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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