Re: [PATCH 1/3] block: add subcluster_size field to BlockDriverInfo

[Eric Blake]

On Mon, Jun 26, 2023 at 07:08:32PM +0300, Andrey Drobyshev via wrote:
> This is going to be used in the subsequent commit as requests alignment
> (in particular, during copy-on-read).  This value only makes sense for
> the formats which support subclusters (currently QCOW2 only).  If this
> field isn't set by driver's own bdrv_get_info() implementation, we
> simply set it equal to the cluster size thus treating each cluster as having
> a single subcluster.
> 
> Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
> ---
>  block.c                      | 7 +++++++
>  block/qcow2.c                | 1 +
>  include/block/block-common.h | 5 +++++
>  3 files changed, 13 insertions(+)
> 
> diff --git a/block.c b/block.c
> index 0637265c26..4fe1743cfb 100644
> --- a/block.c
> +++ b/block.c
> @@ -6392,6 +6392,13 @@ int coroutine_fn bdrv_co_get_info(BlockDriverState 
> *bs, BlockDriverInfo *bdi)
>      }
>      memset(bdi, 0, sizeof(*bdi));
>      ret = drv->bdrv_co_get_info(bs, bdi);
> +    if (bdi->subcluster_size == 0) {
> +        /*
> +         * If the driver left this unset, subclusters either not supported.

s/either/are/

> +         * Then it is safe to treat each cluster as having only one 
> subcluster.
> +         */
> +        bdi->subcluster_size = bdi->cluster_size;
> +    }

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

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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