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Date: Wed, 6 Apr 2016 15:42:17 +0200
From: Cornelia Huck <cornelia.huck@de.ibm.com>
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Subject: Re: [Qemu-devel] [PATCH 4/7] virtio: add aio handler
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: famz@redhat.com, borntraeger@de.ibm.com, mst@redhat.com, qemu-devel@nongnu.org, tubo@linux.vnet.ibm.com, stefanha@redhat.com

On Wed, 6 Apr 2016 14:09:12 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 06/04/2016 13:11, Cornelia Huck wrote:
> >> > +static void virtio_queue_notify_aio_vq(VirtQueue *vq)
> >> > +{
> >> > +    if (vq->vring.desc && vq->handle_aio_output) {
> >> > +        VirtIODevice *vdev = vq->vdev;
> >> > +
> >> > +        trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
> >> > +        vq->handle_aio_output(vdev, vq);
> >> > +    }
> >> > +}
> >> > +
> > So this avoids reentrancy, but might we miss one notify if
> > ->handle_aio_output has already been unset? What am I missing?
> 
> Calling the notifier just before unset is handled by using "false,
> false" when unsetting the notifier, and only setting
> vq->handle_aio_output after the notifier has been unset.

Actually, the code is not quite right until the next two patches have
been applied, but I think we can live with that.

> Patch 7 makes things clearer.

That as well.