#include <sys/types.h>
#include <sys/mman.h> int
shm_open (const char *path int flags mode_t mode); int
shm_unlink (const char *path);
DESCRIPTION
The
shm_open ();
function opens (or optionally creates) a
POSIX
shared memory object named
Fa path .
The
shm_unlink ();
function removes a shared memory object named
Fa path .
#include <the>
Fx implementation,
POSIX
shared memory objects are implemented as ordinary files.
The
shm_open ();
and
shm_unlink ();
act as wrappers around the
open(2)
and
unlink(2)
routines, and
Fa path ,
Fa flags ,
and
Fa mode
arguments are as specified for those functions.
The
Fa flags
argument is checked to ensure that the access mode specified is not
O_WRONLY
(which is not defined for shared memory objects).
In addition, the
Fx implementation causes
mmap ();
of a descriptor returned by
shm_open ();
to behave as if the
MAP_NOSYNC
flag had been specified to
mmap(2).
(It does so by setting a special file flag using
fcntl(2).)
The
shm_unlink ();
function makes no effort to ensure that
Fa path
refers to a shared memory object.
RETURN VALUES
If successful,
shm_open ();
returns a non-negative integer;
shm_unlink ();
returns zero.
Both functions return -1 on failure, and set
errno
to indicate the error.
COMPATIBILITY
The
Fa path
argument does not necessarily represent a pathname (although it does in this
and most other implementations).
Two processes opening the same
Fa path
are guaranteed to access the same shared memory object if and only if
Fa path
begins with a slash
(`/'
)
character.
Only the
O_RDONLYO_RDWRO_CREATO_EXCL
and
O_TRUNC
flags may be used in portable programs.
The result of using
open(2),
read(2),
or
write(2)
on a shared memory object, or on the descriptor returned by
shm_open (,);
is undefined.
It is also undefined whether the shared memory object itself, or its
contents, persist across reboots.
ERRORS
The
shm_open ();
and
shm_unlink ();
functions can fail with any error defined for
open ();
and
unlink (,);
respectively.
In addition, the following errors are defined for
shm_open (:);
Bq Er EINVAL
The object named by
Fa path
is not a shared memory object
(i.e., it is not a regular file).
Bq Er EINVAL
The
Fa flags
argument to
shm_open ();
specifies an access mode of
O_WRONLY
