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: apic-common.legacy-instance-id set for abstract class apic-common.vapic set for abstract class i386-cpu.arat set for abstract class i386-cpu.check set for abstract class i386-cpu.cpuid-0xb set for abstract class i386-cpu.fill-mtrr-mask set for abstract class i386-cpu.full-cpuid-auto-level set for abstract class i386-cpu.l3-cache set for abstract class i386-cpu.pmu set for abstract class pci-device.command_serr_enable set for abstract class pci-device.rombar set for abstract class pci-device.x-pcie-lnksta-dllla set for abstract class powerpc64-cpu.pre-2.8-migration set for abstract class s390-skeys.migration-enabled set for abstract class spapr-pci-host-bridge.ddw set for superclass spapr-pci-host-bridge.dynamic-reconfiguration set for superclass spapr-pci-host-bridge.mem64_win_size set for superclass spapr-pci-host-bridge.mem_win_size set for superclass spapr-pci-host-bridge.pre-2.8-migration set for superclass usb-device.full-path set for abstract class usb-device.msos-desc set for abstract class virtio-pci.disable-legacy set for abstract class virtio-pci.disable-modern set for abstract class virtio-pci.migrate-extra set for abstract class virtio-pci.page-per-vq set for abstract class virtio-pci.virtio-pci-bus-master-bug-migration set for abstract class virtio-pci.x-disable-pcie set for abstract class x86_64-cpu.arat set for abstract class x86_64-cpu.check set for abstract class x86_64-cpu.cpuid-0xb set for abstract class x86_64-cpu.fill-mtrr-mask set for abstract class x86_64-cpu.full-cpuid-auto-level set for abstract class x86_64-cpu.l3-cache set for abstract class x86_64-cpu.pmu set for abstract class 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. -- Eduardo