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 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 .