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

[Nicola Vetrini <nicola.vetrini@bugseng.com>]

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@bugseng.com>
>> ---
>>  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.

-- 
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)