shmop(2)                                                 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 seg-
          ment of the calling process.  The segment is attached at the
          address specified by one of the following criteria:

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

               If shmaddr is not equal to zero 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 zero and (shmflg & SHM_RND)
               is ``false,'' the segment is attached at the address
               given by shmaddr.

          The segment is attached for reading if (shmflg & SHM_RDONLY)
          is ``true'', otherwise it is attached for reading and writ-
          ing.

     RETURN VALUES
          Upon successful completion, the return value is as follows:

               shmat returns the data segment start address of the at-
               tached shared memory segment.

               shmdt returns a value of 0.

          Otherwise, a value of -1 is returned and errno is set to in-
          dicate the error.

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




     April, 1990                                                     1

     shmop(2)                                                 shmop(2)



          [EINVAL]       shmid is not a valid shared memory identif-
                         ier.

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

          [EAGAIN]       The system has temporarily exhausted its
                         available memory or swap space.

          [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.

          [EINVAL]       shmdt detaches from the calling process's
                         data segment the shared memory segment locat-
                         ed at the address specified by shmaddr.

          [EINVAL]       shmdt will fail and not detach the shared
                         memory segment if shmaddr is not the data
                         segment start address of a shared memory seg-
                         ment.

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




















     2                                                     April, 1990