Re: [Qemu-devel] [PATCH for-2.6] virtio: Register host notifier handler as external

[Fam Zheng <famz@redhat.com>]

On Thu, 04/21 10:07, Kevin Wolf wrote:
> Am 21.04.2016 um 07:05 hat Fam Zheng geschrieben:
> > On Thu, 04/21 10:04, Fam Zheng wrote:
> > > This ensures the bdrv_drained_begin() in block layer is effective and
> > > fixes launchpad bug #1570134.
> > 
> > Forgot to add to the subject, but this patch is for 2.6.
> 
> Also CCing qemu-stable (this affects 2.5) and qemu-block.
> 
> > > Signed-off-by: Fam Zheng <famz@redhat.com>
> > > ---
> > >  hw/virtio/virtio.c | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > > index f745c4a..002c2c6 100644
> > > --- a/hw/virtio/virtio.c
> > > +++ b/hw/virtio/virtio.c
> > > @@ -1829,10 +1829,11 @@ void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
> > >                                                 bool set_handler)
> > >  {
> > >      if (assign && set_handler) {
> > > -        event_notifier_set_handler(&vq->host_notifier,
> > > -                                   virtio_queue_host_notifier_read);
> > > +        aio_set_event_notifier(qemu_get_aio_context(), &vq->host_notifier,
> > > +                               true, virtio_queue_host_notifier_read);
> > >      } else {
> > > -        event_notifier_set_handler(&vq->host_notifier, NULL);
> > > +        aio_set_event_notifier(qemu_get_aio_context(), &vq->host_notifier,
> > > +                               true, NULL);
> > >      }
> 
> This feels like fixing one special case of a more general problem. Are
> we sure that event_notifier_set_handler() should ever result in an
> internal handler? The default should probably be external, and block
> drivers need to take care to use functions that have the is_external
> parameter so they can mark themselves internal.
> 

Looks like this is the only event_notifier_set_handler caller that
should be fixed.  If we see problem in other devices they can be
addressed case by case, I'm not sure marking event_notifier_set_handler
as external is a better idea for 2.6. (The other two callers are
hyperv.c, which seems never set the handler, and ccid-card-emulated.c,
which device I have no idea about.)

Fam