• Fail when the utility is not invoked as rtprio nor idprio.
• use warnx() to tell the user whether a process is running in normal, idle or realtime priority. with the old code it would have been possible for another process to send data to stdout between

printf("%s: ", p);

and

printf("* priority\n");

and thus break the formatting.

• 'rtprio 10 -0' triggeres non-intuitive behavior. It would first set the priority of itself to 10 *and* would then try to execute '-0'. Of course, setting the priority of [id|rt]prio itself doesn't make a lot of sense, but it is intuitive compared to the previous behavior.
• 'rtprio -t --1' will actually pass over the '-1' to rtprio(). Now invoking rtprio like this will catch the wrong usage before passing over the invalid argument to rtprio().
• Garrett Cooper suggested to add further diagnostics where the failure occures, if execvp fails.

PR: bin/154042
Submitted by: arundel
MFC after: 1 month