2013-12-06 12:04:52 +01:00
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.\" $NetBSD: ftok.3,v 1.17 2013/07/20 21:39:57 wiz Exp $
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2011-02-14 20:36:03 +01:00
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.\"
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.\" Copyright (c) 1994 SigmaSoft, Th. Lockert <tholo@sigmasoft.com>
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.\" 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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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.\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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.\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd April 27, 2010
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.Dt FTOK 3
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.Os
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.Sh NAME
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.Nm ftok
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.Nd create IPC identifier from path name
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/ipc.h
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.Ft key_t
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.Fn ftok "const char *path" "int id"
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.Sh DESCRIPTION
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The
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.Fn ftok
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function attempts to create a unique key suitable for use with the
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.Xr msgget 2 ,
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.Xr semget 2
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and
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.Xr shmget 2
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functions given the
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.Fa path
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of an existing file and a user-selectable
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.Fa id .
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.Pp
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The specified
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.Fa path
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must specify an existing file that is accessible to the calling process
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or the call will fail.
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Also, note that links to files will return the same key, given the same
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.Fa id .
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.Pp
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Only the 8 least significant bits of
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.Fa id
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are used in the key generation; the rest of the bits are ignored.
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.Sh RETURN VALUES
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The
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.Fn ftok
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function will return ((key_t)-1) if
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.Fa path
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does not exist or if it cannot be accessed by the calling process.
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.Sh SEE ALSO
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.Xr msgget 2 ,
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.Xr semget 2 ,
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.Xr shmget 2
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.Sh STANDARDS
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The
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.Fn ftok
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function conforms to
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.St -p1003.1 .
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.Sh HISTORY
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The
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.Fn ftok
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function originated with System V and is typically used by programs
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that use the System V IPC routines.
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.Sh AUTHORS
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2013-12-06 12:04:52 +01:00
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.An Thorsten Lockert Aq Mt tholo@sigmasoft.com
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2011-02-14 20:36:03 +01:00
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.Sh BUGS
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The returned key is computed based on the device and inode of the
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specified
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.Fa path
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in combination with the given
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.Fa id .
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Thus it is quite possible for the routine to return duplicate keys
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given that those fields are not 8- and 16-bit quantities like they
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were on System V based systems where this library routine's ancestor
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were originally created.
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