2 files changed, 29 insertions, 4 deletions

diff --git a/lib/libutil/flopen.3 b/lib/libutil/flopen.3
index 53a2132aec4b..0e5fbadacf12 100644
--- a/lib/libutil/flopen.3
+++ b/lib/libutil/flopen.3
@@ -60,6 +60,17 @@ Thus, it is well suited for opening lock files, PID files, spool
 files, mailboxes and other kinds of files which are used for
 synchronization between processes.
 .Pp
+If
+.Va flags
+includes
+.Dv O_NONBLOCK
+and the file is already locked,
+.Fn flopen
+will fail and set
+.Va errno
+to
+.Dv EWOULDBLOCK .
+.Pp
 As with
 .Fn flopen ,
 the additional
@@ -68,7 +79,18 @@ argument is required if
 .Va flags
 includes
 .Dv O_CREAT .
+.Sh RETURN VALUES
+If successful,
+.Fn flopen
+returns a valid file descriptor.
+Otherwise, it returns -1, and sets
+.Va errno
+as described in
+.Xr flock 2
+and
+.Xr open 2 .
 .Sh SEE ALSO
+.Xr errno 2 ,
 .Xr flock 2 ,
 .Xr open 2
 .Sh AUTHORS
diff --git a/lib/libutil/flopen.c b/lib/libutil/flopen.c
index 66d4e470f901..39cb81f1483e 100644
--- a/lib/libutil/flopen.c
+++ b/lib/libutil/flopen.c
@@ -39,29 +39,32 @@ __FBSDID("$FreeBSD$");
 int
 flopen(const char *path, int flags, ...)
 {
+	int fd, operation, serrno;
 	struct stat sb, fsb;
 	mode_t mode;
-	int fd, serrno;
 
 #ifdef O_EXLOCK
 	flags &= ~O_EXLOCK;
 #endif
 
+	mode = 0;
 	if (flags & O_CREAT) {
 		va_list ap;
 
 		va_start(ap, flags);
 		mode = va_arg(ap, int); /* mode_t promoted to int */
 		va_end(ap);
-	} else {
-		mode = 0;
 	}
 
+	operation = LOCK_EX;
+	if (flags & O_NONBLOCK)
+		operation |= LOCK_NB;
+
 	for (;;) {
 		if ((fd = open(path, flags, mode)) == -1)
 			/* non-existent or no access */
 			return (-1);
-		if (flock(fd, LOCK_EX) == -1) {
+		if (flock(fd, operation) == -1) {
 			/* unsupported or interrupted */
 			serrno = errno;
 			close(fd);