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

On 09/27/2011 05:13 AM, Daniel P. Berrange wrote: >On Tue, Sep 27, 2011 at 01:19:20AM -0400, Laine Stump wrote: >>On 09/19/2011 01:32 PM, Daniel P. Berrange wrote: >>>On Mon, Sep 19, 2011 at 07:16:22PM +0200, Marc-André Lureau wrote: >>>>Hi hi >>>> >>>>On Fri, Sep 16, 2011 at 1:38 PM, Marc-André Lureau<mlureau(a)redhat.com> wrote: >>>>>>>How do we allow other devices to share the slot? It seems to me that >>>>>>>qemuDomainPCIAddressSetNextAddr() only allocate whole slot, while >>>>>>>making sure there is no conflicts on the same slot. >>>>>>So, if the user wants to use multi function pci device, he should >>>>>>specify the >>>>>>pci address. >>>>>So adding a check such as: >>>>> >>>>>if (!multiFunc&& info->addr.pci.function != 0) >>>>> return error("The %s device doesn't support multifunction address") >>>>> >>>>Wen, does that sound reasonable to you? >>>> >>>>Daniel, did you had time to verify that PCI allocation is per-slot? >>>> >>>>(It would be nice to get this "workaround" for the next release) >>>IMHO this kind of hack doesn't belong in libvirt. It is fine for distro >>>vendors to consider as a one off quick-hack for their packages of libvirt, >>>if they don't have time to fix the real QXL bug, but not for libvirt >>>upstream releases. QXL/QEMU should really be fixed since that's where the >>>problem appears to lie. >>As it stands, Fedora 16 (currently using unpatched libvirt-0.9.6) >>will be going into beta with QXL video broken for Windows guests, so >>we need some kind of Fedora-only patch very soon (see the schedule >>here: https://fedoraproject.org/wiki/Releases/16/Schedule - >>fortunately just delayed another week) >> >>The original patch in this thread: >> >> https://www.redhat.com/archives/libvir-list/2011-September/msg00534.html >> >>of course doesn't include the above mentioned additional code, and >>there isn't a followup patch. It would be very good to push a patch >>to the F16 git for this so it would hopefully get into the beta, but >>want to make sure what I push is the "right" thing, so a "final" >>patch (and some testing by people with F16 hosts) would be very >>helpful! >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. Of course this has been in since 0.9.3, meaning there are official releases with broken ABI compatibility :-(. Still, the sooner it's fixed the better.

>Then we should introduce a new parameter 'multifunction='on' in the ><address type=pci> element to allow it to be optionally enabled per >device. Will it be acceptable to put that in a patch on top of 0.9.6 for Fedora 16? (I think the answer is "yes", since it's only an XML change, but just want to make sure).