POSIX_MEM_OFFSET(3)        POSIX Programmer's Manual       POSIX_MEM_OFFSET(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 .



IEEE/The Open Group                  2017                  POSIX_MEM_OFFSET(3)
