Originální popis anglicky:
shmctl - XSI shared memory control operations
Návod, kniha: POSIX Programmer's Manual
#include <sys/shm.h>
int shmctl(int
shmid, int
cmd, struct shmid_ds
*buf);
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.
Upon successful completion,
shmctl() shall return 0; otherwise, it shall
return -1 and set
errno to indicate the error.
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.
None.
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.
None.
None.
XSI Interprocess Communication ,
Realtime ,
shmat() ,
shmdt() ,
shmget() ,
shm_open() ,
shm_unlink() ,
the Base Definitions volume of IEEE Std 1003.1-2001,
<sys/shm.h>
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
.
