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.
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
If the memory object specified by fildes is not a typed memory
object, then the behavior of this function is implementation-defined.
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.
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
IEEE/The Open Group 2013 POSIX_MEM_OFFSET(3P)