Hi,
I don't know. This seems exactly like the kind of thing we had in mind when we added the virtio pci capability. For example, we have text in spec that requires drivers to skip unknown capabilities.
And yes, if bios pokes at a specific bar then we do need to list this info in the virtio spec so this makes it an issue that is virtio related.
Hmm, virtio-vga is a two-in-one device basically. When virtio is enabled it behaves like virtio-gpu-pci, otherwise it behaves very simliar to stdvga. So you need to know nothing about virtio to handle the vga side, and I want keep it that way.
When no vga compatibility is needed there always is the option to just use virtio-gpu-pci instead.
Yes, it's not about what we put there now. It's about being able to move things about in the future without breaking guests.
We don't have that today for stdvga, and I still fail to see what this buys us.
Completely different thing crossing my mind: I think we can make virtio-vga fully compatible with stdvga. stdvga has two bars, memory (#0) and mmio (#2). We can make the mmio bar larger and place all the virtio regions there.
I think in any case I'll go split off the vga compatibility bits to a different patch (and possible a separate patch series).
cheers, Gerd