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.1‐2008, <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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .