shmat

Attach a shared memory block.

Declaration

Source position: ipc.pp line 406

Description

shmat attaches a shared memory block with identified shmid to the current process. The function returns a pointer to the shared memory block.

If shmaddr is Nil, then the system chooses a free unmapped memory region, as high up in memory space as possible.

If shmaddr is non-nil, and SHM_RND is in shmflg, then the returned address is shmaddr, rounded down to SHMLBA. If SHM_RND is not specified, then shmaddr must be a page-aligned address.

The parameter shmflg can be used to control the behaviour of the shmat call. It consists of a ORed combination of the following constants:

SHM_RND

The suggested address in shmaddr is rounded down to SHMLBA.

SHM_RDONLY

the shared memory is attached for read access only. Otherwise the memory is attached for read-write. The process then needs read-write permissions to access the shared memory.

For an example, see shmctl.

Errors

If an error occurs, -1 is returned, and IPCerror is set.

See also