block: initial VHDX driver support framework - supports open and probe

This is the initial block driver framework for VHDX image support
(i.e. Hyper-V image file formats), that supports opening VHDX files, and
parsing the headers.

This commit does not yet enable:
    - reading
    - writing
    - updating the header
    - differencing files (images with parents)
    - log replay / dirty logs (only clean images)

This is based on Microsoft's VHDX specification:
    "VHDX Format Specification v0.95", published 4/12/2012
    https://www.microsoft.com/en-us/download/details.aspx?id=29681

Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 853 insertions, 0 deletions

diff --git a/block/vhdx.c b/block/vhdx.c
new file mode 100644
index 0000000000..0ee10a76ba
--- /dev/null
+++ b/block/vhdx.c
@@ -0,0 +1,853 @@
+/*
+ * 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 v0.95", published 4/12/2012
+ *  by Microsoft:
+ *      https://www.microsoft.com/en-us/download/details.aspx?id=29681
+ *
+ * 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"
+
+
+/* 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 = { .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 VHDXMetadataEntries {
+    VHDXMetadataTableEntry file_parameters_entry;
+    VHDXMetadataTableEntry virtual_disk_size_entry;
+    VHDXMetadataTableEntry page83_data_entry;
+    VHDXMetadataTableEntry logical_sector_size_entry;
+    VHDXMetadataTableEntry phys_sector_size_entry;
+    VHDXMetadataTableEntry parent_locator_entry;
+    uint16_t present;
+} VHDXMetadataEntries;
+
+
+typedef struct BDRVVHDXState {
+    CoMutex lock;
+
+    int curr_header;
+    VHDXHeader *headers[2];
+
+    VHDXRegionTableHeader rt;
+    VHDXRegionTableEntry bat_rt;         /* region table for the BAT */
+    VHDXRegionTableEntry metadata_rt;    /* region table for the metadata */
+
+    VHDXMetadataTableHeader metadata_hdr;
+    VHDXMetadataEntries metadata_entries;
+
+    VHDXFileParameters params;
+    uint32_t block_size;
+    uint32_t block_size_bits;
+    uint32_t sectors_per_block;
+    uint32_t sectors_per_block_bits;
+
+    uint64_t virtual_disk_size;
+    uint32_t logical_sector_size;
+    uint32_t physical_sector_size;
+
+    uint64_t chunk_ratio;
+    uint32_t chunk_ratio_bits;
+    uint32_t logical_sector_size_bits;
+
+    uint32_t bat_entries;
+    VHDXBatEntry *bat;
+    uint64_t bat_offset;
+
+    VHDXParentLocatorHeader parent_header;
+    VHDXParentLocatorEntry *parent_entries;
+
+} BDRVVHDXState;
+
+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;
+}
+
+
+/*
+ * 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;
+}
+
+/* All VHDX structures on disk are little endian */
+static void vhdx_header_le_import(VHDXHeader *h)
+{
+    assert(h != NULL);
+
+    le32_to_cpus(&h->signature);
+    le32_to_cpus(&h->checksum);
+    le64_to_cpus(&h->sequence_number);
+
+    leguid_to_cpus(&h->file_write_guid);
+    leguid_to_cpus(&h->data_write_guid);
+    leguid_to_cpus(&h->log_guid);
+
+    le16_to_cpus(&h->log_version);
+    le16_to_cpus(&h->version);
+    le32_to_cpus(&h->log_length);
+    le64_to_cpus(&h->log_offset);
+}
+
+
+/* opens the specified header block from the VHDX file header section */
+static int vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s)
+{
+    int ret = 0;
+    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 = 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));
+    vhdx_header_le_import(header1);
+
+    if (vhdx_checksum_is_valid(buffer, VHDX_HEADER_SIZE, 4) &&
+        !memcmp(&header1->signature, "head", 4)             &&
+        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));
+    vhdx_header_le_import(header2);
+
+    if (vhdx_checksum_is_valid(buffer, VHDX_HEADER_SIZE, 4) &&
+        !memcmp(&header2->signature, "head", 4)             &&
+        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) {
+        ret = -EINVAL;
+        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 {
+            ret = -EINVAL;
+            goto fail;
+        }
+    }
+
+    ret = 0;
+
+    goto exit;
+
+fail:
+    qerror_report(ERROR_CLASS_GENERIC_ERROR, "No valid VHDX header found");
+    qemu_vfree(header1);
+    qemu_vfree(header2);
+    s->headers[0] = NULL;
+    s->headers[1] = NULL;
+exit:
+    qemu_vfree(buffer);
+    return ret;
+}
+
+
+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));
+    le32_to_cpus(&s->rt.signature);
+    le32_to_cpus(&s->rt.checksum);
+    le32_to_cpus(&s->rt.entry_count);
+    le32_to_cpus(&s->rt.reserved);
+    offset += sizeof(s->rt);
+
+    if (!vhdx_checksum_is_valid(buffer, VHDX_HEADER_BLOCK_SIZE, 4) ||
+        memcmp(&s->rt.signature, "regi", 4)) {
+        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);
+
+        leguid_to_cpus(&rt_entry.guid);
+        le64_to_cpus(&rt_entry.file_offset);
+        le32_to_cpus(&rt_entry.length);
+        le32_to_cpus(&rt_entry.data_bits);
+
+        /* 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;
+        }
+    }
+    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);
+
+    le64_to_cpus(&s->metadata_hdr.signature);
+    le16_to_cpus(&s->metadata_hdr.reserved);
+    le16_to_cpus(&s->metadata_hdr.entry_count);
+
+    if (memcmp(&s->metadata_hdr.signature, "metadata", 8)) {
+        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);
+
+        leguid_to_cpus(&md_entry.item_id);
+        le32_to_cpus(&md_entry.offset);
+        le32_to_cpus(&md_entry.length);
+        le32_to_cpus(&md_entry.data_bits);
+        le32_to_cpus(&md_entry.reserved2);
+
+        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->logical_sector_size == 0 || s->params.block_size == 0) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    /* both block_size and sector_size are guaranteed powers of 2 */
+    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;
+    }
+
+    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);
+
+    ret = 0;
+
+exit:
+    qemu_vfree(buffer);
+    return ret;
+}
+
+/* Parse the replay log.  Per the VHDX spec, if the log is present
+ * it must be replayed prior to opening the file, even read-only.
+ *
+ * If read-only, we must replay the log in RAM (or refuse to open
+ * a dirty VHDX file read-only */
+static int vhdx_parse_log(BlockDriverState *bs, BDRVVHDXState *s)
+{
+    int ret = 0;
+    int i;
+    VHDXHeader *hdr;
+
+    hdr = s->headers[s->curr_header];
+
+    /* either the log guid, or log length is zero,
+     * then a replay log is present */
+    for (i = 0; i < sizeof(hdr->log_guid.data4); i++) {
+        ret |= hdr->log_guid.data4[i];
+    }
+    if (hdr->log_guid.data1 == 0 &&
+        hdr->log_guid.data2 == 0 &&
+        hdr->log_guid.data3 == 0 &&
+        ret == 0) {
+        goto exit;
+    }
+
+    /* per spec, only log version of 0 is supported */
+    if (hdr->log_version != 0) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    if (hdr->log_length == 0) {
+        goto exit;
+    }
+
+    /* We currently do not support images with logs to replay */
+    ret = -ENOTSUP;
+
+exit:
+    return ret;
+}
+
+
+static int vhdx_open(BlockDriverState *bs, QDict *options, int flags)
+{
+    BDRVVHDXState *s = bs->opaque;
+    int ret = 0;
+    uint32_t i;
+    uint64_t signature;
+    uint32_t data_blocks_cnt, bitmap_blocks_cnt;
+
+
+    s->bat = NULL;
+
+    qemu_co_mutex_init(&s->lock);
+
+    /* 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;
+    }
+
+    ret = vhdx_parse_header(bs, s);
+    if (ret) {
+        goto fail;
+    }
+
+    ret = vhdx_parse_log(bs, s);
+    if (ret) {
+        goto fail;
+    }
+
+    ret = vhdx_open_region_tables(bs, s);
+    if (ret) {
+        goto fail;
+    }
+
+    ret = vhdx_parse_metadata(bs, s);
+    if (ret) {
+        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;
+
+    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);
+    }
+
+    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 = qemu_blockalign(bs, s->bat_rt.length);
+
+    ret = bdrv_pread(bs->file, s->bat_offset, s->bat, s->bat_rt.length);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    for (i = 0; i < s->bat_entries; i++) {
+        le64_to_cpus(&s->bat[i]);
+    }
+
+    if (flags & BDRV_O_RDWR) {
+        ret = -ENOTSUP;
+        goto fail;
+    }
+
+    /* TODO: differencing files, read, write */
+
+    return 0;
+fail:
+    qemu_vfree(s->headers[0]);
+    qemu_vfree(s->headers[1]);
+    qemu_vfree(s->bat);
+    qemu_vfree(s->parent_entries);
+    return ret;
+}
+
+static int vhdx_reopen_prepare(BDRVReopenState *state,
+                               BlockReopenQueue *queue, Error **errp)
+{
+    return 0;
+}
+
+
+static coroutine_fn int vhdx_co_readv(BlockDriverState *bs, int64_t sector_num,
+                                      int nb_sectors, QEMUIOVector *qiov)
+{
+    return -ENOTSUP;
+}
+
+
+
+static coroutine_fn int vhdx_co_writev(BlockDriverState *bs, int64_t sector_num,
+                                      int nb_sectors, QEMUIOVector *qiov)
+{
+    return -ENOTSUP;
+}
+
+
+static void vhdx_close(BlockDriverState *bs)
+{
+    BDRVVHDXState *s = bs->opaque;
+    qemu_vfree(s->headers[0]);
+    qemu_vfree(s->headers[1]);
+    qemu_vfree(s->bat);
+    qemu_vfree(s->parent_entries);
+}
+
+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,
+};
+
+static void bdrv_vhdx_init(void)
+{
+    bdrv_register(&bdrv_vhdx);
+}
+
+block_init(bdrv_vhdx_init);