1POSIX_MEM_OFFSET(P)        POSIX Programmer's Manual       POSIX_MEM_OFFSET(P)
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NAME

6       posix_mem_offset  -  find  offset  and  length of a mapped typed memory
7       block (ADVANCED REALTIME)
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SYNOPSIS

10       #include <sys/mman.h>
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12       int posix_mem_offset(const void *restrict addr, size_t len,
13              off_t *restrict off, size_t *restrict contig_len,
14              int *restrict fildes);
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DESCRIPTION

18       The posix_mem_offset() function shall return in the variable pointed to
19       by  off a value that identifies the offset (or location), within a mem‐
20       ory object, of the memory block currently mapped at addr. The  function
21       shall  return in the variable pointed to by fildes, the descriptor used
22       (via mmap()) to establish the mapping  which  contains  addr.  If  that
23       descriptor  was  closed since the mapping was established, the returned
24       value of fildes shall be -1. The len argument specifies the  length  of
25       the  block  of  the  memory object the user wishes the offset for; upon
26       return, the value pointed to by contig_len shall equal either  len,  or
27       the length of the largest contiguous block of the memory object that is
28       currently mapped to the calling process starting at addr, whichever  is
29       smaller.
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31       If  the  memory object mapped at addr is a typed memory object, then if
32       the off and contig_len values obtained  by  calling  posix_mem_offset()
33       are  used in a call to mmap() with a file descriptor that refers to the
34       same memory pool as fildes (either through the same port or  through  a
35       different    port),    and   that   was   opened   with   neither   the
36       POSIX_TYPED_MEM_ALLOCATE nor the POSIX_TYPED_MEM_ALLOCATE_CONTIG  flag,
37       the  typed  memory  area  that is mapped shall be exactly the same area
38       that was mapped at addr in the address space of the process that called
39       posix_mem_offset().
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41       If  the memory object specified by fildes is not a typed memory object,
42       then the behavior of this function is implementation-defined.
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RETURN VALUE

45       Upon  successful  completion,  the  posix_mem_offset()  function  shall
46       return  zero;  otherwise, the corresponding error status value shall be
47       returned.
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ERRORS

50       The posix_mem_offset() function shall fail if:
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52       EACCES The process has not mapped a memory  object  supported  by  this
53              function at the given address addr.
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56       This function shall not return an error code of [EINTR].
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58       The following sections are informative.
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EXAMPLES

61       None.
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APPLICATION USAGE

64       None.
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RATIONALE

67       None.
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FUTURE DIRECTIONS

70       None.
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SEE ALSO

73       mmap()  ,  posix_typed_mem_open()  ,  the  Base  Definitions  volume of
74       IEEE Std 1003.1-2001, <sys/mman.h>
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77       Portions of this text are reprinted and reproduced in  electronic  form
78       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
79       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
80       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
81       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
82       event of any discrepancy between this version and the original IEEE and
83       The Open Group Standard, the original IEEE and The Open Group  Standard
84       is  the  referee document. The original Standard can be obtained online
85       at http://www.opengroup.org/unix/online.html .
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89IEEE/The Open Group                  2003                  POSIX_MEM_OFFSET(P)
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