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, 2389 insertions, 0 deletions

diff --git a/src/VBox/Storage/QED.cpp b/src/VBox/Storage/QED.cpp
new file mode 100644
index 00000000..d2343c05
--- /dev/null
+++ b/src/VBox/Storage/QED.cpp
@@ -0,0 +1,2389 @@
+/* $Id: QED.cpp $ */
+/** @file
+ * QED - QED Disk image.
+ *
+ * The QED backend implements support for the qemu enhanced disk format (short QED)
+ * The specification for the format is available under http://wiki.qemu.org/Features/QED/Specification
+ *
+ * Missing things to implement:
+ *    - compaction
+ *    - resizing which requires block relocation (very rare case)
+ */
+
+/*
+ * Copyright (C) 2011-2023 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
+ */
+
+
+/*********************************************************************************************************************************
+*   Header Files                                                                                                                 *
+*********************************************************************************************************************************/
+#define LOG_GROUP LOG_GROUP_VD_QED
+#include <VBox/vd-plugin.h>
+#include <VBox/err.h>
+
+#include <VBox/log.h>
+#include <iprt/asm.h>
+#include <iprt/assert.h>
+#include <iprt/string.h>
+#include <iprt/alloc.h>
+#include <iprt/path.h>
+#include <iprt/list.h>
+
+#include "VDBackends.h"
+#include "VDBackendsInline.h"
+
+
+/*********************************************************************************************************************************
+*   Structures in a QED image, little endian                                                                                     *
+*********************************************************************************************************************************/
+
+#pragma pack(1)
+typedef struct QedHeader
+{
+    /** Magic value. */
+    uint32_t    u32Magic;
+    /** Cluster size in bytes. */
+    uint32_t    u32ClusterSize;
+    /** Size of L1 and L2 tables in clusters. */
+    uint32_t    u32TableSize;
+    /** size of this header structure in clusters. */
+    uint32_t    u32HeaderSize;
+    /** Features used for the image. */
+    uint64_t    u64FeatureFlags;
+    /** Compatibility features used for the image. */
+    uint64_t    u64CompatFeatureFlags;
+    /** Self resetting feature bits. */
+    uint64_t    u64AutoresetFeatureFlags;
+    /** Offset of the L1 table in bytes. */
+    uint64_t    u64OffL1Table;
+    /** Logical image size as seen by the guest. */
+    uint64_t    u64Size;
+    /** Offset of the backing filename in bytes. */
+    uint32_t    u32OffBackingFilename;
+    /** Size of the backing filename. */
+    uint32_t    u32BackingFilenameSize;
+} QedHeader;
+#pragma pack()
+/** Pointer to a on disk QED header. */
+typedef QedHeader *PQedHeader;
+
+/** QED magic value. */
+#define QED_MAGIC                            UINT32_C(0x00444551) /* QED\0 */
+/** Cluster size minimum. */
+#define QED_CLUSTER_SIZE_MIN                 RT_BIT(12)
+/** Cluster size maximum. */
+#define QED_CLUSTER_SIZE_MAX                 RT_BIT(26)
+/** L1 and L2 Table size minimum. */
+#define QED_TABLE_SIZE_MIN                   1
+/** L1 and L2 Table size maximum. */
+#define QED_TABLE_SIZE_MAX                   16
+
+/** QED default cluster size when creating an image. */
+#define QED_CLUSTER_SIZE_DEFAULT             (64 * _1K)
+/** The default table size in clusters. */
+#define QED_TABLE_SIZE_DEFAULT               4
+
+/** Feature flags.
+ * @{
+ */
+/** Image uses a backing file to provide data for unallocated clusters. */
+#define QED_FEATURE_BACKING_FILE             RT_BIT_64(0)
+/** Image needs checking before use. */
+#define QED_FEATURE_NEED_CHECK               RT_BIT_64(1)
+/** Don't probe for format of the backing file, treat as raw image. */
+#define QED_FEATURE_BACKING_FILE_NO_PROBE    RT_BIT_64(2)
+/** Mask of valid features. */
+#define QED_FEATURE_MASK (QED_FEATURE_BACKING_FILE | QED_FEATURE_NEED_CHECK | QED_FEATURE_BACKING_FILE_NO_PROBE)
+/** @} */
+
+/** Compatibility feature flags.
+ * @{
+ */
+/** Mask of valid compatibility features. */
+#define QED_COMPAT_FEATURE_MASK (0)
+/** @} */
+
+/** Autoreset feature flags.
+ * @{
+ */
+/** Mask of valid autoreset features. */
+#define QED_AUTORESET_FEATURE_MASK (0)
+/** @} */
+
+
+/*********************************************************************************************************************************
+*   Constants And Macros, Structures and Typedefs                                                                                *
+*********************************************************************************************************************************/
+
+/**
+ * QED L2 cache entry.
+ */
+typedef struct QEDL2CACHEENTRY
+{
+    /** List node for the search list. */
+    RTLISTNODE              NodeSearch;
+    /** List node for the LRU list. */
+    RTLISTNODE              NodeLru;
+    /** Reference counter. */
+    uint32_t                cRefs;
+    /** The offset of the L2 table, used as search key. */
+    uint64_t                offL2Tbl;
+    /** Pointer to the cached L2 table. */
+    uint64_t               *paL2Tbl;
+} QEDL2CACHEENTRY, *PQEDL2CACHEENTRY;
+
+/** Maximum amount of memory the cache is allowed to use. */
+#define QED_L2_CACHE_MEMORY_MAX (2*_1M)
+
+/**
+ * QED image data structure.
+ */
+typedef struct QEDIMAGE
+{
+    /** Image name. */
+    const char          *pszFilename;
+    /** Storage handle. */
+    PVDIOSTORAGE        pStorage;
+
+    /** Pointer to the per-disk VD interface list. */
+    PVDINTERFACE        pVDIfsDisk;
+    /** Pointer to the per-image VD interface list. */
+    PVDINTERFACE        pVDIfsImage;
+    /** Error interface. */
+    PVDINTERFACEERROR   pIfError;
+    /** I/O interface. */
+    PVDINTERFACEIOINT   pIfIo;
+
+    /** Open flags passed by VBoxHD layer. */
+    unsigned            uOpenFlags;
+    /** Image flags defined during creation or determined during open. */
+    unsigned            uImageFlags;
+    /** Total size of the image. */
+    uint64_t            cbSize;
+    /** Physical geometry of this image. */
+    VDGEOMETRY          PCHSGeometry;
+    /** Logical geometry of this image. */
+    VDGEOMETRY          LCHSGeometry;
+
+    /** Filename of the backing file if any. */
+    char               *pszBackingFilename;
+    /** Offset of the filename in the image. */
+    uint32_t            offBackingFilename;
+    /** Size of the backing filename excluding \0. */
+    uint32_t            cbBackingFilename;
+
+    /** Size of the image, multiple of clusters. */
+    uint64_t            cbImage;
+    /** Cluster size in bytes. */
+    uint32_t            cbCluster;
+    /** Number of entries in the L1 and L2 table. */
+    uint32_t            cTableEntries;
+    /** Size of an L1 or L2 table rounded to the next cluster size. */
+    uint32_t            cbTable;
+    /** Pointer to the L1 table. */
+    uint64_t            *paL1Table;
+    /** Offset of the L1 table. */
+    uint64_t            offL1Table;
+
+    /** Offset mask for a cluster. */
+    uint64_t            fOffsetMask;
+    /** L1 table mask to get the L1 index. */
+    uint64_t            fL1Mask;
+    /** Number of bits to shift to get the L1 index. */
+    uint32_t            cL1Shift;
+    /** L2 table mask to get the L2 index. */
+    uint64_t            fL2Mask;
+    /** Number of bits to shift to get the L2 index. */
+    uint32_t            cL2Shift;
+
+    /** Pointer to the L2 table we are currently allocating
+     * (can be only one at a time). */
+    PQEDL2CACHEENTRY    pL2TblAlloc;
+
+    /** Memory occupied by the L2 table cache. */
+    size_t              cbL2Cache;
+    /** The sorted L2 entry list used for searching. */
+    RTLISTNODE          ListSearch;
+    /** The LRU L2 entry list used for eviction. */
+    RTLISTNODE          ListLru;
+    /** The static region list. */
+    VDREGIONLIST        RegionList;
+} QEDIMAGE, *PQEDIMAGE;
+
+/**
+ * State of the async cluster allocation.
+ */
+typedef enum QEDCLUSTERASYNCALLOCSTATE
+{
+    /** Invalid. */
+    QEDCLUSTERASYNCALLOCSTATE_INVALID = 0,
+    /** L2 table allocation. */
+    QEDCLUSTERASYNCALLOCSTATE_L2_ALLOC,
+    /** Link L2 table into L1. */
+    QEDCLUSTERASYNCALLOCSTATE_L2_LINK,
+    /** Allocate user data cluster. */
+    QEDCLUSTERASYNCALLOCSTATE_USER_ALLOC,
+    /** Link user data cluster. */
+    QEDCLUSTERASYNCALLOCSTATE_USER_LINK,
+    /** 32bit blowup. */
+    QEDCLUSTERASYNCALLOCSTATE_32BIT_HACK = 0x7fffffff
+} QEDCLUSTERASYNCALLOCSTATE, *PQEDCLUSTERASYNCALLOCSTATE;
+
+/**
+ * Data needed to track async cluster allocation.
+ */
+typedef struct QEDCLUSTERASYNCALLOC
+{
+    /** The state of the cluster allocation. */
+    QEDCLUSTERASYNCALLOCSTATE enmAllocState;
+    /** Old image size to rollback in case of an error. */
+    uint64_t                  cbImageOld;
+    /** L1 index to link if any. */
+    uint32_t                  idxL1;
+    /** L2 index to link, required in any case. */
+    uint32_t                  idxL2;
+    /** Start offset of the allocated cluster. */
+    uint64_t                  offClusterNew;
+    /** L2 cache entry if a L2 table is allocated. */
+    PQEDL2CACHEENTRY          pL2Entry;
+    /** Number of bytes to write. */
+    size_t                    cbToWrite;
+} QEDCLUSTERASYNCALLOC, *PQEDCLUSTERASYNCALLOC;
+
+
+/*********************************************************************************************************************************
+*   Static Variables                                                                                                             *
+*********************************************************************************************************************************/
+
+/** NULL-terminated array of supported file extensions. */
+static const VDFILEEXTENSION s_aQedFileExtensions[] =
+{
+    {"qed", VDTYPE_HDD},
+    {NULL,  VDTYPE_INVALID}
+};
+
+
+/*********************************************************************************************************************************
+*   Internal Functions                                                                                                           *
+*********************************************************************************************************************************/
+
+/**
+ * Converts the image header to the host endianess and performs basic checks.
+ *
+ * @returns Whether the given header is valid or not.
+ * @param   pHeader    Pointer to the header to convert.
+ */
+static bool qedHdrConvertToHostEndianess(PQedHeader pHeader)
+{
+    pHeader->u32Magic                 = RT_LE2H_U32(pHeader->u32Magic);
+    pHeader->u32ClusterSize           = RT_LE2H_U32(pHeader->u32ClusterSize);
+    pHeader->u32TableSize             = RT_LE2H_U32(pHeader->u32TableSize);
+    pHeader->u32HeaderSize            = RT_LE2H_U32(pHeader->u32HeaderSize);
+    pHeader->u64FeatureFlags          = RT_LE2H_U64(pHeader->u64FeatureFlags);
+    pHeader->u64CompatFeatureFlags    = RT_LE2H_U64(pHeader->u64CompatFeatureFlags);
+    pHeader->u64AutoresetFeatureFlags = RT_LE2H_U64(pHeader->u64AutoresetFeatureFlags);
+    pHeader->u64OffL1Table            = RT_LE2H_U64(pHeader->u64OffL1Table);
+    pHeader->u64Size                  = RT_LE2H_U64(pHeader->u64Size);
+    pHeader->u32OffBackingFilename    = RT_LE2H_U32(pHeader->u32OffBackingFilename);
+    pHeader->u32BackingFilenameSize   = RT_LE2H_U32(pHeader->u32BackingFilenameSize);
+
+    if (RT_UNLIKELY(pHeader->u32Magic != QED_MAGIC))
+        return false;
+    if (RT_UNLIKELY(   pHeader->u32ClusterSize < QED_CLUSTER_SIZE_MIN
+                    || pHeader->u32ClusterSize > QED_CLUSTER_SIZE_MAX))
+        return false;
+    if (RT_UNLIKELY(   pHeader->u32TableSize < QED_TABLE_SIZE_MIN
+                    || pHeader->u32TableSize > QED_TABLE_SIZE_MAX))
+        return false;
+    if (RT_UNLIKELY(pHeader->u64Size % 512 != 0))
+        return false;
+    if (RT_UNLIKELY(   pHeader->u64FeatureFlags & QED_FEATURE_BACKING_FILE
+                    && (   pHeader->u32BackingFilenameSize == 0
+                        || pHeader->u32BackingFilenameSize == UINT32_MAX)))
+        return false;
+
+    return true;
+}
+
+/**
+ * Creates a QED header from the given image state.
+ *
+ * @param   pImage     Image instance data.
+ * @param   pHeader    Pointer to the header to convert.
+ */
+static void qedHdrConvertFromHostEndianess(PQEDIMAGE pImage, PQedHeader pHeader)
+{
+    pHeader->u32Magic                 = RT_H2LE_U32(QED_MAGIC);
+    pHeader->u32ClusterSize           = RT_H2LE_U32(pImage->cbCluster);
+    pHeader->u32TableSize             = RT_H2LE_U32(pImage->cbTable / pImage->cbCluster);
+    pHeader->u32HeaderSize            = RT_H2LE_U32(1);
+    pHeader->u64FeatureFlags          = RT_H2LE_U64(pImage->pszBackingFilename ? QED_FEATURE_BACKING_FILE : UINT64_C(0));
+    pHeader->u64CompatFeatureFlags    = RT_H2LE_U64(UINT64_C(0));
+    pHeader->u64AutoresetFeatureFlags = RT_H2LE_U64(UINT64_C(0));
+    pHeader->u64OffL1Table            = RT_H2LE_U64(pImage->offL1Table);
+    pHeader->u64Size                  = RT_H2LE_U64(pImage->cbSize);
+    pHeader->u32OffBackingFilename    = RT_H2LE_U32(pImage->offBackingFilename);
+    pHeader->u32BackingFilenameSize   = RT_H2LE_U32(pImage->cbBackingFilename);
+}
+
+/**
+ * Convert table entries from little endian to host endianess.
+ *
+ * @param   paTbl       Pointer to the table.
+ * @param   cEntries    Number of entries in the table.
+ */
+static void qedTableConvertToHostEndianess(uint64_t *paTbl, uint32_t cEntries)
+{
+    while (cEntries-- > 0)
+    {
+        *paTbl = RT_LE2H_U64(*paTbl);
+        paTbl++;
+    }
+}
+
+#if defined(RT_BIG_ENDIAN)
+/**
+ * Convert table entries from host to little endian format.
+ *
+ * @param   paTblImg    Pointer to the table which will store the little endian table.
+ * @param   paTbl       The source table to convert.
+ * @param   cEntries    Number of entries in the table.
+ */
+static void qedTableConvertFromHostEndianess(uint64_t *paTblImg, uint64_t const *paTbl,
+                                             uint32_t cEntries)
+{
+    while (cEntries-- > 0)
+    {
+        *paTblImg = RT_H2LE_U64(*paTbl);
+        paTbl++;
+        paTblImg++;
+    }
+}
+#endif
+
+/**
+ * Creates the L2 table cache.
+ *
+ * @returns VBox status code.
+ * @param   pImage    The image instance data.
+ */
+static int qedL2TblCacheCreate(PQEDIMAGE pImage)
+{
+    pImage->cbL2Cache = 0;
+    RTListInit(&pImage->ListSearch);
+    RTListInit(&pImage->ListLru);
+
+    return VINF_SUCCESS;
+}
+
+/**
+ * Destroys the L2 table cache.
+ *
+ * @param   pImage    The image instance data.
+ */
+static void qedL2TblCacheDestroy(PQEDIMAGE pImage)
+{
+    PQEDL2CACHEENTRY pL2Entry;
+    PQEDL2CACHEENTRY pL2Next;
+    RTListForEachSafe(&pImage->ListSearch, pL2Entry, pL2Next, QEDL2CACHEENTRY, NodeSearch)
+    {
+        Assert(!pL2Entry->cRefs);
+
+        RTListNodeRemove(&pL2Entry->NodeSearch);
+        RTMemPageFree(pL2Entry->paL2Tbl, pImage->cbTable);
+        RTMemFree(pL2Entry);
+    }
+
+    pImage->cbL2Cache       = 0;
+    RTListInit(&pImage->ListSearch);
+    RTListInit(&pImage->ListLru);
+}
+
+/**
+ * Returns the L2 table matching the given offset or NULL if none could be found.
+ *
+ * @returns Pointer to the L2 table cache entry or NULL.
+ * @param   pImage    The image instance data.
+ * @param   offL2Tbl  Offset of the L2 table to search for.
+ */
+static PQEDL2CACHEENTRY qedL2TblCacheRetain(PQEDIMAGE pImage, uint64_t offL2Tbl)
+{
+    if (   pImage->pL2TblAlloc
+        && pImage->pL2TblAlloc->offL2Tbl == offL2Tbl)
+    {
+        pImage->pL2TblAlloc->cRefs++;
+        return pImage->pL2TblAlloc;
+    }
+
+    PQEDL2CACHEENTRY pL2Entry;
+    RTListForEach(&pImage->ListSearch, pL2Entry, QEDL2CACHEENTRY, NodeSearch)
+    {
+        if (pL2Entry->offL2Tbl == offL2Tbl)
+            break;
+    }
+
+    if (!RTListNodeIsDummy(&pImage->ListSearch, pL2Entry, QEDL2CACHEENTRY, NodeSearch))
+    {
+        /* Update LRU list. */
+        RTListNodeRemove(&pL2Entry->NodeLru);
+        RTListPrepend(&pImage->ListLru, &pL2Entry->NodeLru);
+        pL2Entry->cRefs++;
+        return pL2Entry;
+    }
+    else
+        return NULL;
+}
+
+/**
+ * Releases a L2 table cache entry.
+ *
+ * @param   pL2Entry    The L2 cache entry.
+ */
+static void qedL2TblCacheEntryRelease(PQEDL2CACHEENTRY pL2Entry)
+{
+    Assert(pL2Entry->cRefs > 0);
+    pL2Entry->cRefs--;
+}
+
+/**
+ * Allocates a new L2 table from the cache evicting old entries if required.
+ *
+ * @returns Pointer to the L2 cache entry or NULL.
+ * @param   pImage    The image instance data.
+ */
+static PQEDL2CACHEENTRY qedL2TblCacheEntryAlloc(PQEDIMAGE pImage)
+{
+    PQEDL2CACHEENTRY pL2Entry = NULL;
+
+    if (pImage->cbL2Cache + pImage->cbTable <= QED_L2_CACHE_MEMORY_MAX)
+    {
+        /* Add a new entry. */
+        pL2Entry = (PQEDL2CACHEENTRY)RTMemAllocZ(sizeof(QEDL2CACHEENTRY));
+        if (pL2Entry)
+        {
+            pL2Entry->paL2Tbl = (uint64_t *)RTMemPageAllocZ(pImage->cbTable);
+            if (RT_UNLIKELY(!pL2Entry->paL2Tbl))
+            {
+                RTMemFree(pL2Entry);
+                pL2Entry = NULL;
+            }
+            else
+            {
+                pL2Entry->cRefs    = 1;
+                pImage->cbL2Cache += pImage->cbTable;
+            }
+        }
+    }
+    else
+    {
+        /* Evict the last not in use entry and use it */
+        Assert(!RTListIsEmpty(&pImage->ListLru));
+
+        RTListForEachReverse(&pImage->ListLru, pL2Entry, QEDL2CACHEENTRY, NodeLru)
+        {
+            if (!pL2Entry->cRefs)
+                break;
+        }
+
+        if (!RTListNodeIsDummy(&pImage->ListSearch, pL2Entry, QEDL2CACHEENTRY, NodeSearch))
+        {
+            RTListNodeRemove(&pL2Entry->NodeSearch);
+            RTListNodeRemove(&pL2Entry->NodeLru);
+            pL2Entry->offL2Tbl = 0;
+            pL2Entry->cRefs    = 1;
+        }
+        else
+            pL2Entry = NULL;
+    }
+
+    return pL2Entry;
+}
+
+/**
+ * Frees a L2 table cache entry.
+ *
+ * @param   pImage    The image instance data.
+ * @param   pL2Entry  The L2 cache entry to free.
+ */
+static void qedL2TblCacheEntryFree(PQEDIMAGE pImage, PQEDL2CACHEENTRY pL2Entry)
+{
+    Assert(!pL2Entry->cRefs);
+    RTMemPageFree(pL2Entry->paL2Tbl, pImage->cbTable);
+    RTMemFree(pL2Entry);
+
+    pImage->cbL2Cache -= pImage->cbTable;
+}
+
+/**
+ * Inserts an entry in the L2 table cache.
+ *
+ * @param   pImage    The image instance data.
+ * @param   pL2Entry  The L2 cache entry to insert.
+ */
+static void qedL2TblCacheEntryInsert(PQEDIMAGE pImage, PQEDL2CACHEENTRY pL2Entry)
+{
+    Assert(pL2Entry->offL2Tbl > 0);
+
+    /* Insert at the top of the LRU list. */
+    RTListPrepend(&pImage->ListLru, &pL2Entry->NodeLru);
+
+    if (RTListIsEmpty(&pImage->ListSearch))
+    {
+        RTListAppend(&pImage->ListSearch, &pL2Entry->NodeSearch);
+    }
+    else
+    {
+        /* Insert into search list. */
+        PQEDL2CACHEENTRY pIt;
+        pIt = RTListGetFirst(&pImage->ListSearch, QEDL2CACHEENTRY, NodeSearch);
+        if (pIt->offL2Tbl > pL2Entry->offL2Tbl)
+            RTListPrepend(&pImage->ListSearch, &pL2Entry->NodeSearch);
+        else
+        {
+            bool fInserted = false;
+
+            RTListForEach(&pImage->ListSearch, pIt, QEDL2CACHEENTRY, NodeSearch)
+            {
+                Assert(pIt->offL2Tbl != pL2Entry->offL2Tbl);
+                if (pIt->offL2Tbl < pL2Entry->offL2Tbl)
+                {
+                    RTListNodeInsertAfter(&pIt->NodeSearch, &pL2Entry->NodeSearch);
+                    fInserted = true;
+                    break;
+                }
+            }
+            Assert(fInserted);
+        }
+    }
+}
+
+/**
+ * Fetches the L2 from the given offset trying the LRU cache first and
+ * reading it from the image after a cache miss - version for async I/O.
+ *
+ * @returns VBox status code.
+ * @param   pImage    Image instance data.
+ * @param   pIoCtx    The I/O context.
+ * @param   offL2Tbl  The offset of the L2 table in the image.
+ * @param   ppL2Entry Where to store the L2 table on success.
+ */
+static int qedL2TblCacheFetchAsync(PQEDIMAGE pImage, PVDIOCTX pIoCtx,
+                                   uint64_t offL2Tbl, PQEDL2CACHEENTRY *ppL2Entry)
+{
+    int rc = VINF_SUCCESS;
+
+    /* Try to fetch the L2 table from the cache first. */
+    PQEDL2CACHEENTRY pL2Entry = qedL2TblCacheRetain(pImage, offL2Tbl);
+    if (!pL2Entry)
+    {
+        pL2Entry = qedL2TblCacheEntryAlloc(pImage);
+
+        if (pL2Entry)
+        {
+            /* Read from the image. */
+            PVDMETAXFER pMetaXfer;
+
+            pL2Entry->offL2Tbl = offL2Tbl;
+            rc = vdIfIoIntFileReadMeta(pImage->pIfIo, pImage->pStorage,
+                                       offL2Tbl, pL2Entry->paL2Tbl,
+                                       pImage->cbTable, pIoCtx,
+                                       &pMetaXfer, NULL, NULL);
+            if (RT_SUCCESS(rc))
+            {
+                vdIfIoIntMetaXferRelease(pImage->pIfIo, pMetaXfer);
+#if defined(RT_BIG_ENDIAN)
+                qedTableConvertToHostEndianess(pL2Entry->paL2Tbl, pImage->cTableEntries);
+#endif
+                qedL2TblCacheEntryInsert(pImage, pL2Entry);
+            }
+            else
+            {
+                qedL2TblCacheEntryRelease(pL2Entry);
+                qedL2TblCacheEntryFree(pImage, pL2Entry);
+            }
+        }
+        else
+            rc = VERR_NO_MEMORY;
+    }
+
+    if (RT_SUCCESS(rc))
+        *ppL2Entry = pL2Entry;
+
+    return rc;
+}
+
+/**
+ * Return power of 2 or 0 if num error.
+ *
+ * @returns The power of 2 or 0 if the given number is not a power of 2.
+ * @param   u32    The number.
+ */
+static uint32_t qedGetPowerOfTwo(uint32_t u32)
+{
+    if (u32 == 0)
+        return 0;
+    uint32_t uPower2 = 0;
+    while ((u32 & 1) == 0)
+    {
+        u32 >>= 1;
+        uPower2++;
+    }
+    return u32 == 1 ? uPower2 : 0;
+}
+
+/**
+ * Sets the L1, L2 and offset bitmasks and L1 and L2 bit shift members.
+ *
+ * @param   pImage    The image instance data.
+ */
+static void qedTableMasksInit(PQEDIMAGE pImage)
+{
+    uint32_t cClusterBits, cTableBits;
+
+    cClusterBits = qedGetPowerOfTwo(pImage->cbCluster);
+    cTableBits   = qedGetPowerOfTwo(pImage->cTableEntries);
+
+    Assert(cClusterBits + 2 * cTableBits <= 64);
+
+    pImage->fOffsetMask = ((uint64_t)pImage->cbCluster - 1);
+    pImage->fL2Mask     = ((uint64_t)pImage->cTableEntries - 1) << cClusterBits;
+    pImage->cL2Shift    = cClusterBits;
+    pImage->fL1Mask     = ((uint64_t)pImage->cTableEntries - 1) << (cClusterBits + cTableBits);
+    pImage->cL1Shift    = cClusterBits + cTableBits;
+}
+
+/**
+ * Converts a given logical offset into the
+ *
+ * @param   pImage         The image instance data.
+ * @param   off            The logical offset to convert.
+ * @param   pidxL1         Where to store the index in the L1 table on success.
+ * @param   pidxL2         Where to store the index in the L2 table on success.
+ * @param   poffCluster    Where to store the offset in the cluster on success.
+ */
+DECLINLINE(void) qedConvertLogicalOffset(PQEDIMAGE pImage, uint64_t off, uint32_t *pidxL1,
+                                         uint32_t *pidxL2, uint32_t *poffCluster)
+{
+    AssertPtr(pidxL1);
+    AssertPtr(pidxL2);
+    AssertPtr(poffCluster);
+
+    *poffCluster = off & pImage->fOffsetMask;
+    *pidxL1      = (off & pImage->fL1Mask) >> pImage->cL1Shift;
+    *pidxL2      = (off & pImage->fL2Mask) >> pImage->cL2Shift;
+}
+
+/**
+ * Converts Cluster size to a byte size.
+ *
+ * @returns Number of bytes derived from the given number of clusters.
+ * @param   pImage    The image instance data.
+ * @param   cClusters The clusters to convert.
+ */
+DECLINLINE(uint64_t) qedCluster2Byte(PQEDIMAGE pImage, uint64_t cClusters)
+{
+    return cClusters * pImage->cbCluster;
+}
+
+/**
+ * Converts number of bytes to cluster size rounding to the next cluster.
+ *
+ * @returns Number of bytes derived from the given number of clusters.
+ * @param   pImage    The image instance data.
+ * @param   cb        Number of bytes to convert.
+ */
+DECLINLINE(uint64_t) qedByte2Cluster(PQEDIMAGE pImage, uint64_t cb)
+{
+    return cb / pImage->cbCluster + (cb % pImage->cbCluster ? 1 : 0);
+}
+
+/**
+ * Allocates a new cluster in the image.
+ *
+ * @returns The start offset of the new cluster in the image.
+ * @param   pImage    The image instance data.
+ * @param   cClusters Number of clusters to allocate.
+ */
+DECLINLINE(uint64_t) qedClusterAllocate(PQEDIMAGE pImage, uint32_t cClusters)
+{
+    uint64_t offCluster;
+
+    offCluster = pImage->cbImage;
+    pImage->cbImage += cClusters*pImage->cbCluster;
+
+    return offCluster;
+}
+
+/**
+ * Returns the real image offset for a given cluster or an error if the cluster is not
+ * yet allocated.
+ *
+ * @returns VBox status code.
+ *          VERR_VD_BLOCK_FREE if the cluster is not yet allocated.
+ * @param   pImage        The image instance data.
+ * @param   pIoCtx        The I/O context.
+ * @param   idxL1         The L1 index.
+ * @param   idxL2         The L2 index.
+ * @param   offCluster    Offset inside the cluster.
+ * @param   poffImage     Where to store the image offset on success;
+ */
+static int qedConvertToImageOffset(PQEDIMAGE pImage, PVDIOCTX pIoCtx,
+                                   uint32_t idxL1, uint32_t idxL2,
+                                   uint32_t offCluster, uint64_t *poffImage)
+{
+    int rc = VERR_VD_BLOCK_FREE;
+
+    AssertReturn(idxL1 < pImage->cTableEntries, VERR_INVALID_PARAMETER);
+    AssertReturn(idxL2 < pImage->cTableEntries, VERR_INVALID_PARAMETER);
+
+    if (pImage->paL1Table[idxL1])
+    {
+        PQEDL2CACHEENTRY pL2Entry;
+
+        rc = qedL2TblCacheFetchAsync(pImage, pIoCtx, pImage->paL1Table[idxL1],
+                                     &pL2Entry);
+        if (RT_SUCCESS(rc))
+        {
+            /* Get real file offset. */
+            if (pL2Entry->paL2Tbl[idxL2])
+                *poffImage = pL2Entry->paL2Tbl[idxL2] + offCluster;
+            else
+                rc = VERR_VD_BLOCK_FREE;
+
+            qedL2TblCacheEntryRelease(pL2Entry);
+        }
+    }
+
+    return rc;
+}
+
+/**
+ * Write the given table to image converting to the image endianess if required.
+ *
+ * @returns VBox status code.
+ * @param   pImage        The image instance data.
+ * @param   pIoCtx        The I/O context.
+ * @param   offTbl        The offset the table should be written to.
+ * @param   paTbl         The table to write.
+ * @param   pfnComplete   Callback called when the write completes.
+ * @param   pvUser        Opaque user data to pass in the completion callback.
+ */
+static int qedTblWrite(PQEDIMAGE pImage, PVDIOCTX pIoCtx, uint64_t offTbl, uint64_t *paTbl,
+                       PFNVDXFERCOMPLETED pfnComplete, void *pvUser)
+{
+    int rc = VINF_SUCCESS;
+
+#if defined(RT_BIG_ENDIAN)
+    uint64_t *paTblImg = (uint64_t *)RTMemAllocZ(pImage->cbTable);
+    if (paTblImg)
+    {
+        qedTableConvertFromHostEndianess(paTblImg, paTbl,
+                                         pImage->cTableEntries);
+        rc = vdIfIoIntFileWriteMeta(pImage->pIfIo, pImage->pStorage,
+                                    offTbl, paTblImg, pImage->cbTable,
+                                    pIoCtx, pfnComplete, pvUser);
+        RTMemFree(paTblImg);
+    }
+    else
+        rc = VERR_NO_MEMORY;
+#else
+    /* Write table directly. */
+    rc = vdIfIoIntFileWriteMeta(pImage->pIfIo, pImage->pStorage,
+                                offTbl, paTbl, pImage->cbTable, pIoCtx,
+                                pfnComplete, pvUser);
+#endif
+
+    return rc;
+}
+
+/**
+ * Internal. Flush image data to disk.
+ */
+static int qedFlushImage(PQEDIMAGE pImage)
+{
+    int rc = VINF_SUCCESS;
+
+    if (   pImage->pStorage
+        && !(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        QedHeader Header;
+
+        Assert(!(pImage->cbTable % pImage->cbCluster));
+#if defined(RT_BIG_ENDIAN)
+        uint64_t *paL1TblImg = (uint64_t *)RTMemAllocZ(pImage->cbTable);
+        if (paL1TblImg)
+        {
+            qedTableConvertFromHostEndianess(paL1TblImg, pImage->paL1Table,
+                                             pImage->cTableEntries);
+            rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage,
+                                        pImage->offL1Table, paL1TblImg,
+                                        pImage->cbTable);
+            RTMemFree(paL1TblImg);
+        }
+        else
+            rc = VERR_NO_MEMORY;
+#else
+        /* Write L1 table directly. */
+        rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage, pImage->offL1Table,
+                                    pImage->paL1Table, pImage->cbTable);
+#endif
+        if (RT_SUCCESS(rc))
+        {
+            /* Write header. */
+            qedHdrConvertFromHostEndianess(pImage, &Header);
+            rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage, 0, &Header,
+                                        sizeof(Header));
+            if (RT_SUCCESS(rc))
+                rc = vdIfIoIntFileFlushSync(pImage->pIfIo, pImage->pStorage);
+        }
+    }
+
+    return rc;
+}
+
+/**
+ * Checks whether the given cluster offset is valid.
+ *
+ * @returns Whether the given cluster offset is valid.
+ * @param   offCluster    The table offset to check.
+ * @param   cbFile        The real file size of the image.
+ * @param   cbCluster     The cluster size in bytes.
+ */
+DECLINLINE(bool) qedIsClusterOffsetValid(uint64_t offCluster, uint64_t cbFile, size_t cbCluster)
+{
+    return    (offCluster <= cbFile - cbCluster)
+           && !(offCluster & (cbCluster - 1));
+}
+
+/**
+ * Checks whether the given table offset is valid.
+ *
+ * @returns Whether the given table offset is valid.
+ * @param   offTbl    The table offset to check.
+ * @param   cbFile    The real file size of the image.
+ * @param   cbTable   The table size in bytes.
+ * @param   cbCluster The cluster size in bytes.
+ */
+DECLINLINE(bool) qedIsTblOffsetValid(uint64_t offTbl, uint64_t cbFile, size_t cbTable, size_t cbCluster)
+{
+    return    (offTbl <= cbFile - cbTable)
+           && !(offTbl & (cbCluster - 1));
+}
+
+/**
+ * Sets the specified range in the cluster bitmap checking whether any of the clusters is already
+ * used before.
+ *
+ * @returns Whether the range was clear and is set now.
+ * @param   pvClusterBitmap    The cluster bitmap to use.
+ * @param   offClusterStart    The first cluster to check and set.
+ * @param   offClusterEnd      The first cluster to not check and set anymore.
+ */
+static bool qedClusterBitmapCheckAndSet(void *pvClusterBitmap, uint32_t offClusterStart, uint32_t offClusterEnd)
+{
+    for (uint32_t offCluster = offClusterStart; offCluster < offClusterEnd; offCluster++)
+        if (ASMBitTest(pvClusterBitmap, offCluster))
+            return false;
+
+    ASMBitSetRange(pvClusterBitmap, offClusterStart, offClusterEnd);
+    return true;
+}
+
+/**
+ * Checks the given image for consistency, usually called when the
+ * QED_FEATURE_NEED_CHECK bit is set.
+ *
+ * @returns VBox status code.
+ * @retval VINF_SUCCESS when the image can be accessed.
+ * @param   pImage    The image instance data.
+ * @param   pHeader   The header to use for checking.
+ *
+ * @note It is not required that the image state is fully initialized  Only
+ *       The I/O interface and storage handle need to be valid.
+ * @note The header must be converted to the host CPU endian format already
+ *       and should be validated already.
+ */
+static int qedCheckImage(PQEDIMAGE pImage, PQedHeader pHeader)
+{
+    uint64_t cbFile;
+    uint32_t cbTable;
+    uint32_t cTableEntries;
+    uint64_t *paL1Tbl = NULL;
+    uint64_t *paL2Tbl = NULL;
+    void *pvClusterBitmap = NULL;
+    uint32_t offClusterStart;
+    int rc = VINF_SUCCESS;
+
+    pImage->cbCluster = pHeader->u32ClusterSize;
+    cbTable       = pHeader->u32TableSize * pHeader->u32ClusterSize;
+    cTableEntries = cbTable / sizeof(uint64_t);
+
+    do
+    {
+        rc = vdIfIoIntFileGetSize(pImage->pIfIo, pImage->pStorage, &cbFile);
+        if (RT_FAILURE(rc))
+        {
+            rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS,
+                           N_("Qed: Querying the file size of image '%s' failed"),
+                           pImage->pszFilename);
+            break;
+        }
+
+        /* Allocate L1 table. */
+        paL1Tbl = (uint64_t *)RTMemAllocZ(cbTable);
+        if (!paL1Tbl)
+        {
+            rc = vdIfError(pImage->pIfError, VERR_NO_MEMORY, RT_SRC_POS,
+                          N_("Qed: Allocating memory for the L1 table for image '%s' failed"),
+                          pImage->pszFilename);
+            break;
+        }
+
+        paL2Tbl = (uint64_t *)RTMemAllocZ(cbTable);
+        if (!paL2Tbl)
+        {
+            rc = vdIfError(pImage->pIfError, VERR_NO_MEMORY, RT_SRC_POS,
+                           N_("Qed: Allocating memory for the L2 table for image '%s' failed"),
+                           pImage->pszFilename);
+            break;
+        }
+
+        pvClusterBitmap = RTMemAllocZ(cbFile / pHeader->u32ClusterSize / 8);
+        if (!pvClusterBitmap)
+        {
+            rc = vdIfError(pImage->pIfError, VERR_NO_MEMORY, RT_SRC_POS,
+                           N_("Qed: Allocating memory for the cluster bitmap for image '%s' failed"),
+                           pImage->pszFilename);
+            break;
+        }
+
+        /* Validate L1 table offset. */
+        if (!qedIsTblOffsetValid(pHeader->u64OffL1Table, cbFile, cbTable, pHeader->u32ClusterSize))
+        {
+            rc = vdIfError(pImage->pIfError, VERR_VD_GEN_INVALID_HEADER, RT_SRC_POS,
+                           N_("Qed: L1 table offset of image '%s' is corrupt (%llu)"),
+                           pImage->pszFilename, pHeader->u64OffL1Table);
+            break;
+        }
+
+        /* Read L1 table. */
+        rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage,
+                                   pHeader->u64OffL1Table, paL1Tbl, cbTable);
+        if (RT_FAILURE(rc))
+        {
+            rc = vdIfError(pImage->pIfError, VERR_VD_GEN_INVALID_HEADER, RT_SRC_POS,
+                           N_("Qed: Reading the L1 table from image '%s' failed"),
+                           pImage->pszFilename);
+            break;
+        }
+
+        /* Mark the L1 table in cluster bitmap. */
+        ASMBitSet(pvClusterBitmap, 0); /* Header is always in cluster 0. */
+        offClusterStart = qedByte2Cluster(pImage, pHeader->u64OffL1Table);
+        bool fSet = qedClusterBitmapCheckAndSet(pvClusterBitmap, offClusterStart, offClusterStart + pHeader->u32TableSize);
+        Assert(fSet);
+
+        /* Scan the L1 and L2 tables for invalid entries. */
+        qedTableConvertToHostEndianess(paL1Tbl, cTableEntries);
+
+        for (unsigned iL1 = 0; iL1 < cTableEntries; iL1++)
+        {
+            if (!paL1Tbl[iL1])
+                continue; /* Skip unallocated clusters. */
+
+            if (!qedIsTblOffsetValid(paL1Tbl[iL1], cbFile, cbTable, pHeader->u32ClusterSize))
+            {
+                rc = vdIfError(pImage->pIfError, VERR_VD_GEN_INVALID_HEADER, RT_SRC_POS,
+                               N_("Qed: Entry %d of the L1 table from image '%s' is invalid (%llu)"),
+                               iL1, pImage->pszFilename, paL1Tbl[iL1]);
+                break;
+            }
+
+            /* Now check that the clusters are not allocated already. */
+            offClusterStart = qedByte2Cluster(pImage, paL1Tbl[iL1]);
+            fSet = qedClusterBitmapCheckAndSet(pvClusterBitmap, offClusterStart, offClusterStart + pHeader->u32TableSize);
+            if (!fSet)
+            {
+                rc = vdIfError(pImage->pIfError, VERR_VD_GEN_INVALID_HEADER, RT_SRC_POS,
+                               N_("Qed: Entry %d of the L1 table from image '%s' points to a already used cluster (%llu)"),
+                               iL1, pImage->pszFilename, paL1Tbl[iL1]);
+                break;
+            }
+
+            /* Read the linked L2 table and check it. */
+            rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage,
+                                       paL1Tbl[iL1], paL2Tbl, cbTable);
+            if (RT_FAILURE(rc))
+            {
+                rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS,
+                               N_("Qed: Reading the L2 table from image '%s' failed"),
+                               pImage->pszFilename);
+                break;
+            }
+
+            /* Check all L2 entries. */
+            for (unsigned iL2 = 0; iL2 < cTableEntries; iL2++)
+            {
+                if (paL2Tbl[iL2])
+                    continue; /* Skip unallocated clusters. */
+
+                if (!qedIsClusterOffsetValid(paL2Tbl[iL2], cbFile, pHeader->u32ClusterSize))
+                {
+                    rc = vdIfError(pImage->pIfError, VERR_VD_GEN_INVALID_HEADER, RT_SRC_POS,
+                                   N_("Qed: Entry %d of the L2 table from image '%s' is invalid (%llu)"),
+                                   iL2, pImage->pszFilename, paL2Tbl[iL2]);
+                    break;
+                }
+
+                /* Now check that the clusters are not allocated already. */
+                offClusterStart = qedByte2Cluster(pImage, paL2Tbl[iL2]);
+                fSet = qedClusterBitmapCheckAndSet(pvClusterBitmap, offClusterStart, offClusterStart + 1);
+                if (!fSet)
+                {
+                    rc = vdIfError(pImage->pIfError, VERR_VD_GEN_INVALID_HEADER, RT_SRC_POS,
+                                   N_("Qed: Entry %d of the L2 table from image '%s' points to a already used cluster (%llu)"),
+                                   iL2, pImage->pszFilename, paL2Tbl[iL2]);
+                    break;
+                }
+            }
+        }
+    } while(0);
+
+    if (paL1Tbl)
+        RTMemFree(paL1Tbl);
+    if (paL2Tbl)
+        RTMemFree(paL2Tbl);
+    if (pvClusterBitmap)
+        RTMemFree(pvClusterBitmap);
+
+    return rc;
+}
+
+/**
+ * Internal. Free all allocated space for representing an image except pImage,
+ * and optionally delete the image from disk.
+ */
+static int qedFreeImage(PQEDIMAGE pImage, bool fDelete)
+{
+    int rc = VINF_SUCCESS;
+
+    /* Freeing a never allocated image (e.g. because the open failed) is
+     * not signalled as an error. After all nothing bad happens. */
+    if (pImage)
+    {
+        if (pImage->pStorage)
+        {
+            /* No point updating the file that is deleted anyway. */
+            if (!fDelete)
+                qedFlushImage(pImage);
+
+            rc = vdIfIoIntFileClose(pImage->pIfIo, pImage->pStorage);
+            pImage->pStorage = NULL;
+        }
+
+        if (pImage->paL1Table)
+            RTMemFree(pImage->paL1Table);
+
+        if (pImage->pszBackingFilename)
+        {
+            RTStrFree(pImage->pszBackingFilename);
+            pImage->pszBackingFilename = NULL;
+        }
+
+        qedL2TblCacheDestroy(pImage);
+
+        if (fDelete && pImage->pszFilename)
+            vdIfIoIntFileDelete(pImage->pIfIo, pImage->pszFilename);
+    }
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/**
+ * Internal: Open an image, constructing all necessary data structures.
+ */
+static int qedOpenImage(PQEDIMAGE pImage, unsigned uOpenFlags)
+{
+    pImage->uOpenFlags = uOpenFlags;
+
+    pImage->pIfError = VDIfErrorGet(pImage->pVDIfsDisk);
+    pImage->pIfIo = VDIfIoIntGet(pImage->pVDIfsImage);
+    AssertPtrReturn(pImage->pIfIo, VERR_INVALID_PARAMETER);
+
+    /*
+     * Create the L2 cache before opening the image so we can call qedFreeImage()
+     * even if opening the image file fails.
+     */
+    int rc = qedL2TblCacheCreate(pImage);
+    if (RT_SUCCESS(rc))
+    {
+        /* Open the image. */
+        rc = vdIfIoIntFileOpen(pImage->pIfIo, pImage->pszFilename,
+                               VDOpenFlagsToFileOpenFlags(uOpenFlags,
+                                                          false /* fCreate */),
+                               &pImage->pStorage);
+        if (RT_SUCCESS(rc))
+        {
+            uint64_t cbFile;
+            rc = vdIfIoIntFileGetSize(pImage->pIfIo, pImage->pStorage, &cbFile);
+            if (   RT_SUCCESS(rc)
+                && cbFile > sizeof(QedHeader))
+            {
+                QedHeader Header;
+
+                rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage, 0, &Header, sizeof(Header));
+                if (   RT_SUCCESS(rc)
+                    && qedHdrConvertToHostEndianess(&Header))
+                {
+                    if (   !(Header.u64FeatureFlags & ~QED_FEATURE_MASK)
+                        && !(Header.u64FeatureFlags & QED_FEATURE_BACKING_FILE_NO_PROBE))
+                    {
+                        if (Header.u64FeatureFlags & QED_FEATURE_NEED_CHECK)
+                        {
+                            /* Image needs checking. */
+                            if (!(uOpenFlags & VD_OPEN_FLAGS_READONLY))
+                                rc = qedCheckImage(pImage, &Header);
+                            else
+                                rc = vdIfError(pImage->pIfError, VERR_NOT_SUPPORTED, RT_SRC_POS,
+                                               N_("Qed: Image '%s' needs checking but is opened readonly"),
+                                               pImage->pszFilename);
+                        }
+
+                        if (   RT_SUCCESS(rc)
+                            && (Header.u64FeatureFlags & QED_FEATURE_BACKING_FILE))
+                        {
+                            /* Load backing filename from image. */
+                            pImage->pszBackingFilename = RTStrAlloc(Header.u32BackingFilenameSize + 1); /* +1 for \0 terminator. */
+                            if (pImage->pszBackingFilename)
+                            {
+                                RT_BZERO(pImage->pszBackingFilename, Header.u32BackingFilenameSize + 1);
+                                pImage->cbBackingFilename  = Header.u32BackingFilenameSize;
+                                pImage->offBackingFilename = Header.u32OffBackingFilename;
+                                rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage,
+                                                           Header.u32OffBackingFilename, pImage->pszBackingFilename,
+                                                           Header.u32BackingFilenameSize);
+                                if (RT_SUCCESS(rc))
+                                    rc = RTStrValidateEncoding(pImage->pszBackingFilename);
+                            }
+                            else
+                                rc = VERR_NO_STR_MEMORY;
+                        }
+
+                        if (RT_SUCCESS(rc))
+                        {
+                            pImage->cbImage       = cbFile;
+                            pImage->cbCluster     = Header.u32ClusterSize;
+                            pImage->cbTable       = Header.u32TableSize * pImage->cbCluster;
+                            pImage->cTableEntries = pImage->cbTable / sizeof(uint64_t);
+                            pImage->offL1Table    = Header.u64OffL1Table;
+                            pImage->cbSize        = Header.u64Size;
+                            qedTableMasksInit(pImage);
+
+                            /* Allocate L1 table. */
+                            pImage->paL1Table     = (uint64_t *)RTMemAllocZ(pImage->cbTable);
+                            if (pImage->paL1Table)
+                            {
+                                /* Read from the image. */
+                                rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage,
+                                                           pImage->offL1Table, pImage->paL1Table,
+                                                           pImage->cbTable);
+                                if (RT_SUCCESS(rc))
+                                {
+                                    qedTableConvertToHostEndianess(pImage->paL1Table, pImage->cTableEntries);
+
+                                    /* If the consistency check succeeded, clear the flag by flushing the image. */
+                                    if (Header.u64FeatureFlags & QED_FEATURE_NEED_CHECK)
+                                        rc = qedFlushImage(pImage);
+                                }
+                                else
+                                    rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS,
+                                                   N_("Qed: Reading the L1 table for image '%s' failed"),
+                                                   pImage->pszFilename);
+                            }
+                            else
+                                rc = vdIfError(pImage->pIfError, VERR_NO_MEMORY, RT_SRC_POS,
+                                               N_("Qed: Out of memory allocating L1 table for image '%s'"),
+                                               pImage->pszFilename);
+                        }
+                    }
+                    else
+                        rc = vdIfError(pImage->pIfError, VERR_NOT_SUPPORTED, RT_SRC_POS,
+                                       N_("Qed: The image '%s' makes use of unsupported features"),
+                                       pImage->pszFilename);
+                }
+                else if (RT_SUCCESS(rc))
+                    rc = VERR_VD_GEN_INVALID_HEADER;
+            }
+            else if (RT_SUCCESS(rc))
+                rc = VERR_VD_GEN_INVALID_HEADER;
+        }
+        /* else: Do NOT signal an appropriate error here, as the VD layer has the
+         *       choice of retrying the open if it failed. */
+    }
+    else
+        rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS,
+                       N_("Qed: Creating the L2 table cache for image '%s' failed"),
+                       pImage->pszFilename);
+
+    if (RT_SUCCESS(rc))
+    {
+        PVDREGIONDESC pRegion = &pImage->RegionList.aRegions[0];
+        pImage->RegionList.fFlags   = 0;
+        pImage->RegionList.cRegions = 1;
+
+        pRegion->offRegion            = 0; /* Disk start. */
+        pRegion->cbBlock              = 512;
+        pRegion->enmDataForm          = VDREGIONDATAFORM_RAW;
+        pRegion->enmMetadataForm      = VDREGIONMETADATAFORM_NONE;
+        pRegion->cbData               = 512;
+        pRegion->cbMetadata           = 0;
+        pRegion->cRegionBlocksOrBytes = pImage->cbSize;
+    }
+    else
+        qedFreeImage(pImage, false);
+    return rc;
+}
+
+/**
+ * Internal: Create a qed image.
+ */
+static int qedCreateImage(PQEDIMAGE pImage, uint64_t cbSize,
+                          unsigned uImageFlags, const char *pszComment,
+                          PCVDGEOMETRY pPCHSGeometry,
+                          PCVDGEOMETRY pLCHSGeometry, unsigned uOpenFlags,
+                          PVDINTERFACEPROGRESS pIfProgress,
+                          unsigned uPercentStart, unsigned uPercentSpan)
+{
+    RT_NOREF1(pszComment);
+    int rc;
+
+    if (!(uImageFlags & VD_IMAGE_FLAGS_FIXED))
+    {
+        rc = qedL2TblCacheCreate(pImage);
+        if (RT_SUCCESS(rc))
+        {
+            pImage->uOpenFlags   = uOpenFlags & ~VD_OPEN_FLAGS_READONLY;
+            pImage->uImageFlags  = uImageFlags;
+            pImage->PCHSGeometry = *pPCHSGeometry;
+            pImage->LCHSGeometry = *pLCHSGeometry;
+
+            pImage->pIfError = VDIfErrorGet(pImage->pVDIfsDisk);
+            pImage->pIfIo = VDIfIoIntGet(pImage->pVDIfsImage);
+            AssertPtrReturn(pImage->pIfIo, VERR_INVALID_PARAMETER);
+
+            /* Create image file. */
+            uint32_t fOpen = VDOpenFlagsToFileOpenFlags(pImage->uOpenFlags, true /* fCreate */);
+            rc = vdIfIoIntFileOpen(pImage->pIfIo, pImage->pszFilename, fOpen, &pImage->pStorage);
+            if (RT_SUCCESS(rc))
+            {
+                /* Init image state. */
+                pImage->cbSize             = cbSize;
+                pImage->cbCluster          = QED_CLUSTER_SIZE_DEFAULT;
+                pImage->cbTable            = qedCluster2Byte(pImage, QED_TABLE_SIZE_DEFAULT);
+                pImage->cTableEntries      = pImage->cbTable / sizeof(uint64_t);
+                pImage->offL1Table         = qedCluster2Byte(pImage, 1); /* Cluster 0 is the header. */
+                pImage->cbImage            = (1 * pImage->cbCluster) + pImage->cbTable; /* Header + L1 table size. */
+                pImage->cbBackingFilename  = 0;
+                pImage->offBackingFilename = 0;
+                qedTableMasksInit(pImage);
+
+                /* Init L1 table. */
+                pImage->paL1Table = (uint64_t *)RTMemAllocZ(pImage->cbTable);
+                if (RT_LIKELY(pImage->paL1Table))
+                {
+                    vdIfProgress(pIfProgress, uPercentStart + uPercentSpan * 98 / 100);
+                    rc = qedFlushImage(pImage);
+                }
+                else
+                    rc = vdIfError(pImage->pIfError, VERR_NO_MEMORY, RT_SRC_POS, N_("Qed: cannot allocate memory for L1 table of image '%s'"),
+                                   pImage->pszFilename);
+            }
+            else
+                rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("Qed: cannot create image '%s'"), pImage->pszFilename);
+        }
+        else
+            rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("Qed: Failed to create L2 cache for image '%s'"),
+                           pImage->pszFilename);
+    }
+    else
+        rc = vdIfError(pImage->pIfError, VERR_VD_INVALID_TYPE, RT_SRC_POS, N_("Qed: cannot create fixed image '%s'"), pImage->pszFilename);
+
+    if (RT_SUCCESS(rc))
+    {
+        PVDREGIONDESC pRegion = &pImage->RegionList.aRegions[0];
+        pImage->RegionList.fFlags   = 0;
+        pImage->RegionList.cRegions = 1;
+
+        pRegion->offRegion            = 0; /* Disk start. */
+        pRegion->cbBlock              = 512;
+        pRegion->enmDataForm          = VDREGIONDATAFORM_RAW;
+        pRegion->enmMetadataForm      = VDREGIONMETADATAFORM_NONE;
+        pRegion->cbData               = 512;
+        pRegion->cbMetadata           = 0;
+        pRegion->cRegionBlocksOrBytes = pImage->cbSize;
+
+        vdIfProgress(pIfProgress, uPercentStart + uPercentSpan);
+    }
+    else
+        qedFreeImage(pImage, rc != VERR_ALREADY_EXISTS);
+
+    return rc;
+}
+
+/**
+ * Rollback anything done during async cluster allocation.
+ *
+ * @returns VBox status code.
+ * @param   pImage           The image instance data.
+ * @param   pIoCtx           The I/O context.
+ * @param   pClusterAlloc    The cluster allocation to rollback.
+ */
+static int qedAsyncClusterAllocRollback(PQEDIMAGE pImage, PVDIOCTX pIoCtx, PQEDCLUSTERASYNCALLOC pClusterAlloc)
+{
+    RT_NOREF1(pIoCtx);
+    int rc = VINF_SUCCESS;
+
+    switch (pClusterAlloc->enmAllocState)
+    {
+        case QEDCLUSTERASYNCALLOCSTATE_L2_ALLOC:
+        case QEDCLUSTERASYNCALLOCSTATE_L2_LINK:
+        {
+            /* Revert the L1 table entry */
+            pImage->paL1Table[pClusterAlloc->idxL1] = 0;
+            pImage->pL2TblAlloc = NULL;
+
+            /* Assumption right now is that the L1 table is not modified on storage if the link fails. */
+            rc = vdIfIoIntFileSetSize(pImage->pIfIo, pImage->pStorage, pClusterAlloc->cbImageOld);
+            qedL2TblCacheEntryRelease(pClusterAlloc->pL2Entry); /* Release L2 cache entry. */
+            Assert(!pClusterAlloc->pL2Entry->cRefs);
+            qedL2TblCacheEntryFree(pImage, pClusterAlloc->pL2Entry); /* Free it, it is not in the cache yet. */
+            break;
+        }
+        case QEDCLUSTERASYNCALLOCSTATE_USER_ALLOC:
+        case QEDCLUSTERASYNCALLOCSTATE_USER_LINK:
+        {
+            /* Assumption right now is that the L2 table is not modified if the link fails. */
+            pClusterAlloc->pL2Entry->paL2Tbl[pClusterAlloc->idxL2] = 0;
+            rc = vdIfIoIntFileSetSize(pImage->pIfIo, pImage->pStorage, pClusterAlloc->cbImageOld);
+            qedL2TblCacheEntryRelease(pClusterAlloc->pL2Entry); /* Release L2 cache entry. */
+            break;
+        }
+        default:
+            AssertMsgFailed(("Invalid cluster allocation state %d\n", pClusterAlloc->enmAllocState));
+            rc = VERR_INVALID_STATE;
+    }
+
+    RTMemFree(pClusterAlloc);
+    return rc;
+}
+
+/**
+ * Updates the state of the async cluster allocation.
+ *
+ * @returns VBox status code.
+ * @param   pBackendData    The opaque backend data.
+ * @param   pIoCtx          I/O context associated with this request.
+ * @param   pvUser          Opaque user data passed during a read/write request.
+ * @param   rcReq           Status code for the completed request.
+ */
+static DECLCALLBACK(int) qedAsyncClusterAllocUpdate(void *pBackendData, PVDIOCTX pIoCtx, void *pvUser, int rcReq)
+{
+    int rc = VINF_SUCCESS;
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    PQEDCLUSTERASYNCALLOC pClusterAlloc = (PQEDCLUSTERASYNCALLOC)pvUser;
+
+    if (RT_FAILURE(rcReq))
+        return qedAsyncClusterAllocRollback(pImage, pIoCtx, pClusterAlloc);
+
+    AssertPtr(pClusterAlloc->pL2Entry);
+
+    switch (pClusterAlloc->enmAllocState)
+    {
+        case QEDCLUSTERASYNCALLOCSTATE_L2_ALLOC:
+        {
+            /* Update the link in the in memory L1 table now. */
+            pImage->paL1Table[pClusterAlloc->idxL1] = pClusterAlloc->pL2Entry->offL2Tbl;
+
+            /* Update the link in the on disk L1 table now. */
+            pClusterAlloc->enmAllocState = QEDCLUSTERASYNCALLOCSTATE_L2_LINK;
+            rc = qedTblWrite(pImage, pIoCtx, pImage->offL1Table, pImage->paL1Table,
+                             qedAsyncClusterAllocUpdate, pClusterAlloc);
+            if (rc == VERR_VD_ASYNC_IO_IN_PROGRESS)
+                break;
+            else if (RT_FAILURE(rc))
+            {
+                /* Rollback. */
+                qedAsyncClusterAllocRollback(pImage, pIoCtx, pClusterAlloc);
+                break;
+            }
+        }
+        RT_FALL_THRU();
+        case QEDCLUSTERASYNCALLOCSTATE_L2_LINK:
+        {
+            /* L2 link updated in L1 , save L2 entry in cache and allocate new user data cluster. */
+            uint64_t offData = qedClusterAllocate(pImage, 1);
+
+            pImage->pL2TblAlloc = NULL;
+            qedL2TblCacheEntryInsert(pImage, pClusterAlloc->pL2Entry);
+
+            pClusterAlloc->enmAllocState = QEDCLUSTERASYNCALLOCSTATE_USER_ALLOC;
+            pClusterAlloc->cbImageOld    = offData;
+            pClusterAlloc->offClusterNew = offData;
+
+            /* Write data. */
+            rc = vdIfIoIntFileWriteUser(pImage->pIfIo, pImage->pStorage,
+                                        offData, pIoCtx, pClusterAlloc->cbToWrite,
+                                        qedAsyncClusterAllocUpdate, pClusterAlloc);
+            if (rc == VERR_VD_ASYNC_IO_IN_PROGRESS)
+                break;
+            else if (RT_FAILURE(rc))
+            {
+                qedAsyncClusterAllocRollback(pImage, pIoCtx, pClusterAlloc);
+                RTMemFree(pClusterAlloc);
+                break;
+            }
+        }
+        RT_FALL_THRU();
+        case QEDCLUSTERASYNCALLOCSTATE_USER_ALLOC:
+        {
+            pClusterAlloc->enmAllocState = QEDCLUSTERASYNCALLOCSTATE_USER_LINK;
+            pClusterAlloc->pL2Entry->paL2Tbl[pClusterAlloc->idxL2] = pClusterAlloc->offClusterNew;
+
+            /* Link L2 table and update it. */
+            rc = qedTblWrite(pImage, pIoCtx, pImage->paL1Table[pClusterAlloc->idxL1],
+                             pClusterAlloc->pL2Entry->paL2Tbl,
+                             qedAsyncClusterAllocUpdate, pClusterAlloc);
+            if (rc == VERR_VD_ASYNC_IO_IN_PROGRESS)
+                break;
+            else if (RT_FAILURE(rc))
+            {
+                qedAsyncClusterAllocRollback(pImage, pIoCtx, pClusterAlloc);
+                RTMemFree(pClusterAlloc);
+                break;
+            }
+        }
+        RT_FALL_THRU();
+        case QEDCLUSTERASYNCALLOCSTATE_USER_LINK:
+        {
+            /* Everything done without errors, signal completion. */
+            qedL2TblCacheEntryRelease(pClusterAlloc->pL2Entry);
+            RTMemFree(pClusterAlloc);
+            rc = VINF_SUCCESS;
+            break;
+        }
+        default:
+            AssertMsgFailed(("Invalid async cluster allocation state %d\n",
+                             pClusterAlloc->enmAllocState));
+    }
+
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnProbe */
+static DECLCALLBACK(int) qedProbe(const char *pszFilename, PVDINTERFACE pVDIfsDisk,
+                                  PVDINTERFACE pVDIfsImage, VDTYPE enmDesiredType, VDTYPE *penmType)
+{
+    RT_NOREF(pVDIfsDisk, enmDesiredType);
+    LogFlowFunc(("pszFilename=\"%s\" pVDIfsDisk=%#p pVDIfsImage=%#p\n", pszFilename, pVDIfsDisk, pVDIfsImage));
+    PVDIOSTORAGE pStorage = NULL;
+    int rc = VINF_SUCCESS;
+
+    /* Get I/O interface. */
+    PVDINTERFACEIOINT pIfIo = VDIfIoIntGet(pVDIfsImage);
+    AssertPtrReturn(pIfIo, VERR_INVALID_PARAMETER);
+    AssertPtrReturn(pszFilename, VERR_INVALID_POINTER);
+    AssertReturn(*pszFilename != '\0', VERR_INVALID_PARAMETER);
+
+
+    /*
+     * Open the file and read the footer.
+     */
+    rc = vdIfIoIntFileOpen(pIfIo, pszFilename,
+                           VDOpenFlagsToFileOpenFlags(VD_OPEN_FLAGS_READONLY,
+                                                      false /* fCreate */),
+                           &pStorage);
+    if (RT_SUCCESS(rc))
+    {
+        uint64_t cbFile;
+
+        rc = vdIfIoIntFileGetSize(pIfIo, pStorage, &cbFile);
+        if (   RT_SUCCESS(rc)
+            && cbFile > sizeof(QedHeader))
+        {
+            QedHeader Header;
+
+            rc = vdIfIoIntFileReadSync(pIfIo, pStorage, 0, &Header, sizeof(Header));
+            if (   RT_SUCCESS(rc)
+                && qedHdrConvertToHostEndianess(&Header))
+                *penmType = VDTYPE_HDD;
+            else
+                rc = VERR_VD_GEN_INVALID_HEADER;
+        }
+        else
+            rc = VERR_VD_GEN_INVALID_HEADER;
+    }
+
+    if (pStorage)
+        vdIfIoIntFileClose(pIfIo, pStorage);
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnOpen */
+static DECLCALLBACK(int) qedOpen(const char *pszFilename, unsigned uOpenFlags,
+                                 PVDINTERFACE pVDIfsDisk, PVDINTERFACE pVDIfsImage,
+                                 VDTYPE enmType, void **ppBackendData)
+{
+    RT_NOREF1(enmType); /**< @todo r=klaus make use of the type info. */
+
+    LogFlowFunc(("pszFilename=\"%s\" uOpenFlags=%#x pVDIfsDisk=%#p pVDIfsImage=%#p enmType=%u ppBackendData=%#p\n",
+                 pszFilename, uOpenFlags, pVDIfsDisk, pVDIfsImage, enmType, ppBackendData));
+    int rc;
+
+    /* Check open flags. All valid flags are supported. */
+    AssertReturn(!(uOpenFlags & ~VD_OPEN_FLAGS_MASK), VERR_INVALID_PARAMETER);
+    AssertPtrReturn(pszFilename, VERR_INVALID_POINTER);
+    AssertReturn(*pszFilename != '\0', VERR_INVALID_PARAMETER);
+
+
+    PQEDIMAGE pImage = (PQEDIMAGE)RTMemAllocZ(RT_UOFFSETOF(QEDIMAGE, RegionList.aRegions[1]));
+    if (RT_LIKELY(pImage))
+    {
+        pImage->pszFilename = pszFilename;
+        pImage->pStorage = NULL;
+        pImage->pVDIfsDisk = pVDIfsDisk;
+        pImage->pVDIfsImage = pVDIfsImage;
+
+        rc = qedOpenImage(pImage, uOpenFlags);
+        if (RT_SUCCESS(rc))
+            *ppBackendData = pImage;
+        else
+            RTMemFree(pImage);
+    }
+    else
+        rc = VERR_NO_MEMORY;
+
+    LogFlowFunc(("returns %Rrc (pBackendData=%#p)\n", rc, *ppBackendData));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnCreate */
+static DECLCALLBACK(int) qedCreate(const char *pszFilename, uint64_t cbSize,
+                                   unsigned uImageFlags, const char *pszComment,
+                                   PCVDGEOMETRY pPCHSGeometry, PCVDGEOMETRY pLCHSGeometry,
+                                   PCRTUUID pUuid, unsigned uOpenFlags,
+                                   unsigned uPercentStart, unsigned uPercentSpan,
+                                   PVDINTERFACE pVDIfsDisk, PVDINTERFACE pVDIfsImage,
+                                   PVDINTERFACE pVDIfsOperation, VDTYPE enmType,
+                                   void **ppBackendData)
+{
+    RT_NOREF1(pUuid);
+    LogFlowFunc(("pszFilename=\"%s\" cbSize=%llu uImageFlags=%#x pszComment=\"%s\" pPCHSGeometry=%#p pLCHSGeometry=%#p Uuid=%RTuuid uOpenFlags=%#x uPercentStart=%u uPercentSpan=%u pVDIfsDisk=%#p pVDIfsImage=%#p pVDIfsOperation=%#p enmType=%d ppBackendData=%#p",
+                 pszFilename, cbSize, uImageFlags, pszComment, pPCHSGeometry, pLCHSGeometry, pUuid, uOpenFlags, uPercentStart, uPercentSpan, pVDIfsDisk, pVDIfsImage, pVDIfsOperation, enmType, ppBackendData));
+    int rc;
+
+    /* Check the VD container type. */
+    if (enmType != VDTYPE_HDD)
+        return VERR_VD_INVALID_TYPE;
+
+    /* Check open flags. All valid flags are supported. */
+    AssertReturn(!(uOpenFlags & ~VD_OPEN_FLAGS_MASK), VERR_INVALID_PARAMETER);
+    AssertPtrReturn(pszFilename, VERR_INVALID_POINTER);
+    AssertReturn(*pszFilename != '\0', VERR_INVALID_PARAMETER);
+    AssertPtrReturn(pPCHSGeometry, VERR_INVALID_POINTER);
+    AssertPtrReturn(pLCHSGeometry, VERR_INVALID_POINTER);
+
+    PQEDIMAGE pImage = (PQEDIMAGE)RTMemAllocZ(RT_UOFFSETOF(QEDIMAGE, RegionList.aRegions[1]));
+    if (RT_LIKELY(pImage))
+    {
+        PVDINTERFACEPROGRESS pIfProgress = VDIfProgressGet(pVDIfsOperation);
+
+        pImage->pszFilename = pszFilename;
+        pImage->pStorage = NULL;
+        pImage->pVDIfsDisk = pVDIfsDisk;
+        pImage->pVDIfsImage = pVDIfsImage;
+
+        rc = qedCreateImage(pImage, cbSize, uImageFlags, pszComment,
+                            pPCHSGeometry, pLCHSGeometry, uOpenFlags,
+                            pIfProgress, uPercentStart, uPercentSpan);
+        if (RT_SUCCESS(rc))
+        {
+            /* So far the image is opened in read/write mode. Make sure the
+             * image is opened in read-only mode if the caller requested that. */
+            if (uOpenFlags & VD_OPEN_FLAGS_READONLY)
+            {
+                qedFreeImage(pImage, false);
+                rc = qedOpenImage(pImage, uOpenFlags);
+            }
+
+            if (RT_SUCCESS(rc))
+                *ppBackendData = pImage;
+        }
+
+        if (RT_FAILURE(rc))
+            RTMemFree(pImage);
+    }
+    else
+        rc = VERR_NO_MEMORY;
+
+    LogFlowFunc(("returns %Rrc (pBackendData=%#p)\n", rc, *ppBackendData));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnRename */
+static DECLCALLBACK(int) qedRename(void *pBackendData, const char *pszFilename)
+{
+    LogFlowFunc(("pBackendData=%#p pszFilename=%#p\n", pBackendData, pszFilename));
+    int rc = VINF_SUCCESS;
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+
+    /* Check arguments. */
+    AssertReturn((pImage && pszFilename && *pszFilename), VERR_INVALID_PARAMETER);
+
+    /* Close the image. */
+    rc = qedFreeImage(pImage, false);
+    if (RT_SUCCESS(rc))
+    {
+        /* Rename the file. */
+        rc = vdIfIoIntFileMove(pImage->pIfIo, pImage->pszFilename, pszFilename, 0);
+        if (RT_SUCCESS(rc))
+        {
+            /* Update pImage with the new information. */
+            pImage->pszFilename = pszFilename;
+
+            /* Open the old image with new name. */
+            rc = qedOpenImage(pImage, pImage->uOpenFlags);
+        }
+        else
+        {
+            /* The move failed, try to reopen the original image. */
+            int rc2 = qedOpenImage(pImage, pImage->uOpenFlags);
+            if (RT_FAILURE(rc2))
+                rc = rc2;
+        }
+    }
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnClose */
+static DECLCALLBACK(int) qedClose(void *pBackendData, bool fDelete)
+{
+    LogFlowFunc(("pBackendData=%#p fDelete=%d\n", pBackendData, fDelete));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+
+    int rc = qedFreeImage(pImage, fDelete);
+    RTMemFree(pImage);
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnRead */
+static DECLCALLBACK(int) qedRead(void *pBackendData, uint64_t uOffset, size_t cbToRead,
+                                 PVDIOCTX pIoCtx, size_t *pcbActuallyRead)
+{
+    LogFlowFunc(("pBackendData=%#p uOffset=%llu pIoCtx=%#p cbToRead=%zu pcbActuallyRead=%#p\n",
+                 pBackendData, uOffset, pIoCtx, cbToRead, pcbActuallyRead));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    uint32_t offCluster = 0;
+    uint32_t idxL1      = 0;
+    uint32_t idxL2      = 0;
+    uint64_t offFile    = 0;
+
+    AssertPtr(pImage);
+    Assert(uOffset % 512 == 0);
+    Assert(cbToRead % 512 == 0);
+    AssertPtrReturn(pIoCtx, VERR_INVALID_POINTER);
+    AssertReturn(cbToRead, VERR_INVALID_PARAMETER);
+    AssertReturn(uOffset + cbToRead <= pImage->cbSize, VERR_INVALID_PARAMETER);
+
+    qedConvertLogicalOffset(pImage, uOffset, &idxL1, &idxL2, &offCluster);
+
+    /* Clip read size to remain in the cluster. */
+    cbToRead = RT_MIN(cbToRead, pImage->cbCluster - offCluster);
+
+    /* Get offset in image. */
+    int rc = qedConvertToImageOffset(pImage, pIoCtx, idxL1, idxL2, offCluster, &offFile);
+    if (RT_SUCCESS(rc))
+        rc = vdIfIoIntFileReadUser(pImage->pIfIo, pImage->pStorage, offFile,
+                                   pIoCtx, cbToRead);
+
+    if (   (   RT_SUCCESS(rc)
+            || rc == VERR_VD_BLOCK_FREE
+            || rc == VERR_VD_ASYNC_IO_IN_PROGRESS)
+        && pcbActuallyRead)
+        *pcbActuallyRead = cbToRead;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnWrite */
+static DECLCALLBACK(int) qedWrite(void *pBackendData, uint64_t uOffset, size_t cbToWrite,
+                                  PVDIOCTX pIoCtx, size_t *pcbWriteProcess, size_t *pcbPreRead,
+                                  size_t *pcbPostRead, unsigned fWrite)
+{
+    LogFlowFunc(("pBackendData=%#p uOffset=%llu pIoCtx=%#p cbToWrite=%zu pcbWriteProcess=%#p pcbPreRead=%#p pcbPostRead=%#p\n",
+                 pBackendData, uOffset, pIoCtx, cbToWrite, pcbWriteProcess, pcbPreRead, pcbPostRead));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    uint32_t offCluster = 0;
+    uint32_t idxL1      = 0;
+    uint32_t idxL2      = 0;
+    uint64_t offImage   = 0;
+    int rc = VINF_SUCCESS;
+
+    AssertPtr(pImage);
+    Assert(!(uOffset % 512));
+    Assert(!(cbToWrite % 512));
+    AssertPtrReturn(pIoCtx, VERR_INVALID_POINTER);
+    AssertReturn(cbToWrite, VERR_INVALID_PARAMETER);
+    AssertReturn(uOffset + cbToWrite <= pImage->cbSize, VERR_INVALID_PARAMETER);
+
+    if (!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        /* Convert offset to L1, L2 index and cluster offset. */
+        qedConvertLogicalOffset(pImage, uOffset, &idxL1, &idxL2, &offCluster);
+
+        /* Clip write size to remain in the cluster. */
+        cbToWrite = RT_MIN(cbToWrite, pImage->cbCluster - offCluster);
+        Assert(!(cbToWrite % 512));
+
+        /* Get offset in image. */
+        rc = qedConvertToImageOffset(pImage, pIoCtx, idxL1, idxL2, offCluster, &offImage);
+        if (RT_SUCCESS(rc))
+            rc = vdIfIoIntFileWriteUser(pImage->pIfIo, pImage->pStorage,
+                                        offImage, pIoCtx, cbToWrite, NULL, NULL);
+        else if (rc == VERR_VD_BLOCK_FREE)
+        {
+            if (   cbToWrite == pImage->cbCluster
+                && !(fWrite & VD_WRITE_NO_ALLOC))
+            {
+                PQEDL2CACHEENTRY pL2Entry = NULL;
+
+                /* Full cluster write to previously unallocated cluster.
+                 * Allocate cluster and write data. */
+                Assert(!offCluster);
+
+                do
+                {
+                    /* Check if we have to allocate a new cluster for L2 tables. */
+                    if (!pImage->paL1Table[idxL1])
+                    {
+                        uint64_t offL2Tbl;
+                        PQEDCLUSTERASYNCALLOC pL2ClusterAlloc = NULL;
+
+                        /* Allocate new async cluster allocation state. */
+                        pL2ClusterAlloc = (PQEDCLUSTERASYNCALLOC)RTMemAllocZ(sizeof(QEDCLUSTERASYNCALLOC));
+                        if (RT_UNLIKELY(!pL2ClusterAlloc))
+                        {
+                            rc = VERR_NO_MEMORY;
+                            break;
+                        }
+
+                        pL2Entry = qedL2TblCacheEntryAlloc(pImage);
+                        if (!pL2Entry)
+                        {
+                            rc = VERR_NO_MEMORY;
+                            RTMemFree(pL2ClusterAlloc);
+                            break;
+                        }
+
+                        offL2Tbl = qedClusterAllocate(pImage, qedByte2Cluster(pImage, pImage->cbTable));
+                        pL2Entry->offL2Tbl = offL2Tbl;
+                        memset(pL2Entry->paL2Tbl, 0, pImage->cbTable);
+
+                        pL2ClusterAlloc->enmAllocState = QEDCLUSTERASYNCALLOCSTATE_L2_ALLOC;
+                        pL2ClusterAlloc->cbImageOld    = offL2Tbl;
+                        pL2ClusterAlloc->offClusterNew = offL2Tbl;
+                        pL2ClusterAlloc->idxL1         = idxL1;
+                        pL2ClusterAlloc->idxL2         = idxL2;
+                        pL2ClusterAlloc->cbToWrite     = cbToWrite;
+                        pL2ClusterAlloc->pL2Entry      = pL2Entry;
+
+                        pImage->pL2TblAlloc = pL2Entry;
+
+                        LogFlowFunc(("Allocating new L2 table at cluster offset %llu\n", offL2Tbl));
+
+                        /*
+                         * Write the L2 table first and link to the L1 table afterwards.
+                         * If something unexpected happens the worst case which can happen
+                         * is a leak of some clusters.
+                         */
+                        rc = vdIfIoIntFileWriteMeta(pImage->pIfIo, pImage->pStorage,
+                                                    offL2Tbl, pL2Entry->paL2Tbl, pImage->cbTable, pIoCtx,
+                                                    qedAsyncClusterAllocUpdate, pL2ClusterAlloc);
+                        if (rc == VERR_VD_ASYNC_IO_IN_PROGRESS)
+                            break;
+                        else if (RT_FAILURE(rc))
+                        {
+                            RTMemFree(pL2ClusterAlloc);
+                            qedL2TblCacheEntryFree(pImage, pL2Entry);
+                            break;
+                        }
+
+                        rc = qedAsyncClusterAllocUpdate(pImage, pIoCtx, pL2ClusterAlloc, rc);
+                    }
+                    else
+                    {
+                        LogFlowFunc(("Fetching L2 table at cluster offset %llu\n", pImage->paL1Table[idxL1]));
+
+                        rc = qedL2TblCacheFetchAsync(pImage, pIoCtx, pImage->paL1Table[idxL1],
+                                                     &pL2Entry);
+
+                        if (RT_SUCCESS(rc))
+                        {
+                            PQEDCLUSTERASYNCALLOC pDataClusterAlloc = NULL;
+
+                            /* Allocate new async cluster allocation state. */
+                            pDataClusterAlloc = (PQEDCLUSTERASYNCALLOC)RTMemAllocZ(sizeof(QEDCLUSTERASYNCALLOC));
+                            if (RT_UNLIKELY(!pDataClusterAlloc))
+                            {
+                                rc = VERR_NO_MEMORY;
+                                break;
+                            }
+
+                            /* Allocate new cluster for the data. */
+                            uint64_t offData = qedClusterAllocate(pImage, 1);
+
+                            pDataClusterAlloc->enmAllocState = QEDCLUSTERASYNCALLOCSTATE_USER_ALLOC;
+                            pDataClusterAlloc->cbImageOld    = offData;
+                            pDataClusterAlloc->offClusterNew = offData;
+                            pDataClusterAlloc->idxL1         = idxL1;
+                            pDataClusterAlloc->idxL2         = idxL2;
+                            pDataClusterAlloc->cbToWrite     = cbToWrite;
+                            pDataClusterAlloc->pL2Entry      = pL2Entry;
+
+                            /* Write data. */
+                            rc = vdIfIoIntFileWriteUser(pImage->pIfIo, pImage->pStorage,
+                                                        offData, pIoCtx, cbToWrite,
+                                                        qedAsyncClusterAllocUpdate, pDataClusterAlloc);
+                            if (rc == VERR_VD_ASYNC_IO_IN_PROGRESS)
+                                break;
+                            else if (RT_FAILURE(rc))
+                            {
+                                RTMemFree(pDataClusterAlloc);
+                                break;
+                            }
+
+                            rc = qedAsyncClusterAllocUpdate(pImage, pIoCtx, pDataClusterAlloc, rc);
+                        }
+                    }
+
+                } while (0);
+
+                *pcbPreRead = 0;
+                *pcbPostRead = 0;
+            }
+            else
+            {
+                /* Trying to do a partial write to an unallocated cluster. Don't do
+                 * anything except letting the upper layer know what to do. */
+                *pcbPreRead = offCluster;
+                *pcbPostRead = pImage->cbCluster - cbToWrite - *pcbPreRead;
+            }
+        }
+
+        if (pcbWriteProcess)
+            *pcbWriteProcess = cbToWrite;
+    }
+    else
+        rc = VERR_VD_IMAGE_READ_ONLY;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnFlush */
+static DECLCALLBACK(int) qedFlush(void *pBackendData, PVDIOCTX pIoCtx)
+{
+    LogFlowFunc(("pBackendData=%#p\n", pBackendData));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    int rc = VINF_SUCCESS;
+
+    AssertPtr(pImage);
+    AssertPtrReturn(pIoCtx, VERR_INVALID_PARAMETER);
+
+    if (   pImage->pStorage
+        && !(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        QedHeader Header;
+
+        Assert(!(pImage->cbTable % pImage->cbCluster));
+        rc = qedTblWrite(pImage, pIoCtx, pImage->offL1Table, pImage->paL1Table,
+                         NULL, NULL);
+        if (RT_SUCCESS(rc) || rc == VERR_VD_ASYNC_IO_IN_PROGRESS)
+        {
+            /* Write header. */
+            qedHdrConvertFromHostEndianess(pImage, &Header);
+            rc = vdIfIoIntFileWriteMeta(pImage->pIfIo, pImage->pStorage,
+                                        0, &Header, sizeof(Header),
+                                        pIoCtx, NULL, NULL);
+            if (RT_SUCCESS(rc) || rc == VERR_VD_ASYNC_IO_IN_PROGRESS)
+                rc = vdIfIoIntFileFlush(pImage->pIfIo, pImage->pStorage,
+                                        pIoCtx, NULL, NULL);
+        }
+    }
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetVersion */
+static DECLCALLBACK(unsigned) qedGetVersion(void *pBackendData)
+{
+    LogFlowFunc(("pBackendData=%#p\n", pBackendData));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+
+    AssertPtrReturn(pImage, 0);
+
+    return 1;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetFileSize */
+static DECLCALLBACK(uint64_t) qedGetFileSize(void *pBackendData)
+{
+    LogFlowFunc(("pBackendData=%#p\n", pBackendData));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    uint64_t cb = 0;
+
+    AssertPtrReturn(pImage, 0);
+
+    uint64_t cbFile;
+    if (pImage->pStorage)
+    {
+        int rc = vdIfIoIntFileGetSize(pImage->pIfIo, pImage->pStorage, &cbFile);
+        if (RT_SUCCESS(rc))
+            cb += cbFile;
+    }
+
+    LogFlowFunc(("returns %lld\n", cb));
+    return cb;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetPCHSGeometry */
+static DECLCALLBACK(int) qedGetPCHSGeometry(void *pBackendData,
+                                            PVDGEOMETRY pPCHSGeometry)
+{
+    LogFlowFunc(("pBackendData=%#p pPCHSGeometry=%#p\n", pBackendData, pPCHSGeometry));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    int rc = VINF_SUCCESS;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    if (pImage->PCHSGeometry.cCylinders)
+        *pPCHSGeometry = pImage->PCHSGeometry;
+    else
+        rc = VERR_VD_GEOMETRY_NOT_SET;
+
+    LogFlowFunc(("returns %Rrc (PCHS=%u/%u/%u)\n", rc, pPCHSGeometry->cCylinders, pPCHSGeometry->cHeads, pPCHSGeometry->cSectors));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnSetPCHSGeometry */
+static DECLCALLBACK(int) qedSetPCHSGeometry(void *pBackendData,
+                                            PCVDGEOMETRY pPCHSGeometry)
+{
+    LogFlowFunc(("pBackendData=%#p pPCHSGeometry=%#p PCHS=%u/%u/%u\n",
+                 pBackendData, pPCHSGeometry, pPCHSGeometry->cCylinders, pPCHSGeometry->cHeads, pPCHSGeometry->cSectors));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    int rc = VINF_SUCCESS;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    if (pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY)
+        rc = VERR_VD_IMAGE_READ_ONLY;
+    else
+        pImage->PCHSGeometry = *pPCHSGeometry;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetLCHSGeometry */
+static DECLCALLBACK(int) qedGetLCHSGeometry(void *pBackendData, PVDGEOMETRY pLCHSGeometry)
+{
+    LogFlowFunc(("pBackendData=%#p pLCHSGeometry=%#p\n", pBackendData, pLCHSGeometry));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    int rc = VINF_SUCCESS;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    if (pImage->LCHSGeometry.cCylinders)
+        *pLCHSGeometry = pImage->LCHSGeometry;
+    else
+        rc = VERR_VD_GEOMETRY_NOT_SET;
+
+    LogFlowFunc(("returns %Rrc (LCHS=%u/%u/%u)\n", rc, pLCHSGeometry->cCylinders,
+                 pLCHSGeometry->cHeads, pLCHSGeometry->cSectors));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnSetLCHSGeometry */
+static DECLCALLBACK(int) qedSetLCHSGeometry(void *pBackendData, PCVDGEOMETRY pLCHSGeometry)
+{
+    LogFlowFunc(("pBackendData=%#p pLCHSGeometry=%#p LCHS=%u/%u/%u\n", pBackendData,
+                 pLCHSGeometry, pLCHSGeometry->cCylinders, pLCHSGeometry->cHeads, pLCHSGeometry->cSectors));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    int rc = VINF_SUCCESS;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    if (pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY)
+        rc = VERR_VD_IMAGE_READ_ONLY;
+    else
+        pImage->LCHSGeometry = *pLCHSGeometry;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnQueryRegions */
+static DECLCALLBACK(int) qedQueryRegions(void *pBackendData, PCVDREGIONLIST *ppRegionList)
+{
+    LogFlowFunc(("pBackendData=%#p ppRegionList=%#p\n", pBackendData, ppRegionList));
+    PQEDIMAGE pThis = (PQEDIMAGE)pBackendData;
+
+    AssertPtrReturn(pThis, VERR_VD_NOT_OPENED);
+
+    *ppRegionList = &pThis->RegionList;
+    LogFlowFunc(("returns %Rrc\n", VINF_SUCCESS));
+    return VINF_SUCCESS;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnRegionListRelease */
+static DECLCALLBACK(void) qedRegionListRelease(void *pBackendData, PCVDREGIONLIST pRegionList)
+{
+    RT_NOREF1(pRegionList);
+    LogFlowFunc(("pBackendData=%#p pRegionList=%#p\n", pBackendData, pRegionList));
+    PQEDIMAGE pThis = (PQEDIMAGE)pBackendData;
+    AssertPtr(pThis); RT_NOREF(pThis);
+
+    /* Nothing to do here. */
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetImageFlags */
+static DECLCALLBACK(unsigned) qedGetImageFlags(void *pBackendData)
+{
+    LogFlowFunc(("pBackendData=%#p\n", pBackendData));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+
+    AssertPtrReturn(pImage, 0);
+
+    LogFlowFunc(("returns %#x\n", pImage->uImageFlags));
+    return pImage->uImageFlags;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetOpenFlags */
+static DECLCALLBACK(unsigned) qedGetOpenFlags(void *pBackendData)
+{
+    LogFlowFunc(("pBackendData=%#p\n", pBackendData));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+
+    AssertPtrReturn(pImage, 0);
+
+    LogFlowFunc(("returns %#x\n", pImage->uOpenFlags));
+    return pImage->uOpenFlags;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnSetOpenFlags */
+static DECLCALLBACK(int) qedSetOpenFlags(void *pBackendData, unsigned uOpenFlags)
+{
+    LogFlowFunc(("pBackendData=%#p\n uOpenFlags=%#x", pBackendData, uOpenFlags));
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    int rc = VINF_SUCCESS;
+
+    /* Image must be opened and the new flags must be valid. */
+    if (!pImage || (uOpenFlags & ~(  VD_OPEN_FLAGS_READONLY | VD_OPEN_FLAGS_INFO
+                                   | VD_OPEN_FLAGS_ASYNC_IO | VD_OPEN_FLAGS_SHAREABLE
+                                   | VD_OPEN_FLAGS_SEQUENTIAL | VD_OPEN_FLAGS_SKIP_CONSISTENCY_CHECKS)))
+        rc = VERR_INVALID_PARAMETER;
+    else
+    {
+        /* Implement this operation via reopening the image. */
+        rc = qedFreeImage(pImage, false);
+        if (RT_SUCCESS(rc))
+            rc = qedOpenImage(pImage, uOpenFlags);
+    }
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetComment */
+VD_BACKEND_CALLBACK_GET_COMMENT_DEF_NOT_SUPPORTED(qedGetComment);
+
+/** @copydoc VDIMAGEBACKEND::pfnSetComment */
+VD_BACKEND_CALLBACK_SET_COMMENT_DEF_NOT_SUPPORTED(qedSetComment, PQEDIMAGE);
+
+/** @copydoc VDIMAGEBACKEND::pfnGetUuid */
+VD_BACKEND_CALLBACK_GET_UUID_DEF_NOT_SUPPORTED(qedGetUuid);
+
+/** @copydoc VDIMAGEBACKEND::pfnSetUuid */
+VD_BACKEND_CALLBACK_SET_UUID_DEF_NOT_SUPPORTED(qedSetUuid, PQEDIMAGE);
+
+/** @copydoc VDIMAGEBACKEND::pfnGetModificationUuid */
+VD_BACKEND_CALLBACK_GET_UUID_DEF_NOT_SUPPORTED(qedGetModificationUuid);
+
+/** @copydoc VDIMAGEBACKEND::pfnSetModificationUuid */
+VD_BACKEND_CALLBACK_SET_UUID_DEF_NOT_SUPPORTED(qedSetModificationUuid, PQEDIMAGE);
+
+/** @copydoc VDIMAGEBACKEND::pfnGetParentUuid */
+VD_BACKEND_CALLBACK_GET_UUID_DEF_NOT_SUPPORTED(qedGetParentUuid);
+
+/** @copydoc VDIMAGEBACKEND::pfnSetParentUuid */
+VD_BACKEND_CALLBACK_SET_UUID_DEF_NOT_SUPPORTED(qedSetParentUuid, PQEDIMAGE);
+
+/** @copydoc VDIMAGEBACKEND::pfnGetParentModificationUuid */
+VD_BACKEND_CALLBACK_GET_UUID_DEF_NOT_SUPPORTED(qedGetParentModificationUuid);
+
+/** @copydoc VDIMAGEBACKEND::pfnSetParentModificationUuid */
+VD_BACKEND_CALLBACK_SET_UUID_DEF_NOT_SUPPORTED(qedSetParentModificationUuid, PQEDIMAGE);
+
+/** @copydoc VDIMAGEBACKEND::pfnDump */
+static DECLCALLBACK(void) qedDump(void *pBackendData)
+{
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+
+    AssertPtrReturnVoid(pImage);
+    vdIfErrorMessage(pImage->pIfError, "Header: Geometry PCHS=%u/%u/%u LCHS=%u/%u/%u cbSector=%llu\n",
+                     pImage->PCHSGeometry.cCylinders, pImage->PCHSGeometry.cHeads, pImage->PCHSGeometry.cSectors,
+                     pImage->LCHSGeometry.cCylinders, pImage->LCHSGeometry.cHeads, pImage->LCHSGeometry.cSectors,
+                     pImage->cbSize / 512);
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetParentFilename */
+static DECLCALLBACK(int) qedGetParentFilename(void *pBackendData, char **ppszParentFilename)
+{
+    int rc = VINF_SUCCESS;
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    if (pImage->pszBackingFilename)
+        *ppszParentFilename = RTStrDup(pImage->pszBackingFilename);
+    else
+        rc = VERR_NOT_SUPPORTED;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnSetParentFilename */
+static DECLCALLBACK(int) qedSetParentFilename(void *pBackendData, const char *pszParentFilename)
+{
+    int rc = VINF_SUCCESS;
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    if (pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY)
+        rc = VERR_VD_IMAGE_READ_ONLY;
+    else if (   pImage->pszBackingFilename
+             && (strlen(pszParentFilename) > pImage->cbBackingFilename))
+        rc = VERR_NOT_SUPPORTED; /* The new filename is longer than the old one. */
+    else
+    {
+        if (pImage->pszBackingFilename)
+            RTStrFree(pImage->pszBackingFilename);
+        pImage->pszBackingFilename = RTStrDup(pszParentFilename);
+        if (!pImage->pszBackingFilename)
+            rc = VERR_NO_STR_MEMORY;
+        else
+        {
+            if (!pImage->offBackingFilename)
+            {
+                /* Allocate new cluster. */
+                uint64_t offData = qedClusterAllocate(pImage, 1);
+
+                Assert((offData & UINT32_MAX) == offData);
+                pImage->offBackingFilename = (uint32_t)offData;
+                pImage->cbBackingFilename  = (uint32_t)strlen(pszParentFilename);
+                rc = vdIfIoIntFileSetSize(pImage->pIfIo, pImage->pStorage,
+                                          offData + pImage->cbCluster);
+            }
+
+            if (RT_SUCCESS(rc))
+                rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage,
+                                            pImage->offBackingFilename,
+                                            pImage->pszBackingFilename,
+                                            strlen(pImage->pszBackingFilename));
+        }
+    }
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnResize */
+static DECLCALLBACK(int) qedResize(void *pBackendData, uint64_t cbSize,
+                                   PCVDGEOMETRY pPCHSGeometry, PCVDGEOMETRY pLCHSGeometry,
+                                   unsigned uPercentStart, unsigned uPercentSpan,
+                                   PVDINTERFACE pVDIfsDisk, PVDINTERFACE pVDIfsImage,
+                                   PVDINTERFACE pVDIfsOperation)
+{
+    RT_NOREF7(pPCHSGeometry, pLCHSGeometry, uPercentStart, uPercentSpan, pVDIfsDisk, pVDIfsImage, pVDIfsOperation);
+    PQEDIMAGE pImage = (PQEDIMAGE)pBackendData;
+    int rc = VINF_SUCCESS;
+
+    /* Making the image smaller is not supported at the moment. */
+    if (cbSize < pImage->cbSize)
+        rc = VERR_NOT_SUPPORTED;
+    else if (cbSize > pImage->cbSize)
+    {
+        /*
+         * It is enough to just update the size field in the header to complete
+         * growing. With the default cluster and table sizes the image can be expanded
+         * to 64TB without overflowing the L1 and L2 tables making block relocation
+         * superfluous.
+         * @todo: The rare case where block relocation is still required (non default
+         *        table and/or cluster size or images with more than 64TB) is not
+         *        implemented yet and resizing such an image will fail with an error.
+         */
+        if (qedByte2Cluster(pImage, pImage->cbTable)*pImage->cTableEntries*pImage->cTableEntries*pImage->cbCluster < cbSize)
+            rc = vdIfError(pImage->pIfError, VERR_BUFFER_OVERFLOW, RT_SRC_POS,
+                           N_("Qed: Resizing the image '%s' is not supported because it would overflow the L1 and L2 table\n"),
+                           pImage->pszFilename);
+        else
+        {
+            uint64_t cbSizeOld = pImage->cbSize;
+
+            pImage->cbSize = cbSize;
+            rc = qedFlushImage(pImage);
+            if (RT_FAILURE(rc))
+            {
+                pImage->cbSize = cbSizeOld; /* Restore */
+
+                rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("Qed: Resizing the image '%s' failed\n"),
+                               pImage->pszFilename);
+            }
+        }
+    }
+    /* Same size doesn't change the image at all. */
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+
+const VDIMAGEBACKEND g_QedBackend =
+{
+    /* u32Version */
+    VD_IMGBACKEND_VERSION,
+    /* pszBackendName */
+    "QED",
+    /* uBackendCaps */
+    VD_CAP_FILE | VD_CAP_VFS | VD_CAP_CREATE_DYNAMIC | VD_CAP_DIFF | VD_CAP_ASYNC,
+    /* paFileExtensions */
+    s_aQedFileExtensions,
+    /* paConfigInfo */
+    NULL,
+    /* pfnProbe */
+    qedProbe,
+    /* pfnOpen */
+    qedOpen,
+    /* pfnCreate */
+    qedCreate,
+    /* pfnRename */
+    qedRename,
+    /* pfnClose */
+    qedClose,
+    /* pfnRead */
+    qedRead,
+    /* pfnWrite */
+    qedWrite,
+    /* pfnFlush */
+    qedFlush,
+    /* pfnDiscard */
+    NULL,
+    /* pfnGetVersion */
+    qedGetVersion,
+    /* pfnGetFileSize */
+    qedGetFileSize,
+    /* pfnGetPCHSGeometry */
+    qedGetPCHSGeometry,
+    /* pfnSetPCHSGeometry */
+    qedSetPCHSGeometry,
+    /* pfnGetLCHSGeometry */
+    qedGetLCHSGeometry,
+    /* pfnSetLCHSGeometry */
+    qedSetLCHSGeometry,
+    /* pfnQueryRegions */
+    qedQueryRegions,
+    /* pfnRegionListRelease */
+    qedRegionListRelease,
+    /* pfnGetImageFlags */
+    qedGetImageFlags,
+    /* pfnGetOpenFlags */
+    qedGetOpenFlags,
+    /* pfnSetOpenFlags */
+    qedSetOpenFlags,
+    /* pfnGetComment */
+    qedGetComment,
+    /* pfnSetComment */
+    qedSetComment,
+    /* pfnGetUuid */
+    qedGetUuid,
+    /* pfnSetUuid */
+    qedSetUuid,
+    /* pfnGetModificationUuid */
+    qedGetModificationUuid,
+    /* pfnSetModificationUuid */
+    qedSetModificationUuid,
+    /* pfnGetParentUuid */
+    qedGetParentUuid,
+    /* pfnSetParentUuid */
+    qedSetParentUuid,
+    /* pfnGetParentModificationUuid */
+    qedGetParentModificationUuid,
+    /* pfnSetParentModificationUuid */
+    qedSetParentModificationUuid,
+    /* pfnDump */
+    qedDump,
+    /* pfnGetTimestamp */
+    NULL,
+    /* pfnGetParentTimestamp */
+    NULL,
+    /* pfnSetParentTimestamp */
+    NULL,
+    /* pfnGetParentFilename */
+    qedGetParentFilename,
+    /* pfnSetParentFilename */
+    qedSetParentFilename,
+    /* pfnComposeLocation */
+    genericFileComposeLocation,
+    /* pfnComposeName */
+    genericFileComposeName,
+    /* pfnCompact */
+    NULL,
+    /* pfnResize */
+    qedResize,
+    /* pfnRepair */
+    NULL,
+    /* pfnTraverseMetadata */
+    NULL,
+    /* u32Version */
+    VD_IMGBACKEND_VERSION
+};