStateName()), false);
+                    }
+                    break;
+                default:
+                    AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_Unsupported:
+        case kHostUSBDeviceState_UsedByHost:
+        case kHostUSBDeviceState_Capturable:
+        case kHostUSBDeviceState_Unused:
+        case kHostUSBDeviceState_HeldByProxy:
+        case kHostUSBDeviceState_UsedByVM:
+            AssertMsgFailedReturn(("this=%p %s is not transitional\n", this, i_getStateName()), false);
+        case kHostUSBDeviceState_PhysDetached:
+        default:
+            AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, enmState), false);
+
+    }
+
+    bool fRc = i_setState(enmState, enmPending, enmSub);
+    if (aSkipReAttach && mUniSubState == kHostUSBDeviceSubState_AwaitingReAttach)
+        fRc |= i_advanceTransition(false /* don't fast forward re-attach */);
+    return fRc;
+}
+
+/**
+ * A convenience for failing a transitional state.
+ *
+ * @return true if filters should be applied to the device, false if not.
+ * @param   a_enmStateHint  USB device state hint. kHostUSBDeviceState_Invalid
+ *                          if the caller doesn't have a clue to give.
+ *
+ * @note    The caller must own the write lock for this object.
+ */
+bool HostUSBDevice::i_failTransition(HostUSBDeviceState a_enmStateHint)
+{
+    AssertReturn(isWriteLockOnCurrentThread(), false);
+    HostUSBDeviceSubState enmSub = mUniSubState;
+    HostUSBDeviceState enmState = mUniState;
+    switch (enmState)
+    {
+        /*
+         * There are just two cases, either we got back to the
+         * previous state (assumes Capture+Attach-To-VM updates it)
+         * or we assume the device has been unplugged (physically).
+         */
+        case kHostUSBDeviceState_DetachingFromVM:
+        case kHostUSBDeviceState_Capturing:
+        case kHostUSBDeviceState_ReleasingToHost:
+        case kHostUSBDeviceState_AttachingToVM:
+            switch (enmSub)
+            {
+                case kHostUSBDeviceSubState_AwaitingDetach:
+                    enmSub = kHostUSBDeviceSubState_Default;
+                    RT_FALL_THRU();
+                case kHostUSBDeviceSubState_Default:
+                    enmState = mPrevUniState;
+                    break;
+                case kHostUSBDeviceSubState_AwaitingReAttach:
+                    enmSub = kHostUSBDeviceSubState_Default;
+                    if (a_enmStateHint != kHostUSBDeviceState_Invalid)
+                        enmState = mPrevUniState; /** @todo enmState = a_enmStateHint is more correct, but i_setState doesn't like it. It will usually correct itself shortly. */
+                    else
+                        enmState = kHostUSBDeviceState_PhysDetached;
+                    break;
+                default:
+                    AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+            }
+            break;
+
+        case kHostUSBDeviceState_PhysDetachingFromVM:
+            AssertMsgFailedReturn(("this=%p %s shall not fail\n", this, i_getStateName()), false);
+
+        case kHostUSBDeviceState_Unsupported:
+        case kHostUSBDeviceState_UsedByHost:
+        case kHostUSBDeviceState_Capturable:
+        case kHostUSBDeviceState_Unused:
+        case kHostUSBDeviceState_HeldByProxy:
+        case kHostUSBDeviceState_UsedByVM:
+            AssertMsgFailedReturn(("this=%p %s is not transitional\n", this, i_getStateName()), false);
+        case kHostUSBDeviceState_PhysDetached:
+        default:
+            AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), false);
+
+    }
+
+    return i_setState(enmState, kHostUSBDeviceState_Invalid, enmSub);
+}
+
+
+/**
+ * Determines the canonical state of the device.
+ *
+ * @returns canonical state.
+ *
+ * @note    The caller must own the read (or write) lock for this object.
+ */
+USBDeviceState_T HostUSBDevice::i_canonicalState() const
+{
+    switch (mUniState)
+    {
+        /*
+         * Straight forward.
+         */
+        case kHostUSBDeviceState_Unsupported:
+            return USBDeviceState_NotSupported;
+
+        case kHostUSBDeviceState_UsedByHost:
+            return USBDeviceState_Unavailable;
+
+        case kHostUSBDeviceState_Capturable:
+            return USBDeviceState_Busy;
+
+        case kHostUSBDeviceState_Unused:
+            return USBDeviceState_Available;
+
+        case kHostUSBDeviceState_HeldByProxy:
+            return USBDeviceState_Held;
+
+        case kHostUSBDeviceState_UsedByVM:
+            return USBDeviceState_Captured;
+
+        /*
+         * Pretend we've reached the final state.
+         */
+        case kHostUSBDeviceState_Capturing:
+            Assert(   mPendingUniState == kHostUSBDeviceState_UsedByVM
+                   || mPendingUniState == kHostUSBDeviceState_HeldByProxy);
+            return mPendingUniState == kHostUSBDeviceState_UsedByVM ? USBDeviceState_Captured : USBDeviceState_Held;
+            /* The cast ^^^^ is because xidl is using different enums for
+               each of the values. *Very* nice idea... :-) */
+
+        case kHostUSBDeviceState_AttachingToVM:
+            return USBDeviceState_Captured;
+
+        /*
+         * Return the previous state.
+         */
+        case kHostUSBDeviceState_ReleasingToHost:
+            Assert(   mPrevUniState == kHostUSBDeviceState_UsedByVM
+                   || mPrevUniState == kHostUSBDeviceState_HeldByProxy);
+            return mPrevUniState == kHostUSBDeviceState_UsedByVM ? USBDeviceState_Captured : USBDeviceState_Held;
+            /* The cast ^^^^ is because xidl is using different enums for
+               each of the values. *Very* nice idea... :-) */
+
+        case kHostUSBDeviceState_DetachingFromVM:
+            return USBDeviceState_Captured;
+        case kHostUSBDeviceState_PhysDetachingFromVM:
+            return USBDeviceState_Captured;
+
+        case kHostUSBDeviceState_PhysDetached:
+        default:
+            AssertReleaseMsgFailedReturn(("this=%p mUniState=%d\n", this, mUniState), USBDeviceState_NotSupported);
+    }
+    /* won't ever get here. */
+}
+/* vi: set tabstop=4 shiftwidth=4 expandtab: */