On Tue, Jan 15, 2019 at 02:30:14PM +0100, Andrea Bolognani wrote: > On Sun, 2019-01-13 at 18:12 -0500, Cole Robinson wrote: > [...] > > The main RFC bits here are: > > > > * The disk approach. danpb and I briefly discussed on IRC adding > > new bus= values vs a new model= attribute. We decided model= > > is the lesser of two evils, since bus= handling in apps is > > tied with target= generation, so adding new virtio-X bus= > > values will cause more work for apps. These patches add > > a <disk model=X/> attribute > > This sounds fairly reasonable, but I reserve the right to change my > mind after looking at the code and thinking about it a bit more :) > > > * The XML and naming. Previous discussions seemed to favor adding > > new model-style values rather than a 'transitional' attribute > > or similar. So these patches add model='virtio-transitional' > > and model='virtio-non-transitional' > > Yeah, that's what I recall the consensus being. > > > * The PCI address handling. I just mapped virtio-non-transitional > > to imply plain PCI addressing. I think that's all we need but > > I'm not positive so I'd appreciate a review of that approach. > > I don't think that's right. Let me fish up a message I wrote a while > ago summing up interactions between VirtIO devices and PCI (Express) > slots: > > http://lists.nongnu.org/archive/html/qemu-devel/2018-11/msg03133.html > > Basically VirtIO 0.9 requires IO space to be available, and 1.0 did > away with that requirement because PCI Express, unlike conventional > PCI, allows devices *not* to have IO space. > > So transitional devices, which must work with both 0.9 and 1.0, can > depend on IO space being available and as such will only work when > plugged into conventional PCI slots, whereas non-transitional > devices don't need IO space and can thus be plugged into either > conventional PCI and PCI Express slots. > > Ultimately, then, transitional (rather than non-transitional) > devices are the ones that must be forced into conventional PCI > slots. Yes, the existing devices fail when placed in a PCI-X slot with certain guest OS. The -transitional devices are functionally identical to the existing devices. They serve as a hint to libvirt that it should never place them in a PCI-X slot. Non-transitional (aka 1.0) devices work correctly in either slot type Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
