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

[Jan Kiszka]

On 2011-09-02 16:28, Luiz Capitulino wrote:
> On Thu, 01 Sep 2011 22:58:51 +0200
> Jan Kiszka <address@hidden> wrote:
> 
>> On 2011-09-01 20:39, Luiz Capitulino wrote:
>>> On Thu, 01 Sep 2011 20:30:57 +0200
>>> Jan Kiszka <address@hidden> 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 <address@hidden>
>>>>> ---
>>>>>  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();
                }

Jan

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