[PATCH] io: Check at runtime if timestamp supports nanoseconds

[Stefan Liebler]

On 29/03/2021 19:43, Adhemerval Zanella wrote:
> Now that non-LFS stat function is implemented on to on LFS, it will
> use statx when available.  It allows to check for nanosecond timestamp
> if the kernel supports __NR_statx.
> 
> Checked on s390-linux-gnu with 4.12.14 kernel.
> ---
>  io/tst-stat.c                      |  7 ++++-
>  support/support.h                  |  2 +-
>  support/support_stat_nanoseconds.c | 41 +++++++++++++++++++++++++-----
>  3 files changed, 41 insertions(+), 9 deletions(-)
> 
> diff --git a/io/tst-stat.c b/io/tst-stat.c
> index 397d480ecc..22b89bb3e7 100644
> --- a/io/tst-stat.c
> +++ b/io/tst-stat.c
> @@ -25,6 +25,7 @@
>  #include <support/xunistd.h>
>  #include <sys/stat.h>
>  #include <sys/sysmacros.h>
> +#include <stdio.h>
>  #include <unistd.h>
>  
>  static void
> @@ -73,6 +74,10 @@ do_test (void)
>  
>    test_t tests[] = { stat_check, lstat_check, fstat_check, fstatat_check };
>  
> +  bool check_ns = support_stat_nanoseconds (path);
> +  if (!check_ns)
> +    printf ("warning: timestamp with nanoseconds not supportted\n");
> +
>    for (int i = 0; i < array_length (tests); i++)
>      {
>        struct stat st;
> @@ -92,7 +97,7 @@ do_test (void)
>  
>        TEST_COMPARE (stx.stx_ctime.tv_sec, st.st_ctim.tv_sec);
>        TEST_COMPARE (stx.stx_mtime.tv_sec, st.st_mtim.tv_sec);
> -      if (support_stat_nanoseconds ())
> +      if (check_ns)
>  	{
>  	  TEST_COMPARE (stx.stx_ctime.tv_nsec, st.st_ctim.tv_nsec);
>  	  TEST_COMPARE (stx.stx_mtime.tv_nsec, st.st_mtim.tv_nsec);
OK

> diff --git a/support/support.h b/support/support.h
> index b0352726bf..e023d00857 100644
> --- a/support/support.h
> +++ b/support/support.h
> @@ -142,7 +142,7 @@ static __inline bool support_path_support_time64 (const char *path)
>  }
>  
>  /* Return true if stat supports nanoseconds resolution.  */
> -extern bool support_stat_nanoseconds (void);
> +extern bool support_stat_nanoseconds (const char *path);
OK
>  
>  __END_DECLS
>  
> diff --git a/support/support_stat_nanoseconds.c b/support/support_stat_nanoseconds.c
> index c0d5b2c3a9..94953c0868 100644
> --- a/support/support_stat_nanoseconds.c
> +++ b/support/support_stat_nanoseconds.c
> @@ -16,16 +16,43 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <support/check.h>
> +#include <support/support.h>
> +#include <support/timespec.h>
>  #include <stdbool.h>
> +#include <sys/stat.h>
> +#include <sys/syscall.h>
Do we really need syscall.h?
> +#include <sys/types.h>
> +#include <unistd.h>
>  
>  bool
> -support_stat_nanoseconds (void)
> +support_stat_nanoseconds (const char *path)
>  {
> -  /* s390 stat64 compat symbol does not support nanoseconds resolution
> -     and it used on non-LFS [f,l]stat[at] implementations.  */
> -#if defined __linux__ && !defined __s390x__ && defined __s390__
> -  return false;
> -#else
> -  return true;
> +  bool support;
> +#ifdef __linux__
> +  /* Obtain the original timestamp to restore at the end.  */
> +  struct stat ost;
> +  TEST_VERIFY_EXIT (stat (path, &ost) == 0);
> +
> +  const struct timespec tsp[] = { { 0, TIMESPEC_HZ - 1 },
> +				  { 0, TIMESPEC_HZ / 2 } };
> +  TEST_VERIFY_EXIT (utimensat (AT_FDCWD, path, tsp, 0) == 0);
> +
> +  struct stat st;
> +  TEST_VERIFY_EXIT (stat (path, &st) == 0);
> +
> +  support = st.st_atim.tv_nsec == tsp[0].tv_nsec
> +	    && st.st_mtim.tv_nsec == tsp[1].tv_nsec;
> +
> +  /* Reset to original timestamps.  */
> +  const struct timespec otsp[] =
> +  {
> +    { ost.st_atim.tv_sec, ost.st_atim.tv_nsec },
> +    { ost.st_mtim.tv_sec, ost.st_mtim.tv_nsec },
> +  };
> +  TEST_VERIFY_EXIT (utimensat (AT_FDCWD, path, otsp, 0) == 0);
>  #endif
> +  return support;
>  }
> 
OK