SHMOP(2)                             SysV                             SHMOP(2)



NAME
     shmop:  shmat, shmdt - shared memory operations

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

     char *shmat (shmid, shmaddr, shmflg)
     int shmid;
     char *shmaddr;
     int shmflg;

     int shmdt (shmaddr)
     char *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:

     o  If shmaddr is equal to 0, the segment is attached at the first
        available address as selected by the system.

     o  If shmaddr is not equal to 0 and (shmflg & SHM_RND) is "true", the
        segment is attached at the address given by (shmaddr - (shmaddr
        modulus SHMLBA)).

     o  If shmaddr is not equal to 0 and (shmflg & SHM_RND) is "false", the
        segment is attached at the address given by shmaddr.

     shmdt detaches from the calling process' 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}.

ERRORS
     shmat will fail and not attach the shared memory segment if one or more
     of the following are true:

     [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 0, and the value of (shmaddr -
                (shmaddr modulus SHMLBA)) is an illegal address.

     [EINVAL]   shmaddr is not equal to 0, (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.

     shmdt will fail and not detach the shared memory segment if the following
     is true:

     [EINVAL]   shmaddr is not the data segment start address of a shared
                memory segment.

SEE ALSO
     exec(2), exit(2), fork(2), intro(2), shmctl(2), shmget(2).

DIAGNOSTICS
     Upon successful completion, the return value is as follows:

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

     o  shmdt returns a value of 0.

     Otherwise, a value of -1 is returned and errno is set as indicated under
     "Errors."

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