Archipelago » qemu

/*

 * 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>

/* 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 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 resulting checksum is in the CPU endianness, not necessarily

 *       in the file format endianness (LE).  Any header export to disk should

 *       make sure that vhdx_header_le_export() is used to convert to the

 *       correct endianness

 */

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);

    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);

    }

}

/*

 * 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;

}

/* 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;

    VHDXHeader header_le;

    uint8_t *buffer;

    /* 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;

    }

    /* 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, VHDX_HEADER_SIZE);

    /* we can't assume the extra reserved bytes are 0 */

    ret = bdrv_pread(bs->file, header_offset, buffer, VHDX_HEADER_SIZE);

    if (ret < 0) {

        goto exit;

    }

    /* overwrite the actual VHDXHeader portion */

    memcpy(buffer, inactive_header, sizeof(VHDXHeader));

    inactive_header->checksum =

                        vhdx_update_checksum(buffer, VHDX_HEADER_SIZE,

                                             offsetof(VHDXHeader, checksum));

    vhdx_header_le_export(inactive_header, &header_le);

    ret = bdrv_pwrite_sync(bs->file, header_offset, &header_le,

                           sizeof(VHDXHeader));

    if (ret < 0) {

        goto exit;

    }

    s->curr_header = hdr_idx;

exit:

    qemu_vfree(buffer);

    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 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 & 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));

    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;

        }

    }

    vhdx_region_register(s, s->headers[s->curr_header]->log_offset,

                            s->headers[s->curr_header]->log_length);

    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);

        /* 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);

    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;

}

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;

    uint32_t data_blocks_cnt, bitmap_blocks_cnt;

    bool log_flushed = false;

    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);

    ret = vhdx_parse_header(bs, s);

    if (ret < 0) {

        goto fail;

    }

    ret = vhdx_parse_log(bs, s, &log_flushed);

    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;

    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 is freed in vhdx_close() */

    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;

    }