Re: [PATCH 0/2] virtio: non-legacy device handling

[Cornelia Huck]

On Mon, 20 Jul 2020 11:54:06 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Tue,  7 Jul 2020 12:54:44 +0200
> Cornelia Huck <cohuck@redhat.com> wrote:
> 
> > As discussed in "virtio-fs: force virtio 1.x usage", it seems like
> > a good idea to make sure that any new virtio device (which does not
> > support legacy virtio) is indeed a non-transitional device, just to
> > catch accidental misconfigurations. We can easily compile a list
> > of virtio devices with legacy support and have transports verify
> > in their plugged callbacks that legacy support is off for any device
> > not in that list.
> > 
> > Most new virtio devices force non-transitional already, so nothing
> > changes for them. vhost-user-fs-pci even does not allow to configure
> > a non-transitional device, so it is fine as well.
> > 
> > One problematic device, however, is virtio-iommu-pci. It currently
> > offers both the transitional and the non-transitional variety of the
> > device, and does not force anything. I'm unsure whether we should
> > consider transitional virtio-iommu unsupported, or if we should add
> > some compat handling. (The support for legacy or not generally may
> > change based upon the bus, IIUC, so I'm unsure how to come up with
> > something generic.)
> >   
> 
> Both patches look good to me (Acked-by: Halil Pasic
> <pasic@linux.ibm.com>). I tend to agree with Davids comment on how
> this information is coded: the more object oriented way would have
> been to store this at the something like VirtioDeviceClass, but
> Michael's argument stands.
> 
> Another OO option would be to expose this as a virtio property. Would
> enable introspection, and would also give the host admin means to
> force non-legacy for transitional devices. But the juice is probably not
> worth the squeeze.

I agree, that would be a lot of hassle for exposing what is basically
static information.