selftests/ftrace: Add selftest for testing eprobe events on synthetic events

Add a test to test event probes, by creating a synthetic event across
sys_enter_openat and sys_exit_openat that passes the filename pointer from
the enter of the system call to the exit, and then add an event probe to
the synthetic event to make sure that the file name is seen.

Link: https://lore.kernel.org/linux-kselftest/20210819152825.526931866@goodmis.org/
Link: https://lkml.kernel.org/r/20210820204742.463259900@goodmis.org

Cc: "Tzvetomir Stoyanov" <tz.stoyanov@gmail.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: linux-kselftest@vger.kernel.org
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

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

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: event trigger - test inter-event histogram trigger eprobe on synthetic event
+# requires: dynamic_events synthetic_events events/syscalls/sys_enter_openat/hist "e[:[<group>/]<event>] <attached-group>.<attached-event> [<args>]":README
+
+echo 0 > events/enable
+
+clear_dynamic_events
+
+SYSTEM="syscalls"
+START="sys_enter_openat"
+END="sys_exit_openat"
+FIELD="filename"
+SYNTH="synth_open"
+EPROBE="eprobe_open"
+
+echo "$SYNTH u64 filename; s64 ret;" > synthetic_events
+echo "hist:keys=common_pid:__arg__1=$FIELD" > events/$SYSTEM/$START/trigger
+echo "hist:keys=common_pid:filename=\$__arg__1,ret=ret:onmatch($SYSTEM.$START).trace($SYNTH,\$filename,\$ret)" > events/$SYSTEM/$END/trigger
+
+echo "e:$EPROBE synthetic/$SYNTH file=+0(\$filename):ustring ret=\$ret:s64" >> dynamic_events
+
+grep -q "$SYNTH" dynamic_events
+grep -q "$EPROBE" dynamic_events
+test -d events/synthetic/$SYNTH
+test -d events/eprobes/$EPROBE
+
+echo 1 > events/eprobes/$EPROBE/enable
+ls
+echo 0 > events/eprobes/$EPROBE/enable
+
+content=`grep '^ *ls-' trace | grep 'file='`
+nocontent=`grep '^ *ls-' trace | grep 'file=' | grep -v -e '"/' -e '"."'` || true
+
+if [ -z "$content" ]; then
+	exit_fail
+fi
+
+if [ ! -z "$nocontent" ]; then
+	exit_fail
+fi
+
+echo "-:$EPROBE" >> dynamic_events
+echo '!'"hist:keys=common_pid:filename=\$__arg__1,ret=ret:onmatch($SYSTEM.$START).trace($SYNTH,\$filename,\$ret)" > events/$SYSTEM/$END/trigger
+echo '!'"hist:keys=common_pid:__arg__1=$FIELD" > events/$SYSTEM/$START/trigger
+echo '!'"$SYNTH u64 filename; s64 ret;" >> synthetic_events
+
+! grep -q "$SYNTH" dynamic_events
+! grep -q "$EPROBE" dynamic_events
+! test -d events/synthetic/$SYNTH
+! test -d events/eprobes/$EPROBE
+
+clear_trace