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 (con-
       sult 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  vari-
       able  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 spec-
       ifies  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 implementa-
       tion-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>

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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                          POSIX_MEM_OFFSET(3P)