On Wed, Jan 05, 2011 at 09:57:42AM -0500, Laine Stump wrote: > On 01/05/2011 05:19 AM, Daniel P. Berrange wrote: > > > >We should try to keep terminology matching the disk<driver> > >so I think > > > > <driver name='qemu|vhost'/> > > > >with omission of<driver> resulting in us automatically > >adding either 'qemu' or 'vhost' to the XML. We don't > >want to have an explicit 'default' value in the XML, > >because users should be able to see the guest is running > >with. > > Do you mean to add it to the XML that's saved in the config? If so, > that would mean that it would only be possible to configure it as > "use whatever is best for the current situation" for the first > startup of the domain. Once that happened, it would be stuck on > whichever was used the first time (qemu or vhost), so if the domain > was first started when vhost-net was loaded, then later restarted > when vhost-net wasn't loaded (or maybe migrated to another host that > didn't have vhost support), it would fail to start. Yes, I *did* actually mean to set it in the permanent XML config, so once a choice is made, that choice is preserved thereafter. This gives us better reliability in the future if a further possible 'default' options are introduced and we want to avoid existing guests accidentally getting the new option for some reason. > Aside from that, I'd been thinking that the "backend" driver in this > case is virtio, not qemu or vhost; qemu(userland) vs vhost seems > like just a setting within that driver. So it doesn't seem > appropriate to me to have the name decide whether to use userland or > vhost. Hmm, I thought vhost was a property of any tap device based backend, rather than virtio ? > > One other twist - there's already another request for something else > to be set for each network device: sndbuf. > > <https://bugzilla.redhat.com/show_bug.cgi?id=665293> > https://bugzilla.redhat.com/show_bug.cgi?id=665293 > <https://bugzilla.redhat.com/show_bug.cgi?id=665293> > > The sndbuf setting is applicable to any network device that connects > to the real world using a tap device (ie, not just virtio). If we > want to add that setting via the same scheme, we would need > something like: > > <driver name='qemu|vhost' sndbuf='0'/> > > (0 can't be the default, because 0 is actually one of the settings > that they want to explicitly specify (if sndbuf isn't given on the > commandline, qemu defaults to 1048576). sndbuf is much more like a true "tunable" than vhost is, so I think it makes sense to have a generic representation for NIC tunables. Daniel -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list