tools lib api fs tracing_path: Add scandir alphasort

tracing_events__opendir() allows iteration over files in
<debugfs>/tracing/events but with an arbitrary sort order.

Add a scandir alternative where the results are alphabetically sorted.

Signed-off-by: Ian Rogers <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Caleb Biggers <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kajol Jain <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Leo Yan <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Perry Taylor <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Ravi Bangoria <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: Sandipan Das <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Cc: Weilin Wang <[e-mail]>
Cc: Xin Gao <[e-mail]>
Cc: Xing Zhengjun <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/api/fs/tracing_path.c

···
 	return dir;
 }
 
+int tracing_events__scandir_alphasort(struct dirent ***namelist)
+{
+	char *path = get_tracing_file("events");
+	int ret;
+
+	if (!path) {
+		*namelist = NULL;
+		return 0;
+	}
+
+	ret = scandir(path, namelist, NULL, alphasort);
+	put_events_file(path);
+
+	return ret;
+}
+
 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

···
 #include <dirent.h>
 
 DIR *tracing_events__opendir(void);
+int tracing_events__scandir_alphasort(struct dirent ***namelist);
 
 void tracing_path_set(const char *mountpoint);
 const char *tracing_path_mount(void);