Re: [Qemu-devel] [PATCH] virtio-bus: Plug devices after features are negotiated

[Maxime Coquelin]

On 09/10/2016 11:49 AM, Paolo Bonzini wrote:
> On 10/09/2016 10:23, Maxime Coquelin wrote:
> > Currently, devices are plugged before features are negotiated.
> > If the backend doesn't support VIRTIO_F_VERSION_1, the transport
> > need to rewind some settings.
> >
> > This is the case for CCW, for which a post_plugged callback had
> > been introduced, where max_rev field is just updated if
> > VIRTIO_F_VERSION_1 is not supported by the backend.
> > For PCI, implementing the post_plugged would be much more
> > complicated, so it needs to know whether the backend supports
> > VIRTIO_F_VERSION_1 at plug time.
> >
> > Currently, nothing is done for PCI. Modern capabilitities get
> > exposed to the guest even if VIRTIO_F_VERSION_1 is not supported
> > by the backend, which confuses the guest.
> >
> > This patch proposes to replace existing post_plugged solution
> > with an approach that fits with both transports.
> > Features negociation is performed before ->device_plugged() call.
> > A pre_plugged callback is introduced so that the transports can
> > set their supported features.
>
> Have you tested virtio-mmio too?

No, not tested.
But virtio-mmio doesn't have the device_plugged callback,
so no impact here.

Thanks,
Maxime