Index: lib/libc/stdio/flags.c
===================================================================
--- lib/libc/stdio/flags.c	(revision 282268)
+++ lib/libc/stdio/flags.c	(working copy)
@@ -52,6 +52,7 @@
 __sflags(const char *mode, int *optr)
 {
 	int ret, m, o, known;
+	int do_locks = 0;
 
 	switch (*mode++) {
 
@@ -97,6 +98,10 @@
 			/* set close-on-exec */
 			o |= O_CLOEXEC;
 			break;
+		case 'l':
+			/* shared or exclusive locking */
+			do_locks = 1;
+			break;
 		case 'v':
 			/* verify */
 			o |= O_VERIFY;
@@ -112,6 +117,10 @@
 		return (0);
 	}
 
+	if (do_locks != 0) {
+		o |= (m == O_RDONLY) ? O_SHLOCK : O_EXLOCK;
+	}
+
 	*optr = m | o;
 	return (ret);
 }