[LTP] [v2 1/2] lib/tst_pid.c: Count used pid by traversing /proc

[Leo Yu-Chi Liang]

Use "ps -eT | wc -l" to calculate the number of used pid
could have an incorrectly larger result because "ps -eT"
may list the same pid multiple times (with different SPID).

Instead, we could count used pid by traversing /proc
directory and countng the subdirectories that have name
composed of digits.

Suggested-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Leo Yu-Chi Liang <ycliang@andestech.com>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
---
Changes v1 -> v2
* Split into two patches
---
 lib/tst_pid.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/lib/tst_pid.c b/lib/tst_pid.c
index 5595e79bd..a282f8cc9 100644
--- a/lib/tst_pid.c
+++ b/lib/tst_pid.c
@@ -18,6 +18,7 @@
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
@@ -113,21 +114,16 @@ static int get_session_pids_limit(void (*cleanup_fn) (void))
 
 int tst_get_free_pids_(void (*cleanup_fn) (void))
 {
-	FILE *f;
-	int rc, used_pids, max_pids, max_session_pids, max_threads;
-
-	f = popen("ps -eT | wc -l", "r");
-	if (!f) {
-		tst_brkm(TBROK, cleanup_fn, "Could not run 'ps' to calculate used pids");
-		return -1;
-	}
-	rc = fscanf(f, "%i", &used_pids);
-	pclose(f);
-
-	if (rc != 1 || used_pids < 0) {
-		tst_brkm(TBROK, cleanup_fn, "Could not read output of 'ps' to calculate used pids");
-		return -1;
+	DIR *f;
+	struct dirent *ent;
+	int max_pids, max_session_pids, max_threads, used_pids = 0;
+
+	f = SAFE_OPENDIR("/proc");
+	while ((ent = SAFE_READDIR(f))) {
+		if (isdigit(ent->d_name[0]))
+			++used_pids;
 	}
+	SAFE_CLOSEDIR(f);
 
 	SAFE_FILE_SCANF(cleanup_fn, PID_MAX_PATH, "%d", &max_pids);
 	SAFE_FILE_SCANF(cleanup_fn, THREADS_MAX_PATH, "%d", &max_threads);
-- 
2.34.1