Re: [Qemu-block] [PATCH 5/7] qcow2: use byte-based read in qcow2_decompress_cluster

[Alberto Garcia]

On Thu 01 Nov 2018 07:27:36 PM CET, Vladimir Sementsov-Ogievskiy wrote:

> diff --git a/block/qcow2.c b/block/qcow2.c
> index e9d24b801e..950b9f7ec6 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -3956,14 +3956,15 @@ fail:
>  int qcow2_decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset)
>  {
>      BDRVQcow2State *s = bs->opaque;
> -    int ret, csize, nb_csectors, sector_offset;
> +    int ret, csize, nb_csectors;
>      uint64_t coffset;
> +    struct iovec iov;
> +    QEMUIOVector local_qiov;
>  
>      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;
> +        csize = nb_csectors * 512 - (coffset & 511);
>  
>          /* Allocate buffers on first decompress operation, most images are
>           * uncompressed and the memory overhead can be avoided.  The buffers
> @@ -3981,14 +3982,17 @@ int qcow2_decompress_cluster(BlockDriverState *bs, 
> uint64_t cluster_offset)
>              s->cluster_cache = g_malloc(s->cluster_size);
>          }
>  
> +        iov.iov_base = s->cluster_data;
> +        iov.iov_len = csize;
> +        qemu_iovec_init_external(&local_qiov, &iov, 1);
> +
>          BLKDBG_EVENT(bs->file, BLKDBG_READ_COMPRESSED);
> -        ret = bdrv_read(bs->file, coffset >> 9, s->cluster_data,
> -                        nb_csectors);
> +        ret = bdrv_co_preadv(bs->file, coffset, csize, &local_qiov,
> 0);

I think you should annotate the function with coroutine_fn or use
bdrv_pread() instead.

Berto