On Fri, 9 Dec 2016 18:06:50 -0200 Eduardo Habkost <ehabk...@redhat.com> wrote:
> On Wed, Dec 07, 2016 at 02:39:25PM +0100, Greg Kurz wrote: > > On Tue, 6 Dec 2016 17:31:59 -0200 > > Eduardo Habkost <ehabk...@redhat.com> wrote: > > > On Tue, Dec 06, 2016 at 05:19:52PM -0200, Eduardo Habkost wrote: > > > > On Tue, Dec 06, 2016 at 06:50:47PM +0100, Greg Kurz wrote: > > > > > Since commit "9a4c0e220d8a hw/virtio-pci: fix virtio behaviour", > > > > > passing > > > > > -device virtio-blk-pci.disable-modern=off has no effect on 2.6 machine > > > > > types because the internal virtio-pci.disable-modern=on compat > > > > > property > > > > > always prevail. > > > > > > > > > > This should ideally be fixed in the qdev properties core code, but it > > > > > is > > > > > too late in the QEMU 2.8 schedule. So this patch fixes the issue by > > > > > setting > > > > > the compat properties for every virtio-*-pci subtypes instead of the > > > > > base > > > > > virtio-pci type. > > > > > > > > > > Signed-off-by: Greg Kurz <gr...@kaod.org> > > > > > > > > So, it looks like the bug is present in many other cases... > > > > > > > > I have hacked QEMU to print a warning in case the driver name in > > > > compat_props refer to an abstract class or a class that have any > > > > subclasses. The results are below: > > > > > [...] > > > > > > > > I believe the cases where we are likely to cause real-world bugs > > > > are virtio-pci and the *-cpu classes (because -cpu is translated > > > > to -global). > > > > > > > > I'm not sure what should be the right fix in 2.8. I am > > > > considering a temporary hack to translate abstract class names in > > > > compat_props to global properties for all subclasses, in case > > > > they refer to an abstract class. This way we fix the bug where > > > > -global doesn't override compat_props properly, but keep the > > > > rules for -global untouched. > > > > > > What about this? > > > > > > > Indeed that would have been a clever workaround but it is too late anyway. > > :) > > Now my question is: what should we do in 2.8.1? > > 1) Change the rules and apply "[PATCH] qdev: fix the order compat > and global properties are applied" Would it be more acceptable to change the rules in 2.8.1 than it is for 2.8 ? > 2) Fix only virtio-pci (apply a new version of "[PATCH] virtio: > fix HW_COMPAT_2_6 macro for virtio-*-pci drivers") The patch is huge, but we're sure that it doesn't break anything else. > 3) Apply this hack so we fix all compat_props cases without > changing ordering rules. (And then change the ordering rules > in 2.9) > FWIW, I think this patch is ok, and not that hacky: it simply implements the idea that 'compat properties of abstract classes are actually handled at the non-abstract sub-classes level'. Of course, it would be great to document this behavior somewhere. :) Cheers. -- Greg