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

[Cornelia Huck]

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.

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()?