[libvirt] [PATCH 2/2] qemu: Order PCI controllers on the command line

[Andrea Bolognani]

On Mon, 2017-09-11 at 13:22 +0200, Peter Krempa wrote:
> Please make sure that the migration stream does not depend on the
> ordering of the controllers. Re-arranging them could be a problem if we
> don't have a way to migrate them afterwards.

Took me long enough to get around to actually test this, but it
turns out you were completely spot-on: reordering controllers[1]
can indeed break migration.

  2017-09-21T08:43:21.092559Z qemu-kvm: 800000020000001 != 800000020000002
  2017-09-21T08:43:21.092588Z qemu-kvm: Failed to load spapr_pci:buid
  2017-09-21T08:43:21.092596Z qemu-kvm: error while loading state for instance 0x1 of device 'spapr_pci'
  2017-09-21T08:43:21.093561Z qemu-kvm: load of migration failed: Invalid argument

Now, you already have to try pretty hard to get a guest in a state
where controllers are not showing up in the expected order, but
the same can be said for the situation described in the bug report
linked above...

All things considered, I think it's better to avoid the risk of
breaking migration, however small it might be, even though it
means leaving other failure scenarios unaddressed.

So I guess this is will be a SNACK. That's okay, I was starting
to feel a bit hungry anyway.

Thanks for bringing up the issue!


[1] PHBs at least, not sure about others.
-- 
Andrea Bolognani / Red Hat / Virtualization