selftests/ftrace: Add trace_pipe testcase

Add a simple testcase for trace_pipe which can consume
ringbuffer.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>

tools/testing/selftests/ftrace/test.d/00basic/trace_pipe.tc

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: trace_pipe and trace_marker
+# flags: instance
+
+[ ! -f trace_marker ] && exit_unsupported
+
+echo "test input 1" > trace_marker
+
+: "trace interface never consume the ring buffer"
+grep -q "test input 1" trace
+grep -q "test input 1" trace
+
+: "trace interface never consume the ring buffer"
+head -n 1 trace_pipe | grep -q "test input 1"
+! grep -q "test input 1" trace