chrt: do not segfault if policy number is unknown

While at it, improve help text

function                                             old     new   delta
packed_usage                                       33319   33344     +25
policy_name                                            -      22     +22
show_min_max                                          59      64      +5
chrt_main                                            432     429      -3
policies                                              72       -     -72
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 2/1 up/down: 52/-75)            Total: -23 bytes
   text	   data	    bss	    dec	    hex	filename
 982150	    485	   7296	 989931	  f1aeb	busybox_old
 982183	    485	   7296	 989964	  f1b0c	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 34 insertions, 28 deletions

diff --git a/util-linux/chrt.c b/util-linux/chrt.c
index 28e6545..ede9231 100644
--- a/util-linux/chrt.c
+++ b/util-linux/chrt.c
@@ -17,16 +17,16 @@
 //kbuild:lib-$(CONFIG_CHRT) += chrt.o
 
 //usage:#define chrt_trivial_usage
-//usage:       "[-prfombi] [PRIO] [PID | PROG ARGS]"
+//usage:       "-m | -p [PRIO] PID | [-rfobi] PRIO PROG [ARGS]"
 //usage:#define chrt_full_usage "\n\n"
 //usage:       "Change scheduling priority and class for a process\n"
+//usage:     "\n	-m	Show min/max priorities"
 //usage:     "\n	-p	Operate on PID"
 //usage:     "\n	-r	Set SCHED_RR class"
 //usage:     "\n	-f	Set SCHED_FIFO class"
 //usage:     "\n	-o	Set SCHED_OTHER class"
 //usage:     "\n	-b	Set SCHED_BATCH class"
 //usage:     "\n	-i	Set SCHED_IDLE class"
-//usage:     "\n	-m	Show min/max priorities"
 //usage:
 //usage:#define chrt_example_usage
 //usage:       "$ chrt -r 4 sleep 900; x=$!\n"
@@ -39,28 +39,32 @@
 # define SCHED_IDLE 5
 #endif
 
-static const struct {
-	char name[sizeof("SCHED_OTHER")];
-} policies[] = {
-	{ "SCHED_OTHER" }, /* 0:SCHED_OTHER */
-	{ "SCHED_FIFO" },  /* 1:SCHED_FIFO */
-	{ "SCHED_RR" },    /* 2:SCHED_RR */
-	{ "SCHED_BATCH" }, /* 3:SCHED_BATCH */
-	{ "" },            /* 4:SCHED_ISO */
-	{ "SCHED_IDLE" },  /* 5:SCHED_IDLE */
-	/* 6:SCHED_DEADLINE */
-};
+static const char *policy_name(int pol)
+{
+	if (pol > 6)
+		return utoa(pol);
+	return nth_string(
+		"OTHER"   "\0" /* 0:SCHED_OTHER */
+		"FIFO"    "\0" /* 1:SCHED_FIFO */
+		"RR"      "\0" /* 2:SCHED_RR */
+		"BATCH"   "\0" /* 3:SCHED_BATCH */
+		"ISO"     "\0" /* 4:SCHED_ISO */
+		"IDLE"    "\0" /* 5:SCHED_IDLE */
+		"DEADLINE",    /* 6:SCHED_DEADLINE */
+		pol
+	);
+}
 
 static void show_min_max(int pol)
 {
-	const char *fmt = "%s min/max priority\t: %u/%u\n";
+	const char *fmt = "SCHED_%s min/max priority\t: %u/%u\n";
 	int max, min;
 
 	max = sched_get_priority_max(pol);
 	min = sched_get_priority_min(pol);
 	if ((max|min) < 0)
-		fmt = "%s not supported\n";
-	printf(fmt, policies[pol].name, min, max);
+		fmt = "SCHED_%s not supported\n";
+	printf(fmt, policy_name(pol), min, max);
 }
 
 #define OPT_m (1<<0)
@@ -112,11 +116,11 @@ int chrt_main(int argc UNUSED_PARAM, char **argv)
 		bb_show_usage();
 	if (opt & OPT_p) {
 		pid_str = *argv++;
-		if (*argv) { /* "-p <priority> <pid> [...]" */
+		if (*argv) { /* "-p PRIO PID [...]" */
 			priority = pid_str;
 			pid_str = *argv;
 		}
-		/* else "-p <pid>", and *argv == NULL */
+		/* else "-p PID", and *argv == NULL */
 		pid = xatoul_range(pid_str, 1, ((unsigned)(pid_t)ULONG_MAX) >> 1);
 	} else {
 		priority = *argv++;
@@ -130,16 +134,18 @@ int chrt_main(int argc UNUSED_PARAM, char **argv)
  print_rt_info:
 		pol = sched_getscheduler(pid);
 		if (pol < 0)
-			bb_perror_msg_and_die("can't %cet pid %d's policy", 'g', (int)pid);
-		printf("pid %d's %s scheduling policy: %s\n",
-				pid, current_new, policies[pol].name);
+			bb_perror_msg_and_die("can't %cet pid %u's policy", 'g', (int)pid);
+		printf("pid %u's %s scheduling policy: SCHED_%s\n",
+			pid, current_new, policy_name(pol)
+		);
 		if (sched_getparam(pid, &sp))
-			bb_perror_msg_and_die("can't get pid %d's attributes", (int)pid);
-		printf("pid %d's %s scheduling priority: %d\n",
-				(int)pid, current_new, sp.sched_priority);
+			bb_perror_msg_and_die("can't get pid %u's attributes", (int)pid);
+		printf("pid %u's %s scheduling priority: %d\n",
+			(int)pid, current_new, sp.sched_priority
+		);
 		if (!*argv) {
-			/* Either it was just "-p <pid>",
-			 * or it was "-p <priority> <pid>" and we came here
+			/* Either it was just "-p PID",
+			 * or it was "-p PRIO PID" and we came here
 			 * for the second time (see goto below) */
 			return EXIT_SUCCESS;
 		}
@@ -152,9 +158,9 @@ int chrt_main(int argc UNUSED_PARAM, char **argv)
 	);
 
 	if (sched_setscheduler(pid, policy, &sp) < 0)
-		bb_perror_msg_and_die("can't %cet pid %d's policy", 's', (int)pid);
+		bb_perror_msg_and_die("can't %cet pid %u's policy", 's', (int)pid);
 
-	if (!argv[0]) /* "-p <priority> <pid> [...]" */
+	if (!argv[0]) /* "-p PRIO PID [...]" */
 		goto print_rt_info;
 
 	BB_EXECVP_or_die(argv);