[LTP] [PATCH v2] clock_settime: use POSIX runtime detection for CLOCK_MONOTONIC

[Andrea Cervesato]

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

The clock_settime helpers.h used a compile-time #ifdef on
_POSIX_MONOTONIC_CLOCK to select between real and stub
implementations of pts_mono_time_start()/pts_mono_time_check().

On Linux/glibc, _POSIX_MONOTONIC_CLOCK is defined as 0, meaning
support is optional and must be verified at runtime via
sysconf(_SC_MONOTONIC_CLOCK). The #ifdef treated 0 the same as
>0 (always available), which is not POSIX-correct.

Replace the compile-time #ifdef/#else split with a runtime
pts_mono_available() helper that performs proper POSIX detection
via sysconf(). Extract pts_mono_available() into the shared
include/clock.h so it can be reused by nanosleep helpers as well.
Also add a missing #ifndef include guard and #include <unistd.h>
so _POSIX_MONOTONIC_CLOCK is always defined.

Fixes: 9ecb4a004b18 ("clock_settime: Detect external clock adjustments via CLOCK_MONOTONIC")
Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
Changes in v2:
- add testcases/open_posix_testsuite/include/clock.h helper
- Link to v1: https://lore.kernel.org/r/20260416-fix_clock_settime_helper-v1-1-2874202291bf@suse.com
---
 .../conformance/interfaces/clock_settime/helpers.h | 67 ++++++++++++----------
 testcases/open_posix_testsuite/include/clock.h     | 23 ++++++++
 2 files changed, 59 insertions(+), 31 deletions(-)

diff --git a/testcases/open_posix_testsuite/conformance/interfaces/clock_settime/helpers.h b/testcases/open_posix_testsuite/conformance/interfaces/clock_settime/helpers.h
index 37bf30926f039553e9e370751b7938ca5ea1d00a..2802b694133b90f478ee10073bcdfa0e34320f7d 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/clock_settime/helpers.h
+++ b/testcases/open_posix_testsuite/conformance/interfaces/clock_settime/helpers.h
@@ -13,7 +13,12 @@
  * by those tests.
  */
 
+#ifndef CLOCK_SETTIME_HELPERS_H
+#define CLOCK_SETTIME_HELPERS_H
+
 #include <stdlib.h>
+#include <unistd.h>
+#include "clock.h"
 
 static int getBeforeTime(struct timespec *tpget)
 {
@@ -37,53 +42,53 @@ static int setBackTime(struct timespec tpset)
 
 #define PTS_MONO_MAX_RETRIES 3
 
-#ifdef _POSIX_MONOTONIC_CLOCK
-static struct timespec _pts_mono_start;
+static struct timespec pts_mono_start;
 
 static inline int pts_mono_time_start(void)
 {
-	if (clock_gettime(CLOCK_MONOTONIC, &_pts_mono_start) != 0) {
+	if (!pts_mono_available()) {
+		static int warned;
+
+		if (!warned) {
+			printf("CLOCK_MONOTONIC unavailable, test may fail due to clock adjustment\n");
+			warned = 1;
+		}
+		return 0;
+	}
+
+#ifdef _POSIX_MONOTONIC_CLOCK
+	if (clock_gettime(CLOCK_MONOTONIC, &pts_mono_start) != 0) {
 		perror("clock_gettime(CLOCK_MONOTONIC) failed");
 		return -1;
 	}
+#endif
 	return 0;
 }
 
 static inline int pts_mono_time_check(unsigned int expected_secs)
 {
-	struct timespec now;
-	long elapsed;
-
-	if (clock_gettime(CLOCK_MONOTONIC, &now) != 0) {
-		perror("clock_gettime(CLOCK_MONOTONIC) failed");
-		return -1;
-	}
+#ifdef _POSIX_MONOTONIC_CLOCK
+	if (pts_mono_available()) {
+		struct timespec now;
+		long elapsed;
 
-	elapsed = now.tv_sec - _pts_mono_start.tv_sec;
+		if (clock_gettime(CLOCK_MONOTONIC, &now) != 0) {
+			perror("clock_gettime(CLOCK_MONOTONIC) failed");
+			return -1;
+		}
 
-	if (labs(elapsed - (long)expected_secs) > 1) {
-		printf("Clock adjustment detected (elapsed %lds, expected ~%us)\n",
-		       elapsed, expected_secs);
-		return 1;
-	}
-	return 0;
-}
-#else
-static inline int pts_mono_time_start(void)
-{
-	static int warned;
+		elapsed = now.tv_sec - pts_mono_start.tv_sec;
 
-	if (!warned) {
-		printf("CLOCK_MONOTONIC unavailable, test may fail due to clock adjustment\n");
-		warned = 1;
+		if (labs(elapsed - (long)expected_secs) > 1) {
+			printf("Clock adjustment detected (elapsed %lds, expected ~%us)\n",
+			       elapsed, expected_secs);
+			return 1;
+		}
+		return 0;
 	}
-	return 0;
-}
-
-static inline int pts_mono_time_check(unsigned int expected_secs)
-{
+#endif
 	(void)expected_secs;
 	return 0;
 }
-#endif
 
+#endif /* CLOCK_SETTIME_HELPERS_H */
diff --git a/testcases/open_posix_testsuite/include/clock.h b/testcases/open_posix_testsuite/include/clock.h
new file mode 100644
index 0000000000000000000000000000000000000000..351064f988bd1af75aa16da03bf8a545990bbbfc
--- /dev/null
+++ b/testcases/open_posix_testsuite/include/clock.h
@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2026, Linux Test Project
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef PTS_CLOCK_H
+#define PTS_CLOCK_H
+
+#include <unistd.h>
+
+static inline int pts_mono_available(void)
+{
+#ifdef _POSIX_MONOTONIC_CLOCK
+	if (_POSIX_MONOTONIC_CLOCK > 0)
+		return 1;
+
+	if (!_POSIX_MONOTONIC_CLOCK && sysconf(_SC_MONOTONIC_CLOCK) > 0)
+		return 1;
+#endif
+	return 0;
+}
+
+#endif /* PTS_CLOCK_H */

---
base-commit: 068617a55d86f94c21cc8cbaef1c8dd7b31531e3
change-id: 20260416-fix_clock_settime_helper-d47f0db0057e

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