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

[Daniel P. Berrange]

On Fri, Aug 02, 2013 at 10:31:11AM +0200, Paolo Bonzini wrote:
> 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.

Yep, that was the big motivation behind doing it as an I/O port that we
could have enabled by default, as opposed to a virtio serial device or
some other paravirt device that required explicit configuration.

Daniel
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