Re: [Qemu-devel] [PATCH 3/8] RunState: Add additional states

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 02 Sep 2011 16:32:25 +0200
Jan Kiszka <jan.kiszka@siemens.com> wrote:

> On 2011-09-02 16:28, Luiz Capitulino wrote:
> > On Thu, 01 Sep 2011 22:58:51 +0200
> > Jan Kiszka <jan.kiszka@web.de> wrote:
> > 
> >> On 2011-09-01 20:39, Luiz Capitulino wrote:
> >>> On Thu, 01 Sep 2011 20:30:57 +0200
> >>> Jan Kiszka <jan.kiszka@siemens.com> wrote:
> >>>
> >>>> On 2011-09-01 20:12, Luiz Capitulino wrote:
> >>>>> Currently, only vm_start() and vm_stop() change the VM state.
> >>>>> That's, the state is only changed when starting or stopping the VM.
> >>>>>
> >>>>> This commit adds the runstate_set() function, which makes it possible
> >>>>> to also do state transitions when the VM is stopped or running.
> >>>>>
> >>>>> Additional states are also added and the current state is stored.
> >>>>>
> >>>>> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> >>>>> ---
> >>>>>  cpus.c      |    1 +
> >>>>>  migration.c |    8 +++++++-
> >>>>>  sysemu.h    |   10 +++++++++-
> >>>>>  vl.c        |   20 ++++++++++++++++++++
> >>>>>  4 files changed, 37 insertions(+), 2 deletions(-)
> >>>>>
> >>>>
> >>>> ...
> >>>>
> >>>>> diff --git a/vl.c b/vl.c
> >>>>> index f0b56a4..59f71fc 100644
> >>>>> --- a/vl.c
> >>>>> +++ b/vl.c
> >>>>> @@ -321,6 +321,22 @@ static int default_driver_check(QemuOpts *opts, void *opaque)
> >>>>>  }
> >>>>>  
> >>>>>  /***********************************************************/
> >>>>> +/* QEMU state */
> >>>>> +
> >>>>> +static RunState current_run_state = RSTATE_NO_STATE;
> >>>>> +
> >>>>> +bool runstate_check(RunState state)
> >>>>> +{
> >>>>> +    return current_run_state == state;
> >>>>> +}
> >>>>> +
> >>>>> +void runstate_set(RunState state)
> >>>>> +{
> >>>>> +    assert(state < RSTATE_MAX);
> >>>>> +    current_run_state = state;
> >>>>
> >>>> I still think this should check for valid state transitions instead of
> >>>> blindly accepting what the caller passes in.
> >>>
> >>> I thought your comment where more like a future enhancement than
> >>> a request for change.
> >>
> >> I think we want this now to document at a central place which
> >> transitions are valid and which not. State machines without such checks
> >> break sooner or later, subtly.
> > 
> > Ok, I'll do it.
> > 
> > Do you have any suggestion on the preferred way to document it?
> > Should I use english or try some ascii art?
> 
> My idea is programmatic:
> 
> void runstate_set(RunState new_state)
> {
> 	switch (current_state) {
> 	case X:
> 		/* potential comment on why only X->Y or ... is valid */
> 		if (new_state == Y || ...) {
> 			break;
> 		} else {
> 			abort();
> 		}

Ah, ok. I was thinking in having some fancy graph as documentation,
but let's do the simpler way then.