From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48746) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cEckt-0005vY-8d for qemu-devel@nongnu.org; Wed, 07 Dec 2016 08:59:34 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cEckk-0003Nl-7O for qemu-devel@nongnu.org; Wed, 07 Dec 2016 08:59:26 -0500 Date: Wed, 7 Dec 2016 11:59:17 -0200 From: Eduardo Habkost Message-ID: <20161207135917.GI4027@thinpad.lan.raisama.net> References: <148104617887.7699.984921868108236415.stgit@bahia.lab.toulouse-stg.fr.ibm.com> <20161206191952.GD4027@thinpad.lan.raisama.net> <20161206193159.GE4027@thinpad.lan.raisama.net> <20161207143925.7b3a54f2@bahia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161207143925.7b3a54f2@bahia> Subject: Re: [Qemu-devel] [RFC for-2.8] machine: Convert abstract typename on compat_props to subclass names List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Greg Kurz Cc: qemu-devel@nongnu.org, Halil Pasic , "Michael S. Tsirkin" , qemu-stable@nongnu.org, Stefan Hajnoczi , Cornelia Huck , Paolo Bonzini On Wed, Dec 07, 2016 at 02:39:25PM +0100, Greg Kurz wrote: > On Tue, 6 Dec 2016 17:31:59 -0200 > Eduardo Habkost 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 > > > > > > 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. > > > > What about this? > > > > Indeed that would have been a clever workaround but it is too late anyway. :) > > BTW, that makes me think about Halil's comment in another mail, even if it > is not strictly related to the comapt issue (but rather because I mentioned > it in the changelog of my first patch): > > "So I can't even tell if -global virtio-pci.disable-modern=off is even legit > on the command line." > > And indeed, -device doesn't accept abstract classes... shouldn't -global > prohibit setting properties for them ? I'm not sure. Setting disable-modern for all virtio-pci devices with a single -global option sounds very useful, for example. Also, if we start rejecting it we risk breaking existing configurations. We would need to deprecate it first (making it print a warning) and reject it a few releases later. -- Eduardo