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

[Marcel Apfelbaum <marcel@redhat.com>]

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.

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()?
>