[libvirt] [Qemu-devel] [PATCH for-4.0 v4 0/2] virtio: Provide version-specific variants of virtio PCI devices

[Andrea Bolognani]

Sorry to resurrect such an old thread, but I have been wondering...

On Wed, 2018-12-05 at 17:57 -0200, Eduardo Habkost wrote:
[...]
> Changes v1 -> v2:
> * Removed *-0.9 devices.  Nobody will want to use them, if
>   transitional devices work with legacy drivers
>   (Gerd Hoffmann, Michael S. Tsirkin)
> * Drop virtio version from name: rename -1.0-transitional to
>   -transitional (Michael S. Tsirkin)
> * Renamed -1.0 to -non-transitional
> * Don't add any extra variants to modern-only device types
>   (they don't need it)

... if doing this was a good idea after all?

While I understand that something like virtio-gpu, which supports
the 1.0 specification exclusively, only really needs to have a
single device associated with it from the functionality point of
view, looking at it from a user's perspective it seems to me like
providing an explicit non-transitional variant would be appropriate
for consistency reasons, so that your guest could look like

  -device virtio-blk-pci-non-transitional \
  -device virtio-net-pci-non-transitional \
  -device virtio-gpu-pci-non-transitional \

and you wouldn't have to question why you can use the
non-transitional variant for pretty much everything, except for the
few cases where you can't - for no apparent reason...

It would also signal quite clearly which devices support both
transitional and non-transitional variants and which ones don't,
without having to infer that the complete lack of (non-)transitional
variants means that only the non-transitional variant is available -
except you have to use the suffix-less device name to use it.

tl;dr providing the non-transitional variant for virtio 1.0-only
      devices would make using this much more user-friendly.

-- 
Andrea Bolognani / Red Hat / Virtualization