Re: [libvirt] [PATCH 2/2] HACK: qemu: aarch64: Use virtio-pci if user specifies PCI controller

On Fri, 2016-03-04 at 17:05 -0500, Laine Stump wrote: > > I'm not sure I fully understand all of the above, but I'll pitch > > in with my own proposal regardless :) > >  > > First, we make sure that > >  > >    <controller type='pci' index='0' model='pcie-root'/> > >  > > is always added automatically to the domain XML when using the > > mach-virt machine type. Then, if > >  > >    <controller type='pci' index='1' model='dmi-to-pci-bridge'/> > >    <controller type='pci' index='2' model='pci-bridge'/> > >  > > is present as well we default to virtio-pci, otherwise we use > > the current default of virtio-mmio. This should allow management > > applications, based on knowledge about the guest OS, to easily > > pick between the two address schemes. > >  > > Does this sound like a good idea? > ... or a variation of that, anyway :-) >  > What I think: If there are *any* pci controllers *beyond* pcie-root, or  > if there are any devices that already have a PCI address, then assign  > PCI addresses, else use mmio. This sounds reasonable. However, I'm wondering if we shouldn't be even more explicit about this... From libvirt's point of view we just need to agree on some sort of "trigger" that causes it to allocate PCI addresses instead of MMIO addresses, and for that purpose "any PCI controller or any device with a PCI address" is perfectly fine; looking at that from the point of view of an user, though? Not sure about it. What about adding something like   <preferences>     <preference name="defaultAddressType" value="pci"/>   </preferences> to the domain XML? AFAICT libvirt doesn't have any element that could be used for this purpose at the moment, but maybe having a generic way to set domain-wide preferences could be useful in other situations as well?

From the POV of being able to tell libvirt to assign PCI instead of