perf list: Show error if tracepoints not available

Tracepoints are not visible in "perf list" on Fedora 19 because regular
users have no permission to /sys/kernel/debug by default. Show an error
message so that the user knows about it instead of assuming that
tracepoints are not supported on the system.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/1381867647-8594-1-git-send-email-penberg@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/parse-events.c

@@ -998,8 +998,10 @@ void print_tracepoint_events(const char *subsys_glob, const char *event_glob,
 	char evt_path[MAXPATHLEN];
 	char dir_path[MAXPATHLEN];
 
-	if (debugfs_valid_mountpoint(tracing_events_path))
+	if (debugfs_valid_mountpoint(tracing_events_path)) {
+		printf("  [ Tracepoints not available: %s ]\n", strerror(errno));
 		return;
+	}
 
 	sys_dir = opendir(tracing_events_path);
 	if (!sys_dir)