Messages in this thread | | | Date | Sat, 30 Nov 2013 15:06:33 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 02/14] sched: add extended scheduling interface. (new ABI) |
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* Peter Zijlstra <peterz@infradead.org> 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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