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, 3269 insertions, 0 deletions

diff --git a/src/VBox/Storage/VDI.cpp b/src/VBox/Storage/VDI.cpp
new file mode 100644
index 00000000..6e38c593
--- /dev/null
+++ b/src/VBox/Storage/VDI.cpp
@@ -0,0 +1,3269 @@
+/* $Id: VDI.cpp $ */
+/** @file
+ * Virtual Disk Image (VDI), Core Code.
+ */
+
+/*
+ * Copyright (C) 2006-2023 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_VDI
+#include <VBox/vd-plugin.h>
+#include "VDICore.h"
+#include <VBox/err.h>
+
+#include <VBox/log.h>
+#include <iprt/alloc.h>
+#include <iprt/assert.h>
+#include <iprt/uuid.h>
+#include <iprt/string.h>
+#include <iprt/asm.h>
+
+#include "VDBackends.h"
+
+#define VDI_IMAGE_DEFAULT_BLOCK_SIZE _1M
+
+/** Macros for endianess conversion. */
+#define SET_ENDIAN_U32(conv, u32) (conv == VDIECONV_H2F ? RT_H2LE_U32(u32) : RT_LE2H_U32(u32))
+#define SET_ENDIAN_U64(conv, u64) (conv == VDIECONV_H2F ? RT_H2LE_U64(u64) : RT_LE2H_U64(u64))
+
+static const char *vdiAllocationBlockSize = "1048576";
+
+static const VDCONFIGINFO vdiConfigInfo[] =
+{
+    { "AllocationBlockSize",            vdiAllocationBlockSize,           VDCFGVALUETYPE_INTEGER,      VD_CFGKEY_CREATEONLY },
+    { NULL,                             NULL,                             VDCFGVALUETYPE_INTEGER,      0 }
+};
+
+
+/*********************************************************************************************************************************
+*   Static Variables                                                                                                             *
+*********************************************************************************************************************************/
+
+/** NULL-terminated array of supported file extensions. */
+static const VDFILEEXTENSION s_aVdiFileExtensions[] =
+{
+    {"vdi", VDTYPE_HDD},
+    {NULL, VDTYPE_INVALID}
+};
+
+
+/*********************************************************************************************************************************
+*   Internal Functions                                                                                                           *
+*********************************************************************************************************************************/
+static unsigned getPowerOfTwo(unsigned uNumber);
+static void vdiInitPreHeader(PVDIPREHEADER pPreHdr);
+static int  vdiValidatePreHeader(PVDIPREHEADER pPreHdr);
+static int  vdiValidateHeader(PVDIHEADER pHeader);
+static void vdiSetupImageDesc(PVDIIMAGEDESC pImage);
+static int  vdiUpdateHeader(PVDIIMAGEDESC pImage);
+static int  vdiUpdateBlockInfo(PVDIIMAGEDESC pImage, unsigned uBlock);
+static int  vdiUpdateHeaderAsync(PVDIIMAGEDESC pImage, PVDIOCTX pIoCtx);
+static int  vdiUpdateBlockInfoAsync(PVDIIMAGEDESC pImage, unsigned uBlock, PVDIOCTX pIoCtx,
+                                    bool fUpdateHdr);
+
+/**
+ * Internal: Convert the PreHeader fields to the appropriate endianess.
+ * @param   enmConv     Direction of the conversion.
+ * @param   pPreHdrConv Where to store the converted pre header.
+ * @param   pPreHdr     PreHeader pointer.
+ */
+static void vdiConvPreHeaderEndianess(VDIECONV enmConv, PVDIPREHEADER pPreHdrConv,
+                                      PVDIPREHEADER pPreHdr)
+{
+    memcpy(pPreHdrConv->szFileInfo, pPreHdr->szFileInfo, sizeof(pPreHdr->szFileInfo));
+    pPreHdrConv->u32Signature = SET_ENDIAN_U32(enmConv, pPreHdr->u32Signature);
+    pPreHdrConv->u32Version   = SET_ENDIAN_U32(enmConv, pPreHdr->u32Version);
+}
+
+/**
+ * Internal: Convert the VDIDISKGEOMETRY fields to the appropriate endianess.
+ * @param   enmConv      Direction of the conversion.
+ * @param   pDiskGeoConv Where to store the converted geometry.
+ * @param   pDiskGeo     Pointer to the disk geometry to convert.
+ */
+static void vdiConvGeometryEndianess(VDIECONV enmConv, PVDIDISKGEOMETRY pDiskGeoConv,
+                                     PVDIDISKGEOMETRY pDiskGeo)
+{
+    pDiskGeoConv->cCylinders = SET_ENDIAN_U32(enmConv, pDiskGeo->cCylinders);
+    pDiskGeoConv->cHeads     = SET_ENDIAN_U32(enmConv, pDiskGeo->cHeads);
+    pDiskGeoConv->cSectors   = SET_ENDIAN_U32(enmConv, pDiskGeo->cSectors);
+    pDiskGeoConv->cbSector   = SET_ENDIAN_U32(enmConv, pDiskGeo->cbSector);
+}
+
+/**
+ * Internal: Convert the Header - version 0 fields to the appropriate endianess.
+ * @param   enmConv      Direction of the conversion.
+ * @param   pHdrConv     Where to store the converted header.
+ * @param   pHdr         Pointer to the version 0 header.
+ */
+static void vdiConvHeaderEndianessV0(VDIECONV enmConv, PVDIHEADER0 pHdrConv,
+                                     PVDIHEADER0 pHdr)
+{
+    memmove(pHdrConv->szComment, pHdr->szComment, sizeof(pHdr->szComment));
+    pHdrConv->u32Type          = SET_ENDIAN_U32(enmConv, pHdr->u32Type);
+    pHdrConv->fFlags           = SET_ENDIAN_U32(enmConv, pHdr->fFlags);
+    vdiConvGeometryEndianess(enmConv, &pHdrConv->LegacyGeometry, &pHdr->LegacyGeometry);
+    pHdrConv->cbDisk           = SET_ENDIAN_U64(enmConv, pHdr->cbDisk);
+    pHdrConv->cbBlock          = SET_ENDIAN_U32(enmConv, pHdr->cbBlock);
+    pHdrConv->cBlocks          = SET_ENDIAN_U32(enmConv, pHdr->cBlocks);
+    pHdrConv->cBlocksAllocated = SET_ENDIAN_U32(enmConv, pHdr->cBlocksAllocated);
+    /* Don't convert the RTUUID fields. */
+    pHdrConv->uuidCreate       = pHdr->uuidCreate;
+    pHdrConv->uuidModify       = pHdr->uuidModify;
+    pHdrConv->uuidLinkage      = pHdr->uuidLinkage;
+}
+
+/**
+ * Internal: Set the Header - version 1 fields to the appropriate endianess.
+ * @param   enmConv      Direction of the conversion.
+ * @param   pHdrConv     Where to store the converted header.
+ * @param   pHdr         Version 1 Header pointer.
+ */
+static void vdiConvHeaderEndianessV1(VDIECONV enmConv, PVDIHEADER1 pHdrConv,
+                                     PVDIHEADER1 pHdr)
+{
+    memmove(pHdrConv->szComment, pHdr->szComment, sizeof(pHdr->szComment));
+    pHdrConv->cbHeader         = SET_ENDIAN_U32(enmConv, pHdr->cbHeader);
+    pHdrConv->u32Type          = SET_ENDIAN_U32(enmConv, pHdr->u32Type);
+    pHdrConv->fFlags           = SET_ENDIAN_U32(enmConv, pHdr->fFlags);
+    pHdrConv->offBlocks        = SET_ENDIAN_U32(enmConv, pHdr->offBlocks);
+    pHdrConv->offData          = SET_ENDIAN_U32(enmConv, pHdr->offData);
+    vdiConvGeometryEndianess(enmConv, &pHdrConv->LegacyGeometry, &pHdr->LegacyGeometry);
+    pHdrConv->u32Dummy         = SET_ENDIAN_U32(enmConv, pHdr->u32Dummy);
+    pHdrConv->cbDisk           = SET_ENDIAN_U64(enmConv, pHdr->cbDisk);
+    pHdrConv->cbBlock          = SET_ENDIAN_U32(enmConv, pHdr->cbBlock);
+    pHdrConv->cbBlockExtra     = SET_ENDIAN_U32(enmConv, pHdr->cbBlockExtra);
+    pHdrConv->cBlocks          = SET_ENDIAN_U32(enmConv, pHdr->cBlocks);
+    pHdrConv->cBlocksAllocated = SET_ENDIAN_U32(enmConv, pHdr->cBlocksAllocated);
+    /* Don't convert the RTUUID fields. */
+    pHdrConv->uuidCreate       = pHdr->uuidCreate;
+    pHdrConv->uuidModify       = pHdr->uuidModify;
+    pHdrConv->uuidLinkage      = pHdr->uuidLinkage;
+    pHdrConv->uuidParentModify = pHdr->uuidParentModify;
+}
+
+/**
+ * Internal: Set the Header - version 1plus fields to the appropriate endianess.
+ * @param   enmConv      Direction of the conversion.
+ * @param   pHdrConv     Where to store the converted header.
+ * @param   pHdr         Version 1+ Header pointer.
+ */
+static void vdiConvHeaderEndianessV1p(VDIECONV enmConv, PVDIHEADER1PLUS pHdrConv,
+                                      PVDIHEADER1PLUS pHdr)
+{
+    memmove(pHdrConv->szComment, pHdr->szComment, sizeof(pHdr->szComment));
+    pHdrConv->cbHeader         = SET_ENDIAN_U32(enmConv, pHdr->cbHeader);
+    pHdrConv->u32Type          = SET_ENDIAN_U32(enmConv, pHdr->u32Type);
+    pHdrConv->fFlags           = SET_ENDIAN_U32(enmConv, pHdr->fFlags);
+    pHdrConv->offBlocks        = SET_ENDIAN_U32(enmConv, pHdr->offBlocks);
+    pHdrConv->offData          = SET_ENDIAN_U32(enmConv, pHdr->offData);
+    vdiConvGeometryEndianess(enmConv, &pHdrConv->LegacyGeometry, &pHdr->LegacyGeometry);
+    pHdrConv->u32Dummy         = SET_ENDIAN_U32(enmConv, pHdr->u32Dummy);
+    pHdrConv->cbDisk           = SET_ENDIAN_U64(enmConv, pHdr->cbDisk);
+    pHdrConv->cbBlock          = SET_ENDIAN_U32(enmConv, pHdr->cbBlock);
+    pHdrConv->cbBlockExtra     = SET_ENDIAN_U32(enmConv, pHdr->cbBlockExtra);
+    pHdrConv->cBlocks          = SET_ENDIAN_U32(enmConv, pHdr->cBlocks);
+    pHdrConv->cBlocksAllocated = SET_ENDIAN_U32(enmConv, pHdr->cBlocksAllocated);
+    /* Don't convert the RTUUID fields. */
+    pHdrConv->uuidCreate       = pHdr->uuidCreate;
+    pHdrConv->uuidModify       = pHdr->uuidModify;
+    pHdrConv->uuidLinkage      = pHdr->uuidLinkage;
+    pHdrConv->uuidParentModify = pHdr->uuidParentModify;
+    vdiConvGeometryEndianess(enmConv, &pHdrConv->LCHSGeometry, &pHdr->LCHSGeometry);
+}
+
+
+/**
+ * Internal: Set the appropriate endianess on all the Blocks pointed.
+ * @param   enmConv      Direction of the conversion.
+ * @param   paBlocks     Pointer to the block array.
+ * @param   cEntries     Number of entries in the block array.
+ *
+ * @note Unlike the other conversion functions this method does an in place conversion
+ *       to avoid temporary memory allocations when writing the block array.
+ */
+static void vdiConvBlocksEndianess(VDIECONV enmConv, PVDIIMAGEBLOCKPOINTER paBlocks,
+                                   unsigned cEntries)
+{
+    for (unsigned i = 0; i < cEntries; i++)
+        paBlocks[i] = SET_ENDIAN_U32(enmConv, paBlocks[i]);
+}
+
+/**
+ * Internal: Flush the image file to disk.
+ */
+static void vdiFlushImage(PVDIIMAGEDESC pImage)
+{
+    if (!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        /* Save header. */
+        int rc = vdiUpdateHeader(pImage);
+        AssertMsgRC(rc, ("vdiUpdateHeader() failed, filename=\"%s\", rc=%Rrc\n",
+                         pImage->pszFilename, rc));
+        vdIfIoIntFileFlushSync(pImage->pIfIo, pImage->pStorage);
+    }
+}
+
+/**
+ * Internal: Free all allocated space for representing an image, and optionally
+ * delete the image from disk.
+ */
+static int vdiFreeImage(PVDIIMAGEDESC 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)
+                vdiFlushImage(pImage);
+
+            rc = vdIfIoIntFileClose(pImage->pIfIo, pImage->pStorage);
+            pImage->pStorage = NULL;
+        }
+
+        if (pImage->paBlocks)
+        {
+            RTMemFree(pImage->paBlocks);
+            pImage->paBlocks = NULL;
+        }
+
+        if (pImage->paBlocksRev)
+        {
+            RTMemFree(pImage->paBlocksRev);
+            pImage->paBlocksRev = NULL;
+        }
+
+        if (fDelete && pImage->pszFilename)
+        {
+            int rc2 = vdIfIoIntFileDelete(pImage->pIfIo, pImage->pszFilename);
+            if (RT_SUCCESS(rc))
+                rc = rc2;
+        }
+    }
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/**
+ * internal: return power of 2 or 0 if num error.
+ */
+static unsigned getPowerOfTwo(unsigned uNumber)
+{
+    if (uNumber == 0)
+        return 0;
+    unsigned uPower2 = 0;
+    while ((uNumber & 1) == 0)
+    {
+        uNumber >>= 1;
+        uPower2++;
+    }
+    return uNumber == 1 ? uPower2 : 0;
+}
+
+/**
+ * Internal: Init VDI preheader.
+ */
+static void vdiInitPreHeader(PVDIPREHEADER pPreHdr)
+{
+    pPreHdr->u32Signature = VDI_IMAGE_SIGNATURE;
+    pPreHdr->u32Version = VDI_IMAGE_VERSION;
+    memset(pPreHdr->szFileInfo, 0, sizeof(pPreHdr->szFileInfo));
+    strncat(pPreHdr->szFileInfo, VDI_IMAGE_FILE_INFO, sizeof(pPreHdr->szFileInfo)-1);
+}
+
+/**
+ * Internal: check VDI preheader.
+ */
+static int vdiValidatePreHeader(PVDIPREHEADER pPreHdr)
+{
+    if (pPreHdr->u32Signature != VDI_IMAGE_SIGNATURE)
+        return VERR_VD_VDI_INVALID_HEADER;
+
+    if (    VDI_GET_VERSION_MAJOR(pPreHdr->u32Version) != VDI_IMAGE_VERSION_MAJOR
+        &&  pPreHdr->u32Version != 0x00000002)    /* old version. */
+        return VERR_VD_VDI_UNSUPPORTED_VERSION;
+
+    return VINF_SUCCESS;
+}
+
+/**
+ * Internal: translate VD image flags to VDI image type enum.
+ */
+static VDIIMAGETYPE vdiTranslateImageFlags2VDI(unsigned uImageFlags)
+{
+    if (uImageFlags & VD_IMAGE_FLAGS_FIXED)
+        return VDI_IMAGE_TYPE_FIXED;
+    else if (uImageFlags & VD_IMAGE_FLAGS_DIFF)
+        return VDI_IMAGE_TYPE_DIFF;
+    else
+        return VDI_IMAGE_TYPE_NORMAL;
+}
+
+/**
+ * Internal: translate VDI image type enum to VD image type enum.
+ */
+static unsigned vdiTranslateVDI2ImageFlags(VDIIMAGETYPE enmType)
+{
+    switch (enmType)
+    {
+        case VDI_IMAGE_TYPE_NORMAL:
+            return VD_IMAGE_FLAGS_NONE;
+        case VDI_IMAGE_TYPE_FIXED:
+            return VD_IMAGE_FLAGS_FIXED;
+        case VDI_IMAGE_TYPE_DIFF:
+            return VD_IMAGE_FLAGS_DIFF;
+        default:
+            AssertMsgFailed(("invalid VDIIMAGETYPE enmType=%d\n", (int)enmType));
+            return VD_IMAGE_FLAGS_NONE;
+    }
+}
+
+/**
+ * Internal: Init VDI header. Always use latest header version.
+ *
+ * @param   pHeader      Assumes it was initially initialized to all zeros.
+ * @param   uImageFlags  Flags for this image.
+ * @param   pszComment   Optional comment to set for the image.
+ * @param   cbDisk       Size of the disk in bytes.
+ * @param   cbBlock      Size of one block in the image.
+ * @param   cbBlockExtra Extra data for one block private to the image.
+ * @param   cbDataAlign  The alignment for all data structures.
+ */
+static void vdiInitHeader(PVDIHEADER pHeader, uint32_t uImageFlags,
+                          const char *pszComment, uint64_t cbDisk,
+                          uint32_t cbBlock, uint32_t cbBlockExtra,
+                          uint32_t cbDataAlign)
+{
+    pHeader->uVersion = VDI_IMAGE_VERSION;
+    pHeader->u.v1plus.cbHeader = sizeof(VDIHEADER1PLUS);
+    pHeader->u.v1plus.u32Type = (uint32_t)vdiTranslateImageFlags2VDI(uImageFlags);
+    pHeader->u.v1plus.fFlags = (uImageFlags & VD_VDI_IMAGE_FLAGS_ZERO_EXPAND) ? 1 : 0;
+#ifdef VBOX_STRICT
+    char achZero[VDI_IMAGE_COMMENT_SIZE] = {0};
+    Assert(!memcmp(pHeader->u.v1plus.szComment, achZero, VDI_IMAGE_COMMENT_SIZE));
+#endif
+    pHeader->u.v1plus.szComment[0] = '\0';
+    if (pszComment)
+    {
+        AssertMsg(strlen(pszComment) < sizeof(pHeader->u.v1plus.szComment),
+                  ("HDD Comment is too long, cb=%d\n", strlen(pszComment)));
+        strncat(pHeader->u.v1plus.szComment, pszComment, sizeof(pHeader->u.v1plus.szComment)-1);
+    }
+
+    /* Mark the legacy geometry not-calculated. */
+    pHeader->u.v1plus.LegacyGeometry.cCylinders = 0;
+    pHeader->u.v1plus.LegacyGeometry.cHeads = 0;
+    pHeader->u.v1plus.LegacyGeometry.cSectors = 0;
+    pHeader->u.v1plus.LegacyGeometry.cbSector = VDI_GEOMETRY_SECTOR_SIZE;
+    pHeader->u.v1plus.u32Dummy = 0; /* used to be the translation value */
+
+    pHeader->u.v1plus.cbDisk = cbDisk;
+    pHeader->u.v1plus.cbBlock = cbBlock;
+    pHeader->u.v1plus.cBlocks = (uint32_t)(cbDisk / cbBlock);
+    if (cbDisk % cbBlock)
+        pHeader->u.v1plus.cBlocks++;
+    pHeader->u.v1plus.cbBlockExtra = cbBlockExtra;
+    pHeader->u.v1plus.cBlocksAllocated = 0;
+
+    /* Init offsets. */
+    pHeader->u.v1plus.offBlocks = RT_ALIGN_32(sizeof(VDIPREHEADER) + sizeof(VDIHEADER1PLUS), cbDataAlign);
+    pHeader->u.v1plus.offData = RT_ALIGN_32(pHeader->u.v1plus.offBlocks + (pHeader->u.v1plus.cBlocks * sizeof(VDIIMAGEBLOCKPOINTER)), cbDataAlign);
+
+    /* Init uuids. */
+#ifdef _MSC_VER
+# pragma warning(disable:4366) /* (harmless "misalignment") */
+#endif
+    RTUuidCreate(&pHeader->u.v1plus.uuidCreate);
+    RTUuidClear(&pHeader->u.v1plus.uuidModify);
+    RTUuidClear(&pHeader->u.v1plus.uuidLinkage);
+    RTUuidClear(&pHeader->u.v1plus.uuidParentModify);
+#ifdef _MSC_VER
+# pragma warning(default:4366)
+#endif
+
+    /* Mark LCHS geometry not-calculated. */
+    pHeader->u.v1plus.LCHSGeometry.cCylinders = 0;
+    pHeader->u.v1plus.LCHSGeometry.cHeads = 0;
+    pHeader->u.v1plus.LCHSGeometry.cSectors = 0;
+    pHeader->u.v1plus.LCHSGeometry.cbSector = VDI_GEOMETRY_SECTOR_SIZE;
+}
+
+/**
+ * Internal: Check VDI header.
+ */
+static int vdiValidateHeader(PVDIHEADER pHeader)
+{
+    /* Check version-dependent header parameters. */
+    switch (GET_MAJOR_HEADER_VERSION(pHeader))
+    {
+        case 0:
+        {
+            /* Old header version. */
+            break;
+        }
+        case 1:
+        {
+            /* Current header version. */
+
+            if (pHeader->u.v1.cbHeader < sizeof(VDIHEADER1))
+            {
+                LogRel(("VDI: v1 header size wrong (%d < %d)\n",
+                       pHeader->u.v1.cbHeader, sizeof(VDIHEADER1)));
+                return VERR_VD_VDI_INVALID_HEADER;
+            }
+
+            if (getImageBlocksOffset(pHeader) < (sizeof(VDIPREHEADER) + sizeof(VDIHEADER1)))
+            {
+                LogRel(("VDI: v1 blocks offset wrong (%d < %d)\n",
+                       getImageBlocksOffset(pHeader), sizeof(VDIPREHEADER) + sizeof(VDIHEADER1)));
+                return VERR_VD_VDI_INVALID_HEADER;
+            }
+
+            if (getImageDataOffset(pHeader) < (getImageBlocksOffset(pHeader) + getImageBlocks(pHeader) * sizeof(VDIIMAGEBLOCKPOINTER)))
+            {
+                LogRel(("VDI: v1 image data offset wrong (%d < %d)\n",
+                       getImageDataOffset(pHeader), getImageBlocksOffset(pHeader) + getImageBlocks(pHeader) * sizeof(VDIIMAGEBLOCKPOINTER)));
+                return VERR_VD_VDI_INVALID_HEADER;
+            }
+
+            break;
+        }
+        default:
+            /* Unsupported. */
+            return VERR_VD_VDI_UNSUPPORTED_VERSION;
+    }
+
+    /* Check common header parameters. */
+
+    bool fFailed = false;
+
+    if (    getImageType(pHeader) < VDI_IMAGE_TYPE_FIRST
+        ||  getImageType(pHeader) > VDI_IMAGE_TYPE_LAST)
+    {
+        LogRel(("VDI: bad image type %d\n", getImageType(pHeader)));
+        fFailed = true;
+    }
+
+    if (getImageFlags(pHeader) & ~VD_VDI_IMAGE_FLAGS_MASK)
+    {
+        LogRel(("VDI: bad image flags %08x\n", getImageFlags(pHeader)));
+        fFailed = true;
+    }
+
+    if (   getImageLCHSGeometry(pHeader)
+        && (getImageLCHSGeometry(pHeader))->cbSector != VDI_GEOMETRY_SECTOR_SIZE)
+    {
+        LogRel(("VDI: wrong sector size (%d != %d)\n",
+               (getImageLCHSGeometry(pHeader))->cbSector, VDI_GEOMETRY_SECTOR_SIZE));
+        fFailed = true;
+    }
+
+    if (    getImageDiskSize(pHeader) == 0
+        ||  getImageBlockSize(pHeader) == 0
+        ||  getImageBlocks(pHeader) == 0
+        ||  getPowerOfTwo(getImageBlockSize(pHeader)) == 0)
+    {
+        LogRel(("VDI: wrong size (%lld, %d, %d, %d)\n",
+              getImageDiskSize(pHeader), getImageBlockSize(pHeader),
+              getImageBlocks(pHeader), getPowerOfTwo(getImageBlockSize(pHeader))));
+        fFailed = true;
+    }
+
+    if (getImageBlocksAllocated(pHeader) > getImageBlocks(pHeader))
+    {
+        LogRel(("VDI: too many blocks allocated (%d > %d)\n"
+                "     blocksize=%d disksize=%lld\n",
+              getImageBlocksAllocated(pHeader), getImageBlocks(pHeader),
+              getImageBlockSize(pHeader), getImageDiskSize(pHeader)));
+        fFailed = true;
+    }
+
+    if (    getImageExtraBlockSize(pHeader) != 0
+        &&  getPowerOfTwo(getImageExtraBlockSize(pHeader)) == 0)
+    {
+        LogRel(("VDI: wrong extra size (%d, %d)\n",
+               getImageExtraBlockSize(pHeader), getPowerOfTwo(getImageExtraBlockSize(pHeader))));
+        fFailed = true;
+    }
+
+    if ((uint64_t)getImageBlockSize(pHeader) * getImageBlocks(pHeader) < getImageDiskSize(pHeader))
+    {
+        LogRel(("VDI: wrong disk size (%d, %d, %lld)\n",
+               getImageBlockSize(pHeader), getImageBlocks(pHeader), getImageDiskSize(pHeader)));
+        fFailed = true;
+    }
+
+    if (RTUuidIsNull(getImageCreationUUID(pHeader)))
+    {
+        LogRel(("VDI: uuid of creator is 0\n"));
+        fFailed = true;
+    }
+
+    if (RTUuidIsNull(getImageModificationUUID(pHeader)))
+    {
+        LogRel(("VDI: uuid of modifier is 0\n"));
+        fFailed = true;
+    }
+
+    return fFailed ? VERR_VD_VDI_INVALID_HEADER : VINF_SUCCESS;
+}
+
+/**
+ * Internal: Set up VDIIMAGEDESC structure by image header.
+ */
+static void vdiSetupImageDesc(PVDIIMAGEDESC pImage)
+{
+    pImage->uImageFlags        = getImageFlags(&pImage->Header);
+    pImage->uImageFlags       |= vdiTranslateVDI2ImageFlags(getImageType(&pImage->Header));
+    pImage->offStartBlocks     = getImageBlocksOffset(&pImage->Header);
+    pImage->offStartData       = getImageDataOffset(&pImage->Header);
+    pImage->uBlockMask         = getImageBlockSize(&pImage->Header) - 1;
+    pImage->uShiftOffset2Index = getPowerOfTwo(getImageBlockSize(&pImage->Header));
+    pImage->offStartBlockData  = getImageExtraBlockSize(&pImage->Header);
+    pImage->cbAllocationBlock  = getImageBlockSize(&pImage->Header);
+    pImage->cbTotalBlockData   = pImage->offStartBlockData
+                                 + getImageBlockSize(&pImage->Header);
+}
+
+/**
+ * Sets up the complete image state from the given parameters.
+ *
+ * @returns VBox status code.
+ * @param   pImage            The VDI image descriptor.
+ * @param   uImageFlags       Image flags.
+ * @param   pszComment        The comment for the image (optional).
+ * @param   cbSize            Size of the resulting image in bytes.
+ * @param   cbAllocationBlock Size of blocks allocated
+ * @param   cbDataAlign       Data alignment in bytes.
+ * @param   pPCHSGeometry     Physical CHS geometry for the image.
+ * @param   pLCHSGeometry     Logical CHS geometry for the image.
+ */
+static int vdiSetupImageState(PVDIIMAGEDESC pImage, unsigned uImageFlags, const char *pszComment,
+                              uint64_t cbSize, uint32_t cbAllocationBlock, uint32_t cbDataAlign, PCVDGEOMETRY pPCHSGeometry,
+                              PCVDGEOMETRY pLCHSGeometry)
+{
+    int rc = VINF_SUCCESS;
+
+    vdiInitPreHeader(&pImage->PreHeader);
+    vdiInitHeader(&pImage->Header, uImageFlags, pszComment, cbSize, cbAllocationBlock, 0,
+                  cbDataAlign);
+    /* Save PCHS geometry. Not much work, and makes the flow of information
+     * quite a bit clearer - relying on the higher level isn't obvious. */
+    pImage->PCHSGeometry = *pPCHSGeometry;
+    /* Set LCHS geometry (legacy geometry is ignored for the current 1.1+). */
+    pImage->Header.u.v1plus.LCHSGeometry.cCylinders = pLCHSGeometry->cCylinders;
+    pImage->Header.u.v1plus.LCHSGeometry.cHeads = pLCHSGeometry->cHeads;
+    pImage->Header.u.v1plus.LCHSGeometry.cSectors = pLCHSGeometry->cSectors;
+    pImage->Header.u.v1plus.LCHSGeometry.cbSector = VDI_GEOMETRY_SECTOR_SIZE;
+
+    pImage->paBlocks = (PVDIIMAGEBLOCKPOINTER)RTMemAlloc(sizeof(VDIIMAGEBLOCKPOINTER) * getImageBlocks(&pImage->Header));
+    if (RT_LIKELY(pImage->paBlocks))
+    {
+        if (!(uImageFlags & VD_IMAGE_FLAGS_FIXED))
+        {
+            /* for growing images mark all blocks in paBlocks as free. */
+            for (unsigned i = 0; i < pImage->Header.u.v1.cBlocks; i++)
+                pImage->paBlocks[i] = VDI_IMAGE_BLOCK_FREE;
+        }
+        else
+        {
+            /* for fixed images mark all blocks in paBlocks as allocated */
+            for (unsigned i = 0; i < pImage->Header.u.v1.cBlocks; i++)
+                pImage->paBlocks[i] = i;
+            pImage->Header.u.v1.cBlocksAllocated = pImage->Header.u.v1.cBlocks;
+        }
+
+        /* Setup image parameters. */
+        vdiSetupImageDesc(pImage);
+    }
+    else
+        rc = VERR_NO_MEMORY;
+
+    return rc;
+}
+
+/**
+ * Creates the image file from the given descriptor.
+ *
+ * @returns VBox status code.
+ * @param   pImage          The VDI image descriptor.
+ * @param   uOpenFlags      Open flags.
+ * @param   pIfProgress     The progress interface.
+ * @param   uPercentStart   Progress starting point.
+ * @param   uPercentSpan    How many percent for this part of the operation is used.
+ */
+static int vdiImageCreateFile(PVDIIMAGEDESC pImage, unsigned uOpenFlags,
+                              PVDINTERFACEPROGRESS pIfProgress, unsigned uPercentStart,
+                              unsigned uPercentSpan)
+{
+    int rc = vdIfIoIntFileOpen(pImage->pIfIo, pImage->pszFilename,
+                               VDOpenFlagsToFileOpenFlags(uOpenFlags & ~VD_OPEN_FLAGS_READONLY,
+                                                          true /* fCreate */),
+                               &pImage->pStorage);
+    if (RT_SUCCESS(rc))
+    {
+        if (pImage->uImageFlags & VD_IMAGE_FLAGS_FIXED)
+        {
+            uint64_t cbTotal =   pImage->offStartData
+                               + (uint64_t)getImageBlocks(&pImage->Header) * pImage->cbTotalBlockData;
+
+            /* Check the free space on the disk and leave early if there is not
+             * sufficient space available. */
+            int64_t cbFree = 0;
+            rc = vdIfIoIntFileGetFreeSpace(pImage->pIfIo, pImage->pszFilename, &cbFree);
+            if (RT_SUCCESS(rc) /* ignore errors */ && ((uint64_t)cbFree < cbTotal))
+                rc = vdIfError(pImage->pIfError, VERR_DISK_FULL, RT_SRC_POS,
+                               N_("VDI: disk would overflow creating image '%s'"), pImage->pszFilename);
+            else
+            {
+                /*
+                 * Allocate & commit whole file if fixed image, it must be more
+                 * effective than expanding file by write operations.
+                 */
+                rc = vdIfIoIntFileSetAllocationSize(pImage->pIfIo, pImage->pStorage, cbTotal, 0 /* fFlags */,
+                                                    pIfProgress, uPercentStart, uPercentSpan);
+                pImage->cbImage = cbTotal;
+            }
+        }
+        else
+        {
+            /* Set file size to hold header and blocks array. */
+            rc = vdIfIoIntFileSetSize(pImage->pIfIo, pImage->pStorage, pImage->offStartData);
+            pImage->cbImage = pImage->offStartData;
+        }
+        if (RT_SUCCESS(rc))
+        {
+            /* Write pre-header. */
+            VDIPREHEADER PreHeader;
+            vdiConvPreHeaderEndianess(VDIECONV_H2F, &PreHeader, &pImage->PreHeader);
+            rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage, 0,
+                                        &PreHeader, sizeof(PreHeader));
+            if (RT_SUCCESS(rc))
+            {
+                /* Write header. */
+                VDIHEADER1PLUS Hdr;
+                vdiConvHeaderEndianessV1p(VDIECONV_H2F, &Hdr, &pImage->Header.u.v1plus);
+                rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage, sizeof(pImage->PreHeader),
+                                            &Hdr, sizeof(Hdr));
+                if (RT_SUCCESS(rc))
+                {
+                    vdiConvBlocksEndianess(VDIECONV_H2F, pImage->paBlocks, getImageBlocks(&pImage->Header));
+                    rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage, pImage->offStartBlocks, pImage->paBlocks,
+                                                getImageBlocks(&pImage->Header) * sizeof(VDIIMAGEBLOCKPOINTER));
+                    vdiConvBlocksEndianess(VDIECONV_F2H, pImage->paBlocks, getImageBlocks(&pImage->Header));
+                    if (RT_FAILURE(rc))
+                        rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: writing block pointers failed for '%s'"),
+                                       pImage->pszFilename);
+                }
+                else
+                    rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: writing header failed for '%s'"),
+                                   pImage->pszFilename);
+            }
+            else
+                rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: writing pre-header failed for '%s'"),
+                               pImage->pszFilename);
+        }
+        else
+            rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: setting image size failed for '%s'"),
+                           pImage->pszFilename);
+    }
+    else
+        rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: cannot create image '%s'"),
+                       pImage->pszFilename);
+
+    return rc;
+}
+
+/**
+ * Internal: Create VDI image file.
+ */
+static int vdiCreateImage(PVDIIMAGEDESC pImage, uint64_t cbSize,
+                          unsigned uImageFlags, const char *pszComment,
+                          PCVDGEOMETRY pPCHSGeometry, PCVDGEOMETRY pLCHSGeometry,
+                          PCRTUUID pUuid, unsigned uOpenFlags,
+                          PVDINTERFACEPROGRESS pIfProgress, unsigned uPercentStart,
+                          unsigned uPercentSpan, PVDINTERFACECONFIG pIfCfg)
+{
+    int rc = VINF_SUCCESS;
+    uint32_t cbDataAlign = VDI_DATA_ALIGN;
+    AssertPtr(pPCHSGeometry);
+    AssertPtr(pLCHSGeometry);
+
+    pImage->pIfError = VDIfErrorGet(pImage->pVDIfsDisk);
+    pImage->pIfIo = VDIfIoIntGet(pImage->pVDIfsImage);
+    AssertPtrReturn(pImage->pIfIo, VERR_INVALID_PARAMETER);
+
+    /* Special check for comment length. */
+    if (   RT_VALID_PTR(pszComment)
+        && strlen(pszComment) >= VDI_IMAGE_COMMENT_SIZE)
+        rc = vdIfError(pImage->pIfError, VERR_VD_VDI_COMMENT_TOO_LONG, RT_SRC_POS,
+                       N_("VDI: comment is too long for '%s'"), pImage->pszFilename);
+
+    PVDINTERFACECONFIG pImgCfg = VDIfConfigGet(pImage->pVDIfsImage);
+    if (pImgCfg)
+    {
+        rc = VDCFGQueryU32Def(pImgCfg, "AllocationBlockSize",
+                &pImage->cbAllocationBlock, VDI_IMAGE_DEFAULT_BLOCK_SIZE);
+        if (RT_FAILURE(rc))
+            rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS,
+                           N_("VDI: Getting AllocationBlockSize for '%s' failed (%Rrc)"), pImage->pszFilename, rc);
+    } else
+        pImage->cbAllocationBlock = VDI_IMAGE_DEFAULT_BLOCK_SIZE;
+
+    if (pIfCfg)
+    {
+        rc = VDCFGQueryU32Def(pIfCfg, "DataAlignment", &cbDataAlign, VDI_DATA_ALIGN);
+        if (RT_FAILURE(rc))
+            rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS,
+                           N_("VDI: Getting data alignment for '%s' failed (%Rrc)"), pImage->pszFilename, rc);
+    }
+
+    if (RT_SUCCESS(rc))
+    {
+
+        rc = vdiSetupImageState(pImage, uImageFlags, pszComment, cbSize,
+                pImage->cbAllocationBlock, cbDataAlign, pPCHSGeometry, pLCHSGeometry);
+
+        if (RT_SUCCESS(rc))
+        {
+            /* Use specified image uuid */
+            *getImageCreationUUID(&pImage->Header) = *pUuid;
+            /* Generate image last-modify uuid */
+            RTUuidCreate(getImageModificationUUID(&pImage->Header));
+
+            rc = vdiImageCreateFile(pImage, uOpenFlags, pIfProgress,
+                                    uPercentStart, uPercentSpan);
+        }
+    }
+
+    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 = getImageDiskSize(&pImage->Header);
+
+        vdIfProgress(pIfProgress, uPercentStart + uPercentSpan);
+    }
+
+    if (RT_FAILURE(rc))
+        vdiFreeImage(pImage, rc != VERR_ALREADY_EXISTS);
+    return rc;
+}
+
+/**
+ * Reads and validates the header for the given image descriptor.
+ *
+ * @returns VBox status code.
+ * @param   pImage          The VDI image descriptor.
+ */
+static int vdiImageReadHeader(PVDIIMAGEDESC pImage)
+{
+    /* Get file size. */
+    int rc = vdIfIoIntFileGetSize(pImage->pIfIo, pImage->pStorage,
+                                  &pImage->cbImage);
+    if (RT_SUCCESS(rc))
+    {
+        /* Read pre-header. */
+        VDIPREHEADER PreHeader;
+        rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage, 0,
+                                   &PreHeader, sizeof(PreHeader));
+        if (RT_SUCCESS(rc))
+        {
+            vdiConvPreHeaderEndianess(VDIECONV_F2H, &pImage->PreHeader, &PreHeader);
+            rc = vdiValidatePreHeader(&pImage->PreHeader);
+            if (RT_SUCCESS(rc))
+            {
+                /* Read header. */
+                pImage->Header.uVersion = pImage->PreHeader.u32Version;
+                switch (GET_MAJOR_HEADER_VERSION(&pImage->Header))
+                {
+                    case 0:
+                        rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage, sizeof(pImage->PreHeader),
+                                                   &pImage->Header.u.v0, sizeof(pImage->Header.u.v0));
+                        if (RT_SUCCESS(rc))
+                            vdiConvHeaderEndianessV0(VDIECONV_F2H, &pImage->Header.u.v0, &pImage->Header.u.v0);
+                        else
+                            rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: error reading v0 header in '%s'"), pImage->pszFilename);
+                        break;
+                    case 1:
+                        rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage, sizeof(pImage->PreHeader),
+                                                   &pImage->Header.u.v1, sizeof(pImage->Header.u.v1));
+                        if (RT_SUCCESS(rc))
+                        {
+                            vdiConvHeaderEndianessV1(VDIECONV_F2H, &pImage->Header.u.v1, &pImage->Header.u.v1);
+                            /* Convert VDI 1.1 images to VDI 1.1+ on open in read/write mode.
+                             * Conversion is harmless, as any VirtualBox version supporting VDI
+                             * 1.1 doesn't touch fields it doesn't know about. */
+                            if (   !(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY)
+                                && GET_MINOR_HEADER_VERSION(&pImage->Header) == 1
+                                && pImage->Header.u.v1.cbHeader < sizeof(pImage->Header.u.v1plus))
+                            {
+                                pImage->Header.u.v1plus.cbHeader = sizeof(pImage->Header.u.v1plus);
+                                /* Mark LCHS geometry not-calculated. */
+                                pImage->Header.u.v1plus.LCHSGeometry.cCylinders = 0;
+                                pImage->Header.u.v1plus.LCHSGeometry.cHeads = 0;
+                                pImage->Header.u.v1plus.LCHSGeometry.cSectors = 0;
+                                pImage->Header.u.v1plus.LCHSGeometry.cbSector = VDI_GEOMETRY_SECTOR_SIZE;
+                            }
+                            else if (pImage->Header.u.v1.cbHeader >= sizeof(pImage->Header.u.v1plus))
+                            {
+                                /* Read the actual VDI 1.1+ header completely. */
+                                rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage, sizeof(pImage->PreHeader),
+                                                           &pImage->Header.u.v1plus,
+                                                           sizeof(pImage->Header.u.v1plus));
+                                if (RT_SUCCESS(rc))
+                                    vdiConvHeaderEndianessV1p(VDIECONV_F2H, &pImage->Header.u.v1plus, &pImage->Header.u.v1plus);
+                                else
+                                    rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: error reading v1.1+ header in '%s'"), pImage->pszFilename);
+                            }
+                        }
+                        else
+                            rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: error reading v1 header in '%s'"), pImage->pszFilename);
+                        break;
+                    default:
+                        rc = vdIfError(pImage->pIfError, VERR_VD_VDI_UNSUPPORTED_VERSION, RT_SRC_POS,
+                                       N_("VDI: unsupported major version %u in '%s'"), GET_MAJOR_HEADER_VERSION(&pImage->Header), pImage->pszFilename);
+                }
+
+                if (RT_SUCCESS(rc))
+                {
+                    rc = vdiValidateHeader(&pImage->Header);
+                    if (RT_SUCCESS(rc))
+                    {
+                        /* Setup image parameters by header. */
+                        vdiSetupImageDesc(pImage);
+
+                        /*
+                         * Until revision r111992 there was no check that the size was sector aligned
+                         * when creating a new image and a bug in the VirtualBox GUI on OS X resulted
+                         * in such images being created which caused issues when writing to the
+                         * end of the image.
+                         *
+                         * Detect such images and repair the small damage by rounding down to the next
+                         * aligned size. This is no problem as the guest would see a sector count
+                         * only anyway from the device emulations so it already sees only the smaller
+                         * size as result of the integer division of the size and sector size.
+                         *
+                         * This might not be written to the image if it is opened readonly
+                         * which is not much of a problem because only writing to the last block
+                         * causes trouble.
+                         */
+                        uint64_t cbDisk = getImageDiskSize(&pImage->Header);
+                        if (cbDisk & 0x1ff)
+                            setImageDiskSize(&pImage->Header, cbDisk & ~UINT64_C(0x1ff));
+                    }
+                    else
+                        rc = vdIfError(pImage->pIfError, VERR_VD_VDI_INVALID_HEADER, RT_SRC_POS,
+                                       N_("VDI: invalid header in '%s'"), pImage->pszFilename);
+                }
+            }
+            else
+                rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: invalid pre-header in '%s'"), pImage->pszFilename);
+        }
+        else
+        {
+            vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: error reading pre-header in '%s'"), pImage->pszFilename);
+            rc = VERR_VD_VDI_INVALID_HEADER;
+        }
+    }
+    else
+    {
+        vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: error getting the image size in '%s'"), pImage->pszFilename);
+        rc = VERR_VD_VDI_INVALID_HEADER;
+    }
+
+    return rc;
+}
+
+/**
+ * Creates the back resolving table for the image for the discard operation.
+ *
+ * @returns VBox status code.
+ * @param   pImage          The VDI image descriptor.
+ */
+static int vdiImageBackResolvTblCreate(PVDIIMAGEDESC pImage)
+{
+    int rc = VINF_SUCCESS;
+
+    /*
+     * Any error or inconsistency results in a fail because this might
+     * get us into trouble later on.
+     */
+    pImage->paBlocksRev = (unsigned *)RTMemAllocZ(sizeof(unsigned) * getImageBlocks(&pImage->Header));
+    if (pImage->paBlocksRev)
+    {
+        unsigned cBlocksAllocated = getImageBlocksAllocated(&pImage->Header);
+        unsigned cBlocks = getImageBlocks(&pImage->Header);
+
+        for (unsigned i = 0; i < cBlocks; i++)
+            pImage->paBlocksRev[i] = VDI_IMAGE_BLOCK_FREE;
+
+        for (unsigned i = 0; i < cBlocks; i++)
+        {
+            VDIIMAGEBLOCKPOINTER ptrBlock = pImage->paBlocks[i];
+            if (IS_VDI_IMAGE_BLOCK_ALLOCATED(ptrBlock))
+            {
+                if (ptrBlock < cBlocksAllocated)
+                {
+                    if (pImage->paBlocksRev[ptrBlock] == VDI_IMAGE_BLOCK_FREE)
+                        pImage->paBlocksRev[ptrBlock] = i;
+                    else
+                    {
+                        rc = VERR_VD_VDI_INVALID_HEADER;
+                        break;
+                    }
+                }
+                else
+                {
+                    rc = VERR_VD_VDI_INVALID_HEADER;
+                    break;
+                }
+            }
+        }
+    }
+    else
+        rc = VERR_NO_MEMORY;
+
+    return rc;
+}
+
+/**
+ * Internal: Open a VDI image.
+ */
+static int vdiOpenImage(PVDIIMAGEDESC pImage, unsigned uOpenFlags)
+{
+    pImage->uOpenFlags = uOpenFlags;
+
+    pImage->pIfError = VDIfErrorGet(pImage->pVDIfsDisk);
+    pImage->pIfIo = VDIfIoIntGet(pImage->pVDIfsImage);
+    AssertPtrReturn(pImage->pIfIo, VERR_INVALID_PARAMETER);
+
+    /*
+     * Open the image.
+     */
+    int rc = vdIfIoIntFileOpen(pImage->pIfIo, pImage->pszFilename,
+                               VDOpenFlagsToFileOpenFlags(uOpenFlags, false /* fCreate */),
+                               &pImage->pStorage);
+    if (RT_SUCCESS(rc))
+    {
+        rc = vdiImageReadHeader(pImage);
+        if (RT_SUCCESS(rc))
+        {
+            /* Allocate memory for blocks array. */
+            pImage->paBlocks = (PVDIIMAGEBLOCKPOINTER)RTMemAlloc(sizeof(VDIIMAGEBLOCKPOINTER) * getImageBlocks(&pImage->Header));
+            if (RT_LIKELY(pImage->paBlocks))
+            {
+                /* Read blocks array. */
+                rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage, pImage->offStartBlocks, pImage->paBlocks,
+                                           getImageBlocks(&pImage->Header) * sizeof(VDIIMAGEBLOCKPOINTER));
+                if (RT_SUCCESS(rc))
+                {
+                    vdiConvBlocksEndianess(VDIECONV_F2H, pImage->paBlocks, getImageBlocks(&pImage->Header));
+
+                    if (uOpenFlags & VD_OPEN_FLAGS_DISCARD)
+                        rc = vdiImageBackResolvTblCreate(pImage);
+                }
+                else
+                    rc = vdIfError(pImage->pIfError, rc, RT_SRC_POS, N_("VDI: Error reading the block table in '%s'"), pImage->pszFilename);
+            }
+            else
+                rc = vdIfError(pImage->pIfError, VERR_NO_MEMORY, RT_SRC_POS,
+                               N_("VDI: Error allocating memory for the block table in '%s'"), pImage->pszFilename);;
+        }
+    }
+    /* else: Do NOT signal an appropriate error here, as the VD layer has the
+     *       choice of retrying the open if it failed. */
+
+    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 = getImageDiskSize(&pImage->Header);
+        if (uOpenFlags & VD_OPEN_FLAGS_INFO)
+        {
+            PVDINTERFACECONFIG pImgCfg = VDIfConfigGet(pImage->pVDIfsImage);
+            if (pImgCfg)
+            {
+                rc = VDCFGUpdateU64(pImgCfg, true, "AllocationBlockSize", pImage->cbAllocationBlock);
+                if (RT_FAILURE(rc))
+                    return rc;
+            }
+        }
+    }
+    else
+        vdiFreeImage(pImage, false);
+    return rc;
+}
+
+/**
+ * Internal: Save header to file.
+ */
+static int vdiUpdateHeader(PVDIIMAGEDESC pImage)
+{
+    int rc;
+    switch (GET_MAJOR_HEADER_VERSION(&pImage->Header))
+    {
+        case 0:
+        {
+            VDIHEADER0 Hdr;
+            vdiConvHeaderEndianessV0(VDIECONV_H2F, &Hdr, &pImage->Header.u.v0);
+            rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage, sizeof(VDIPREHEADER),
+                                        &Hdr, sizeof(Hdr));
+            break;
+        }
+        case 1:
+            if (pImage->Header.u.v1plus.cbHeader < sizeof(pImage->Header.u.v1plus))
+            {
+                VDIHEADER1 Hdr;
+                vdiConvHeaderEndianessV1(VDIECONV_H2F, &Hdr, &pImage->Header.u.v1);
+                rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage, sizeof(VDIPREHEADER),
+                                            &Hdr, sizeof(Hdr));
+            }
+            else
+            {
+                VDIHEADER1PLUS Hdr;
+                vdiConvHeaderEndianessV1p(VDIECONV_H2F, &Hdr, &pImage->Header.u.v1plus);
+                rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage, sizeof(VDIPREHEADER),
+                                            &Hdr, sizeof(Hdr));
+            }
+            break;
+        default:
+            rc = VERR_VD_VDI_UNSUPPORTED_VERSION;
+            break;
+    }
+    AssertMsgRC(rc, ("vdiUpdateHeader failed, filename=\"%s\" rc=%Rrc\n", pImage->pszFilename, rc));
+    return rc;
+}
+
+/**
+ * Internal: Save header to file - async version.
+ */
+static int vdiUpdateHeaderAsync(PVDIIMAGEDESC pImage, PVDIOCTX pIoCtx)
+{
+    int rc;
+    switch (GET_MAJOR_HEADER_VERSION(&pImage->Header))
+    {
+        case 0:
+        {
+            VDIHEADER0 Hdr;
+            vdiConvHeaderEndianessV0(VDIECONV_H2F, &Hdr, &pImage->Header.u.v0);
+            rc = vdIfIoIntFileWriteMeta(pImage->pIfIo, pImage->pStorage,
+                                        sizeof(VDIPREHEADER), &Hdr, sizeof(Hdr),
+                                        pIoCtx, NULL, NULL);
+            break;
+        }
+        case 1:
+            if (pImage->Header.u.v1plus.cbHeader < sizeof(pImage->Header.u.v1plus))
+            {
+                VDIHEADER1 Hdr;
+                vdiConvHeaderEndianessV1(VDIECONV_H2F, &Hdr, &pImage->Header.u.v1);
+                rc = vdIfIoIntFileWriteMeta(pImage->pIfIo, pImage->pStorage,
+                                            sizeof(VDIPREHEADER), &Hdr, sizeof(Hdr),
+                                            pIoCtx, NULL, NULL);
+            }
+            else
+            {
+                VDIHEADER1PLUS Hdr;
+                vdiConvHeaderEndianessV1p(VDIECONV_H2F, &Hdr, &pImage->Header.u.v1plus);
+                rc = vdIfIoIntFileWriteMeta(pImage->pIfIo, pImage->pStorage,
+                                            sizeof(VDIPREHEADER), &Hdr, sizeof(Hdr),
+                                            pIoCtx, NULL, NULL);
+            }
+            break;
+        default:
+            rc = VERR_VD_VDI_UNSUPPORTED_VERSION;
+            break;
+    }
+    AssertMsg(RT_SUCCESS(rc) || rc == VERR_VD_ASYNC_IO_IN_PROGRESS,
+              ("vdiUpdateHeader failed, filename=\"%s\" rc=%Rrc\n", pImage->pszFilename, rc));
+    return rc;
+}
+
+/**
+ * Internal: Save block pointer to file, save header to file.
+ */
+static int vdiUpdateBlockInfo(PVDIIMAGEDESC pImage, unsigned uBlock)
+{
+    /* Update image header. */
+    int rc = vdiUpdateHeader(pImage);
+    if (RT_SUCCESS(rc))
+    {
+        /* write only one block pointer. */
+        VDIIMAGEBLOCKPOINTER ptrBlock = RT_H2LE_U32(pImage->paBlocks[uBlock]);
+        rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage,
+                                    pImage->offStartBlocks + uBlock * sizeof(VDIIMAGEBLOCKPOINTER),
+                                    &ptrBlock, sizeof(VDIIMAGEBLOCKPOINTER));
+        AssertMsgRC(rc, ("vdiUpdateBlockInfo failed to update block=%u, filename=\"%s\", rc=%Rrc\n",
+                         uBlock, pImage->pszFilename, rc));
+    }
+    return rc;
+}
+
+/**
+ * Internal: Save block pointer to file, save header to file - async version.
+ */
+static int vdiUpdateBlockInfoAsync(PVDIIMAGEDESC pImage, unsigned uBlock,
+                                   PVDIOCTX pIoCtx, bool fUpdateHdr)
+{
+    int rc = VINF_SUCCESS;
+
+    /* Update image header. */
+    if (fUpdateHdr)
+        rc = vdiUpdateHeaderAsync(pImage, pIoCtx);
+
+    if (RT_SUCCESS(rc) || rc == VERR_VD_ASYNC_IO_IN_PROGRESS)
+    {
+        /* write only one block pointer. */
+        VDIIMAGEBLOCKPOINTER ptrBlock = RT_H2LE_U32(pImage->paBlocks[uBlock]);
+        rc = vdIfIoIntFileWriteMeta(pImage->pIfIo, pImage->pStorage,
+                                    pImage->offStartBlocks + uBlock * sizeof(VDIIMAGEBLOCKPOINTER),
+                                    &ptrBlock, sizeof(VDIIMAGEBLOCKPOINTER),
+                                    pIoCtx, NULL, NULL);
+        AssertMsg(RT_SUCCESS(rc) || rc == VERR_VD_ASYNC_IO_IN_PROGRESS,
+                  ("vdiUpdateBlockInfo failed to update block=%u, filename=\"%s\", rc=%Rrc\n",
+                  uBlock, pImage->pszFilename, rc));
+    }
+    return rc;
+}
+
+/**
+ * Internal: Flush the image file to disk - async version.
+ */
+static int vdiFlushImageIoCtx(PVDIIMAGEDESC pImage, PVDIOCTX pIoCtx)
+{
+    int rc = VINF_SUCCESS;
+
+    if (!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        /* Save header. */
+        rc = vdiUpdateHeaderAsync(pImage, pIoCtx);
+        AssertMsg(RT_SUCCESS(rc) || rc == VERR_VD_ASYNC_IO_IN_PROGRESS,
+                  ("vdiUpdateHeaderAsync() failed, filename=\"%s\", rc=%Rrc\n",
+                  pImage->pszFilename, rc));
+        rc = vdIfIoIntFileFlush(pImage->pIfIo, pImage->pStorage, pIoCtx, NULL, NULL);
+        AssertMsg(RT_SUCCESS(rc) || rc == VERR_VD_ASYNC_IO_IN_PROGRESS,
+                  ("Flushing data to disk failed rc=%Rrc\n", rc));
+    }
+
+    return rc;
+}
+
+/**
+ * Completion callback for meta/userdata reads or writes.
+ *
+ * @return  VBox status code.
+ *          VINF_SUCCESS if everything was successful and the transfer can continue.
+ *          VERR_VD_ASYNC_IO_IN_PROGRESS if there is another data transfer pending.
+ * @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) vdiDiscardBlockAsyncUpdate(void *pBackendData, PVDIOCTX pIoCtx, void *pvUser, int rcReq)
+{
+    RT_NOREF1(rcReq);
+    int rc = VINF_SUCCESS;
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    PVDIBLOCKDISCARDASYNC pDiscardAsync = (PVDIBLOCKDISCARDASYNC)pvUser;
+
+    switch (pDiscardAsync->enmState)
+    {
+        case VDIBLOCKDISCARDSTATE_READ_BLOCK:
+        {
+            PVDMETAXFER pMetaXfer;
+            uint64_t u64Offset = (uint64_t)pDiscardAsync->idxLastBlock * pImage->cbTotalBlockData + pImage->offStartData;
+            rc = vdIfIoIntFileReadMeta(pImage->pIfIo, pImage->pStorage, u64Offset,
+                                       pDiscardAsync->pvBlock, pImage->cbTotalBlockData, pIoCtx,
+                                       &pMetaXfer, vdiDiscardBlockAsyncUpdate, pDiscardAsync);
+            if (RT_FAILURE(rc))
+                break;
+
+            /* Release immediately and go to next step. */
+            vdIfIoIntMetaXferRelease(pImage->pIfIo, pMetaXfer);
+            pDiscardAsync->enmState = VDIBLOCKDISCARDSTATE_WRITE_BLOCK;
+        }
+        RT_FALL_THRU();
+        case VDIBLOCKDISCARDSTATE_WRITE_BLOCK:
+        {
+            /* Block read complete. Write to the new location (discarded block). */
+            uint64_t u64Offset = (uint64_t)pDiscardAsync->ptrBlockDiscard * pImage->cbTotalBlockData + pImage->offStartData;
+            rc = vdIfIoIntFileWriteMeta(pImage->pIfIo, pImage->pStorage, u64Offset,
+                                        pDiscardAsync->pvBlock, pImage->cbTotalBlockData, pIoCtx,
+                                        vdiDiscardBlockAsyncUpdate, pDiscardAsync);
+
+            pDiscardAsync->enmState = VDIBLOCKDISCARDSTATE_UPDATE_METADATA;
+            if (RT_FAILURE(rc))
+                break;
+        }
+        RT_FALL_THRU();
+        case VDIBLOCKDISCARDSTATE_UPDATE_METADATA:
+        {
+            int rc2;
+
+            /* Block write complete. Update metadata. */
+            pImage->paBlocksRev[pDiscardAsync->idxLastBlock] = VDI_IMAGE_BLOCK_FREE;
+            pImage->paBlocks[pDiscardAsync->uBlock] = VDI_IMAGE_BLOCK_ZERO;
+
+            if (pDiscardAsync->idxLastBlock != pDiscardAsync->ptrBlockDiscard)
+            {
+                pImage->paBlocks[pDiscardAsync->uBlockLast] = pDiscardAsync->ptrBlockDiscard;
+                pImage->paBlocksRev[pDiscardAsync->ptrBlockDiscard] = pDiscardAsync->uBlockLast;
+
+                rc = vdiUpdateBlockInfoAsync(pImage, pDiscardAsync->uBlockLast, pIoCtx, false /* fUpdateHdr */);
+                if (   RT_FAILURE(rc)
+                    && rc != VERR_VD_ASYNC_IO_IN_PROGRESS)
+                    break;
+            }
+
+            setImageBlocksAllocated(&pImage->Header, pDiscardAsync->idxLastBlock);
+            rc = vdiUpdateBlockInfoAsync(pImage, pDiscardAsync->uBlock, pIoCtx, true /* fUpdateHdr */);
+            if (   RT_FAILURE(rc)
+                && rc != VERR_VD_ASYNC_IO_IN_PROGRESS)
+                break;
+
+            pImage->cbImage -= pImage->cbTotalBlockData;
+            LogFlowFunc(("Set new size %llu\n", pImage->cbImage));
+            rc2 = vdIfIoIntFileSetSize(pImage->pIfIo, pImage->pStorage, pImage->cbImage);
+            if (RT_FAILURE(rc2))
+                rc = rc2;
+
+            /* Free discard state. */
+            RTMemFree(pDiscardAsync->pvBlock);
+            RTMemFree(pDiscardAsync);
+            break;
+        }
+        default:
+            AssertMsgFailed(("Invalid state %d\n", pDiscardAsync->enmState));
+    }
+
+    if (rc == VERR_VD_NOT_ENOUGH_METADATA)
+        rc = VERR_VD_ASYNC_IO_IN_PROGRESS;
+
+    return rc;
+}
+
+/**
+ * Internal: Discard a whole block from the image filling the created hole with
+ * data from another block - async I/O version.
+ *
+ * @returns VBox status code.
+ * @param   pImage    VDI image instance data.
+ * @param   pIoCtx    I/O context associated with this request.
+ * @param   uBlock    The block to discard.
+ * @param   pvBlock   Memory to use for the I/O.
+ */
+static int vdiDiscardBlockAsync(PVDIIMAGEDESC pImage, PVDIOCTX pIoCtx,
+                                unsigned uBlock, void *pvBlock)
+{
+    int rc = VINF_SUCCESS;
+    PVDIBLOCKDISCARDASYNC pDiscardAsync = NULL;
+
+    LogFlowFunc(("pImage=%#p uBlock=%u pvBlock=%#p\n",
+                 pImage, uBlock, pvBlock));
+
+    pDiscardAsync = (PVDIBLOCKDISCARDASYNC)RTMemAllocZ(sizeof(VDIBLOCKDISCARDASYNC));
+    if (RT_UNLIKELY(!pDiscardAsync))
+        return VERR_NO_MEMORY;
+
+    /* Init block discard state. */
+    pDiscardAsync->uBlock  = uBlock;
+    pDiscardAsync->pvBlock = pvBlock;
+    pDiscardAsync->ptrBlockDiscard = pImage->paBlocks[uBlock];
+    pDiscardAsync->idxLastBlock = getImageBlocksAllocated(&pImage->Header) - 1;
+    pDiscardAsync->uBlockLast = pImage->paBlocksRev[pDiscardAsync->idxLastBlock];
+
+    /*
+     * The block is empty, remove it.
+     * Read the last block of the image first.
+     */
+    if (pDiscardAsync->idxLastBlock != pDiscardAsync->ptrBlockDiscard)
+    {
+        LogFlowFunc(("Moving block [%u]=%u into [%u]=%u\n",
+                     pDiscardAsync->uBlockLast, pDiscardAsync->idxLastBlock,
+                     uBlock, pImage->paBlocks[uBlock]));
+        pDiscardAsync->enmState = VDIBLOCKDISCARDSTATE_READ_BLOCK;
+    }
+    else
+    {
+        pDiscardAsync->enmState = VDIBLOCKDISCARDSTATE_UPDATE_METADATA; /* Start immediately to shrink the image. */
+        LogFlowFunc(("Discard last block [%u]=%u\n", uBlock, pImage->paBlocks[uBlock]));
+    }
+
+    /* Call the update callback directly. */
+    rc = vdiDiscardBlockAsyncUpdate(pImage, pIoCtx, pDiscardAsync, VINF_SUCCESS);
+
+    LogFlowFunc(("returns rc=%Rrc\n", rc));
+    return rc;
+}
+
+/**
+ * Internal: Creates a allocation bitmap from the given data.
+ * Sectors which contain only 0 are marked as unallocated and sectors with
+ * other data as allocated.
+ *
+ * @returns Pointer to the allocation bitmap or NULL on failure.
+ * @param   pvData    The data to create the allocation bitmap for.
+ * @param   cbData    Number of bytes in the buffer.
+ */
+static void *vdiAllocationBitmapCreate(void *pvData, size_t cbData)
+{
+    Assert(cbData <= UINT32_MAX / 8);
+    uint32_t cSectors = (uint32_t)(cbData / 512);
+    uint32_t uSectorCur = 0;
+    void *pbmAllocationBitmap = NULL;
+
+    Assert(!(cbData % 512));
+    Assert(!(cSectors % 8));
+
+    pbmAllocationBitmap = RTMemAllocZ(cSectors / 8);
+    if (!pbmAllocationBitmap)
+        return NULL;
+
+    while (uSectorCur < cSectors)
+    {
+        int idxSet = ASMBitFirstSet((uint8_t *)pvData + uSectorCur * 512, (uint32_t)cbData * 8);
+
+        if (idxSet != -1)
+        {
+            unsigned idxSectorAlloc = idxSet / 8 / 512;
+            ASMBitSet(pbmAllocationBitmap, uSectorCur + idxSectorAlloc);
+
+            uSectorCur += idxSectorAlloc + 1;
+            cbData     -= (idxSectorAlloc + 1) * 512;
+        }
+        else
+            break;
+    }
+
+    return pbmAllocationBitmap;
+}
+
+
+/**
+ * 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) vdiBlockAllocUpdate(void *pBackendData, PVDIOCTX pIoCtx, void *pvUser, int rcReq)
+{
+    int rc = VINF_SUCCESS;
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    PVDIASYNCBLOCKALLOC pBlockAlloc = (PVDIASYNCBLOCKALLOC)pvUser;
+
+    if (RT_SUCCESS(rcReq))
+    {
+        pImage->cbImage += pImage->cbTotalBlockData;
+        pImage->paBlocks[pBlockAlloc->uBlock] = pBlockAlloc->cBlocksAllocated;
+
+        if (pImage->paBlocksRev)
+            pImage->paBlocksRev[pBlockAlloc->cBlocksAllocated] = pBlockAlloc->uBlock;
+
+        setImageBlocksAllocated(&pImage->Header, pBlockAlloc->cBlocksAllocated + 1);
+        rc = vdiUpdateBlockInfoAsync(pImage, pBlockAlloc->uBlock, pIoCtx,
+                                     true /* fUpdateHdr */);
+    }
+    /* else: I/O error don't update the block table. */
+
+    RTMemFree(pBlockAlloc);
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnProbe */
+static DECLCALLBACK(int) vdiProbe(const char *pszFilename, PVDINTERFACE pVDIfsDisk,
+                                  PVDINTERFACE pVDIfsImage, VDTYPE enmDesiredType, VDTYPE *penmType)
+{
+    RT_NOREF(enmDesiredType);
+    LogFlowFunc(("pszFilename=\"%s\"\n", pszFilename));
+    int rc = VINF_SUCCESS;
+
+    AssertPtrReturn(pszFilename, VERR_INVALID_POINTER);
+    AssertReturn(*pszFilename != '\0', VERR_INVALID_PARAMETER);
+
+
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)RTMemAllocZ(RT_UOFFSETOF(VDIIMAGEDESC, RegionList.aRegions[1]));
+    if (RT_LIKELY(pImage))
+    {
+        pImage->pszFilename = pszFilename;
+        pImage->pStorage = NULL;
+        pImage->paBlocks = NULL;
+        pImage->pVDIfsDisk = pVDIfsDisk;
+        pImage->pVDIfsImage = pVDIfsImage;
+
+        rc = vdiOpenImage(pImage, VD_OPEN_FLAGS_INFO | VD_OPEN_FLAGS_READONLY);
+        vdiFreeImage(pImage, false);
+        RTMemFree(pImage);
+
+        if (RT_SUCCESS(rc))
+            *penmType = VDTYPE_HDD;
+    }
+    else
+        rc = VERR_NO_MEMORY;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnOpen */
+static DECLCALLBACK(int) vdiOpen(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);
+
+
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)RTMemAllocZ(RT_UOFFSETOF(VDIIMAGEDESC, RegionList.aRegions[1]));
+    if (RT_LIKELY(pImage))
+    {
+        pImage->pszFilename = pszFilename;
+        pImage->pStorage = NULL;
+        pImage->paBlocks = NULL;
+        pImage->pVDIfsDisk = pVDIfsDisk;
+        pImage->pVDIfsImage = pVDIfsImage;
+
+        rc = vdiOpenImage(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) vdiCreate(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)
+{
+    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=%u ppBackendData=%#p\n",
+                 pszFilename, cbSize, uImageFlags, pszComment, pPCHSGeometry, pLCHSGeometry, pUuid, uOpenFlags, uPercentStart, uPercentSpan, pVDIfsDisk, pVDIfsImage, pVDIfsOperation, enmType, ppBackendData));
+    int rc;
+
+    /* Check the VD container type and image flags. */
+    if (   enmType != VDTYPE_HDD
+        || (uImageFlags & ~VD_VDI_IMAGE_FLAGS_MASK) != 0)
+        return VERR_VD_INVALID_TYPE;
+
+    /* Check size. Maximum 4PB-3M. No tricks with adjusting the 1M block size
+     * so far, which would extend the size. */
+    if (   !cbSize
+        || cbSize >= _1P * 4 - _1M * 3
+        || cbSize < VDI_IMAGE_DEFAULT_BLOCK_SIZE
+        || (cbSize % 512))
+        return VERR_VD_INVALID_SIZE;
+
+    /* 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);
+
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)RTMemAllocZ(RT_UOFFSETOF(VDIIMAGEDESC, RegionList.aRegions[1]));
+    if (RT_LIKELY(pImage))
+    {
+        PVDINTERFACEPROGRESS pIfProgress = VDIfProgressGet(pVDIfsOperation);
+        PVDINTERFACECONFIG pIfCfg = VDIfConfigGet(pVDIfsOperation);
+        pImage->pszFilename = pszFilename;
+        pImage->pStorage = NULL;
+        pImage->paBlocks = NULL;
+        pImage->pVDIfsDisk = pVDIfsDisk;
+        pImage->pVDIfsImage = pVDIfsImage;
+
+        rc = vdiCreateImage(pImage, cbSize, uImageFlags, pszComment,
+                            pPCHSGeometry, pLCHSGeometry, pUuid, uOpenFlags,
+                            pIfProgress, uPercentStart, uPercentSpan, pIfCfg);
+        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)
+            {
+                vdiFreeImage(pImage, false);
+                rc = vdiOpenImage(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) vdiRename(void *pBackendData, const char *pszFilename)
+{
+    LogFlowFunc(("pBackendData=%#p pszFilename=%#p\n", pBackendData, pszFilename));
+    int rc = VINF_SUCCESS;
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    /* Check arguments. */
+    AssertReturn((pImage && pszFilename && *pszFilename), VERR_INVALID_PARAMETER);
+
+    /* Close the image. */
+    rc = vdiFreeImage(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 new image. */
+            rc = vdiOpenImage(pImage, pImage->uOpenFlags);
+        }
+        else
+        {
+            /* The move failed, try to reopen the original image. */
+            int rc2 = vdiOpenImage(pImage, pImage->uOpenFlags);
+            if (RT_FAILURE(rc2))
+                rc = rc2;
+        }
+    }
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnClose */
+static DECLCALLBACK(int) vdiClose(void *pBackendData, bool fDelete)
+{
+    LogFlowFunc(("pBackendData=%#p fDelete=%d\n", pBackendData, fDelete));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    int rc = vdiFreeImage(pImage, fDelete);
+    RTMemFree(pImage);
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+static DECLCALLBACK(int) vdiRead(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));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    unsigned uBlock;
+    unsigned offRead;
+    int rc = VINF_SUCCESS;
+
+    AssertPtr(pImage);
+    Assert(!(uOffset % 512));
+    Assert(!(cbToRead % 512));
+    AssertPtrReturn(pIoCtx, VERR_INVALID_POINTER);
+    AssertReturn(cbToRead, VERR_INVALID_PARAMETER);
+    AssertReturn(uOffset + cbToRead <= getImageDiskSize(&pImage->Header), VERR_INVALID_PARAMETER);
+
+    /* Calculate starting block number and offset inside it. */
+    uBlock = (unsigned)(uOffset >> pImage->uShiftOffset2Index);
+    offRead = (unsigned)uOffset & pImage->uBlockMask;
+
+    /* Clip read range to at most the rest of the block. */
+    cbToRead = RT_MIN(cbToRead, getImageBlockSize(&pImage->Header) - offRead);
+    Assert(!(cbToRead % 512));
+
+    if (pImage->paBlocks[uBlock] == VDI_IMAGE_BLOCK_FREE)
+        rc = VERR_VD_BLOCK_FREE;
+    else if (pImage->paBlocks[uBlock] == VDI_IMAGE_BLOCK_ZERO)
+    {
+        size_t cbSet;
+
+        cbSet = vdIfIoIntIoCtxSet(pImage->pIfIo, pIoCtx, 0, cbToRead);
+        Assert(cbSet == cbToRead);
+    }
+    else
+    {
+        /* Block present in image file, read relevant data. */
+        uint64_t u64Offset = (uint64_t)pImage->paBlocks[uBlock] * pImage->cbTotalBlockData
+                           + (pImage->offStartData + pImage->offStartBlockData + offRead);
+
+        if (u64Offset + cbToRead <= pImage->cbImage)
+            rc = vdIfIoIntFileReadUser(pImage->pIfIo, pImage->pStorage, u64Offset,
+                                       pIoCtx, cbToRead);
+        else
+        {
+            LogRel(("VDI: Out of range access (%llu) in image %s, image size %llu\n",
+                    u64Offset, pImage->pszFilename, pImage->cbImage));
+            vdIfIoIntIoCtxSet(pImage->pIfIo, pIoCtx, 0, cbToRead);
+            rc = VERR_VD_READ_OUT_OF_RANGE;
+        }
+    }
+
+    if (pcbActuallyRead)
+        *pcbActuallyRead = cbToRead;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+static DECLCALLBACK(int) vdiWrite(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));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    unsigned uBlock;
+    unsigned offWrite;
+    int rc = VINF_SUCCESS;
+
+    AssertPtr(pImage);
+    Assert(!(uOffset % 512));
+    Assert(!(cbToWrite % 512));
+    AssertPtrReturn(pIoCtx, VERR_INVALID_POINTER);
+    AssertReturn(cbToWrite, VERR_INVALID_PARAMETER);
+
+    if (!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        /* No size check here, will do that later.  For dynamic images which are
+         * not multiples of the block size in length, this would prevent writing to
+         * the last block. */
+
+        /* Calculate starting block number and offset inside it. */
+        uBlock = (unsigned)(uOffset >> pImage->uShiftOffset2Index);
+        offWrite = (unsigned)uOffset & pImage->uBlockMask;
+
+        /* Clip write range to at most the rest of the block. */
+        cbToWrite = RT_MIN(cbToWrite, getImageBlockSize(&pImage->Header) - offWrite);
+        Assert(!(cbToWrite % 512));
+
+        do
+        {
+            if (!IS_VDI_IMAGE_BLOCK_ALLOCATED(pImage->paBlocks[uBlock]))
+            {
+                /* Block is either free or zero. */
+                if (   !(pImage->uOpenFlags & VD_OPEN_FLAGS_HONOR_ZEROES)
+                    && (   pImage->paBlocks[uBlock] == VDI_IMAGE_BLOCK_ZERO
+                        || cbToWrite == getImageBlockSize(&pImage->Header)))
+                {
+                    /* If the destination block is unallocated at this point, it's
+                     * either a zero block or a block which hasn't been used so far
+                     * (which also means that it's a zero block. Don't need to write
+                     * anything to this block  if the data consists of just zeroes. */
+                    if (vdIfIoIntIoCtxIsZero(pImage->pIfIo, pIoCtx, cbToWrite, true))
+                    {
+                        pImage->paBlocks[uBlock] = VDI_IMAGE_BLOCK_ZERO;
+                        *pcbPreRead = 0;
+                        *pcbPostRead = 0;
+                        break;
+                    }
+                }
+
+                if (   cbToWrite == getImageBlockSize(&pImage->Header)
+                    && !(fWrite & VD_WRITE_NO_ALLOC))
+                {
+                    /* Full block write to previously unallocated block.
+                     * Allocate block and write data. */
+                    Assert(!offWrite);
+                    PVDIASYNCBLOCKALLOC pBlockAlloc = (PVDIASYNCBLOCKALLOC)RTMemAllocZ(sizeof(VDIASYNCBLOCKALLOC));
+                    if (!pBlockAlloc)
+                    {
+                        rc = VERR_NO_MEMORY;
+                        break;
+                    }
+
+                    unsigned cBlocksAllocated = getImageBlocksAllocated(&pImage->Header);
+                    uint64_t u64Offset = (uint64_t)cBlocksAllocated * pImage->cbTotalBlockData
+                                       + (pImage->offStartData + pImage->offStartBlockData);
+
+                    pBlockAlloc->cBlocksAllocated = cBlocksAllocated;
+                    pBlockAlloc->uBlock           = uBlock;
+
+                    *pcbPreRead = 0;
+                    *pcbPostRead = 0;
+
+                    rc = vdIfIoIntFileWriteUser(pImage->pIfIo, pImage->pStorage,
+                                                u64Offset, pIoCtx, cbToWrite,
+                                                vdiBlockAllocUpdate, pBlockAlloc);
+                    if (rc == VERR_VD_ASYNC_IO_IN_PROGRESS)
+                        break;
+                    else if (RT_FAILURE(rc))
+                    {
+                        RTMemFree(pBlockAlloc);
+                        break;
+                    }
+
+                    rc = vdiBlockAllocUpdate(pImage, pIoCtx, pBlockAlloc, rc);
+                }
+                else
+                {
+                    /* Trying to do a partial write to an unallocated block. Don't do
+                     * anything except letting the upper layer know what to do. */
+                    *pcbPreRead = offWrite % getImageBlockSize(&pImage->Header);
+                    *pcbPostRead = getImageBlockSize(&pImage->Header) - cbToWrite - *pcbPreRead;
+                    rc = VERR_VD_BLOCK_FREE;
+                }
+            }
+            else
+            {
+                /* Block present in image file, write relevant data. */
+                uint64_t u64Offset = (uint64_t)pImage->paBlocks[uBlock] * pImage->cbTotalBlockData
+                                   + (pImage->offStartData + pImage->offStartBlockData + offWrite);
+                rc = vdIfIoIntFileWriteUser(pImage->pIfIo, pImage->pStorage,
+                                            u64Offset, pIoCtx, cbToWrite, NULL, NULL);
+            }
+        } while (0);
+
+        if (pcbWriteProcess)
+            *pcbWriteProcess = cbToWrite;
+    }
+    else
+        rc = VERR_VD_IMAGE_READ_ONLY;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+static DECLCALLBACK(int) vdiFlush(void *pBackendData, PVDIOCTX pIoCtx)
+{
+    LogFlowFunc(("pBackendData=%#p\n", pBackendData));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    int rc = VINF_SUCCESS;
+
+    Assert(pImage);
+
+    rc = vdiFlushImageIoCtx(pImage, pIoCtx);
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetVersion */
+static DECLCALLBACK(unsigned) vdiGetVersion(void *pBackendData)
+{
+    LogFlowFunc(("pBackendData=%#p\n", pBackendData));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, 0);
+
+    LogFlowFunc(("returns %#x\n", pImage->PreHeader.u32Version));
+    return pImage->PreHeader.u32Version;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetFileSize */
+static DECLCALLBACK(uint64_t) vdiGetFileSize(void *pBackendData)
+{
+    LogFlowFunc(("pBackendData=%#p\n", pBackendData));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    uint64_t cb = 0;
+
+    AssertPtrReturn(pImage, 0);
+
+    if (pImage->pStorage)
+    {
+        uint64_t cbFile;
+        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) vdiGetPCHSGeometry(void *pBackendData, PVDGEOMETRY pPCHSGeometry)
+{
+    LogFlowFunc(("pBackendData=%#p pPCHSGeometry=%#p\n", pBackendData, pPCHSGeometry));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)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) vdiSetPCHSGeometry(void *pBackendData, PCVDGEOMETRY pPCHSGeometry)
+{
+    LogFlowFunc(("pBackendData=%#p pPCHSGeometry=%#p PCHS=%u/%u/%u\n",
+                 pBackendData, pPCHSGeometry, pPCHSGeometry->cCylinders, pPCHSGeometry->cHeads, pPCHSGeometry->cSectors));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)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) vdiGetLCHSGeometry(void *pBackendData, PVDGEOMETRY pLCHSGeometry)
+{
+    LogFlowFunc(("pBackendData=%#p pLCHSGeometry=%#p\n", pBackendData, pLCHSGeometry));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    int rc = VINF_SUCCESS;
+    VDIDISKGEOMETRY DummyGeo = { 0, 0, 0, VDI_GEOMETRY_SECTOR_SIZE };
+    PVDIDISKGEOMETRY pGeometry = getImageLCHSGeometry(&pImage->Header);
+    if (!pGeometry)
+        pGeometry = &DummyGeo;
+
+    if (    pGeometry->cCylinders > 0
+        &&  pGeometry->cHeads > 0
+        &&  pGeometry->cSectors > 0)
+    {
+        pLCHSGeometry->cCylinders = pGeometry->cCylinders;
+        pLCHSGeometry->cHeads = pGeometry->cHeads;
+        pLCHSGeometry->cSectors = pGeometry->cSectors;
+    }
+    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) vdiSetLCHSGeometry(void *pBackendData, PCVDGEOMETRY pLCHSGeometry)
+{
+    LogFlowFunc(("pBackendData=%#p pLCHSGeometry=%#p LCHS=%u/%u/%u\n",
+                 pBackendData, pLCHSGeometry, pLCHSGeometry->cCylinders, pLCHSGeometry->cHeads, pLCHSGeometry->cSectors));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    PVDIDISKGEOMETRY pGeometry;
+    int rc = VINF_SUCCESS;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    if (!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        pGeometry = getImageLCHSGeometry(&pImage->Header);
+        if (pGeometry)
+        {
+            pGeometry->cCylinders = pLCHSGeometry->cCylinders;
+            pGeometry->cHeads = pLCHSGeometry->cHeads;
+            pGeometry->cSectors = pLCHSGeometry->cSectors;
+            pGeometry->cbSector = VDI_GEOMETRY_SECTOR_SIZE;
+
+            /* Update header information in base image file. */
+            vdiFlushImage(pImage);
+        }
+    }
+    else
+        rc = VERR_VD_IMAGE_READ_ONLY;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnQueryRegions */
+static DECLCALLBACK(int) vdiQueryRegions(void *pBackendData, PCVDREGIONLIST *ppRegionList)
+{
+    LogFlowFunc(("pBackendData=%#p ppRegionList=%#p\n", pBackendData, ppRegionList));
+    PVDIIMAGEDESC pThis = (PVDIIMAGEDESC)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) vdiRegionListRelease(void *pBackendData, PCVDREGIONLIST pRegionList)
+{
+    RT_NOREF1(pRegionList);
+    LogFlowFunc(("pBackendData=%#p pRegionList=%#p\n", pBackendData, pRegionList));
+    PVDIIMAGEDESC pThis = (PVDIIMAGEDESC)pBackendData;
+    AssertPtr(pThis); RT_NOREF(pThis);
+
+    /* Nothing to do here. */
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetImageFlags */
+static DECLCALLBACK(unsigned) vdiGetImageFlags(void *pBackendData)
+{
+    LogFlowFunc(("pBackendData=%#p\n", pBackendData));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, 0);
+
+    LogFlowFunc(("returns %#x\n", pImage->uImageFlags));
+    return pImage->uImageFlags;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetOpenFlags */
+static DECLCALLBACK(unsigned) vdiGetOpenFlags(void *pBackendData)
+{
+    LogFlowFunc(("pBackendData=%#p\n", pBackendData));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, 0);
+
+    LogFlowFunc(("returns %#x\n", pImage->uOpenFlags));
+    return pImage->uOpenFlags;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnSetOpenFlags */
+static DECLCALLBACK(int) vdiSetOpenFlags(void *pBackendData, unsigned uOpenFlags)
+{
+    LogFlowFunc(("pBackendData=%#p uOpenFlags=%#x\n", pBackendData, uOpenFlags));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    int rc;
+    const char *pszFilename;
+
+    /* 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_DISCARD
+                                   | VD_OPEN_FLAGS_SKIP_CONSISTENCY_CHECKS)))
+        rc = VERR_INVALID_PARAMETER;
+    else
+    {
+        /* Implement this operation via reopening the image. */
+        pszFilename = pImage->pszFilename;
+        rc = vdiFreeImage(pImage, false);
+        if (RT_SUCCESS(rc))
+            rc = vdiOpenImage(pImage, uOpenFlags);
+    }
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetComment */
+static DECLCALLBACK(int) vdiGetComment(void *pBackendData, char *pszComment,
+                                       size_t cbComment)
+{
+    LogFlowFunc(("pBackendData=%#p pszComment=%#p cbComment=%zu\n", pBackendData, pszComment, cbComment));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    int rc = VINF_SUCCESS;
+    char *pszTmp = getImageComment(&pImage->Header);
+    /* Make this foolproof even if the image doesn't have the zero
+     * termination. With some luck the repaired header will be saved. */
+    size_t cb = RTStrNLen(pszTmp, VDI_IMAGE_COMMENT_SIZE);
+    if (cb == VDI_IMAGE_COMMENT_SIZE)
+    {
+        pszTmp[VDI_IMAGE_COMMENT_SIZE-1] = '\0';
+        cb--;
+    }
+    if (cb < cbComment)
+    {
+        /* memcpy is much better than strncpy. */
+        memcpy(pszComment, pszTmp, cb + 1);
+    }
+    else
+        rc = VERR_BUFFER_OVERFLOW;
+
+    LogFlowFunc(("returns %Rrc comment=\"%s\"\n", rc, pszComment));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnSetComment */
+static DECLCALLBACK(int) vdiSetComment(void *pBackendData, const char *pszComment)
+{
+    LogFlowFunc(("pBackendData=%#p pszComment=\"%s\"\n", pBackendData, pszComment));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    int rc;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    if (!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        size_t cchComment = pszComment ? strlen(pszComment) : 0;
+        if (cchComment < VDI_IMAGE_COMMENT_SIZE)
+        {
+            /* we don't support old style images */
+            if (GET_MAJOR_HEADER_VERSION(&pImage->Header) == 1)
+            {
+                /*
+                 * Update the comment field, making sure to zero out all of the previous comment.
+                 */
+                memset(pImage->Header.u.v1.szComment, '\0', VDI_IMAGE_COMMENT_SIZE);
+                memcpy(pImage->Header.u.v1.szComment, pszComment, cchComment);
+
+                /* write out new the header */
+                rc = vdiUpdateHeader(pImage);
+            }
+            else
+                rc = VERR_VD_VDI_UNSUPPORTED_VERSION;
+        }
+        else
+        {
+            LogFunc(("pszComment is too long, %d bytes!\n", cchComment));
+            rc = VERR_VD_VDI_COMMENT_TOO_LONG;
+        }
+    }
+    else
+        rc = VERR_VD_IMAGE_READ_ONLY;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetUuid */
+static DECLCALLBACK(int) vdiGetUuid(void *pBackendData, PRTUUID pUuid)
+{
+    LogFlowFunc(("pBackendData=%#p pUuid=%#p\n", pBackendData, pUuid));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    *pUuid = *getImageCreationUUID(&pImage->Header);
+
+    LogFlowFunc(("returns %Rrc (%RTuuid)\n", VINF_SUCCESS, pUuid));
+    return VINF_SUCCESS;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnSetUuid */
+static DECLCALLBACK(int) vdiSetUuid(void *pBackendData, PCRTUUID pUuid)
+{
+    LogFlowFunc(("pBackendData=%#p Uuid=%RTuuid\n", pBackendData, pUuid));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    int rc = VINF_SUCCESS;
+    if (!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        if (GET_MAJOR_HEADER_VERSION(&pImage->Header) == 1)
+            pImage->Header.u.v1.uuidCreate = *pUuid;
+        /* Make it possible to clone old VDIs. */
+        else if (GET_MAJOR_HEADER_VERSION(&pImage->Header) == 0)
+            pImage->Header.u.v0.uuidCreate = *pUuid;
+        else
+        {
+            LogFunc(("Version is not supported!\n"));
+            rc = VERR_VD_VDI_UNSUPPORTED_VERSION;
+        }
+    }
+    else
+        rc = VERR_VD_IMAGE_READ_ONLY;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetModificationUuid */
+static DECLCALLBACK(int) vdiGetModificationUuid(void *pBackendData, PRTUUID pUuid)
+{
+    LogFlowFunc(("pBackendData=%#p pUuid=%#p\n", pBackendData, pUuid));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    *pUuid = *getImageModificationUUID(&pImage->Header);
+
+    LogFlowFunc(("returns %Rrc (%RTuuid)\n", VINF_SUCCESS, pUuid));
+    return VINF_SUCCESS;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnSetModificationUuid */
+static DECLCALLBACK(int) vdiSetModificationUuid(void *pBackendData, PCRTUUID pUuid)
+{
+    LogFlowFunc(("pBackendData=%#p Uuid=%RTuuid\n", pBackendData, pUuid));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    int rc = VINF_SUCCESS;
+    if (!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        if (GET_MAJOR_HEADER_VERSION(&pImage->Header) == 1)
+            pImage->Header.u.v1.uuidModify = *pUuid;
+        /* Make it possible to clone old VDIs. */
+        else if (GET_MAJOR_HEADER_VERSION(&pImage->Header) == 0)
+            pImage->Header.u.v0.uuidModify = *pUuid;
+        else
+        {
+            LogFunc(("Version is not supported!\n"));
+            rc = VERR_VD_VDI_UNSUPPORTED_VERSION;
+        }
+    }
+    else
+        rc = VERR_VD_IMAGE_READ_ONLY;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetParentUuid */
+static DECLCALLBACK(int) vdiGetParentUuid(void *pBackendData, PRTUUID pUuid)
+{
+    LogFlowFunc(("pBackendData=%#p pUuid=%#p\n", pBackendData, pUuid));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    *pUuid = *getImageParentUUID(&pImage->Header);
+
+    LogFlowFunc(("returns %Rrc (%RTuuid)\n", VINF_SUCCESS, pUuid));
+    return VINF_SUCCESS;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnSetParentUuid */
+static DECLCALLBACK(int) vdiSetParentUuid(void *pBackendData, PCRTUUID pUuid)
+{
+    LogFlowFunc(("pBackendData=%#p Uuid=%RTuuid\n", pBackendData, pUuid));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    int rc = VINF_SUCCESS;
+    if (!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        if (GET_MAJOR_HEADER_VERSION(&pImage->Header) == 1)
+            pImage->Header.u.v1.uuidLinkage = *pUuid;
+        /* Make it possible to clone old VDIs. */
+        else if (GET_MAJOR_HEADER_VERSION(&pImage->Header) == 0)
+            pImage->Header.u.v0.uuidLinkage = *pUuid;
+        else
+        {
+            LogFunc(("Version is not supported!\n"));
+            rc = VERR_VD_VDI_UNSUPPORTED_VERSION;
+        }
+    }
+    else
+        rc = VERR_VD_IMAGE_READ_ONLY;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnGetParentModificationUuid */
+static DECLCALLBACK(int) vdiGetParentModificationUuid(void *pBackendData, PRTUUID pUuid)
+{
+    LogFlowFunc(("pBackendData=%#p pUuid=%#p\n", pBackendData, pUuid));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    *pUuid = *getImageParentModificationUUID(&pImage->Header);
+
+    LogFlowFunc(("returns %Rrc (%RTuuid)\n", VINF_SUCCESS, pUuid));
+    return VINF_SUCCESS;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnSetParentModificationUuid */
+static DECLCALLBACK(int) vdiSetParentModificationUuid(void *pBackendData, PCRTUUID pUuid)
+{
+    LogFlowFunc(("pBackendData=%#p Uuid=%RTuuid\n", pBackendData, pUuid));
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturn(pImage, VERR_VD_NOT_OPENED);
+
+    int rc = VINF_SUCCESS;
+    if (!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY))
+    {
+        if (GET_MAJOR_HEADER_VERSION(&pImage->Header) == 1)
+            pImage->Header.u.v1.uuidParentModify = *pUuid;
+        else
+        {
+            LogFunc(("Version is not supported!\n"));
+            rc = VERR_VD_VDI_UNSUPPORTED_VERSION;
+        }
+    }
+    else
+        rc = VERR_VD_IMAGE_READ_ONLY;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnDump */
+static DECLCALLBACK(void) vdiDump(void *pBackendData)
+{
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+
+    AssertPtrReturnVoid(pImage);
+    vdIfErrorMessage(pImage->pIfError, "Dumping VDI image \"%s\" mode=%s uOpenFlags=%X File=%#p\n",
+                     pImage->pszFilename,
+                     (pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY) ? "r/o" : "r/w",
+                     pImage->uOpenFlags,
+                     pImage->pStorage);
+    vdIfErrorMessage(pImage->pIfError, "Header: Version=%08X Type=%X Flags=%X Size=%llu\n",
+                     pImage->PreHeader.u32Version,
+                     getImageType(&pImage->Header),
+                     getImageFlags(&pImage->Header),
+                     getImageDiskSize(&pImage->Header));
+    vdIfErrorMessage(pImage->pIfError, "Header: cbBlock=%u cbBlockExtra=%u cBlocks=%u cBlocksAllocated=%u\n",
+                     getImageBlockSize(&pImage->Header),
+                     getImageExtraBlockSize(&pImage->Header),
+                     getImageBlocks(&pImage->Header),
+                     getImageBlocksAllocated(&pImage->Header));
+    vdIfErrorMessage(pImage->pIfError, "Header: offBlocks=%u offData=%u\n",
+                     getImageBlocksOffset(&pImage->Header),
+                     getImageDataOffset(&pImage->Header));
+    PVDIDISKGEOMETRY pg = getImageLCHSGeometry(&pImage->Header);
+    if (pg)
+        vdIfErrorMessage(pImage->pIfError, "Header: Geometry: C/H/S=%u/%u/%u cbSector=%u\n",
+                         pg->cCylinders, pg->cHeads, pg->cSectors, pg->cbSector);
+    vdIfErrorMessage(pImage->pIfError, "Header: uuidCreation={%RTuuid}\n", getImageCreationUUID(&pImage->Header));
+    vdIfErrorMessage(pImage->pIfError, "Header: uuidModification={%RTuuid}\n", getImageModificationUUID(&pImage->Header));
+    vdIfErrorMessage(pImage->pIfError, "Header: uuidParent={%RTuuid}\n", getImageParentUUID(&pImage->Header));
+    if (GET_MAJOR_HEADER_VERSION(&pImage->Header) >= 1)
+        vdIfErrorMessage(pImage->pIfError, "Header: uuidParentModification={%RTuuid}\n", getImageParentModificationUUID(&pImage->Header));
+    vdIfErrorMessage(pImage->pIfError, "Image:  fFlags=%08X offStartBlocks=%u offStartData=%u\n",
+                     pImage->uImageFlags, pImage->offStartBlocks, pImage->offStartData);
+    vdIfErrorMessage(pImage->pIfError, "Image:  uBlockMask=%08X cbTotalBlockData=%u uShiftOffset2Index=%u offStartBlockData=%u\n",
+                     pImage->uBlockMask,
+                     pImage->cbTotalBlockData,
+                     pImage->uShiftOffset2Index,
+                     pImage->offStartBlockData);
+
+    unsigned uBlock, cBlocksNotFree, cBadBlocks, cBlocks = getImageBlocks(&pImage->Header);
+    for (uBlock=0, cBlocksNotFree=0, cBadBlocks=0; uBlock<cBlocks; uBlock++)
+    {
+        if (IS_VDI_IMAGE_BLOCK_ALLOCATED(pImage->paBlocks[uBlock]))
+        {
+            cBlocksNotFree++;
+            if (pImage->paBlocks[uBlock] >= cBlocks)
+                cBadBlocks++;
+        }
+    }
+    if (cBlocksNotFree != getImageBlocksAllocated(&pImage->Header))
+    {
+        vdIfErrorMessage(pImage->pIfError, "!! WARNING: %u blocks actually allocated (cBlocksAllocated=%u) !!\n",
+                         cBlocksNotFree, getImageBlocksAllocated(&pImage->Header));
+    }
+    if (cBadBlocks)
+    {
+        vdIfErrorMessage(pImage->pIfError, "!! WARNING: %u bad blocks found !!\n",
+                         cBadBlocks);
+    }
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnCompact */
+static DECLCALLBACK(int) vdiCompact(void *pBackendData, unsigned uPercentStart,
+                                    unsigned uPercentSpan, PVDINTERFACE pVDIfsDisk,
+                                    PVDINTERFACE pVDIfsImage, PVDINTERFACE pVDIfsOperation)
+{
+    RT_NOREF2(pVDIfsDisk, pVDIfsImage);
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    int rc = VINF_SUCCESS;
+    void *pvBuf = NULL, *pvTmp = NULL;
+    unsigned *paBlocks2 = NULL;
+
+    PFNVDPARENTREAD pfnParentRead = NULL;
+    void *pvParent = NULL;
+    PVDINTERFACEPARENTSTATE pIfParentState = VDIfParentStateGet(pVDIfsOperation);
+    if (pIfParentState)
+    {
+        pfnParentRead = pIfParentState->pfnParentRead;
+        pvParent = pIfParentState->Core.pvUser;
+    }
+
+    PVDINTERFACEPROGRESS pIfProgress = VDIfProgressGet(pVDIfsOperation);
+    PVDINTERFACEQUERYRANGEUSE pIfQueryRangeUse = VDIfQueryRangeUseGet(pVDIfsOperation);
+
+    do
+    {
+        AssertBreakStmt(pImage, rc = VERR_INVALID_PARAMETER);
+
+        AssertBreakStmt(!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY),
+                        rc = VERR_VD_IMAGE_READ_ONLY);
+
+        unsigned cBlocks;
+        unsigned cBlocksToMove = 0;
+        size_t cbBlock;
+        cBlocks = getImageBlocks(&pImage->Header);
+        cbBlock = getImageBlockSize(&pImage->Header);
+        if (pfnParentRead)
+        {
+            pvBuf = RTMemTmpAlloc(cbBlock);
+            AssertBreakStmt(pvBuf, rc = VERR_NO_MEMORY);
+        }
+        pvTmp = RTMemTmpAlloc(cbBlock);
+        AssertBreakStmt(pvTmp, rc = VERR_NO_MEMORY);
+
+        uint64_t cbFile;
+        rc = vdIfIoIntFileGetSize(pImage->pIfIo, pImage->pStorage, &cbFile);
+        AssertRCBreak(rc);
+        unsigned cBlocksAllocated = (unsigned)((cbFile - pImage->offStartData - pImage->offStartBlockData) >> pImage->uShiftOffset2Index);
+        if (cBlocksAllocated == 0)
+        {
+            /* No data blocks in this image, no need to compact. */
+            rc = VINF_SUCCESS;
+            break;
+        }
+
+        /* Allocate block array for back resolving. */
+        paBlocks2 = (unsigned *)RTMemAlloc(sizeof(unsigned *) * cBlocksAllocated);
+        AssertBreakStmt(paBlocks2, rc = VERR_NO_MEMORY);
+        /* Fill out back resolving, check/fix allocation errors before
+         * compacting the image, just to be on the safe side. Update the
+         * image contents straight away, as this enables cancelling. */
+        for (unsigned i = 0; i < cBlocksAllocated; i++)
+            paBlocks2[i] = VDI_IMAGE_BLOCK_FREE;
+        rc = VINF_SUCCESS;
+        for (unsigned i = 0; i < cBlocks; i++)
+        {
+            VDIIMAGEBLOCKPOINTER ptrBlock = pImage->paBlocks[i];
+            if (IS_VDI_IMAGE_BLOCK_ALLOCATED(ptrBlock))
+            {
+                if (ptrBlock < cBlocksAllocated)
+                {
+                    if (paBlocks2[ptrBlock] == VDI_IMAGE_BLOCK_FREE)
+                        paBlocks2[ptrBlock] = i;
+                    else
+                    {
+                        LogFunc(("Freed cross-linked block %u in file \"%s\"\n",
+                                 i, pImage->pszFilename));
+                        pImage->paBlocks[i] = VDI_IMAGE_BLOCK_FREE;
+                        rc = vdiUpdateBlockInfo(pImage, i);
+                        if (RT_FAILURE(rc))
+                            break;
+                    }
+                }
+                else
+                {
+                    LogFunc(("Freed out of bounds reference for block %u in file \"%s\"\n",
+                             i, pImage->pszFilename));
+                    pImage->paBlocks[i] = VDI_IMAGE_BLOCK_FREE;
+                    rc = vdiUpdateBlockInfo(pImage, i);
+                    if (RT_FAILURE(rc))
+                        break;
+                }
+            }
+        }
+        if (RT_FAILURE(rc))
+            break;
+
+        /* Find redundant information and update the block pointers
+         * accordingly, creating bubbles. Keep disk up to date, as this
+         * enables cancelling. */
+        for (unsigned i = 0; i < cBlocks; i++)
+        {
+            VDIIMAGEBLOCKPOINTER ptrBlock = pImage->paBlocks[i];
+            if (IS_VDI_IMAGE_BLOCK_ALLOCATED(ptrBlock))
+            {
+                /* Block present in image file, read relevant data. */
+                uint64_t u64Offset = (uint64_t)ptrBlock * pImage->cbTotalBlockData
+                                   + (pImage->offStartData + pImage->offStartBlockData);
+                rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage, u64Offset, pvTmp, cbBlock);
+                if (RT_FAILURE(rc))
+                    break;
+
+                if (ASMBitFirstSet((volatile void *)pvTmp, (uint32_t)cbBlock * 8) == -1)
+                {
+                    pImage->paBlocks[i] = VDI_IMAGE_BLOCK_ZERO;
+                    rc = vdiUpdateBlockInfo(pImage, i);
+                    if (RT_FAILURE(rc))
+                        break;
+                    paBlocks2[ptrBlock] = VDI_IMAGE_BLOCK_FREE;
+                    /* Adjust progress info, one block to be relocated. */
+                    cBlocksToMove++;
+                }
+                else if (pfnParentRead)
+                {
+                    rc = pfnParentRead(pvParent, (uint64_t)i * cbBlock, pvBuf, cbBlock);
+                    if (RT_FAILURE(rc))
+                        break;
+                    if (!memcmp(pvTmp, pvBuf, cbBlock))
+                    {
+                        pImage->paBlocks[i] = VDI_IMAGE_BLOCK_FREE;
+                        rc = vdiUpdateBlockInfo(pImage, i);
+                        if (RT_FAILURE(rc))
+                            break;
+                        paBlocks2[ptrBlock] = VDI_IMAGE_BLOCK_FREE;
+                        /* Adjust progress info, one block to be relocated. */
+                        cBlocksToMove++;
+                    }
+                }
+            }
+
+            /* Check if the range is in use if the block is still allocated. */
+            ptrBlock = pImage->paBlocks[i];
+            if (   IS_VDI_IMAGE_BLOCK_ALLOCATED(ptrBlock)
+                && pIfQueryRangeUse)
+            {
+                bool fUsed = true;
+
+                rc = vdIfQueryRangeUse(pIfQueryRangeUse, (uint64_t)i * cbBlock, cbBlock, &fUsed);
+                if (RT_FAILURE(rc))
+                    break;
+                if (!fUsed)
+                {
+                    pImage->paBlocks[i] = VDI_IMAGE_BLOCK_ZERO;
+                    rc = vdiUpdateBlockInfo(pImage, i);
+                    if (RT_FAILURE(rc))
+                        break;
+                    paBlocks2[ptrBlock] = VDI_IMAGE_BLOCK_FREE;
+                    /* Adjust progress info, one block to be relocated. */
+                    cBlocksToMove++;
+                }
+            }
+
+            vdIfProgress(pIfProgress, (uint64_t)i * uPercentSpan / (cBlocks + cBlocksToMove) + uPercentStart);
+            if (RT_FAILURE(rc))
+                break;
+        }
+        if (RT_FAILURE(rc))
+            break;
+
+        /* Fill bubbles with other data (if available). */
+        unsigned cBlocksMoved = 0;
+        unsigned uBlockUsedPos = cBlocksAllocated;
+        for (unsigned i = 0; i < cBlocksAllocated; i++)
+        {
+            unsigned uBlock = paBlocks2[i];
+            if (uBlock == VDI_IMAGE_BLOCK_FREE)
+            {
+                unsigned uBlockData = VDI_IMAGE_BLOCK_FREE;
+                while (uBlockUsedPos > i && uBlockData == VDI_IMAGE_BLOCK_FREE)
+                {
+                    uBlockUsedPos--;
+                    uBlockData = paBlocks2[uBlockUsedPos];
+                }
+                /* Terminate early if there is no block which needs copying. */
+                if (uBlockUsedPos == i)
+                    break;
+                uint64_t u64Offset = (uint64_t)uBlockUsedPos * pImage->cbTotalBlockData
+                                   + (pImage->offStartData + pImage->offStartBlockData);
+                rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage, u64Offset,
+                                           pvTmp, cbBlock);
+                u64Offset = (uint64_t)i * pImage->cbTotalBlockData
+                          + (pImage->offStartData + pImage->offStartBlockData);
+                rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage, u64Offset,
+                                            pvTmp, cbBlock);
+                pImage->paBlocks[uBlockData] = i;
+                setImageBlocksAllocated(&pImage->Header, cBlocksAllocated - cBlocksMoved);
+                rc = vdiUpdateBlockInfo(pImage, uBlockData);
+                if (RT_FAILURE(rc))
+                    break;
+                paBlocks2[i] = uBlockData;
+                paBlocks2[uBlockUsedPos] = VDI_IMAGE_BLOCK_FREE;
+                cBlocksMoved++;
+            }
+
+            rc = vdIfProgress(pIfProgress, (uint64_t)(cBlocks + cBlocksMoved) * uPercentSpan / (cBlocks + cBlocksToMove) + uPercentStart);
+            if (RT_FAILURE(rc))
+                break;
+        }
+        if (RT_FAILURE(rc))
+            break;
+
+        /* Update image header. */
+        setImageBlocksAllocated(&pImage->Header, uBlockUsedPos);
+        vdiUpdateHeader(pImage);
+
+        /* Truncate the image to the proper size to finish compacting. */
+        rc = vdIfIoIntFileSetSize(pImage->pIfIo, pImage->pStorage,
+                                  (uint64_t)uBlockUsedPos * pImage->cbTotalBlockData
+                                  + pImage->offStartData + pImage->offStartBlockData);
+    } while (0);
+
+    if (paBlocks2)
+        RTMemTmpFree(paBlocks2);
+    if (pvTmp)
+        RTMemTmpFree(pvTmp);
+    if (pvBuf)
+        RTMemTmpFree(pvBuf);
+
+    if (RT_SUCCESS(rc))
+        vdIfProgress(pIfProgress, uPercentStart + uPercentSpan);
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+
+/** @copydoc VDIMAGEBACKEND::pfnResize */
+static DECLCALLBACK(int) vdiResize(void *pBackendData, uint64_t cbSize,
+                                   PCVDGEOMETRY pPCHSGeometry, PCVDGEOMETRY pLCHSGeometry,
+                                   unsigned uPercentStart, unsigned uPercentSpan,
+                                   PVDINTERFACE pVDIfsDisk, PVDINTERFACE pVDIfsImage,
+                                   PVDINTERFACE pVDIfsOperation)
+{
+    RT_NOREF5(uPercentStart, uPercentSpan, pVDIfsDisk, pVDIfsImage, pVDIfsOperation);
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    int rc = VINF_SUCCESS;
+
+    /* Check size. Maximum 4PB-3M. No tricks with adjusting the 1M block size
+     * so far, which would extend the size. */
+    if (   !cbSize
+        || cbSize >= _1P * 4 - _1M * 3
+        || cbSize < VDI_IMAGE_DEFAULT_BLOCK_SIZE)
+        return VERR_VD_INVALID_SIZE;
+
+    /*
+     * Making the image smaller is not supported at the moment.
+     * Resizing is also not supported for fixed size images and
+     * very old images.
+     */
+    /** @todo implement making the image smaller, it is the responsibility of
+     * the user to know what he's doing. */
+    if (cbSize < getImageDiskSize(&pImage->Header))
+        rc = VERR_VD_SHRINK_NOT_SUPPORTED;
+    else if (   GET_MAJOR_HEADER_VERSION(&pImage->Header) == 0
+             || pImage->uImageFlags & VD_IMAGE_FLAGS_FIXED)
+        rc = VERR_NOT_SUPPORTED;
+    else if (cbSize > getImageDiskSize(&pImage->Header))
+    {
+        unsigned cBlocksAllocated = getImageBlocksAllocated(&pImage->Header); /** < Blocks currently allocated, doesn't change during resize */
+        unsigned const cbBlock = RT_MAX(getImageBlockSize(&pImage->Header), 1);
+        uint32_t cBlocksNew = cbSize / cbBlock;                               /** < New number of blocks in the image after the resize */
+        if (cbSize % cbBlock)
+            cBlocksNew++;
+
+        uint32_t cBlocksOld      = getImageBlocks(&pImage->Header);           /** < Number of blocks before the resize. */
+        uint64_t cbBlockspaceNew = cBlocksNew * sizeof(VDIIMAGEBLOCKPOINTER); /** < Required space for the block array after the resize. */
+        uint64_t offStartDataNew = RT_ALIGN_32(pImage->offStartBlocks + cbBlockspaceNew, VDI_DATA_ALIGN); /** < New start offset for block data after the resize */
+
+        if (pImage->offStartData < offStartDataNew)
+        {
+            if (cBlocksAllocated > 0)
+            {
+                /* Calculate how many sectors need to be relocated. */
+                uint64_t cbOverlapping = offStartDataNew - pImage->offStartData;
+                unsigned cBlocksReloc = cbOverlapping / cbBlock;
+                if (cbOverlapping % cbBlock)
+                    cBlocksReloc++;
+
+                /* Since only full blocks can be relocated the new data start is
+                 * determined by moving it block by block. */
+                cBlocksReloc = RT_MIN(cBlocksReloc, cBlocksAllocated);
+                offStartDataNew = pImage->offStartData;
+
+                /* Do the relocation. */
+                LogFlow(("Relocating %u blocks\n", cBlocksReloc));
+
+                /*
+                 * Get the blocks we need to relocate first, they are appended to the end
+                 * of the image.
+                 */
+                void *pvBuf = NULL, *pvZero = NULL;
+                do
+                {
+                    /* Allocate data buffer. */
+                    pvBuf = RTMemAllocZ(pImage->cbTotalBlockData);
+                    if (!pvBuf)
+                    {
+                        rc = VERR_NO_MEMORY;
+                        break;
+                    }
+
+                    /* Allocate buffer for overwriting with zeroes. */
+                    pvZero = RTMemAllocZ(pImage->cbTotalBlockData);
+                    if (!pvZero)
+                    {
+                        rc = VERR_NO_MEMORY;
+                        break;
+                    }
+
+                    for (unsigned i = 0; i < cBlocksReloc; i++)
+                    {
+                        /* Search the index in the block table. */
+                        for (unsigned idxBlock = 0; idxBlock < cBlocksOld; idxBlock++)
+                        {
+                            if (!pImage->paBlocks[idxBlock])
+                            {
+                                /* Read data and append to the end of the image. */
+                                rc = vdIfIoIntFileReadSync(pImage->pIfIo, pImage->pStorage,
+                                                           offStartDataNew, pvBuf,
+                                                           pImage->cbTotalBlockData);
+                                if (RT_FAILURE(rc))
+                                    break;
+
+                                uint64_t offBlockAppend;
+                                rc = vdIfIoIntFileGetSize(pImage->pIfIo, pImage->pStorage, &offBlockAppend);
+                                if (RT_FAILURE(rc))
+                                    break;
+
+                                rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage,
+                                                            offBlockAppend, pvBuf,
+                                                            pImage->cbTotalBlockData);
+                                if (RT_FAILURE(rc))
+                                    break;
+
+                                /* Zero out the old block area. */
+                                rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage,
+                                                            offStartDataNew, pvZero,
+                                                            pImage->cbTotalBlockData);
+                                if (RT_FAILURE(rc))
+                                    break;
+
+                                /* Update block counter. */
+                                pImage->paBlocks[idxBlock] = cBlocksAllocated - 1;
+
+                                /*
+                                 * Decrease the block number of all other entries in the array.
+                                 * They were moved one block to the front.
+                                 * Doing it as a separate step iterating over the array again
+                                 * because an error while relocating the block might end up
+                                 * in a corrupted image otherwise.
+                                 */
+                                for (unsigned idxBlock2 = 0; idxBlock2 < cBlocksOld; idxBlock2++)
+                                {
+                                    if (   idxBlock2 != idxBlock
+                                        && IS_VDI_IMAGE_BLOCK_ALLOCATED(pImage->paBlocks[idxBlock2]))
+                                        pImage->paBlocks[idxBlock2]--;
+                                }
+
+                                /* Continue with the next block. */
+                                break;
+                            }
+                        }
+
+                        if (RT_FAILURE(rc))
+                            break;
+
+                        offStartDataNew += pImage->cbTotalBlockData;
+                    }
+                } while (0);
+
+                if (pvBuf)
+                    RTMemFree(pvBuf);
+                if (pvZero)
+                    RTMemFree(pvZero);
+            }
+
+            /*
+             * We need to update the new offsets for the image data in the out of memory
+             * case too because we relocated the blocks already.
+             */
+            pImage->offStartData = offStartDataNew;
+            setImageDataOffset(&pImage->Header, offStartDataNew);
+        }
+
+        /*
+         * Relocation done, expand the block array and update the header with
+         * the new data.
+         */
+        if (RT_SUCCESS(rc))
+        {
+            PVDIIMAGEBLOCKPOINTER paBlocksNew = (PVDIIMAGEBLOCKPOINTER)RTMemRealloc(pImage->paBlocks, cbBlockspaceNew);
+            if (paBlocksNew)
+            {
+                pImage->paBlocks = paBlocksNew;
+
+                /* Mark the new blocks as unallocated. */
+                for (unsigned idxBlock = cBlocksOld; idxBlock < cBlocksNew; idxBlock++)
+                    pImage->paBlocks[idxBlock] = VDI_IMAGE_BLOCK_FREE;
+            }
+            else
+                rc = VERR_NO_MEMORY;
+
+            /* Write the block array before updating the rest. */
+            vdiConvBlocksEndianess(VDIECONV_H2F, pImage->paBlocks, cBlocksNew);
+            rc = vdIfIoIntFileWriteSync(pImage->pIfIo, pImage->pStorage, pImage->offStartBlocks,
+                                        pImage->paBlocks, cbBlockspaceNew);
+            vdiConvBlocksEndianess(VDIECONV_F2H, pImage->paBlocks, cBlocksNew);
+
+            if (RT_SUCCESS(rc))
+            {
+                /* Update size and new block count. */
+                setImageDiskSize(&pImage->Header, cbSize);
+                setImageBlocks(&pImage->Header, cBlocksNew);
+                /* Update geometry. */
+                pImage->PCHSGeometry = *pPCHSGeometry;
+                pImage->cbImage = cbSize;
+
+                PVDIDISKGEOMETRY pGeometry = getImageLCHSGeometry(&pImage->Header);
+                if (pGeometry)
+                {
+                    pGeometry->cCylinders = pLCHSGeometry->cCylinders;
+                    pGeometry->cHeads = pLCHSGeometry->cHeads;
+                    pGeometry->cSectors = pLCHSGeometry->cSectors;
+                    pGeometry->cbSector = VDI_GEOMETRY_SECTOR_SIZE;
+                }
+            }
+        }
+
+        /* Update header information in base image file. */
+        vdiFlushImage(pImage);
+    }
+    /* Same size doesn't change the image at all. */
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnDiscard */
+static DECLCALLBACK(int) vdiDiscard(void *pBackendData, PVDIOCTX pIoCtx,
+                                    uint64_t uOffset, size_t cbDiscard,
+                                    size_t *pcbPreAllocated, size_t *pcbPostAllocated,
+                                    size_t *pcbActuallyDiscarded, void **ppbmAllocationBitmap,
+                                    unsigned fDiscard)
+{
+    PVDIIMAGEDESC pImage = (PVDIIMAGEDESC)pBackendData;
+    unsigned uBlock;
+    unsigned offDiscard;
+    int rc = VINF_SUCCESS;
+    void *pvBlock = NULL;
+
+    LogFlowFunc(("pBackendData=%#p pIoCtx=%#p uOffset=%llu cbDiscard=%zu pcbPreAllocated=%#p pcbPostAllocated=%#p pcbActuallyDiscarded=%#p ppbmAllocationBitmap=%#p fDiscard=%#x\n",
+                 pBackendData, pIoCtx, uOffset, cbDiscard, pcbPreAllocated, pcbPostAllocated, pcbActuallyDiscarded, ppbmAllocationBitmap, fDiscard));
+
+    AssertPtr(pImage);
+    Assert(!(uOffset % 512));
+    Assert(!(cbDiscard % 512));
+
+    AssertMsgReturn(!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY),
+                    ("Image is readonly\n"), VERR_VD_IMAGE_READ_ONLY);
+    AssertMsgReturn(   uOffset + cbDiscard <= getImageDiskSize(&pImage->Header)
+                    && cbDiscard,
+                    ("Invalid parameters uOffset=%llu cbDiscard=%zu\n",
+                     uOffset, cbDiscard),
+                     VERR_INVALID_PARAMETER);
+
+    do
+    {
+        AssertMsgBreakStmt(!(pImage->uOpenFlags & VD_OPEN_FLAGS_READONLY),
+                           ("Image is opened readonly\n"),
+                           rc = VERR_VD_IMAGE_READ_ONLY);
+
+        AssertMsgBreakStmt(cbDiscard,
+                           ("cbDiscard=%u\n", cbDiscard),
+                           rc = VERR_INVALID_PARAMETER);
+
+        /* Calculate starting block number and offset inside it. */
+        uBlock = (unsigned)(uOffset >> pImage->uShiftOffset2Index);
+        offDiscard = (unsigned)uOffset & pImage->uBlockMask;
+
+        /* Clip range to at most the rest of the block. */
+        cbDiscard = RT_MIN(cbDiscard, getImageBlockSize(&pImage->Header) - offDiscard);
+        Assert(!(cbDiscard % 512));
+
+        if (pcbPreAllocated)
+            *pcbPreAllocated = 0;
+
+        if (pcbPostAllocated)
+            *pcbPostAllocated = 0;
+
+        if (IS_VDI_IMAGE_BLOCK_ALLOCATED(pImage->paBlocks[uBlock]))
+        {
+            unsigned const cbBlock = RT_MAX(getImageBlockSize(&pImage->Header), 1);
+            size_t const cbPreAllocated = offDiscard % cbBlock;
+            size_t const cbPostAllocated = getImageBlockSize(&pImage->Header) - cbDiscard - cbPreAllocated;
+            uint8_t *pbBlockData;
+
+            /* Read the block data. */
+            pvBlock = RTMemAlloc(pImage->cbTotalBlockData);
+            if (!pvBlock)
+            {
+                rc = VERR_NO_MEMORY;
+                break;
+            }
+
+            if (!cbPreAllocated && !cbPostAllocated)
+            {
+                /*
+                 * Discarding a whole block, don't check for allocated sectors.
+                 * It is possible to just remove the whole block which avoids
+                 * one read and checking the whole block for data.
+                 */
+                rc = vdiDiscardBlockAsync(pImage, pIoCtx, uBlock, pvBlock);
+            }
+            else if (fDiscard & VD_DISCARD_MARK_UNUSED)
+            {
+                /* Just zero out the given range. */
+                memset(pvBlock, 0, cbDiscard);
+
+                uint64_t u64Offset = (uint64_t)pImage->paBlocks[uBlock] * pImage->cbTotalBlockData + pImage->offStartData + offDiscard;
+                rc = vdIfIoIntFileWriteMeta(pImage->pIfIo, pImage->pStorage,
+                                            u64Offset, pvBlock, cbDiscard, pIoCtx,
+                                            NULL, NULL);
+                RTMemFree(pvBlock);
+            }
+            else
+            {
+                /*
+                 * Read complete block as metadata, the I/O context has no memory buffer
+                 * and we need to access the content directly anyway.
+                 */
+                PVDMETAXFER pMetaXfer;
+                pbBlockData = (uint8_t *)pvBlock + pImage->offStartBlockData;
+
+                uint64_t u64Offset = (uint64_t)pImage->paBlocks[uBlock] * pImage->cbTotalBlockData + pImage->offStartData;
+                rc = vdIfIoIntFileReadMeta(pImage->pIfIo, pImage->pStorage, u64Offset,
+                                           pbBlockData, pImage->cbTotalBlockData,
+                                           pIoCtx, &pMetaXfer, NULL, NULL);
+                if (RT_FAILURE(rc))
+                {
+                    RTMemFree(pvBlock);
+                    break;
+                }
+
+                vdIfIoIntMetaXferRelease(pImage->pIfIo, pMetaXfer);
+
+                /* Clear data. */
+                memset(pbBlockData + offDiscard , 0, cbDiscard);
+
+                Assert(!(cbDiscard % 4));
+                Assert(getImageBlockSize(&pImage->Header) * 8 <= UINT32_MAX);
+                if (ASMBitFirstSet((volatile void *)pbBlockData, getImageBlockSize(&pImage->Header) * 8) == -1)
+                    rc = vdiDiscardBlockAsync(pImage, pIoCtx, uBlock, pvBlock);
+                else
+                {
+                    /* Block has data, create allocation bitmap. */
+                    *pcbPreAllocated = cbPreAllocated;
+                    *pcbPostAllocated = cbPostAllocated;
+                    *ppbmAllocationBitmap = vdiAllocationBitmapCreate(pbBlockData, getImageBlockSize(&pImage->Header));
+                    if (RT_UNLIKELY(!*ppbmAllocationBitmap))
+                        rc = VERR_NO_MEMORY;
+                    else
+                        rc = VERR_VD_DISCARD_ALIGNMENT_NOT_MET;
+
+                    RTMemFree(pvBlock);
+                }
+            } /* if: no complete block discarded */
+        } /* if: Block is allocated. */
+        /* else: nothing to do. */
+    } while (0);
+
+    if (pcbActuallyDiscarded)
+        *pcbActuallyDiscarded = cbDiscard;
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+/** @copydoc VDIMAGEBACKEND::pfnRepair */
+static DECLCALLBACK(int) vdiRepair(const char *pszFilename, PVDINTERFACE pVDIfsDisk,
+                                   PVDINTERFACE pVDIfsImage, uint32_t fFlags)
+{
+    LogFlowFunc(("pszFilename=\"%s\" pVDIfsDisk=%#p pVDIfsImage=%#p\n", pszFilename, pVDIfsDisk, pVDIfsImage));
+    int rc;
+    PVDINTERFACEERROR pIfError;
+    PVDINTERFACEIOINT pIfIo;
+    PVDIOSTORAGE pStorage = NULL;
+    uint64_t cbFile;
+    PVDIIMAGEBLOCKPOINTER paBlocks = NULL;
+    uint32_t *pu32BlockBitmap = NULL;
+    VDIPREHEADER PreHdr;
+    VDIHEADER    Hdr;
+
+    pIfIo = VDIfIoIntGet(pVDIfsImage);
+    AssertPtrReturn(pIfIo, VERR_INVALID_PARAMETER);
+
+    pIfError = VDIfErrorGet(pVDIfsDisk);
+
+    do
+    {
+        bool fRepairBlockArray = false;
+        bool fRepairHdr = false;
+
+        rc = vdIfIoIntFileOpen(pIfIo, pszFilename,
+                               VDOpenFlagsToFileOpenFlags(  fFlags & VD_REPAIR_DRY_RUN
+                                                          ? VD_OPEN_FLAGS_READONLY
+                                                          : 0,
+                                                          false /* fCreate */),
+                               &pStorage);
+        if (RT_FAILURE(rc))
+        {
+            rc = vdIfError(pIfError, rc, RT_SRC_POS, "VDI: Failed to open image \"%s\"", pszFilename);
+            break;
+        }
+
+        rc = vdIfIoIntFileGetSize(pIfIo, pStorage, &cbFile);
+        if (RT_FAILURE(rc))
+        {
+            rc = vdIfError(pIfError, rc, RT_SRC_POS, "VDI: Failed to query image size");
+            break;
+        }
+
+        /* Read pre-header. */
+        rc = vdIfIoIntFileReadSync(pIfIo, pStorage, 0, &PreHdr, sizeof(PreHdr));
+        if (RT_FAILURE(rc))
+        {
+            rc = vdIfError(pIfError, rc, RT_SRC_POS, N_("VDI: Error reading pre-header in '%s'"), pszFilename);
+            break;
+        }
+        vdiConvPreHeaderEndianess(VDIECONV_F2H, &PreHdr, &PreHdr);
+        rc = vdiValidatePreHeader(&PreHdr);
+        if (RT_FAILURE(rc))
+        {
+            rc = vdIfError(pIfError, VERR_VD_IMAGE_REPAIR_IMPOSSIBLE, RT_SRC_POS,
+                           N_("VDI: invalid pre-header in '%s'"), pszFilename);
+            break;
+        }
+
+        /* Read header. */
+        Hdr.uVersion = PreHdr.u32Version;
+        switch (GET_MAJOR_HEADER_VERSION(&Hdr))
+        {
+            case 0:
+                rc = vdIfIoIntFileReadSync(pIfIo, pStorage, sizeof(PreHdr),
+                                           &Hdr.u.v0, sizeof(Hdr.u.v0));
+                if (RT_FAILURE(rc))
+                    rc = vdIfError(pIfError, rc, RT_SRC_POS, N_("VDI: error reading v0 header in '%s'"),
+                                   pszFilename);
+                vdiConvHeaderEndianessV0(VDIECONV_F2H, &Hdr.u.v0, &Hdr.u.v0);
+                break;
+            case 1:
+                rc = vdIfIoIntFileReadSync(pIfIo, pStorage, sizeof(PreHdr),
+                                           &Hdr.u.v1, sizeof(Hdr.u.v1));
+                if (RT_FAILURE(rc))
+                {
+                    rc = vdIfError(pIfError, rc, RT_SRC_POS, N_("VDI: error reading v1 header in '%s'"),
+                                   pszFilename);
+                }
+                vdiConvHeaderEndianessV1(VDIECONV_F2H, &Hdr.u.v1, &Hdr.u.v1);
+                if (Hdr.u.v1.cbHeader >= sizeof(Hdr.u.v1plus))
+                {
+                    /* Read the VDI 1.1+ header completely. */
+                    rc = vdIfIoIntFileReadSync(pIfIo, pStorage, sizeof(PreHdr),
+                                               &Hdr.u.v1plus, sizeof(Hdr.u.v1plus));
+                    if (RT_FAILURE(rc))
+                        rc = vdIfError(pIfError, rc, RT_SRC_POS, N_("VDI: error reading v1.1+ header in '%s'"),
+                                       pszFilename);
+                    vdiConvHeaderEndianessV1p(VDIECONV_F2H, &Hdr.u.v1plus, &Hdr.u.v1plus);
+                }
+                break;
+            default:
+                rc = vdIfError(pIfError, VERR_VD_IMAGE_REPAIR_IMPOSSIBLE, RT_SRC_POS,
+                               N_("VDI: unsupported major version %u in '%s'"),
+                               GET_MAJOR_HEADER_VERSION(&Hdr), pszFilename);
+                break;
+        }
+
+        if (RT_SUCCESS(rc))
+        {
+            rc = vdiValidateHeader(&Hdr);
+            if (RT_FAILURE(rc))
+            {
+                rc = vdIfError(pIfError, VERR_VD_IMAGE_REPAIR_IMPOSSIBLE, RT_SRC_POS,
+                               N_("VDI: invalid header in '%s'"), pszFilename);
+                break;
+            }
+        }
+
+        /*
+         * Check that the disk size is correctly aligned,
+         * see comment above the same check in vdiImageReadHeader().
+         */
+        uint64_t cbDisk = getImageDiskSize(&Hdr);
+        if (cbDisk & 0x1ff)
+        {
+            uint64_t cbDiskNew = cbDisk & ~UINT64_C(0x1ff);
+            vdIfErrorMessage(pIfError, "Disk size in the header is not sector aligned, rounding down (%llu -> %llu)\n",
+                             cbDisk, cbDiskNew);
+            setImageDiskSize(&Hdr, cbDiskNew);
+            fRepairHdr = true;
+        }
+
+        /* Setup image parameters by header. */
+        uint64_t offStartBlocks, offStartData;
+        size_t cbTotalBlockData;
+
+        offStartBlocks     = getImageBlocksOffset(&Hdr);
+        offStartData       = getImageDataOffset(&Hdr);
+        cbTotalBlockData   = getImageExtraBlockSize(&Hdr) + getImageBlockSize(&Hdr);
+
+        /* Allocate memory for blocks array. */
+        paBlocks = (PVDIIMAGEBLOCKPOINTER)RTMemAlloc(sizeof(VDIIMAGEBLOCKPOINTER) * getImageBlocks(&Hdr));
+        if (!paBlocks)
+        {
+            rc = vdIfError(pIfError, VERR_NO_MEMORY, RT_SRC_POS,
+                           "Failed to allocate memory for block array");
+            break;
+        }
+
+        /* Read blocks array. */
+        rc = vdIfIoIntFileReadSync(pIfIo, pStorage, offStartBlocks, paBlocks,
+                                   getImageBlocks(&Hdr) * sizeof(VDIIMAGEBLOCKPOINTER));
+        if (RT_FAILURE(rc))
+        {
+            rc = vdIfError(pIfError, VERR_VD_IMAGE_REPAIR_IMPOSSIBLE, RT_SRC_POS,
+                           "Failed to read block array (at %llu), %Rrc",
+                           offStartBlocks, rc);
+            break;
+        }
+        vdiConvBlocksEndianess(VDIECONV_F2H, paBlocks, getImageBlocks(&Hdr));
+
+        pu32BlockBitmap = (uint32_t *)RTMemAllocZ(RT_ALIGN_Z(getImageBlocks(&Hdr) / 8, 4));
+        if (!pu32BlockBitmap)
+        {
+            rc = vdIfError(pIfError, VERR_NO_MEMORY, RT_SRC_POS,
+                           "Failed to allocate memory for block bitmap");
+            break;
+        }
+
+        for (uint32_t i = 0; i < getImageBlocks(&Hdr); i++)
+        {
+            if (IS_VDI_IMAGE_BLOCK_ALLOCATED(paBlocks[i]))
+            {
+                uint64_t offBlock =   (uint64_t)paBlocks[i] * cbTotalBlockData
+                                    + offStartData;
+
+                /*
+                 * Check that the offsets are valid (inside of the image) and
+                 * that there are no double references.
+                 */
+                if (offBlock + cbTotalBlockData > cbFile)
+                {
+                    vdIfErrorMessage(pIfError, "Entry %u points to invalid offset %llu, clearing\n",
+                                     i, offBlock);
+                    paBlocks[i] = VDI_IMAGE_BLOCK_FREE;
+                    fRepairBlockArray = true;
+                }
+                else if (ASMBitTestAndSet(pu32BlockBitmap, paBlocks[i]))
+                {
+                    vdIfErrorMessage(pIfError, "Entry %u points to an already referenced data block, clearing\n",
+                                     i);
+                    paBlocks[i] = VDI_IMAGE_BLOCK_FREE;
+                    fRepairBlockArray = true;
+                }
+            }
+        }
+
+        /* Write repaired structures now. */
+        if (!fRepairBlockArray && !fRepairHdr)
+            vdIfErrorMessage(pIfError, "VDI image is in a consistent state, no repair required\n");
+        else if (!(fFlags & VD_REPAIR_DRY_RUN))
+        {
+            if (fRepairHdr)
+            {
+                switch (GET_MAJOR_HEADER_VERSION(&Hdr))
+                {
+                    case 0:
+                    {
+                        VDIHEADER0 Hdr0;
+                        vdiConvHeaderEndianessV0(VDIECONV_H2F, &Hdr0, &Hdr.u.v0);
+                        rc = vdIfIoIntFileWriteSync(pIfIo, pStorage, sizeof(VDIPREHEADER),
+                                                    &Hdr0, sizeof(Hdr0));
+                        break;
+                    }
+                    case 1:
+                        if (Hdr.u.v1plus.cbHeader < sizeof(Hdr.u.v1plus))
+                        {
+                            VDIHEADER1 Hdr1;
+                            vdiConvHeaderEndianessV1(VDIECONV_H2F, &Hdr1, &Hdr.u.v1);
+                            rc = vdIfIoIntFileWriteSync(pIfIo, pStorage, sizeof(VDIPREHEADER),
+                                                        &Hdr1, sizeof(Hdr1));
+                        }
+                        else
+                        {
+                            VDIHEADER1PLUS Hdr1plus;
+                            vdiConvHeaderEndianessV1p(VDIECONV_H2F, &Hdr1plus, &Hdr.u.v1plus);
+                            rc = vdIfIoIntFileWriteSync(pIfIo, pStorage, sizeof(VDIPREHEADER),
+                                                        &Hdr1plus, sizeof(Hdr1plus));
+                        }
+                        break;
+                    default:
+                        AssertMsgFailed(("Header indicates unsupported version which should not happen here!\n"));
+                        rc = VERR_VD_VDI_UNSUPPORTED_VERSION;
+                        break;
+                }
+            }
+
+            if (fRepairBlockArray)
+            {
+                vdIfErrorMessage(pIfError, "Writing repaired block allocation table...\n");
+
+                vdiConvBlocksEndianess(VDIECONV_H2F, paBlocks, getImageBlocks(&Hdr));
+                rc = vdIfIoIntFileWriteSync(pIfIo, pStorage, offStartBlocks, paBlocks,
+                                            getImageBlocks(&Hdr) * sizeof(VDIIMAGEBLOCKPOINTER));
+                if (RT_FAILURE(rc))
+                {
+                    rc = vdIfError(pIfError, VERR_VD_IMAGE_REPAIR_IMPOSSIBLE, RT_SRC_POS,
+                                   "Could not write repaired block allocation table (at %llu), %Rrc",
+                                   offStartBlocks, rc);
+                    break;
+                }
+            }
+        }
+
+        vdIfErrorMessage(pIfError, "Corrupted VDI image repaired successfully\n");
+    } while(0);
+
+    if (paBlocks)
+        RTMemFree(paBlocks);
+
+    if (pu32BlockBitmap)
+        RTMemFree(pu32BlockBitmap);
+
+    if (pStorage)
+    {
+        int rc2 = vdIfIoIntFileClose(pIfIo, pStorage);
+        if (RT_SUCCESS(rc))
+            rc = rc2; /* Propagate error code only if repairing was successful. */
+    }
+
+    LogFlowFunc(("returns %Rrc\n", rc));
+    return rc;
+}
+
+const VDIMAGEBACKEND g_VDIBackend =
+{
+    /* u32Version */
+    VD_IMGBACKEND_VERSION,
+    /* pszBackendName */
+    "VDI",
+    /* uBackendCaps */
+      VD_CAP_UUID | VD_CAP_CREATE_FIXED | VD_CAP_CREATE_DYNAMIC
+    | VD_CAP_DIFF | VD_CAP_FILE | VD_CAP_ASYNC | VD_CAP_VFS | VD_CAP_DISCARD
+    | VD_CAP_PREFERRED,
+    /* paFileExtensions */
+    s_aVdiFileExtensions,
+    /* paConfigInfo */
+    vdiConfigInfo,
+    /* pfnProbe */
+    vdiProbe,
+    /* pfnOpen */
+    vdiOpen,
+    /* pfnCreate */
+    vdiCreate,
+    /* pfnRename */
+    vdiRename,
+    /* pfnClose */
+    vdiClose,
+    /* pfnRead */
+    vdiRead,
+    /* pfnWrite */
+    vdiWrite,
+    /* pfnFlush */
+    vdiFlush,
+    /* pfnDiscard */
+    vdiDiscard,
+    /* pfnGetVersion */
+    vdiGetVersion,
+    /* pfnGetFileSize */
+    vdiGetFileSize,
+    /* pfnGetPCHSGeometry */
+    vdiGetPCHSGeometry,
+    /* pfnSetPCHSGeometry */
+    vdiSetPCHSGeometry,
+    /* pfnGetLCHSGeometry */
+    vdiGetLCHSGeometry,
+    /* pfnSetLCHSGeometry */
+    vdiSetLCHSGeometry,
+    /* pfnQueryRegions */
+    vdiQueryRegions,
+    /* pfnRegionListRelease */
+    vdiRegionListRelease,
+    /* pfnGetImageFlags */
+    vdiGetImageFlags,
+    /* pfnGetOpenFlags */
+    vdiGetOpenFlags,
+    /* pfnSetOpenFlags */
+    vdiSetOpenFlags,
+    /* pfnGetComment */
+    vdiGetComment,
+    /* pfnSetComment */
+    vdiSetComment,
+    /* pfnGetUuid */
+    vdiGetUuid,
+    /* pfnSetUuid */
+    vdiSetUuid,
+    /* pfnGetModificationUuid */
+    vdiGetModificationUuid,
+    /* pfnSetModificationUuid */
+    vdiSetModificationUuid,
+    /* pfnGetParentUuid */
+    vdiGetParentUuid,
+    /* pfnSetParentUuid */
+    vdiSetParentUuid,
+    /* pfnGetParentModificationUuid */
+    vdiGetParentModificationUuid,
+    /* pfnSetParentModificationUuid */
+    vdiSetParentModificationUuid,
+    /* pfnDump */
+    vdiDump,
+    /* pfnGetTimestamp */
+    NULL,
+    /* pfnGetParentTimestamp */
+    NULL,
+    /* pfnSetParentTimestamp */
+    NULL,
+    /* pfnGetParentFilename */
+    NULL,
+    /* pfnSetParentFilename */
+    NULL,
+    /* pfnComposeLocation */
+    genericFileComposeLocation,
+    /* pfnComposeName */
+    genericFileComposeName,
+    /* pfnCompact */
+    vdiCompact,
+    /* pfnResize */
+    vdiResize,
+    /* pfnRepair */
+    vdiRepair,
+    /* pfnTraverseMetadata */
+    NULL,
+    /* u32VersionEnd */
+    VD_IMGBACKEND_VERSION
+};