int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,

    int *num, uint64_t *cluster_offset)

{

    BDRVQcowState *s = bs->opaque;

    unsigned int l2_index;

    uint64_t l1_index, 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], 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], QCOW_OFLAG_ZERO);

        *cluster_offset &= L2E_OFFSET_MASK;

        break;

    default:

        abort();

    }






    nb_available = (c * s->cluster_sectors);



out:

    if (nb_available > nb_needed)

        nb_available = nb_needed;



    *num = nb_available - index_in_cluster;



    return ret;

}