Re: [XEN PATCH] xen/sched: mechanical renaming to address MISRA C:2012 Rule 5.3

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Sat, 22 Jul 2023, Nicola Vetrini wrote:
> On 22/07/23 01:06, Stefano Stabellini wrote:
> > On Fri, 21 Jul 2023, Nicola Vetrini wrote:
> > > Rule 5.3 has the following headline:
> > > "An identifier declared in an inner scope shall not hide an
> > > identifier declared in an outer scope"
> > > 
> > > The renaming s/sched_id/scheduler_id of the function defined in
> > > 'xen/common/sched/core.c' prevents any hiding of that function
> > > by the many instances of omonymous function parameters.
> > > 
> > > Similarly, the renames
> > > - s/ops/operations
> > > - s/do_softirq/exec_softirq
> > > - s/loop/it
> > > are introduced for parameter names, to avoid any conflict
> > > with the homonymous variable or function defined in an enclosing
> > > scope.
> > > 
> > > Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> > > ---
> > >   xen/common/sched/core.c    | 18 +++++++++---------
> > >   xen/common/sched/credit2.c |  4 ++--
> > >   xen/common/sysctl.c        |  2 +-
> > >   xen/include/xen/sched.h    |  2 +-
> > >   4 files changed, 13 insertions(+), 13 deletions(-)
> > > 
> > > diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
> > > index 022f548652..e74b1208bd 100644
> > > --- a/xen/common/sched/core.c
> > > +++ b/xen/common/sched/core.c
> > > @@ -99,13 +99,13 @@ static void sched_set_affinity(
> > >       struct sched_unit *unit, const cpumask_t *hard, const cpumask_t
> > > *soft);
> > >     static struct sched_resource *cf_check
> > > -sched_idle_res_pick(const struct scheduler *ops, const struct sched_unit
> > > *unit)
> > > +sched_idle_res_pick(const struct scheduler *operations, const struct
> > > sched_unit *unit)
> > 
> > nit: code style, now the line is over 80 chars, could be fixed on commit
> > 
> 
> Ok
> 
> 
> > > -/* sched_id - fetch ID of current scheduler */
> > > -int sched_id(void)
> > > +/* scheduler_id - fetch ID of current scheduler */
> > > +int scheduler_id(void)
> > >   {
> > >       return ops.sched_id;
> > >   }
> > > @@ -2579,7 +2579,7 @@ static void cf_check sched_slave(void)
> > >       struct sched_unit    *prev = vprev->sched_unit, *next;
> > >       s_time_t              now;
> > >       spinlock_t           *lock;
> > > -    bool                  do_softirq = false;
> > > +    bool                  exec_softirq = false;
> > 
> > We don't typically use "exec" especially in the context of softirqs.
> > I would just change it to "softirq".
> > 
> 
> Ok
> 
> > 
> > >       unsigned int          cpu = smp_processor_id();
> > >         ASSERT_NOT_IN_ATOMIC();
> > > @@ -2604,7 +2604,7 @@ static void cf_check sched_slave(void)
> > >               return;
> > >           }
> > >   -        do_softirq = true;
> > > +        exec_softirq = true;
> > >       }
> > >         if ( !prev->rendezvous_in_cnt )
> > > @@ -2614,7 +2614,7 @@ static void cf_check sched_slave(void)
> > >           rcu_read_unlock(&sched_res_rculock);
> > >             /* Check for failed forced context switch. */
> > > -        if ( do_softirq )
> > > +        if ( exec_softirq )
> > >               raise_softirq(SCHEDULE_SOFTIRQ);
> > >             return;
> > > diff --git a/xen/common/sched/credit2.c b/xen/common/sched/credit2.c
> > > index 87a1e31ee9..aba51a7963 100644
> > > --- a/xen/common/sched/credit2.c
> > > +++ b/xen/common/sched/credit2.c
> > > @@ -3884,7 +3884,7 @@ csched2_dump(const struct scheduler *ops)
> > >       list_for_each_entry ( rqd, &prv->rql, rql )
> > >       {
> > >           struct list_head *iter, *runq = &rqd->runq;
> > > -        int loop = 0;
> > > +        int it = 0;
> > 
> > Nice catch! This is almost a bug fix.
> > 
> > 
> > >           /* We need the lock to scan the runqueue. */
> > >           spin_lock(&rqd->lock);
> > > @@ -3901,7 +3901,7 @@ csched2_dump(const struct scheduler *ops)
> > >                 if ( svc )
> > >               {
> > > -                printk("\t%3d: ", loop++);
> > > +                printk("\t%3d: ", it++);
> > >                   csched2_dump_unit(prv, svc);
> > >               }
> > >           }
> > > diff --git a/xen/common/sysctl.c b/xen/common/sysctl.c
> > > index 0cbfe8bd44..7cabfb0230 100644
> > > --- a/xen/common/sysctl.c
> > > +++ b/xen/common/sysctl.c
> > > @@ -71,7 +71,7 @@ long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t)
> > > u_sysctl)
> > >           break;
> > >         case XEN_SYSCTL_sched_id:
> > > -        op->u.sched_id.sched_id = sched_id();
> > > +        op->u.sched_id.sched_id = scheduler_id();
> > 
> > I am confused about this one. There is no global variable or no other
> > global function named "sched_id". Why do we need to rename sched_id to
> > scheduler_id?
> > 
> 
> sched_id is also a common parameter name used by functions declared where the
> declaration of function 'sched_id' is also visible, so it's entirely
> equivalent whether to change parameter names or the function identifier, but
> since there's just one usage of the function (in 'xen/common/sysctl.c') I
> preferred to make the minimal change in the patch. If you prefer this done the
> other way around, no problem.

I searched through the code and there aren't that many parameters or
local variables called "sched_id" maybe only 5-6. Still, thinking about
it, I think it is better to rename the function to scheduler_id() as you
did in this patch.

Cheers,

Stefano