On Mon, 19 Sep 2016 22:07:13 +0300
"Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> On Wed, Sep 07, 2016 at 09:38:04PM +0200, Sascha Silbe wrote:
> > Dear Laine,
> >
> > Laine Stump <laine@xxxxxxxxx> writes:
> >
> > > On 09/07/2016 02:35 PM, Sascha Silbe wrote:
> > >> "Daniel P. Berrange" <berrange@xxxxxxxxxx> writes:
> > >> [...]
> > >>> <sound model="virtio"/> == QEMU virtio
> > >>> <sound model="virtio1.0"/> == QEMU virtio + disable-legacy
> > >> What would this do for devices using the virtio-ccw transport?
> > >
> > > From libvirt's point of view, the option "disable-legacy=on" would be
> > > added to the device's commandline argument.
> >
> > Which would break s390x guests. virtio-ccw doesn't have any concept of
> > "legacy" or "modern" devices (that's purely a virtio-pci concept),
>
> Legacy is a generic concept found in virtio 1 spec.
> Modern isn't, virtio 1 only has transitional/non-transitional.
>
> If you want to stick to the spec you should therefore
> use
> legacy/transitional/non-transitional
> at the API level.
>
> It is true that not all transports have all options.
> ccw does not support non-transitional devices,
> mmio does not support transitional ones.
We basically have:
- legacy devices: pci, ccw
- standard-compliant devices: pci, ccw, mmio
- of these, pci and ccw have transitional support, which can be
disabled for pci
Per default, I don't think libvirt should offer legacy devices - I see
this as a machine-version backwards-compatibility option which should
be handled via the machine version only.
It makes sense to have a way to force pci devices to either
transitional or non-transitional. For ccw and mmio, this is not
applicable. Therefore, I think libvirt should offer a switch to handle
transitional/non-transitional pci only and not provide any other
virtio-version switches.
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