Re: [Qemu-devel] [PATCH for-2.5] virtio: handle non-virtio-1-capable backend

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

On Wed, 2 Dec 2015 18:43:05 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Wed, Dec 02, 2015 at 03:09:58PM +0100, Cornelia Huck wrote:
> > If you run a qemu advertising VERSION_1 with an old kernel where
> > vhost did not yet support VERSION_1, you'll end up with a device
> > that is {modern pci|ccw revision 1} but does not advertise VERSION_1.
> > This is not a sensible configuration and is rejected by the Linux
> > guest drivers.
> > 
> > To fix this, add a ->post_plugged() callback invoked after features
> > have been queried that can handle the VERSION_1 bit being withdrawn
> > and change pci (only setup modern if VERSION_1 is still present) and
> > ccw (fall back to revision 0 if VERSION_1 is gone).
> > 
> > Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> 
> 
> Unfortunately this is too late: we need to know
> whether modern will be supported to know whether
> to add the pci express capability :(
> 
> Maybe this should be moved into plugged
> callback?

As discussed on irc: I'll cut this down to ccw only for 2.5, and we'll
rethink for 2.6. Patch in progress.