Work around bug in open(2) wrt O_TRUNC and O_SHLOCK|O_EXLOCK.

src/lib/libutil/passwd.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: passwd.c,v 1.12 1997/09/29 19:18:21 deraadt Exp $	*/
+/*	$OpenBSD: passwd.c,v 1.13 1997/11/17 20:56:57 millert Exp $	*/
 
 /*
  * Copyright (c) 1987, 1993, 1994, 1995
@@ -34,7 +34,7 @@
  */
 
 #if defined(LIBC_SCCS) && !defined(lint)
-static char rcsid[] = "$OpenBSD: passwd.c,v 1.12 1997/09/29 19:18:21 deraadt Exp $";
+static char rcsid[] = "$OpenBSD: passwd.c,v 1.13 1997/11/17 20:56:57 millert Exp $";
 #endif /* LIBC_SCCS and not lint */
 
 #include <sys/types.h>
@@ -252,11 +252,14 @@ pw_lock(retries)
 		return (-1);
 	/* Acquire the lock file. */
 	old_mode = umask(0);
-	fd = open(pw_lck, O_WRONLY|O_CREAT|O_TRUNC|O_NONBLOCK|O_EXLOCK, 0600);
+	fd = open(pw_lck, O_WRONLY|O_CREAT|O_NONBLOCK|O_EXLOCK, 0600);
 	for (i = 0; i < retries && fd < 0 && errno == EAGAIN; i++) {
 		sleep(1);
-		fd = open(pw_lck, O_WRONLY|O_CREAT|O_TRUNC|O_NONBLOCK|O_EXLOCK, 0600);
+		fd = open(pw_lck, O_WRONLY|O_CREAT|O_NONBLOCK|O_EXLOCK, 0600);
 	}
+	/* Really want to use O_TRUNC above but there is a bug in open(2) */
+	if (fd != -1)
+		ftruncate(fd, 0);
 	umask(old_mode);
 	return (fd);
 }