rtla/tests: Test timerlat -P option using actions

The -P option is used to set priority of osnoise and timerlat threads.

Extend the test for -P with --on-threshold calling a script that looks
for running timerlat threads and checks if their priority is set
correctly.

As --on-threshold is only supported by timerlat at the moment, this is
only implemented there so far.

Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Cc: Chang Yin <cyin@redhat.com>
Cc: Costa Shulyupin <costa.shul@redhat.com>
Link: https://lore.kernel.org/20250725133817.59237-3-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

tools/tracing/rtla/tests/engine.sh

@@ -69,7 +69,7 @@ check() {
 			# Add rtla output and exit code as comments in case of failure
 			echo "$result" | col -b | while read line; do echo "# $line"; done
 			printf "#\n# exit code %s\n" $exitcode
-			[ -n "$expected_output" ] && \
+			[ -n "$expected_output" ] && [ $grep_result -ne 0 ] && \
 				printf "# Output match failed: \"%s\"\n" "$expected_output"
 		fi
 	fi

tools/tracing/rtla/tests/scripts/check-priority.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+pids="$(pgrep ^$1)" || exit 1
+for pid in $pids
+do
+  chrt -p $pid | cut -d ':' -f 2 | head -n1 | grep "^ $2\$" >/dev/null
+  chrt -p $pid | cut -d ':' -f 2 | tail -n1 | grep "^ $3\$" >/dev/null
+done && echo "Priorities are set correctly"

tools/tracing/rtla/tests/timerlat.t

@@ -25,7 +25,8 @@ check "verify help page" \
 check "verify -s/--stack" \
 	"timerlat top -s 3 -T 10 -t" 2 "Blocking thread stack trace"
 check "verify -P/--priority" \
-	"timerlat top -P F:1 -c 0 -d 10s -q"
+	"timerlat top -P F:1 -c 0 -d 10s -q -T 1 --on-threshold shell,command=\"tests/scripts/check-priority.sh timerlatu/ SCHED_FIFO 1\"" \
+	2 "Priorities are set correctly"
 check "test in nanoseconds" \
 	"timerlat top -i 2 -c 0 -n -d 10s" 2 "ns"
 check "set the automatic trace mode" \