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Re: [libvirt] [PATCH for-4.0 v2] virtio: Provide version-specific variants of virtio PCI devices



On Tue, 2018-11-20 at 14:14 -0500, Michael S. Tsirkin wrote:
> On Tue, Nov 20, 2018 at 01:27:05PM +0100, Andrea Bolognani wrote:
> > On Mon, 2018-11-19 at 14:14 -0500, Michael S. Tsirkin wrote:
> > > Well it works now - connect it to a bus and it figures out whether it
> > > should do transitional or not. You can force transitional in PCIe anyway
> > > but then you are limited to about 15 devices - probably sufficient for
> > > most people ...
> > 
> > That's not how it works, though: current virtio-*-pci devices will
> > be transitional (and thus support older guest OS) or not based on
> > the kind of slot you plug them into.
> > 
> > From the management point of view that's problematic, because libvirt
> > (which takes care of the virtual hardware, including assigning PCI
> > addresses to devices) has no knowledge of the guest OS running on
> > said hardware, and management apps (which know about the guest OS and
> > can figure out its capabilities using libosinfo) don't want to be in
> > the business of assigning PCI addresses themselves.
> > 
> > Having separate transitional and non-transitional variants solves the
> > issue because now management apps can query libosinfo to figure out
> > whether the guest OS supports non-transitional virtio devices, and
> > based on that they can ask libvirt to use either the transitional or
> > non-transitional variant; from that, libvirt will be able to choose
> > the correct slot for the device.
> > 
> > None of the above quite works if we have a single variant that
> > morphs based on the slot, as we have today.
> 
> So can we get an ack on the patchset then?

Sure thing - whatever it might be worth :)

  Acked-by: Andrea Bolognani <abologna redhat com>

-- 
Andrea Bolognani / Red Hat / Virtualization


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