xref: /netbsd-src/lib/libc/gen/ftok.3 (revision 23c8222edbfb0f0932d88a8351d3a0cf817dfb9e)
1.\"	$NetBSD: ftok.3,v 1.13 2004/09/15 19:45:17 hubertf Exp $
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3.\" Copyright (c) 1994 SigmaSoft, Th. Lockert <tholo@sigmasoft.com>
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26.Dd June 24, 1994
27.Os
28.Dt FTOK 3
29.Sh NAME
30.Nm ftok
31.Nd create IPC identifier from path name
32.Sh LIBRARY
33.Lb libc
34.Sh SYNOPSIS
35.In sys/types.h
36.In sys/ipc.h
37.Ft key_t
38.Fn ftok "const char *path" "int id"
39.Sh DESCRIPTION
40The
41.Fn ftok
42function attempts to create a unique key suitable for use with the
43.Xr msgget 2 ,
44.Xr semget 2
45and
46.Xr shmget 2
47functions given the
48.Fa path
49of an existing file and a user-selectable
50.Fa id .
51.Pp
52The specified
53.Fa path
54must specify an existing file that is accessible to the calling process
55or the call will fail.
56Also, note that links to files will return the same key, given the same
57.Fa id .
58.Pp
59Only the 8 least significant bits of
60.Fa id
61are used in the key generation; the rest of the bits are ignored.
62.Sh RETURN VALUES
63The
64.Fn ftok
65function will return ((key_t)-1) if
66.Fa path
67does not exist or if it cannot be accessed by the calling process.
68.Sh SEE ALSO
69.Xr msgget 2 ,
70.Xr semget 2 ,
71.Xr shmget 2
72.Sh HISTORY
73The
74.Fn ftok
75function originated with System V and is typically used by programs
76that use the System V IPC routines.
77.Sh AUTHORS
78.Bl -tag
79Thorsten Lockert \*[Lt]tholo@sigmasoft.com\*[Gt]
80.El
81.Sh BUGS
82The returned key is computed based on the device and inode of the
83specified
84.Fa path
85in combination with the given
86.Fa id .
87Thus it is quite possible for the routine to return duplicate keys
88given that those fields are not 8- and 16-bit quantities like they
89were on System V based systems where this library routine's ancestor
90were originally created.
91