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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>msync</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="msync"></a> <a name="tag_03_397"></a><!-- msync --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_397_01"></a>NAME</h4><blockquote>msync - synchronize memory with physical storage</blockquote><h4><a name="tag_03_397_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('MF SIO')">MF SIO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/sys/mman.h.html">sys/mman.h</a>><br><br> 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"alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_397_03"></a>DESCRIPTION</h4><blockquote><p>The <i>msync</i>() function shall write all modified data to permanent storage locations, if any, in those whole pagescontaining any part of the address space of the process starting at address <i>addr</i> and continuing for <i>len</i> bytes. If nosuch storage exists, <i>msync</i>() need not have any effect. If requested, the <i>msync</i>() function shall then invalidatecached copies of data.</p><p>The implementation shall require that <i>addr</i> be a multiple of the page size as returned by <a href="../functions/sysconf.html"><i>sysconf</i>()</a>.</p><p>For mappings to files, the <i>msync</i>() function shall ensure that all write operations are completed as defined forsynchronized I/O data integrity completion. It is unspecified whether the implementation also writes out other file attributes.When the <i>msync</i>() function is called on MAP_PRIVATE mappings, any modified data shall not be written to the underlying objectand shall not cause such data to be made visible to other processes. It is unspecified whether data in MAP_PRIVATE mappings has anypermanent storage locations. <sup>[<a href="javascript:open_code('SHM')">SHM|TYM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The effect of <i>msync</i>() on a shared memory object or a typed memory object is unspecified.<img src="../images/opt-end.gif" alt="[Option End]" border="0"> The behavior of this function is unspecified if the mapping was notestablished by a call to <a href="../functions/mmap.html"><i>mmap</i>()</a>.</p><p>The <i>flags</i> argument is constructed from the bitwise-inclusive OR of one or more of the following flags defined in the <ahref="../basedefs/sys/mman.h.html"><i><sys/mman.h></i></a> header:</p><center><table border="1" cellpadding="3" align="center"><tr valign="top"><th align="center"><p class="tent"><b>Symbolic Constant</b></p></th><th align="center"><p class="tent"><b>Description</b></p></th></tr><tr valign="top"><td align="left"><p class="tent">MS_ASYNC</p></td><td align="left"><p class="tent">Perform asynchronous writes.</p></td></tr><tr valign="top"><td align="left"><p class="tent">MS_SYNC</p></td><td align="left"><p class="tent">Perform synchronous writes.</p></td></tr><tr valign="top"><td align="left"><p class="tent">MS_INVALIDATE</p></td><td align="left"><p class="tent">Invalidate cached data.</p></td></tr></table></center><p>When MS_ASYNC is specified, <i>msync</i>() shall return immediately once all the write operations are initiated or queued forservicing; when MS_SYNC is specified, <i>msync</i>() shall not return until all write operations are completed as defined forsynchronized I/O data integrity completion. Either MS_ASYNC or MS_SYNC is specified, but not both.</p><p>When MS_INVALIDATE is specified, <i>msync</i>() shall invalidate all cached copies of mapped data that are inconsistent with thepermanent storage locations such that subsequent references shall obtain data that was consistent with the permanent storagelocations sometime between the call to <i>msync</i>() and the first subsequent memory reference to the data.</p><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 forupdate.</p></blockquote><h4><a name="tag_03_397_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, <i>msync</i>() shall return 0; otherwise, it shall return -1 and set <i>errno</i> to indicate theerror.</p></blockquote><h4><a name="tag_03_397_05"></a>ERRORS</h4><blockquote><p>The <i>msync</i>() function shall fail if:</p><dl compact><dt>[EBUSY]</dt><dd>Some or all of the addresses in the range starting at <i>addr</i> and continuing for <i>len</i> bytes are locked, andMS_INVALIDATE is specified.</dd><dt>[EINVAL]</dt><dd>The value of <i>flags</i> is invalid.</dd><dt>[EINVAL]</dt><dd>The value of <i>addr</i> is not a multiple of the page size {PAGESIZE}.</dd><dt>[ENOMEM]</dt><dd>The addresses in the range starting at <i>addr</i> and continuing for <i>len</i> bytes are outside the range allowed for theaddress space of a process or specify one or more pages that are not mapped.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_397_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_397_07"></a>APPLICATION USAGE</h4><blockquote><p>The <i>msync</i>() function is only supported if the Memory Mapped Files option and the Synchronized Input and Output option aresupported, and thus need not be available on all implementations.</p><p>The <i>msync</i>() function should be used by programs that require a memory object to be in a known state; for example, inbuilding transaction facilities.</p><p>Normal system activity can cause pages to be written to disk. Therefore, there are no guarantees that <i>msync</i>() is the onlycontrol over when pages are or are not written to disk.</p></blockquote><h4><a name="tag_03_397_08"></a>RATIONALE</h4><blockquote><p>The <i>msync</i>() function writes out data in a mapped region to the permanent storage for the underlying object. The call to<i>msync</i>() ensures data integrity of the file.</p><p>After the data is written out, any cached data may be invalidated if the MS_INVALIDATE flag was specified. This is useful onsystems that do not support read/write consistency.</p></blockquote><h4><a name="tag_03_397_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_397_10"></a>SEE ALSO</h4><blockquote><p><a href="mmap.html"><i>mmap</i>()</a> , <a href="sysconf.html"><i>sysconf</i>()</a> , the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/sys/mman.h.html"><i><sys/mman.h></i></a></p></blockquote><h4><a name="tag_03_397_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4, Version 2.</p></blockquote><h4><a name="tag_03_397_12"></a>Issue 5</h4><blockquote><p>Moved from X/OPEN UNIX extension to BASE.</p><p>Aligned with <i>msync</i>() in the POSIX Realtime Extension as follows:</p><ul><li><p>The DESCRIPTION is extensively reworded.</p></li><li><p>[EBUSY] and a new form of [EINVAL] are added as mandatory error conditions.</p></li></ul></blockquote><h4><a name="tag_03_397_13"></a>Issue 6</h4><blockquote><p>The <i>msync</i>() function is marked as part of the Memory Mapped Files and Synchronized Input and Output options.</p><p>The following changes are made for alignment with the ISO POSIX-1:1996 standard:</p><ul><li><p>The [EBUSY] mandatory error condition is added.</p></li></ul><p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p><ul><li><p>The DESCRIPTION is updated to state that implementations require <i>addr</i> to be a multiple of the page size.</p></li><li><p>The second [EINVAL] error condition is made mandatory.</p></li></ul><p>The DESCRIPTION is updated for alignment with IEEE Std 1003.1j-2000 by adding reference to typed memory objects.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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