Document F_DUPFD_CLOEXEC. Also provide some wording changes for

F_DUPFD to make it less confusing, at least for me.

MFC after:	1 week

1 files changed, 15 insertions, 4 deletions

diff --git a/lib/libc/sys/fcntl.2 b/lib/libc/sys/fcntl.2
index beceb72539fa..0844e876d313 100644
--- a/lib/libc/sys/fcntl.2
+++ b/lib/libc/sys/fcntl.2
@@ -28,7 +28,7 @@
 .\"     @(#)fcntl.2	8.2 (Berkeley) 1/12/94
 .\" $FreeBSD$
 .\"
-.Dd January 28, 2012
+.Dd July 18, 2012
 .Dt FCNTL 2
 .Os
 .Sh NAME
@@ -54,7 +54,7 @@ Depending on the value of
 .Fn fcntl
 can take an additional third argument
 .Fa "int arg" .
-.Bl -tag -width F_GETOWNX
+.Bl -tag -width F_DUPFD_CLOEXEC
 .It Dv F_DUPFD
 Return a new descriptor as follows:
 .Pp
@@ -73,11 +73,22 @@ Same access mode (read, write or read/write).
 Same file status flags (i.e., both file descriptors
 share the same file status flags).
 .It
-The close-on-exec flag associated with the new file descriptor
-is set to remain open across
+The close-on-exec flag
+.Dv FD_CLOEXEC
+associated with the new file descriptor is cleared, so the file descriptor is
+to remain open across
 .Xr execve 2
 system calls.
 .El
+.It Dv F_DUPFD_CLOEXEC
+Like
+.Dv F_DUPFD ,
+but the
+.Dv FD_CLOEXEC
+flag associated with the new file descriptor is set, so the file descriptor
+is closed when
+.Xr execve 2
+system call executes.
 .It Dv F_DUP2FD
 It is functionally equivalent to
 .Bd -literal -offset indent