Re: [Qemu-block] [PATCH v2] mirror: Only mirror granularity-aligned chunks

[Vladimir Sementsov-Ogievskiy]

05.08.2019 17:55, Max Reitz wrote:
> In write-blocking mode, all writes to the top node directly go to the
> target.  We must only mirror chunks of data that are aligned to the
> job's granularity, because that is how the dirty bitmap works.
> Therefore, the request alignment for writes must be the job's
> granularity (in write-blocking mode).
> 
> Unfortunately, this forces all reads and writes to have the same
> granularity (we only need this alignment for writes to the target, not
> the source), but that is something to be fixed another time.
> 
> Cc: address@hidden
> Signed-off-by: Max Reitz <address@hidden>
> ---
> v2: Fix the placement of our bdrv_refresh_limits() call [Vladimir]
> ---
>   block/mirror.c | 25 +++++++++++++++++++++++++
>   1 file changed, 25 insertions(+)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 8cb75fb409..7f0ff01beb 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -1481,6 +1481,15 @@ static void 
> bdrv_mirror_top_child_perm(BlockDriverState *bs, BdrvChild *c,
>       *nshared = BLK_PERM_ALL;
>   }
>   
> +static void bdrv_mirror_top_refresh_limits(BlockDriverState *bs, Error 
> **errp)
> +{
> +    MirrorBDSOpaque *s = bs->opaque;
> +
> +    if (s && s->job && s->job->copy_mode == MIRROR_COPY_MODE_WRITE_BLOCKING) 
> {
> +        bs->bl.request_alignment = s->job->granularity;
> +    }
> +}
> +
>   /* Dummy node that provides consistent read to its users without requiring 
> it
>    * from its backing file and that allows writes on the backing file chain. 
> */
>   static BlockDriver bdrv_mirror_top = {
> @@ -1493,6 +1502,7 @@ static BlockDriver bdrv_mirror_top = {
>       .bdrv_co_block_status       = bdrv_co_block_status_from_backing,
>       .bdrv_refresh_filename      = bdrv_mirror_top_refresh_filename,
>       .bdrv_child_perm            = bdrv_mirror_top_child_perm,
> +    .bdrv_refresh_limits        = bdrv_mirror_top_refresh_limits,
>   };
>   
>   static BlockJob *mirror_start_job(
> @@ -1637,6 +1647,21 @@ static BlockJob *mirror_start_job(
>           s->should_complete = true;
>       }
>   
> +    /*
> +     * Must be called before we start tracking writes, but after
> +     *
> +     *     ((MirrorBlockJob *)
> +     *         ((MirrorBDSOpaque *)
> +     *             mirror_top_bs->opaque
> +     *         )->job
> +     *     )->copy_mode
> +     *
> +     * has the correct value.
> +     * (We start tracking writes as of the following
> +     * bdrv_create_dirty_bitmap() call.)
> +     */
> +    bdrv_refresh_limits(mirror_top_bs, &error_abort);

Also, I'm not sure about error_abort() here. why not use local_err and return 
NULL
if failed?

> +
>       s->dirty_bitmap = bdrv_create_dirty_bitmap(bs, granularity, NULL, errp);
>       if (!s->dirty_bitmap) {
>           goto fail;
> 


-- 
Best regards,
Vladimir