mirror of https://github.com/mkerrisk/man-pages
152 lines
4.1 KiB
Plaintext
152 lines
4.1 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "POSIX_OPENPT" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" posix_openpt
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.SH NAME
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posix_openpt \- open a pseudo-terminal device
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.SH SYNOPSIS
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.LP
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\fB#include <stdlib.h>
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.br
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#include <fcntl.h>
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.br
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.sp
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int posix_openpt(int\fP \fIoflag\fP\fB); \fP
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\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIposix_openpt\fP() function shall establish a connection between
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a master device for a pseudo-terminal and a file
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descriptor. The file descriptor is used by other I/O functions that
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refer to that pseudo-terminal.
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.LP
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The file status flags and file access modes of the open file description
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shall be set according to the value of
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\fIoflag\fP.
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.LP
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Values for \fIoflag\fP are constructed by a bitwise-inclusive OR of
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flags from the following list, defined in \fI<fcntl.h>\fP:
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.TP 7
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O_RDWR
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Open for reading and writing.
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.TP 7
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O_NOCTTY
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If set \fIposix_openpt\fP() shall not cause the terminal device to
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become the controlling terminal for the process.
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.sp
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.LP
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The behavior of other values for the \fIoflag\fP argument is unspecified.
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.SH RETURN VALUE
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.LP
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Upon successful completion, the \fIposix_openpt\fP() function shall
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open a master pseudo-terminal device and return a
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non-negative integer representing the lowest numbered unused file
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descriptor. Otherwise, -1 shall be returned and \fIerrno\fP set
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to indicate the error.
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.SH ERRORS
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.LP
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The \fIposix_openpt\fP() function shall fail if:
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.TP 7
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.B EMFILE
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{OPEN_MAX} file descriptors are currently open in the calling process.
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.TP 7
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.B ENFILE
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The maximum allowable number of files is currently open in the system.
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.sp
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.LP
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The \fIposix_openpt\fP() function may fail if:
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.TP 7
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.B EINVAL
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The value of \fIoflag\fP is not valid.
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.TP 7
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.B EAGAIN
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Out of pseudo-terminal resources.
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.TP 7
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.B ENOSR
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Out of STREAMS resources.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.SS Opening a Pseudo-Terminal and Returning the Name of the Slave
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Device and a File Descriptor
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.sp
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.RS
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.nf
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\fB#include <fcntl.h>
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#include <stdio.h>
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.sp
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int masterfd, slavefd;
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char *slavedevice;
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.sp
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masterfd = posix_openpt(O_RDWR|O_NOCTTY);
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.sp
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if (masterfd == -1
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|| grantpt (masterfd) == -1
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|| unlockpt (masterfd) == -1
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|| (slavedevice = ptsname (masterfd)) == NULL)
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return -1;
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.sp
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printf("slave device is: %s\\n", slavedevice);
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.sp
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slavefd = open(slave, O_RDWR|O_NOCTTY);
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if (slavefd < 0)
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return -1;
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\fP
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.fi
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.RE
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.SH APPLICATION USAGE
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.LP
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This function is a method for portably obtaining a file descriptor
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of a master terminal device for a pseudo-terminal. The \fIgrantpt\fP()
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and \fIptsname\fP() functions can be
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used to manipulate mode and ownership permissions, and to obtain the
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name of the slave device, respectively.
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.SH RATIONALE
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.LP
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The standard developers considered the matter of adding a special
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device for cloning master pseudo-terminals: the
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\fB/dev/ptmx\fP device. However, consensus could not be reached, and
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it was felt that adding a new function would permit other
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implementations. The \fIposix_openpt\fP() function is designed to
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complement the \fIgrantpt\fP(), \fIptsname\fP(), and \fIunlockpt\fP()
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functions.
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.LP
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On implementations supporting the \fB/dev/ptmx\fP clone device, opening
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the master device of a pseudo-terminal is simply:
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.sp
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.RS
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.nf
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\fBmfdp = open("/dev/ptmx", oflag );
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if (mfdp < 0)
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return -1;
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\fP
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.fi
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.RE
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIgrantpt\fP() , \fIopen\fP() , \fIptsname\fP() , \fIunlockpt\fP()
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, the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, \fI<fcntl.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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