Re: [Qemu-devel] Attaching PCI devices to the PCIe root complex

[Laine Stump <laine@redhat.com>]

On 09/30/2013 05:55 AM, Markus Armbruster wrote:
> "Michael S. Tsirkin" <mst@redhat.com> writes:
>> I never heard of a pci/pci express
>> one but it's not impossible I think.
> PCI on one side of the card, PCIe on the other, and a switchable
> backplate?  Weird :)
>
> Again, I can't see why we'd want to model this, even if it existed.

Unfortunately that's what's been done, so libvirt will have to deal with
it, even after qemu gets it fixed.

> The current interface munges together all PCIish connectors, and the
> result is a mess: users can't see which device can be plugged into which
> socket.  Libvirt needs to know, and it has grown a bunch of hardcoded ad
> hoc rules, which aren't quite right.

The good news is that libvirt has only recently started dealing with
anything other than vanilla PCI slots. The bad news is that it has. I
guess everything should work out okay if we just keep the current "wild
guess" code around, but only fall back on it if the new more accurate
information is unavailable.