int shmctl(int shmid, intcmd, struct shmid_ds
*buf);
DESCRIPTION
The shmctl() function operates on XSI shared memory (see the
Base Definitions volume of IEEE Std 1003.1-2001,
Section 3.340, Shared Memory Object). It is unspecified whether this
function
interoperates with the realtime interprocess communication facilities
defined in Realtime .
The shmctl() function provides a variety of shared memory control
operations as specified by cmd. The following
values for cmd are available:
IPC_STAT
Place the current value of each member of the shmid_ds data
structure associated with shmid into the structure
pointed to by buf. The contents of the structure are defined
in <sys/shm.h>.
IPC_SET
Set the value of the following members of the shmid_ds data
structure associated with shmid to the corresponding
value found in the structure pointed to by buf:
shm_perm.uid
shm_perm.gid
shm_perm.mode Low-order nine bits.
IPC_SET can only be executed by a process that has an effective user
ID equal to either that of a process with appropriate
privileges or to the value of shm_perm.cuid or shm_perm.uid
in the shmid_ds data structure associated with
shmid.
IPC_RMID
Remove the shared memory identifier specified by shmid from
the system and destroy the shared memory segment and
shmid_ds data structure associated with it. IPC_RMID can only
be executed by a process that has an effective user ID equal
to either that of a process with appropriate privileges or to the
value of shm_perm.cuid or shm_perm.uid in the
shmid_ds data structure associated with shmid.
RETURN VALUE
Upon successful completion, shmctl() shall return 0; otherwise,
it shall return -1 and set errno to indicate the
error.
ERRORS
The shmctl() function shall fail if:
EACCES
The argument cmd is equal to IPC_STAT and the calling process
does not have read permission; see XSI Interprocess Communication
.
EINVAL
The value of shmid is not a valid shared memory identifier,
or the value of cmd is not a valid command.
EPERM
The argument cmd is equal to IPC_RMID or IPC_SET and the effective
user ID of the calling process is not equal to that
of a process with appropriate privileges and it is not equal to the
value of shm_perm.cuid or shm_perm.uid in the
data structure associated with shmid.
The shmctl() function may fail if:
EOVERFLOW
The cmd argument is IPC_STAT and the gid or uid
value is too large to be stored in the structure pointed
to by the buf argument.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The POSIX Realtime Extension defines alternative interfaces for interprocess
communication. Application developers who need to
use IPC should design their applications so that modules using the
IPC routines described in XSI Interprocess Communication can
be easily modified to use the alternative
interfaces.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
XSI Interprocess Communication , Realtime , shmat()
, shmdt() , shmget() , shm_open() , shm_unlink()
, the Base Definitions volume of IEEE Std 1003.1-2001, <sys/shm.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
