Merge branch 'jk/maint-status-keep-index-timestamp'

* jk/maint-status-keep-index-timestamp:
  do not write out index when status does not have to

builtin/commit.c

@@ -343,9 +343,13 @@ static char *prepare_index(int argc, const char **argv, const char *prefix, int
 	if (!pathspec || !*pathspec) {
 		fd = hold_locked_index(&index_lock, 1);
 		refresh_cache_or_die(refresh_flags);
+		if (active_cache_changed) {
 			if (write_cache(fd, active_cache, active_nr) ||
 			    commit_locked_index(&index_lock))
 				die("unable to write new_index file");
+		} else {
+			rollback_lock_file(&index_lock);
+		}
 		commit_style = COMMIT_AS_IS;
 		return get_index_file();
 	}
@@ -1085,8 +1089,10 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 
 	fd = hold_locked_index(&index_lock, 0);
 	if (0 <= fd) {
-		if (!write_cache(fd, active_cache, active_nr))
+		if (active_cache_changed &&
+		    !write_cache(fd, active_cache, active_nr))
 			commit_locked_index(&index_lock);
+		else
 			rollback_lock_file(&index_lock);
 	}