FTOK (3)
convert a pathname and a project identifier to a System V IPC key
SYNOPSIS
# include <sys/types.h>
# include <sys/ipc.h>
key_t ftok ( char * pathname ,
char proj )
DESCRIPTION
The function converts the pathname of an existing accessible
file and a project identifier into a
key_t
type System V IPC key.
RETURN VALUE
On success the return value will be the converted
key_t
value,
otherwise
-1
with
errno
indicating the error as for the
stat (2)
system call.
BUGS
The generated
key_t
value is obtained
stat -ing
the disk file corresponding to
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
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
Two different names linking to the same file produce same
key values.
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.
Not discriminating among major device numbers,
gives some chance of collision (also usually small) for
systems with multiple disk controllers.
SEE ALSO
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