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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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POSIX_MEM_OFFSET(3P) POSIX Programmer's Manual POSIX_MEM_OFFSET(3P)
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.
posix_mem_offset — find offset and length of a mapped typed memory
block (ADVANCED REALTIME)
#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);
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.
Upon successful completion, the posix_mem_offset() function shall
return zero; otherwise, the corresponding error status value shall
be returned.
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.
None.
None.
None.
None.
mmap(3p), posix_typed_mem_open(3p)
The Base Definitions volume of POSIX.1‐2017, sys_mman.h(0p)
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 .
IEEE/The Open Group 2017 POSIX_MEM_OFFSET(3P)
Pages that refer to this page: sys_mman.h(0p), posix_typed_mem_open(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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