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

[Paolo Bonzini <pbonzini@redhat.com>]

On 08/02/2013 12:42 AM, Eric Blake wrote:
> On 08/01/2013 04:23 PM, Paolo Bonzini wrote:
>>> 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).
>
> That may "fix" the issue of a windows guest showing the yellow ! mark,
> but what if, down the road, someone writes an actual windows driver that
> is aware of that port and how to make a windows BSOD write a panic
> notification to the port?  How does a user go about installing such a
> driver if the device is not exposed in the user interface list of devices?

The user can still manually install a driver even for a device that is 
not exposed.

Having to manually specify the pvpanic device would be yet another knob 
that nobody uses.  Panic notification is a useful feature that should be 
supported with no particular intervention from the user.

Paolo