Re: [Qemu-devel] [PATCH][RESEND] Add monitor command for system_reboot

["Daniel P. Berrange" <berrange@redhat.com>]

On Wed, Jul 08, 2009 at 04:47:46PM +0100, Stefano Stabellini wrote:
> On Wed, 8 Jul 2009, Avi Kivity wrote:
> > On 07/08/2009 05:10 PM, Daniel P. Berrange wrote:
> > >>> Indeed.  This is what has kept me from applying this but I just can't
> > >>> think of any better solution.
> > >>>
> > >>> Any ideas?
> > >>>
> > >>> The drive behind implementing this feature is so that we can implement
> > >>> a proper virDomainReboot in libvirt.
> > >>>
> > >>>        
> > >> How does Xen hvm implement it?
> > >>      
> > >
> > > You have to install the Xen paravirt drivers, so Xen HVM handles graceful
> > > shutdown/reboot in the same way as pure Xen paravirt. They watch a flag
> > > in xenstore and invoke shutdown -r / -h according to the flag.
> > >    
> > 
> > What happens if the driver is not installed?  The guest just keeps 
> > going, right?
> > 
> 
> There are ways to detect if the guest has pv drivers installed or not,
> if they are present soft shutdown/reboot is available; if they are
> not installed soft shutdown/reboot is not available.

Having the drivers installed though, still doesn't guarentee that the
guest will honour the operation :-) Both graceful shutdown & reboot are
just *requests* by the host admin, which cannot be expected to work
all the time, it is just best effort. The admin can choose to forcably
destroy a VM if it didn't honour their request to shutdown/reboot.

Similarly this is all the libvirt APIs for shutdown/reboot define
for semantics - best effort, not a firm guarentee.

Regards,
Daniel
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