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

Petr Vorel
2026-04-17T12:54:00Z

> 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