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Ref-docs/POSIX/susv3/functions/msync.html
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Ref-docs/POSIX/susv3/functions/msync.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>msync</title>
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</head>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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</script>
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<basefont size="3"> <a name="msync"></a> <a name="tag_03_397"></a><!-- msync -->
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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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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_397_01"></a>NAME</h4>
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<blockquote>msync - synchronize memory with physical storage</blockquote>
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<h4><a name="tag_03_397_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('MF SIO')">MF SIO</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 msync(void *</tt><i>addr</i><tt>, size_t</tt> <i>len</i><tt>, int</tt> <i>flags</i><tt>); <img src="../images/opt-end.gif"
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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_397_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>msync</i>() function shall write all modified data to permanent storage locations, if any, in those whole pages
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containing any part of the address space of the process starting at address <i>addr</i> and continuing for <i>len</i> bytes. If no
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such storage exists, <i>msync</i>() need not have any effect. If requested, the <i>msync</i>() function shall then invalidate
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cached copies of data.</p>
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<p>The implementation shall require that <i>addr</i> be a multiple of the page size as returned by <a href=
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"../functions/sysconf.html"><i>sysconf</i>()</a>.</p>
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<p>For mappings to files, the <i>msync</i>() function shall ensure that all write operations are completed as defined for
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synchronized I/O data integrity completion. It is unspecified whether the implementation also writes out other file attributes.
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When the <i>msync</i>() function is called on MAP_PRIVATE mappings, any modified data shall not be written to the underlying object
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and shall not cause such data to be made visible to other processes. It is unspecified whether data in MAP_PRIVATE mappings has any
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permanent storage locations. <sup>[<a href="javascript:open_code('SHM')">SHM|TYM</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> The effect of <i>msync</i>() on a shared memory object or a typed memory object is unspecified.
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<img src="../images/opt-end.gif" alt="[Option End]" border="0"> The behavior of this function is unspecified if the mapping was not
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established by a call to <a href="../functions/mmap.html"><i>mmap</i>()</a>.</p>
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<p>The <i>flags</i> argument is constructed from the bitwise-inclusive OR of one or more of the following flags defined in the <a
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href="../basedefs/sys/mman.h.html"><i><sys/mman.h></i></a> header:</p>
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<center>
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<table border="1" cellpadding="3" align="center">
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<tr valign="top">
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<th align="center">
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<p class="tent"><b>Symbolic Constant</b></p>
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</th>
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<th align="center">
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<p class="tent"><b>Description</b></p>
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</th>
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</tr>
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<tr valign="top">
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<td align="left">
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<p class="tent">MS_ASYNC</p>
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</td>
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<td align="left">
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<p class="tent">Perform asynchronous writes.</p>
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</td>
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</tr>
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<tr valign="top">
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<td align="left">
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<p class="tent">MS_SYNC</p>
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</td>
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<td align="left">
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<p class="tent">Perform synchronous writes.</p>
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</td>
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</tr>
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<tr valign="top">
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<td align="left">
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<p class="tent">MS_INVALIDATE</p>
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</td>
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<td align="left">
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<p class="tent">Invalidate cached data.</p>
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</td>
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</tr>
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</table>
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</center>
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<p>When MS_ASYNC is specified, <i>msync</i>() shall return immediately once all the write operations are initiated or queued for
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servicing; when MS_SYNC is specified, <i>msync</i>() shall not return until all write operations are completed as defined for
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synchronized I/O data integrity completion. Either MS_ASYNC or MS_SYNC is specified, but not both.</p>
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<p>When MS_INVALIDATE is specified, <i>msync</i>() shall invalidate all cached copies of mapped data that are inconsistent with the
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permanent storage locations such that subsequent references shall obtain data that was consistent with the permanent storage
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locations sometime between the call to <i>msync</i>() and the first subsequent memory reference to the data.</p>
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<p>If <i>msync</i>() causes any write to a file, the file's <i>st_ctime</i> and <i>st_mtime</i> fields shall be marked for
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update.</p>
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</blockquote>
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<h4><a name="tag_03_397_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>msync</i>() shall return 0; otherwise, it shall return -1 and set <i>errno</i> to indicate the
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error.</p>
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</blockquote>
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<h4><a name="tag_03_397_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>msync</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EBUSY]</dt>
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<dd>Some or all of the addresses in the range starting at <i>addr</i> and continuing for <i>len</i> bytes are locked, and
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MS_INVALIDATE is specified.</dd>
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<dt>[EINVAL]</dt>
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<dd>The value of <i>flags</i> is invalid.</dd>
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<dt>[EINVAL]</dt>
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<dd>The value of <i>addr</i> is not a multiple of the page size {PAGESIZE}.</dd>
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<dt>[ENOMEM]</dt>
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<dd>The addresses in the range starting at <i>addr</i> and continuing for <i>len</i> bytes are outside the range allowed for the
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address space of a process or specify one or more pages that are not mapped.</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_397_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_397_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>msync</i>() function is only supported if the Memory Mapped Files option and the Synchronized Input and Output option are
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supported, and thus need not be available on all implementations.</p>
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<p>The <i>msync</i>() function should be used by programs that require a memory object to be in a known state; for example, in
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building transaction facilities.</p>
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<p>Normal system activity can cause pages to be written to disk. Therefore, there are no guarantees that <i>msync</i>() is the only
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control over when pages are or are not written to disk.</p>
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</blockquote>
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<h4><a name="tag_03_397_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The <i>msync</i>() function writes out data in a mapped region to the permanent storage for the underlying object. The call to
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<i>msync</i>() ensures data integrity of the file.</p>
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<p>After the data is written out, any cached data may be invalidated if the MS_INVALIDATE flag was specified. This is useful on
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systems that do not support read/write consistency.</p>
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</blockquote>
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<h4><a name="tag_03_397_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_397_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="sysconf.html"><i>sysconf</i>()</a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../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_397_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 4, Version 2.</p>
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</blockquote>
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<h4><a name="tag_03_397_12"></a>Issue 5</h4>
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<blockquote>
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<p>Moved from X/OPEN UNIX extension to BASE.</p>
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<p>Aligned with <i>msync</i>() in the POSIX Realtime Extension as follows:</p>
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<ul>
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<li>
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<p>The DESCRIPTION is extensively reworded.</p>
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</li>
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<li>
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<p>[EBUSY] and a new form of [EINVAL] are added as mandatory error conditions.</p>
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</li>
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</ul>
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</blockquote>
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<h4><a name="tag_03_397_13"></a>Issue 6</h4>
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<blockquote>
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<p>The <i>msync</i>() function is marked as part of the Memory Mapped Files and Synchronized Input and Output options.</p>
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<p>The following changes are made for alignment with the ISO POSIX-1:1996 standard:</p>
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<ul>
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<li>
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<p>The [EBUSY] mandatory error condition is added.</p>
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</li>
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</ul>
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<p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p>
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<ul>
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<li>
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<p>The DESCRIPTION is updated to state that implementations require <i>addr</i> to be a multiple of the page size.</p>
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</li>
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<li>
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<p>The second [EINVAL] error condition is made mandatory.</p>
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</li>
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</ul>
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<p>The DESCRIPTION is updated for alignment with IEEE Std 1003.1j-2000 by adding reference to typed memory objects.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<hr size="2" noshade>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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