Re: [PATCH 2/3] block/io: align requests to subcluster_size

[Eric Blake]

On Mon, Jun 26, 2023 at 07:08:33PM +0300, Andrey Drobyshev via wrote:
> When target image is using subclusters, and we align the request during
> copy-on-read, it makes sense to align to subcluster_size rather than
> cluster_size.  Otherwise we end up with unnecessary allocations.
> 
> This commit renames bdrv_round_to_clusters() to bdrv_round_to_subclusters()
> and utilizes subcluster_size field of BlockDriverInfo to make necessary
> alignments.  It affects copy-on-read as well as mirror job (which is
> using bdrv_round_to_clusters()).
> 
> This change also fixes the following bug with failing assert (covered by
> the test in the subsequent commit):
> 
> qemu-img create -f qcow2 base.qcow2 64K
> qemu-img create -f qcow2 -o 
> extended_l2=on,backing_file=base.qcow2,backing_fmt=qcow2 img.qcow2 64K
> qemu-io -c "write -P 0xaa 0 2K" img.qcow2
> qemu-io -C -c "read -P 0x00 2K 62K" img.qcow2
> 
> qemu-io: ../block/io.c:1236: bdrv_co_do_copy_on_readv: Assertion `skip_bytes 
> < pnum' failed.
> 
> Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
> ---
>  block/io.c               | 50 ++++++++++++++++++++--------------------
>  block/mirror.c           |  8 +++----
>  include/block/block-io.h |  2 +-
>  3 files changed, 30 insertions(+), 30 deletions(-)
> 
> +++ b/include/block/block-io.h
> @@ -189,7 +189,7 @@ bdrv_get_info(BlockDriverState *bs, BlockDriverInfo *bdi);
>  ImageInfoSpecific *bdrv_get_specific_info(BlockDriverState *bs,
>                                            Error **errp);
>  BlockStatsSpecific *bdrv_get_specific_stats(BlockDriverState *bs);
> -void bdrv_round_to_clusters(BlockDriverState *bs,
> +void bdrv_round_to_subclusters(BlockDriverState *bs,
>                              int64_t offset, int64_t bytes,
>                              int64_t *cluster_offset,
>                              int64_t *cluster_bytes);

Indentation on subsequent lines should be fixed.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org