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

[Laine Stump]

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?