[glibc] io: Fix sporadic test failures in io/tst-stat

[glibc] io: Fix sporadic test failures in io/tst-stat

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=acc85ea1eb046eee9296fbc4803b82cb485ced07

commit acc85ea1eb046eee9296fbc4803b82cb485ced07
Author: Florian Weimer <fweimer@redhat.com>
Date:   Thu Jun 10 10:09:51 2021 +0200

    io: Fix sporadic test failures in io/tst-stat
    
    support_stat_nanoseconds cannot restore the ctime time, and
    this may lead to sporadic test failures.  Therefore, probe for
    nanoseconds support before the initial statx call.
    
    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Diff:
---
 io/tst-stat.c     | 8 ++++----
 support/support.h | 3 ++-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/io/tst-stat.c b/io/tst-stat.c
index b3e8dc2170..82e965de6a 100644
--- a/io/tst-stat.c
+++ b/io/tst-stat.c
@@ -69,15 +69,15 @@ do_test (void)
   TEST_VERIFY_EXIT (fd >= 0);
   support_write_file_string (path, "abc");
 
+  bool check_ns = support_stat_nanoseconds (path);
+  if (!check_ns)
+    printf ("warning: timestamp with nanoseconds not supported\n");
+
   struct statx stx;
   TEST_COMPARE (statx (fd, path, 0, STATX_BASIC_STATS, &stx), 0);
 
   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 supported\n");
-
   for (int i = 0; i < array_length (tests); i++)
     {
       struct stat st;
diff --git a/support/support.h b/support/support.h
index db264e3db7..874204b7fc 100644
--- a/support/support.h
+++ b/support/support.h
@@ -141,7 +141,8 @@ static __inline bool support_path_support_time64 (const char *path)
 					    0x80000002ULL);
 }
 
-/* Return true if stat supports nanoseconds resolution.  */
+/* Return true if stat supports nanoseconds resolution.  PATH is used
+   for tests and its ctime may change.  */
 extern bool support_stat_nanoseconds (const char *path);
 
 /* Return true if select modify the timeout to reflect the amount of time