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

[Marcel Apfelbaum]

On 09/09/2016 01:40 PM, Cornelia Huck wrote:
> On Fri,  9 Sep 2016 12:14:32 +0200
> Maxime Coquelin <address@hidden> 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 <address@hidden>
> > Cc: Michael S. Tsirkin <address@hidden>
> > Cc: address@hidden
> > Signed-off-by: Maxime Coquelin <address@hidden>
> > ---
> >  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.

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()?