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Re: [Qemu-block] [PATCH v2 05/12] block: Introduce "drained begin/end" A
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From: |
Kevin Wolf |
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Subject: |
Re: [Qemu-block] [PATCH v2 05/12] block: Introduce "drained begin/end" API |
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Date: |
Tue, 13 Oct 2015 11:31:42 +0200 |
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User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 12.10.2015 um 16:27 hat Paolo Bonzini geschrieben:
>
>
> On 12/10/2015 13:50, Fam Zheng wrote:
> > +void bdrv_drained_begin(BlockDriverState *bs)
> > +{
> > + if (bs->quiesce_counter++) {
> > + return;
> > + }
> > + aio_disable_external(bdrv_get_aio_context(bs));
> > + bdrv_drain(bs);
> > +}
>
> I think bdrv_drain should be called unconditionally, i.e. before the
> "if". This should also solve Kevin's doubt about new allocating write
> request reenabling the timer: any write request from the drained section
> happens normally, until you get a nested drain request and then the
> callback completes the requests.
This would mean that once you've sent an I/O request inside a drain
section, you have to expect that more internal I/O might be going on
after the request has completed. If you don't want this, you have to
issue another bdrv_drain() or use a nested bdrv_drained_begin/end()
section.
Sounds reasonable enough to me, but I guess this should be explicitly
documented.
Kevin
[Qemu-block] [PATCH v2 08/12] block: Add "drained begin/end" for transactional blockdev-backup, Fam Zheng, 2015/10/12
[Qemu-block] [PATCH v2 07/12] block: Add "drained begin/end" for transactional backup, Fam Zheng, 2015/10/12
[Qemu-block] [PATCH v2 11/12] qed: Implement .bdrv_drain, Fam Zheng, 2015/10/12
[Qemu-block] [PATCH v2 10/12] block: Introduce BlockDriver.bdrv_drain callback, Fam Zheng, 2015/10/12
[Qemu-block] [PATCH v2 12/12] tests: Add test case for aio_disable_external, Fam Zheng, 2015/10/12
[Qemu-block] [PATCH v2 01/12] aio: Add "is_external" flag for event handlers, Fam Zheng, 2015/10/15