NAME

shmop, shmat, shmdt − shared memory operations

SYNOPSIS

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

void ∗shmat(int shmid, void ∗shmaddr, int shmflg);

int shmdt(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 permission required for a shared memory control operation is given as {token}, where token is the type of permission needed.  The types of permission are interpreted as follows:

 00400READ by user
00200WRITE by user
00040READ by group
00020WRITE by group
00004READ by others
00002WRITE by others
 

See the Shared Memory Operation Permissions section of intro(2) for more information. 

The data segment of the calling process 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

Upon successful completion, the return value is as follows:

shmat() returns the data segment start address of the attached shared memory segment. 

shmdt() returns a value of 0. 

Otherwise, a value of −1 is returned and errno is set to indicate the error. 

ERRORS

shmat() fails and does not attach the shared memory segment if one or more of the following are true:

EACCES Operation permission is denied to the calling process (see intro(2)). 

EINVAL shmid is not a valid shared memory identifier. 

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. 

EINVAL shmdt() fails and does not detach the shared memory segment if shmaddr is not the data segment start address of a shared memory segment. 

EMFILE The number of shared memory segments attached to the calling process would exceed the system-imposed limit. 

ENOMEM The available data space is not large enough to accommodate the shared memory segment. 

SEE ALSO

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

NOTES

The user must explicitly remove shared memory segments after the last reference to them has been removed. 

SunOS 5.1/SPARC  —  Last change: 29 Jul 1991