[PATCH 2/2] trace-cmd: Check if ftrace file exists, before writing in it.

["Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>]

Depending of the kernel configuration, some ftrace files are optional
and may not exist. This should not confuse trace-cmd, as it is a valid
case. One such case is tracing_max_latency file, when CONFIG_TRACER_MAX_TRACE
or CONFIG_HWLAT_TRACER are not set.
A check is added in write_instance_file() to ensure the file exist before trying
to write in it.

https://bugzilla.kernel.org/show_bug.cgi?id=205241

Reported-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 tracecmd/trace-record.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 81aca1f..c65731f 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -813,11 +813,14 @@ static int
 write_instance_file(struct buffer_instance *instance,
 		    const char *file, const char *str, const char *type)
 {
+	struct stat st;
 	char *path;
 	int ret;
 
 	path = get_instance_file(instance, file);
-	ret = write_file(path, str, type);
+	ret = stat(path, &st);
+	if (ret == 0)
+		ret = write_file(path, str, type);
 	tracecmd_put_tracing_file(path);
 
 	return ret;
-- 
2.21.0