On Tue, Aug 06, 2013 at 12:20:27PM +0300, Gleb Natapov wrote: > On Tue, Aug 06, 2013 at 10:45:01AM +0200, Andreas Färber wrote: > > Am 06.08.2013 10:36, schrieb Gleb Natapov: > > > On Tue, Aug 06, 2013 at 11:33:10AM +0300, Michael S. Tsirkin wrote: > > >> On Tue, Aug 06, 2013 at 10:21:52AM +0300, Gleb Natapov wrote: > > >>>> If you see a mouse in a room, how likely is it that there's > > >>>> a single mouse there? > > >>>> > > >>>> This is a PV technology which to me looks like it was > > >>>> rushed through and not only set on by default, but > > >>>> without a way to disable it - apparently on the assumption > > >>>> there's 0 chance it can cause any damage. Now that > > >>>> we do know the chance it's not there, why not go back > > >>>> to the standard interface, and why not give > > >>>> users a chance to enable/disable it? > > >>> You should be able to disable it with: -device pvpanic,ioport=0 > > >> > > >> Doesn't work for me. > > > Bug that should be fixed. With this command line _STA should return > > > zero. > > > > > >> Besides, both -device pvpanic and use of ioport=0 to disable it > > >> are completely undocumented. > > >> > > > Not the only undocumented thing in QEMU command line :) > > [snip] > > > > I disagree: -device adds a device, not removes one. It will still be > > present. > > > I assume you are answering to the quote about ioport=0, not > documentation here. ioport=0 does not removes the device, it disables > it. The claim was it cannot be disabled, it can (assuming no bugs), but > it should not be. > > > I am neutral as to whether qemu-system-x86_64 should have it enabled by > > default or not. But if we want to suppress it, then -nodefaults should > > disable it. Since libvirt uses that though, it would mean libvirt would > > need to add it back, whether via user's XML domain config or by libvirt > > itself based on some version/etc. heuristics. > > > There is no clear definition of what -nodefaults should or should not > do. > Should it disable PV ACPI hotplug device? > Should it create a machine > with no mmio/io regions registered at all?
We can't change the meaning for existing devices. So we need to keep everything that it historically included. But it's a good question whether e.g. ACPI hotplug for q35 should be a separate device, and disabled with -nodefaults. > > -- > Gleb. pvpanic presents itself as a separate device, this is different from PV ACPI hotplug which is part of PIIX.
