Re: [Qemu-devel] [PATCH 2/2] virtio-pci: Disable modern interface if backend without VIRTIO_F_VERSION_1

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Fri, 9 Sep 2016 14:04:55 +0300
Marcel Apfelbaum <marcel@redhat.com> wrote:

> On 09/09/2016 01:40 PM, Cornelia Huck wrote:
> > On Fri,  9 Sep 2016 12:14:32 +0200
> > Maxime Coquelin <maxime.coquelin@redhat.com> wrote:
> >
> >> This patch makes pci devices plugging more robust, by not confusing
> >> guest with modern interface when the backend doesn't support
> >> VIRTIO_F_VERSION_1.
> >>
> >> Cc: Marcel Apfelbaum <marcel@redhat.com>
> >> Cc: Michael S. Tsirkin <mst@redhat.com>
> >> Cc: qemu-stable@nongnu.org
> >> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> >> ---
> >>  hw/virtio/virtio-pci.c | 15 +++++++++++++++
> >>  hw/virtio/virtio-pci.h |  5 +++++
> >>  2 files changed, 20 insertions(+)
> >
> > Note that 11380b361 ("virtio: handle non-virtio-1-capable backend for
> > ccw") fixes this issue for ccw via the introduction of a
> > ->post_plugged() callback. Unfortunately, we did not find a good way to
> > make it work for pci back then.
> 
> It seems that for ccw is enough to rewind dev->rev_max,
> sadly for pci we need to rewind a lot of settings/resources.

Yes, that what I meant with 'more flexibility for ccw'.

> 
> Thanks,
> Marcel
> 
> >
> > Two comments:
> > - ->post_plugged() handles the dependencies (as noticed for your first
> > patch) - and this is due to it being called after the plugging is
> > already done.
> > - I don't really like pci and ccw being too different. We have probably
> > more flexibility with the handling for ccw, so I could probably convert
> > ccw to the same mechanism that pci uses. Maybe there are other uses for
> > ->post_plugged()?
> >
>