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Date: Thu, 27 Jun 2013 15:29:38 +0200
From: Stefan Hajnoczi <stefanha@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v4 01/17] block: stop relying on io_flush()
 in bdrv_drain_all()
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Ping Fan Liu <pingfank@linux.vnet.ibm.com>, qemu-devel@nongnu.org

On Thu, Jun 27, 2013 at 03:13:19PM +0200, Paolo Bonzini wrote:
> Il 14/06/2013 13:43, Stefan Hajnoczi ha scritto:
> > If a block driver has no file descriptors to monitor but there are still
> > active requests, it can return 1 from .io_flush().  This is used to spin
> > during synchronous I/O.
> > 
> > Stop relying on .io_flush() and instead check
> > QLIST_EMPTY(&bs->tracked_requests) to decide whether there are active
> > requests.
> > 
> > This is the first step in removing .io_flush() so that event loops no
> > longer need to have the concept of synchronous I/O.  Eventually we may
> > be able to kill synchronous I/O completely by running everything in a
> > coroutine, but that is future work.
> > 
> > Note this patch moves bs->throttled_reqs initialization to bdrv_new() so
> > that bdrv_requests_pending(bs) can safely access it.  In practice bs is
> > g_malloc0() so the memory is already zeroed but it's safer to initialize
> > the queue properly.
> > 
> > In bdrv_delete() make sure to call bdrv_make_anon() *after* bdrv_close()
> > so that the device is still seen by bdrv_drain_all() when iterating
> > bdrv_states.
> 
> I wonder if this last change should be separated out and CCed to
> qemu-stable.  It seems like a bug if you close a device that has pending
> throttled operations.

Seems like a good idea.  I'll send the next version with a separated Cc:
qemu-stable@nongnu.org patch.

Stefan