git.saurik.com Git - apple/xnu.git/blame_incremental

... / ...

Commit	Line	Data
	1	.\" $NetBSD: dup.2,v 1.4 1995/02/27 12:32:21 cgd Exp $
	2	.\"
	3	.\" Copyright (c) 1980, 1991, 1993
	4	.\" The Regents of the University of California. All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" @(#)dup.2 8.1 (Berkeley) 6/4/93
	35	.\"
	36	.Dd December 1, 2010
	37	.Dt DUP 2
	38	.Os BSD 4
	39	.Sh NAME
	40	.Nm dup ,
	41	.Nm dup2
	42	.Nd duplicate an existing file descriptor
	43	.Sh SYNOPSIS
	44	.Fd #include <unistd.h>
	45	.Ft int
	46	.Fo dup
	47	.Fa "int fildes"
	48	.Fc
	49	.Ft int
	50	.Fo dup2
	51	.Fa "int fildes"
	52	.Fa "int fildes2"
	53	.Fc
	54	.Sh DESCRIPTION
	55	.Fn dup
	56	duplicates an existing object descriptor
	57	and returns its value to the calling process
	58	.Fa ( fildes2
	59	=
	60	.Fn dup fildes ) .
	61	The argument
	62	.Fa fildes
	63	is a small non-negative integer index
	64	in the per-process descriptor table.
	65	The value must be less than the size of the table,
	66	which is returned by
	67	.Xr getdtablesize 2 .
	68	The new descriptor returned by the call
	69	is the lowest numbered descriptor
	70	currently not in use by the process.
	71	.Pp
	72	The object referenced by the descriptor does not distinguish
	73	between
	74	.Fa fildes
	75	and
	76	.Fa fildes2
	77	in any way.
	78	Thus if
	79	.Fa fildes2
	80	and
	81	.Fa fildes
	82	are duplicate references to an open
	83	file,
	84	.Xr read 2 ,
	85	.Xr write 2
	86	and
	87	.Xr lseek 2
	88	calls all move a single pointer into the file,
	89	and append mode, non-blocking I/O and asynchronous I/O options
	90	are shared between the references.
	91	If a separate pointer into the file is desired,
	92	a different object reference to the file must be obtained
	93	by issuing an additional
	94	.Xr open 2
	95	call.
	96	The close-on-exec flag on the new file descriptor is unset.
	97	.Pp
	98	In
	99	.Fn dup2 ,
	100	the value of the new descriptor
	101	.Fa fildes2
	102	is specified.
	103	If
	104	.Fa fildes
	105	and
	106	.Fa fildes2
	107	are equal, then
	108	.Fn dup2
	109	just returns
	110	.Fa fildes2 ;
	111	no other changes are made to the existing descriptor.
	112	Otherwise, if descriptor
	113	.Fa fildes2
	114	is already in use, it is first deallocated as if a
	115	.Xr close 2
	116	call had been done first.
	117	.Sh RETURN VALUES
	118	Upon successful completion, the new file descriptor is returned.
	119	Otherwise, a value of -1 is returned and the global integer variable
	120	.Va errno
	121	is set to indicate the error.
	122	.Sh ERRORS
	123	The
	124	.Fn dup
	125	and
	126	.Fn dup2
	127	system calls will fail if:
	128	.Bl -tag -width Er
	129	.\" ==========
	130	.It Bq Er EBADF
	131	.Fa fildes
	132	is not an active, valid file descriptor.
	133	.\" ==========
	134	.It Bq Er EINTR
	135	Execution is interrupted by a signal.
	136	.\" ==========
	137	.It Bq Er EMFILE
	138	Too many file descriptors are active.
	139	.El
	140	.Pp
	141	The
	142	.Fn dup2
	143	system call will fail if:
	144	.Bl -tag -width Er
	145	.\" ==========
	146	.It Bq Er EBADF
	147	.Fa fildes2
	148	is negative or greater than the maximum allowable number (see getdtablesize(2)).
	149	.El
	150	.Sh SEE ALSO
	151	.Xr accept 2 ,
	152	.Xr close 2 ,
	153	.Xr fcntl 2 ,
	154	.Xr getdtablesize 2 ,
	155	.Xr open 2 ,
	156	.Xr pipe 2 ,
	157	.Xr socket 2 ,
	158	.Xr socketpair 2
	159	.Sh STANDARDS
	160	.Fn dup
	161	and
	162	.Fn dup2
	163	are expected to conform to
	164	.St -p1003.1-88 .