sched: Consolidate open coded implementations of nice level frobbing into nice_to_rlimit() and rlimit_to_nice()

Signed-off-by: Dongsheng Yang <[e-mail]>
Signed-off-by: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/a56[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

drivers/staging/android/binder.c

···
 		set_user_nice(current, nice);
 		return;
 	}
-	min_nice = 20 - current->signal->rlim[RLIMIT_NICE].rlim_cur;
+	min_nice = rlimit_to_nice(current->signal->rlim[RLIMIT_NICE].rlim_cur);
 	binder_debug(BINDER_DEBUG_PRIORITY_CAP,
 		     "%d: nice value %ld not allowed use %ld instead\n",
 		      current->pid, nice, min_nice);

include/linux/sched/prio.h

···
 #define TASK_USER_PRIO(p)	USER_PRIO((p)->static_prio)
 #define MAX_USER_PRIO		(USER_PRIO(MAX_PRIO))
 
+/*
+ * Convert nice value [19,-20] to rlimit style value [1,40].
+ */
+static inline long nice_to_rlimit(long nice)
+{
+	return (MAX_NICE - nice + 1);
+}
+
+/*
+ * Convert rlimit style value [1,40] to nice value [-20, 19].
+ */
+static inline long rlimit_to_nice(long prio)
+{
+	return (MAX_NICE - prio + 1);
+}
+
 #endif /* _SCHED_PRIO_H */

kernel/sched/core.c

···
 int can_nice(const struct task_struct *p, const int nice)
 {
 	/* convert nice value [19,-20] to rlimit style value [1,40] */
-	int nice_rlim = 20 - nice;
+	int nice_rlim = nice_to_rlimit(nice);
 
 	return (nice_rlim <= task_rlimit(p, RLIMIT_NICE) ||
 		capable(CAP_SYS_NICE));

kernel/sys.c

···
 			else
 				p = current;
 			if (p) {
-				niceval = 20 - task_nice(p);
+				niceval = nice_to_rlimit(task_nice(p));
 				if (niceval > retval)
 					retval = niceval;
 			}
···
 			else
 				pgrp = task_pgrp(current);
 			do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
-				niceval = 20 - task_nice(p);
+				niceval = nice_to_rlimit(task_nice(p));
 				if (niceval > retval)
 					retval = niceval;
 			} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
···
 
 			do_each_thread(g, p) {
 				if (uid_eq(task_uid(p), uid)) {
-					niceval = 20 - task_nice(p);
+					niceval = nice_to_rlimit(task_nice(p));
 					if (niceval > retval)
 						retval = niceval;
 				}