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 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 POSIX.1‐2017, <sys_mman.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 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 .

       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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                              POSIX_MEM_OFFSET(3POSIX)