ftrace/selftest: Add tests to test register_ftrace_direct()

Add two test cases that test the new ftrace direct functionality if the
ftrace-direct sample module is available. One test case tests against each
available tracer (function, function_graph, mmiotrace, etc), and the other
test tests against a kprobe at the same location as the direct caller. Both
tests follow the same pattern of testing combinations:

  enable test (either the tracer or the kprobe)
  load direct function module
  unload direct function module
  disable test

  enable test
  load direct function module
  disable test
  unload direct function module

  load direct function module
  enable test
  disable test
  unload direct function module

  load direct function module
  enable test
  unload direct function module
  disable test

As most the bugs in development happened with various ways of enabling or
disabling the direct calls with function tracer in one of these
combinations.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

tools/testing/selftests/ftrace/test.d/direct/ftrace-direct.tc

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test ftrace direct functions against tracers
+
+rmmod ftrace-direct ||:
+if ! modprobe ftrace-direct ; then
+  echo "No ftrace-direct sample module - please make CONFIG_SAMPLE_FTRACE_DIRECT=m"
+  exit_unresolved;
+fi
+
+echo "Let the module run a little"
+sleep 1
+
+grep -q "my_direct_func: wakeing up" trace
+
+rmmod ftrace-direct
+
+test_tracer() {
+	tracer=$1
+
+	# tracer -> direct -> no direct > no tracer
+	echo $tracer > current_tracer
+	modprobe ftrace-direct
+	rmmod ftrace-direct
+	echo nop > current_tracer
+
+	# tracer -> direct -> no tracer > no direct
+	echo $tracer > current_tracer
+	modprobe ftrace-direct
+	echo nop > current_tracer
+	rmmod ftrace-direct
+
+	# direct -> tracer -> no tracer > no direct
+	modprobe ftrace-direct
+	echo $tracer > current_tracer
+	echo nop > current_tracer
+	rmmod ftrace-direct
+
+	# direct -> tracer -> no direct > no notracer
+	modprobe ftrace-direct
+	echo $tracer > current_tracer
+	rmmod ftrace-direct
+	echo nop > current_tracer
+}
+
+for t in `cat available_tracers`; do
+	if [ "$t" != "nop" ]; then
+		test_tracer $t
+	fi
+done
+
+echo nop > current_tracer
+rmmod ftrace-direct ||:

tools/testing/selftests/ftrace/test.d/direct/kprobe-direct.tc

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test ftrace direct functions against kprobes
+
+rmmod ftrace-direct ||:
+if ! modprobe ftrace-direct ; then
+  echo "No ftrace-direct sample module - please build with CONFIG_SAMPLE_FTRACE_DIRECT=m"
+  exit_unresolved;
+fi
+
+if [ ! -f kprobe_events ]; then
+	echo "No kprobe_events file -please build CONFIG_KPROBE_EVENTS"
+	exit_unresolved;
+fi
+
+echo "Let the module run a little"
+sleep 1
+
+grep -q "my_direct_func: wakeing up" trace
+
+rmmod ftrace-direct
+
+echo 'p:kwake wake_up_process task=$arg1' > kprobe_events
+
+start_direct() {
+	echo > trace
+	modprobe ftrace-direct
+	sleep 1
+	grep -q "my_direct_func: wakeing up" trace
+}
+
+stop_direct() {
+	rmmod ftrace-direct
+}
+
+enable_probe() {
+	echo > trace
+	echo 1 > events/kprobes/kwake/enable
+	sleep 1
+	grep -q "kwake:" trace
+}
+
+disable_probe() {
+	echo 0 > events/kprobes/kwake/enable
+}
+
+# probe -> direct -> no direct > no probe
+enable_probe
+start_direct
+stop_direct
+disable_probe
+
+# probe -> direct -> no probe > no direct
+enable_probe
+start_direct
+disable_probe
+stop_direct
+
+# direct -> probe -> no probe > no direct
+start_direct
+enable_probe
+disable_probe
+stop_direct
+
+# direct -> probe -> no direct > no noprobe
+start_direct
+enable_probe
+stop_direct
+disable_probe
+
+echo > kprobe_events