[LTP] [PATCH] clock_settime/4-1: CLOCK_MONOTONIC for timer validation

[Andrea Cervesato]

From: Andrea Cervesato <andrea.cervesato@suse.com>

During test execution, any service which is operating on clock might
interfere with the final result. For this reason, we use CLOCK_MONOTONIC
(when available) in order to the compute the right delta between
clock_gettime() calls.

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
 .../conformance/interfaces/clock_settime/4-1.c     | 36 ++++++++++++++++------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/testcases/open_posix_testsuite/conformance/interfaces/clock_settime/4-1.c b/testcases/open_posix_testsuite/conformance/interfaces/clock_settime/4-1.c
index ebd609963a3651212447ff2ab0885e20b19ba302..cd33ccde5030f54e2c60ee5e2c616dea6c375910 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/clock_settime/4-1.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/clock_settime/4-1.c
@@ -16,12 +16,10 @@
  * - set time back to T0
  * - wait for the timer to expire
  * - get time T2
- * - ensure that:  T2 >= T1 and (T2-T1) <= ACCEPTABLEDELTA
+ * - ensure the timer fired ~TIMEROFFSET seconds after clock_settime()
+ *   using CLOCK_MONOTONIC when available (immune to NTP adjustments)
  *
  * signal SIGTOTEST is used.
- *
- * adam.li: I think should check that (abs(T2-T1) <= ACCEPTABLEDELTA)
- * 2004-04-30
  */
 #include <stdio.h>
 #include <time.h>
@@ -43,12 +41,14 @@ int test_main(int argc PTS_ATTRIBUTE_UNUSED, char **argv PTS_ATTRIBUTE_UNUSED)
 {
 	struct sigevent ev;
 	struct timespec tpT0, tpT2, tpreset;
+	struct timespec mono_before, mono_after;
 	struct itimerspec its;
 	timer_t tid;
-	int delta;
+	long delta;
 	int sig;
 	sigset_t set;
 	int attempt, ret;
+	int use_mono = pts_mono_available();
 
 	/* Check that we're root...can't call clock_settime with CLOCK_REALTIME otherwise */
 	if (geteuid() != 0) {
@@ -103,6 +103,10 @@ int test_main(int argc PTS_ATTRIBUTE_UNUSED, char **argv PTS_ATTRIBUTE_UNUSED)
 
 		sleep(SLEEPTIME);
 		getBeforeTime(&tpreset);
+
+		if (use_mono)
+			clock_gettime(CLOCK_MONOTONIC, &mono_before);
+
 		if (clock_settime(CLOCK_REALTIME, &tpT0) != 0) {
 			perror("clock_settime() was not successful");
 			return PTS_UNRESOLVED;
@@ -113,12 +117,24 @@ int test_main(int argc PTS_ATTRIBUTE_UNUSED, char **argv PTS_ATTRIBUTE_UNUSED)
 			return PTS_UNRESOLVED;
 		}
 
+		if (use_mono)
+			clock_gettime(CLOCK_MONOTONIC, &mono_after);
+
 		if (clock_gettime(CLOCK_REALTIME, &tpT2) != 0) {
 			printf("clock_gettime() was not successful\n");
 			return PTS_UNRESOLVED;
 		}
 
-		delta = tpT2.tv_sec - its.it_value.tv_sec;
+		/*
+		 * Use CLOCK_MONOTONIC to compute delta when available
+		 * since CLOCK_REALTIME may be adjusted by NTP between
+		 * clock_settime() and clock_gettime(). The timer
+		 * should fire TIMEROFFSET seconds after the reset.
+		 */
+		if (use_mono)
+			delta = (mono_after.tv_sec - mono_before.tv_sec) - TIMEROFFSET;
+		else
+			delta = tpT2.tv_sec - its.it_value.tv_sec;
 
 		// add back time waited to reset value and reset time
 		tpreset.tv_sec += tpT2.tv_sec - tpT0.tv_sec;
@@ -137,13 +153,13 @@ int test_main(int argc PTS_ATTRIBUTE_UNUSED, char **argv PTS_ATTRIBUTE_UNUSED)
 		return PTS_UNTESTED;
 	}
 
-	printf("delta: %d\n", delta);
-	if ((delta <= ACCEPTABLEDELTA) && (delta >= 0)) {
+	printf("delta: %ld\n", delta);
+	if (labs(delta) <= ACCEPTABLEDELTA) {
 		printf("Test PASSED\n");
 		return PTS_PASS;
 	}
 
-	printf("FAIL:  Ended %d, not %d\n",
-	       (int)tpT2.tv_sec, (int)its.it_value.tv_sec);
+	printf("FAIL:  Timer fired %ld seconds %s expected\n",
+	       labs(delta), delta > 0 ? "after" : "before");
 	return PTS_FAIL;
 }

---
base-commit: b4d31ea5d5c16628b9c45932fc98b929ca2ceece
change-id: 20260616-fix_clock_gettime_openposix-c6779c9f4d92

Best regards,
-- 
Andrea Cervesato <andrea.cervesato@suse.com>