Update to better describe reality, i.e. disklabel(8) UID usage.

ok jmc@ jsing@

src/lib/libutil/opendev.3

@@ -1,4 +1,4 @@
-.\"	$OpenBSD: opendev.3,v 1.19 2010/12/17 19:35:34 millert Exp $
+.\"	$OpenBSD: opendev.3,v 1.20 2011/01/03 14:26:51 krw Exp $
 .\"
 .\" Copyright (c) 2000, Todd C. Miller.  All rights reserved.
 .\" Copyright (c) 1996, Jason Downs.  All rights reserved.
@@ -24,7 +24,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: December 17 2010 $
+.Dd $Mdocdate: January 3 2011 $
 .Dt OPENDEV 3
 .Os
 .Sh NAME
@@ -37,23 +37,35 @@
 .Sh DESCRIPTION
 The
 .Fn opendev
-function opens a device using the
+function opens a device using a
 .Dq short form
-name.
-This is typically
+name or
+.Xr disklabel 8
+UID
+.Pq DUID .
+For instance
 .Dq sd0
 or
-.Dq sd0c ,
-for instance, which will be expanded to
+.Dq sd0c
+will be expanded to
 .Pa /dev/rsd0c
 on most architectures.
 .Pp
 Device name lookup is done by first checking
 .Fa path
 for a
-.Dq /
+.Sq /
 and if one is found attempting to open that file.
-Otherwise
+If not,
+.Fa path
+is checked to see if it is a valid DUID.
+If it is, the corresponding device is obtained via
+.Xr diskmap 4 .
+If
+.Fa path
+has no
+.Sq /
+and is not a DUID,
 .Fa /dev
 is searched for a matching device.
 .Pp
@@ -86,7 +98,9 @@ return value and errors are the same as the return value and errors of
 .Xr open 2 .
 .Sh SEE ALSO
 .Xr open 2 ,
-.Xr getrawpartition 3
+.Xr getrawpartition 3 ,
+.Xr diskmap 4 ,
+.Xr disklabel 8
 .Sh HISTORY
 The
 .Fn opendev