DragonFly On-Line Manual Pages

SHMAT(2)                 DragonFly System Calls Manual                SHMAT(2)

NAME
     shmat, shmdt -- attach or detach shared memory

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <machine/param.h>
     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/shm.h>

     void *
     shmat(int shmid, const void *addr, int flag);

     int
     shmdt(const void *addr);

DESCRIPTION
     Shmat() attaches the shared memory segment identified by shmid to the
     calling process's address space.  The address where the segment is
     attached is determined as follows:

     o   If addr is 0, the segment is attached at an address selected by the
         kernel.

     o   If addr is nonzero and SHM_RND is not specified in flag, the segment
         is attached the specified address.

     o   If addr is specified and SHM_RND is specified, addr is rounded down
         to the nearest multiple of SHMLBA.

     Shmdt() detaches the shared memory segment at the address specified by
     addr from the calling process's address space.

RETURN VALUES
     Upon success, shmat() returns the address where the segment is attached;
     otherwise, -1 is returned and errno is set to indicate the error.

     The shmdt() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ENVIRONMENT
     The XSI Interprocess Communication family of functions is also available
     as an implementation in userspace.  To use it, the sysvipcd(8) daemon has
     to be running.

     If the USR_SYSVIPC variable is set in a process' environment, the process
     and its children will use the userspace implementation.

ERRORS
     Shmat() will fail if:

     [EINVAL]           No shared memory segment was found corresponding to
                        shmid.

     [EINVAL]           addr was not an acceptable address.

     Shmdt() will fail if:

     [EINVAL]           addr does not point to a shared memory segment.

SEE ALSO
     shmctl(2), shmget(2)

AUTHORS
     The DragonFly specific userspace implementation (see ENVIRONMENT) was
     written by Larisa Grigore.

DragonFly 4.3                   January 4, 2014                  DragonFly 4.3