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Re: [libvirt] [RFC PATCH v2 0/3] Start fixing the pvpanic mess



On Wed, Aug 21, 2013 at 06:56:52PM +0200, Paolo Bonzini wrote:
> Il 21/08/2013 18:55, Daniel P. Berrange ha scritto:
> > On Wed, Aug 21, 2013 at 06:51:11PM +0200, Paolo Bonzini wrote:
> >> Il 21/08/2013 18:48, Daniel P. Berrange ha scritto:
> >>> No, <on_crash> is the right thing to be using for this from
> >>> libvirt's pov & I don't think we should invent something new.
> >>> The <on_crash> element has always been intended to represent
> >>> handling of guest panics, not qemu internal errors.
> >>
> >> Actually for Xen HVM guests, it mostly traps things such as failed
> >> vmentries.  The Xen PV-on-HVM drivers do not register a panic notifier
> >> that moves the guest to the "crashed" state.
> >>
> >> <on_crash> cannot be salvaged, in my opinion, because all domain XMLs in
> >> the wild will have a setting that causes libvirt to add "-device
> >> isa-pvpanic".  Thus changing libvirt versions will change guest
> >> hardware, which is _very_ bad.
> >>
> >> In addition, Windows XP and 2003 will show the annoying device wizard
> >> upon a libvirt upgrade, and fixing this is what surfaced all the mess.
> > 
> > The existance of a <on_crash> element should not be having any
> > effect on what hardware we create. That is merely a lifecycle
> > policy setting that should be completely independant of the
> > guest device model.
> > 
> > eg it is valid to have <on_crash> present in the XML at all
> > times, even if there's no pvpanic device present. That simply
> > means the actions will never be triggered.
> 
> So are you suggesting to add a <pvpanic/> element to <devices>?  That
> may be fine, but it doesn't seem very user-friendly.

Yes, if we're going to have pvpanic be user controllable, it must be
via an explicit device element. 

None of the <on_XXXX> elements should have any impact on guest ABI
model. They're purely lifecycle policy settings.

Daniel
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