chrt: Only display current settings when no policy is specified

Previously, running "chrt --pid <pid>" with no policy options
would display the process’s current scheduling attributes, but
specifying a policy without a priority (e.g. chrt --rr --pid <pid>)
would silently fallback to displaying the same info. This was
confusing, since a policy option normally implies an intent to
change something.

This patch changes the behavior so that
chrt --pid <pid> continues to show the current settings:

chrt --pid 10862
pid 10862's current scheduling policy:  SCHED_OTHER
pid 10862's current scheduling priority: 0
pid 10862's current runtime parameter:  2800000

If a policy is specified but no priority follows, chrt now
errors out:

chrt --rr --pid 10862
chrt: policy SCHED_RR requires a priority argument

Verbose output (-v) still prints the current settings when a
valid policy+priority is provided.

Signed-off-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>

diff --git a/schedutils/chrt.c b/schedutils/chrt.c
index 8fe748f434b5c4b41210bc7b5300cc9da8429060..d694845ac763cc7d32dae243365364630c17025c 100644 (file)
--- a/schedutils/chrt.c
+++ b/schedutils/chrt.c
@@ -64,7 +64,7 @@ static void __attribute__((__noreturn__)) usage(void)
        " chrt [options] --pid <priority> <pid>\n"), out);
        fputs(USAGE_SEPARATOR, out);
        fputs(_("Get policy:\n"
-       " chrt [options] --pid <pid>\n"), out);
+       " chrt --pid <pid>\n"), out);
 
        fputs(USAGE_SEPARATOR, out);
        fputs(_("Policy options:\n"), out);
@@ -399,6 +399,7 @@ int main(int argc, char **argv)
 {
        struct chrt_ctl _ctl = { .pid = -1, .policy = SCHED_RR }, *ctl = &_ctl;
        int c;
+       bool policy_given = false;
 
        static const struct option longopts[] = {
                { "all-tasks",  no_argument, NULL, 'a' },
@@ -435,21 +436,25 @@ int main(int argc, char **argv)
                case 'b':
 #ifdef SCHED_BATCH
                        ctl->policy = SCHED_BATCH;
+                       policy_given = true;
 #endif
                        break;
 
                case 'd':
 #ifdef SCHED_DEADLINE
                        ctl->policy = SCHED_DEADLINE;
+                       policy_given = true;
 #endif
                        break;
                case 'e':
 #ifdef SCHED_EXT
                        ctl->policy = SCHED_EXT;
+                       policy_given = true;
 #endif
                        break;
                case 'f':
                        ctl->policy = SCHED_FIFO;
+                       policy_given = true;
                        break;
                case 'R':
                        ctl->reset_on_fork = 1;
@@ -457,6 +462,7 @@ int main(int argc, char **argv)
                case 'i':
 #ifdef SCHED_IDLE
                        ctl->policy = SCHED_IDLE;
+                       policy_given = true;
 #endif
                        break;
                case 'm':
@@ -464,6 +470,7 @@ int main(int argc, char **argv)
                        return EXIT_SUCCESS;
                case 'o':
                        ctl->policy = SCHED_OTHER;
+                       policy_given = true;
                        break;
                case 'p':
                        errno = 0;
@@ -472,6 +479,7 @@ int main(int argc, char **argv)
                        break;
                case 'r':
                        ctl->policy = SCHED_RR;
+                       policy_given = true;
                        break;
                case 'v':
                        ctl->verbose = 1;
@@ -501,12 +509,21 @@ int main(int argc, char **argv)
                errtryhelp(EXIT_FAILURE);
        }
 
-       if ((ctl->pid > -1) && (ctl->verbose || argc - optind == 1)) {
+       /* pid exists but priority not given */
+       if (ctl->pid > -1 && argc - optind == 1) {
+               /* Error if a policy was specified but no priority given */
+               if (policy_given)
+                       errx(EXIT_FAILURE, ("policy %s requires a priority argument"),
+                                               get_policy_name(ctl->policy));
+
+               /* If no policy specified, show current settings */
                show_sched_info(ctl);
-               if (argc - optind == 1)
-                       return EXIT_SUCCESS;
+               return EXIT_SUCCESS;
        }
 
+       if (ctl->verbose)
+               show_sched_info(ctl);
+
        errno = 0;
        ctl->priority = strtos32_or_err(argv[optind], _("invalid priority argument"));