shmop(S)
shmop: shmat, shmdt --
shared memory operations
Synopsis
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
void shmat(int shmid, const void shmaddr, int shmflg);
int shmdt(const void shmaddr);
Description
shmat attaches the shared memory segment associated with the shared
memory identifier specified by
shmid
to the data segment of the calling process.
The segment is attached at the address specified by one of the following
criteria:
-
If shmaddr is equal to (void *) 0, the segment is attached at
the first available address as selected by the system.
-
If shmaddr is not equal to (void *) 0 and
(shmflg&SHM_RND) is true, the segment is attached at the address
given by (shmaddr - (shmaddr modulus SHMLBA)).
-
If shmaddr is not equal to (void *) 0 and
(shmflg&SHM_RND)
is false, the segment is attached at the address given by
shmaddr.
shmdt detaches from the calling process's data segment
the shared memory segment located at the address specified by
shmaddr.
The segment is attached for reading if (shmflg&SHM_RDONLY)
is true
{READ},
otherwise it is attached for reading and writing
{READ/WRITE}.
Return values
On success:
-
shmat returns the data segment start address of the attached shared
memory segment.
-
shmdt returns 0.
On failure, shmat and shmdt return -1 and set errno to
identify the error.
Errors
In the following conditions, shmat fails and sets errno to:
EINVAL-
shmid
is not a valid shared memory identifier.
EACCES-
Operation permission is denied to the calling process [see
intro(S)].
ENOMEM-
The available data space is not large enough to accommodate the shared
memory segment.
EINVAL-
shmaddr is not equal to zero, and the value of (shmaddr -
(shmaddr modulus SHMLBA)) is an illegal address.
EINVAL-
shmaddr is not equal to zero, (shmflg&SHM_RND)
is false, and the value of shmaddr is an illegal address.
EMFILE-
The number of shared memory segments attached to the calling process would
exceed the system-imposed limit.
In the following conditions, shmdt fails and sets errno to:
EINVAL-
shmaddr is not the data segment start address of a shared memory segment.
References
exec(S),
exit(S),
fork(S),
intro(S),
shmctl(S),
shmget(S)
Notices
The user must explicitly remove shared memory segments
after the last reference to them has been removed.
© 2005 The SCO Group, Inc. All rights reserved.
SCO OpenServer Release 6.0.0 - 01 June 2005