On Fri, Aug 12, 2016 at 10:47:13AM +0200, Cornelia Huck wrote:
On Thu, 11 Aug 2016 16:17:10 +0200 Ján Tomko <jto...@redhat.com> wrote:On Thu, Aug 11, 2016 at 02:31:55PM +0100, Daniel P. Berrange wrote: >On Thu, Aug 11, 2016 at 03:25:53PM +0200, Ján Tomko wrote: >> On Thu, Aug 11, 2016 at 01:00:08PM +0100, Daniel P. Berrange wrote: >> > On Wed, Aug 10, 2016 at 03:27:15PM +0200, Ján Tomko wrote: >> > > <controller type='scsi' index='0' model='virtio-scsi'> >> > > <virtio revision='0.9'/> >> > >> > I'm wondering about generalizing this. eg what if there are >> > other device models where we want the ability to set a >> > revision. We don't really want to invent a new sub-elment >> > named after each device model >> >> Not even a new attribute? :) >> <revision virtio='0.9'/> >> >> How about: >> <revision type='virtio' version='0.9'/> > >Both of those are quite repetative - we already know its virtio. > I guess one device having <revision>s of different types is unlikely. >Most devices we have alrady include a <driver> or <model> sub-element, >so we should really just add a revision= attrbute to those existing What I liked about having it as a separate element is that it can be repeated, e.g.: <revision type='virtio' version='0.9'/> <revision type='virtio' version='1.0'/> for a device with both 0.9 and 1.0. I could not come up with a nice way to represent that in a single attribute: * '0.9+1.0' feels like the two values should rather be separated at the XML level * 'all' will not be true if there happens to be another virtio revision in the future[not a libvirt developer, but let me comment from the qemu virtio perspective] I don't think you are expressing the concept of virtio (standard) revisions (more like releases!) here correctly. Let me elaborate: - The disable-legacy/disable-modern attributes are virtio-pci only. Moreover, they don't express 'compliant to virtio-1.0' or so: They do exactly What It Says On The Tin. A device with both disable attributes off is in fact virtio-1.0 compliant (transitional devices are compliant), as is a device with disable-legacy off. But it might also be virtio-1.1 compliant! (That's the most likely release of the standard in the near future.) - virtio-ccw does not have the concept of these disable switches. Instead, there are virtio-ccw specific 'revisions' which count upwards and may be limited by the 'max_revision' attribute. However, this is not an attribute that is supposed to be set by the user, but for backwards compatibility only. Unlike pci, ccw has nothing to gain by disabling legacy support. - We may actually want to add some kind of versioning scheme to virtio devices in future versions of the standard. But that's just a very vague idea right now. Am I right in assuming that you simply want to be able to control whether your virtio-pci devices are legacy, transitional or modern?
Yes.
Then I think you'd be best off adding these as virtio-pci attributes only and leave the concept of a 'virtio revision' for the future when we might introduce it in the standard.
So XML like this: <model legacy='on/off' modern='on/off'/> or <model compatibility='legacy/transitional/modern'/> (which could possibly be reused for other hypervisors with a similar concept, not just QEMU and virtio) was what we needed all along, but I misunderstood their purpose. That's good to know :) Jan
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