Add qemu 2.4.0

Change-Id: Ic99cbad4b61f8b127b7dc74d04576c0bcbaaf4f5
Signed-off-by: Yang Zhang <yang.z.zhang@intel.com>

1 files changed, 1980 insertions, 0 deletions

diff --git a/qemu/block/vhdx.c b/qemu/block/vhdx.c
new file mode 100644
index 000000000..0776de717
--- /dev/null
+++ b/qemu/block/vhdx.c
@@ -0,0 +1,1980 @@
+/*
+ * Block driver for Hyper-V VHDX Images
+ *
+ * Copyright (c) 2013 Red Hat, Inc.,
+ *
+ * Authors:
+ *  Jeff Cody <jcody@redhat.com>
+ *
+ *  This is based on the "VHDX Format Specification v1.00", published 8/25/2012
+ *  by Microsoft:
+ *      https://www.microsoft.com/en-us/download/details.aspx?id=34750
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#include "qemu-common.h"
+#include "block/block_int.h"
+#include "qemu/module.h"
+#include "qemu/crc32c.h"
+#include "block/vhdx.h"
+#include "migration/migration.h"
+
+#include <uuid/uuid.h>
+#include <glib.h>
+
+/* Options for VHDX creation */
+
+#define VHDX_BLOCK_OPT_LOG_SIZE   "log_size"
+#define VHDX_BLOCK_OPT_BLOCK_SIZE "block_size"
+#define VHDX_BLOCK_OPT_ZERO "block_state_zero"
+
+typedef enum VHDXImageType {
+    VHDX_TYPE_DYNAMIC = 0,
+    VHDX_TYPE_FIXED,
+    VHDX_TYPE_DIFFERENCING,   /* Currently unsupported */
+} VHDXImageType;
+
+/* Several metadata and region table data entries are identified by
+ * guids in  a MS-specific GUID format. */
+
+
+/* ------- Known Region Table GUIDs ---------------------- */
+static const MSGUID bat_guid =      { .data1 = 0x2dc27766,
+                                      .data2 = 0xf623,
+                                      .data3 = 0x4200,
+                                      .data4 = { 0x9d, 0x64, 0x11, 0x5e,
+                                                 0x9b, 0xfd, 0x4a, 0x08} };
+
+static const MSGUID metadata_guid = { .data1 = 0x8b7ca206,
+                                      .data2 = 0x4790,
+                                      .data3 = 0x4b9a,
+                                      .data4 = { 0xb8, 0xfe, 0x57, 0x5f,
+                                                 0x05, 0x0f, 0x88, 0x6e} };
+
+
+
+/* ------- Known Metadata Entry GUIDs ---------------------- */
+static const MSGUID file_param_guid =   { .data1 = 0xcaa16737,
+                                          .data2 = 0xfa36,
+                                          .data3 = 0x4d43,
+                                          .data4 = { 0xb3, 0xb6, 0x33, 0xf0,
+                                                     0xaa, 0x44, 0xe7, 0x6b} };
+
+static const MSGUID virtual_size_guid = { .data1 = 0x2FA54224,
+                                          .data2 = 0xcd1b,
+                                          .data3 = 0x4876,
+                                          .data4 = { 0xb2, 0x11, 0x5d, 0xbe,
+                                                     0xd8, 0x3b, 0xf4, 0xb8} };
+
+static const MSGUID page83_guid =       { .data1 = 0xbeca12ab,
+                                          .data2 = 0xb2e6,
+                                          .data3 = 0x4523,
+                                          .data4 = { 0x93, 0xef, 0xc3, 0x09,
+                                                     0xe0, 0x00, 0xc7, 0x46} };
+
+
+static const MSGUID phys_sector_guid =  { .data1 = 0xcda348c7,
+                                          .data2 = 0x445d,
+                                          .data3 = 0x4471,
+                                          .data4 = { 0x9c, 0xc9, 0xe9, 0x88,
+                                                     0x52, 0x51, 0xc5, 0x56} };
+
+static const MSGUID parent_locator_guid = { .data1 = 0xa8d35f2d,
+                                            .data2 = 0xb30b,
+                                            .data3 = 0x454d,
+                                            .data4 = { 0xab, 0xf7, 0xd3,
+                                                       0xd8, 0x48, 0x34,
+                                                       0xab, 0x0c} };
+
+static const MSGUID logical_sector_guid = { .data1 = 0x8141bf1d,
+                                            .data2 = 0xa96f,
+                                            .data3 = 0x4709,
+                                            .data4 = { 0xba, 0x47, 0xf2,
+                                                       0x33, 0xa8, 0xfa,
+                                                       0xab, 0x5f} };
+
+/* Each parent type must have a valid GUID; this is for parent images
+ * of type 'VHDX'.  If we were to allow e.g. a QCOW2 parent, we would
+ * need to make up our own QCOW2 GUID type */
+static const MSGUID parent_vhdx_guid __attribute__((unused))
+                                     = { .data1 = 0xb04aefb7,
+                                         .data2 = 0xd19e,
+                                         .data3 = 0x4a81,
+                                         .data4 = { 0xb7, 0x89, 0x25, 0xb8,
+                                                    0xe9, 0x44, 0x59, 0x13} };
+
+
+#define META_FILE_PARAMETER_PRESENT      0x01
+#define META_VIRTUAL_DISK_SIZE_PRESENT   0x02
+#define META_PAGE_83_PRESENT             0x04
+#define META_LOGICAL_SECTOR_SIZE_PRESENT 0x08
+#define META_PHYS_SECTOR_SIZE_PRESENT    0x10
+#define META_PARENT_LOCATOR_PRESENT      0x20
+
+#define META_ALL_PRESENT    \
+    (META_FILE_PARAMETER_PRESENT | META_VIRTUAL_DISK_SIZE_PRESENT | \
+     META_PAGE_83_PRESENT | META_LOGICAL_SECTOR_SIZE_PRESENT | \
+     META_PHYS_SECTOR_SIZE_PRESENT)
+
+
+typedef struct VHDXSectorInfo {
+    uint32_t bat_idx;       /* BAT entry index */
+    uint32_t sectors_avail; /* sectors available in payload block */
+    uint32_t bytes_left;    /* bytes left in the block after data to r/w */
+    uint32_t bytes_avail;   /* bytes available in payload block */
+    uint64_t file_offset;   /* absolute offset in bytes, in file */
+    uint64_t block_offset;  /* block offset, in bytes */
+} VHDXSectorInfo;
+
+/* Calculates new checksum.
+ *
+ * Zero is substituted during crc calculation for the original crc field
+ * crc_offset: byte offset in buf of the buffer crc
+ * buf: buffer pointer
+ * size: size of buffer (must be > crc_offset+4)
+ *
+ * Note: The buffer should have all multi-byte data in little-endian format,
+ *       and the resulting checksum is in little endian format.
+ */
+uint32_t vhdx_update_checksum(uint8_t *buf, size_t size, int crc_offset)
+{
+    uint32_t crc;
+
+    assert(buf != NULL);
+    assert(size > (crc_offset + sizeof(crc)));
+
+    memset(buf + crc_offset, 0, sizeof(crc));
+    crc =  crc32c(0xffffffff, buf, size);
+    cpu_to_le32s(&crc);
+    memcpy(buf + crc_offset, &crc, sizeof(crc));
+
+    return crc;
+}
+
+uint32_t vhdx_checksum_calc(uint32_t crc, uint8_t *buf, size_t size,
+                            int crc_offset)
+{
+    uint32_t crc_new;
+    uint32_t crc_orig;
+    assert(buf != NULL);
+
+    if (crc_offset > 0) {
+        memcpy(&crc_orig, buf + crc_offset, sizeof(crc_orig));
+        memset(buf + crc_offset, 0, sizeof(crc_orig));
+    }
+
+    crc_new = crc32c(crc, buf, size);
+    if (crc_offset > 0) {
+        memcpy(buf + crc_offset, &crc_orig, sizeof(crc_orig));
+    }
+
+    return crc_new;
+}
+
+/* Validates the checksum of the buffer, with an in-place CRC.
+ *
+ * Zero is substituted during crc calculation for the original crc field,
+ * and the crc field is restored afterwards.  But the buffer will be modifed
+ * during the calculation, so this may not be not suitable for multi-threaded
+ * use.
+ *
+ * crc_offset: byte offset in buf of the buffer crc
+ * buf: buffer pointer
+ * size: size of buffer (must be > crc_offset+4)
+ *
+ * returns true if checksum is valid, false otherwise
+ */
+bool vhdx_checksum_is_valid(uint8_t *buf, size_t size, int crc_offset)
+{
+    uint32_t crc_orig;
+    uint32_t crc;
+
+    assert(buf != NULL);
+    assert(size > (crc_offset + 4));
+
+    memcpy(&crc_orig, buf + crc_offset, sizeof(crc_orig));
+    crc_orig = le32_to_cpu(crc_orig);
+
+    crc = vhdx_checksum_calc(0xffffffff, buf, size, crc_offset);
+
+    return crc == crc_orig;
+}
+
+
+/*
+ * This generates a UUID that is compliant with the MS GUIDs used
+ * in the VHDX spec (and elsewhere).
+ */
+void vhdx_guid_generate(MSGUID *guid)
+{
+    uuid_t uuid;
+    assert(guid != NULL);
+
+    uuid_generate(uuid);
+    memcpy(guid, uuid, sizeof(MSGUID));
+}
+
+/* Check for region overlaps inside the VHDX image */
+static int vhdx_region_check(BDRVVHDXState *s, uint64_t start, uint64_t length)
+{
+    int ret = 0;
+    uint64_t end;
+    VHDXRegionEntry *r;
+
+    end = start + length;
+    QLIST_FOREACH(r, &s->regions, entries) {
+        if (!((start >= r->end) || (end <= r->start))) {
+            ret = -EINVAL;
+            goto exit;
+        }
+    }
+
+exit:
+    return ret;
+}
+
+/* Register a region for future checks */
+static void vhdx_region_register(BDRVVHDXState *s,
+                                 uint64_t start, uint64_t length)
+{
+    VHDXRegionEntry *r;
+
+    r = g_malloc0(sizeof(*r));
+
+    r->start = start;
+    r->end = start + length;
+
+    QLIST_INSERT_HEAD(&s->regions, r, entries);
+}
+
+/* Free all registered regions */
+static void vhdx_region_unregister_all(BDRVVHDXState *s)
+{
+    VHDXRegionEntry *r, *r_next;
+
+    QLIST_FOREACH_SAFE(r, &s->regions, entries, r_next) {
+        QLIST_REMOVE(r, entries);
+        g_free(r);
+    }
+}
+
+static void vhdx_set_shift_bits(BDRVVHDXState *s)
+{
+    s->logical_sector_size_bits = 31 - clz32(s->logical_sector_size);
+    s->sectors_per_block_bits =   31 - clz32(s->sectors_per_block);
+    s->chunk_ratio_bits =         63 - clz64(s->chunk_ratio);
+    s->block_size_bits =          31 - clz32(s->block_size);
+}
+
+/*
+ * Per the MS VHDX Specification, for every VHDX file:
+ *      - The header section is fixed size - 1 MB
+ *      - The header section is always the first "object"
+ *      - The first 64KB of the header is the File Identifier
+ *      - The first uint64 (8 bytes) is the VHDX Signature ("vhdxfile")
+ *      - The following 512 bytes constitute a UTF-16 string identifiying the
+ *        software that created the file, and is optional and diagnostic only.
+ *
+ *  Therefore, we probe by looking for the vhdxfile signature "vhdxfile"
+ */
+static int vhdx_probe(const uint8_t *buf, int buf_size, const char *filename)
+{
+    if (buf_size >= 8 && !memcmp(buf, "vhdxfile", 8)) {
+        return 100;
+    }
+    return 0;
+}
+
+/*
+ * Writes the header to the specified offset.
+ *
+ * This will optionally read in buffer data from disk (otherwise zero-fill),
+ * and then update the header checksum.  Header is converted to proper
+ * endianness before being written to the specified file offset
+ */
+static int vhdx_write_header(BlockDriverState *bs_file, VHDXHeader *hdr,
+                             uint64_t offset, bool read)
+{
+    uint8_t *buffer = NULL;
+    int ret;
+    VHDXHeader *header_le;
+
+    assert(bs_file != NULL);
+    assert(hdr != NULL);
+
+    /* the header checksum is not over just the packed size of VHDXHeader,
+     * but rather over the entire 'reserved' range for the header, which is
+     * 4KB (VHDX_HEADER_SIZE). */
+
+    buffer = qemu_blockalign(bs_file, VHDX_HEADER_SIZE);
+    if (read) {
+        /* if true, we can't assume the extra reserved bytes are 0 */
+        ret = bdrv_pread(bs_file, offset, buffer, VHDX_HEADER_SIZE);
+        if (ret < 0) {
+            goto exit;
+        }
+    } else {
+        memset(buffer, 0, VHDX_HEADER_SIZE);
+    }
+
+    /* overwrite the actual VHDXHeader portion */
+    header_le = (VHDXHeader *)buffer;
+    memcpy(header_le, hdr, sizeof(VHDXHeader));
+    vhdx_header_le_export(hdr, header_le);
+    vhdx_update_checksum(buffer, VHDX_HEADER_SIZE,
+                         offsetof(VHDXHeader, checksum));
+    ret = bdrv_pwrite_sync(bs_file, offset, header_le, sizeof(VHDXHeader));
+
+exit:
+    qemu_vfree(buffer);
+    return ret;
+}
+
+/* Update the VHDX headers
+ *
+ * This follows the VHDX spec procedures for header updates.
+ *
+ *  - non-current header is updated with largest sequence number
+ */
+static int vhdx_update_header(BlockDriverState *bs, BDRVVHDXState *s,
+                              bool generate_data_write_guid, MSGUID *log_guid)
+{
+    int ret = 0;
+    int hdr_idx = 0;
+    uint64_t header_offset = VHDX_HEADER1_OFFSET;
+
+    VHDXHeader *active_header;
+    VHDXHeader *inactive_header;
+
+    /* operate on the non-current header */
+    if (s->curr_header == 0) {
+        hdr_idx = 1;
+        header_offset = VHDX_HEADER2_OFFSET;
+    }
+
+    active_header   = s->headers[s->curr_header];
+    inactive_header = s->headers[hdr_idx];
+
+    inactive_header->sequence_number = active_header->sequence_number + 1;
+
+    /* a new file guid must be generated before any file write, including
+     * headers */
+    inactive_header->file_write_guid = s->session_guid;
+
+    /* a new data guid only needs to be generated before any guest-visible
+     * writes (i.e. something observable via virtual disk read) */
+    if (generate_data_write_guid) {
+        vhdx_guid_generate(&inactive_header->data_write_guid);
+    }
+
+    /* update the log guid if present */
+    if (log_guid) {
+        inactive_header->log_guid = *log_guid;
+    }
+
+    ret = vhdx_write_header(bs->file, inactive_header, header_offset, true);
+    if (ret < 0) {
+        goto exit;
+    }
+    s->curr_header = hdr_idx;
+
+exit:
+    return ret;
+}
+
+/*
+ * The VHDX spec calls for header updates to be performed twice, so that both
+ * the current and non-current header have valid info
+ */
+int vhdx_update_headers(BlockDriverState *bs, BDRVVHDXState *s,
+                        bool generate_data_write_guid, MSGUID *log_guid)
+{
+    int ret;
+
+    ret = vhdx_update_header(bs, s, generate_data_write_guid, log_guid);
+    if (ret < 0) {
+        return ret;
+    }
+    ret = vhdx_update_header(bs, s, generate_data_write_guid, log_guid);
+    return ret;
+}
+
+/* opens the specified header block from the VHDX file header section */
+static void vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s,
+                              Error **errp)
+{
+    int ret;
+    VHDXHeader *header1;
+    VHDXHeader *header2;
+    bool h1_valid = false;
+    bool h2_valid = false;
+    uint64_t h1_seq = 0;
+    uint64_t h2_seq = 0;
+    uint8_t *buffer;
+
+    /* header1 & header2 are freed in vhdx_close() */
+    header1 = qemu_blockalign(bs, sizeof(VHDXHeader));
+    header2 = qemu_blockalign(bs, sizeof(VHDXHeader));
+
+    buffer = qemu_blockalign(bs, VHDX_HEADER_SIZE);
+
+    s->headers[0] = header1;
+    s->headers[1] = header2;
+
+    /* We have to read the whole VHDX_HEADER_SIZE instead of
+     * sizeof(VHDXHeader), because the checksum is over the whole
+     * region */
+    ret = bdrv_pread(bs->file, VHDX_HEADER1_OFFSET, buffer, VHDX_HEADER_SIZE);
+    if (ret < 0) {
+        goto fail;
+    }
+    /* copy over just the relevant portion that we need */
+    memcpy(header1, buffer, sizeof(VHDXHeader));
+
+    if (vhdx_checksum_is_valid(buffer, VHDX_HEADER_SIZE, 4)) {
+        vhdx_header_le_import(header1);
+        if (header1->signature == VHDX_HEADER_SIGNATURE &&
+            header1->version == 1) {
+            h1_seq = header1->sequence_number;
+            h1_valid = true;
+        }
+    }
+
+    ret = bdrv_pread(bs->file, VHDX_HEADER2_OFFSET, buffer, VHDX_HEADER_SIZE);
+    if (ret < 0) {
+        goto fail;
+    }
+    /* copy over just the relevant portion that we need */
+    memcpy(header2, buffer, sizeof(VHDXHeader));
+
+    if (vhdx_checksum_is_valid(buffer, VHDX_HEADER_SIZE, 4)) {
+        vhdx_header_le_import(header2);
+        if (header2->signature == VHDX_HEADER_SIGNATURE &&
+            header2->version == 1) {
+            h2_seq = header2->sequence_number;
+            h2_valid = true;
+        }
+    }
+
+    /* If there is only 1 valid header (or no valid headers), we
+     * don't care what the sequence numbers are */
+    if (h1_valid && !h2_valid) {
+        s->curr_header = 0;
+    } else if (!h1_valid && h2_valid) {
+        s->curr_header = 1;
+    } else if (!h1_valid && !h2_valid) {
+        goto fail;
+    } else {
+        /* If both headers are valid, then we choose the active one by the
+         * highest sequence number.  If the sequence numbers are equal, that is
+         * invalid */
+        if (h1_seq > h2_seq) {
+            s->curr_header = 0;
+        } else if (h2_seq > h1_seq) {
+            s->curr_header = 1;
+        } else {
+            /* The Microsoft Disk2VHD tool will create 2 identical
+             * headers, with identical sequence numbers.  If the headers are
+             * identical, don't consider the file corrupt */
+            if (!memcmp(header1, header2, sizeof(VHDXHeader))) {
+                s->curr_header = 0;
+            } else {
+                goto fail;
+            }
+        }
+    }
+
+    vhdx_region_register(s, s->headers[s->curr_header]->log_offset,
+                            s->headers[s->curr_header]->log_length);
+    goto exit;
+
+fail:
+    error_setg_errno(errp, -ret, "No valid VHDX header found");
+    qemu_vfree(header1);
+    qemu_vfree(header2);
+    s->headers[0] = NULL;
+    s->headers[1] = NULL;
+exit:
+    qemu_vfree(buffer);
+}
+
+
+static int vhdx_open_region_tables(BlockDriverState *bs, BDRVVHDXState *s)
+{
+    int ret = 0;
+    uint8_t *buffer;
+    int offset = 0;
+    VHDXRegionTableEntry rt_entry;
+    uint32_t i;
+    bool bat_rt_found = false;
+    bool metadata_rt_found = false;
+
+    /* We have to read the whole 64KB block, because the crc32 is over the
+     * whole block */
+    buffer = qemu_blockalign(bs, VHDX_HEADER_BLOCK_SIZE);
+
+    ret = bdrv_pread(bs->file, VHDX_REGION_TABLE_OFFSET, buffer,
+                     VHDX_HEADER_BLOCK_SIZE);
+    if (ret < 0) {
+        goto fail;
+    }
+    memcpy(&s->rt, buffer, sizeof(s->rt));
+    offset += sizeof(s->rt);
+
+    if (!vhdx_checksum_is_valid(buffer, VHDX_HEADER_BLOCK_SIZE, 4)) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    vhdx_region_header_le_import(&s->rt);
+
+    if (s->rt.signature != VHDX_REGION_SIGNATURE) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+
+    /* Per spec, maximum region table entry count is 2047 */
+    if (s->rt.entry_count > 2047) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    for (i = 0; i < s->rt.entry_count; i++) {
+        memcpy(&rt_entry, buffer + offset, sizeof(rt_entry));
+        offset += sizeof(rt_entry);
+
+        vhdx_region_entry_le_import(&rt_entry);
+
+        /* check for region overlap between these entries, and any
+         * other memory regions in the file */
+        ret = vhdx_region_check(s, rt_entry.file_offset, rt_entry.length);
+        if (ret < 0) {
+            goto fail;
+        }
+
+        vhdx_region_register(s, rt_entry.file_offset, rt_entry.length);
+
+        /* see if we recognize the entry */
+        if (guid_eq(rt_entry.guid, bat_guid)) {
+            /* must be unique; if we have already found it this is invalid */
+            if (bat_rt_found) {
+                ret = -EINVAL;
+                goto fail;
+            }
+            bat_rt_found = true;
+            s->bat_rt = rt_entry;
+            continue;
+        }
+
+        if (guid_eq(rt_entry.guid, metadata_guid)) {
+            /* must be unique; if we have already found it this is invalid */
+            if (metadata_rt_found) {
+                ret = -EINVAL;
+                goto fail;
+            }
+            metadata_rt_found = true;
+            s->metadata_rt = rt_entry;
+            continue;
+        }
+
+        if (rt_entry.data_bits & VHDX_REGION_ENTRY_REQUIRED) {
+            /* cannot read vhdx file - required region table entry that
+             * we do not understand.  per spec, we must fail to open */
+            ret = -ENOTSUP;
+            goto fail;
+        }
+    }
+
+    if (!bat_rt_found || !metadata_rt_found) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    ret = 0;
+
+fail:
+    qemu_vfree(buffer);
+    return ret;
+}
+
+
+
+/* Metadata initial parser
+ *
+ * This loads all the metadata entry fields.  This may cause additional
+ * fields to be processed (e.g. parent locator, etc..).
+ *
+ * There are 5 Metadata items that are always required:
+ *      - File Parameters (block size, has a parent)
+ *      - Virtual Disk Size (size, in bytes, of the virtual drive)
+ *      - Page 83 Data (scsi page 83 guid)
+ *      - Logical Sector Size (logical sector size in bytes, either 512 or
+ *                             4096.  We only support 512 currently)
+ *      - Physical Sector Size (512 or 4096)
+ *
+ * Also, if the File Parameters indicate this is a differencing file,
+ * we must also look for the Parent Locator metadata item.
+ */
+static int vhdx_parse_metadata(BlockDriverState *bs, BDRVVHDXState *s)
+{
+    int ret = 0;
+    uint8_t *buffer;
+    int offset = 0;
+    uint32_t i = 0;
+    VHDXMetadataTableEntry md_entry;
+
+    buffer = qemu_blockalign(bs, VHDX_METADATA_TABLE_MAX_SIZE);
+
+    ret = bdrv_pread(bs->file, s->metadata_rt.file_offset, buffer,
+                     VHDX_METADATA_TABLE_MAX_SIZE);
+    if (ret < 0) {
+        goto exit;
+    }
+    memcpy(&s->metadata_hdr, buffer, sizeof(s->metadata_hdr));
+    offset += sizeof(s->metadata_hdr);
+
+    vhdx_metadata_header_le_import(&s->metadata_hdr);
+
+    if (s->metadata_hdr.signature != VHDX_METADATA_SIGNATURE) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    s->metadata_entries.present = 0;
+
+    if ((s->metadata_hdr.entry_count * sizeof(md_entry)) >
+        (VHDX_METADATA_TABLE_MAX_SIZE - offset)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    for (i = 0; i < s->metadata_hdr.entry_count; i++) {
+        memcpy(&md_entry, buffer + offset, sizeof(md_entry));
+        offset += sizeof(md_entry);
+
+        vhdx_metadata_entry_le_import(&md_entry);
+
+        if (guid_eq(md_entry.item_id, file_param_guid)) {
+            if (s->metadata_entries.present & META_FILE_PARAMETER_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.file_parameters_entry = md_entry;
+            s->metadata_entries.present |= META_FILE_PARAMETER_PRESENT;
+            continue;
+        }
+
+        if (guid_eq(md_entry.item_id, virtual_size_guid)) {
+            if (s->metadata_entries.present & META_VIRTUAL_DISK_SIZE_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.virtual_disk_size_entry = md_entry;
+            s->metadata_entries.present |= META_VIRTUAL_DISK_SIZE_PRESENT;
+            continue;
+        }
+
+        if (guid_eq(md_entry.item_id, page83_guid)) {
+            if (s->metadata_entries.present & META_PAGE_83_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.page83_data_entry = md_entry;
+            s->metadata_entries.present |= META_PAGE_83_PRESENT;
+            continue;
+        }
+
+        if (guid_eq(md_entry.item_id, logical_sector_guid)) {
+            if (s->metadata_entries.present &
+                META_LOGICAL_SECTOR_SIZE_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.logical_sector_size_entry = md_entry;
+            s->metadata_entries.present |= META_LOGICAL_SECTOR_SIZE_PRESENT;
+            continue;
+        }
+
+        if (guid_eq(md_entry.item_id, phys_sector_guid)) {
+            if (s->metadata_entries.present & META_PHYS_SECTOR_SIZE_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.phys_sector_size_entry = md_entry;
+            s->metadata_entries.present |= META_PHYS_SECTOR_SIZE_PRESENT;
+            continue;
+        }
+
+        if (guid_eq(md_entry.item_id, parent_locator_guid)) {
+            if (s->metadata_entries.present & META_PARENT_LOCATOR_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.parent_locator_entry = md_entry;
+            s->metadata_entries.present |= META_PARENT_LOCATOR_PRESENT;
+            continue;
+        }
+
+        if (md_entry.data_bits & VHDX_META_FLAGS_IS_REQUIRED) {
+            /* cannot read vhdx file - required region table entry that
+             * we do not understand.  per spec, we must fail to open */
+            ret = -ENOTSUP;
+            goto exit;
+        }
+    }
+
+    if (s->metadata_entries.present != META_ALL_PRESENT) {
+        ret = -ENOTSUP;
+        goto exit;
+    }
+
+    ret = bdrv_pread(bs->file,
+                     s->metadata_entries.file_parameters_entry.offset
+                                         + s->metadata_rt.file_offset,
+                     &s->params,
+                     sizeof(s->params));
+
+    if (ret < 0) {
+        goto exit;
+    }
+
+    le32_to_cpus(&s->params.block_size);
+    le32_to_cpus(&s->params.data_bits);
+
+
+    /* We now have the file parameters, so we can tell if this is a
+     * differencing file (i.e.. has_parent), is dynamic or fixed
+     * sized (leave_blocks_allocated), and the block size */
+
+    /* The parent locator required iff the file parameters has_parent set */
+    if (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) {
+        if (s->metadata_entries.present & META_PARENT_LOCATOR_PRESENT) {
+            /* TODO: parse  parent locator fields */
+            ret = -ENOTSUP; /* temp, until differencing files are supported */
+            goto exit;
+        } else {
+            /* if has_parent is set, but there is not parent locator present,
+             * then that is an invalid combination */
+            ret = -EINVAL;
+            goto exit;
+        }
+    }
+
+    /* determine virtual disk size, logical sector size,
+     * and phys sector size */
+
+    ret = bdrv_pread(bs->file,
+                     s->metadata_entries.virtual_disk_size_entry.offset
+                                           + s->metadata_rt.file_offset,
+                     &s->virtual_disk_size,
+                     sizeof(uint64_t));
+    if (ret < 0) {
+        goto exit;
+    }
+    ret = bdrv_pread(bs->file,
+                     s->metadata_entries.logical_sector_size_entry.offset
+                                             + s->metadata_rt.file_offset,
+                     &s->logical_sector_size,
+                     sizeof(uint32_t));
+    if (ret < 0) {
+        goto exit;
+    }
+    ret = bdrv_pread(bs->file,
+                     s->metadata_entries.phys_sector_size_entry.offset
+                                          + s->metadata_rt.file_offset,
+                     &s->physical_sector_size,
+                     sizeof(uint32_t));
+    if (ret < 0) {
+        goto exit;
+    }
+
+    le64_to_cpus(&s->virtual_disk_size);
+    le32_to_cpus(&s->logical_sector_size);
+    le32_to_cpus(&s->physical_sector_size);
+
+    if (s->params.block_size < VHDX_BLOCK_SIZE_MIN ||
+        s->params.block_size > VHDX_BLOCK_SIZE_MAX) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    /* only 2 supported sector sizes */
+    if (s->logical_sector_size != 512 && s->logical_sector_size != 4096) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    /* Both block_size and sector_size are guaranteed powers of 2, below.
+       Due to range checks above, s->sectors_per_block can never be < 256 */
+    s->sectors_per_block = s->params.block_size / s->logical_sector_size;
+    s->chunk_ratio = (VHDX_MAX_SECTORS_PER_BLOCK) *
+                     (uint64_t)s->logical_sector_size /
+                     (uint64_t)s->params.block_size;
+
+    /* These values are ones we will want to use for division / multiplication
+     * later on, and they are all guaranteed (per the spec) to be powers of 2,
+     * so we can take advantage of that for shift operations during
+     * reads/writes */
+    if (s->logical_sector_size & (s->logical_sector_size - 1)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+    if (s->sectors_per_block & (s->sectors_per_block - 1)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+    if (s->chunk_ratio & (s->chunk_ratio - 1)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+    s->block_size = s->params.block_size;
+    if (s->block_size & (s->block_size - 1)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    vhdx_set_shift_bits(s);
+
+    ret = 0;
+
+exit:
+    qemu_vfree(buffer);
+    return ret;
+}
+
+/*
+ * Calculate the number of BAT entries, including sector
+ * bitmap entries.
+ */
+static void vhdx_calc_bat_entries(BDRVVHDXState *s)
+{
+    uint32_t data_blocks_cnt, bitmap_blocks_cnt;
+
+    data_blocks_cnt = s->virtual_disk_size >> s->block_size_bits;
+    if (s->virtual_disk_size - (data_blocks_cnt << s->block_size_bits)) {
+        data_blocks_cnt++;
+    }
+    bitmap_blocks_cnt = data_blocks_cnt >> s->chunk_ratio_bits;
+    if (data_blocks_cnt - (bitmap_blocks_cnt << s->chunk_ratio_bits)) {
+        bitmap_blocks_cnt++;
+    }
+
+    if (s->parent_entries) {
+        s->bat_entries = bitmap_blocks_cnt * (s->chunk_ratio + 1);
+    } else {
+        s->bat_entries = data_blocks_cnt +
+                         ((data_blocks_cnt - 1) >> s->chunk_ratio_bits);
+    }
+
+}
+
+static void vhdx_close(BlockDriverState *bs)
+{
+    BDRVVHDXState *s = bs->opaque;
+    qemu_vfree(s->headers[0]);
+    s->headers[0] = NULL;
+    qemu_vfree(s->headers[1]);
+    s->headers[1] = NULL;
+    qemu_vfree(s->bat);
+    s->bat = NULL;
+    qemu_vfree(s->parent_entries);
+    s->parent_entries = NULL;
+    migrate_del_blocker(s->migration_blocker);
+    error_free(s->migration_blocker);
+    qemu_vfree(s->log.hdr);
+    s->log.hdr = NULL;
+    vhdx_region_unregister_all(s);
+}
+
+static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
+                     Error **errp)
+{
+    BDRVVHDXState *s = bs->opaque;
+    int ret = 0;
+    uint32_t i;
+    uint64_t signature;
+    Error *local_err = NULL;
+
+    s->bat = NULL;
+    s->first_visible_write = true;
+
+    qemu_co_mutex_init(&s->lock);
+    QLIST_INIT(&s->regions);
+
+    /* validate the file signature */
+    ret = bdrv_pread(bs->file, 0, &signature, sizeof(uint64_t));
+    if (ret < 0) {
+        goto fail;
+    }
+    if (memcmp(&signature, "vhdxfile", 8)) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    /* This is used for any header updates, for the file_write_guid.
+     * The spec dictates that a new value should be used for the first
+     * header update */
+    vhdx_guid_generate(&s->session_guid);
+
+    vhdx_parse_header(bs, s, &local_err);
+    if (local_err != NULL) {
+        error_propagate(errp, local_err);
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    ret = vhdx_parse_log(bs, s, &s->log_replayed_on_open, errp);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    ret = vhdx_open_region_tables(bs, s);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    ret = vhdx_parse_metadata(bs, s);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    s->block_size = s->params.block_size;
+
+    /* the VHDX spec dictates that virtual_disk_size is always a multiple of
+     * logical_sector_size */
+    bs->total_sectors = s->virtual_disk_size >> s->logical_sector_size_bits;
+
+    vhdx_calc_bat_entries(s);
+
+    s->bat_offset = s->bat_rt.file_offset;
+
+    if (s->bat_entries > s->bat_rt.length / sizeof(VHDXBatEntry)) {
+        /* BAT allocation is not large enough for all entries */
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    /* s->bat is freed in vhdx_close() */
+    s->bat = qemu_try_blockalign(bs->file, s->bat_rt.length);
+    if (s->bat == NULL) {
+        ret = -ENOMEM;
+        goto fail;
+    }
+
+    ret = bdrv_pread(bs->file, s->bat_offset, s->bat, s->bat_rt.length);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    uint64_t payblocks = s->chunk_ratio;
+    /* endian convert, and verify populated BAT field file offsets against
+     * region table and log entries */
+    for (i = 0; i < s->bat_entries; i++) {
+        le64_to_cpus(&s->bat[i]);
+        if (payblocks--) {
+            /* payload bat entries */
+            if ((s->bat[i] & VHDX_BAT_STATE_BIT_MASK) ==
+                    PAYLOAD_BLOCK_FULLY_PRESENT) {
+                ret = vhdx_region_check(s, s->bat[i] & VHDX_BAT_FILE_OFF_MASK,
+                                        s->block_size);
+                if (ret < 0) {
+                    goto fail;
+                }
+            }
+        } else {
+            payblocks = s->chunk_ratio;
+            /* Once differencing files are supported, verify sector bitmap
+             * blocks here */
+        }
+    }
+
+    if (flags & BDRV_O_RDWR) {
+        ret = vhdx_update_headers(bs, s, false, NULL);
+        if (ret < 0) {
+            goto fail;
+        }
+    }
+
+    /* TODO: differencing files */
+
+    /* Disable migration when VHDX images are used */
+    error_setg(&s->migration_blocker, "The vhdx format used by node '%s' "
+               "does not support live migration",
+               bdrv_get_device_or_node_name(bs));
+    migrate_add_blocker(s->migration_blocker);
+
+    return 0;
+fail:
+    vhdx_close(bs);
+    return ret;
+}
+
+static int vhdx_reopen_prepare(BDRVReopenState *state,
+                               BlockReopenQueue *queue, Error **errp)
+{
+    return 0;
+}
+
+
+/*
+ * Perform sector to block offset translations, to get various
+ * sector and file offsets into the image.  See VHDXSectorInfo
+ */
+static void vhdx_block_translate(BDRVVHDXState *s, int64_t sector_num,
+                                 int nb_sectors, VHDXSectorInfo *sinfo)
+{
+    uint32_t block_offset;
+
+    sinfo->bat_idx = sector_num >> s->sectors_per_block_bits;
+    /* effectively a modulo - this gives us the offset into the block
+     * (in sector sizes) for our sector number */
+    block_offset = sector_num - (sinfo->bat_idx << s->sectors_per_block_bits);
+    /* the chunk ratio gives us the interleaving of the sector
+     * bitmaps, so we need to advance our page block index by the
+     * sector bitmaps entry number */
+    sinfo->bat_idx += sinfo->bat_idx >> s->chunk_ratio_bits;
+
+    /* the number of sectors we can read/write in this cycle */
+    sinfo->sectors_avail = s->sectors_per_block - block_offset;
+
+    sinfo->bytes_left = sinfo->sectors_avail << s->logical_sector_size_bits;
+
+    if (sinfo->sectors_avail > nb_sectors) {
+        sinfo->sectors_avail = nb_sectors;
+    }
+
+    sinfo->bytes_avail = sinfo->sectors_avail << s->logical_sector_size_bits;
+
+    sinfo->file_offset = s->bat[sinfo->bat_idx] & VHDX_BAT_FILE_OFF_MASK;
+
+    sinfo->block_offset = block_offset << s->logical_sector_size_bits;
+
+    /* The file offset must be past the header section, so must be > 0 */
+    if (sinfo->file_offset == 0) {
+        return;
+    }
+
+    /* block offset is the offset in vhdx logical sectors, in
+     * the payload data block. Convert that to a byte offset
+     * in the block, and add in the payload data block offset
+     * in the file, in bytes, to get the final read address */
+
+    sinfo->file_offset += sinfo->block_offset;
+}
+
+
+static int vhdx_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
+{
+    BDRVVHDXState *s = bs->opaque;
+
+    bdi->cluster_size = s->block_size;
+
+    bdi->unallocated_blocks_are_zero =
+        (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) == 0;
+
+    return 0;
+}
+
+
+static coroutine_fn int vhdx_co_readv(BlockDriverState *bs, int64_t sector_num,
+                                      int nb_sectors, QEMUIOVector *qiov)
+{
+    BDRVVHDXState *s = bs->opaque;
+    int ret = 0;
+    VHDXSectorInfo sinfo;
+    uint64_t bytes_done = 0;
+    QEMUIOVector hd_qiov;
+
+    qemu_iovec_init(&hd_qiov, qiov->niov);
+
+    qemu_co_mutex_lock(&s->lock);
+
+    while (nb_sectors > 0) {
+        /* We are a differencing file, so we need to inspect the sector bitmap
+         * to see if we have the data or not */
+        if (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) {
+            /* not supported yet */
+            ret = -ENOTSUP;
+            goto exit;
+        } else {
+            vhdx_block_translate(s, sector_num, nb_sectors, &sinfo);
+
+            qemu_iovec_reset(&hd_qiov);
+            qemu_iovec_concat(&hd_qiov, qiov,  bytes_done, sinfo.bytes_avail);
+
+            /* check the payload block state */
+            switch (s->bat[sinfo.bat_idx] & VHDX_BAT_STATE_BIT_MASK) {
+            case PAYLOAD_BLOCK_NOT_PRESENT: /* fall through */
+            case PAYLOAD_BLOCK_UNDEFINED:
+            case PAYLOAD_BLOCK_UNMAPPED:
+            case PAYLOAD_BLOCK_UNMAPPED_v095:
+            case PAYLOAD_BLOCK_ZERO:
+                /* return zero */
+                qemu_iovec_memset(&hd_qiov, 0, 0, sinfo.bytes_avail);
+                break;
+            case PAYLOAD_BLOCK_FULLY_PRESENT:
+                qemu_co_mutex_unlock(&s->lock);
+                ret = bdrv_co_readv(bs->file,
+                                    sinfo.file_offset >> BDRV_SECTOR_BITS,
+                                    sinfo.sectors_avail, &hd_qiov);
+                qemu_co_mutex_lock(&s->lock);
+                if (ret < 0) {
+                    goto exit;
+                }
+                break;
+            case PAYLOAD_BLOCK_PARTIALLY_PRESENT:
+                /* we don't yet support difference files, fall through
+                 * to error */
+            default:
+                ret = -EIO;
+                goto exit;
+                break;
+            }
+            nb_sectors -= sinfo.sectors_avail;
+            sector_num += sinfo.sectors_avail;
+            bytes_done += sinfo.bytes_avail;
+        }
+    }
+    ret = 0;
+exit:
+    qemu_co_mutex_unlock(&s->lock);
+    qemu_iovec_destroy(&hd_qiov);
+    return ret;
+}
+
+/*
+ * Allocate a new payload block at the end of the file.
+ *
+ * Allocation will happen at 1MB alignment inside the file
+ *
+ * Returns the file offset start of the new payload block
+ */
+static int vhdx_allocate_block(BlockDriverState *bs, BDRVVHDXState *s,
+                                    uint64_t *new_offset)
+{
+    *new_offset = bdrv_getlength(bs->file);
+
+    /* per the spec, the address for a block is in units of 1MB */
+    *new_offset = ROUND_UP(*new_offset, 1024 * 1024);
+
+    return bdrv_truncate(bs->file, *new_offset + s->block_size);
+}
+
+/*
+ * Update the BAT table entry with the new file offset, and the new entry
+ * state */
+static void vhdx_update_bat_table_entry(BlockDriverState *bs, BDRVVHDXState *s,
+                                       VHDXSectorInfo *sinfo,
+                                       uint64_t *bat_entry_le,
+                                       uint64_t *bat_offset, int state)
+{
+    /* The BAT entry is a uint64, with 44 bits for the file offset in units of
+     * 1MB, and 3 bits for the block state. */
+    if ((state == PAYLOAD_BLOCK_ZERO)        ||
+        (state == PAYLOAD_BLOCK_UNDEFINED)   ||
+        (state == PAYLOAD_BLOCK_NOT_PRESENT) ||
+        (state == PAYLOAD_BLOCK_UNMAPPED)) {
+        s->bat[sinfo->bat_idx]  = 0;  /* For PAYLOAD_BLOCK_ZERO, the
+                                         FileOffsetMB field is denoted as
+                                         'reserved' in the v1.0 spec.  If it is
+                                         non-zero, MS Hyper-V will fail to read
+                                         the disk image */
+    } else {
+        s->bat[sinfo->bat_idx]  = sinfo->file_offset;
+    }
+
+    s->bat[sinfo->bat_idx] |= state & VHDX_BAT_STATE_BIT_MASK;
+
+    *bat_entry_le = cpu_to_le64(s->bat[sinfo->bat_idx]);
+    *bat_offset = s->bat_offset + sinfo->bat_idx * sizeof(VHDXBatEntry);
+
+}
+
+/* Per the spec, on the first write of guest-visible data to the file the
+ * data write guid must be updated in the header */
+int vhdx_user_visible_write(BlockDriverState *bs, BDRVVHDXState *s)
+{
+    int ret = 0;
+    if (s->first_visible_write) {
+        s->first_visible_write = false;
+        ret = vhdx_update_headers(bs, s, true, NULL);
+    }
+    return ret;
+}
+
+static coroutine_fn int vhdx_co_writev(BlockDriverState *bs, int64_t sector_num,
+                                      int nb_sectors, QEMUIOVector *qiov)
+{
+    int ret = -ENOTSUP;
+    BDRVVHDXState *s = bs->opaque;
+    VHDXSectorInfo sinfo;
+    uint64_t bytes_done = 0;
+    uint64_t bat_entry = 0;
+    uint64_t bat_entry_offset = 0;
+    QEMUIOVector hd_qiov;
+    struct iovec iov1 = { 0 };
+    struct iovec iov2 = { 0 };
+    int sectors_to_write;
+    int bat_state;
+    uint64_t bat_prior_offset = 0;
+    bool bat_update = false;
+
+    qemu_iovec_init(&hd_qiov, qiov->niov);
+
+    qemu_co_mutex_lock(&s->lock);
+
+    ret = vhdx_user_visible_write(bs, s);
+    if (ret < 0) {
+        goto exit;
+    }
+
+    while (nb_sectors > 0) {
+        bool use_zero_buffers = false;
+        bat_update = false;
+        if (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) {
+            /* not supported yet */
+            ret = -ENOTSUP;
+            goto exit;
+        } else {
+            vhdx_block_translate(s, sector_num, nb_sectors, &sinfo);
+            sectors_to_write = sinfo.sectors_avail;
+
+            qemu_iovec_reset(&hd_qiov);
+            /* check the payload block state */
+            bat_state = s->bat[sinfo.bat_idx] & VHDX_BAT_STATE_BIT_MASK;
+            switch (bat_state) {
+            case PAYLOAD_BLOCK_ZERO:
+                /* in this case, we need to preserve zero writes for
+                 * data that is not part of this write, so we must pad
+                 * the rest of the buffer to zeroes */
+
+                /* if we are on a posix system with ftruncate() that extends
+                 * a file, then it is zero-filled for us.  On Win32, the raw
+                 * layer uses SetFilePointer and SetFileEnd, which does not
+                 * zero fill AFAIK */
+
+                /* Queue another write of zero buffers if the underlying file
+                 * does not zero-fill on file extension */
+
+                if (bdrv_has_zero_init(bs->file) == 0) {
+                    use_zero_buffers = true;
+
+                    /* zero fill the front, if any */
+                    if (sinfo.block_offset) {
+                        iov1.iov_len = sinfo.block_offset;
+                        iov1.iov_base = qemu_blockalign(bs, iov1.iov_len);
+                        memset(iov1.iov_base, 0, iov1.iov_len);
+                        qemu_iovec_concat_iov(&hd_qiov, &iov1, 1, 0,
+                                              iov1.iov_len);
+                        sectors_to_write += iov1.iov_len >> BDRV_SECTOR_BITS;
+                    }
+
+                    /* our actual data */
+                    qemu_iovec_concat(&hd_qiov, qiov,  bytes_done,
+                                      sinfo.bytes_avail);
+
+                    /* zero fill the back, if any */
+                    if ((sinfo.bytes_avail - sinfo.block_offset) <
+                         s->block_size) {
+                        iov2.iov_len = s->block_size -
+                                      (sinfo.bytes_avail + sinfo.block_offset);
+                        iov2.iov_base = qemu_blockalign(bs, iov2.iov_len);
+                        memset(iov2.iov_base, 0, iov2.iov_len);
+                        qemu_iovec_concat_iov(&hd_qiov, &iov2, 1, 0,
+                                              iov2.iov_len);
+                        sectors_to_write += iov2.iov_len >> BDRV_SECTOR_BITS;
+                    }
+                }
+                /* fall through */
+            case PAYLOAD_BLOCK_NOT_PRESENT: /* fall through */
+            case PAYLOAD_BLOCK_UNMAPPED:
+            case PAYLOAD_BLOCK_UNMAPPED_v095:
+            case PAYLOAD_BLOCK_UNDEFINED:
+                bat_prior_offset = sinfo.file_offset;
+                ret = vhdx_allocate_block(bs, s, &sinfo.file_offset);
+                if (ret < 0) {
+                    goto exit;
+                }
+                /* once we support differencing files, this may also be
+                 * partially present */
+                /* update block state to the newly specified state */
+                vhdx_update_bat_table_entry(bs, s, &sinfo, &bat_entry,
+                                            &bat_entry_offset,
+                                            PAYLOAD_BLOCK_FULLY_PRESENT);
+                bat_update = true;
+                /* since we just allocated a block, file_offset is the
+                 * beginning of the payload block. It needs to be the
+                 * write address, which includes the offset into the block */
+                if (!use_zero_buffers) {
+                    sinfo.file_offset += sinfo.block_offset;
+                }
+                /* fall through */
+            case PAYLOAD_BLOCK_FULLY_PRESENT:
+                /* if the file offset address is in the header zone,
+                 * there is a problem */
+                if (sinfo.file_offset < (1024 * 1024)) {
+                    ret = -EFAULT;
+                    goto error_bat_restore;
+                }
+
+                if (!use_zero_buffers) {
+                    qemu_iovec_concat(&hd_qiov, qiov,  bytes_done,
+                                      sinfo.bytes_avail);
+                }
+                /* block exists, so we can just overwrite it */
+                qemu_co_mutex_unlock(&s->lock);
+                ret = bdrv_co_writev(bs->file,
+                                    sinfo.file_offset >> BDRV_SECTOR_BITS,
+                                    sectors_to_write, &hd_qiov);
+                qemu_co_mutex_lock(&s->lock);
+                if (ret < 0) {
+                    goto error_bat_restore;
+                }
+                break;
+            case PAYLOAD_BLOCK_PARTIALLY_PRESENT:
+                /* we don't yet support difference files, fall through
+                 * to error */
+            default:
+                ret = -EIO;
+                goto exit;
+                break;
+            }
+
+            if (bat_update) {
+                /* this will update the BAT entry into the log journal, and
+                 * then flush the log journal out to disk */
+                ret =  vhdx_log_write_and_flush(bs, s, &bat_entry,
+                                                sizeof(VHDXBatEntry),
+                                                bat_entry_offset);
+                if (ret < 0) {
+                    goto exit;
+                }
+            }
+
+            nb_sectors -= sinfo.sectors_avail;
+            sector_num += sinfo.sectors_avail;
+            bytes_done += sinfo.bytes_avail;
+
+        }
+    }
+
+    goto exit;
+
+error_bat_restore:
+    if (bat_update) {
+        /* keep metadata in sync, and restore the bat entry state
+         * if error. */
+        sinfo.file_offset = bat_prior_offset;
+        vhdx_update_bat_table_entry(bs, s, &sinfo, &bat_entry,
+                                    &bat_entry_offset, bat_state);
+    }
+exit:
+    qemu_vfree(iov1.iov_base);
+    qemu_vfree(iov2.iov_base);
+    qemu_co_mutex_unlock(&s->lock);
+    qemu_iovec_destroy(&hd_qiov);
+    return ret;
+}
+
+
+
+/*
+ * Create VHDX Headers
+ *
+ * There are 2 headers, and the highest sequence number will represent
+ * the active header
+ */
+static int vhdx_create_new_headers(BlockDriverState *bs, uint64_t image_size,
+                                   uint32_t log_size)
+{
+    int ret = 0;
+    VHDXHeader *hdr = NULL;
+
+    hdr = g_new0(VHDXHeader, 1);
+
+    hdr->signature       = VHDX_HEADER_SIGNATURE;
+    hdr->sequence_number = g_random_int();
+    hdr->log_version     = 0;
+    hdr->version         = 1;
+    hdr->log_length      = log_size;
+    hdr->log_offset      = VHDX_HEADER_SECTION_END;
+    vhdx_guid_generate(&hdr->file_write_guid);
+    vhdx_guid_generate(&hdr->data_write_guid);
+
+    ret = vhdx_write_header(bs, hdr, VHDX_HEADER1_OFFSET, false);
+    if (ret < 0) {
+        goto exit;
+    }
+    hdr->sequence_number++;
+    ret = vhdx_write_header(bs, hdr, VHDX_HEADER2_OFFSET, false);
+    if (ret < 0) {
+        goto exit;
+    }
+
+exit:
+    g_free(hdr);
+    return ret;
+}
+
+#define VHDX_METADATA_ENTRY_BUFFER_SIZE \
+                                    (sizeof(VHDXFileParameters)               +\
+                                     sizeof(VHDXVirtualDiskSize)              +\
+                                     sizeof(VHDXPage83Data)                   +\
+                                     sizeof(VHDXVirtualDiskLogicalSectorSize) +\
+                                     sizeof(VHDXVirtualDiskPhysicalSectorSize))
+
+/*
+ * Create the Metadata entries.
+ *
+ * For more details on the entries, see section 3.5 (pg 29) in the
+ * VHDX 1.00 specification.
+ *
+ * We support 5 metadata entries (all required by spec):
+ *          File Parameters,
+ *          Virtual Disk Size,
+ *          Page 83 Data,
+ *          Logical Sector Size,
+ *          Physical Sector Size
+ *
+ * The first 64KB of the Metadata section is reserved for the metadata
+ * header and entries; beyond that, the metadata items themselves reside.
+ */
+static int vhdx_create_new_metadata(BlockDriverState *bs,
+                                    uint64_t image_size,
+                                    uint32_t block_size,
+                                    uint32_t sector_size,
+                                    uint64_t metadata_offset,
+                                    VHDXImageType type)
+{
+    int ret = 0;
+    uint32_t offset = 0;
+    void *buffer = NULL;
+    void *entry_buffer;
+    VHDXMetadataTableHeader *md_table;;
+    VHDXMetadataTableEntry  *md_table_entry;
+
+    /* Metadata entries */
+    VHDXFileParameters     *mt_file_params;
+    VHDXVirtualDiskSize    *mt_virtual_size;
+    VHDXPage83Data         *mt_page83;
+    VHDXVirtualDiskLogicalSectorSize  *mt_log_sector_size;
+    VHDXVirtualDiskPhysicalSectorSize *mt_phys_sector_size;
+
+    entry_buffer = g_malloc0(VHDX_METADATA_ENTRY_BUFFER_SIZE);
+
+    mt_file_params = entry_buffer;
+    offset += sizeof(VHDXFileParameters);
+    mt_virtual_size = entry_buffer + offset;
+    offset += sizeof(VHDXVirtualDiskSize);
+    mt_page83 = entry_buffer + offset;
+    offset += sizeof(VHDXPage83Data);
+    mt_log_sector_size = entry_buffer + offset;
+    offset += sizeof(VHDXVirtualDiskLogicalSectorSize);
+    mt_phys_sector_size = entry_buffer + offset;
+
+    mt_file_params->block_size = cpu_to_le32(block_size);
+    if (type == VHDX_TYPE_FIXED) {
+        mt_file_params->data_bits |= VHDX_PARAMS_LEAVE_BLOCKS_ALLOCED;
+        cpu_to_le32s(&mt_file_params->data_bits);
+    }
+
+    vhdx_guid_generate(&mt_page83->page_83_data);
+    cpu_to_leguids(&mt_page83->page_83_data);
+    mt_virtual_size->virtual_disk_size        = cpu_to_le64(image_size);
+    mt_log_sector_size->logical_sector_size   = cpu_to_le32(sector_size);
+    mt_phys_sector_size->physical_sector_size = cpu_to_le32(sector_size);
+
+    buffer = g_malloc0(VHDX_HEADER_BLOCK_SIZE);
+    md_table = buffer;
+
+    md_table->signature   = VHDX_METADATA_SIGNATURE;
+    md_table->entry_count = 5;
+    vhdx_metadata_header_le_export(md_table);
+
+
+    /* This will reference beyond the reserved table portion */
+    offset = 64 * KiB;
+
+    md_table_entry = buffer + sizeof(VHDXMetadataTableHeader);
+
+    md_table_entry[0].item_id = file_param_guid;
+    md_table_entry[0].offset  = offset;
+    md_table_entry[0].length  = sizeof(VHDXFileParameters);
+    md_table_entry[0].data_bits |= VHDX_META_FLAGS_IS_REQUIRED;
+    offset += md_table_entry[0].length;
+    vhdx_metadata_entry_le_export(&md_table_entry[0]);
+
+    md_table_entry[1].item_id = virtual_size_guid;
+    md_table_entry[1].offset  = offset;
+    md_table_entry[1].length  = sizeof(VHDXVirtualDiskSize);
+    md_table_entry[1].data_bits |= VHDX_META_FLAGS_IS_REQUIRED |
+                                   VHDX_META_FLAGS_IS_VIRTUAL_DISK;
+    offset += md_table_entry[1].length;
+    vhdx_metadata_entry_le_export(&md_table_entry[1]);
+
+    md_table_entry[2].item_id = page83_guid;
+    md_table_entry[2].offset  = offset;
+    md_table_entry[2].length  = sizeof(VHDXPage83Data);
+    md_table_entry[2].data_bits |= VHDX_META_FLAGS_IS_REQUIRED |
+                                   VHDX_META_FLAGS_IS_VIRTUAL_DISK;
+    offset += md_table_entry[2].length;
+    vhdx_metadata_entry_le_export(&md_table_entry[2]);
+
+    md_table_entry[3].item_id = logical_sector_guid;
+    md_table_entry[3].offset  = offset;
+    md_table_entry[3].length  = sizeof(VHDXVirtualDiskLogicalSectorSize);
+    md_table_entry[3].data_bits |= VHDX_META_FLAGS_IS_REQUIRED |
+                                   VHDX_META_FLAGS_IS_VIRTUAL_DISK;
+    offset += md_table_entry[3].length;
+    vhdx_metadata_entry_le_export(&md_table_entry[3]);
+
+    md_table_entry[4].item_id = phys_sector_guid;
+    md_table_entry[4].offset  = offset;
+    md_table_entry[4].length  = sizeof(VHDXVirtualDiskPhysicalSectorSize);
+    md_table_entry[4].data_bits |= VHDX_META_FLAGS_IS_REQUIRED |
+                                   VHDX_META_FLAGS_IS_VIRTUAL_DISK;
+    vhdx_metadata_entry_le_export(&md_table_entry[4]);
+
+    ret = bdrv_pwrite(bs, metadata_offset, buffer, VHDX_HEADER_BLOCK_SIZE);
+    if (ret < 0) {
+        goto exit;
+    }
+
+    ret = bdrv_pwrite(bs, metadata_offset + (64 * KiB), entry_buffer,
+                      VHDX_METADATA_ENTRY_BUFFER_SIZE);
+    if (ret < 0) {
+        goto exit;
+    }
+
+
+exit:
+    g_free(buffer);
+    g_free(entry_buffer);
+    return ret;
+}
+
+/* This create the actual BAT itself.  We currently only support
+ * 'Dynamic' and 'Fixed' image types.
+ *
+ *  Dynamic images: default state of the BAT is all zeroes.
+ *
+ *  Fixed images: default state of the BAT is fully populated, with
+ *                file offsets and state PAYLOAD_BLOCK_FULLY_PRESENT.
+ */
+static int vhdx_create_bat(BlockDriverState *bs, BDRVVHDXState *s,
+                           uint64_t image_size, VHDXImageType type,
+                           bool use_zero_blocks, uint64_t file_offset,
+                           uint32_t length)
+{
+    int ret = 0;
+    uint64_t data_file_offset;
+    uint64_t total_sectors = 0;
+    uint64_t sector_num = 0;
+    uint64_t unused;
+    int block_state;
+    VHDXSectorInfo sinfo;
+
+    assert(s->bat == NULL);
+
+    /* this gives a data start after BAT/bitmap entries, and well
+     * past any metadata entries (with a 4 MB buffer for future
+     * expansion */
+    data_file_offset = file_offset + length + 5 * MiB;
+    total_sectors = image_size >> s->logical_sector_size_bits;
+
+    if (type == VHDX_TYPE_DYNAMIC) {
+        /* All zeroes, so we can just extend the file - the end of the BAT
+         * is the furthest thing we have written yet */
+        ret = bdrv_truncate(bs, data_file_offset);
+        if (ret < 0) {
+            goto exit;
+        }
+    } else if (type == VHDX_TYPE_FIXED) {
+        ret = bdrv_truncate(bs, data_file_offset + image_size);
+        if (ret < 0) {
+            goto exit;
+        }
+    } else {
+        ret = -ENOTSUP;
+        goto exit;
+    }
+
+    if (type == VHDX_TYPE_FIXED ||
+                use_zero_blocks ||
+                bdrv_has_zero_init(bs) == 0) {
+        /* for a fixed file, the default BAT entry is not zero */
+        s->bat = g_try_malloc0(length);
+        if (length && s->bat == NULL) {
+            ret = -ENOMEM;
+            goto exit;
+        }
+        block_state = type == VHDX_TYPE_FIXED ? PAYLOAD_BLOCK_FULLY_PRESENT :
+                                                PAYLOAD_BLOCK_NOT_PRESENT;
+        block_state = use_zero_blocks ? PAYLOAD_BLOCK_ZERO : block_state;
+        /* fill the BAT by emulating sector writes of sectors_per_block size */
+        while (sector_num < total_sectors) {
+            vhdx_block_translate(s, sector_num, s->sectors_per_block, &sinfo);
+            sinfo.file_offset = data_file_offset +
+                                (sector_num << s->logical_sector_size_bits);
+            sinfo.file_offset = ROUND_UP(sinfo.file_offset, MiB);
+            vhdx_update_bat_table_entry(bs, s, &sinfo, &unused, &unused,
+                                        block_state);
+            cpu_to_le64s(&s->bat[sinfo.bat_idx]);
+            sector_num += s->sectors_per_block;
+        }
+        ret = bdrv_pwrite(bs, file_offset, s->bat, length);
+        if (ret < 0) {
+            goto exit;
+        }
+    }
+
+
+
+exit:
+    g_free(s->bat);
+    return ret;
+}
+
+/* Creates the region table header, and region table entries.
+ * There are 2 supported region table entries: BAT, and Metadata/
+ *
+ * As the calculations for the BAT region table are also needed
+ * to create the BAT itself, we will also cause the BAT to be
+ * created.
+ */
+static int vhdx_create_new_region_table(BlockDriverState *bs,
+                                        uint64_t image_size,
+                                        uint32_t block_size,
+                                        uint32_t sector_size,
+                                        uint32_t log_size,
+                                        bool use_zero_blocks,
+                                        VHDXImageType type,
+                                        uint64_t *metadata_offset)
+{
+    int ret = 0;
+    uint32_t offset = 0;
+    void *buffer = NULL;
+    uint64_t bat_file_offset;
+    uint32_t bat_length;
+    BDRVVHDXState *s = NULL;
+    VHDXRegionTableHeader *region_table;
+    VHDXRegionTableEntry *rt_bat;
+    VHDXRegionTableEntry *rt_metadata;
+
+    assert(metadata_offset != NULL);
+
+    /* Populate enough of the BDRVVHDXState to be able to use the
+     * pre-existing BAT calculation, translation, and update functions */
+    s = g_new0(BDRVVHDXState, 1);
+
+    s->chunk_ratio = (VHDX_MAX_SECTORS_PER_BLOCK) *
+                     (uint64_t) sector_size / (uint64_t) block_size;
+
+    s->sectors_per_block = block_size / sector_size;
+    s->virtual_disk_size = image_size;
+    s->block_size = block_size;
+    s->logical_sector_size = sector_size;
+
+    vhdx_set_shift_bits(s);
+
+    vhdx_calc_bat_entries(s);
+
+    /* At this point the VHDX state is populated enough for creation */
+
+    /* a single buffer is used so we can calculate the checksum over the
+     * entire 64KB block */
+    buffer = g_malloc0(VHDX_HEADER_BLOCK_SIZE);
+    region_table = buffer;
+    offset += sizeof(VHDXRegionTableHeader);
+    rt_bat = buffer + offset;
+    offset += sizeof(VHDXRegionTableEntry);
+    rt_metadata  = buffer + offset;
+
+    region_table->signature = VHDX_REGION_SIGNATURE;
+    region_table->entry_count = 2;   /* BAT and Metadata */
+
+    rt_bat->guid        = bat_guid;
+    rt_bat->length      = ROUND_UP(s->bat_entries * sizeof(VHDXBatEntry), MiB);
+    rt_bat->file_offset = ROUND_UP(VHDX_HEADER_SECTION_END + log_size, MiB);
+    s->bat_offset = rt_bat->file_offset;
+
+    rt_metadata->guid        = metadata_guid;
+    rt_metadata->file_offset = ROUND_UP(rt_bat->file_offset + rt_bat->length,
+                                        MiB);
+    rt_metadata->length      = 1 * MiB; /* min size, and more than enough */
+    *metadata_offset = rt_metadata->file_offset;
+
+    bat_file_offset = rt_bat->file_offset;
+    bat_length = rt_bat->length;
+
+    vhdx_region_header_le_export(region_table);
+    vhdx_region_entry_le_export(rt_bat);
+    vhdx_region_entry_le_export(rt_metadata);
+
+    vhdx_update_checksum(buffer, VHDX_HEADER_BLOCK_SIZE,
+                         offsetof(VHDXRegionTableHeader, checksum));
+
+
+    /* The region table gives us the data we need to create the BAT,
+     * so do that now */
+    ret = vhdx_create_bat(bs, s, image_size, type, use_zero_blocks,
+                          bat_file_offset, bat_length);
+    if (ret < 0) {
+        goto exit;
+    }
+
+    /* Now write out the region headers to disk */
+    ret = bdrv_pwrite(bs, VHDX_REGION_TABLE_OFFSET, buffer,
+                      VHDX_HEADER_BLOCK_SIZE);
+    if (ret < 0) {
+        goto exit;
+    }
+
+    ret = bdrv_pwrite(bs, VHDX_REGION_TABLE2_OFFSET, buffer,
+                      VHDX_HEADER_BLOCK_SIZE);
+    if (ret < 0) {
+        goto exit;
+    }
+
+exit:
+    g_free(s);
+    g_free(buffer);
+    return ret;
+}
+
+/* We need to create the following elements:
+ *
+ *    .-----------------------------------------------------------------.
+ *    |   (A)    |   (B)    |    (C)    |     (D)       |     (E)       |
+ *    |  File ID |  Header1 |  Header 2 |  Region Tbl 1 |  Region Tbl 2 |
+ *    |          |          |           |               |               |
+ *    .-----------------------------------------------------------------.
+ *    0         64KB      128KB       192KB           256KB           320KB
+ *
+ *
+ *    .---- ~ ----------- ~ ------------ ~ ---------------- ~ -----------.
+ *    |     (F)     |     (G)       |    (H)    |                        |
+ *    | Journal Log |  BAT / Bitmap |  Metadata |  .... data ......      |
+ *    |             |               |           |                        |
+ *    .---- ~ ----------- ~ ------------ ~ ---------------- ~ -----------.
+ *   1MB
+ */
+static int vhdx_create(const char *filename, QemuOpts *opts, Error **errp)
+{
+    int ret = 0;
+    uint64_t image_size = (uint64_t) 2 * GiB;
+    uint32_t log_size   = 1 * MiB;
+    uint32_t block_size = 0;
+    uint64_t signature;
+    uint64_t metadata_offset;
+    bool use_zero_blocks = false;
+
+    gunichar2 *creator = NULL;
+    glong creator_items;
+    BlockDriverState *bs;
+    char *type = NULL;
+    VHDXImageType image_type;
+    Error *local_err = NULL;
+
+    image_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
+                          BDRV_SECTOR_SIZE);
+    log_size = qemu_opt_get_size_del(opts, VHDX_BLOCK_OPT_LOG_SIZE, 0);
+    block_size = qemu_opt_get_size_del(opts, VHDX_BLOCK_OPT_BLOCK_SIZE, 0);
+    type = qemu_opt_get_del(opts, BLOCK_OPT_SUBFMT);
+    use_zero_blocks = qemu_opt_get_bool_del(opts, VHDX_BLOCK_OPT_ZERO, true);
+
+    if (image_size > VHDX_MAX_IMAGE_SIZE) {
+        error_setg_errno(errp, EINVAL, "Image size too large; max of 64TB");
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    if (type == NULL) {
+        type = g_strdup("dynamic");
+    }
+
+    if (!strcmp(type, "dynamic")) {
+        image_type = VHDX_TYPE_DYNAMIC;
+    } else if (!strcmp(type, "fixed")) {
+        image_type = VHDX_TYPE_FIXED;
+    } else if (!strcmp(type, "differencing")) {
+        error_setg_errno(errp, ENOTSUP,
+                         "Differencing files not yet supported");
+        ret = -ENOTSUP;
+        goto exit;
+    } else {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    /* These are pretty arbitrary, and mainly designed to keep the BAT
+     * size reasonable to load into RAM */
+    if (block_size == 0) {
+        if (image_size > 32 * TiB) {
+            block_size = 64 * MiB;
+        } else if (image_size > (uint64_t) 100 * GiB) {
+            block_size = 32 * MiB;
+        } else if (image_size > 1 * GiB) {
+            block_size = 16 * MiB;
+        } else {
+            block_size = 8 * MiB;
+        }
+    }
+
+
+    /* make the log size close to what was specified, but must be
+     * min 1MB, and multiple of 1MB */
+    log_size = ROUND_UP(log_size, MiB);
+
+    block_size = ROUND_UP(block_size, MiB);
+    block_size = block_size > VHDX_BLOCK_SIZE_MAX ? VHDX_BLOCK_SIZE_MAX :
+                                                    block_size;
+
+    ret = bdrv_create_file(filename, opts, &local_err);
+    if (ret < 0) {
+        error_propagate(errp, local_err);
+        goto exit;
+    }
+
+    bs = NULL;
+    ret = bdrv_open(&bs, filename, NULL, NULL, BDRV_O_RDWR | BDRV_O_PROTOCOL,
+                    NULL, &local_err);
+    if (ret < 0) {
+        error_propagate(errp, local_err);
+        goto exit;
+    }
+
+    /* Create (A) */
+
+    /* The creator field is optional, but may be useful for
+     * debugging / diagnostics */
+    creator = g_utf8_to_utf16("QEMU v" QEMU_VERSION, -1, NULL,
+                              &creator_items, NULL);
+    signature = cpu_to_le64(VHDX_FILE_SIGNATURE);
+    ret = bdrv_pwrite(bs, VHDX_FILE_ID_OFFSET, &signature, sizeof(signature));
+    if (ret < 0) {
+        goto delete_and_exit;
+    }
+    if (creator) {
+        ret = bdrv_pwrite(bs, VHDX_FILE_ID_OFFSET + sizeof(signature),
+                          creator, creator_items * sizeof(gunichar2));
+        if (ret < 0) {
+            goto delete_and_exit;
+        }
+    }
+
+
+    /* Creates (B),(C) */
+    ret = vhdx_create_new_headers(bs, image_size, log_size);
+    if (ret < 0) {
+        goto delete_and_exit;
+    }
+
+    /* Creates (D),(E),(G) explicitly. (F) created as by-product */
+    ret = vhdx_create_new_region_table(bs, image_size, block_size, 512,
+                                       log_size, use_zero_blocks, image_type,
+                                       &metadata_offset);
+    if (ret < 0) {
+        goto delete_and_exit;
+    }
+
+    /* Creates (H) */
+    ret = vhdx_create_new_metadata(bs, image_size, block_size, 512,
+                                   metadata_offset, image_type);
+    if (ret < 0) {
+        goto delete_and_exit;
+    }
+
+
+delete_and_exit:
+    bdrv_unref(bs);
+exit:
+    g_free(type);
+    g_free(creator);
+    return ret;
+}
+
+/* If opened r/w, the VHDX driver will automatically replay the log,
+ * if one is present, inside the vhdx_open() call.
+ *
+ * If qemu-img check -r all is called, the image is automatically opened
+ * r/w and any log has already been replayed, so there is nothing (currently)
+ * for us to do here
+ */
+static int vhdx_check(BlockDriverState *bs, BdrvCheckResult *result,
+                       BdrvCheckMode fix)
+{
+    BDRVVHDXState *s = bs->opaque;
+
+    if (s->log_replayed_on_open) {
+        result->corruptions_fixed++;
+    }
+    return 0;
+}
+
+static QemuOptsList vhdx_create_opts = {
+    .name = "vhdx-create-opts",
+    .head = QTAILQ_HEAD_INITIALIZER(vhdx_create_opts.head),
+    .desc = {
+        {
+           .name = BLOCK_OPT_SIZE,
+           .type = QEMU_OPT_SIZE,
+           .help = "Virtual disk size; max of 64TB."
+       },
+       {
+           .name = VHDX_BLOCK_OPT_LOG_SIZE,
+           .type = QEMU_OPT_SIZE,
+           .def_value_str = stringify(DEFAULT_LOG_SIZE),
+           .help = "Log size; min 1MB."
+       },
+       {
+           .name = VHDX_BLOCK_OPT_BLOCK_SIZE,
+           .type = QEMU_OPT_SIZE,
+           .def_value_str = stringify(0),
+           .help = "Block Size; min 1MB, max 256MB. " \
+                   "0 means auto-calculate based on image size."
+       },
+       {
+           .name = BLOCK_OPT_SUBFMT,
+           .type = QEMU_OPT_STRING,
+           .help = "VHDX format type, can be either 'dynamic' or 'fixed'. "\
+                   "Default is 'dynamic'."
+       },
+       {
+           .name = VHDX_BLOCK_OPT_ZERO,
+           .type = QEMU_OPT_BOOL,
+           .help = "Force use of payload blocks of type 'ZERO'. "\
+                   "Non-standard, but default.  Do not set to 'off' when "\
+                   "using 'qemu-img convert' with subformat=dynamic."
+       },
+       { NULL }
+    }
+};
+
+static BlockDriver bdrv_vhdx = {
+    .format_name            = "vhdx",
+    .instance_size          = sizeof(BDRVVHDXState),
+    .bdrv_probe             = vhdx_probe,
+    .bdrv_open              = vhdx_open,
+    .bdrv_close             = vhdx_close,
+    .bdrv_reopen_prepare    = vhdx_reopen_prepare,
+    .bdrv_co_readv          = vhdx_co_readv,
+    .bdrv_co_writev         = vhdx_co_writev,
+    .bdrv_create            = vhdx_create,
+    .bdrv_get_info          = vhdx_get_info,
+    .bdrv_check             = vhdx_check,
+    .bdrv_has_zero_init     = bdrv_has_zero_init_1,
+
+    .create_opts            = &vhdx_create_opts,
+};
+
+static void bdrv_vhdx_init(void)
+{
+    bdrv_register(&bdrv_vhdx);
+}
+
+block_init(bdrv_vhdx_init);