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

COPYRIGHT
       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 .