Re: [Qemu-devel] pvpanic device should not be automatically included as an internal device

[Marcel Apfelbaum <marcel.a@redhat.com>]

On Thu, 2013-08-01 at 19:31 +0300, Michael S. Tsirkin wrote:
> On Thu, Aug 01, 2013 at 10:26:53AM -0600, Eric Blake wrote:
> > On 08/01/2013 08:18 AM, Gerd Hoffmann wrote:
> > > On 08/01/13 15:08, Marcel Apfelbaum wrote:
> > >> Hi,
> > >>
> > >> The problem with pvpanic being an internal device is that VMs running
> > >> operating systems without a driver for this device will have problems
> > >> when qemu will be upgraded (from qemu without this pvpanic).
> > >>
> > >> The outcome may be, for example: in Windows(let's say XP) the Device manager
> > >> will open a "new device" wizard and the device will appear as an unrecognized device.
> > > 
> > > Only happens when also changing the machine type on upgrade as it is
> > > turned off on old machine types.
> > > 
> > > But, yes, pvpanic will show up as "Unknown device" without driver and
> > > with the funky yellow exclamation mark in device manager in windows
> > > guests.  Newer windows versions don't kick the "new device" wizard.  But
> > > still I have my doubts that it is a good idea to add it unconditionally ...
> > 
> > Automatic devices with no command line argument have proven to be a
> > nightmare for libvirt as well.  Although the just-released libvirt 1.1.1
> > now supports the <on_crash> element for controlling the command line
> > parameters of qemu related to how qemu will behave when the pvpanic
> > device is triggered, I would also welcome having the ability to control
> > whether the guest even has a pvpanic device exposed, just as we can
> > control whether a guest has a memballoon device exposed.
> 
> 
> A natural way to do this would be with -device pvpanic.
> I'm not sure why it wasn't done like this from the beginning,
> but it shouldn't be hard to redo, hopefully we can fix this
> bug in time for 1.6.
> 
I'll come up with something, hopefully in time.
Marcel