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.

       For shared memory segments created with the SHM_SHARE_MMU or SHM_PAGEABLE flags, the default protections cannot be changed so as to prevent
       a single process from affecting other processes sharing the same shared segment.

       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 per-
		  mission 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.

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

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

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

		 SHM_SHARE_MMU is not supported in certain architectures.

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

		 (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.

       ENOMEM	 (shmflg&SHM_SHARE_MMU) is true and attaching to the shared memory segment would exceed a limit or resource control on locked mem-
		 ory.

WARNINGS

       Using a fixed value for the shmaddr argument can adversely affect performance on certain platforms due to D-cache aliasing.

ATTRIBUTES

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

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Committed 		   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+
       |Standard		     |See standards(5). 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       Intro(2), exec(2), exit(2), fork(2), shmctl(2), shmget(2), attributes(5), standards(5)

SunOS 5.11							    10 Mar 2008 							  shmop(2)