Add new block driver for the VDI format (only aio supported)

This is a new block driver written from scratch
to support the VDI format in QEMU.

VDI is the native format used by Innotek / SUN VirtualBox.

Latest changes:

* stripped down version
  (code for synchronous operations and experimental code removed)

* don't open VDI snapshot images (with uuid_link or uuid_parent)

* modified vdi_aio_cancel

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Message-Id: 

1 files changed, 951 insertions, 0 deletions

diff --git a/block/vdi.c b/block/vdi.c
new file mode 100644
index 0000000000..db3fe1633a
--- /dev/null
+++ b/block/vdi.c
@@ -0,0 +1,951 @@
+/*
+ * Block driver for the Virtual Disk Image (VDI) format
+ *
+ * Copyright (c) 2009 Stefan Weil
+ *
+ * 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, either version 2 of the License, or
+ * (at your option) version 3 or any later version.
+ *
+ * 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 <http://www.gnu.org/licenses/>.
+ *
+ * Reference:
+ * http://forums.virtualbox.org/viewtopic.php?t=8046
+ *
+ * This driver supports create / read / write operations on VDI images.
+ *
+ * Todo (see also TODO in code):
+ *
+ * Some features like snapshots are still missing.
+ *
+ * Deallocation of zero-filled blocks and shrinking images are missing, too
+ * (might be added to common block layer).
+ *
+ * Allocation of blocks could be optimized (less writes to block map and
+ * header).
+ *
+ * Read and write of adjacents blocks could be done in one operation
+ * (current code uses one operation per block (1 MiB).
+ *
+ * The code is not thread safe (missing locks for changes in header and
+ * block table, no problem with current QEMU).
+ *
+ * Hints:
+ *
+ * Blocks (VDI documentation) correspond to clusters (QEMU).
+ * QEMU's backing files could be implemented using VDI snapshot files (TODO).
+ * VDI snapshot files may also contain the complete machine state.
+ * Maybe this machine state can be converted to QEMU PC machine snapshot data.
+ *
+ * The driver keeps a block cache (little endian entries) in memory.
+ * For the standard block size (1 MiB), a 1 TiB disk will use 4 MiB RAM,
+ * so this seems to be reasonable.
+ */
+
+#include "qemu-common.h"
+#include "block_int.h"
+#include "module.h"
+
+#if defined(HAVE_UUID_H)
+#include <uuid/uuid.h>
+#else
+/* TODO: move uuid emulation to some central place in QEMU. */
+#include "sysemu.h"     /* UUID_FMT */
+typedef unsigned char uuid_t[16];
+void uuid_generate(uuid_t out);
+int uuid_is_null(const uuid_t uu);
+void uuid_unparse(const uuid_t uu, char *out);
+#endif
+
+/* Code configuration options. */
+
+/* Enable debug messages. */
+//~ #define CONFIG_VDI_DEBUG
+
+/* Support write operations on VDI images. */
+#define CONFIG_VDI_WRITE
+
+/* Support non-standard block (cluster) size. This is untested.
+ * Maybe it will be needed for very large images.
+ */
+//~ #define CONFIG_VDI_BLOCK_SIZE
+
+/* Support static (fixed, pre-allocated) images. */
+#define CONFIG_VDI_STATIC_IMAGE
+
+/* Command line option for static images. */
+#define BLOCK_OPT_STATIC "static"
+
+#define KiB     1024
+#define MiB     (KiB * KiB)
+
+#define SECTOR_SIZE 512
+
+#if defined(CONFIG_VDI_DEBUG)
+#define logout(fmt, ...) \
+                fprintf(stderr, "vdi\t%-24s" fmt, __func__, ##__VA_ARGS__)
+#else
+#define logout(fmt, ...) ((void)0)
+#endif
+
+/* Image signature. */
+#define VDI_SIGNATURE 0xbeda107f
+
+/* Image version. */
+#define VDI_VERSION_1_1 0x00010001
+
+/* Image type. */
+#define VDI_TYPE_DYNAMIC 1
+#define VDI_TYPE_STATIC  2
+
+/* Innotek / SUN images use these strings in header.text:
+ * "<<< innotek VirtualBox Disk Image >>>\n"
+ * "<<< Sun xVM VirtualBox Disk Image >>>\n"
+ * "<<< Sun VirtualBox Disk Image >>>\n"
+ * The value does not matter, so QEMU created images use a different text.
+ */
+#define VDI_TEXT "<<< QEMU VM Virtual Disk Image >>>\n"
+
+/* Unallocated blocks use this index (no need to convert endianess). */
+#define VDI_UNALLOCATED UINT32_MAX
+
+#if !defined(HAVE_UUID_H)
+void uuid_generate(uuid_t out)
+{
+    memset(out, 0, sizeof(out));
+}
+
+int uuid_is_null(const uuid_t uu)
+{
+    uuid_t null_uuid = { 0 };
+    return memcmp(uu, null_uuid, sizeof(uu)) == 0;
+}
+
+void uuid_unparse(const uuid_t uu, char *out)
+{
+    snprintf(out, 37, UUID_FMT,
+            uu[0], uu[1], uu[2], uu[3], uu[4], uu[5], uu[6], uu[7],
+            uu[8], uu[9], uu[10], uu[11], uu[12], uu[13], uu[14], uu[15]);
+}
+#endif
+
+typedef struct {
+    BlockDriverAIOCB common;
+    int64_t sector_num;
+    QEMUIOVector *qiov;
+    uint8_t *buf;
+    /* Total number of sectors. */
+    int nb_sectors;
+    /* Number of sectors for current AIO. */
+    int n_sectors;
+    /* New allocated block map entry. */
+    uint32_t bmap_first;
+    uint32_t bmap_last;
+    /* Buffer for new allocated block. */
+    void *block_buffer;
+    void *orig_buf;
+    int header_modified;
+    BlockDriverAIOCB *hd_aiocb;
+    struct iovec hd_iov;
+    QEMUIOVector hd_qiov;
+    QEMUBH *bh;
+} VdiAIOCB;
+
+typedef struct {
+    char text[0x40];
+    uint32_t signature;
+    uint32_t version;
+    uint32_t header_size;
+    uint32_t image_type;
+    uint32_t image_flags;
+    char description[256];
+    uint32_t offset_bmap;
+    uint32_t offset_data;
+    uint32_t cylinders;         /* disk geometry, unused here */
+    uint32_t heads;             /* disk geometry, unused here */
+    uint32_t sectors;           /* disk geometry, unused here */
+    uint32_t sector_size;
+    uint32_t unused1;
+    uint64_t disk_size;
+    uint32_t block_size;
+    uint32_t block_extra;       /* unused here */
+    uint32_t blocks_in_image;
+    uint32_t blocks_allocated;
+    uuid_t uuid_image;
+    uuid_t uuid_last_snap;
+    uuid_t uuid_link;
+    uuid_t uuid_parent;
+    uint64_t unused2[7];
+} VdiHeader;
+
+typedef struct {
+    BlockDriverState *hd;
+    /* The block map entries are little endian (even in memory). */
+    uint32_t *bmap;
+    /* Size of block (bytes). */
+    uint32_t block_size;
+    /* Size of block (sectors). */
+    uint32_t block_sectors;
+    /* First sector of block map. */
+    uint32_t bmap_sector;
+    /* VDI header (converted to host endianess). */
+    VdiHeader header;
+} BDRVVdiState;
+
+/* Change UUID from little endian (IPRT = VirtualBox format) to big endian
+ * format (network byte order, standard, see RFC 4122) and vice versa.
+ */
+static void uuid_convert(uuid_t uuid)
+{
+    bswap32s((uint32_t *)&uuid[0]);
+    bswap16s((uint16_t *)&uuid[4]);
+    bswap16s((uint16_t *)&uuid[6]);
+}
+
+static void vdi_header_to_cpu(VdiHeader *header)
+{
+    le32_to_cpus(&header->signature);
+    le32_to_cpus(&header->version);
+    le32_to_cpus(&header->header_size);
+    le32_to_cpus(&header->image_type);
+    le32_to_cpus(&header->image_flags);
+    le32_to_cpus(&header->offset_bmap);
+    le32_to_cpus(&header->offset_data);
+    le32_to_cpus(&header->cylinders);
+    le32_to_cpus(&header->heads);
+    le32_to_cpus(&header->sectors);
+    le32_to_cpus(&header->sector_size);
+    le64_to_cpus(&header->disk_size);
+    le32_to_cpus(&header->block_size);
+    le32_to_cpus(&header->block_extra);
+    le32_to_cpus(&header->blocks_in_image);
+    le32_to_cpus(&header->blocks_allocated);
+    uuid_convert(header->uuid_image);
+    uuid_convert(header->uuid_last_snap);
+    uuid_convert(header->uuid_link);
+    uuid_convert(header->uuid_parent);
+}
+
+static void vdi_header_to_le(VdiHeader *header)
+{
+    cpu_to_le32s(&header->signature);
+    cpu_to_le32s(&header->version);
+    cpu_to_le32s(&header->header_size);
+    cpu_to_le32s(&header->image_type);
+    cpu_to_le32s(&header->image_flags);
+    cpu_to_le32s(&header->offset_bmap);
+    cpu_to_le32s(&header->offset_data);
+    cpu_to_le32s(&header->cylinders);
+    cpu_to_le32s(&header->heads);
+    cpu_to_le32s(&header->sectors);
+    cpu_to_le32s(&header->sector_size);
+    cpu_to_le64s(&header->disk_size);
+    cpu_to_le32s(&header->block_size);
+    cpu_to_le32s(&header->block_extra);
+    cpu_to_le32s(&header->blocks_in_image);
+    cpu_to_le32s(&header->blocks_allocated);
+    cpu_to_le32s(&header->blocks_allocated);
+    uuid_convert(header->uuid_image);
+    uuid_convert(header->uuid_last_snap);
+    uuid_convert(header->uuid_link);
+    uuid_convert(header->uuid_parent);
+}
+
+#if defined(CONFIG_VDI_DEBUG)
+static void vdi_header_print(VdiHeader *header)
+{
+    char uuid[37];
+    logout("text        %s", header->text);
+    logout("signature   0x%04x\n", header->signature);
+    logout("header size 0x%04x\n", header->header_size);
+    logout("image type  0x%04x\n", header->image_type);
+    logout("image flags 0x%04x\n", header->image_flags);
+    logout("description %s\n", header->description);
+    logout("offset bmap 0x%04x\n", header->offset_bmap);
+    logout("offset data 0x%04x\n", header->offset_data);
+    logout("cylinders   0x%04x\n", header->cylinders);
+    logout("heads       0x%04x\n", header->heads);
+    logout("sectors     0x%04x\n", header->sectors);
+    logout("sector size 0x%04x\n", header->sector_size);
+    logout("image size  0x%" PRIx64 " B (%" PRIu64 " MiB)\n",
+           header->disk_size, header->disk_size / MiB);
+    logout("block size  0x%04x\n", header->block_size);
+    logout("block extra 0x%04x\n", header->block_extra);
+    logout("blocks tot. 0x%04x\n", header->blocks_in_image);
+    logout("blocks all. 0x%04x\n", header->blocks_allocated);
+    uuid_unparse(header->uuid_image, uuid);
+    logout("uuid image  %s\n", uuid);
+    uuid_unparse(header->uuid_last_snap, uuid);
+    logout("uuid snap   %s\n", uuid);
+    uuid_unparse(header->uuid_link, uuid);
+    logout("uuid link   %s\n", uuid);
+    uuid_unparse(header->uuid_parent, uuid);
+    logout("uuid parent %s\n", uuid);
+}
+#endif
+
+static int vdi_check(BlockDriverState *bs)
+{
+    /* TODO: additional checks possible. */
+    BDRVVdiState *s = (BDRVVdiState *)bs->opaque;
+    int n_errors = 0;
+    uint32_t blocks_allocated = 0;
+    uint32_t block;
+    uint32_t *bmap;
+    logout("\n");
+
+    bmap = qemu_malloc(s->header.blocks_in_image * sizeof(uint32_t));
+    memset(bmap, 0xff, s->header.blocks_in_image * sizeof(uint32_t));
+
+    /* Check block map and value of blocks_allocated. */
+    for (block = 0; block < s->header.blocks_in_image; block++) {
+        uint32_t bmap_entry = le32_to_cpu(s->bmap[block]);
+        if (bmap_entry != VDI_UNALLOCATED) {
+            if (bmap_entry < s->header.blocks_in_image) {
+                blocks_allocated++;
+                if (bmap[bmap_entry] == VDI_UNALLOCATED) {
+                    bmap[bmap_entry] = bmap_entry;
+                } else {
+                    fprintf(stderr, "ERROR: block index %" PRIu32
+                            " also used by %" PRIu32 "\n", bmap[bmap_entry], bmap_entry);
+                }
+            } else {
+                fprintf(stderr, "ERROR: block index %" PRIu32
+                        " too large, is %" PRIu32 "\n", block, bmap_entry);
+                n_errors++;
+            }
+        }
+    }
+    if (blocks_allocated != s->header.blocks_allocated) {
+        fprintf(stderr, "ERROR: allocated blocks mismatch, is %" PRIu32
+               ", should be %" PRIu32 "\n",
+               blocks_allocated, s->header.blocks_allocated);
+        n_errors++;
+    }
+
+    qemu_free(bmap);
+
+    return n_errors;
+}
+
+static int vdi_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
+{
+    /* TODO: vdi_get_info would be needed for machine snapshots.
+       vm_state_offset is still missing. */
+    BDRVVdiState *s = (BDRVVdiState *)bs->opaque;
+    logout("\n");
+    bdi->cluster_size = s->block_size;
+    bdi->vm_state_offset = 0;
+    return 0;
+}
+
+static int vdi_make_empty(BlockDriverState *bs)
+{
+    /* TODO: missing code. */
+    logout("\n");
+    /* The return value for missing code must be 0, see block.c. */
+    return 0;
+}
+
+static int vdi_probe(const uint8_t *buf, int buf_size, const char *filename)
+{
+    const VdiHeader *header = (const VdiHeader *)buf;
+    int result = 0;
+
+    logout("\n");
+
+    if (buf_size < sizeof(*header)) {
+        /* Header too small, no VDI. */
+    } else if (le32_to_cpu(header->signature) == VDI_SIGNATURE) {
+        result = 100;
+    }
+
+    if (result == 0) {
+        logout("no vdi image\n");
+    } else {
+        logout("%s", header->text);
+    }
+
+    return result;
+}
+
+static int vdi_open(BlockDriverState *bs, const char *filename, int flags)
+{
+    BDRVVdiState *s = bs->opaque;
+    VdiHeader header;
+    size_t bmap_size;
+    int ret;
+
+    logout("\n");
+
+    ret = bdrv_file_open(&s->hd, filename, flags);
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (bdrv_read(s->hd, 0, (uint8_t *)&header, 1) < 0) {
+        goto fail;
+    }
+
+    vdi_header_to_cpu(&header);
+#if defined(CONFIG_VDI_DEBUG)
+    vdi_header_print(&header);
+#endif
+
+    if (header.version != VDI_VERSION_1_1) {
+        logout("unsupported version %u.%u\n",
+               header.version >> 16, header.version & 0xffff);
+        goto fail;
+    } else if (header.offset_bmap % SECTOR_SIZE != 0) {
+        /* We only support block maps which start on a sector boundary. */
+        logout("unsupported block map offset 0x%x B\n", header.offset_bmap);
+        goto fail;
+    } else if (header.offset_data % SECTOR_SIZE != 0) {
+        /* We only support data blocks which start on a sector boundary. */
+        logout("unsupported data offset 0x%x B\n", header.offset_data);
+        goto fail;
+    } else if (header.sector_size != SECTOR_SIZE) {
+        logout("unsupported sector size %u B\n", header.sector_size);
+        goto fail;
+    } else if (header.block_size != 1 * MiB) {
+        logout("unsupported block size %u B\n", header.block_size);
+        goto fail;
+    } else if (header.disk_size !=
+               (uint64_t)header.blocks_in_image * header.block_size) {
+        logout("unexpected block number %u B\n", header.blocks_in_image);
+        goto fail;
+    } else if (!uuid_is_null(header.uuid_link)) {
+        logout("link uuid != 0, unsupported\n");
+        goto fail;
+    } else if (!uuid_is_null(header.uuid_parent)) {
+        logout("parent uuid != 0, unsupported\n");
+        goto fail;
+    }
+
+    bs->total_sectors = header.disk_size / SECTOR_SIZE;
+
+    s->block_size = header.block_size;
+    s->block_sectors = header.block_size / SECTOR_SIZE;
+    s->bmap_sector = header.offset_bmap / SECTOR_SIZE;
+    s->header = header;
+
+    bmap_size = header.blocks_in_image * sizeof(uint32_t);
+    s->bmap = qemu_malloc(bmap_size);
+    if (bdrv_read(s->hd, s->bmap_sector,
+                  (uint8_t *)s->bmap, bmap_size / SECTOR_SIZE) < 0) {
+        goto fail_free_bmap;
+    }
+
+    return 0;
+
+ fail_free_bmap:
+    qemu_free(s->bmap);
+
+ fail:
+    bdrv_delete(s->hd);
+    return -1;
+}
+
+static int vdi_is_allocated(BlockDriverState *bs, int64_t sector_num,
+                             int nb_sectors, int *pnum)
+{
+    /* TODO: Check for too large sector_num (in bdrv_is_allocated or here). */
+    BDRVVdiState *s = (BDRVVdiState *)bs->opaque;
+    size_t bmap_index = sector_num / s->block_sectors;
+    size_t sector_in_block = sector_num % s->block_sectors;
+    int n_sectors = s->block_sectors - sector_in_block;
+    uint32_t bmap_entry = le32_to_cpu(s->bmap[bmap_index]);
+    logout("%p, %" PRId64 ", %d, %p\n", bs, sector_num, nb_sectors, pnum);
+    if (n_sectors > nb_sectors) {
+        n_sectors = nb_sectors;
+    }
+    *pnum = n_sectors;
+    return bmap_entry != VDI_UNALLOCATED;
+}
+
+static void vdi_aio_cancel(BlockDriverAIOCB *blockacb)
+{
+    /* TODO: This code is untested. How can I get it executed? */
+    VdiAIOCB *acb = (VdiAIOCB *)blockacb;
+    logout("\n");
+    if (acb->hd_aiocb) {
+        bdrv_aio_cancel(acb->hd_aiocb);
+    }
+    qemu_aio_release(acb);
+}
+
+static AIOPool vdi_aio_pool = {
+    .aiocb_size = sizeof(VdiAIOCB),
+    .cancel = vdi_aio_cancel,
+};
+
+static VdiAIOCB *vdi_aio_setup(BlockDriverState *bs, int64_t sector_num,
+        QEMUIOVector *qiov, int nb_sectors,
+        BlockDriverCompletionFunc *cb, void *opaque, int is_write)
+{
+    VdiAIOCB *acb;
+
+    logout("%p, %" PRId64 ", %p, %d, %p, %p, %d\n",
+           bs, sector_num, qiov, nb_sectors, cb, opaque, is_write);
+
+    acb = qemu_aio_get(&vdi_aio_pool, bs, cb, opaque);
+    if (acb) {
+        acb->hd_aiocb = NULL;
+        acb->sector_num = sector_num;
+        acb->qiov = qiov;
+        if (qiov->niov > 1) {
+            acb->buf = qemu_blockalign(bs, qiov->size);
+            acb->orig_buf = acb->buf;
+            if (is_write) {
+                qemu_iovec_to_buffer(qiov, acb->buf);
+            }
+        } else {
+            acb->buf = (uint8_t *)qiov->iov->iov_base;
+        }
+        acb->nb_sectors = nb_sectors;
+        acb->n_sectors = 0;
+        acb->bmap_first = VDI_UNALLOCATED;
+        acb->bmap_last = VDI_UNALLOCATED;
+        acb->block_buffer = NULL;
+        acb->header_modified = 0;
+    }
+    return acb;
+}
+
+static int vdi_schedule_bh(QEMUBHFunc *cb, VdiAIOCB *acb)
+{
+    logout("\n");
+
+    if (acb->bh) {
+        return -EIO;
+    }
+
+    acb->bh = qemu_bh_new(cb, acb);
+    if (!acb->bh) {
+        return -EIO;
+    }
+
+    qemu_bh_schedule(acb->bh);
+
+    return 0;
+}
+
+static void vdi_aio_read_cb(void *opaque, int ret);
+
+static void vdi_aio_read_bh(void *opaque)
+{
+    VdiAIOCB *acb = opaque;
+    logout("\n");
+    qemu_bh_delete(acb->bh);
+    acb->bh = NULL;
+    vdi_aio_read_cb(opaque, 0);
+}
+
+static void vdi_aio_read_cb(void *opaque, int ret)
+{
+    VdiAIOCB *acb = opaque;
+    BlockDriverState *bs = acb->common.bs;
+    BDRVVdiState *s = bs->opaque;
+    uint32_t bmap_entry;
+    uint32_t block_index;
+    uint32_t sector_in_block;
+    uint32_t n_sectors;
+
+    logout("%u sectors read\n", acb->n_sectors);
+
+    acb->hd_aiocb = NULL;
+
+    if (ret < 0) {
+        goto done;
+    }
+
+    acb->nb_sectors -= acb->n_sectors;
+
+    if (acb->nb_sectors == 0) {
+        /* request completed */
+        ret = 0;
+        goto done;
+    }
+
+    acb->sector_num += acb->n_sectors;
+    acb->buf += acb->n_sectors * SECTOR_SIZE;
+
+    block_index = acb->sector_num / s->block_sectors;
+    sector_in_block = acb->sector_num % s->block_sectors;
+    n_sectors = s->block_sectors - sector_in_block;
+    if (n_sectors > acb->nb_sectors) {
+        n_sectors = acb->nb_sectors;
+    }
+
+    logout("will read %u sectors starting at sector %" PRIu64 "\n",
+           n_sectors, acb->sector_num);
+
+    /* prepare next AIO request */
+    acb->n_sectors = n_sectors;
+    bmap_entry = le32_to_cpu(s->bmap[block_index]);
+    if (bmap_entry == VDI_UNALLOCATED) {
+        /* Block not allocated, return zeros, no need to wait. */
+        memset(acb->buf, 0, n_sectors * SECTOR_SIZE);
+        ret = vdi_schedule_bh(vdi_aio_read_bh, acb);
+        if (ret < 0) {
+            goto done;
+        }
+    } else {
+        uint64_t offset = s->header.offset_data / SECTOR_SIZE +
+                          (uint64_t)bmap_entry * s->block_sectors +
+                          sector_in_block;
+        acb->hd_iov.iov_base = (void *)acb->buf;
+        acb->hd_iov.iov_len = n_sectors * SECTOR_SIZE;
+        qemu_iovec_init_external(&acb->hd_qiov, &acb->hd_iov, 1);
+        acb->hd_aiocb = bdrv_aio_readv(s->hd, offset, &acb->hd_qiov,
+                                       n_sectors, vdi_aio_read_cb, acb);
+        if (acb->hd_aiocb == NULL) {
+            goto done;
+        }
+    }
+    return;
+done:
+    if (acb->qiov->niov > 1) {
+        qemu_iovec_from_buffer(acb->qiov, acb->orig_buf, acb->qiov->size);
+        qemu_vfree(acb->orig_buf);
+    }
+    acb->common.cb(acb->common.opaque, ret);
+    qemu_aio_release(acb);
+}
+
+static BlockDriverAIOCB *vdi_aio_readv(BlockDriverState *bs,
+        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
+        BlockDriverCompletionFunc *cb, void *opaque)
+{
+    VdiAIOCB *acb;
+    logout("\n");
+    acb = vdi_aio_setup(bs, sector_num, qiov, nb_sectors, cb, opaque, 0);
+    if (!acb) {
+        return NULL;
+    }
+    vdi_aio_read_cb(acb, 0);
+    return &acb->common;
+}
+
+static void vdi_aio_write_cb(void *opaque, int ret)
+{
+    VdiAIOCB *acb = opaque;
+    BlockDriverState *bs = acb->common.bs;
+    BDRVVdiState *s = bs->opaque;
+    uint32_t bmap_entry;
+    uint32_t block_index;
+    uint32_t sector_in_block;
+    uint32_t n_sectors;
+
+    acb->hd_aiocb = NULL;
+
+    if (ret < 0) {
+        goto done;
+    }
+
+    acb->nb_sectors -= acb->n_sectors;
+    acb->sector_num += acb->n_sectors;
+    acb->buf += acb->n_sectors * SECTOR_SIZE;
+
+    if (acb->nb_sectors == 0) {
+        logout("finished data write\n");
+        acb->n_sectors = 0;
+        if (acb->header_modified) {
+            VdiHeader *header = acb->block_buffer;
+            logout("now writing modified header\n");
+            assert(acb->bmap_first != VDI_UNALLOCATED);
+            *header = s->header;
+            vdi_header_to_le(header);
+            acb->header_modified = 0;
+            acb->hd_iov.iov_base = acb->block_buffer;
+            acb->hd_iov.iov_len = SECTOR_SIZE;
+            qemu_iovec_init_external(&acb->hd_qiov, &acb->hd_iov, 1);
+            acb->hd_aiocb = bdrv_aio_writev(s->hd, 0, &acb->hd_qiov, 1,
+                                            vdi_aio_write_cb, acb);
+            if (acb->hd_aiocb == NULL) {
+                goto done;
+            }
+            return;
+        } else if (acb->bmap_first != VDI_UNALLOCATED) {
+            /* One or more new blocks were allocated. */
+            uint64_t offset;
+            uint32_t bmap_first;
+            uint32_t bmap_last;
+            qemu_free(acb->block_buffer);
+            acb->block_buffer = NULL;
+            bmap_first = acb->bmap_first;
+            bmap_last = acb->bmap_last;
+            logout("now writing modified block map entry %u...%u\n",
+                   bmap_first, bmap_last);
+            /* Write modified sectors from block map. */
+            bmap_first /= (SECTOR_SIZE / sizeof(uint32_t));
+            bmap_last /= (SECTOR_SIZE / sizeof(uint32_t));
+            n_sectors = bmap_last - bmap_first + 1;
+            offset = s->bmap_sector + bmap_first;
+            acb->bmap_first = VDI_UNALLOCATED;
+            acb->hd_iov.iov_base = (uint8_t *)&s->bmap[0] +
+                                   bmap_first * SECTOR_SIZE;
+            acb->hd_iov.iov_len = n_sectors * SECTOR_SIZE;
+            qemu_iovec_init_external(&acb->hd_qiov, &acb->hd_iov, 1);
+            logout("will write %u block map sectors starting from entry %u\n",
+                   n_sectors, bmap_first);
+            acb->hd_aiocb = bdrv_aio_writev(s->hd, offset, &acb->hd_qiov,
+                                            n_sectors, vdi_aio_write_cb, acb);
+            if (acb->hd_aiocb == NULL) {
+                goto done;
+            }
+            return;
+        }
+        ret = 0;
+        goto done;
+    }
+
+    logout("%u sectors written\n", acb->n_sectors);
+
+    block_index = acb->sector_num / s->block_sectors;
+    sector_in_block = acb->sector_num % s->block_sectors;
+    n_sectors = s->block_sectors - sector_in_block;
+    if (n_sectors > acb->nb_sectors) {
+        n_sectors = acb->nb_sectors;
+    }
+
+    logout("will write %u sectors starting at sector %" PRIu64 "\n",
+           n_sectors, acb->sector_num);
+
+    /* prepare next AIO request */
+    acb->n_sectors = n_sectors;
+    bmap_entry = le32_to_cpu(s->bmap[block_index]);
+    if (bmap_entry == VDI_UNALLOCATED) {
+        /* Allocate new block and write to it. */
+        uint64_t offset;
+        uint8_t *block;
+        bmap_entry = s->header.blocks_allocated;
+        s->bmap[block_index] = cpu_to_le32(bmap_entry);
+        s->header.blocks_allocated++;
+        offset = s->header.offset_data / SECTOR_SIZE +
+                 (uint64_t)bmap_entry * s->block_sectors;
+        block = acb->block_buffer;
+        if (block == NULL) {
+            block = qemu_mallocz(s->block_size);
+            acb->block_buffer = block;
+            acb->bmap_first = block_index;
+            assert(!acb->header_modified);
+            acb->header_modified = 1;
+        }
+        acb->bmap_last = block_index;
+        memcpy(block + sector_in_block * SECTOR_SIZE,
+               acb->buf, n_sectors * SECTOR_SIZE);
+        acb->hd_iov.iov_base = block;
+        acb->hd_iov.iov_len = s->block_size;
+        qemu_iovec_init_external(&acb->hd_qiov, &acb->hd_iov, 1);
+        acb->hd_aiocb = bdrv_aio_writev(s->hd, offset,
+                                        &acb->hd_qiov, s->block_sectors,
+                                        vdi_aio_write_cb, acb);
+        if (acb->hd_aiocb == NULL) {
+            goto done;
+        }
+    } else {
+        uint64_t offset = s->header.offset_data / SECTOR_SIZE +
+                          (uint64_t)bmap_entry * s->block_sectors +
+                          sector_in_block;
+        acb->hd_iov.iov_base = acb->buf;
+        acb->hd_iov.iov_len = n_sectors * SECTOR_SIZE;
+        qemu_iovec_init_external(&acb->hd_qiov, &acb->hd_iov, 1);
+        acb->hd_aiocb = bdrv_aio_writev(s->hd, offset, &acb->hd_qiov,
+                                        n_sectors, vdi_aio_write_cb, acb);
+        if (acb->hd_aiocb == NULL) {
+            goto done;
+        }
+    }
+
+    return;
+
+done:
+    if (acb->qiov->niov > 1) {
+        qemu_vfree(acb->orig_buf);
+    }
+    acb->common.cb(acb->common.opaque, ret);
+    qemu_aio_release(acb);
+}
+
+static BlockDriverAIOCB *vdi_aio_writev(BlockDriverState *bs,
+        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
+        BlockDriverCompletionFunc *cb, void *opaque)
+{
+    VdiAIOCB *acb;
+    logout("\n");
+    acb = vdi_aio_setup(bs, sector_num, qiov, nb_sectors, cb, opaque, 1);
+    if (!acb) {
+        return NULL;
+    }
+    vdi_aio_write_cb(acb, 0);
+    return &acb->common;
+}
+
+static int vdi_create(const char *filename, QEMUOptionParameter *options)
+{
+    int fd;
+    int result = 0;
+    uint64_t bytes = 0;
+    uint32_t blocks;
+    size_t block_size = 1 * MiB;
+    uint32_t image_type = VDI_TYPE_DYNAMIC;
+    VdiHeader header;
+    size_t i;
+    size_t bmap_size;
+    uint32_t *bmap;
+
+    logout("\n");
+
+    /* Read out options. */
+    while (options && options->name) {
+        if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
+            bytes = options->value.n;
+#if defined(CONFIG_VDI_BLOCK_SIZE)
+        } else if (!strcmp(options->name, BLOCK_OPT_CLUSTER_SIZE)) {
+            if (options->value.n) {
+                /* TODO: Additional checks (SECTOR_SIZE * 2^n, ...). */
+                block_size = options->value.n;
+            }
+#endif
+#if defined(CONFIG_VDI_STATIC_IMAGE)
+        } else if (!strcmp(options->name, BLOCK_OPT_STATIC)) {
+            image_type = VDI_TYPE_STATIC;
+#endif
+        }
+        options++;
+    }
+
+    fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE,
+              0644);
+    if (fd < 0) {
+        return -errno;
+    }
+
+    blocks = bytes / block_size;
+    bmap_size = blocks * sizeof(uint32_t);
+    bmap_size = ((bmap_size + SECTOR_SIZE - 1) & ~(SECTOR_SIZE -1));
+
+    memset(&header, 0, sizeof(header));
+    strcpy(header.text, VDI_TEXT);
+    header.signature = VDI_SIGNATURE;
+    header.version = VDI_VERSION_1_1;
+    header.header_size = 0x180;
+    header.image_type = image_type;
+    header.offset_bmap = 0x200;
+    header.offset_data = 0x200 + bmap_size;
+    header.sector_size = SECTOR_SIZE;
+    header.disk_size = bytes;
+    header.block_size = block_size;
+    header.blocks_in_image = blocks;
+    uuid_generate(header.uuid_image);
+    uuid_generate(header.uuid_last_snap);
+    /* There is no need to set header.uuid_link or header.uuid_parent here. */
+#if defined(CONFIG_VDI_DEBUG)
+    vdi_header_print(&header);
+#endif
+    vdi_header_to_le(&header);
+    if (write(fd, &header, sizeof(header)) < 0) {
+        result = -errno;
+    }
+
+    bmap = (uint32_t *)qemu_mallocz(bmap_size);
+    for (i = 0; i < blocks; i++) {
+        if (image_type == VDI_TYPE_STATIC) {
+            bmap[i] = i;
+        } else {
+            bmap[i] = VDI_UNALLOCATED;
+        }
+    }
+    if (write(fd, bmap, bmap_size) < 0) {
+        result = -errno;
+    }
+    qemu_free(bmap);
+    if (image_type == VDI_TYPE_STATIC) {
+        if (ftruncate(fd, sizeof(header) + bmap_size + blocks * block_size)) {
+            result = -errno;
+        }
+    }
+
+    if (close(fd) < 0) {
+        result = -errno;
+    }
+
+    return result;
+}
+
+static void vdi_close(BlockDriverState *bs)
+{
+    BDRVVdiState *s = bs->opaque;
+    logout("\n");
+    bdrv_delete(s->hd);
+}
+
+static void vdi_flush(BlockDriverState *bs)
+{
+    BDRVVdiState *s = bs->opaque;
+    logout("\n");
+    bdrv_flush(s->hd);
+}
+
+
+static QEMUOptionParameter vdi_create_options[] = {
+    {
+        .name = BLOCK_OPT_SIZE,
+        .type = OPT_SIZE,
+        .help = "Virtual disk size"
+    },
+#if defined(CONFIG_VDI_BLOCK_SIZE)
+    {
+        .name = BLOCK_OPT_CLUSTER_SIZE,
+        .type = OPT_SIZE,
+        .help = "VDI cluster (block) size"
+    },
+#endif
+#if defined(CONFIG_VDI_STATIC_IMAGE)
+    {
+        .name = BLOCK_OPT_STATIC,
+        .type = OPT_FLAG,
+        .help = "VDI static (pre-allocated) image"
+    },
+#endif
+    /* TODO: An additional option to set UUID values might be useful. */
+    { NULL }
+};
+
+static BlockDriver bdrv_vdi = {
+    .format_name = "vdi",
+    .instance_size = sizeof(BDRVVdiState),
+    .bdrv_probe = vdi_probe,
+    .bdrv_open = vdi_open,
+    .bdrv_close = vdi_close,
+    .bdrv_create = vdi_create,
+    .bdrv_flush = vdi_flush,
+    .bdrv_is_allocated = vdi_is_allocated,
+    .bdrv_make_empty = vdi_make_empty,
+
+    .bdrv_aio_readv = vdi_aio_readv,
+#if defined(CONFIG_VDI_WRITE)
+    .bdrv_aio_writev = vdi_aio_writev,
+#endif
+
+    .bdrv_get_info = vdi_get_info,
+
+    .create_options = vdi_create_options,
+    .bdrv_check = vdi_check,
+};
+
+static void bdrv_vdi_init(void)
+{
+    logout("\n");
+    bdrv_register(&bdrv_vdi);
+}
+
+block_init(bdrv_vdi_init);