perf ftrace: Show trace column header

This makes 'perf ftrace' display column header before printing trace.

  $ sudo perf ftrace
  # tracer: function
  #
  # entries-in-buffer/entries-written: 0/0   #P:8
  #
  #            TASK-PID     CPU#   TIMESTAMP  FUNCTION
  #              | |         |       |         |
             <...>-9246  [006]  10726.262760: mutex_unlock <-rb_simple_write
             <...>-9246  [006]  10726.262764: __fsnotify_parent <-vfs_write
             <...>-9246  [006]  10726.262765: fsnotify <-vfs_write
             <...>-9246  [006]  10726.262766: __sb_end_write <-vfs_write
             <...>-9246  [006]  10726.262767: fpregs_assert_state_consistent <-do_syscall_64

Signed-off-by: Changbin Du <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt (VMware) <[email protected]>
Link: http://lore.kernel.org/lkml/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: changbindu

tools/perf/builtin-ftrace.c

@@ -435,6 +435,9 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
 	fcntl(trace_fd, F_SETFL, O_NONBLOCK);
 	pollfd.fd = trace_fd;
 
+	/* display column headers */
+	read_tracing_file_to_stdout("trace");
+
 	if (write_tracing_file("tracing_on", "1") < 0) {
 		pr_err("can't enable tracing\n");
 		goto out_close_fd;