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shmop(2)


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:

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:

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(2)].

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(2), exit(2), fork(2), intro(2), shmctl(2), shmget(2)

Notices

The user must explicitly remove shared memory segments after the last reference to them has been removed.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004