Messages in this thread | | | Date | Thu, 28 Nov 2013 12:28:58 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 02/14] sched: add extended scheduling interface. (new ABI) |
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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?
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