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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 17:17:46 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 |
On 05.08.19 17:14, Max Reitz wrote:
> 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?
Ah. That’s why. Because the children can fail.
That is so stupid. Like, really.
Max
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