* Peter Zijlstra <[email protected]> wrote:
> On Thu, Nov 28, 2013 at 12:14:03PM +0100, Juri Lelli wrote:
> > +SYSCALL_DEFINE2(sched_getattr, pid_t, pid, struct sched_attr __user *,
> > attr)
> > {
> > - struct sched_param2 lp;
> > + struct sched_attr lp;
> > struct task_struct *p;
> > int retval;
> >
> > - if (!param2 || pid < 0)
> > + if (!attr || pid < 0)
> > return -EINVAL;
> >
> > + memset(&lp, 0, sizeof(struct sched_attr));
> > +
> > rcu_read_lock();
> > p = find_process_by_pid(pid);
> > retval = -ESRCH;
> > @@ -3427,7 +3495,7 @@ SYSCALL_DEFINE2(sched_getparam2, pid_t, pid, struct
> > sched_param2 __user *, param
> > lp.sched_priority = p->rt_priority;
> > rcu_read_unlock();
> >
> > - retval = copy_to_user(param2, &lp, sizeof(lp)) ? -EFAULT : 0;
> > + retval = copy_to_user(attr, &lp, sizeof(lp)) ? -EFAULT : 0;
> > return retval;
> >
> > out_unlock:
>
>
> So this side needs a bit more care; suppose the kernel has a larger attr
> than userspace knows about.
>
> What would make more sense; add another syscall argument with the
> userspace sizeof(struct sched_attr), or expect userspace to initialize
> attr->size to the right value before calling sched_getattr() ?
>
> To me the extra argument makes more sense; that is:
>
> struct sched_attr attr;
>
> ret = sched_getattr(0, &attr, sizeof(attr));
>
> seems like a saner thing than:
>
> struct sched_attr attr = { .size = sizeof(attr), };
>
> ret = sched_getattr(0, &attr);
>
> Mostly because the former has a clear separation between input and
> output arguments, whereas for the second form the attr argument is
> both input and output.
>
> Ingo?
I suppose so - in the sys_perf_event_open() case we ran out of
arguments, so attr::size was the only sane way to do it.
[ Btw., perf events side note: for completeness and for debugging we
probably want to add a sys_perf_event_get() method as well, to
recover the attributes of an existing event. Unidirectional APIs are
not very nice. ]
Thanks,
Ingo
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