POSIX_MEM_OFFSET
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
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.1-2017,
<sys_mman.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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 .
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 .