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 corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAMEposix_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 mem‐
ory 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 ALSOmmap(), 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 .
IEEE/The Open Group 2003 POSIX_MEM_OFFSET(3P)
