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/block_int.h"

#include "block/qcow2.h"

#include "trace.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

    fprintf(stderr, "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 = g_malloc0(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) {

        g_free(new_l1_table);

        return new_l1_table_offset;

    }

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

    if (ret < 0) {

        goto fail;

    }

    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;

    }

    g_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:

    g_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];

    trace_qcow2_l2_allocate(bs, 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 */

    trace_qcow2_l2_allocate_get_empty(bs, l1_index);

    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 & L1E_OFFSET_MASK) == 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 & L1E_OFFSET_MASK,

            (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);

    trace_qcow2_l2_allocate_write_l2(bs, l1_index);

    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 */

    trace_qcow2_l2_allocate_write_l1(bs, l1_index);

    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;

    trace_qcow2_l2_allocate_done(bs, l1_index, 0);

    return 0;

fail:

    trace_qcow2_l2_allocate_done(bs, l1_index, ret);

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

    s->l1_table[l1_index] = old_l2_offset;

    return ret;

}

/*

 * Checks how many clusters in a given L2 table are contiguous in the image

 * file. As soon as one of the flags in the bitmask stop_flags changes compared

 * to the first cluster, the search is stopped and the cluster is not counted

 * as contiguous. (This allows it, for example, to stop at the first compressed

 * cluster which may require a different handling)

 */

static int count_contiguous_clusters(uint64_t nb_clusters, int cluster_size,

        uint64_t *l2_table, uint64_t start, uint64_t stop_flags)

{

    int i;

    uint64_t mask = stop_flags | L2E_OFFSET_MASK;

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

    if (!offset)

        return 0;

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

        uint64_t l2_entry = be64_to_cpu(l2_table[i]) & mask;

        if (offset + (uint64_t) i * cluster_size != l2_entry) {

            break;

        }

    }

        return (i - start);

}

static int count_contiguous_free_clusters(uint64_t nb_clusters, uint64_t *l2_table)

{

    int i;

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

        int type = qcow2_get_cluster_type(be64_to_cpu(l2_table[i]));

        if (type != QCOW2_CLUSTER_UNALLOCATED) {

            break;

        }

    }

    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 coroutine_fn copy_sectors(BlockDriverState *bs,

                                     uint64_t start_sect,

                                     uint64_t cluster_offset,

                                     int n_start, int n_end)

{

    BDRVQcowState *s = bs->opaque;

    QEMUIOVector qiov;

    struct iovec iov;

    int n, ret;

    /*

     * If this is the last cluster and it is only partially used, we must only

     * copy until the end of the image, or bdrv_check_request will fail for the

     * bdrv_read/write calls below.

     */

    if (start_sect + n_end > bs->total_sectors) {

        n_end = bs->total_sectors - start_sect;

    }

    n = n_end - n_start;

    if (n <= 0) {

        return 0;

    }

    iov.iov_len = n * BDRV_SECTOR_SIZE;

    iov.iov_base = qemu_blockalign(bs, iov.iov_len);

    qemu_iovec_init_external(&qiov, &iov, 1);

    BLKDBG_EVENT(bs->file, BLKDBG_COW_READ);

    /* Call .bdrv_co_readv() directly instead of using the public block-layer

     * interface.  This avoids double I/O throttling and request tracking,

     * which can lead to deadlock when block layer copy-on-read is enabled.

     */

    ret = bs->drv->bdrv_co_readv(bs, start_sect + n_start, n, &qiov);

    if (ret < 0) {

        goto out;

    }

    if (s->crypt_method) {

        qcow2_encrypt_sectors(s, start_sect + n_start,

                        iov.iov_base, iov.iov_base, n, 1,

                        &s->aes_encrypt_key);

    }

    BLKDBG_EVENT(bs->file, BLKDBG_COW_WRITE);

    ret = bdrv_co_writev(bs->file, (cluster_offset >> 9) + n_start, n, &qiov);

    if (ret < 0) {

        goto out;

    }

    ret = 0;

out:

    qemu_vfree(iov.iov_base);

    return ret;

}

/*

 * 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 sectors we'd like to

 * access following offset.

 *

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

 *

 * Returns the cluster type (QCOW2_CLUSTER_*) on success, -errno in error

 * cases.

 */

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) {

        ret = QCOW2_CLUSTER_UNALLOCATED;

        goto out;

    }

    l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;

    if (!l2_offset) {

        ret = QCOW2_CLUSTER_UNALLOCATED;

        goto out;

    }

    /* load the l2 table in memory */

    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);

    ret = qcow2_get_cluster_type(*cluster_offset);

    switch (ret) {

    case QCOW2_CLUSTER_COMPRESSED:

        /* Compressed clusters can only be processed one by one */

        c = 1;

        *cluster_offset &= L2E_COMPRESSED_OFFSET_SIZE_MASK;

        break;

    case QCOW2_CLUSTER_ZERO:

        if (s->qcow_version < 3) {

            return -EIO;

        }

        c = count_contiguous_clusters(nb_clusters, s->cluster_size,

                &l2_table[l2_index], 0,

                QCOW_OFLAG_COMPRESSED | QCOW_OFLAG_ZERO);

        *cluster_offset = 0;

        break;

    case QCOW2_CLUSTER_UNALLOCATED:

        /* how many empty clusters ? */

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

        *cluster_offset = 0;

        break;

    case QCOW2_CLUSTER_NORMAL:

        /* how many allocated clusters ? */

        c = count_contiguous_clusters(nb_clusters, s->cluster_size,

                &l2_table[l2_index], 0,

                QCOW_OFLAG_COMPRESSED | QCOW_OFLAG_ZERO);

        *cluster_offset &= L2E_OFFSET_MASK;

        break;

    default:

        abort();

    }

    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;

    return ret;

}

/*

 * 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,

                             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] & L1E_OFFSET_MASK;

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

    if (s->l1_table[l1_index] & QCOW_OFLAG_COPIED) {

        /* load the l2 table in memory */

        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));

        }

    }

    /* 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_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_table;

    int64_t cluster_offset;

    int nb_csectors;

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

    if (ret < 0) {

        return 0;

    }

    /* Compression can't overwrite anything. Fail if the cluster was already

     * allocated. */

    cluster_offset = be64_to_cpu(l2_table[l2_index]);

    if (cluster_offset & L2E_OFFSET_MASK) {

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

        return 0;

    }

    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;

}

static int perform_cow(BlockDriverState *bs, QCowL2Meta *m, Qcow2COWRegion *r)

{

    BDRVQcowState *s = bs->opaque;

    int ret;

    if (r->nb_sectors == 0) {

        return 0;

    }

    qemu_co_mutex_unlock(&s->lock);

    ret = copy_sectors(bs, m->offset / BDRV_SECTOR_SIZE, m->alloc_offset,

                       r->offset / BDRV_SECTOR_SIZE,

                       r->offset / BDRV_SECTOR_SIZE + r->nb_sectors);

    qemu_co_mutex_lock(&s->lock);

    if (ret < 0) {

        return ret;

    }

    /*

     * 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.

     */

    qcow2_cache_depends_on_flush(s->l2_table_cache);

    return 0;

}

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, *l2_table;

    uint64_t cluster_offset = m->alloc_offset;

    trace_qcow2_cluster_link_l2(qemu_coroutine_self(), m->nb_clusters);

    assert(m->nb_clusters > 0);

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

    /* copy content of unmodified sectors */

    ret = perform_cow(bs, m, &m->cow_start);

    if (ret < 0) {

        goto err;

    }

    ret = perform_cow(bs, m, &m->cow_end);

    if (ret < 0) {

        goto err;

    }

    /* Update L2 table. */

    if (s->use_lazy_refcounts) {

        qcow2_mark_dirty(bs);

    }

    if (qcow2_need_accurate_refcounts(s)) {

        qcow2_cache_set_dependency(bs, s->l2_table_cache,

                                   s->refcount_block_cache);

    }

    ret = get_cluster_table(bs, m->offset, &l2_table, &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]), 1);

        }

    }

    ret = 0;

err:

    g_free(old_cluster);

    return ret;

 }

/*

 * Returns the number of contiguous clusters that can be used for an allocating

 * write, but require COW to be performed (this includes yet unallocated space,

 * which must copy from the backing file)

 */

static int count_cow_clusters(BDRVQcowState *s, int nb_clusters,

    uint64_t *l2_table, int l2_index)

{

    int i;

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

        uint64_t l2_entry = be64_to_cpu(l2_table[l2_index + i]);

        int cluster_type = qcow2_get_cluster_type(l2_entry);

        switch(cluster_type) {

        case QCOW2_CLUSTER_NORMAL:

            if (l2_entry & QCOW_OFLAG_COPIED) {

                goto out;

            }

            break;

        case QCOW2_CLUSTER_UNALLOCATED:

        case QCOW2_CLUSTER_COMPRESSED:

        case QCOW2_CLUSTER_ZERO:

            break;

        default:

            abort();

        }

    }

out:

    assert(i <= nb_clusters);

    return 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.

 *

 * Returns:

 *   0       if there was no dependency. *cur_bytes indicates the number of

 *           bytes from guest_offset that can be read before the next

 *           dependency must be processed (or the request is complete)

 *

 *   -EAGAIN if we had to wait for another request, previously gathered

 *           information on cluster allocation may be invalid now. The caller

 *           must start over anyway, so consider *cur_bytes undefined.

 */

static int handle_dependencies(BlockDriverState *bs, uint64_t guest_offset,

    uint64_t *cur_bytes, QCowL2Meta **m)

{

    BDRVQcowState *s = bs->opaque;

    QCowL2Meta *old_alloc;

    uint64_t bytes = *cur_bytes;

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

        uint64_t start = guest_offset;

        uint64_t end = start + bytes;

        uint64_t old_start = l2meta_cow_start(old_alloc);

        uint64_t old_end = l2meta_cow_end(old_alloc);

        if (end <= old_start || start >= old_end) {

            /* No intersection */

        } else {

            if (start < old_start) {

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

                bytes = old_start - start;

            } else {

                bytes = 0;

            }

            /* Stop if already an l2meta exists. After yielding, it wouldn't

             * be valid any more, so we'd have to clean up the old L2Metas

             * and deal with requests depending on them before starting to

             * gather new ones. Not worth the trouble. */

            if (bytes == 0 && *m) {

                *cur_bytes = 0;

                return 0;

            }

            if (bytes == 0) {

                /* Wait for the dependency to complete. We need to recheck

                 * the free/allocated clusters when we continue. */

                qemu_co_mutex_unlock(&s->lock);

                qemu_co_queue_wait(&old_alloc->dependent_requests);

                qemu_co_mutex_lock(&s->lock);

                return -EAGAIN;

            }

        }

    }

    /* Make sure that existing clusters and new allocations are only used up to

     * the next dependency if we shortened the request above */

    *cur_bytes = bytes;

    return 0;

}

/*

 * Checks how many already allocated clusters that don't require a copy on

 * write there are at the given guest_offset (up to *bytes). If

 * *host_offset is not zero, only physically contiguous clusters beginning at

 * this host offset are counted.

 *

 * Note that guest_offset may not be cluster aligned. In this case, the

 * returned *host_offset points to exact byte referenced by guest_offset and

 * therefore isn't cluster aligned as well.

 *

 * Returns:

 *   0:     if no allocated clusters are available at the given offset.

 *          *bytes is normally unchanged. It is set to 0 if the cluster

 *          is allocated and doesn't need COW, but doesn't have the right

 *          physical offset.

 *

 *   1:     if allocated clusters that don't require a COW are available at

 *          the requested offset. *bytes may have decreased and describes

 *          the length of the area that can be written to.

 *

 *  -errno: in error cases

 */

static int handle_copied(BlockDriverState *bs, uint64_t guest_offset,

    uint64_t *host_offset, uint64_t *bytes, QCowL2Meta **m)

{

    BDRVQcowState *s = bs->opaque;

    int l2_index;

    uint64_t cluster_offset;

    uint64_t *l2_table;

    unsigned int nb_clusters;

    unsigned int keep_clusters;

    int ret, pret;

    trace_qcow2_handle_copied(qemu_coroutine_self(), guest_offset, *host_offset,

                              *bytes);

    assert(*host_offset == 0 ||    offset_into_cluster(s, guest_offset)

                                == offset_into_cluster(s, *host_offset));

    /*

     * Calculate the number of clusters to look for. We stop at L2 table

     * boundaries to keep things simple.

     */

    nb_clusters =

        size_to_clusters(s, offset_into_cluster(s, guest_offset) + *bytes);

    l2_index = offset_to_l2_index(s, guest_offset);

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

    /* Find L2 entry for the first involved cluster */

    ret = get_cluster_table(bs, guest_offset, &l2_table, &l2_index);

    if (ret < 0) {

        return ret;

    }

    cluster_offset = be64_to_cpu(l2_table[l2_index]);

    /* Check how many clusters are already allocated and don't need COW */

    if (qcow2_get_cluster_type(cluster_offset) == QCOW2_CLUSTER_NORMAL

        && (cluster_offset & QCOW_OFLAG_COPIED))

    {

        /* If a specific host_offset is required, check it */

        bool offset_matches =

            (cluster_offset & L2E_OFFSET_MASK) == *host_offset;

        if (*host_offset != 0 && !offset_matches) {

            *bytes = 0;

            ret = 0;

            goto out;

        }

        /* We keep all QCOW_OFLAG_COPIED clusters */

        keep_clusters =

            count_contiguous_clusters(nb_clusters, s->cluster_size,

                                      &l2_table[l2_index], 0,

                                      QCOW_OFLAG_COPIED | QCOW_OFLAG_ZERO);

        assert(keep_clusters <= nb_clusters);

        *bytes = MIN(*bytes,

                 keep_clusters * s->cluster_size

                 - offset_into_cluster(s, guest_offset));

        ret = 1;

    } else {

        ret = 0;

    }

    /* Cleanup */

out:

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

    if (pret < 0) {

        return pret;

    }