selftests/ftrace: Add test to test new set_ftrace_notrace_pid file

A new file was added to the tracing directory that will allow a user to
place a PID into it and the task associated to that PID will not be traced
by the function tracer. If the function-fork option is enabled, then neither
will the children of that task be traced by the function tracer.

Cc: linux-kselftest@vger.kernel.org
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

tools/testing/selftests/ftrace/test.d/ftrace/func-filter-notrace-pid.tc

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: ftrace - function pid notrace filters
+# flags: instance
+
+# Make sure that function pid matching filter with notrace works.
+
+if ! grep -q function available_tracers; then
+    echo "no function tracer configured"
+    exit_unsupported
+fi
+
+if [ ! -f set_ftrace_notrace_pid ]; then
+    echo "set_ftrace_notrace_pid not found? Is function tracer not set?"
+    exit_unsupported
+fi
+
+if [ ! -f set_ftrace_filter ]; then
+    echo "set_ftrace_filter not found? Is function tracer not set?"
+    exit_unsupported
+fi
+
+do_function_fork=1
+
+if [ ! -f options/function-fork ]; then
+    do_function_fork=0
+    echo "no option for function-fork found. Option will not be tested."
+fi
+
+read PID _ < /proc/self/stat
+
+if [ $do_function_fork -eq 1 ]; then
+    # default value of function-fork option
+    orig_value=`grep function-fork trace_options`
+fi
+
+do_reset() {
+    if [ $do_function_fork -eq 0 ]; then
+	return
+    fi
+
+    echo > set_ftrace_notrace_pid
+    echo $orig_value > trace_options
+}
+
+fail() { # msg
+    do_reset
+    echo $1
+    exit_fail
+}
+
+do_test() {
+    disable_tracing
+
+    echo do_execve* > set_ftrace_filter
+    echo *do_fork >> set_ftrace_filter
+
+    echo $PID > set_ftrace_notrace_pid
+    echo function > current_tracer
+
+    if [ $do_function_fork -eq 1 ]; then
+	# don't allow children to be traced
+	echo nofunction-fork > trace_options
+    fi
+
+    enable_tracing
+    yield
+
+    count_pid=`cat trace | grep -v ^# | grep $PID | wc -l`
+    count_other=`cat trace | grep -v ^# | grep -v $PID | wc -l`
+
+    # count_pid should be 0
+    if [ $count_pid -ne 0 -o $count_other -eq 0 ]; then
+	fail "PID filtering not working? traced task = $count_pid; other tasks = $count_other "
+    fi
+
+    disable_tracing
+    clear_trace
+
+    if [ $do_function_fork -eq 0 ]; then
+	return
+    fi
+
+    # allow children to be traced
+    echo function-fork > trace_options
+
+    # With pid in both set_ftrace_pid and set_ftrace_notrace_pid
+    # there should not be any tasks traced.
+
+    echo $PID > set_ftrace_pid
+
+    enable_tracing
+    yield
+
+    count_pid=`cat trace | grep -v ^# | grep $PID | wc -l`
+    count_other=`cat trace | grep -v ^# | grep -v $PID | wc -l`
+
+    # both should be zero
+    if [ $count_pid -ne 0 -o $count_other -ne 0 ]; then
+	fail "PID filtering not following fork? traced task = $count_pid; other tasks = $count_other "
+    fi
+}
+
+do_test
+
+do_reset
+
+exit 0