1POSIX_TYPED_MEM_GET_INFO(3P)POSIX Programmer's ManuaPlOSIX_TYPED_MEM_GET_INFO(3P)
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PROLOG

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

13       posix_typed_mem_get_info — query  typed  memory  information  (ADVANCED
14       REALTIME)
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SYNOPSIS

17       #include <sys/mman.h>
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19       int posix_typed_mem_get_info(int fildes,
20           struct posix_typed_mem_info *info);
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DESCRIPTION

23       The   posix_typed_mem_get_info()   function   shall   return,   in  the
24       posix_tmi_length field of the posix_typed_mem_info structure pointed to
25       by  info, the maximum length which may be successfully allocated by the
26       typed memory object designated by fildes.  This  maximum  length  shall
27       take    into    account    the    flag    POSIX_TYPED_MEM_ALLOCATE   or
28       POSIX_TYPED_MEM_ALLOCATE_CONTIG specified when the typed memory  object
29       represented by fildes was opened. The maximum length is dynamic; there‐
30       fore, the value returned is valid only while the current mapping of the
31       corresponding typed memory pool remains unchanged.
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33       If  fildes  represents  a  typed  memory object opened with neither the
34       POSIX_TYPED_MEM_ALLOCATE flag nor  the  POSIX_TYPED_MEM_ALLOCATE_CONTIG
35       flag specified, the returned value of info->posix_tmi_length is unspec‐
36       ified.
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38       The posix_typed_mem_get_info() function may return additional implemen‐
39       tation-defined  information in other fields of the posix_typed_mem_info
40       structure pointed to by info.
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42       If the memory object specified by fildes is not a typed memory  object,
43       then the behavior of this function is undefined.
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RETURN VALUE

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

51       The posix_typed_mem_get_info() function shall fail if:
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53       EBADF  The fildes argument is not a valid open file descriptor.
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55       ENODEV The  fildes  argument  is  not connected to a memory object sup‐
56              ported by this function.
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58       This function shall not return an error code of [EINTR].
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60       The following sections are informative.
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EXAMPLES

63       None.
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APPLICATION USAGE

66       None.
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RATIONALE

69       An application that needs to allocate a  block  of  typed  memory  with
70       length  dependent  upon  the  amount of memory currently available must
71       either query the typed memory object to obtain the amount available, or
72       repeatedly  invoke  mmap()  attempting  to guess an appropriate length.
73       While the latter method is existing practice with malloc(), it is  awk‐
74       ward  and  imprecise. The posix_typed_mem_get_info() function allows an
75       application to immediately determine available memory. This is particu‐
76       larly  important  for  typed  memory  objects that may in some cases be
77       scarce resources. Note that when  a  typed  memory  pool  is  a  shared
78       resource,  some  form  of  mutual-exclusion  or  synchronization may be
79       required while typed memory is being queried and allocated  to  prevent
80       race conditions.
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82       The  existing  fstat()  function  is  not suitable for this purpose. We
83       realize that implementations may wish to provide  other  attributes  of
84       typed  memory  objects (for example, alignment requirements, page size,
85       and so on).  The fstat() function returns  a  structure  which  is  not
86       extensible  and,  furthermore, contains substantial information that is
87       inappropriate for typed memory objects.
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FUTURE DIRECTIONS

90       None.
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SEE ALSO

93       fstat(), mmap(), posix_typed_mem_open()
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95       The Base Definitions volume of POSIX.1‐2008, <sys_mman.h>
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98       Portions of this text are reprinted and reproduced in  electronic  form
99       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
100       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
101       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
102       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
103       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
104       event of any discrepancy between this version and the original IEEE and
105       The  Open Group Standard, the original IEEE and The Open Group Standard
106       is the referee document. The original Standard can be  obtained  online
107       at http://www.unix.org/online.html .
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109       Any  typographical  or  formatting  errors that appear in this page are
110       most likely to have been introduced during the conversion of the source
111       files  to  man page format. To report such errors, see https://www.ker
112       nel.org/doc/man-pages/reporting_bugs.html .
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116IEEE/The Open Group                  2013         POSIX_TYPED_MEM_GET_INFO(3P)
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