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 correspond-
       ing 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 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 Technol-
       ogy -- 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 .

IEEE
/The Open Group						       2003						      POSIX_MEM_OFFSET(3P)