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

[Halil Pasic]

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.

Regards,
Halil