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Re: [Qemu-devel] [PATCH v6 11/12] qed: Implement .bdrv_drain
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH v6 11/12] qed: Implement .bdrv_drain |
Date: |
Fri, 23 Oct 2015 11:07:11 +0800 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Thu, 10/22 22:59, Paolo Bonzini wrote:
>
>
> On 22/10/2015 12:53, Kevin Wolf wrote:
> > Am 22.10.2015 um 08:32 hat Fam Zheng geschrieben:
> >> The "need_check_timer" is used to clear the "NEED_CHECK" flag in the
> >> image header after a grace period once metadata update has finished. In
> >> compliance to the bdrv_drain semantics we should make sure it remains
> >> deleted once .bdrv_drain is called.
> >>
> >> We cannot reuse qed_need_check_timer_cb because it calls bdrv_aio_flush
> >> with a completion callback that starts more I/O, bdrv_drain cannot cope
> >> with this.
> >
> > For the record: I discussed this with Fam on IRC and we came to the
> > conclusion that we should instead fix bdrv_drain() to correctly drain
> > in-flight flushes.
> >
> > In order to achieve this, Fam will send a series that adds a
> > BdrvTrackedRequest to all remaining asynchronous operations. So far we
> > have identified flush, discard and aio_ioctl. At the same time he will
> > send a rebased version of this series that goes back to asynchronous
> > flushing in bdrv_qed_drain().
>
> This is a completely separate bug. Can you at least merge all patches
> except this, so that everything except QED can do snapshots with
> dataplane? Of course there will be a v7 at least for patch 9.
>
So I'll drop the two patches for QED in v7, and let them follow the bdrv_drain
fixing series.
Actually, I think the current being of the QED timer doesn't change guest
visible data - if the callback would dequeue more allocating requests
(qed_unplug_allocating_write_reqs), the loop in bdrv_drain will wait for them.
So it's not a big problem for the sake of transaction after all.
Fam
- [Qemu-devel] [PATCH v6 06/12] block: Add "drained begin/end" for transactional external snapshot, (continued)
- [Qemu-devel] [PATCH v6 06/12] block: Add "drained begin/end" for transactional external snapshot, Fam Zheng, 2015/10/22
- [Qemu-devel] [PATCH v6 07/12] block: Add "drained begin/end" for transactional backup, Fam Zheng, 2015/10/22
- [Qemu-devel] [PATCH v6 08/12] block: Add "drained begin/end" for transactional blockdev-backup, Fam Zheng, 2015/10/22
- [Qemu-devel] [PATCH v6 09/12] block: Add "drained begin/end" for internal snapshot, Fam Zheng, 2015/10/22
- [Qemu-devel] [PATCH v6 10/12] block: Introduce BlockDriver.bdrv_drain callback, Fam Zheng, 2015/10/22
- [Qemu-devel] [PATCH v6 11/12] qed: Implement .bdrv_drain, Fam Zheng, 2015/10/22
- [Qemu-devel] [PATCH v6 12/12] tests: Add test case for aio_disable_external, Fam Zheng, 2015/10/22