tracing/function-graph-tracer: implement a print_headers function

Impact: provide trace headers to explain a bit the output

This patch implements the print_headers callback for the function graph
tracer. These headers are output according to the current trace options.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_functions_graph.c

@@ -570,11 +570,36 @@ print_graph_function(struct trace_iterator *iter)
 	}
 }
 
+static void print_graph_headers(struct seq_file *s)
+{
+	/* 1st line */
+	seq_printf(s, "# ");
+	if (tracer_flags.val & TRACE_GRAPH_PRINT_CPU)
+		seq_printf(s, "CPU ");
+	if (tracer_flags.val & TRACE_GRAPH_PRINT_PROC)
+		seq_printf(s, "TASK/PID     ");
+	if (tracer_flags.val & TRACE_GRAPH_PRINT_OVERHEAD)
+		seq_printf(s, "OVERHEAD/");
+	seq_printf(s, "DURATION            FUNCTION CALLS\n");
+
+	/* 2nd line */
+	seq_printf(s, "# ");
+	if (tracer_flags.val & TRACE_GRAPH_PRINT_CPU)
+		seq_printf(s, "|   ");
+	if (tracer_flags.val & TRACE_GRAPH_PRINT_PROC)
+		seq_printf(s, "|      |     ");
+	if (tracer_flags.val & TRACE_GRAPH_PRINT_OVERHEAD) {
+		seq_printf(s, "|        ");
+		seq_printf(s, "|                   |   |   |   |\n");
+	} else
+		seq_printf(s, "    |               |   |   |   |\n");
+}
 static struct tracer graph_trace __read_mostly = {
 	.name	     	= "function_graph",
 	.init	     	= graph_trace_init,
 	.reset	     	= graph_trace_reset,
 	.print_line	= print_graph_function,
+	.print_header	= print_graph_headers,
 	.flags		= &tracer_flags,
 };