[Qemu-devel] Re: [PATCHv3 RFC] qemu-kvm: stop devices on vmstop

[Michael S. Tsirkin]

On Mon, Nov 22, 2010 at 10:57:34AM +0100, Gerd Hoffmann wrote:
> On 11/21/10 20:16, Michael S. Tsirkin wrote:
> >Stop running devices on vmstop, so that VM does not interact with
> >outside world at that time.
> >
> >Whitelist system handlers which run even when VM is stopped.
> >These are specific handlers like monitor, gdbstub, migration.
> >I'm not really sure about ui: spice and vnc: do they need to run?
> 
> Yes, vnc and spice should run.  They serve the clients.  They also
> don't change device state.
> 
> cheers,
>   Gerd
> 
> PS: Well, in the spice case this isn't 100% true, the handlers can
> change qxl device state in some cases.  But spice has a start/stop
> handler which takes care to flush all outstanding work which could
> change device state on vmstop, so it is save to keep the handlers
> active when the vm is in stopped state.

So here's how I see it so far: assuming we want to avoid changing vm
state on vmstop

        - flush bdrv and aio on vmstop
                (this is so we don't need to stop them)
        - keep running aio
        - stop running bh
        - stop running slirp
        - keep running host/rt timers
        - keep running fd callbacks for migration
        - keep running fd callbacks for ui: vnc, spice

Note: only clock=vm can satisfy this requirement.
Default clock=rtc keeps running when VM is stopped,
this is by design.

-- 
MST