Archipelago » qemu

/*

 * Block driver for the VMDK format

 *

 * Copyright (c) 2004 Fabrice Bellard

 * Copyright (c) 2005 Filip Navara

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL

 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

 * THE SOFTWARE.

 */

#include "qemu-common.h"

#include "block_int.h"

#include "module.h"

#define VMDK3_MAGIC (('C' << 24) | ('O' << 16) | ('W' << 8) | 'D')

#define VMDK4_MAGIC (('K' << 24) | ('D' << 16) | ('M' << 8) | 'V')

typedef struct {

    uint32_t version;

    uint32_t flags;

    uint32_t disk_sectors;

    uint32_t granularity;

    uint32_t l1dir_offset;

    uint32_t l1dir_size;

    uint32_t file_sectors;

    uint32_t cylinders;

    uint32_t heads;

    uint32_t sectors_per_track;

} VMDK3Header;

typedef struct {

    uint32_t version;

    uint32_t flags;

    int64_t capacity;

    int64_t granularity;

    int64_t desc_offset;

    int64_t desc_size;

    int32_t num_gtes_per_gte;

    int64_t rgd_offset;

    int64_t gd_offset;

    int64_t grain_offset;

    char filler[1];

    char check_bytes[4];

} __attribute__((packed)) VMDK4Header;

#define L2_CACHE_SIZE 16

typedef struct VmdkExtent {

    BlockDriverState *file;

    bool flat;

    int64_t sectors;

    int64_t end_sector;

    int64_t l1_table_offset;

    int64_t l1_backup_table_offset;

    uint32_t *l1_table;

    uint32_t *l1_backup_table;

    unsigned int l1_size;

    uint32_t l1_entry_sectors;

    unsigned int l2_size;

    uint32_t *l2_cache;

    uint32_t l2_cache_offsets[L2_CACHE_SIZE];

    uint32_t l2_cache_counts[L2_CACHE_SIZE];

    unsigned int cluster_sectors;

} VmdkExtent;

typedef struct BDRVVmdkState {

    uint32_t parent_cid;

    int num_extents;

    /* Extent array with num_extents entries, ascend ordered by address */

    VmdkExtent *extents;

} BDRVVmdkState;

typedef struct VmdkMetaData {

    uint32_t offset;

    unsigned int l1_index;

    unsigned int l2_index;

    unsigned int l2_offset;

    int valid;

} VmdkMetaData;

static int vmdk_probe(const uint8_t *buf, int buf_size, const char *filename)

{

    uint32_t magic;

    if (buf_size < 4)

        return 0;

    magic = be32_to_cpu(*(uint32_t *)buf);

    if (magic == VMDK3_MAGIC ||

        magic == VMDK4_MAGIC) {

        return 100;

    } else {

        const char *p = (const char *)buf;

        const char *end = p + buf_size;

        while (p < end) {

            if (*p == '#') {

                /* skip comment line */

                while (p < end && *p != '\n') {

                    p++;

                }

                p++;

                continue;

            }

            if (*p == ' ') {

                while (p < end && *p == ' ') {

                    p++;

                }

                /* skip '\r' if windows line endings used. */

                if (p < end && *p == '\r') {

                    p++;

                }

                /* only accept blank lines before 'version=' line */

                if (p == end || *p != '\n') {

                    return 0;

                }

                p++;

                continue;

            }

            if (end - p >= strlen("version=X\n")) {

                if (strncmp("version=1\n", p, strlen("version=1\n")) == 0 ||

                    strncmp("version=2\n", p, strlen("version=2\n")) == 0) {

                    return 100;

                }

            }

            if (end - p >= strlen("version=X\r\n")) {

                if (strncmp("version=1\r\n", p, strlen("version=1\r\n")) == 0 ||

                    strncmp("version=2\r\n", p, strlen("version=2\r\n")) == 0) {

                    return 100;

                }

            }

            return 0;

        }

        return 0;

    }

}

#define CHECK_CID 1

#define SECTOR_SIZE 512

#define DESC_SIZE 20*SECTOR_SIZE        // 20 sectors of 512 bytes each

#define HEADER_SIZE 512                           // first sector of 512 bytes

static void vmdk_free_extents(BlockDriverState *bs)

{

    int i;

    BDRVVmdkState *s = bs->opaque;

    for (i = 0; i < s->num_extents; i++) {

        qemu_free(s->extents[i].l1_table);

        qemu_free(s->extents[i].l2_cache);

        qemu_free(s->extents[i].l1_backup_table);

    }

    qemu_free(s->extents);

}

static uint32_t vmdk_read_cid(BlockDriverState *bs, int parent)

{

    char desc[DESC_SIZE];

    uint32_t cid;

    const char *p_name, *cid_str;

    size_t cid_str_size;

    /* the descriptor offset = 0x200 */

    if (bdrv_pread(bs->file, 0x200, desc, DESC_SIZE) != DESC_SIZE)

        return 0;

    if (parent) {

        cid_str = "parentCID";

        cid_str_size = sizeof("parentCID");

    } else {

        cid_str = "CID";

        cid_str_size = sizeof("CID");

    }

    if ((p_name = strstr(desc,cid_str)) != NULL) {

        p_name += cid_str_size;

        sscanf(p_name,"%x",&cid);

    }

    return cid;

}

static int vmdk_write_cid(BlockDriverState *bs, uint32_t cid)

{

    char desc[DESC_SIZE], tmp_desc[DESC_SIZE];

    char *p_name, *tmp_str;

    /* the descriptor offset = 0x200 */

    if (bdrv_pread(bs->file, 0x200, desc, DESC_SIZE) != DESC_SIZE)

        return -1;

    tmp_str = strstr(desc,"parentCID");

    pstrcpy(tmp_desc, sizeof(tmp_desc), tmp_str);

    if ((p_name = strstr(desc,"CID")) != NULL) {

        p_name += sizeof("CID");

        snprintf(p_name, sizeof(desc) - (p_name - desc), "%x\n", cid);

        pstrcat(desc, sizeof(desc), tmp_desc);

    }

    if (bdrv_pwrite_sync(bs->file, 0x200, desc, DESC_SIZE) < 0)

        return -1;

    return 0;

}

static int vmdk_is_cid_valid(BlockDriverState *bs)

{

#ifdef CHECK_CID

    BDRVVmdkState *s = bs->opaque;

    BlockDriverState *p_bs = bs->backing_hd;

    uint32_t cur_pcid;

    if (p_bs) {

        cur_pcid = vmdk_read_cid(p_bs,0);

        if (s->parent_cid != cur_pcid)

            // CID not valid

            return 0;

    }

#endif

    // CID valid

    return 1;

}

static int vmdk_snapshot_create(const char *filename, const char *backing_file)

{

    int snp_fd, p_fd;

    int ret;

    uint32_t p_cid;

    char *p_name, *gd_buf, *rgd_buf;

    const char *real_filename, *temp_str;

    VMDK4Header header;

    uint32_t gde_entries, gd_size;

    int64_t gd_offset, rgd_offset, capacity, gt_size;

    char p_desc[DESC_SIZE], s_desc[DESC_SIZE], hdr[HEADER_SIZE];

    static const char desc_template[] =

    "# Disk DescriptorFile\n"

    "version=1\n"

    "CID=%x\n"

    "parentCID=%x\n"

    "createType=\"monolithicSparse\"\n"

    "parentFileNameHint=\"%s\"\n"

    "\n"

    "# Extent description\n"

    "RW %u SPARSE \"%s\"\n"

    "\n"

    "# The Disk Data Base \n"

    "#DDB\n"

    "\n";

    snp_fd = open(filename, O_RDWR | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE, 0644);

    if (snp_fd < 0)

        return -errno;

    p_fd = open(backing_file, O_RDONLY | O_BINARY | O_LARGEFILE);

    if (p_fd < 0) {

        close(snp_fd);

        return -errno;

    }

    /* read the header */

    if (lseek(p_fd, 0x0, SEEK_SET) == -1) {

        ret = -errno;

        goto fail;

    }

    if (read(p_fd, hdr, HEADER_SIZE) != HEADER_SIZE) {

        ret = -errno;

        goto fail;

    }

    /* write the header */

    if (lseek(snp_fd, 0x0, SEEK_SET) == -1) {

        ret = -errno;

        goto fail;

    }

    if (write(snp_fd, hdr, HEADER_SIZE) == -1) {

        ret = -errno;

        goto fail;

    }

    memset(&header, 0, sizeof(header));

    memcpy(&header,&hdr[4], sizeof(header)); // skip the VMDK4_MAGIC

    if (ftruncate(snp_fd, header.grain_offset << 9)) {

        ret = -errno;

        goto fail;

    }

    /* the descriptor offset = 0x200 */

    if (lseek(p_fd, 0x200, SEEK_SET) == -1) {

        ret = -errno;

        goto fail;

    }

    if (read(p_fd, p_desc, DESC_SIZE) != DESC_SIZE) {

        ret = -errno;

        goto fail;

    }

    if ((p_name = strstr(p_desc,"CID")) != NULL) {

        p_name += sizeof("CID");

        sscanf(p_name,"%x",&p_cid);

    }

    real_filename = filename;

    if ((temp_str = strrchr(real_filename, '\\')) != NULL)

        real_filename = temp_str + 1;

    if ((temp_str = strrchr(real_filename, '/')) != NULL)

        real_filename = temp_str + 1;

    if ((temp_str = strrchr(real_filename, ':')) != NULL)

        real_filename = temp_str + 1;

    snprintf(s_desc, sizeof(s_desc), desc_template, p_cid, p_cid, backing_file,

             (uint32_t)header.capacity, real_filename);

    /* write the descriptor */

    if (lseek(snp_fd, 0x200, SEEK_SET) == -1) {

        ret = -errno;

        goto fail;

    }

    if (write(snp_fd, s_desc, strlen(s_desc)) == -1) {

        ret = -errno;

        goto fail;

    }

    gd_offset = header.gd_offset * SECTOR_SIZE;     // offset of GD table

    rgd_offset = header.rgd_offset * SECTOR_SIZE;   // offset of RGD table

    capacity = header.capacity * SECTOR_SIZE;       // Extent size

    /*

     * Each GDE span 32M disk, means:

     * 512 GTE per GT, each GTE points to grain

     */

    gt_size = (int64_t)header.num_gtes_per_gte * header.granularity * SECTOR_SIZE;

    if (!gt_size) {

        ret = -EINVAL;

        goto fail;

    }

    gde_entries = (uint32_t)(capacity / gt_size);  // number of gde/rgde

    gd_size = gde_entries * sizeof(uint32_t);

    /* write RGD */

    rgd_buf = qemu_malloc(gd_size);

    if (lseek(p_fd, rgd_offset, SEEK_SET) == -1) {

        ret = -errno;

        goto fail_rgd;

    }

    if (read(p_fd, rgd_buf, gd_size) != gd_size) {

        ret = -errno;

        goto fail_rgd;

    }

    if (lseek(snp_fd, rgd_offset, SEEK_SET) == -1) {

        ret = -errno;

        goto fail_rgd;

    }

    if (write(snp_fd, rgd_buf, gd_size) == -1) {

        ret = -errno;

        goto fail_rgd;

    }

    /* write GD */

    gd_buf = qemu_malloc(gd_size);

    if (lseek(p_fd, gd_offset, SEEK_SET) == -1) {

        ret = -errno;

        goto fail_gd;

    }

    if (read(p_fd, gd_buf, gd_size) != gd_size) {

        ret = -errno;

        goto fail_gd;

    }

    if (lseek(snp_fd, gd_offset, SEEK_SET) == -1) {

        ret = -errno;

        goto fail_gd;

    }

    if (write(snp_fd, gd_buf, gd_size) == -1) {

        ret = -errno;

        goto fail_gd;

    }

    ret = 0;

fail_gd:

    qemu_free(gd_buf);

fail_rgd:

    qemu_free(rgd_buf);

fail:

    close(p_fd);

    close(snp_fd);

    return ret;

}

static int vmdk_parent_open(BlockDriverState *bs)

{

    char *p_name;

    char desc[DESC_SIZE];

    /* the descriptor offset = 0x200 */

    if (bdrv_pread(bs->file, 0x200, desc, DESC_SIZE) != DESC_SIZE)

        return -1;

    if ((p_name = strstr(desc,"parentFileNameHint")) != NULL) {

        char *end_name;

        p_name += sizeof("parentFileNameHint") + 1;

        if ((end_name = strchr(p_name,'\"')) == NULL)

            return -1;

        if ((end_name - p_name) > sizeof (bs->backing_file) - 1)

            return -1;

        pstrcpy(bs->backing_file, end_name - p_name + 1, p_name);

    }

    return 0;

}

/* Create and append extent to the extent array. Return the added VmdkExtent

 * address. return NULL if allocation failed. */

static VmdkExtent *vmdk_add_extent(BlockDriverState *bs,

                           BlockDriverState *file, bool flat, int64_t sectors,

                           int64_t l1_offset, int64_t l1_backup_offset,

                           uint32_t l1_size,

                           int l2_size, unsigned int cluster_sectors)

{

    VmdkExtent *extent;

    BDRVVmdkState *s = bs->opaque;

    s->extents = qemu_realloc(s->extents,

                              (s->num_extents + 1) * sizeof(VmdkExtent));

    extent = &s->extents[s->num_extents];

    s->num_extents++;

    memset(extent, 0, sizeof(VmdkExtent));

    extent->file = file;

    extent->flat = flat;

    extent->sectors = sectors;

    extent->l1_table_offset = l1_offset;

    extent->l1_backup_table_offset = l1_backup_offset;

    extent->l1_size = l1_size;

    extent->l1_entry_sectors = l2_size * cluster_sectors;

    extent->l2_size = l2_size;

    extent->cluster_sectors = cluster_sectors;

    if (s->num_extents > 1) {

        extent->end_sector = (*(extent - 1)).end_sector + extent->sectors;

    } else {

        extent->end_sector = extent->sectors;

    }

    bs->total_sectors = extent->end_sector;

    return extent;

}

static int vmdk_init_tables(BlockDriverState *bs, VmdkExtent *extent)

{

    int ret;

    int l1_size, i;

    /* read the L1 table */

    l1_size = extent->l1_size * sizeof(uint32_t);

    extent->l1_table = qemu_malloc(l1_size);

    ret = bdrv_pread(extent->file,

                    extent->l1_table_offset,

                    extent->l1_table,

                    l1_size);

    if (ret < 0) {

        goto fail_l1;

    }

    for (i = 0; i < extent->l1_size; i++) {

        le32_to_cpus(&extent->l1_table[i]);

    }

    if (extent->l1_backup_table_offset) {

        extent->l1_backup_table = qemu_malloc(l1_size);

        ret = bdrv_pread(extent->file,

                        extent->l1_backup_table_offset,

                        extent->l1_backup_table,

                        l1_size);

        if (ret < 0) {

            goto fail_l1b;

        }

        for (i = 0; i < extent->l1_size; i++) {

            le32_to_cpus(&extent->l1_backup_table[i]);

        }

    }

    extent->l2_cache =

        qemu_malloc(extent->l2_size * L2_CACHE_SIZE * sizeof(uint32_t));

    return 0;

 fail_l1b:

    qemu_free(extent->l1_backup_table);

 fail_l1:

    qemu_free(extent->l1_table);

    return ret;

}

static int vmdk_open_vmdk3(BlockDriverState *bs, int flags)

{

    int ret;

    uint32_t magic;

    VMDK3Header header;

    VmdkExtent *extent;

    ret = bdrv_pread(bs->file, sizeof(magic), &header, sizeof(header));

    if (ret < 0) {

        goto fail;

    }

    extent = vmdk_add_extent(bs,

                             bs->file, false,

                             le32_to_cpu(header.disk_sectors),

                             le32_to_cpu(header.l1dir_offset) << 9,

                             0, 1 << 6, 1 << 9,

                             le32_to_cpu(header.granularity));

    ret = vmdk_init_tables(bs, extent);

    if (ret) {

        /* vmdk_init_tables cleans up on fail, so only free allocation of

         * vmdk_add_extent here. */

        goto fail;

    }

    return 0;

 fail:

    vmdk_free_extents(bs);

    return ret;

}

static int vmdk_open_vmdk4(BlockDriverState *bs, int flags)

{

    int ret;

    uint32_t magic;

    uint32_t l1_size, l1_entry_sectors;

    VMDK4Header header;

    BDRVVmdkState *s = bs->opaque;

    VmdkExtent *extent;

    ret = bdrv_pread(bs->file, sizeof(magic), &header, sizeof(header));

    if (ret < 0) {

        goto fail;

    }

    l1_entry_sectors = le32_to_cpu(header.num_gtes_per_gte)

                        * le64_to_cpu(header.granularity);

    l1_size = (le64_to_cpu(header.capacity) + l1_entry_sectors - 1)

                / l1_entry_sectors;

    extent = vmdk_add_extent(bs, bs->file, false,

                          le64_to_cpu(header.capacity),

                          le64_to_cpu(header.gd_offset) << 9,

                          le64_to_cpu(header.rgd_offset) << 9,

                          l1_size,

                          le32_to_cpu(header.num_gtes_per_gte),

                          le64_to_cpu(header.granularity));

    if (extent->l1_entry_sectors <= 0) {

        ret = -EINVAL;

        goto fail;

    }

    /* try to open parent images, if exist */

    ret = vmdk_parent_open(bs);

    if (ret) {

        goto fail;

    }

    s->parent_cid = vmdk_read_cid(bs, 1);

    ret = vmdk_init_tables(bs, extent);

    if (ret) {

        goto fail;

    }

    return 0;

 fail:

    vmdk_free_extents(bs);

    return ret;

}

static int vmdk_open(BlockDriverState *bs, int flags)

{

    uint32_t magic;

    if (bdrv_pread(bs->file, 0, &magic, sizeof(magic)) != sizeof(magic)) {

        return -EIO;

    }

    magic = be32_to_cpu(magic);

    if (magic == VMDK3_MAGIC) {

        return vmdk_open_vmdk3(bs, flags);

    } else if (magic == VMDK4_MAGIC) {

        return vmdk_open_vmdk4(bs, flags);

    } else {

        return -EINVAL;

    }

}

static int get_whole_cluster(BlockDriverState *bs,

                VmdkExtent *extent,

                uint64_t cluster_offset,

                uint64_t offset,

                bool allocate)

{

    /* 128 sectors * 512 bytes each = grain size 64KB */

    uint8_t  whole_grain[extent->cluster_sectors * 512];

    /* we will be here if it's first write on non-exist grain(cluster).

     * try to read from parent image, if exist */

    if (bs->backing_hd) {

        int ret;

        if (!vmdk_is_cid_valid(bs))

            return -1;

        /* floor offset to cluster */

        offset -= offset % (extent->cluster_sectors * 512);

        ret = bdrv_read(bs->backing_hd, offset >> 9, whole_grain,

                extent->cluster_sectors);

        if (ret < 0) {

            return -1;

        }

        /* Write grain only into the active image */

        ret = bdrv_write(extent->file, cluster_offset, whole_grain,

                extent->cluster_sectors);

        if (ret < 0) {

            return -1;

        }

    }

    return 0;

}

static int vmdk_L2update(VmdkExtent *extent, VmdkMetaData *m_data)

{

    /* update L2 table */

    if (bdrv_pwrite_sync(

                extent->file,

                ((int64_t)m_data->l2_offset * 512)

                    + (m_data->l2_index * sizeof(m_data->offset)),

                &(m_data->offset),

                sizeof(m_data->offset)

            ) < 0) {

        return -1;

    }

    /* update backup L2 table */

    if (extent->l1_backup_table_offset != 0) {

        m_data->l2_offset = extent->l1_backup_table[m_data->l1_index];

        if (bdrv_pwrite_sync(

                    extent->file,

                    ((int64_t)m_data->l2_offset * 512)

                        + (m_data->l2_index * sizeof(m_data->offset)),

                    &(m_data->offset), sizeof(m_data->offset)

                ) < 0) {

            return -1;

        }

    }

    return 0;

}

static uint64_t get_cluster_offset(BlockDriverState *bs,

                                    VmdkExtent *extent,

                                    VmdkMetaData *m_data,

                                    uint64_t offset, int allocate)

{

    unsigned int l1_index, l2_offset, l2_index;

    int min_index, i, j;

    uint32_t min_count, *l2_table, tmp = 0;

    uint64_t cluster_offset;

    if (m_data)

        m_data->valid = 0;

    l1_index = (offset >> 9) / extent->l1_entry_sectors;

    if (l1_index >= extent->l1_size) {

        return 0;

    }

    l2_offset = extent->l1_table[l1_index];

    if (!l2_offset) {

        return 0;

    }

    for (i = 0; i < L2_CACHE_SIZE; i++) {

        if (l2_offset == extent->l2_cache_offsets[i]) {

            /* increment the hit count */

            if (++extent->l2_cache_counts[i] == 0xffffffff) {

                for (j = 0; j < L2_CACHE_SIZE; j++) {

                    extent->l2_cache_counts[j] >>= 1;

                }

            }

            l2_table = extent->l2_cache + (i * extent->l2_size);

            goto found;

        }

    }

    /* not found: load a new entry in the least used one */

    min_index = 0;

    min_count = 0xffffffff;

    for (i = 0; i < L2_CACHE_SIZE; i++) {

        if (extent->l2_cache_counts[i] < min_count) {

            min_count = extent->l2_cache_counts[i];

            min_index = i;

        }

    }

    l2_table = extent->l2_cache + (min_index * extent->l2_size);

    if (bdrv_pread(

                extent->file,

                (int64_t)l2_offset * 512,

                l2_table,

                extent->l2_size * sizeof(uint32_t)

            ) != extent->l2_size * sizeof(uint32_t)) {

        return 0;

    }

    extent->l2_cache_offsets[min_index] = l2_offset;

    extent->l2_cache_counts[min_index] = 1;

 found:

    l2_index = ((offset >> 9) / extent->cluster_sectors) % extent->l2_size;

    cluster_offset = le32_to_cpu(l2_table[l2_index]);

    if (!cluster_offset) {

        if (!allocate)

            return 0;

        // Avoid the L2 tables update for the images that have snapshots.

        cluster_offset = bdrv_getlength(extent->file);

        bdrv_truncate(

            extent->file,

            cluster_offset + (extent->cluster_sectors << 9)

        );

        cluster_offset >>= 9;

        tmp = cpu_to_le32(cluster_offset);

        l2_table[l2_index] = tmp;

        /* First of all we write grain itself, to avoid race condition

         * that may to corrupt the image.

         * This problem may occur because of insufficient space on host disk

         * or inappropriate VM shutdown.

         */

        if (get_whole_cluster(

                bs, extent, cluster_offset, offset, allocate) == -1)

            return 0;

        if (m_data) {

            m_data->offset = tmp;

            m_data->l1_index = l1_index;

            m_data->l2_index = l2_index;

            m_data->l2_offset = l2_offset;

            m_data->valid = 1;

        }

    }

    cluster_offset <<= 9;

    return cluster_offset;

}

static VmdkExtent *find_extent(BDRVVmdkState *s,

                                int64_t sector_num, VmdkExtent *start_hint)

{

    VmdkExtent *extent = start_hint;

    if (!extent) {

        extent = &s->extents[0];

    }

    while (extent < &s->extents[s->num_extents]) {

        if (sector_num < extent->end_sector) {

            return extent;

        }

        extent++;

    }

    return NULL;

}

static int vmdk_is_allocated(BlockDriverState *bs, int64_t sector_num,

                             int nb_sectors, int *pnum)

{

    BDRVVmdkState *s = bs->opaque;

    int64_t index_in_cluster, n, ret;

    uint64_t offset;

    VmdkExtent *extent;

    extent = find_extent(s, sector_num, NULL);

    if (!extent) {

        return 0;

    }

    if (extent->flat) {

        n = extent->end_sector - sector_num;

        ret = 1;

    } else {

        offset = get_cluster_offset(bs, extent, NULL, sector_num * 512, 0);

        index_in_cluster = sector_num % extent->cluster_sectors;

        n = extent->cluster_sectors - index_in_cluster;

        ret = offset ? 1 : 0;

    }

    if (n > nb_sectors)

        n = nb_sectors;

    *pnum = n;

    return ret;

}

static int vmdk_read(BlockDriverState *bs, int64_t sector_num,

                    uint8_t *buf, int nb_sectors)

{

    BDRVVmdkState *s = bs->opaque;

    int ret;

    uint64_t n, index_in_cluster;

    VmdkExtent *extent = NULL;

    uint64_t cluster_offset;

    while (nb_sectors > 0) {

        extent = find_extent(s, sector_num, extent);

        if (!extent) {

            return -EIO;

        }

        cluster_offset = get_cluster_offset(

                            bs, extent, NULL, sector_num << 9, 0);

        index_in_cluster = sector_num % extent->cluster_sectors;

        n = extent->cluster_sectors - index_in_cluster;

        if (n > nb_sectors)

            n = nb_sectors;

        if (!cluster_offset) {

            // try to read from parent image, if exist

            if (bs->backing_hd) {

                if (!vmdk_is_cid_valid(bs))

                    return -1;

                ret = bdrv_read(bs->backing_hd, sector_num, buf, n);

                if (ret < 0)

                    return -1;

            } else {

                memset(buf, 0, 512 * n);

            }

        } else {

            if(bdrv_pread(bs->file, cluster_offset + index_in_cluster * 512, buf, n * 512) != n * 512)

                return -1;

        }

        nb_sectors -= n;

        sector_num += n;

        buf += n * 512;

    }

    return 0;

}

static int vmdk_write(BlockDriverState *bs, int64_t sector_num,

                     const uint8_t *buf, int nb_sectors)

{

    BDRVVmdkState *s = bs->opaque;

    VmdkExtent *extent = NULL;

    int n;

    int64_t index_in_cluster;

    uint64_t cluster_offset;

    static int cid_update = 0;

    VmdkMetaData m_data;

    if (sector_num > bs->total_sectors) {

        fprintf(stderr,

                "(VMDK) Wrong offset: sector_num=0x%" PRIx64

                " total_sectors=0x%" PRIx64 "\n",

                sector_num, bs->total_sectors);

        return -1;

    }

    while (nb_sectors > 0) {

        extent = find_extent(s, sector_num, extent);

        if (!extent) {

            return -EIO;

        }

        cluster_offset = get_cluster_offset(

                                bs,

                                extent,

                                &m_data,

                                sector_num << 9, 1);

        if (!cluster_offset) {

            return -1;

        }

        index_in_cluster = sector_num % extent->cluster_sectors;

        n = extent->cluster_sectors - index_in_cluster;

        if (n > nb_sectors) {

            n = nb_sectors;

        }

        if (bdrv_pwrite(bs->file,

                        cluster_offset + index_in_cluster * 512,

                        buf, n * 512)

                != n * 512) {

            return -1;

        }

        if (m_data.valid) {

            /* update L2 tables */

            if (vmdk_L2update(extent, &m_data) == -1) {