NAME    [Toc]    [Back]

     shmat, shmdt -- attach or detach shared memory

LIBRARY    [Toc]    [Back]

     Standard C Library (libc, -lc)

SYNOPSIS    [Toc]    [Back]

     #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    [Toc]    [Back]

     The shmat() system call 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.

     The shmdt() system call detaches the shared memory segment at the address
     specified by addr from the calling process's address space.

RETURN VALUES    [Toc]    [Back]

     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.

ERRORS    [Toc]    [Back]

     The shmat() system call will fail if:

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

     [EINVAL]		The addr argument was not an acceptable address.

     The shmdt() system call will fail if:

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

SEE ALSO    [Toc]    [Back]

     shmctl(2), shmget(2)


FreeBSD 5.2.1			August 2, 1995			 FreeBSD 5.2.1