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 <zlib.h>

#include "qemu-common.h"

#include "block_int.h"

#include "block/qcow2.h"

int qcow2_grow_l1_table(BlockDriverState *bs, int min_size, bool exact_size)

{

    BDRVQcowState *s = bs->opaque;

    int new_l1_size, new_l1_size2, ret, i;

    uint64_t *new_l1_table;

    int64_t new_l1_table_offset;

    uint8_t data[12];

    if (min_size <= s->l1_size)

        return 0;

    if (exact_size) {

        new_l1_size = min_size;

    } else {

        /* Bump size up to reduce the number of times we have to grow */

        new_l1_size = s->l1_size;

        if (new_l1_size == 0) {

            new_l1_size = 1;

        }

        while (min_size > new_l1_size) {

            new_l1_size = (new_l1_size * 3 + 1) / 2;

        }

    }

#ifdef DEBUG_ALLOC2

    printf("grow l1_table from %d to %d\n", s->l1_size, new_l1_size);

#endif

    new_l1_size2 = sizeof(uint64_t) * new_l1_size;

    new_l1_table = qemu_mallocz(align_offset(new_l1_size2, 512));

    memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));

    /* write new table (align to cluster) */

    BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_ALLOC_TABLE);

    new_l1_table_offset = qcow2_alloc_clusters(bs, new_l1_size2);

    if (new_l1_table_offset < 0) {

        qemu_free(new_l1_table);

        return new_l1_table_offset;

    }

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

    if (ret < 0) {

        return ret;

    }

    BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_WRITE_TABLE);

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

        new_l1_table[i] = cpu_to_be64(new_l1_table[i]);

    ret = bdrv_pwrite_sync(bs->file, new_l1_table_offset, new_l1_table, new_l1_size2);

    if (ret < 0)

        goto fail;

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

        new_l1_table[i] = be64_to_cpu(new_l1_table[i]);

    /* set new table */

    BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_ACTIVATE_TABLE);

    cpu_to_be32w((uint32_t*)data, new_l1_size);

    cpu_to_be64wu((uint64_t*)(data + 4), new_l1_table_offset);

    ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, l1_size), data,sizeof(data));

    if (ret < 0) {

        goto fail;

    }

    qemu_free(s->l1_table);

    qcow2_free_clusters(bs, s->l1_table_offset, s->l1_size * sizeof(uint64_t));

    s->l1_table_offset = new_l1_table_offset;

    s->l1_table = new_l1_table;

    s->l1_size = new_l1_size;

    return 0;

 fail:

    qemu_free(new_l1_table);

    qcow2_free_clusters(bs, new_l1_table_offset, new_l1_size2);

    return ret;

}

/*

 * l2_load

 *

 * Loads a L2 table into memory. If the table is in the cache, the cache

 * is used; otherwise the L2 table is loaded from the image file.

 *

 * Returns a pointer to the L2 table on success, or NULL if the read from

 * the image file failed.

 */

static int l2_load(BlockDriverState *bs, uint64_t l2_offset,

    uint64_t **l2_table)

{

    BDRVQcowState *s = bs->opaque;

    int ret;

    ret = qcow2_cache_get(bs, s->l2_table_cache, l2_offset, (void**) l2_table);

    return ret;

}

/*

 * Writes one sector of the L1 table to the disk (can't update single entries

 * and we really don't want bdrv_pread to perform a read-modify-write)

 */

#define L1_ENTRIES_PER_SECTOR (512 / 8)

static int write_l1_entry(BlockDriverState *bs, int l1_index)

{

    BDRVQcowState *s = bs->opaque;

    uint64_t buf[L1_ENTRIES_PER_SECTOR];

    int l1_start_index;

    int i, ret;

    l1_start_index = l1_index & ~(L1_ENTRIES_PER_SECTOR - 1);

    for (i = 0; i < L1_ENTRIES_PER_SECTOR; i++) {

        buf[i] = cpu_to_be64(s->l1_table[l1_start_index + i]);

    }

    BLKDBG_EVENT(bs->file, BLKDBG_L1_UPDATE);

    ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset + 8 * l1_start_index,

        buf, sizeof(buf));

    if (ret < 0) {

        return ret;

    }

    return 0;

}

/*

 * l2_allocate

 *

 * Allocate a new l2 entry in the file. If l1_index points to an already

 * used entry in the L2 table (i.e. we are doing a copy on write for the L2

 * table) copy the contents of the old L2 table into the newly allocated one.

 * Otherwise the new table is initialized with zeros.

 *

 */

static int l2_allocate(BlockDriverState *bs, int l1_index, uint64_t **table)

{

    BDRVQcowState *s = bs->opaque;

    uint64_t old_l2_offset;

    uint64_t *l2_table;

    int64_t l2_offset;

    int ret;

    old_l2_offset = s->l1_table[l1_index];

    /* allocate a new l2 entry */

    l2_offset = qcow2_alloc_clusters(bs, s->l2_size * sizeof(uint64_t));

    if (l2_offset < 0) {

        return l2_offset;

    }

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

    if (ret < 0) {

        goto fail;

    }

    /* allocate a new entry in the l2 cache */

    ret = qcow2_cache_get_empty(bs, s->l2_table_cache, l2_offset, (void**) table);

    if (ret < 0) {

        return ret;

    }

    l2_table = *table;

    if (old_l2_offset == 0) {

        /* if there was no old l2 table, clear the new table */

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

    } else {

        uint64_t* old_table;

        /* if there was an old l2 table, read it from the disk */

        BLKDBG_EVENT(bs->file, BLKDBG_L2_ALLOC_COW_READ);

        ret = qcow2_cache_get(bs, s->l2_table_cache, old_l2_offset,

            (void**) &old_table);

        if (ret < 0) {

            goto fail;

        }

        memcpy(l2_table, old_table, s->cluster_size);

        ret = qcow2_cache_put(bs, s->l2_table_cache, (void**) &old_table);

        if (ret < 0) {

            goto fail;

        }

    }

    /* write the l2 table to the file */

    BLKDBG_EVENT(bs->file, BLKDBG_L2_ALLOC_WRITE);

    qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);

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

    if (ret < 0) {

        goto fail;

    }

    /* update the L1 entry */

    s->l1_table[l1_index] = l2_offset | QCOW_OFLAG_COPIED;

    ret = write_l1_entry(bs, l1_index);

    if (ret < 0) {

        goto fail;

    }

    *table = l2_table;

    return 0;

fail:

    qcow2_cache_put(bs, s->l2_table_cache, (void**) table);

    s->l1_table[l1_index] = old_l2_offset;

    return ret;

}

static int count_contiguous_clusters(uint64_t nb_clusters, int cluster_size,

        uint64_t *l2_table, uint64_t start, uint64_t mask)

{

    int i;

    uint64_t offset = be64_to_cpu(l2_table[0]) & ~mask;

    if (!offset)

        return 0;

    for (i = start; i < start + nb_clusters; i++)

        if (offset + (uint64_t) i * cluster_size != (be64_to_cpu(l2_table[i]) & ~mask))

            break;

        return (i - start);

}

static int count_contiguous_free_clusters(uint64_t nb_clusters, uint64_t *l2_table)

{

    int i = 0;

    while(nb_clusters-- && l2_table[i] == 0)

        i++;

    return i;

}

/* The crypt function is compatible with the linux cryptoloop

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

   supported */

void qcow2_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;

    }

}

static int qcow2_read(BlockDriverState *bs, int64_t sector_num,

                      uint8_t *buf, int nb_sectors)

{

    BDRVQcowState *s = bs->opaque;

    int ret, index_in_cluster, n, n1;

    uint64_t cluster_offset;

    struct iovec iov;

    QEMUIOVector qiov;

    while (nb_sectors > 0) {

        n = nb_sectors;

        ret = qcow2_get_cluster_offset(bs, sector_num << 9, &n,

            &cluster_offset);

        if (ret < 0) {

            return ret;

        }

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

        if (!cluster_offset) {

            if (bs->backing_hd) {

                /* read from the base image */

                iov.iov_base = buf;

                iov.iov_len = n * 512;

                qemu_iovec_init_external(&qiov, &iov, 1);

                n1 = qcow2_backing_read1(bs->backing_hd, &qiov, sector_num, n);

                if (n1 > 0) {

                    BLKDBG_EVENT(bs->file, BLKDBG_READ_BACKING);

                    ret = bdrv_read(bs->backing_hd, sector_num, buf, n1);

                    if (ret < 0)

                        return -1;

                }

            } else {

                memset(buf, 0, 512 * n);

            }

        } else if (cluster_offset & QCOW_OFLAG_COMPRESSED) {

            if (qcow2_decompress_cluster(bs, cluster_offset) < 0)

                return -1;

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

        } else {

            BLKDBG_EVENT(bs->file, BLKDBG_READ);

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

            if (ret != n * 512)

                return -1;

            if (s->crypt_method) {

                qcow2_encrypt_sectors(s, sector_num, buf, buf, n, 0,

                                &s->aes_decrypt_key);

            }

        }

        nb_sectors -= n;

        sector_num += n;

        buf += n * 512;

    }

    return 0;

}

static int copy_sectors(BlockDriverState *bs, uint64_t start_sect,

                        uint64_t cluster_offset, int n_start, int n_end)

{

    BDRVQcowState *s = bs->opaque;

    int n, ret;

    n = n_end - n_start;

    if (n <= 0)

        return 0;

    BLKDBG_EVENT(bs->file, BLKDBG_COW_READ);

    ret = qcow2_read(bs, start_sect + n_start, s->cluster_data, n);

    if (ret < 0)

        return ret;

    if (s->crypt_method) {

        qcow2_encrypt_sectors(s, start_sect + n_start,

                        s->cluster_data,

                        s->cluster_data, n, 1,

                        &s->aes_encrypt_key);

    }

    BLKDBG_EVENT(bs->file, BLKDBG_COW_WRITE);

    ret = bdrv_write(bs->file, (cluster_offset >> 9) + n_start,

        s->cluster_data, n);

    if (ret < 0)

        return ret;

    return 0;

}

/*

 * get_cluster_offset

 *

 * For a given offset of the disk image, find the cluster offset in

 * qcow2 file. The offset is stored in *cluster_offset.

 *

 * on entry, *num is the number of contiguous clusters we'd like to

 * access following offset.

 *

 * on exit, *num is the number of contiguous clusters we can read.

 *

 * Return 0, if the offset is found

 * Return -errno, otherwise.

 *

 */

int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,

    int *num, uint64_t *cluster_offset)

{

    BDRVQcowState *s = bs->opaque;

    unsigned int l1_index, l2_index;

    uint64_t l2_offset, *l2_table;

    int l1_bits, c;

    unsigned int index_in_cluster, nb_clusters;

    uint64_t nb_available, nb_needed;

    int ret;

    index_in_cluster = (offset >> 9) & (s->cluster_sectors - 1);

    nb_needed = *num + index_in_cluster;

    l1_bits = s->l2_bits + s->cluster_bits;

    /* compute how many bytes there are between the offset and

     * the end of the l1 entry

     */

    nb_available = (1ULL << l1_bits) - (offset & ((1ULL << l1_bits) - 1));

    /* compute the number of available sectors */

    nb_available = (nb_available >> 9) + index_in_cluster;

    if (nb_needed > nb_available) {

        nb_needed = nb_available;

    }

    *cluster_offset = 0;

    /* seek the the l2 offset in the l1 table */

    l1_index = offset >> l1_bits;

    if (l1_index >= s->l1_size)

        goto out;

    l2_offset = s->l1_table[l1_index];

    /* seek the l2 table of the given l2 offset */

    if (!l2_offset)

        goto out;

    /* load the l2 table in memory */

    l2_offset &= ~QCOW_OFLAG_COPIED;

    ret = l2_load(bs, l2_offset, &l2_table);

    if (ret < 0) {

        return ret;

    }

    /* find the cluster offset for the given disk offset */

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

    *cluster_offset = be64_to_cpu(l2_table[l2_index]);

    nb_clusters = size_to_clusters(s, nb_needed << 9);

    if (!*cluster_offset) {

        /* how many empty clusters ? */

        c = count_contiguous_free_clusters(nb_clusters, &l2_table[l2_index]);

    } else {

        /* how many allocated clusters ? */

        c = count_contiguous_clusters(nb_clusters, s->cluster_size,

                &l2_table[l2_index], 0, QCOW_OFLAG_COPIED);

    }

    qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);

   nb_available = (c * s->cluster_sectors);

out:

    if (nb_available > nb_needed)

        nb_available = nb_needed;

    *num = nb_available - index_in_cluster;

    *cluster_offset &=~QCOW_OFLAG_COPIED;

    return 0;

}

/*

 * get_cluster_table

 *

 * for a given disk offset, load (and allocate if needed)

 * the l2 table.

 *

 * the l2 table offset in the qcow2 file and the cluster index

 * in the l2 table are given to the caller.

 *

 * Returns 0 on success, -errno in failure case

 */

static int get_cluster_table(BlockDriverState *bs, uint64_t offset,

                             uint64_t **new_l2_table,

                             uint64_t *new_l2_offset,

                             int *new_l2_index)

{

    BDRVQcowState *s = bs->opaque;

    unsigned int l1_index, l2_index;

    uint64_t l2_offset;

    uint64_t *l2_table = NULL;

    int ret;

    /* seek the the l2 offset in the l1 table */

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

    if (l1_index >= s->l1_size) {

        ret = qcow2_grow_l1_table(bs, l1_index + 1, false);

        if (ret < 0) {

            return ret;

        }

    }

    l2_offset = s->l1_table[l1_index];

    /* seek the l2 table of the given l2 offset */

    if (l2_offset & QCOW_OFLAG_COPIED) {

        /* load the l2 table in memory */

        l2_offset &= ~QCOW_OFLAG_COPIED;

        ret = l2_load(bs, l2_offset, &l2_table);

        if (ret < 0) {

            return ret;

        }

    } else {

        /* First allocate a new L2 table (and do COW if needed) */

        ret = l2_allocate(bs, l1_index, &l2_table);

        if (ret < 0) {

            return ret;

        }

        /* Then decrease the refcount of the old table */

        if (l2_offset) {

            qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t));

        }

        l2_offset = s->l1_table[l1_index] & ~QCOW_OFLAG_COPIED;

    }

    /* find the cluster offset for the given disk offset */

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

    *new_l2_table = l2_table;

    *new_l2_offset = l2_offset;

    *new_l2_index = l2_index;

    return 0;

}

/*

 * alloc_compressed_cluster_offset

 *

 * For a given offset of the disk image, return cluster offset in

 * qcow2 file.

 *

 * If the offset is not found, allocate a new compressed cluster.

 *

 * Return the cluster offset if successful,

 * Return 0, otherwise.

 *

 */

uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,

                                               uint64_t offset,

                                               int compressed_size)

{

    BDRVQcowState *s = bs->opaque;

    int l2_index, ret;

    uint64_t l2_offset, *l2_table;

    int64_t cluster_offset;

    int nb_csectors;

    ret = get_cluster_table(bs, offset, &l2_table, &l2_offset, &l2_index);

    if (ret < 0) {

        return 0;

    }

    cluster_offset = be64_to_cpu(l2_table[l2_index]);

    if (cluster_offset & QCOW_OFLAG_COPIED)

        return cluster_offset & ~QCOW_OFLAG_COPIED;

    if (cluster_offset)

        qcow2_free_any_clusters(bs, cluster_offset, 1);

    cluster_offset = qcow2_alloc_bytes(bs, compressed_size);

    if (cluster_offset < 0) {

        qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);

        return 0;

    }

    nb_csectors = ((cluster_offset + compressed_size - 1) >> 9) -

                  (cluster_offset >> 9);

    cluster_offset |= QCOW_OFLAG_COMPRESSED |

                      ((uint64_t)nb_csectors << s->csize_shift);

    /* update L2 table */

    /* compressed clusters never have the copied flag */

    BLKDBG_EVENT(bs->file, BLKDBG_L2_UPDATE_COMPRESSED);

    qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);

    l2_table[l2_index] = cpu_to_be64(cluster_offset);

    ret = qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);

    if (ret < 0) {

        return 0;

    }

    return cluster_offset;

}

int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)

{

    BDRVQcowState *s = bs->opaque;

    int i, j = 0, l2_index, ret;

    uint64_t *old_cluster, start_sect, l2_offset, *l2_table;

    uint64_t cluster_offset = m->cluster_offset;

    bool cow = false;

    if (m->nb_clusters == 0)

        return 0;

    old_cluster = qemu_malloc(m->nb_clusters * sizeof(uint64_t));

    /* copy content of unmodified sectors */

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

    if (m->n_start) {

        cow = true;

        ret = copy_sectors(bs, start_sect, cluster_offset, 0, m->n_start);

        if (ret < 0)

            goto err;

    }

    if (m->nb_available & (s->cluster_sectors - 1)) {

        uint64_t end = m->nb_available & ~(uint64_t)(s->cluster_sectors - 1);

        cow = true;

        ret = copy_sectors(bs, start_sect + end, cluster_offset + (end << 9),

                m->nb_available - end, s->cluster_sectors);

        if (ret < 0)

            goto err;

    }

    /*

     * Update L2 table.

     *

     * Before we update the L2 table to actually point to the new cluster, we

     * need to be sure that the refcounts have been increased and COW was

     * handled.

     */

    if (cow) {

        qcow2_cache_depends_on_flush(s->l2_table_cache);

    }

    qcow2_cache_set_dependency(bs, s->l2_table_cache, s->refcount_block_cache);

    ret = get_cluster_table(bs, m->offset, &l2_table, &l2_offset, &l2_index);

    if (ret < 0) {

        goto err;

    }

    qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);

    for (i = 0; i < m->nb_clusters; i++) {

        /* if two concurrent writes happen to the same unallocated cluster

         * each write allocates separate cluster and writes data concurrently.

         * The first one to complete updates l2 table with pointer to its

         * cluster the second one has to do RMW (which is done above by

         * copy_sectors()), update l2 table with its cluster pointer and free

         * old cluster. This is what this loop does */

        if(l2_table[l2_index + i] != 0)

            old_cluster[j++] = l2_table[l2_index + i];

        l2_table[l2_index + i] = cpu_to_be64((cluster_offset +

                    (i << s->cluster_bits)) | QCOW_OFLAG_COPIED);

     }

    ret = qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);

    if (ret < 0) {

        goto err;

    }

    /*

     * If this was a COW, we need to decrease the refcount of the old cluster.

     * Also flush bs->file to get the right order for L2 and refcount update.

     */

    if (j != 0) {

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

            qcow2_free_any_clusters(bs,

                be64_to_cpu(old_cluster[i]) & ~QCOW_OFLAG_COPIED, 1);

        }

    }

    ret = 0;

err:

    qemu_free(old_cluster);

    return ret;

 }

/*

 * alloc_cluster_offset

 *

 * For a given offset of the disk image, return cluster offset in qcow2 file.

 * If the offset is not found, allocate a new cluster.

 *

 * If the cluster was already allocated, m->nb_clusters is set to 0,

 * m->depends_on is set to NULL and the other fields in m are meaningless.

 *

 * If the cluster is newly allocated, m->nb_clusters is set to the number of

 * contiguous clusters that have been allocated. This may be 0 if the request

 * conflict with another write request in flight; in this case, m->depends_on

 * is set and the remaining fields of m are meaningless.

 *

 * If m->nb_clusters is non-zero, the other fields of m are valid and contain

 * information about the first allocated cluster.

 *

 * Return 0 on success and -errno in error cases

 */

int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,

    int n_start, int n_end, int *num, QCowL2Meta *m)

{

    BDRVQcowState *s = bs->opaque;

    int l2_index, ret;

    uint64_t l2_offset, *l2_table;

    int64_t cluster_offset;

    unsigned int nb_clusters, i = 0;

    QCowL2Meta *old_alloc;

    ret = get_cluster_table(bs, offset, &l2_table, &l2_offset, &l2_index);

    if (ret < 0) {

        return ret;

    }

    nb_clusters = size_to_clusters(s, n_end << 9);

    nb_clusters = MIN(nb_clusters, s->l2_size - l2_index);

    cluster_offset = be64_to_cpu(l2_table[l2_index]);

    /* We keep all QCOW_OFLAG_COPIED clusters */

    if (cluster_offset & QCOW_OFLAG_COPIED) {

        nb_clusters = count_contiguous_clusters(nb_clusters, s->cluster_size,

                &l2_table[l2_index], 0, 0);

        cluster_offset &= ~QCOW_OFLAG_COPIED;

        m->nb_clusters = 0;

        m->depends_on = NULL;

        goto out;

    }

    /* for the moment, multiple compressed clusters are not managed */

    if (cluster_offset & QCOW_OFLAG_COMPRESSED)

        nb_clusters = 1;

    /* how many available clusters ? */

    while (i < nb_clusters) {

        i += count_contiguous_clusters(nb_clusters - i, s->cluster_size,

                &l2_table[l2_index], i, 0);

        if ((i >= nb_clusters) || be64_to_cpu(l2_table[l2_index + i])) {

            break;

        }

        i += count_contiguous_free_clusters(nb_clusters - i,

                &l2_table[l2_index + i]);

        if (i >= nb_clusters) {

            break;

        }

        cluster_offset = be64_to_cpu(l2_table[l2_index + i]);

        if ((cluster_offset & QCOW_OFLAG_COPIED) ||

                (cluster_offset & QCOW_OFLAG_COMPRESSED))

            break;

    }

    assert(i <= nb_clusters);

    nb_clusters = i;

    /*

     * Check if there already is an AIO write request in flight which allocates

     * the same cluster. In this case we need to wait until the previous

     * request has completed and updated the L2 table accordingly.

     */

    QLIST_FOREACH(old_alloc, &s->cluster_allocs, next_in_flight) {

        uint64_t end_offset = offset + nb_clusters * s->cluster_size;

        uint64_t old_offset = old_alloc->offset;

        uint64_t old_end_offset = old_alloc->offset +

            old_alloc->nb_clusters * s->cluster_size;

        if (end_offset < old_offset || offset > old_end_offset) {

            /* No intersection */

        } else {

            if (offset < old_offset) {

                /* Stop at the start of a running allocation */

                nb_clusters = (old_offset - offset) >> s->cluster_bits;

            } else {

                nb_clusters = 0;

            }

            if (nb_clusters == 0) {

                /* Set dependency and wait for a callback */

                m->depends_on = old_alloc;

                m->nb_clusters = 0;

                *num = 0;

                ret = 0;

                goto fail;

            }

        }

    }

    if (!nb_clusters) {

        abort();

    }

    QLIST_INSERT_HEAD(&s->cluster_allocs, m, next_in_flight);

    /* allocate a new cluster */

    cluster_offset = qcow2_alloc_clusters(bs, nb_clusters * s->cluster_size);

    if (cluster_offset < 0) {

        QLIST_REMOVE(m, next_in_flight);

        ret = cluster_offset;

        goto fail;

    }

    /* save info needed for meta data update */

    m->offset = offset;

    m->n_start = n_start;

    m->nb_clusters = nb_clusters;

out:

    ret = qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);

    if (ret < 0) {

        return ret;

    }

    m->nb_available = MIN(nb_clusters << (s->cluster_bits - 9), n_end);

    m->cluster_offset = cluster_offset;

    *num = m->nb_available - n_start;

    return 0;

fail:

    qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);

    return ret;

}

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;

}

int qcow2_decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset)

{

    BDRVQcowState *s = bs->opaque;

    int ret, csize, nb_csectors, sector_offset;

    uint64_t coffset;

    coffset = cluster_offset & s->cluster_offset_mask;

    if (s->cluster_cache_offset != coffset) {

        nb_csectors = ((cluster_offset >> s->csize_shift) & s->csize_mask) + 1;

        sector_offset = coffset & 511;

        csize = nb_csectors * 512 - sector_offset;

        BLKDBG_EVENT(bs->file, BLKDBG_READ_COMPRESSED);

        ret = bdrv_read(bs->file, coffset >> 9, s->cluster_data, nb_csectors);

        if (ret < 0) {

            return ret;

        }

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

                              s->cluster_data + sector_offset, csize) < 0) {

            return -EIO;

        }

        s->cluster_cache_offset = coffset;

    }

    return 0;

}

/*

 * This discards as many clusters of nb_clusters as possible at once (i.e.

 * all clusters in the same L2 table) and returns the number of discarded

 * clusters.

 */

static int discard_single_l2(BlockDriverState *bs, uint64_t offset,

    unsigned int nb_clusters)

{

    BDRVQcowState *s = bs->opaque;

    uint64_t l2_offset, *l2_table;

    int l2_index;

    int ret;

    int i;

    ret = get_cluster_table(bs, offset, &l2_table, &l2_offset, &l2_index);

    if (ret < 0) {

        return ret;

    }

    /* Limit nb_clusters to one L2 table */