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Re: [Qemu-devel] [PATCH v2] mirror: Only mirror granularity-aligned chun
From: |
Max Reitz |
Subject: |
Re: [Qemu-devel] [PATCH v2] mirror: Only mirror granularity-aligned chunks |
Date: |
Mon, 5 Aug 2019 17:14:52 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 |
On 05.08.19 17:09, Vladimir Sementsov-Ogievskiy wrote:
> 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?
Why would it fail?
Max
>> +
>> s->dirty_bitmap = bdrv_create_dirty_bitmap(bs, granularity, NULL,
>> errp);
>> if (!s->dirty_bitmap) {
>> goto fail;
>>
>
>
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