Re: [Qemu-devel] [RFC] Introduce vm_stop_permanent()

[Luiz Capitulino <lcapitulino@redhat.com>]

On Thu, 28 Jul 2011 17:20:41 +0200
Jan Kiszka <jan.kiszka@web.de> wrote:

> On 2011-07-28 17:18, Luiz Capitulino wrote:
> > On Thu, 28 Jul 2011 16:19:19 +0200
> > Jan Kiszka <jan.kiszka@web.de> wrote:
> > 
> >> On 2011-07-28 15:37, Avi Kivity wrote:
> >>> On 07/28/2011 04:31 PM, Luiz Capitulino wrote:
> >>>> On Thu, 28 Jul 2011 10:23:22 +0300
> >>>> Avi Kivity<avi@redhat.com>  wrote:
> >>>>
> >>>>>  On 07/28/2011 12:44 AM, Blue Swirl wrote:
> >>>>>  >  On Wed, Jul 27, 2011 at 9:42 PM, Luiz
> >>>> Capitulino<lcapitulino@redhat.com>   wrote:
> >>>>>  >  >   This function should be used when the VM is not supposed to
> >>>> resume
> >>>>>  >  >   execution (eg. by issuing 'cont' monitor command).
> >>>>>  >  >
> >>>>>  >  >   Today, we allow the user to resume execution even when:
> >>>>>  >  >
> >>>>>  >  >     o the guest shuts down and -no-shutdown is used
> >>>>>  >  >     o there's a kvm internal error
> >>>>>  >  >     o loading the VM state with -loadvm or "loadvm" in the
> >>>> monitor fails
> >>>>>  >  >
> >>>>>  >  >   I think only badness can happen from the cases above.
> >>>>>  >
> >>>>>  >  I'd suppose a system_reset should bring the system back to
> >>>> sanity and
> >>>>>  >  then clear vm_permanent_stopped (where's -ly?)
> >>>>
> >>>> What's -ly?
> >>>>
> >>>
> >>> permanent-ly.
> >>>
> >>>>>  >  except maybe for KVM
> >>>>>  >  internal error if that can't be recovered. Then it would not very
> >>>>>  >  permanent anymore, so the name would need adjusting.
> >>>>>
> >>>>>  Currently, all kvm internal errors are recoverable by reset (and
> >>>>>  possibly by fiddling with memory/registers).
> >>>>
> >>>> Ok, but a poweroff in the guest isn't recoverable with system_reset
> >>>> right? Or does it depend on the guest?
> >>>
> >>> Right, it's not recoverable if you shut the power down where the tractor
> >>> beam is coupled to the main reactor.
> >>
> >> system_reset will bring all emulated devices back into their power-on
> >> state - unless we have remaining bugs to fix. Actually, one may consider
> >> issuing this reset automatically on vm_start after "permant" vm_stop.

The only permanent vm_stop we'd have is poweroff when -no-shutdown is used.

Are you saying that system_reset should be able to recover from that too?

If yes, then I guess the right place is do_cont(). But I'm not sure we
should do that (if -no-shutdown is not used, we'll exit() anyway).

> > 
> > I'm going to abandon the vm_stop_permanent() idea.
> > 
> > I'm thinking something towards having a stop_kind argument to vm_stop(),
> > which could be temporary (which is what we have today), only with
> > system_reset or permanent.
> > 
> > Or maybe vm_stop_opt(), which allows for fine grained control of stop
> > (vm_stop() would default to today's behavior)...
> 
> But the right point for reset is start, not stop. Otherwise we loose the
> state before the stop.