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.\" Copyright 1993 Giorgio Ciucci (giorgio@crcc.it)
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.TH FTOK 3 "November 1, 1993" "Linux 0.99.13" "Linux Programmer's Manual"
.SH NAME
ftok \- convert a pathname and a project identifier to a System V IPC key
.SH SYNOPSIS
.nf
.B
# include <sys/types.h>
.B
# include <sys/ipc.h>
.fi
.sp
.BI "key_t ftok ( char *" pathname ,
.BI "char " proj " )"
.SH DESCRIPTION
The function converts the pathname of an existing accessible
file and a project identifier into a
.B key_t
type System V IPC key.
.SH "RETURN VALUE"
On success the return value will be the converted
.B key_t
value,
otherwise
.B \-1
with
.B errno
indicating the error as for the
.BR stat (2)
system call.
.SH BUGS
The generated
.B key_t
value is obtained
.BR stat \-ing
the disk file corresponding to
.I pathname
in order to get its i\-node number and the minor device number of the
filesystem on which the disk file resides,
then by combining the 8 bit
.I proj
value along with the lower 16 bits of the i\-node number,
along with the 8 bits of the minor device number.
The algorithm does not guarantee a unique key value.
In fact
.IP \(bu
Two different names linking to the same file produce same
key values.
.IP \(bu
Using the lower 16 bits of the i\-node number, gives some
chance (also usually small) to have same key values for file names
referring to different i\-nodes.
.IP \(bu
Not discriminating among major device numbers,
gives some chance of collision (also usually small) for
systems with multiple disk controllers.
.SH "SEE ALSO"
.BR ipc (5),
.BR msgget (2),
.BR semget (2),
.BR shmget (2),
.BR stat (2).
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