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

[Paolo Bonzini <pbonzini@redhat.com>]

On 08/01/2013 06:26 PM, 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.

This is quite different from memballoon.

pvpanic is a single I/O port, it doesn't use up a PCI slot (thus
causing conflicts with other devices at the same address).

Perhaps this issue is simply fixed by making the _STA method
return 0x0B instead of 0x0F (i.e. turning off the "show in user
interface" bit).

Paolo