shmop(2)                  AT&T SYSTEM V                  shmop(2)



NAME
     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'' {READ}; otherwise it is attached for reading and
     writing {READ/WRITE}.

     If (shmflg & SHM_FLMEM) is ``true'', then allow an attach-
     ment to a shared memory segment even when it is bound to a
     foreign local memory.  When this bit is set, mpadvise(2)
     will ignore this shared memory segment's memory bindings
     when validating a new cpu bias mask for this process.  See
     the mpadvise(2) man for more information on setting a
     process's cpu bias mask.

     Shmdt detaches from the calling process's data segment the
     shared memory segment located at the address specified by
     shmaddr.

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




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

     [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.

     [EACCES]       The shared memory region referenced by shmid
                    is loaded into the local memory of a proces-
                    sor other than the one the calling process is
                    executing on, and (shmflg & SHM_FLMEM) is
                    ``false''.  A region loaded into a given
                    processor's local memory can normally only be
                    accessed by processes being executed on that
                    CPU [see memory(7)].

     [EINVAL]       The shared memory segment specified by shmid
                    is in physical memory and a shmbind(2) call
                    has not yet been made [see shmbind(2)].

     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), mpadvise(2), shmctl(2),
     shmget(2), shmbind(2).
     ipcrm(1), ipcs(1), shmdefine(1) in the CX/UX User's Refer-
     ence Manual.
     memory(7) in the CX/UX Administrator's Reference Manual.

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






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shmop(2)                  AT&T SYSTEM V                  shmop(2)



          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.

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












































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