tools lib api fs tracing_path: Introduce opendir() method

That takes care of using the right call to get the tracing_path
directory, the one that will end up calling tracing_path_set() to figure
out where tracefs is mounted.

One more step in doing just lazy reading of system structures to reduce
the number of operations done unconditionaly at 'perf' start.

Cc: Adrian Hunter <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: https://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/api/fs/tracing_path.c

···
 	free(file);
 }
 
+DIR *tracing_events__opendir(void)
+{
+	DIR *dir = NULL;
+	char *path = get_tracing_file("events");
+
+	if (path) {
+		dir = opendir(path);
+		put_events_file(path);
+	}
+
+	return dir;
+}
+
 int tracing_path__strerror_open_tp(int err, char *buf, size_t size,
 				   const char *sys, const char *name)
 {

tools/lib/api/fs/tracing_path.h

···
 #define __API_FS_TRACING_PATH_H
 
 #include <linux/types.h>
+#include <dirent.h>
 
 extern char tracing_events_path[];
+
+DIR *tracing_events__opendir(void);
 
 void tracing_path_set(const char *mountpoint);
 const char *tracing_path_mount(void);

tools/perf/tests/parse-events.c

···
 	DIR *events_dir;
 	int cnt = 0;
 
-	events_dir = opendir(tracing_events_path);
+	events_dir = tracing_events__opendir();
 
 	TEST_ASSERT_VAL("Can't open events dir", events_dir);
 

tools/perf/util/parse-events.c

···
 	char evt_path[MAXPATHLEN];
 	char *dir_path;
 
-	sys_dir = opendir(tracing_events_path);
+	sys_dir = tracing_events__opendir();
 	if (!sys_dir)
 		return NULL;
 
···
 	DIR *events_dir;
 	int ret = 0;
 
-	events_dir = opendir(tracing_events_path);
+	events_dir = tracing_events__opendir();
 	if (!events_dir) {
 		tracepoint_error(err, errno, sys_name, evt_name);
 		return -1;
···
 	bool evt_num_known = false;
 
 restart:
-	sys_dir = opendir(tracing_events_path);
+	sys_dir = tracing_events__opendir();
 	if (!sys_dir)
 		return;
 
···
 	char evt_path[MAXPATHLEN];
 	char *dir_path;
 
-	sys_dir = opendir(tracing_events_path);
+	sys_dir = tracing_events__opendir();
 	if (!sys_dir)
 		return 0;