fbbd9655e5
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
179 lines
4.5 KiB
Groff
179 lines
4.5 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)pipe.2 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd July 20, 2016
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.Dt PIPE 2
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.Os
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.Sh NAME
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.Nm pipe ,
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.Nm pipe2
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.Nd create descriptor pair for interprocess communication
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn pipe "int fildes[2]"
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.Ft int
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.Fn pipe2 "int fildes[2]" "int flags"
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.Sh DESCRIPTION
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The
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.Fn pipe
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function
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creates a
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.Em pipe ,
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which is an object allowing
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bidirectional data flow,
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and allocates a pair of file descriptors.
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.Pp
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The
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.Fn pipe2
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system call allows control over the attributes of the file descriptors
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via the
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.Fa flags
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argument.
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Values for
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.Fa flags
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are constructed by a bitwise-inclusive OR of flags from the following
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list, defined in
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.In fcntl.h :
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.Bl -tag -width ".Dv O_NONBLOCK"
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.It Dv O_CLOEXEC
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Set the close-on-exec flag for the new file descriptors.
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.It Dv O_NONBLOCK
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Set the non-blocking flag for the ends of the pipe.
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.El
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.Pp
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If the
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.Fa flags
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argument is 0, the behavior is identical to a call to
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.Fn pipe .
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.Pp
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By convention, the first descriptor is normally used as the
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.Em read end
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of the pipe,
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and the second is normally the
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.Em write end ,
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so that data written to
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.Fa fildes[1]
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appears on (i.e., can be read from)
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.Fa fildes[0] .
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This allows the output of one program to be
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sent
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to another program:
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the source's standard output is set up to be
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the write end of the pipe,
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and the sink's standard input is set up to be
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the read end of the pipe.
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The pipe itself persists until all its associated descriptors are
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closed.
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.Pp
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A pipe that has had an end closed is considered
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.Em widowed .
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Writing on such a pipe causes the writing process to receive
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a
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.Dv SIGPIPE
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signal.
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Widowing a pipe is the only way to deliver end-of-file to a reader:
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after the reader consumes any buffered data, reading a widowed pipe
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returns a zero count.
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.Pp
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The bidirectional nature of this implementation of pipes is not
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portable to older systems, so it is recommended to use the convention
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for using the endpoints in the traditional manner when using a
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pipe in one direction.
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.Sh IMPLEMENTATION NOTES
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The
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.Fn pipe
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function calls the
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.Fn pipe2
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system call.
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As a result, system call traces such as those captured by
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.Xr dtrace 1
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or
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.Xr ktrace 1
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will show calls to
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.Fn pipe2 .
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.Sh RETURN VALUES
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.Rv -std pipe
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.Sh ERRORS
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The
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.Fn pipe
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and
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.Fn pipe2
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system calls will fail if:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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.Ar fildes
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argument points to an invalid memory location.
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.It Bq Er EMFILE
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Too many descriptors are active.
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.It Bq Er ENFILE
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The system file table is full.
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.It Bq Er ENOMEM
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Not enough kernel memory to establish a pipe.
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.El
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.Pp
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The
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.Fn pipe2
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system call will also fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa flags
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argument is invalid.
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.El
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.Sh SEE ALSO
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.Xr sh 1 ,
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.Xr fork 2 ,
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.Xr read 2 ,
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.Xr socketpair 2 ,
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.Xr write 2
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.Sh HISTORY
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The
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.Fn pipe
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function appeared in
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.At v3 .
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.Pp
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Bidirectional pipes were first used on
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.At V.4 .
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.Pp
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The
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.Fn pipe2
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function appeared in
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.Fx 10.0 .
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.Pp
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The
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.Fn pipe
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function became a wrapper around
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.Fn pipe2
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in
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.Fx 11.0 .
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