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

[Luiz Capitulino <lcapitulino@redhat.com>]

On Tue, 2 Aug 2011 11:22:15 +0100
"Daniel P. Berrange" <berrange@redhat.com> wrote:

> On Thu, Jul 28, 2011 at 10:31:43AM -0300, 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?
> > 
> > > > 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?
> > 
> > I get funny results if qemu is started with -no-shutdown and I run cont after
> > a poweroff in a F15 guest. Sometimes qemu will exit after a few seconds,
> > sometimes 'info status' will say 'running'.
> 
> libvirt uses this approach to fake a controlled soft reboot of guests.
> eg
> 
>   $ qemu .... -no-shutdown
>   ...some time later...
>   system_shutdown
>   ...wait for SHUTDOWN event...
>   system_reset
>   cont
> 
> Previous releases of QEMU had a bug in some device backends which would
> cause a crash sometimes, but in general it ought to work IMHO.

Yes, you're doing a system_reset before cont, that's ok.

The problem happens when you issue cont w/o issuing system_reset first.