184 lines
6.3 KiB
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184 lines
6.3 KiB
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<title>posix_madvise</title>
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<basefont size="3"> <a name="posix_madvise"></a> <a name="tag_03_423"></a><!-- posix_madvise -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<hr size="2" noshade>
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<h4><a name="tag_03_423_01"></a>NAME</h4>
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<blockquote>posix_madvise - memory advisory information and alignment control (<b>ADVANCED REALTIME</b>)</blockquote>
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<h4><a name="tag_03_423_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('ADV')">ADV</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/sys/mman.h.html">sys/mman.h</a>><br>
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<br>
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int posix_madvise(void *</tt><i>addr</i><tt>, size_t</tt> <i>len</i><tt>, int</tt> <i>advice</i><tt>); <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_423_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p><sup>[<a href="javascript:open_code('MF')">MF|SHM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The <i>posix_madvise</i>() function need only be supported if either the Memory Mapped Files or the Shared Memory Objects options
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are supported. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p>The <i>posix_madvise</i>() function shall advise the implementation on the expected behavior of the application with respect to
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the data in the memory starting at address <i>addr</i>, and continuing for <i>len</i> bytes. The implementation may use this
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information to optimize handling of the specified data. The <i>posix_madvise</i>() function shall have no effect on the semantics
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of access to memory in the specified range, although it may affect the performance of access.</p>
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<p>The implementation may require that <i>addr</i> be a multiple of the page size, which is the value returned by <a href=
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"../functions/sysconf.html"><i>sysconf</i>()</a> when the name value _SC_PAGESIZE is used.</p>
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<p>The advice to be applied to the memory range is specified by the <i>advice</i> parameter and may be one of the following
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values:</p>
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<dl compact>
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<dt>POSIX_MADV_NORMAL</dt>
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<dd><br>
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Specifies that the application has no advice to give on its behavior with respect to the specified range. It is the default
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characteristic if no advice is given for a range of memory.</dd>
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<dt>POSIX_MADV_SEQUENTIAL</dt>
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<dd><br>
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Specifies that the application expects to access the specified range sequentially from lower addresses to higher addresses.</dd>
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<dt>POSIX_MADV_RANDOM</dt>
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<dd><br>
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Specifies that the application expects to access the specified range in a random order.</dd>
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<dt>POSIX_MADV_WILLNEED</dt>
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<dd><br>
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Specifies that the application expects to access the specified range in the near future.</dd>
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<dt>POSIX_MADV_DONTNEED</dt>
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<dd><br>
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Specifies that the application expects that it will not access the specified range in the near future.</dd>
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</dl>
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<p>These values are defined in the <a href="../basedefs/sys/mman.h.html"><i><sys/mman.h></i></a> header.</p>
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</blockquote>
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<h4><a name="tag_03_423_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>posix_madvise</i>() shall return zero; otherwise, an error number shall be returned to indicate
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the error.</p>
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</blockquote>
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<h4><a name="tag_03_423_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>posix_madvise</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The value of <i>advice</i> is invalid.</dd>
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<dt>[ENOMEM]</dt>
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<dd>Addresses in the range starting at <i>addr</i> and continuing for <i>len</i> bytes are partly or completely outside the range
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allowed for the address space of the calling process.</dd>
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</dl>
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<p>The <i>posix_madvise</i>() function may fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The value of <i>addr</i> is not a multiple of the value returned by <a href="../functions/sysconf.html"><i>sysconf</i>()</a>
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when the name value _SC_PAGESIZE is used.</dd>
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<dt>[EINVAL]</dt>
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<dd>The value of <i>len</i> is zero.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_423_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_423_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>posix_madvise</i>() function is part of the Advisory Information option and need not be provided on all
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implementations.</p>
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</blockquote>
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<h4><a name="tag_03_423_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_423_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_423_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="mmap.html"><i>mmap</i>()</a> , <a href="posix_fadvise.html"><i>posix_fadvise</i>()</a> , <a href=
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"sysconf.html"><i>sysconf</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/sys/mman.h.html"><i><sys/mman.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_423_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 6. Derived from IEEE Std 1003.1d-1999.</p>
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<p>IEEE PASC Interpretation 1003.1 #102 is applied.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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