Re: [XEN PATCH 3/7] xen/sched: address a violation of MISRA C:2012 Rule 16.3

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.04.2024 02:18, Stefano Stabellini wrote:
> On Wed, 3 Apr 2024, Nicola Vetrini wrote:
>> On 2024-04-03 08:33, Jan Beulich wrote:
>>> On 02.04.2024 09:22, Federico Serafini wrote:
>>>> Use pseudo-keyword fallthrough to meet the requirements to deviate
>>>> MISRA C:2012 Rule 16.3 ("An unconditional `break' statement shall
>>>> terminate every switch-clause").
>>>>
>>>> No functional change.
>>>>
>>>> Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>
>>>> ---
>>>>  xen/common/sched/credit2.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/xen/common/sched/credit2.c b/xen/common/sched/credit2.c
>>>> index c76330d79d..0962b52415 100644
>>>> --- a/xen/common/sched/credit2.c
>>>> +++ b/xen/common/sched/credit2.c
>>>> @@ -3152,8 +3152,8 @@ static int cf_check csched2_sys_cntl(
>>>>              printk(XENLOG_INFO "Disabling context switch rate
>>>> limiting\n");
>>>>          prv->ratelimit_us = params->ratelimit_us;
>>>>          write_unlock_irqrestore(&prv->lock, flags);
>>>> +        fallthrough;
>>>>
>>>> -    /* FALLTHRU */
>>>>      case XEN_SYSCTL_SCHEDOP_getinfo:
>>>>          params->ratelimit_us = prv->ratelimit_us;
>>>>          break;
>>>
>>> Hmm, the description doesn't say what's wrong with the comment. Furthermore
>>> docs/misra/rules.rst doesn't mention "fallthrough" at all, nor the
>>> alternative of using comments. I notice docs/misra/deviations.rst does, and
>>> there the specific comment used here isn't covered. That would want saying
>>> in the description.
>>>
>>> Stefano (and others) - in this context it becomes noticeable that having
>>> stuff scattered across multiple doc files isn't necessarily helpful. Other
>>> permissible keywords are mentioned in rules.rst. The pseudo-keyword
>>> "fallthrough" as well as comments are mentioned on deviations.rst. Could
>>> you remind me of the reason(s) why things aren't recorded in a single,
>>> central place?
>>>
>>> Jan
>>
>> If I recall correctly, the idea was to avoid rules.rst from getting too long
>> and too specific about which patterns were deviated, while also having a
>> precise record of the MISRA deviations that didn't live in ECLAIR-specific
>> files. Maybe the use of the pseudo-keyword emerged after the rule was added 
>> to
>> rules.rst, since deviations.rst is updated more frequently.
> 
> Yes exactly.
> 
> I agree with Jan that a single central place is easiest but we cannot
> move everything that is in deviations.rst in the note section of the
> rules.rst table. Of the two, it would be best to reduce the amount of
> notes in rules.rst and move all the deviations listed in rules.rst to
> deviations.rst. That way at least the info is present only once,
> although they are 2 files.

Could every rules.rst section having a deviations.rst counterpart then perhaps
have a standardized referral to there?

Jan