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

[LTP] [PATCH] 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(). 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>
---
 .../conformance/interfaces/clock_settime/helpers.h | 76 +++++++++++++---------
 1 file changed, 46 insertions(+), 30 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..b568ec8122d3bba8246b09a5b694f1263084a408 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 +13,11 @@
  * by those tests.
  */
 
+#ifndef CLOCK_SETTIME_HELPERS_H
+#define CLOCK_SETTIME_HELPERS_H
+
 #include <stdlib.h>
+#include <unistd.h>
 
 static int getBeforeTime(struct timespec *tpget)
 {
@@ -37,53 +41,65 @@ static int setBackTime(struct timespec tpset)
 
 #define PTS_MONO_MAX_RETRIES 3
 
+static struct timespec pts_mono_start;
+
+static inline int pts_mono_available(void)
+{
 #ifdef _POSIX_MONOTONIC_CLOCK
-static struct timespec _pts_mono_start;
+	if (_POSIX_MONOTONIC_CLOCK > 0)
+		return 1;
+
+	if (!_POSIX_MONOTONIC_CLOCK && sysconf(_SC_MONOTONIC_CLOCK) > 0)
+		return 1;
+#endif
+	return 0;
+}
 
 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 */

---
base-commit: 620d596c79493af089ba6a1c4dc79efcc76a67c7
change-id: 20260416-fix_clock_settime_helper-d47f0db0057e

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


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Re: [LTP] clock_settime: use POSIX runtime detection for CLOCK_MONOTONIC

[linuxtestproject.agent]

Hi Andrea,

On Thu, 16 Apr 2026, Andrea Cervesato wrote:
> clock_settime: use POSIX runtime detection for CLOCK_MONOTONIC

Reviewed-by: LTP AI Reviewer <ltp-ai@noreply.github.com>

---
Note:

Our agent completed the review of the patch. The full review can be
found at: https://github.com/linux-test-project/ltp-agent/actions/runs/24513029369

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

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

[Petr Vorel]

> 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(). 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>
> ---
>  .../conformance/interfaces/clock_settime/helpers.h | 76 +++++++++++++---------
>  1 file changed, 46 insertions(+), 30 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..b568ec8122d3bba8246b09a5b694f1263084a408 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 +13,11 @@
>   * by those tests.
>   */

> +#ifndef CLOCK_SETTIME_HELPERS_H
> +#define CLOCK_SETTIME_HELPERS_H
> +
>  #include <stdlib.h>
> +#include <unistd.h>

>  static int getBeforeTime(struct timespec *tpget)
>  {
> @@ -37,53 +41,65 @@ static int setBackTime(struct timespec tpset)

>  #define PTS_MONO_MAX_RETRIES 3

> +static struct timespec pts_mono_start;
> +
> +static inline int pts_mono_available(void)
> +{
>  #ifdef _POSIX_MONOTONIC_CLOCK
> -static struct timespec _pts_mono_start;
> +	if (_POSIX_MONOTONIC_CLOCK > 0)
> +		return 1;
> +
> +	if (!_POSIX_MONOTONIC_CLOCK && sysconf(_SC_MONOTONIC_CLOCK) > 0)
This and the previous condition is the same as in patch for nanosleep.
It's a simple code, but because it's still a bit specific, wouldn't it make
sense to move the function from nanosleep/helpers.h [1]
to newly created file in testcases/open_posix_testsuite/include/clock.h?
And both tests would use it?

Kind regards,
Petr

[1] https://patchwork.ozlabs.org/project/ltp/patch/20260416-fix_nanosleep_include-v2-1-b3147763acb8@suse.com/

> +		return 1;
> +#endif
> +	return 0;
> +}


Kind regards,
Petr

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