[PATCH 2/2] perf: Fix ftrace builtin when kernel doesn't have function_graph

[Julien Thierry <julien.thierry@arm.com>]

When linux is built without support for function graph tracer, the ftrace
builtin of perf will fail when trying to reset max_graph_depth because the
file does not exist. This prevents the use of function tracer from perf.

Do not attempt to write this file when the tracer in use is not
function_graph.

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-kernel@vger.kernel.org
---
 tools/perf/builtin-ftrace.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 25a42ac..48120f2 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -130,7 +130,8 @@ 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)
+	if (!strcmp(ftrace->tracer, "function_graph") &&
+	    write_tracing_file("max_graph_depth", "0") < 0)
 		return -1;

 	reset_tracing_filters();
--
1.9.1