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RocketLink!--> Man page versions: OpenBSD FreeBSD NetBSD Others

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

     shmat, shmdt - map/unmap shared memory

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

     void *
     shmat(int shmid, const void *shmaddr, int shmflg);

     shmdt(const void *shmaddr);

     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-

     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.

     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 sys-
                   tem-wide limit.

     shmdt() will fail if:

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

     mmap(2),  shmctl(2),  shmget(2)

OpenBSD 2.6                     August 17, 1995                              1

Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.

(Corrections, notes, and links courtesy of RocketAware.com)

[Detailed Topics]

[Overview Topics]

Up to: Memory blocks (Sometimes called "Byte Strings") - Memory blocks. Allocated, shared, mmaped, kernel et al

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