Archipelago » qemu

/*

 * Block driver for the QCOW format

 *

 * Copyright (c) 2004-2006 Fabrice Bellard

 *

 * 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/block_int.h"

#include "qemu/module.h"

#include <zlib.h>

#include "qemu/aes.h"

#include "migration/migration.h"

/**************************************************************/

/* QEMU COW block driver with compression and encryption support */

#define QCOW_MAGIC (('Q' << 24) | ('F' << 16) | ('I' << 8) | 0xfb)

#define QCOW_VERSION 1

#define QCOW_CRYPT_NONE 0

#define QCOW_CRYPT_AES  1

#define QCOW_OFLAG_COMPRESSED (1LL << 63)

typedef struct QCowHeader {

    uint32_t magic;

    uint32_t version;

    uint64_t backing_file_offset;

    uint32_t backing_file_size;

    uint32_t mtime;

    uint64_t size; /* in bytes */

    uint8_t cluster_bits;

    uint8_t l2_bits;

    uint32_t crypt_method;

    uint64_t l1_table_offset;

} QCowHeader;

#define L2_CACHE_SIZE 16

typedef struct BDRVQcowState {

    int cluster_bits;

    int cluster_size;

    int cluster_sectors;

    int l2_bits;

    int l2_size;

    int l1_size;

    uint64_t cluster_offset_mask;

    uint64_t l1_table_offset;

    uint64_t *l1_table;

    uint64_t *l2_cache;

    uint64_t l2_cache_offsets[L2_CACHE_SIZE];

    uint32_t l2_cache_counts[L2_CACHE_SIZE];

    uint8_t *cluster_cache;

    uint8_t *cluster_data;

    uint64_t cluster_cache_offset;

    uint32_t crypt_method; /* current crypt method, 0 if no key yet */

    uint32_t crypt_method_header;

    AES_KEY aes_encrypt_key;

    AES_KEY aes_decrypt_key;

    CoMutex lock;

    Error *migration_blocker;

} BDRVQcowState;

static int decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset);

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

{

    const QCowHeader *cow_header = (const void *)buf;

    if (buf_size >= sizeof(QCowHeader) &&

        be32_to_cpu(cow_header->magic) == QCOW_MAGIC &&

        be32_to_cpu(cow_header->version) == QCOW_VERSION)

        return 100;

    else

        return 0;

}

static int qcow_open(BlockDriverState *bs, QDict *options, int flags,

                     Error **errp)

{

    BDRVQcowState *s = bs->opaque;

    int len, i, shift, ret;

    QCowHeader header;

    ret = bdrv_pread(bs->file, 0, &header, sizeof(header));

    if (ret < 0) {

        goto fail;

    }

    be32_to_cpus(&header.magic);

    be32_to_cpus(&header.version);

    be64_to_cpus(&header.backing_file_offset);

    be32_to_cpus(&header.backing_file_size);

    be32_to_cpus(&header.mtime);

    be64_to_cpus(&header.size);

    be32_to_cpus(&header.crypt_method);

    be64_to_cpus(&header.l1_table_offset);

    if (header.magic != QCOW_MAGIC) {

        ret = -EMEDIUMTYPE;

        goto fail;

    }

    if (header.version != QCOW_VERSION) {

        char version[64];

        snprintf(version, sizeof(version), "QCOW version %d", header.version);

        qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,

            bs->device_name, "qcow", version);

        ret = -ENOTSUP;

        goto fail;

    }

    if (header.size <= 1 || header.cluster_bits < 9) {

        ret = -EINVAL;

        goto fail;

    }

    if (header.crypt_method > QCOW_CRYPT_AES) {

        ret = -EINVAL;

        goto fail;

    }

    s->crypt_method_header = header.crypt_method;

    if (s->crypt_method_header) {

        bs->encrypted = 1;

    }

    s->cluster_bits = header.cluster_bits;

    s->cluster_size = 1 << s->cluster_bits;

    s->cluster_sectors = 1 << (s->cluster_bits - 9);

    s->l2_bits = header.l2_bits;

    s->l2_size = 1 << s->l2_bits;

    bs->total_sectors = header.size / 512;

    s->cluster_offset_mask = (1LL << (63 - s->cluster_bits)) - 1;

    /* read the level 1 table */

    shift = s->cluster_bits + s->l2_bits;

    s->l1_size = (header.size + (1LL << shift) - 1) >> shift;

    s->l1_table_offset = header.l1_table_offset;

    s->l1_table = g_malloc(s->l1_size * sizeof(uint64_t));

    ret = bdrv_pread(bs->file, s->l1_table_offset, s->l1_table,

               s->l1_size * sizeof(uint64_t));

    if (ret < 0) {

        goto fail;

    }

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

        be64_to_cpus(&s->l1_table[i]);

    }

    /* alloc L2 cache */

    s->l2_cache = g_malloc(s->l2_size * L2_CACHE_SIZE * sizeof(uint64_t));

    s->cluster_cache = g_malloc(s->cluster_size);

    s->cluster_data = g_malloc(s->cluster_size);

    s->cluster_cache_offset = -1;

    /* read the backing file name */

    if (header.backing_file_offset != 0) {

        len = header.backing_file_size;

        if (len > 1023) {

            len = 1023;

        }

        ret = bdrv_pread(bs->file, header.backing_file_offset,

                   bs->backing_file, len);

        if (ret < 0) {

            goto fail;

        }

        bs->backing_file[len] = '\0';

    }

    /* Disable migration when qcow images are used */

    error_set(&s->migration_blocker,

              QERR_BLOCK_FORMAT_FEATURE_NOT_SUPPORTED,

              "qcow", bs->device_name, "live migration");

    migrate_add_blocker(s->migration_blocker);

    qemu_co_mutex_init(&s->lock);

    return 0;

 fail:

    g_free(s->l1_table);

    g_free(s->l2_cache);

    g_free(s->cluster_cache);

    g_free(s->cluster_data);

    return ret;

}

/* We have nothing to do for QCOW reopen, stubs just return

 * success */

static int qcow_reopen_prepare(BDRVReopenState *state,

                               BlockReopenQueue *queue, Error **errp)

{

    return 0;

}

static int qcow_set_key(BlockDriverState *bs, const char *key)

{

    BDRVQcowState *s = bs->opaque;

    uint8_t keybuf[16];

    int len, i;

    memset(keybuf, 0, 16);

    len = strlen(key);

    if (len > 16)

        len = 16;

    /* XXX: we could compress the chars to 7 bits to increase

       entropy */

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

        keybuf[i] = key[i];

    }

    s->crypt_method = s->crypt_method_header;

    if (AES_set_encrypt_key(keybuf, 128, &s->aes_encrypt_key) != 0)

        return -1;

    if (AES_set_decrypt_key(keybuf, 128, &s->aes_decrypt_key) != 0)

        return -1;

    return 0;

}

/* The crypt function is compatible with the linux cryptoloop

   algorithm for < 4 GB images. NOTE: out_buf == in_buf is

   supported */

static void encrypt_sectors(BDRVQcowState *s, int64_t sector_num,

                            uint8_t *out_buf, const uint8_t *in_buf,

                            int nb_sectors, int enc,

                            const AES_KEY *key)

{

    union {

        uint64_t ll[2];

        uint8_t b[16];

    } ivec;

    int i;

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

        ivec.ll[0] = cpu_to_le64(sector_num);

        ivec.ll[1] = 0;

        AES_cbc_encrypt(in_buf, out_buf, 512, key,

                        ivec.b, enc);

        sector_num++;

        in_buf += 512;

        out_buf += 512;

    }

}

/* 'allocate' is:

 *

 * 0 to not allocate.

 *

 * 1 to allocate a normal cluster (for sector indexes 'n_start' to

 * 'n_end')

 *

 * 2 to allocate a compressed cluster of size

 * 'compressed_size'. 'compressed_size' must be > 0 and <

 * cluster_size

 *

 * return 0 if not allocated.

 */

static uint64_t get_cluster_offset(BlockDriverState *bs,

                                   uint64_t offset, int allocate,

                                   int compressed_size,

                                   int n_start, int n_end)

{

    BDRVQcowState *s = bs->opaque;

    int min_index, i, j, l1_index, l2_index;

    uint64_t l2_offset, *l2_table, cluster_offset, tmp;

    uint32_t min_count;

    int new_l2_table;

    l1_index = offset >> (s->l2_bits + s->cluster_bits);

    l2_offset = s->l1_table[l1_index];

    new_l2_table = 0;

    if (!l2_offset) {

        if (!allocate)

            return 0;

        /* allocate a new l2 entry */

        l2_offset = bdrv_getlength(bs->file);

        /* round to cluster size */

        l2_offset = (l2_offset + s->cluster_size - 1) & ~(s->cluster_size - 1);

        /* update the L1 entry */

        s->l1_table[l1_index] = l2_offset;

        tmp = cpu_to_be64(l2_offset);

        if (bdrv_pwrite_sync(bs->file,

                s->l1_table_offset + l1_index * sizeof(tmp),

                &tmp, sizeof(tmp)) < 0)

            return 0;

        new_l2_table = 1;

    }

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

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

            /* increment the hit count */

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

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

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

                }

            }

            l2_table = s->l2_cache + (i << s->l2_bits);

            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 (s->l2_cache_counts[i] < min_count) {

            min_count = s->l2_cache_counts[i];

            min_index = i;

        }

    }

    l2_table = s->l2_cache + (min_index << s->l2_bits);

    if (new_l2_table) {

        memset(l2_table, 0, s->l2_size * sizeof(uint64_t));

        if (bdrv_pwrite_sync(bs->file, l2_offset, l2_table,

                s->l2_size * sizeof(uint64_t)) < 0)

            return 0;

    } else {

        if (bdrv_pread(bs->file, l2_offset, l2_table, s->l2_size * sizeof(uint64_t)) !=

            s->l2_size * sizeof(uint64_t))

            return 0;

    }

    s->l2_cache_offsets[min_index] = l2_offset;

    s->l2_cache_counts[min_index] = 1;

 found:

    l2_index = (offset >> s->cluster_bits) & (s->l2_size - 1);

    cluster_offset = be64_to_cpu(l2_table[l2_index]);

    if (!cluster_offset ||

        ((cluster_offset & QCOW_OFLAG_COMPRESSED) && allocate == 1)) {

        if (!allocate)

            return 0;

        /* allocate a new cluster */

        if ((cluster_offset & QCOW_OFLAG_COMPRESSED) &&

            (n_end - n_start) < s->cluster_sectors) {

            /* if the cluster is already compressed, we must

               decompress it in the case it is not completely

               overwritten */

            if (decompress_cluster(bs, cluster_offset) < 0)

                return 0;

            cluster_offset = bdrv_getlength(bs->file);

            cluster_offset = (cluster_offset + s->cluster_size - 1) &

                ~(s->cluster_size - 1);

            /* write the cluster content */

            if (bdrv_pwrite(bs->file, cluster_offset, s->cluster_cache, s->cluster_size) !=

                s->cluster_size)

                return -1;

        } else {

            cluster_offset = bdrv_getlength(bs->file);

            if (allocate == 1) {

                /* round to cluster size */

                cluster_offset = (cluster_offset + s->cluster_size - 1) &

                    ~(s->cluster_size - 1);

                bdrv_truncate(bs->file, cluster_offset + s->cluster_size);

                /* if encrypted, we must initialize the cluster

                   content which won't be written */

                if (s->crypt_method &&

                    (n_end - n_start) < s->cluster_sectors) {

                    uint64_t start_sect;

                    start_sect = (offset & ~(s->cluster_size - 1)) >> 9;

                    memset(s->cluster_data + 512, 0x00, 512);

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

                        if (i < n_start || i >= n_end) {

                            encrypt_sectors(s, start_sect + i,

                                            s->cluster_data,

                                            s->cluster_data + 512, 1, 1,

                                            &s->aes_encrypt_key);

                            if (bdrv_pwrite(bs->file, cluster_offset + i * 512,

                                            s->cluster_data, 512) != 512)

                                return -1;

                        }

                    }

                }

            } else if (allocate == 2) {

                cluster_offset |= QCOW_OFLAG_COMPRESSED |

                    (uint64_t)compressed_size << (63 - s->cluster_bits);

            }

        }

        /* update L2 table */

        tmp = cpu_to_be64(cluster_offset);

        l2_table[l2_index] = tmp;

        if (bdrv_pwrite_sync(bs->file, l2_offset + l2_index * sizeof(tmp),

                &tmp, sizeof(tmp)) < 0)

            return 0;

    }

    return cluster_offset;

}

static int64_t coroutine_fn qcow_co_get_block_status(BlockDriverState *bs,

        int64_t sector_num, int nb_sectors, int *pnum)

{

    BDRVQcowState *s = bs->opaque;

    int index_in_cluster, n;

    uint64_t cluster_offset;

    qemu_co_mutex_lock(&s->lock);

    cluster_offset = get_cluster_offset(bs, sector_num << 9, 0, 0, 0, 0);

    qemu_co_mutex_unlock(&s->lock);

    index_in_cluster = sector_num & (s->cluster_sectors - 1);

    n = s->cluster_sectors - index_in_cluster;

    if (n > nb_sectors)

        n = nb_sectors;

    *pnum = n;

    if (!cluster_offset) {

        return 0;

    }

    if ((cluster_offset & QCOW_OFLAG_COMPRESSED) || s->crypt_method) {

        return BDRV_BLOCK_DATA;

    }

    cluster_offset |= (index_in_cluster << BDRV_SECTOR_BITS);

    return BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID | cluster_offset;

}

static int decompress_buffer(uint8_t *out_buf, int out_buf_size,

                             const uint8_t *buf, int buf_size)

{

    z_stream strm1, *strm = &strm1;

    int ret, out_len;

    memset(strm, 0, sizeof(*strm));

    strm->next_in = (uint8_t *)buf;

    strm->avail_in = buf_size;

    strm->next_out = out_buf;

    strm->avail_out = out_buf_size;

    ret = inflateInit2(strm, -12);

    if (ret != Z_OK)

        return -1;

    ret = inflate(strm, Z_FINISH);

    out_len = strm->next_out - out_buf;

    if ((ret != Z_STREAM_END && ret != Z_BUF_ERROR) ||

        out_len != out_buf_size) {

        inflateEnd(strm);

        return -1;

    }

    inflateEnd(strm);

    return 0;

}

static int decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset)

{

    BDRVQcowState *s = bs->opaque;

    int ret, csize;

    uint64_t coffset;

    coffset = cluster_offset & s->cluster_offset_mask;

    if (s->cluster_cache_offset != coffset) {

        csize = cluster_offset >> (63 - s->cluster_bits);

        csize &= (s->cluster_size - 1);

        ret = bdrv_pread(bs->file, coffset, s->cluster_data, csize);

        if (ret != csize)

            return -1;

        if (decompress_buffer(s->cluster_cache, s->cluster_size,

                              s->cluster_data, csize) < 0) {

            return -1;

        }

        s->cluster_cache_offset = coffset;

    }

    return 0;

}

static coroutine_fn int qcow_co_readv(BlockDriverState *bs, int64_t sector_num,

                         int nb_sectors, QEMUIOVector *qiov)

{

    BDRVQcowState *s = bs->opaque;

    int index_in_cluster;

    int ret = 0, n;

    uint64_t cluster_offset;

    struct iovec hd_iov;

    QEMUIOVector hd_qiov;

    uint8_t *buf;

    void *orig_buf;

    if (qiov->niov > 1) {

        buf = orig_buf = qemu_blockalign(bs, qiov->size);

    } else {

        orig_buf = NULL;

        buf = (uint8_t *)qiov->iov->iov_base;

    }

    qemu_co_mutex_lock(&s->lock);

    while (nb_sectors != 0) {

        /* prepare next request */

        cluster_offset = get_cluster_offset(bs, sector_num << 9,

                                                 0, 0, 0, 0);

        index_in_cluster = sector_num & (s->cluster_sectors - 1);

        n = s->cluster_sectors - index_in_cluster;

        if (n > nb_sectors) {

            n = nb_sectors;

        }

        if (!cluster_offset) {

            if (bs->backing_hd) {

                /* read from the base image */

                hd_iov.iov_base = (void *)buf;

                hd_iov.iov_len = n * 512;

                qemu_iovec_init_external(&hd_qiov, &hd_iov, 1);

                qemu_co_mutex_unlock(&s->lock);

                ret = bdrv_co_readv(bs->backing_hd, sector_num,

                                    n, &hd_qiov);

                qemu_co_mutex_lock(&s->lock);

                if (ret < 0) {

                    goto fail;

                }

            } else {

                /* Note: in this case, no need to wait */

                memset(buf, 0, 512 * n);

            }

        } else if (cluster_offset & QCOW_OFLAG_COMPRESSED) {

            /* add AIO support for compressed blocks ? */

            if (decompress_cluster(bs, cluster_offset) < 0) {

                goto fail;

            }

            memcpy(buf,

                   s->cluster_cache + index_in_cluster * 512, 512 * n);

        } else {

            if ((cluster_offset & 511) != 0) {

                goto fail;

            }

            hd_iov.iov_base = (void *)buf;

            hd_iov.iov_len = n * 512;

            qemu_iovec_init_external(&hd_qiov, &hd_iov, 1);

            qemu_co_mutex_unlock(&s->lock);

            ret = bdrv_co_readv(bs->file,

                                (cluster_offset >> 9) + index_in_cluster,

                                n, &hd_qiov);

            qemu_co_mutex_lock(&s->lock);

            if (ret < 0) {

                break;

            }

            if (s->crypt_method) {

                encrypt_sectors(s, sector_num, buf, buf,

                                n, 0,

                                &s->aes_decrypt_key);

            }

        }

        ret = 0;

        nb_sectors -= n;

        sector_num += n;

        buf += n * 512;

    }

done:

    qemu_co_mutex_unlock(&s->lock);

    if (qiov->niov > 1) {

        qemu_iovec_from_buf(qiov, 0, orig_buf, qiov->size);

        qemu_vfree(orig_buf);

    }

    return ret;

fail:

    ret = -EIO;

    goto done;

}

static coroutine_fn int qcow_co_writev(BlockDriverState *bs, int64_t sector_num,

                          int nb_sectors, QEMUIOVector *qiov)

{

    BDRVQcowState *s = bs->opaque;

    int index_in_cluster;

    uint64_t cluster_offset;

    const uint8_t *src_buf;

    int ret = 0, n;

    uint8_t *cluster_data = NULL;

    struct iovec hd_iov;

    QEMUIOVector hd_qiov;

    uint8_t *buf;

    void *orig_buf;

    s->cluster_cache_offset = -1; /* disable compressed cache */

    if (qiov->niov > 1) {

        buf = orig_buf = qemu_blockalign(bs, qiov->size);

        qemu_iovec_to_buf(qiov, 0, buf, qiov->size);

    } else {

        orig_buf = NULL;

        buf = (uint8_t *)qiov->iov->iov_base;

    }

    qemu_co_mutex_lock(&s->lock);

    while (nb_sectors != 0) {

        index_in_cluster = sector_num & (s->cluster_sectors - 1);

        n = s->cluster_sectors - index_in_cluster;

        if (n > nb_sectors) {

            n = nb_sectors;

        }

        cluster_offset = get_cluster_offset(bs, sector_num << 9, 1, 0,

                                            index_in_cluster,

                                            index_in_cluster + n);

        if (!cluster_offset || (cluster_offset & 511) != 0) {

            ret = -EIO;

            break;

        }

        if (s->crypt_method) {

            if (!cluster_data) {

                cluster_data = g_malloc0(s->cluster_size);

            }

            encrypt_sectors(s, sector_num, cluster_data, buf,

                            n, 1, &s->aes_encrypt_key);

            src_buf = cluster_data;

        } else {

            src_buf = buf;

        }

        hd_iov.iov_base = (void *)src_buf;

        hd_iov.iov_len = n * 512;

        qemu_iovec_init_external(&hd_qiov, &hd_iov, 1);

        qemu_co_mutex_unlock(&s->lock);

        ret = bdrv_co_writev(bs->file,

                             (cluster_offset >> 9) + index_in_cluster,

                             n, &hd_qiov);

        qemu_co_mutex_lock(&s->lock);

        if (ret < 0) {

            break;

        }

        ret = 0;

        nb_sectors -= n;

        sector_num += n;

        buf += n * 512;

    }

    qemu_co_mutex_unlock(&s->lock);

    if (qiov->niov > 1) {

        qemu_vfree(orig_buf);

    }

    g_free(cluster_data);

    return ret;

}

static void qcow_close(BlockDriverState *bs)

{

    BDRVQcowState *s = bs->opaque;

    g_free(s->l1_table);

    g_free(s->l2_cache);

    g_free(s->cluster_cache);

    g_free(s->cluster_data);

    migrate_del_blocker(s->migration_blocker);

    error_free(s->migration_blocker);

}

static int qcow_create(const char *filename, QEMUOptionParameter *options,

                       Error **errp)

{

    int header_size, backing_filename_len, l1_size, shift, i;

    QCowHeader header;

    uint8_t *tmp;

    int64_t total_size = 0;

    const char *backing_file = NULL;

    int flags = 0;

    Error *local_err = NULL;

    int ret;

    BlockDriverState *qcow_bs;

    /* Read out options */

    while (options && options->name) {

        if (!strcmp(options->name, BLOCK_OPT_SIZE)) {

            total_size = options->value.n / 512;

        } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {

            backing_file = options->value.s;

        } else if (!strcmp(options->name, BLOCK_OPT_ENCRYPT)) {

            flags |= options->value.n ? BLOCK_FLAG_ENCRYPT : 0;

        }

        options++;

    }

    ret = bdrv_create_file(filename, options, &local_err);

    if (ret < 0) {

        qerror_report_err(local_err);

        error_free(local_err);

        return ret;

    }

    ret = bdrv_file_open(&qcow_bs, filename, NULL, BDRV_O_RDWR, &local_err);

    if (ret < 0) {

        qerror_report_err(local_err);

        error_free(local_err);

        return ret;

    }

    ret = bdrv_truncate(qcow_bs, 0);

    if (ret < 0) {

        goto exit;

    }

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

    header.magic = cpu_to_be32(QCOW_MAGIC);

    header.version = cpu_to_be32(QCOW_VERSION);

    header.size = cpu_to_be64(total_size * 512);

    header_size = sizeof(header);

    backing_filename_len = 0;

    if (backing_file) {

        if (strcmp(backing_file, "fat:")) {

            header.backing_file_offset = cpu_to_be64(header_size);

            backing_filename_len = strlen(backing_file);

            header.backing_file_size = cpu_to_be32(backing_filename_len);

            header_size += backing_filename_len;

        } else {

            /* special backing file for vvfat */

            backing_file = NULL;

        }

        header.cluster_bits = 9; /* 512 byte cluster to avoid copying

                                    unmodifyed sectors */

        header.l2_bits = 12; /* 32 KB L2 tables */

    } else {

        header.cluster_bits = 12; /* 4 KB clusters */

        header.l2_bits = 9; /* 4 KB L2 tables */

    }

    header_size = (header_size + 7) & ~7;

    shift = header.cluster_bits + header.l2_bits;

    l1_size = ((total_size * 512) + (1LL << shift) - 1) >> shift;

    header.l1_table_offset = cpu_to_be64(header_size);

    if (flags & BLOCK_FLAG_ENCRYPT) {

        header.crypt_method = cpu_to_be32(QCOW_CRYPT_AES);

    } else {

        header.crypt_method = cpu_to_be32(QCOW_CRYPT_NONE);

    }

    /* write all the data */

    ret = bdrv_pwrite(qcow_bs, 0, &header, sizeof(header));

    if (ret != sizeof(header)) {

        goto exit;

    }

    if (backing_file) {

        ret = bdrv_pwrite(qcow_bs, sizeof(header),

            backing_file, backing_filename_len);

        if (ret != backing_filename_len) {

            goto exit;

        }

    }

    tmp = g_malloc0(BDRV_SECTOR_SIZE);

    for (i = 0; i < ((sizeof(uint64_t)*l1_size + BDRV_SECTOR_SIZE - 1)/

        BDRV_SECTOR_SIZE); i++) {

        ret = bdrv_pwrite(qcow_bs, header_size +

            BDRV_SECTOR_SIZE*i, tmp, BDRV_SECTOR_SIZE);

        if (ret != BDRV_SECTOR_SIZE) {

            g_free(tmp);

            goto exit;

        }

    }

    g_free(tmp);

    ret = 0;

exit:

    bdrv_unref(qcow_bs);

    return ret;

}

static int qcow_make_empty(BlockDriverState *bs)

{

    BDRVQcowState *s = bs->opaque;

    uint32_t l1_length = s->l1_size * sizeof(uint64_t);

    int ret;

    memset(s->l1_table, 0, l1_length);

    if (bdrv_pwrite_sync(bs->file, s->l1_table_offset, s->l1_table,

            l1_length) < 0)

        return -1;

    ret = bdrv_truncate(bs->file, s->l1_table_offset + l1_length);

    if (ret < 0)

        return ret;

    memset(s->l2_cache, 0, s->l2_size * L2_CACHE_SIZE * sizeof(uint64_t));

    memset(s->l2_cache_offsets, 0, L2_CACHE_SIZE * sizeof(uint64_t));

    memset(s->l2_cache_counts, 0, L2_CACHE_SIZE * sizeof(uint32_t));

    return 0;

}

/* XXX: put compressed sectors first, then all the cluster aligned

   tables to avoid losing bytes in alignment */

static int qcow_write_compressed(BlockDriverState *bs, int64_t sector_num,

                                 const uint8_t *buf, int nb_sectors)

{

    BDRVQcowState *s = bs->opaque;

    z_stream strm;

    int ret, out_len;

    uint8_t *out_buf;

    uint64_t cluster_offset;

    if (nb_sectors != s->cluster_sectors) {

        ret = -EINVAL;

        /* Zero-pad last write if image size is not cluster aligned */

        if (sector_num + nb_sectors == bs->total_sectors &&

            nb_sectors < s->cluster_sectors) {

            uint8_t *pad_buf = qemu_blockalign(bs, s->cluster_size);

            memset(pad_buf, 0, s->cluster_size);

            memcpy(pad_buf, buf, nb_sectors * BDRV_SECTOR_SIZE);

            ret = qcow_write_compressed(bs, sector_num,

                                        pad_buf, s->cluster_sectors);

            qemu_vfree(pad_buf);

        }

        return ret;

    }

    out_buf = g_malloc(s->cluster_size + (s->cluster_size / 1000) + 128);

    /* best compression, small window, no zlib header */

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

    ret = deflateInit2(&strm, Z_DEFAULT_COMPRESSION,

                       Z_DEFLATED, -12,

                       9, Z_DEFAULT_STRATEGY);

    if (ret != 0) {

        ret = -EINVAL;

        goto fail;

    }

    strm.avail_in = s->cluster_size;

    strm.next_in = (uint8_t *)buf;

    strm.avail_out = s->cluster_size;

    strm.next_out = out_buf;

    ret = deflate(&strm, Z_FINISH);

    if (ret != Z_STREAM_END && ret != Z_OK) {

        deflateEnd(&strm);

        ret = -EINVAL;

        goto fail;

    }

    out_len = strm.next_out - out_buf;

    deflateEnd(&strm);

    if (ret != Z_STREAM_END || out_len >= s->cluster_size) {

        /* could not compress: write normal cluster */

        ret = bdrv_write(bs, sector_num, buf, s->cluster_sectors);

        if (ret < 0) {

            goto fail;

        }

    } else {

        cluster_offset = get_cluster_offset(bs, sector_num << 9, 2,

                                            out_len, 0, 0);

        if (cluster_offset == 0) {

            ret = -EIO;

            goto fail;

        }

        cluster_offset &= s->cluster_offset_mask;

        ret = bdrv_pwrite(bs->file, cluster_offset, out_buf, out_len);

        if (ret < 0) {

            goto fail;

        }

    }

    ret = 0;

fail:

    g_free(out_buf);

    return ret;

}

static int qcow_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)

{

    BDRVQcowState *s = bs->opaque;

    bdi->cluster_size = s->cluster_size;

    return 0;

}

static QEMUOptionParameter qcow_create_options[] = {

    {

        .name = BLOCK_OPT_SIZE,

        .type = OPT_SIZE,

        .help = "Virtual disk size"

    },

    {

        .name = BLOCK_OPT_BACKING_FILE,

        .type = OPT_STRING,

        .help = "File name of a base image"

    },

    {

        .name = BLOCK_OPT_ENCRYPT,

        .type = OPT_FLAG,

        .help = "Encrypt the image"

    },

    { NULL }

};

static BlockDriver bdrv_qcow = {

    .format_name        = "qcow",

    .instance_size        = sizeof(BDRVQcowState),

    .bdrv_probe                = qcow_probe,

    .bdrv_open                = qcow_open,

    .bdrv_close                = qcow_close,