X-Git-Url: https://git.saurik.com/apple/xnu.git/blobdiff_plain/2d21ac55c334faf3a56e5634905ed6987fc787d4..4bd07ac2140668789aa3ee8ec4dde4a3e0a3bba5:/bsd/man/man2/dup.2

diff --git a/bsd/man/man2/dup.2 b/bsd/man/man2/dup.2
index 019b13fbf..897966a52 100644
--- a/bsd/man/man2/dup.2
+++ b/bsd/man/man2/dup.2
@@ -33,7 +33,7 @@
 .\"
 .\"     @(#)dup.2	8.1 (Berkeley) 6/4/93
 .\"
-.Dd June 4, 1993
+.Dd December 1, 2010
 .Dt DUP 2
 .Os BSD 4
 .Sh NAME
@@ -100,12 +100,22 @@ In
 the value of the new descriptor
 .Fa fildes2
 is specified.
-If this descriptor is already in use,
-the descriptor is first deallocated as if a
+If
+.Fa fildes
+and
+.Fa fildes2
+are equal, then
+.Fn dup2 
+just returns
+.Fa fildes2 ;
+no other changes are made to the existing descriptor.
+Otherwise, if descriptor
+.Fa fildes2
+is already in use, it is first deallocated as if a
 .Xr close 2
 call had been done first.
 .Sh RETURN VALUES
-Upon successful completion, a value of 0 is returned.
+Upon successful completion, the new file descriptor is returned.
 Otherwise, a value of -1 is returned and the global integer variable
 .Va errno
 is set to indicate the error.
@@ -119,8 +129,6 @@ system calls will fail if:
 .\" ==========
 .It Bq Er EBADF
 .Fa fildes
-or
-.Fa fildes2
 is not an active, valid file descriptor.
 .\" ==========
 .It Bq Er EINTR
@@ -129,6 +137,16 @@ Execution is interrupted by a signal.
 .It Bq Er EMFILE
 Too many file descriptors are active.
 .El
+.Pp
+The
+.Fn dup2
+system call will fail if:
+.Bl -tag -width Er
+.\" ==========
+.It Bq Er EBADF
+.Fa fildes2
+is negative or greater than the maximum allowable number (see getdtablesize(2)).
+.El
 .Sh SEE ALSO
 .Xr accept 2 ,
 .Xr close 2 ,