[libvirt] [PATCH v2 RESEND 00/12] PCI passthrough support on s390

[Yi Min Zhao]

在 2018/7/26 下午7:00, Andrea Bolognani 写道:
>>>>>>> How does the pci-bridge controller show up in the guest, if at all?
>>>> Qemu hides pci-bridge devices and just exposes pci devices to the guest.
>>>> In above example, indeed, qemu will generate a pci-bridge device and it will
>>>> be existing in pci topology. But the guest can't see it. This is very
>>>> special.
>>> Yeah, that's kinda problematic as it violates the principle of least
>>> surprise... If s390 guests can only see a flat PCI topology, then we
>>> should find a way to reject bridges altogether instead of allowing
>>> the user to create them (or even create them automatically) only for
>>> them not to show up in the guest.
>> If we reject bridges, there would be only one pci bus that maximum
>> 32 pci devices could be plugged to. This kind of limitation is more
>> problematic IMO.
> I see how that would be pretty limiting.
>
> >From the test cases I see a zpci devices, with its own uid and fid,
> is created for the pci-bridge as well... Is that intentional?
>
Firstly pci bridge can be auto-generated if a pci device is to be 
plugged to non-existing pci bus.
IIUC, pci-bridge is treated as a controller device in libvirt. So I 
think, it's pretty readable not only
in libvirt xml but also in qtree, if we assign zpci device for it. 
Otherwise address type of pci-bridge
is pci type but has no uid and fid. Isn't it odd?

Of course, we could avoid assigning a zpci device to pci-bridge. 
Actually my old patch did
in this way.