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POSIX_MEM_OFFSET(3P)       POSIX Programmer's Manual      POSIX_MEM_OFFSET(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
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  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
       None.
APPLICATION USAGE
       None.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       mmap(), posix_typed_mem_open()
       The Base Definitions volume of POSIX.1-2008, <sys_mman.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) 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.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                 POSIX_MEM_OFFSET(3P)