shmop(2)							   System Calls 							  shmop(2)

NAME

       shmop, shmat, shmdt - shared memory operations

SYNOPSIS

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

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

       int shmdt(char *shmaddr);

   Standard conforming
       int shmdt(const void *shmaddr);

DESCRIPTION

       The shmat() function attaches the shared memory segment associated with the shared memory identifier specified by shmid to the data segment
       of the calling process.

       The permission required for a shared memory control operation is given as {token}, where token is the type of permission needed. The  types
       of permission are interpreted as follows:

       00400	READ by user
       00200	WRITE by user
       00040	READ by group
       00020	WRITE by group
       00004	READ by others
       00002	WRITE by others

       See the Shared Memory Operation Permissions section of intro(2) for more information.

       When  (shmflg&SHM_SHARE_MMU)  is true, virtual memory resources in addition to shared memory itself are shared among processes that use the
       same shared memory.

       When (shmflg&SHM_PAGEABLE) is true, virtual memory resources are shared and the dynamic shared memory  (DISM)  framework  is  created.  The
       dynamic	shared	memory	can be resized dynamically within the specified size in shmget(2). The DISM shared memory is pageable unless it is
       locked.

       The shared memory segment is attached to the data segment of the calling process at the address specified based on one  of  the	 following
       criteria:

	 o  If shmaddr is equal to (void *) 0, the segment is attached to the first available address as selected by the system.

	 o  If	 shmaddr is equal to  (void *) 0 and ( shmflg&SHM_SHARE_MMU) or (shmflg&SHM_PAGEABLE) is true, then the segment is attached to the
	    first available suitably aligned address. When (shmflg&SHM_SHARE_MMU) or (shmflg&SHM_PAGEABLE) is set, however, the  permission  given
	    by	shmget() determines whether the segment is attached for reading or reading and writing.

	 o  If	shmaddr  is  not  equal  to  (void  *)	0 and (shmflg&SHM_RND) is true, the segment is attached to the address given by (shmaddr -
	    (shmaddr modulus SHMLBA)).

	 o  If shmaddr is not equal to (void *) 0 and (shmflg&SHM_RND) is false, the segment is attached to the address given by shmaddr.

	 o  The segment is attached for reading if (shmflg&SHM_RDONLY)	is  true  {READ},  otherwise  it  is  attached	for  reading  and  writing
	    {READ/WRITE}.

       The  shmdt()  function  detaches  from  the  calling  process's	data segment the shared memory segment located at the address specified by
       shmaddr. If the application is standard-conforming (see standards(5)), the shmaddr argument is of type const void *.  Otherwise	it  is	of
       type char *.

       Shared memory segments must be explicitly removed after the last reference to them has been removed.

RETURN VALUES

       Upon successful completion, shmat() returns the data segment start address of the attached shared memory segment; shmdt() returns 0. Other-
       wise, -1 is returned, the shared memory segment is not attached, and errno is set to indicate the error.

ERRORS

       The shmat() function will fail if:

       EACCES	       Operation permission is denied to the calling process (see intro(2)).

       EINVAL	       The shmid argument is not a valid shared memory identifier.

       EINVAL	       The shmaddr argument is not equal to 0, and the value of (shmaddr -  (shmaddr modulus SHMLBA)) is an illegal address.

       EINVAL	       The shmaddr argument is not equal to 0, is an illegal address, and (shmflg&SHM_RND) is false.

       EINVAL	       The shmaddr argument is not equal to 0, is not properly aligned, and (shmfg&SHM_SHARE_MMU) is true.

       EINVAL	       SHM_SHARE_MMU is not supported in certain architectures.

       EINVAL	       Both (shmflg&SHM_SHARE_MMU) and (shmflg&SHM_PAGEABLE) are true.

       EINVAL	       (shmflg&SHM_SHARE_MMU) is true and the shared memory segment specified by shmid() had previously been attached by a call to
		       shmat() in which (shmflg&SHM_PAGEABLE) was true.

		       (shmflg&SHM_PAGEABLE)  is true and the shared memory segment specified by shmid() had previously been attached by a call to
		       shmat() in which (shmflg&SHM_SHARE_MMU) was true.

       EMFILE	       The number of shared memory segments attached to the calling process would exceed the system-imposed limit.

       ENOMEM	       The available data space  is not large enough to accommodate the shared memory segment.

       The shmdt() function will fail if:

       EINVAL	       The shmaddr argument is not the data segment start address of a shared memory segment.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       intro(2), exec(2), exit(2), fork(2), shmctl(2), shmget(2), standards(5)

SunOS 5.10							    1 Sep 2003								  shmop(2)