On Wed, Jan 19, 2011 at 10:54:10AM -0600, Anthony Liguori wrote: > On 01/19/2011 07:11 AM, Markus Armbruster wrote: > >Gerd Hoffmann<kra...@redhat.com> writes: > > > >>On 01/18/11 18:09, Anthony Liguori wrote: > >>>On 01/18/2011 10:56 AM, Jan Kiszka wrote: > >>>>>The device model topology is 100% a hidden architectural detail. > >>>>This is true for the sysbus, it is obviously not the case for PCI and > >>>>similarly discoverable buses. There we have a guest-explorable topology > >>>>that is currently equivalent to the the qdev layout. > >>>But we also don't do PCI passthrough so we really haven't even explored > >>>how that maps in qdev. I don't know if qemu-kvm has attempted to > >>>qdev-ify it. > >>It is qdev-ified. It is a normal pci device from qdev's point of view. > >> > >>BTW: is there any reason why (vfio-based) pci passthrough couldn't > >>work with tcg? > >> > >>>The -device interface is a stable interface. Right now, you don't > >>>specify any type of identifier of the pci bus when you create a PCI > >>>device. It's implied in the interface. > >>Wrong. You can specify the bus you want attach the device to via > >>bus=<name>. This is true for *every* device, including all pci > >>devices. If unspecified qdev uses the first bus it finds. > >> > >>As long as there is a single pci bus only there is simply no need to > >>specify it, thats why nobody does that today. Once q35 finally > >>arrives this will change of course. > >As far as I know, libvirt does it already. > > I think that's a bad idea from a forward compatibility perspective.
In our past experiance though, *not* specifying attributes like these has also been pretty bad from a forward compatibility perspective too. We're kind of damned either way, so on balance we decided we'd specify every attribute in qdev that's related to unique identification of devices & their inter-relationships. By strictly locking down the topology we were defining, we ought to have a more stable ABI in face of future changes. I accept this might not always work out, so we may have to adjust things over time still. Predicting the future is hard :-) Daniel -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
