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141 lines
4.0 KiB
Plaintext
141 lines
4.0 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "FTOK" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" ftok
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.SH NAME
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ftok \- generate an IPC key
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.SH SYNOPSIS
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.LP
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\fB#include <sys/ipc.h>
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.br
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.sp
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key_t ftok(const char *\fP\fIpath\fP\fB, int\fP \fIid\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 \fIftok\fP() function shall return a key based on \fIpath\fP and
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\fIid\fP that is usable in subsequent calls to \fImsgget\fP(), \fIsemget\fP(),
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and \fIshmget\fP(). The application shall ensure that the \fIpath\fP
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argument is the pathname of an
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existing file that the process is able to \fIstat\fP().
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.LP
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The \fIftok\fP() function shall return the same key value for all
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paths that name the same file, when called with the same
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\fIid\fP value, and return different key values when called with different
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\fIid\fP values or with paths that name different
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files existing on the same file system at the same time. It is unspecified
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whether \fIftok\fP() shall return the same key value
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when called again after the file named by \fIpath\fP is removed and
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recreated with the same name.
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.LP
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Only the low-order 8-bits of \fIid\fP are significant. The behavior
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of \fIftok\fP() is unspecified if these bits are 0.
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIftok\fP() shall return a key. Otherwise,
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\fIftok\fP() shall return (\fBkey_t\fP)-1 and set
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\fIerrno\fP to indicate the error.
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.SH ERRORS
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.LP
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The \fIftok\fP() function shall fail if:
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.TP 7
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.B EACCES
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Search permission is denied for a component of the path prefix.
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.TP 7
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.B ELOOP
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A loop exists in symbolic links encountered during resolution of the
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\fIpath\fP argument.
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.TP 7
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.B ENAMETOOLONG
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The length of the \fIpath\fP argument exceeds {PATH_MAX} or a pathname
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component is longer than {NAME_MAX}.
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.TP 7
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.B ENOENT
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A component of \fIpath\fP does not name an existing file or \fIpath\fP
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is an empty string.
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.TP 7
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.B ENOTDIR
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A component of the path prefix is not a directory.
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.sp
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.LP
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The \fIftok\fP() function may fail if:
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.TP 7
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.B ELOOP
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More than {SYMLOOP_MAX} symbolic links were encountered during resolution
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of the \fIpath\fP argument.
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.TP 7
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.B ENAMETOOLONG
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Pathname resolution of a symbolic link produced an intermediate result
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whose length exceeds {PATH_MAX}.
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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 Getting an IPC Key
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.LP
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The following example gets a unique key that can be used by the IPC
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functions \fIsemget\fP(), \fImsgget\fP(), and \fIshmget\fP(). The
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key returned by \fIftok\fP() for this example is based on the ID value
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\fIS\fP and the pathname \fB/tmp\fP.
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.sp
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.RS
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.nf
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\fB#include <sys/ipc.h>
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\&...
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key_t key;
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char *path = "/tmp";
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int id = 'S';
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.sp
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key = ftok(path, id);
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\fP
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.fi
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.RE
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.SS Saving an IPC Key
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.LP
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The following example gets a unique key based on the pathname \fB/tmp\fP
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and the ID value \fIa\fP. It also assigns the value
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of the resulting key to the \fIsemkey\fP variable so that it will
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be available to a later call to \fIsemget\fP(), \fImsgget\fP(), or
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\fIshmget\fP().
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.sp
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.RS
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.nf
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\fB#include <sys/ipc.h>
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\&...
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key_t semkey;
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.sp
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if ((semkey = ftok("/tmp", 'a')) == (key_t) -1) {
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perror("IPC error: ftok"); exit(1);
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}
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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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For maximum portability, \fIid\fP should be a single-byte character.
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.SH RATIONALE
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.LP
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None.
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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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\fImsgget\fP() , \fIsemget\fP() , \fIshmget\fP() , the Base Definitions
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volume of IEEE\ Std\ 1003.1-2001, \fI<sys/ipc.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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