Mention how big the name can be.

lib/libutil/openpty.3

@@ -1,4 +1,4 @@
-.\"	$NetBSD: openpty.3,v 1.14 2008/11/28 07:17:17 dholland Exp $
+.\"	$NetBSD: openpty.3,v 1.15 2012/07/23 02:21:14 christos Exp $
 .\"
 .\" Copyright (c) 1995
 .\"	The Regents of the University of California.  All rights reserved.
@@ -31,7 +31,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd November 28, 2008
+.Dd July 22, 2012
 .Dt OPENPTY 3
 .Os
 .Sh NAME
@@ -68,6 +68,17 @@ If
 .Fa name
 is non-null, the filename of the slave is returned in
 .Fa name .
+The length of 
+.Fa name
+is limited to
+.Dv 16
+characters in the current
+.Xr ptm 4
+device driver (including the terminating
+.Dv NUL )
+which limits the maximum to 
+.Dv 100,000
+ptys.
 If
 .Fa termp
 is non-null, the terminal parameters of the slave will be set to the