selftests/ftrace: Add test case for synthetic event dynamic strings

Add a selftest that defines and traces a synthetic event that uses a
dynamic string event field.

Link: https://lkml.kernel.org/r/74445afb005046d76d59fb06696a2ceaa164dec9.1601848695.git.zanussi@kernel.orgAcked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-synthetic-event-dynstring.tc

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: event trigger - test inter-event histogram trigger trace action with dynamic string param
+# requires: set_event synthetic_events events/sched/sched_process_exec/hist "char name[]' >> synthetic_events":README
+
+fail() { #msg
+    echo $1
+    exit_fail
+}
+
+echo "Test create synthetic event"
+
+echo 'ping_test_latency u64 lat; char filename[]' > synthetic_events
+if [ ! -d events/synthetic/ping_test_latency ]; then
+    fail "Failed to create ping_test_latency synthetic event"
+fi
+
+echo "Test create histogram for synthetic event using trace action and dynamic strings"
+echo "Test histogram dynamic string variables,simple expression support and trace action"
+
+echo 'hist:key=pid:filenamevar=filename:ts0=common_timestamp.usecs' > events/sched/sched_process_exec/trigger
+echo 'hist:key=pid:lat=common_timestamp.usecs-$ts0:onmatch(sched.sched_process_exec).ping_test_latency($lat,$filenamevar) if comm == "ping"' > events/sched/sched_process_exit/trigger
+echo 'hist:keys=filename,lat:sort=filename,lat' > events/synthetic/ping_test_latency/trigger
+
+ping $LOCALHOST -c 5
+
+if ! grep -q "ping" events/synthetic/ping_test_latency/hist; then
+    fail "Failed to create dynamic string trace action inter-event histogram"
+fi
+
+exit 0