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

[Christian Borntraeger]

On 12/02/2015 05:43 PM, Michael S. Tsirkin 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 have been queried that can handle the VERSION_1 bit being withdrawn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 <address@hidden>
> 
> 
> Unfortunately this is too late: we need to know
> whether modern will be supported to know whether
> to add the pci express capability :(

I can at least confirm that this patch "fixes" the guest error message

virtio_net virtio0: virtio: device uses modern interface but does not have 
VIRTIO_F_VERSION_1
virtio_net: probe of virtio0 failed with error -22

is gone. but yes, its not enough for the other aspects.



> 
> Maybe this should be moved into plugged
> callback?