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Re: [Qemu-devel] [PATCH v2] mirror: Only mirror granularity-aligned chun
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
Re: [Qemu-devel] [PATCH v2] mirror: Only mirror granularity-aligned chunks |
Date: |
Mon, 5 Aug 2019 15:09:24 +0000 |
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