perf ftrace: Add -D option for depth filter

The -D/--graph-depth option is to set max graph depth.  The following
example traces max 2-depth of page fault handler.

  $ sudo perf ftrace -G __do_page_fault -D 2 -- hello
   ...
   0)               |  __do_page_fault() {
   0)   0.063 us    |    down_read_trylock();
   0)   0.251 us    |    find_vma();
   0)   5.374 us    |    handle_mm_fault();
   0)   0.054 us    |    up_read();
   0)   7.463 us    |  }
   ...

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: kernel-team@lge.com
Link: http://lkml.kernel.org/r/20170618142302.25390-4-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-ftrace.txt

@@ -78,6 +78,9 @@ OPTIONS
 	This can be used more than once to specify multiple functions.
 	It will be passed to 'set_graph_notrace' in tracefs.
 
+-D::
+--graph-depth=::
+	Set max depth for function graph tracer to follow
 
 SEE ALSO
 --------

tools/perf/builtin-ftrace.c

@@ -35,6 +35,7 @@ struct perf_ftrace {
 	struct list_head	notrace;
 	struct list_head	graph_funcs;
 	struct list_head	nograph_funcs;
+	int			graph_depth;
 };
 
 struct filter_entry {
@@ -129,6 +130,9 @@ static int reset_tracing_files(struct perf_ftrace *ftrace __maybe_unused)
 	if (reset_tracing_cpu() < 0)
 		return -1;
 
+	if (write_tracing_file("max_graph_depth", "0") < 0)
+		return -1;
+
 	reset_tracing_filters();
 	return 0;
 }
@@ -237,6 +241,26 @@ static void reset_tracing_filters(void)
 	write_tracing_file("set_graph_notrace", " ");
 }
 
+static int set_tracing_depth(struct perf_ftrace *ftrace)
+{
+	char buf[16];
+
+	if (ftrace->graph_depth == 0)
+		return 0;
+
+	if (ftrace->graph_depth < 0) {
+		pr_err("invalid graph depth: %d\n", ftrace->graph_depth);
+		return -1;
+	}
+
+	snprintf(buf, sizeof(buf), "%d", ftrace->graph_depth);
+
+	if (write_tracing_file("max_graph_depth", buf) < 0)
+		return -1;
+
+	return 0;
+}
+
 static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
 {
 	char *trace_file;
@@ -284,6 +308,11 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
 		goto out_reset;
 	}
 
+	if (set_tracing_depth(ftrace) < 0) {
+		pr_err("failed to set graph depth\n");
+		goto out_reset;
+	}
+
 	if (write_tracing_file("current_tracer", ftrace->tracer) < 0) {
 		pr_err("failed to set current_tracer to %s\n", ftrace->tracer);
 		goto out_reset;
@@ -425,6 +454,8 @@ int cmd_ftrace(int argc, const char **argv)
 		     "Set graph filter on given functions", parse_filter_func),
 	OPT_CALLBACK('g', "nograph-funcs", &ftrace.nograph_funcs, "func",
 		     "Set nograph filter on given functions", parse_filter_func),
+	OPT_INTEGER('D', "graph-depth", &ftrace.graph_depth,
+		    "Max depth for function graph tracer"),
 	OPT_END()
 	};