From: Rong Zhang <i@rong.moe>
Date: Sat, 25 Apr 2026 20:29:57 +0000 (+0800)
Subject: chrt: Fix confusing error messages when priority argument is required
X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=13e4823791d2c828e95a0d7727a978bb42c77c94;p=thirdparty%2Futil-linux.git

chrt: Fix confusing error messages when priority argument is required

While making the priority argument optional for non-prio policies, some
confusing error messages were accidentally exposed to users for cases
that do need a priority argument.

  $ chrt true		#1
  chrt: invalid priority argument: 'true'
  $ chrt 1		#2
  chrt: failed to set pid 0's policy: Operation not permitted
  $ sudo chrt 1		#3
  chrt: no command specified
  $ chrt --other 1	#4
  chrt: unsupported priority value for the policy: 1: see --max for valid range

The error message #1 is caused by mixing `have_prio' and `need_prio'
together. Therefore, it always tries to parse the first positional
argument as a priority when `--pid' is not given. #2 shows that
set_sched() is meaninglessly called even when too few arguments are
specified.

At first glance, the error message #3 seems to be correct, but it turns
out to be very wrong -- the only positional argument in this case must
be regarded as a command, and commit 223a502b0208 ("chrt: (man,usage)
mark the priority value as optional in the synopses") also clearly
stated the same in the help message and the manual. In other words, #4
should have tried to execute `1' from PATH.

Fix #1 by decoupling `need_prio' from the priority parsing routine.

Fix #2 by parsing the first argument as a priority only when it's not
the only argument.

Fix #3 and #4 by consuming optind immediately when parsing priority
argument, instead of postponing it with inconsistent conditions (I have
an intuition that the previous code path was vibe-coded...)

Now #1 returns

  chrt: policy SCHED_RR requires a priority argument

... #2, #3 return

  chrt: no command or priority specified

... and #4 returns

  chrt: failed to execute 1: No such file or directory

... which are more sensible and helpful.

This doesn't break existing usage patterns:

  $ chrt --other true
  $ chrt --other 0 true
  $ chrt --other 1 true
  chrt: unsupported priority value for the policy: 1: see --max for valid range
  $ chrt --other echo meow
  meow

Fixes: 4c425142844d ("chrt: Allow optional priority for non‑prio policies without --pid")
Signed-off-by: Rong Zhang <i@rong.moe>
---

diff --git a/schedutils/chrt.c b/schedutils/chrt.c
index ab6e53ac6..5ba9964c1 100644
--- a/schedutils/chrt.c
+++ b/schedutils/chrt.c
@@ -510,9 +510,6 @@ int main(int argc, char **argv)
 
 	/* If option --pid was given, parse the very last argument as a PID. */
 	if (ctl->pid == 0) {
-		if (need_prio && argc - optind < 2)
-			errx(EXIT_FAILURE, _("policy %s requires a priority argument"),
-						get_policy_name(ctl->policy));
 		errno = 0;
 		/* strtopid_or_err() is not suitable here, as 0 can be passed. */
 		ctl->pid = strtos32_or_err(argv[argc - 1], _("invalid PID argument"));
@@ -530,13 +527,17 @@ int main(int argc, char **argv)
 	if (ctl->pid > -1 && ctl->verbose)
 		show_sched_info(ctl);
 
-	bool have_prio = need_prio ||
-		(ctl->pid == -1 ? (optind < argc && isdigit_string(argv[optind])) : (argc - optind > 1));
-
-	if (have_prio) {
+	if (argc - optind > 1 && (ctl->pid > -1 || isdigit_string(argv[optind]))) {
 		errno = 0;
 		ctl->priority = strtos32_or_err(argv[optind], _("invalid priority argument"));
-	} else
+
+		optind++;
+	} else if (need_prio && ctl->pid == -1 && isdigit_string(argv[optind]))
+		errx(EXIT_FAILURE, _("no command or priority specified"));
+	else if (need_prio)
+		errx(EXIT_FAILURE, _("policy %s requires a priority argument"),
+					get_policy_name(ctl->policy));
+	else
 		ctl->priority = 0;
 
 	if (ctl->runtime && !supports_runtime_param(ctl->policy))
@@ -576,11 +577,6 @@ int main(int argc, char **argv)
 	if (!ctl->pid) {
 		argv += optind;
 
-		if (need_prio)
-			argv++;
-		else if (argv[0] && isdigit_string(argv[0]))
-			argv++;
-
 		if (argv[0] && strcmp(argv[0], "--") == 0)
 			argv++;