1FTOK(3)                    Linux Programmer's Manual                   FTOK(3)
2
3
4

NAME

6       ftok  -  convert  a pathname and a project identifier to a System V IPC
7       key
8

SYNOPSIS

10       # include <sys/types.h>
11       # include <sys/ipc.h>
12
13       key_t ftok(const char *pathname, int proj_id);
14

DESCRIPTION

16       The ftok() function uses the identity of the file named  by  the  given
17       pathname  (which  must  refer  to an existing, accessible file) and the
18       least significant 8 bits of proj_id (which must be non-zero) to  gener‐
19       ate  a  key_t  type  System V IPC key, suitable for use with msgget(2),
20       semget(2), or shmget(2).
21
22       The resulting value is the same for all pathnames that  name  the  same
23       file, when the same value of proj_id is used. The value returned should
24       be different when the (simultaneously existing) files  or  the  project
25       IDs differ.
26

RETURN VALUE

28       On  success  the  generated  key_t  value is returned. On failure -1 is
29       returned, with errno indicating the error as  for  the  stat(2)  system
30       call.
31

CONFORMING TO

33       POSIX.1-2001.
34

NOTES

36       Under libc4 and libc5 (and under SunOS 4.x) the prototype was
37              key_t ftok(char *pathname, char proj_id);
38       Today  proj_id is an int, but still only 8 bits are used. Typical usage
39       has an ASCII character proj_id, that is why the behaviour is said to be
40       undefined when proj_id is zero.
41
42       Of course no guarantee can be given that the resulting key_t is unique.
43       Typically, a best effort attempt combines the given proj_id  byte,  the
44       lower  16 bits of the i-node number, and the lower 8 bits of the device
45       number into a 32-bit result.  Collisions may easily happen, for example
46       between files on /dev/hda1 and files on /dev/sda1.
47

SEE ALSO

49       msgget(2), semget(2), shmget(2), stat(2), svipc(7)
50
51
52
53Linux 2.4                         2001-11-28                           FTOK(3)
Impressum