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NAME
       posix_mem_offset - find offset and length of a mapped typed memory block (ADVANCED REALTIME)


SYNOPSIS
       #include <sys/mman.h>

       int posix_mem_offset(const void *restrict addr, size_t len,
              off_t *restrict off, size_t *restrict contig_len,
              int *restrict fildes);


DESCRIPTION
       The  posix_mem_offset()  function  shall return in the variable pointed to by off a value that identifies
       the offset (or location), within a memory object, of the memory  block  currently  mapped  at  addr.  The
       function shall return in the variable pointed to by fildes, the descriptor used (via mmap()) to establish
       the mapping which contains addr. If that descriptor was closed since the  mapping  was  established,  the
       returned  value  of  fildes shall be -1. The len argument specifies the length of the block of the memory
       object the user wishes the offset for; upon return, the value pointed to by contig_len shall equal either
       len,  or  the length of the largest contiguous block of the memory object that is currently mapped to the
       calling process starting at addr, whichever is smaller.

       If the memory object mapped at addr is a typed memory object, then  if  the  off  and  contig_len  values
       obtained by calling posix_mem_offset() are used in a call to mmap() with a file descriptor that refers to
       the same memory pool as fildes (either through the same port or through a different port), and  that  was
       opened  with neither the POSIX_TYPED_MEM_ALLOCATE nor the POSIX_TYPED_MEM_ALLOCATE_CONTIG flag, the typed
       memory area that is mapped shall be exactly the same area that was mapped at addr in the address space of
       the process that called posix_mem_offset().

       If the memory object specified by fildes is not a typed memory object, then the behavior of this function
       is implementation-defined.


RETURN VALUE
       Upon  successful  completion,  the  posix_mem_offset()  function  shall  return  zero;   otherwise,   the
       corresponding error status value shall be returned.


ERRORS
       The posix_mem_offset() function shall fail if:

       EACCES The process has not mapped a memory object supported by this function at the given address addr.

       This function shall not return an error code of [EINTR].

       The following sections are informative.


EXAMPLES
       None.


APPLICATION USAGE
       None.


RATIONALE
       None.


FUTURE DIRECTIONS
       None.


SEE ALSO
       mmap() , posix_typed_mem_open() , the Base Definitions volume of IEEE Std 1003.1-2001, <sys/mman.h>


       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc and The Open Group. In the event of any discrepancy between this version and the  original  IEEE  and
       The  Open  Group  Standard,  the  original  IEEE and The Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .