179 lines
4.5 KiB
Groff
179 lines
4.5 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)pipe.2 8.1 (Berkeley) 6/4/93
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd July 20, 2016
|
|
.Dt PIPE 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm pipe ,
|
|
.Nm pipe2
|
|
.Nd create descriptor pair for interprocess communication
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In unistd.h
|
|
.Ft int
|
|
.Fn pipe "int fildes[2]"
|
|
.Ft int
|
|
.Fn pipe2 "int fildes[2]" "int flags"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn pipe
|
|
function
|
|
creates a
|
|
.Em pipe ,
|
|
which is an object allowing
|
|
bidirectional data flow,
|
|
and allocates a pair of file descriptors.
|
|
.Pp
|
|
The
|
|
.Fn pipe2
|
|
system call allows control over the attributes of the file descriptors
|
|
via the
|
|
.Fa flags
|
|
argument.
|
|
Values for
|
|
.Fa flags
|
|
are constructed by a bitwise-inclusive OR of flags from the following
|
|
list, defined in
|
|
.In fcntl.h :
|
|
.Bl -tag -width ".Dv O_NONBLOCK"
|
|
.It Dv O_CLOEXEC
|
|
Set the close-on-exec flag for the new file descriptors.
|
|
.It Dv O_NONBLOCK
|
|
Set the non-blocking flag for the ends of the pipe.
|
|
.El
|
|
.Pp
|
|
If the
|
|
.Fa flags
|
|
argument is 0, the behavior is identical to a call to
|
|
.Fn pipe .
|
|
.Pp
|
|
By convention, the first descriptor is normally used as the
|
|
.Em read end
|
|
of the pipe,
|
|
and the second is normally the
|
|
.Em write end ,
|
|
so that data written to
|
|
.Fa fildes[1]
|
|
appears on (i.e., can be read from)
|
|
.Fa fildes[0] .
|
|
This allows the output of one program to be
|
|
sent
|
|
to another program:
|
|
the source's standard output is set up to be
|
|
the write end of the pipe,
|
|
and the sink's standard input is set up to be
|
|
the read end of the pipe.
|
|
The pipe itself persists until all its associated descriptors are
|
|
closed.
|
|
.Pp
|
|
A pipe that has had an end closed is considered
|
|
.Em widowed .
|
|
Writing on such a pipe causes the writing process to receive
|
|
a
|
|
.Dv SIGPIPE
|
|
signal.
|
|
Widowing a pipe is the only way to deliver end-of-file to a reader:
|
|
after the reader consumes any buffered data, reading a widowed pipe
|
|
returns a zero count.
|
|
.Pp
|
|
The bidirectional nature of this implementation of pipes is not
|
|
portable to older systems, so it is recommended to use the convention
|
|
for using the endpoints in the traditional manner when using a
|
|
pipe in one direction.
|
|
.Sh IMPLEMENTATION NOTES
|
|
The
|
|
.Fn pipe
|
|
function calls the
|
|
.Fn pipe2
|
|
system call.
|
|
As a result, system call traces such as those captured by
|
|
.Xr dtrace 1
|
|
or
|
|
.Xr ktrace 1
|
|
will show calls to
|
|
.Fn pipe2 .
|
|
.Sh RETURN VALUES
|
|
.Rv -std pipe
|
|
.Sh ERRORS
|
|
The
|
|
.Fn pipe
|
|
and
|
|
.Fn pipe2
|
|
system calls will fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EFAULT
|
|
.Ar fildes
|
|
argument points to an invalid memory location.
|
|
.It Bq Er EMFILE
|
|
Too many descriptors are active.
|
|
.It Bq Er ENFILE
|
|
The system file table is full.
|
|
.It Bq Er ENOMEM
|
|
Not enough kernel memory to establish a pipe.
|
|
.El
|
|
.Pp
|
|
The
|
|
.Fn pipe2
|
|
system call will also fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
The
|
|
.Fa flags
|
|
argument is invalid.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr sh 1 ,
|
|
.Xr fork 2 ,
|
|
.Xr read 2 ,
|
|
.Xr socketpair 2 ,
|
|
.Xr write 2
|
|
.Sh HISTORY
|
|
The
|
|
.Fn pipe
|
|
function appeared in
|
|
.At v3 .
|
|
.Pp
|
|
Bidirectional pipes were first used on
|
|
.At V.4 .
|
|
.Pp
|
|
The
|
|
.Fn pipe2
|
|
function appeared in
|
|
.Fx 10.0 .
|
|
.Pp
|
|
The
|
|
.Fn pipe
|
|
function became a wrapper around
|
|
.Fn pipe2
|
|
in
|
|
.Fx 11.0 .
|