Archipelago » qemu

/*

 * Block driver for the QCOW version 2 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_int.h"

#include "module.h"

#include <zlib.h>

#include "aes.h"

#include "block/qcow2.h"

#include "qemu-error.h"

#include "qerror.h"

/*

  Differences with QCOW:

  - Support for multiple incremental snapshots.

  - Memory management by reference counts.

  - Clusters which have a reference count of one have the bit

    QCOW_OFLAG_COPIED to optimize write performance.

  - Size of compressed clusters is stored in sectors to reduce bit usage

    in the cluster offsets.

  - Support for storing additional data (such as the VM state) in the

    snapshots.

  - If a backing store is used, the cluster size is not constrained

    (could be backported to QCOW).

  - L2 tables have always a size of one cluster.

*/

typedef struct {

    uint32_t magic;

    uint32_t len;

} QCowExtension;

#define  QCOW2_EXT_MAGIC_END 0

#define  QCOW2_EXT_MAGIC_BACKING_FORMAT 0xE2792ACA

static int qcow2_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;

}

/* 

 * read qcow2 extension and fill bs

 * start reading from start_offset

 * finish reading upon magic of value 0 or when end_offset reached

 * unknown magic is skipped (future extension this version knows nothing about)

 * return 0 upon success, non-0 otherwise

 */

static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,

                                 uint64_t end_offset)

{

    QCowExtension ext;

    uint64_t offset;

#ifdef DEBUG_EXT

    printf("qcow2_read_extensions: start=%ld end=%ld\n", start_offset, end_offset);

#endif

    offset = start_offset;

    while (offset < end_offset) {

#ifdef DEBUG_EXT

        BDRVQcowState *s = bs->opaque;

        /* Sanity check */

        if (offset > s->cluster_size)

            printf("qcow2_read_extension: suspicious offset %lu\n", offset);

        printf("attemting to read extended header in offset %lu\n", offset);

#endif

        if (bdrv_pread(bs->file, offset, &ext, sizeof(ext)) != sizeof(ext)) {

            fprintf(stderr, "qcow2_read_extension: ERROR: "

                    "pread fail from offset %" PRIu64 "\n",

                    offset);

            return 1;

        }

        be32_to_cpus(&ext.magic);

        be32_to_cpus(&ext.len);

        offset += sizeof(ext);

#ifdef DEBUG_EXT

        printf("ext.magic = 0x%x\n", ext.magic);

#endif

        switch (ext.magic) {

        case QCOW2_EXT_MAGIC_END:

            return 0;

        case QCOW2_EXT_MAGIC_BACKING_FORMAT:

            if (ext.len >= sizeof(bs->backing_format)) {

                fprintf(stderr, "ERROR: ext_backing_format: len=%u too large"

                        " (>=%zu)\n",

                        ext.len, sizeof(bs->backing_format));

                return 2;

            }

            if (bdrv_pread(bs->file, offset , bs->backing_format,

                           ext.len) != ext.len)

                return 3;

            bs->backing_format[ext.len] = '\0';

#ifdef DEBUG_EXT

            printf("Qcow2: Got format extension %s\n", bs->backing_format);

#endif

            offset = ((offset + ext.len + 7) & ~7);

            break;

        default:

            /* unknown magic -- just skip it */

            offset = ((offset + ext.len + 7) & ~7);

            break;

        }

    }

    return 0;

}

static int qcow2_open(BlockDriverState *bs, int flags)

{

    BDRVQcowState *s = bs->opaque;

    int len, i, ret = 0;

    QCowHeader header;

    uint64_t ext_end;

    bool writethrough;

    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);

    be64_to_cpus(&header.size);

    be32_to_cpus(&header.cluster_bits);

    be32_to_cpus(&header.crypt_method);

    be64_to_cpus(&header.l1_table_offset);

    be32_to_cpus(&header.l1_size);

    be64_to_cpus(&header.refcount_table_offset);

    be32_to_cpus(&header.refcount_table_clusters);

    be64_to_cpus(&header.snapshots_offset);

    be32_to_cpus(&header.nb_snapshots);

    if (header.magic != QCOW_MAGIC) {

        ret = -EINVAL;

        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, "qcow2", version);

        ret = -ENOTSUP;

        goto fail;

    }

    if (header.cluster_bits < MIN_CLUSTER_BITS ||

        header.cluster_bits > MAX_CLUSTER_BITS) {

        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 = s->cluster_bits - 3; /* L2 is always one cluster */

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

    bs->total_sectors = header.size / 512;

    s->csize_shift = (62 - (s->cluster_bits - 8));

    s->csize_mask = (1 << (s->cluster_bits - 8)) - 1;

    s->cluster_offset_mask = (1LL << s->csize_shift) - 1;

    s->refcount_table_offset = header.refcount_table_offset;

    s->refcount_table_size =

        header.refcount_table_clusters << (s->cluster_bits - 3);

    s->snapshots_offset = header.snapshots_offset;

    s->nb_snapshots = header.nb_snapshots;

    /* read the level 1 table */

    s->l1_size = header.l1_size;

    s->l1_vm_state_index = size_to_l1(s, header.size);

    /* the L1 table must contain at least enough entries to put

       header.size bytes */

    if (s->l1_size < s->l1_vm_state_index) {

        ret = -EINVAL;

        goto fail;

    }

    s->l1_table_offset = header.l1_table_offset;

    if (s->l1_size > 0) {

        s->l1_table = g_malloc0(

            align_offset(s->l1_size * sizeof(uint64_t), 512));

        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 table/refcount block cache */

    writethrough = ((flags & BDRV_O_CACHE_WB) == 0);

    s->l2_table_cache = qcow2_cache_create(bs, L2_CACHE_SIZE, writethrough);

    s->refcount_block_cache = qcow2_cache_create(bs, REFCOUNT_CACHE_SIZE,

        writethrough);

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

    /* one more sector for decompressed data alignment */

    s->cluster_data = g_malloc(QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size

                                  + 512);

    s->cluster_cache_offset = -1;

    ret = qcow2_refcount_init(bs);

    if (ret != 0) {

        goto fail;

    }

    QLIST_INIT(&s->cluster_allocs);

    /* read qcow2 extensions */

    if (header.backing_file_offset) {

        ext_end = header.backing_file_offset;

    } else {

        ext_end = s->cluster_size;

    }

    if (qcow2_read_extensions(bs, sizeof(header), ext_end)) {

        ret = -EINVAL;

        goto fail;

    }

    /* 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';

    }

    if (qcow2_read_snapshots(bs) < 0) {

        ret = -EINVAL;

        goto fail;

    }

    /* Initialise locks */

    qemu_co_mutex_init(&s->lock);

#ifdef DEBUG_ALLOC

    {

        BdrvCheckResult result = {0};

        qcow2_check_refcounts(bs, &result);

    }

#endif

    return ret;

 fail:

    qcow2_free_snapshots(bs);

    qcow2_refcount_close(bs);

    g_free(s->l1_table);

    if (s->l2_table_cache) {

        qcow2_cache_destroy(bs, s->l2_table_cache);

    }

    g_free(s->cluster_cache);

    g_free(s->cluster_data);

    return ret;

}

static int qcow2_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;

#if 0

    /* test */

    {

        uint8_t in[16];

        uint8_t out[16];

        uint8_t tmp[16];

        for(i=0;i<16;i++)

            in[i] = i;

        AES_encrypt(in, tmp, &s->aes_encrypt_key);

        AES_decrypt(tmp, out, &s->aes_decrypt_key);

        for(i = 0; i < 16; i++)

            printf(" %02x", tmp[i]);

        printf("\n");

        for(i = 0; i < 16; i++)

            printf(" %02x", out[i]);

        printf("\n");

    }

#endif

    return 0;

}

static int qcow2_is_allocated(BlockDriverState *bs, int64_t sector_num,

                              int nb_sectors, int *pnum)

{

    uint64_t cluster_offset;

    int ret;

    *pnum = nb_sectors;

    /* FIXME We can get errors here, but the bdrv_is_allocated interface can't

     * pass them on today */

    ret = qcow2_get_cluster_offset(bs, sector_num << 9, pnum, &cluster_offset);

    if (ret < 0) {

        *pnum = 0;

    }

    return (cluster_offset != 0);

}

/* handle reading after the end of the backing file */

int qcow2_backing_read1(BlockDriverState *bs, QEMUIOVector *qiov,

                  int64_t sector_num, int nb_sectors)

{

    int n1;

    if ((sector_num + nb_sectors) <= bs->total_sectors)

        return nb_sectors;

    if (sector_num >= bs->total_sectors)

        n1 = 0;

    else

        n1 = bs->total_sectors - sector_num;

    qemu_iovec_memset_skip(qiov, 0, 512 * (nb_sectors - n1), 512 * n1);

    return n1;

}

typedef struct QCowAIOCB {

    BlockDriverAIOCB common;

    int64_t sector_num;

    QEMUIOVector *qiov;

    int remaining_sectors;

    uint64_t bytes_done;

    uint64_t cluster_offset;

    uint8_t *cluster_data;

    QEMUIOVector hd_qiov;

    QCowL2Meta l2meta;

} QCowAIOCB;

/*

 * Returns 0 when the request is completed successfully, 1 when there is still

 * a part left to do and -errno in error cases.

 */

static int qcow2_aio_read_cb(QCowAIOCB *acb)

{

    BlockDriverState *bs = acb->common.bs;

    BDRVQcowState *s = bs->opaque;

    int index_in_cluster, n1;

    int ret;

    int cur_nr_sectors; /* number of sectors in current iteration */

    if (acb->remaining_sectors == 0) {

        /* request completed */

        return 0;

    }

    /* prepare next request */

    cur_nr_sectors = acb->remaining_sectors;

    if (s->crypt_method) {

        cur_nr_sectors = MIN(cur_nr_sectors,

            QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors);

    }

    ret = qcow2_get_cluster_offset(bs, acb->sector_num << 9,

        &cur_nr_sectors, &acb->cluster_offset);

    if (ret < 0) {

        return ret;

    }

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

    qemu_iovec_reset(&acb->hd_qiov);

    qemu_iovec_copy(&acb->hd_qiov, acb->qiov, acb->bytes_done,

        cur_nr_sectors * 512);

    if (!acb->cluster_offset) {

        if (bs->backing_hd) {

            /* read from the base image */

            n1 = qcow2_backing_read1(bs->backing_hd, &acb->hd_qiov,

                acb->sector_num, cur_nr_sectors);

            if (n1 > 0) {

                BLKDBG_EVENT(bs->file, BLKDBG_READ_BACKING_AIO);

                qemu_co_mutex_unlock(&s->lock);

                ret = bdrv_co_readv(bs->backing_hd, acb->sector_num,

                                    n1, &acb->hd_qiov);

                qemu_co_mutex_lock(&s->lock);

                if (ret < 0) {

                    return ret;

                }

            }

        } else {

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

            qemu_iovec_memset(&acb->hd_qiov, 0, 512 * cur_nr_sectors);

        }

    } else if (acb->cluster_offset & QCOW_OFLAG_COMPRESSED) {

        /* add AIO support for compressed blocks ? */

        ret = qcow2_decompress_cluster(bs, acb->cluster_offset);

        if (ret < 0) {

            return ret;

        }

        qemu_iovec_from_buffer(&acb->hd_qiov,

            s->cluster_cache + index_in_cluster * 512,

            512 * cur_nr_sectors);

    } else {

        if ((acb->cluster_offset & 511) != 0) {

            return -EIO;

        }

        if (s->crypt_method) {

            /*

             * For encrypted images, read everything into a temporary

             * contiguous buffer on which the AES functions can work.

             */

            if (!acb->cluster_data) {

                acb->cluster_data =

                    g_malloc0(QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);

            }

            assert(cur_nr_sectors <=

                QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors);

            qemu_iovec_reset(&acb->hd_qiov);

            qemu_iovec_add(&acb->hd_qiov, acb->cluster_data,

                512 * cur_nr_sectors);

        }

        BLKDBG_EVENT(bs->file, BLKDBG_READ_AIO);

        qemu_co_mutex_unlock(&s->lock);

        ret = bdrv_co_readv(bs->file,

                            (acb->cluster_offset >> 9) + index_in_cluster,

                            cur_nr_sectors, &acb->hd_qiov);

        qemu_co_mutex_lock(&s->lock);

        if (ret < 0) {

            return ret;

        }

        if (s->crypt_method) {

            qcow2_encrypt_sectors(s, acb->sector_num,  acb->cluster_data,

                acb->cluster_data, cur_nr_sectors, 0, &s->aes_decrypt_key);

            qemu_iovec_reset(&acb->hd_qiov);

            qemu_iovec_copy(&acb->hd_qiov, acb->qiov, acb->bytes_done,

                cur_nr_sectors * 512);

            qemu_iovec_from_buffer(&acb->hd_qiov, acb->cluster_data,

                512 * cur_nr_sectors);

        }

    }

    acb->remaining_sectors -= cur_nr_sectors;

    acb->sector_num += cur_nr_sectors;

    acb->bytes_done += cur_nr_sectors * 512;

    return 1;

}

static QCowAIOCB *qcow2_aio_setup(BlockDriverState *bs, int64_t sector_num,

                                  QEMUIOVector *qiov, int nb_sectors,

                                  BlockDriverCompletionFunc *cb,

                                  void *opaque, QCowAIOCB *acb)

{

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

    acb->common.bs = bs;

    acb->sector_num = sector_num;

    acb->qiov = qiov;

    qemu_iovec_init(&acb->hd_qiov, qiov->niov);

    acb->bytes_done = 0;

    acb->remaining_sectors = nb_sectors;

    acb->cluster_offset = 0;

    acb->l2meta.nb_clusters = 0;

    qemu_co_queue_init(&acb->l2meta.dependent_requests);

    return acb;

}

static int qcow2_co_readv(BlockDriverState *bs, int64_t sector_num,

                          int nb_sectors, QEMUIOVector *qiov)

{

    BDRVQcowState *s = bs->opaque;

    QCowAIOCB acb;

    int ret;

    qcow2_aio_setup(bs, sector_num, qiov, nb_sectors, NULL, NULL, &acb);

    qemu_co_mutex_lock(&s->lock);

    do {

        ret = qcow2_aio_read_cb(&acb);

    } while (ret > 0);

    qemu_co_mutex_unlock(&s->lock);

    qemu_iovec_destroy(&acb.hd_qiov);

    return ret;

}

static void run_dependent_requests(BDRVQcowState *s, QCowL2Meta *m)

{

    /* Take the request off the list of running requests */

    if (m->nb_clusters != 0) {

        QLIST_REMOVE(m, next_in_flight);

    }

    /* Restart all dependent requests */

    if (!qemu_co_queue_empty(&m->dependent_requests)) {

        qemu_co_mutex_unlock(&s->lock);

        while(qemu_co_queue_next(&m->dependent_requests));

        qemu_co_mutex_lock(&s->lock);

    }

}

/*

 * Returns 0 when the request is completed successfully, 1 when there is still

 * a part left to do and -errno in error cases.

 */

static int qcow2_aio_write_cb(QCowAIOCB *acb)

{

    BlockDriverState *bs = acb->common.bs;

    BDRVQcowState *s = bs->opaque;

    int index_in_cluster;

    int n_end;

    int ret;

    int cur_nr_sectors; /* number of sectors in current iteration */

    if (acb->remaining_sectors == 0) {

        /* request completed */

        return 0;

    }

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

    n_end = index_in_cluster + acb->remaining_sectors;

    if (s->crypt_method &&

        n_end > QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors)

        n_end = QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors;

    ret = qcow2_alloc_cluster_offset(bs, acb->sector_num << 9,

        index_in_cluster, n_end, &cur_nr_sectors, &acb->l2meta);

    if (ret < 0) {

        return ret;

    }

    acb->cluster_offset = acb->l2meta.cluster_offset;

    assert((acb->cluster_offset & 511) == 0);

    qemu_iovec_reset(&acb->hd_qiov);

    qemu_iovec_copy(&acb->hd_qiov, acb->qiov, acb->bytes_done,

        cur_nr_sectors * 512);

    if (s->crypt_method) {

        if (!acb->cluster_data) {

            acb->cluster_data = g_malloc0(QCOW_MAX_CRYPT_CLUSTERS *

                                             s->cluster_size);

        }

        assert(acb->hd_qiov.size <= QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);

        qemu_iovec_to_buffer(&acb->hd_qiov, acb->cluster_data);

        qcow2_encrypt_sectors(s, acb->sector_num, acb->cluster_data,

            acb->cluster_data, cur_nr_sectors, 1, &s->aes_encrypt_key);

        qemu_iovec_reset(&acb->hd_qiov);

        qemu_iovec_add(&acb->hd_qiov, acb->cluster_data,

            cur_nr_sectors * 512);

    }

    BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);

    qemu_co_mutex_unlock(&s->lock);

    ret = bdrv_co_writev(bs->file,

                         (acb->cluster_offset >> 9) + index_in_cluster,

                         cur_nr_sectors, &acb->hd_qiov);

    qemu_co_mutex_lock(&s->lock);

    if (ret < 0) {

        return ret;

    }

    ret = qcow2_alloc_cluster_link_l2(bs, &acb->l2meta);

    run_dependent_requests(s, &acb->l2meta);

    if (ret < 0) {

        return ret;

    }

    acb->remaining_sectors -= cur_nr_sectors;

    acb->sector_num += cur_nr_sectors;

    acb->bytes_done += cur_nr_sectors * 512;

    return 1;

}

static int qcow2_co_writev(BlockDriverState *bs,

                           int64_t sector_num,

                           int nb_sectors,

                           QEMUIOVector *qiov)

{

    BDRVQcowState *s = bs->opaque;

    QCowAIOCB acb;

    int ret;

    qcow2_aio_setup(bs, sector_num, qiov, nb_sectors, NULL, NULL, &acb);

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

    qemu_co_mutex_lock(&s->lock);

    do {

        ret = qcow2_aio_write_cb(&acb);

    } while (ret > 0);

    qemu_co_mutex_unlock(&s->lock);

    qemu_iovec_destroy(&acb.hd_qiov);

    return ret;

}

static void qcow2_close(BlockDriverState *bs)

{

    BDRVQcowState *s = bs->opaque;

    g_free(s->l1_table);

    qcow2_cache_flush(bs, s->l2_table_cache);

    qcow2_cache_flush(bs, s->refcount_block_cache);

    qcow2_cache_destroy(bs, s->l2_table_cache);

    qcow2_cache_destroy(bs, s->refcount_block_cache);

    g_free(s->cluster_cache);

    g_free(s->cluster_data);

    qcow2_refcount_close(bs);

}

/*

 * Updates the variable length parts of the qcow2 header, i.e. the backing file

 * name and all extensions. qcow2 was not designed to allow such changes, so if

 * we run out of space (we can only use the first cluster) this function may

 * fail.

 *

 * Returns 0 on success, -errno in error cases.

 */

static int qcow2_update_ext_header(BlockDriverState *bs,

    const char *backing_file, const char *backing_fmt)

{

    size_t backing_file_len = 0;

    size_t backing_fmt_len = 0;

    BDRVQcowState *s = bs->opaque;

    QCowExtension ext_backing_fmt = {0, 0};

    int ret;

    /* Backing file format doesn't make sense without a backing file */

    if (backing_fmt && !backing_file) {

        return -EINVAL;

    }

    /* Prepare the backing file format extension if needed */

    if (backing_fmt) {

        ext_backing_fmt.len = cpu_to_be32(strlen(backing_fmt));

        ext_backing_fmt.magic = cpu_to_be32(QCOW2_EXT_MAGIC_BACKING_FORMAT);

        backing_fmt_len = ((sizeof(ext_backing_fmt)

            + strlen(backing_fmt) + 7) & ~7);

    }

    /* Check if we can fit the new header into the first cluster */

    if (backing_file) {

        backing_file_len = strlen(backing_file);

    }

    size_t header_size = sizeof(QCowHeader) + backing_file_len

        + backing_fmt_len;

    if (header_size > s->cluster_size) {

        return -ENOSPC;

    }

    /* Rewrite backing file name and qcow2 extensions */

    size_t ext_size = header_size - sizeof(QCowHeader);

    uint8_t buf[ext_size];

    size_t offset = 0;

    size_t backing_file_offset = 0;

    if (backing_file) {

        if (backing_fmt) {

            int padding = backing_fmt_len -

                (sizeof(ext_backing_fmt) + strlen(backing_fmt));

            memcpy(buf + offset, &ext_backing_fmt, sizeof(ext_backing_fmt));

            offset += sizeof(ext_backing_fmt);

            memcpy(buf + offset, backing_fmt, strlen(backing_fmt));

            offset += strlen(backing_fmt);

            memset(buf + offset, 0, padding);

            offset += padding;

        }

        memcpy(buf + offset, backing_file, backing_file_len);

        backing_file_offset = sizeof(QCowHeader) + offset;

    }

    ret = bdrv_pwrite_sync(bs->file, sizeof(QCowHeader), buf, ext_size);

    if (ret < 0) {

        goto fail;

    }

    /* Update header fields */

    uint64_t be_backing_file_offset = cpu_to_be64(backing_file_offset);

    uint32_t be_backing_file_size = cpu_to_be32(backing_file_len);

    ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, backing_file_offset),

        &be_backing_file_offset, sizeof(uint64_t));

    if (ret < 0) {

        goto fail;

    }

    ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, backing_file_size),

        &be_backing_file_size, sizeof(uint32_t));

    if (ret < 0) {

        goto fail;

    }

    ret = 0;

fail:

    return ret;

}

static int qcow2_change_backing_file(BlockDriverState *bs,

    const char *backing_file, const char *backing_fmt)

{

    return qcow2_update_ext_header(bs, backing_file, backing_fmt);

}

static int preallocate(BlockDriverState *bs)

{

    uint64_t nb_sectors;

    uint64_t offset;

    int num;

    int ret;

    QCowL2Meta meta;

    nb_sectors = bdrv_getlength(bs) >> 9;

    offset = 0;

    qemu_co_queue_init(&meta.dependent_requests);

    meta.cluster_offset = 0;

    while (nb_sectors) {

        num = MIN(nb_sectors, INT_MAX >> 9);

        ret = qcow2_alloc_cluster_offset(bs, offset, 0, num, &num, &meta);

        if (ret < 0) {

            return ret;

        }

        ret = qcow2_alloc_cluster_link_l2(bs, &meta);

        if (ret < 0) {

            qcow2_free_any_clusters(bs, meta.cluster_offset, meta.nb_clusters);

            return ret;

        }

        /* There are no dependent requests, but we need to remove our request

         * from the list of in-flight requests */

        run_dependent_requests(bs->opaque, &meta);

        /* TODO Preallocate data if requested */

        nb_sectors -= num;

        offset += num << 9;

    }

    /*

     * It is expected that the image file is large enough to actually contain

     * all of the allocated clusters (otherwise we get failing reads after

     * EOF). Extend the image to the last allocated sector.

     */

    if (meta.cluster_offset != 0) {

        uint8_t buf[512];

        memset(buf, 0, 512);

        ret = bdrv_write(bs->file, (meta.cluster_offset >> 9) + num - 1, buf, 1);

        if (ret < 0) {

            return ret;

        }

    }

    return 0;

}

static int qcow2_create2(const char *filename, int64_t total_size,

                         const char *backing_file, const char *backing_format,

                         int flags, size_t cluster_size, int prealloc,

                         QEMUOptionParameter *options)

{

    /* Calulate cluster_bits */

    int cluster_bits;

    cluster_bits = ffs(cluster_size) - 1;

    if (cluster_bits < MIN_CLUSTER_BITS || cluster_bits > MAX_CLUSTER_BITS ||

        (1 << cluster_bits) != cluster_size)

    {

        error_report(

            "Cluster size must be a power of two between %d and %dk",

            1 << MIN_CLUSTER_BITS, 1 << (MAX_CLUSTER_BITS - 10));

        return -EINVAL;

    }

    /*

     * Open the image file and write a minimal qcow2 header.

     *

     * We keep things simple and start with a zero-sized image. We also

     * do without refcount blocks or a L1 table for now. We'll fix the

     * inconsistency later.

     *

     * We do need a refcount table because growing the refcount table means

     * allocating two new refcount blocks - the seconds of which would be at

     * 2 GB for 64k clusters, and we don't want to have a 2 GB initial file

     * size for any qcow2 image.

     */

    BlockDriverState* bs;

    QCowHeader header;

    uint8_t* refcount_table;

    int ret;

    ret = bdrv_create_file(filename, options);

    if (ret < 0) {

        return ret;

    }

    ret = bdrv_file_open(&bs, filename, BDRV_O_RDWR);

    if (ret < 0) {

        return ret;

    }

    /* Write the header */

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

    header.magic = cpu_to_be32(QCOW_MAGIC);

    header.version = cpu_to_be32(QCOW_VERSION);

    header.cluster_bits = cpu_to_be32(cluster_bits);

    header.size = cpu_to_be64(0);

    header.l1_table_offset = cpu_to_be64(0);

    header.l1_size = cpu_to_be32(0);

    header.refcount_table_offset = cpu_to_be64(cluster_size);

    header.refcount_table_clusters = cpu_to_be32(1);

    if (flags & BLOCK_FLAG_ENCRYPT) {

        header.crypt_method = cpu_to_be32(QCOW_CRYPT_AES);

    } else {

        header.crypt_method = cpu_to_be32(QCOW_CRYPT_NONE);

    }

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

    if (ret < 0) {

        goto out;

    }

    /* Write an empty refcount table */

    refcount_table = g_malloc0(cluster_size);

    ret = bdrv_pwrite(bs, cluster_size, refcount_table, cluster_size);

    g_free(refcount_table);

    if (ret < 0) {

        goto out;

    }

    bdrv_close(bs);

    /*

     * And now open the image and make it consistent first (i.e. increase the

     * refcount of the cluster that is occupied by the header and the refcount

     * table)

     */

    BlockDriver* drv = bdrv_find_format("qcow2");

    assert(drv != NULL);

    ret = bdrv_open(bs, filename,

        BDRV_O_RDWR | BDRV_O_CACHE_WB | BDRV_O_NO_FLUSH, drv);

    if (ret < 0) {

        goto out;

    }

    ret = qcow2_alloc_clusters(bs, 2 * cluster_size);

    if (ret < 0) {

        goto out;

    } else if (ret != 0) {

        error_report("Huh, first cluster in empty image is already in use?");

        abort();

    }

    /* Okay, now that we have a valid image, let's give it the right size */

    ret = bdrv_truncate(bs, total_size * BDRV_SECTOR_SIZE);

    if (ret < 0) {

        goto out;

    }

    /* Want a backing file? There you go.*/

    if (backing_file) {

        ret = bdrv_change_backing_file(bs, backing_file, backing_format);

        if (ret < 0) {

            goto out;

        }

    }

    /* And if we're supposed to preallocate metadata, do that now */

    if (prealloc) {

        ret = preallocate(bs);

        if (ret < 0) {

            goto out;

        }

    }

    ret = 0;

out:

    bdrv_delete(bs);

    return ret;

}

static int qcow2_create(const char *filename, QEMUOptionParameter *options)

{

    const char *backing_file = NULL;

    const char *backing_fmt = NULL;

    uint64_t sectors = 0;

    int flags = 0;

    size_t cluster_size = DEFAULT_CLUSTER_SIZE;

    int prealloc = 0;

    /* Read out options */

    while (options && options->name) {

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

            sectors = 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_BACKING_FMT)) {

            backing_fmt = options->value.s;

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

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

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

            if (options->value.n) {

                cluster_size = options->value.n;

            }

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

            if (!options->value.s || !strcmp(options->value.s, "off")) {

                prealloc = 0;

            } else if (!strcmp(options->value.s, "metadata")) {

                prealloc = 1;

            } else {

                fprintf(stderr, "Invalid preallocation mode: '%s'\n",

                    options->value.s);

                return -EINVAL;

            }

        }

        options++;

    }

    if (backing_file && prealloc) {

        fprintf(stderr, "Backing file and preallocation cannot be used at "

            "the same time\n");

        return -EINVAL;

    }

    return qcow2_create2(filename, sectors, backing_file, backing_fmt, flags,

                         cluster_size, prealloc, options);

}

static int qcow2_make_empty(BlockDriverState *bs)

{

#if 0

    /* XXX: not correct */

    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(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;

    l2_cache_reset(bs);

#endif

    return 0;

}

static int qcow2_discard(BlockDriverState *bs, int64_t sector_num,

    int nb_sectors)

{

    return qcow2_discard_clusters(bs, sector_num << BDRV_SECTOR_BITS,

        nb_sectors);

}

static int qcow2_truncate(BlockDriverState *bs, int64_t offset)

{

    BDRVQcowState *s = bs->opaque;

    int ret, new_l1_size;

    if (offset & 511) {

        return -EINVAL;

    }

    /* cannot proceed if image has snapshots */

    if (s->nb_snapshots) {

        return -ENOTSUP;

    }

    /* shrinking is currently not supported */

    if (offset < bs->total_sectors * 512) {

        return -ENOTSUP;

    }

    new_l1_size = size_to_l1(s, offset);

    ret = qcow2_grow_l1_table(bs, new_l1_size, true);

    if (ret < 0) {

        return ret;

    }

    /* write updated header.size */

    offset = cpu_to_be64(offset);

    ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, size),

                           &offset, sizeof(uint64_t));

    if (ret < 0) {

        return ret;

    }

    s->l1_vm_state_index = new_l1_size;

    return 0;

}

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

   tables to avoid losing bytes in alignment */

static int qcow2_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 == 0) {

        /* align end of file to a sector boundary to ease reading with

           sector based I/Os */

        cluster_offset = bdrv_getlength(bs->file);

        cluster_offset = (cluster_offset + 511) & ~511;

        bdrv_truncate(bs->file, cluster_offset);

        return 0;

    }

    if (nb_sectors != s->cluster_sectors)

        return -EINVAL;

    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) {

        g_free(out_buf);

        return -1;

    }

    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) {

        g_free(out_buf);

        deflateEnd(&strm);

        return -1;

    }

    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 */

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

    } else {

        cluster_offset = qcow2_alloc_compressed_cluster_offset(bs,

            sector_num << 9, out_len);

        if (!cluster_offset)

            return -1;

        cluster_offset &= s->cluster_offset_mask;

        BLKDBG_EVENT(bs->file, BLKDBG_WRITE_COMPRESSED);

        if (bdrv_pwrite(bs->file, cluster_offset, out_buf, out_len) != out_len) {

            g_free(out_buf);

            return -1;

        }

    }

    g_free(out_buf);

    return 0;

}

static int qcow2_flush(BlockDriverState *bs)

{

    BDRVQcowState *s = bs->opaque;

    int ret;

    ret = qcow2_cache_flush(bs, s->l2_table_cache);

    if (ret < 0) {

        return ret;

    }

    ret = qcow2_cache_flush(bs, s->refcount_block_cache);

    if (ret < 0) {

        return ret;

    }

    return bdrv_flush(bs->file);

}

static BlockDriverAIOCB *qcow2_aio_flush(BlockDriverState *bs,

                                         BlockDriverCompletionFunc *cb,

                                         void *opaque)

{

    BDRVQcowState *s = bs->opaque;

    int ret;

    ret = qcow2_cache_flush(bs, s->l2_table_cache);

    if (ret < 0) {

        return NULL;

    }

    ret = qcow2_cache_flush(bs, s->refcount_block_cache);

    if (ret < 0) {

        return NULL;

    }

    return bdrv_aio_flush(bs->file, cb, opaque);

}

static int64_t qcow2_vm_state_offset(BDRVQcowState *s)

{

        return (int64_t)s->l1_vm_state_index << (s->cluster_bits + s->l2_bits);

}

static int qcow2_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)

{

    BDRVQcowState *s = bs->opaque;

    bdi->cluster_size = s->cluster_size;

    bdi->vm_state_offset = qcow2_vm_state_offset(s);

    return 0;

}

static int qcow2_check(BlockDriverState *bs, BdrvCheckResult *result)

{

    return qcow2_check_refcounts(bs, result);

}

#if 0

static void dump_refcounts(BlockDriverState *bs)

{

    BDRVQcowState *s = bs->opaque;

    int64_t nb_clusters, k, k1, size;

    int refcount;

    size = bdrv_getlength(bs->file);

    nb_clusters = size_to_clusters(s, size);

    for(k = 0; k < nb_clusters;) {

        k1 = k;

        refcount = get_refcount(bs, k);

        k++;

        while (k < nb_clusters && get_refcount(bs, k) == refcount)

            k++;

        printf("%" PRId64 ": refcount=%d nb=%" PRId64 "\n", k, refcount,

               k - k1);

    }

}

#endif

static int qcow2_save_vmstate(BlockDriverState *bs, const uint8_t *buf,

                              int64_t pos, int size)

{

    BDRVQcowState *s = bs->opaque;

    int growable = bs->growable;

    int ret;

    BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_SAVE);

    bs->growable = 1;

    ret = bdrv_pwrite(bs, qcow2_vm_state_offset(s) + pos, buf, size);

    bs->growable = growable;

    return ret;

}

static int qcow2_load_vmstate(BlockDriverState *bs, uint8_t *buf,

                              int64_t pos, int size)

{

    BDRVQcowState *s = bs->opaque;

    int growable = bs->growable;

    int ret;

    BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_LOAD);

    bs->growable = 1;

    ret = bdrv_pread(bs, qcow2_vm_state_offset(s) + pos, buf, size);

    bs->growable = growable;

    return ret;

}

static QEMUOptionParameter qcow2_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_BACKING_FMT,

        .type = OPT_STRING,

        .help = "Image format of the base image"

    },

    {

        .name = BLOCK_OPT_ENCRYPT,

        .type = OPT_FLAG,

        .help = "Encrypt the image"

    },

    {

        .name = BLOCK_OPT_CLUSTER_SIZE,

        .type = OPT_SIZE,

        .help = "qcow2 cluster size",

        .value = { .n = DEFAULT_CLUSTER_SIZE },

    },

    {

        .name = BLOCK_OPT_PREALLOC,

        .type = OPT_STRING,

        .help = "Preallocation mode (allowed values: off, metadata)"

    },

    { NULL }

};

static BlockDriver bdrv_qcow2 = {

    .format_name        = "qcow2",

    .instance_size      = sizeof(BDRVQcowState),

    .bdrv_probe         = qcow2_probe,

    .bdrv_open          = qcow2_open,

    .bdrv_close         = qcow2_close,

    .bdrv_create        = qcow2_create,

    .bdrv_flush         = qcow2_flush,

    .bdrv_is_allocated  = qcow2_is_allocated,

    .bdrv_set_key       = qcow2_set_key,

    .bdrv_make_empty    = qcow2_make_empty,

    .bdrv_co_readv      = qcow2_co_readv,

    .bdrv_co_writev     = qcow2_co_writev,

    .bdrv_aio_flush     = qcow2_aio_flush,

    .bdrv_discard           = qcow2_discard,

    .bdrv_truncate          = qcow2_truncate,

    .bdrv_write_compressed  = qcow2_write_compressed,

    .bdrv_snapshot_create   = qcow2_snapshot_create,

    .bdrv_snapshot_goto     = qcow2_snapshot_goto,

    .bdrv_snapshot_delete   = qcow2_snapshot_delete,

    .bdrv_snapshot_list     = qcow2_snapshot_list,

    .bdrv_snapshot_load_tmp     = qcow2_snapshot_load_tmp,

    .bdrv_get_info      = qcow2_get_info,

    .bdrv_save_vmstate    = qcow2_save_vmstate,

    .bdrv_load_vmstate    = qcow2_load_vmstate,

    .bdrv_change_backing_file   = qcow2_change_backing_file,

    .create_options = qcow2_create_options,

    .bdrv_check = qcow2_check,

};

static void bdrv_qcow2_init(void)

{

    bdrv_register(&bdrv_qcow2);

}

block_init(bdrv_qcow2_init);