shmop(2)                                                    shmop(2)


       NAME
             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.





                           Copyright 1994 Novell, Inc.               Page 1

      shmop(2)                                                    shmop(2)


            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.











                          Copyright 1994 Novell, Inc.               Page 2