On Thu, Jul 26, 2018 at 07:17:03PM +0800, Yi Min Zhao wrote: > > > 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? >From the libvirt side we must avoid any scenario where QEMU auto-adds devices behind our back. If adding a device requires adding a controller libvirt must do this explicitly and record it in the XML. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
