MirOS Manual: shmat(2), shmdt(2)

SHMAT(2)                   BSD Programmer's Manual                    SHMAT(2)

NAME

     shmat, shmdt - map/unmap shared memory

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() maps the shared memory segment associated with the shared memory
     identifier shmid into the address space of the calling process. The ad-
     dress at which the segment is mapped is determined by the shmaddr parame-
     ter. If it is equal to 0, the system will pick an address itself. Other-
     wise, an attempt is made to map the shared memory segment at the address
     shmaddr specifies. If SHM_RND is set in shmflg, the system will round the
     address down to a multiple of SHMLBA bytes (SHMLBA is defined in
     <sys/shm.h>).

     A shared memory segment can be mapped read-only by specifying the
     SHM_RDONLY flag in shmflg.

     shmdt() unmaps the shared memory segment that is currently mapped at
     shmaddr from the calling process' address space. shmaddr must be a value
     returned by a prior shmat() call. A shared memory segment will remain ex-
     istent until it is removed by a call to shmctl(2) with the IPC_RMID com-
     mand.

RETURN VALUES

     shmat() returns the address at which the shared memory segment has been
     mapped into the calling process' address space when successful, shmdt()
     returns 0 on successful completion. Otherwise, a value of -1 is returned,
     and the global variable errno is set to indicate the error.

ERRORS

     shmat() will fail if:

     [EACCES]      The calling process has no permission to access this shared
                   memory segment.

     [ENOMEM]      There is not enough available data space for the calling
                   process to map the shared memory segment.

     [EINVAL]      shmid is not a valid shared memory identifier.

                   shmaddr specifies an illegal address.

     [EMFILE]      The number of shared memory segments has reached the
                   system-wide limit.

     shmdt() will fail if:

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

SEE ALSO

     ipcrm(1), ipcs(1), mmap(2), shmctl(2), shmget(2)

MirOS BSD #10-current          August 17, 1995                               1

Generated on 2014-07-04 21:17:45 by $MirOS: src/scripts/roff2htm,v 1.79 2014/02/10 00:36:11 tg Exp $

These manual pages and other documentation are copyrighted by their respective writers; their source is available at our CVSweb, AnonCVS, and other mirrors. The rest is Copyright © 2002‒2014 The MirOS Project, Germany.
This product includes material provided by Thorsten Glaser.

This manual page’s HTML representation is supposed to be valid XHTML/1.1; if not, please send a bug report – diffs preferred.