Re: [libvirt] [PATCH] qemu: qxl devices don't support multifunction yet

On 09/27/2011 05:13 AM, Daniel P. Berrange wrote: > When we originally enabled multifunction for all PCI devices, we did so > in the belief that this was effectively a no-op for guest OSes. ie it > should not have changed guest OS behaviour at all, unless multiple > devices > were actually inserted in the slot. > > Evidentally this turns out to be incorrect. In other words we introduced > a guest ABI change. This is very bad, because our stated goal is to have > a stable guest ABI across libvirt& QEMU releases. > > Thus IMHO we need to disable *all* setting of the 'multifunction=on' > parameter for all guests by default, to unbreak the ABI compatibility. > > Then we should introduce a new parameter 'multifunction='on' in the > <address type=pci> element to allow it to be optionally enabled per > device. A couple of questions: 1) Is it possible/useful to have function > 0 without multifunction=on in the qemu commandline? 2) If the answer to (1) is "No", if the XML has function > 0 but no multifunction=on, should we implicitly add multifunction=on, or should we log an error?