On Wed, Aug 23, 2017 at 11:16:27PM +0300, Marcel Apfelbaum wrote: > On 23/08/2017 19:46, Andrea Bolognani wrote: > > AFAIK some PCI controllers, particularly: > > > > * PCIe Root Port (pcie-root-port, ioh3420) > > * PCIe Switch Downstream Port (xio3130-downstream) > > > > only have a single usable slot. libvirt knows about this > > fact, and will prevent you from adding more than one > > device to the respective bus. > > > > However, as Lukáš recently noticed, QEMU won't complain > > if you add more devices: > > > > $ qemu-system-x86_64 \ > > -nodefaults -nographic \ > > -M q35 -monitor stdio \ > > -device pcie-root-port,id=pci.1 \ > > -device virtio-scsi-pci,bus=pci.1 \ > > -device virtio-scsi-pci,bus=pci.1 > > QEMU 2.9.0 monitor - type 'help' for more information > > (qemu) info qtree > > bus: main-system-bus > > type System > > [...] > > dev: q35-pcihost, id "" > > [...] > > bus: pcie.0 > > type PCIE > > dev: pcie-root-port, id "pci.1" > > [...] > > bus: pci.1 > > type PCIE > > dev: virtio-scsi-pci, id "" > > [...] > > addr = 01.0 > > bus: virtio-bus > > type virtio-pci-bus > > dev: virtio-scsi-device, id "" > > [...] > > bus: scsi.1 > > type SCSI > > dev: virtio-scsi-pci, id "" > > [...] > > addr = 00.0 > > bus: virtio-bus > > type virtio-pci-bus > > dev: virtio-scsi-device, id "" > > [...] > > bus: scsi.0 > > type SCSI > > (qemu) > > > > Hi Andrea, > > > As you can see, all devices will show up in the qtree; > > only the one with addr=00.0, however, will actually be > > visible to the guest OS according to my tests. > > > > Is such a configuration considered valid? > > Definitely no. > > > Should QEMU > > complain loudly about it and refuse to start? > > Yes, but we need a clean way to do it. Eduardo is working > on a series that would expose to libvirt this info, > Eduardo can you please confirm?
The work has two parts: 1) actually preventing invalid configurations; 2) providing a query interface to let libvirt know which configurations are valid. My focus is on (2) (adding a query-device-slots interface), but we surely need to address bugs related to (1) first, so both the device-plugging code and slot-querying code are correct and agree with each other. -- Eduardo
