Subject: [PATCH] CodingGuidelines: st_mtimespec vs st_mtim vs st_mtime

From: Junio C Hamano <[email-masked]>
Date: Fri, 10 Apr 2026 11:10:48 -0700

Most unfortunately macOS does not support st_[amc]tim for timestamps
down to nanosecond resolution as POSIX systems.

Signed-off-by: Junio C Hamano <[email-masked]>
---
 Documentation/CodingGuidelines | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git c/Documentation/CodingGuidelines w/Documentation/CodingGuidelines
index 4992e52093..4e54139fd7 100644
--- c/Documentation/CodingGuidelines
+++ w/Documentation/CodingGuidelines
@@ -693,6 +693,12 @@ For C programs:
          char *dogs[] = ...;
          walk_all_dogs(dogs);
 
+ - For file timestamps, do not use "st_mtim" (and other timestamp
+   members in "struct stat") unconditionally; not everybody is POSIX
+   (grep for USE_ST_TIMESPEC).  If you only need timestamp in whole
+   second resolution, "st_mtime" should work fine everywhere.
+
+
 For Perl programs:
 
  - Most of the C guidelines above apply.