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

                      Error **errp)

{

    BDRVCloopState *s = bs->opaque;

    uint32_t offsets_size, max_compressed_block_size = 1, i;

    int ret;



    bs->read_only = 1;



    /* read header */

    ret = bdrv_pread(bs->file, 128, &s->block_size, 4);

    if (ret < 0) {

        return ret;

    }

    s->block_size = be32_to_cpu(s->block_size);

    if (s->block_size % 512) {

        error_setg(errp, "block_size %u must be a multiple of 512",

                   s->block_size);

        return -EINVAL;

    }

    if (s->block_size == 0) {

        error_setg(errp, "block_size cannot be zero");

        return -EINVAL;

    }



    /* cloop's create_compressed_fs.c warns about block sizes beyond 256 KB but

     * we can accept more.  Prevent ridiculous values like 4 GB - 1 since we

     * need a buffer this big.

     */

    if (s->block_size > MAX_BLOCK_SIZE) {

        error_setg(errp, "block_size %u must be %u MB or less",

                   s->block_size,

                   MAX_BLOCK_SIZE / (1024 * 1024));

        return -EINVAL;

    }



    ret = bdrv_pread(bs->file, 128 + 4, &s->n_blocks, 4);

    if (ret < 0) {

        return ret;

    }

    s->n_blocks = be32_to_cpu(s->n_blocks);



    /* read offsets */

    if (s->n_blocks > UINT32_MAX / sizeof(uint64_t)) {

        /* Prevent integer overflow */

        error_setg(errp, "n_blocks %u must be %zu or less",

                   s->n_blocks,

                   UINT32_MAX / sizeof(uint64_t));

        return -EINVAL;

    }

    offsets_size = s->n_blocks * sizeof(uint64_t);

    if (offsets_size > 512 * 1024 * 1024) {

        /* Prevent ridiculous offsets_size which causes memory allocation to

         * fail or overflows bdrv_pread() size.  In practice the 512 MB

         * offsets[] limit supports 16 TB images at 256 KB block size.

         */

        error_setg(errp, "image requires too many offsets, "

                   "try increasing block size");

        return -EINVAL;

    }

    s->offsets = g_malloc(offsets_size);



    ret = bdrv_pread(bs->file, 128 + 4 + 4, s->offsets, offsets_size);

    if (ret < 0) {

        goto fail;

    }



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

        s->offsets[i] = be64_to_cpu(s->offsets[i]);

        if (i > 0) {

            uint32_t size = s->offsets[i] - s->offsets[i - 1];

            if (size > max_compressed_block_size) {

                max_compressed_block_size = size;

            }

        }

    }



    /* initialize zlib engine */

    s->compressed_block = g_malloc(max_compressed_block_size + 1);

    s->uncompressed_block = g_malloc(s->block_size);

    if (inflateInit(&s->zstream) != Z_OK) {

        ret = -EINVAL;

        goto fail;

    }

    s->current_block = s->n_blocks;



    s->sectors_per_block = s->block_size/512;

    bs->total_sectors = s->n_blocks * s->sectors_per_block;

    qemu_co_mutex_init(&s->lock);

    return 0;



fail:

    g_free(s->offsets);

    g_free(s->compressed_block);

    g_free(s->uncompressed_block);

    return ret;

}
