Linux: Accept null arguments for utimensat pathname

This matches kernel behavior.  With this change, it is possible
to use utimensat as a replacement for the futimens interface,
similar to what glibc does internally.

Reviewed-by: Paul Eggert <eggert@cs.ucla.edu>

2 files changed, 34 insertions, 2 deletions

diff --git a/io/sys/stat.h b/io/sys/stat.h
index 0e4edb483d..dd96b88d0f 100644
--- a/io/sys/stat.h
+++ b/io/sys/stat.h
@@ -433,13 +433,13 @@ extern int mkfifoat (int __fd, const char *__path, __mode_t __mode)
 extern int utimensat (int __fd, const char *__path,
 		      const struct timespec __times[2],
 		      int __flags)
-     __THROW __nonnull ((2));
+     __THROW;
 # else
 #  ifdef __REDIRECT_NTH
 extern int __REDIRECT_NTH (utimensat, (int fd, const char *__path,
                                        const struct timespec __times[2],
                                        int flags),
-                           __utimensat64) __nonnull ((2));
+                           __utimensat64);
 #  else
 #   define utimensat __utimensat64
 #  endif
diff --git a/io/tst-utimensat.c b/io/tst-utimensat.c
index 2a756d7b07..43786817b5 100644
--- a/io/tst-utimensat.c
+++ b/io/tst-utimensat.c
@@ -39,6 +39,38 @@ test_utimesat_helper (const char *testfile, int fd, const char *testlink,
     TEST_COMPARE (st.stx_mtime.tv_sec, ts[1].tv_sec);
   }
 
+  /* Alter the timestamp using a NULL path.  */
+  {
+    struct timespec ts1[2] = {ts[0], ts[1]};
+    ts1[0].tv_sec ^= 1;
+    ts1[1].tv_sec ^= 1;
+
+    TEST_VERIFY_EXIT (utimensat (fd, NULL, ts1, 0) == 0);
+
+    struct statx st;
+    xstatx (fd, "", AT_EMPTY_PATH, STATX_BASIC_STATS, &st);
+
+    /* Check if seconds for atime match */
+    TEST_COMPARE (st.stx_atime.tv_sec, ts[0].tv_sec ^ 1);
+
+    /* Check if seconds for mtime match */
+    TEST_COMPARE (st.stx_mtime.tv_sec, ts[1].tv_sec ^ 1);
+  }
+
+  /* And switch it back using a NULL path.  */
+  {
+    TEST_VERIFY_EXIT (utimensat (fd, NULL, ts, 0) == 0);
+
+    struct statx st;
+    xstatx (fd, "", AT_EMPTY_PATH, STATX_BASIC_STATS, &st);
+
+    /* Check if seconds for atime match */
+    TEST_COMPARE (st.stx_atime.tv_sec, ts[0].tv_sec);
+
+    /* Check if seconds for mtime match */
+    TEST_COMPARE (st.stx_mtime.tv_sec, ts[1].tv_sec);
+  }
+
   {
     struct statx stfile_orig;
     xstatx (AT_FDCWD, testfile, AT_SYMLINK_NOFOLLOW, STATX_BASIC_STATS,