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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>msync</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_007_835"> </a>NAME</h4><blockquote>msync - synchronise memory with physical storage</blockquote><h4><a name = "tag_000_007_836"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="sysmman.h.html">sys/mman.h</a>>int msync(void *<i>addr</i>, size_t <i>len</i>, int <i>flags</i>);</code></pre></blockquote><h4><a name = "tag_000_007_837"> </a>DESCRIPTION</h4><blockquote>The<i>msync()</i>function writes all modified data to permanent storage locations, if any,in those whole pages containing any part of theaddress space of the process starting at address<i>addr</i>and continuing for<i>len</i>bytes.If no such storage exists,<i>msync()</i>need not have any effect.If requested, the<i>msync()</i>function then invalidates cached copies of data.<p>The implementation willrequire that<i>addr</i>be a multiple of the page size as returned by<i><a href="sysconf.html">sysconf()</a></i>.<p>For mappings to files, the<i>msync()</i>function ensures that all write operations are completedas defined forsynchronised I/O data integrity completion.It is unspecified whether the implementation also writes outother file attributes.When the<i>msync()</i>function is called on MAP_PRIVATE mappings, any modified data willnot be written to the underlying objectand will not cause such data to be made visible to other processes.It is unspecified whether data in MAP_PRIVATEmappings has any permanent storage locations.The effect of<i>msync()</i>on shared memory objects is unspecified.<p>The<i>flags</i>argument is constructed from the bitwise inclusive OR of one or moreof the following flags defined in the header<i><a href="sysmman.h.html"><sys/mman.h></a></i>:<p><table bordercolor=#000000 border=1 align=center><tr valign=top><th align=center><b>Symbolic Constant</b><th align=center><b>Description</b><tr valign=top><td align=left>MS_ASYNC<td align=left>Perform asynchronous writes.<tr valign=top><td align=left>MS_SYNC<td align=left>Perform synchronous writes.<tr valign=top><td align=left>MS_INVALIDATE<td align=left>Invalidate cached data.</table><p>When MS_ASYNC is specified,<i>msync()</i>returns immediately once all the write operations areinitiated or queued for servicing; when MS_SYNC is specified,<i>msync()</i>will not return until all write operations are completedas defined for synchronised I/O data integrity completion.Either MS_ASYNC or MS_SYNC is specified, but not both.<p>When MS_INVALIDATE is specified,<i>msync()</i>invalidates all cached copies of mapped datathat are inconsistent with the permanent storage locationssuch that subsequent references obtain datathat was consistent with the permanent storage locationssometime between the call to<i>msync()</i>and the first subsequent memory reference to the data.<p>The behaviour of this function is unspecifiedif the mapping was not established by a call to<i><a href="mmap.html">mmap()</a></i>.<p>If<i>msync()</i>causes any write to a file, the file's<i>st_ctime</i>and<i>st_mtime</i>fields are marked for update.</blockquote><h4><a name = "tag_000_007_838"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>msync()</i>returns 0. Otherwise, it returns -1 and sets<i>errno</i> to indicate the error.</blockquote><h4><a name = "tag_000_007_839"> </a>ERRORS</h4><blockquote>The <i>msync()</i>function will fail if:<dl compact><dt>[EBUSY]<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 MS_INVALIDATE is specified.<dt>[EINVAL]<dd>The value in<i>flags</i>is invalid.<dt>[EINVAL]<dd>The value of<i>addr</i>is not a multiple of the page size, {PAGESIZE}.<dt>[ENOMEM]<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 address space of a processor specify one or more pages that are not mapped.</dl></blockquote><h4><a name = "tag_000_007_840"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_841"> </a>APPLICATION USAGE</h4><blockquote>The<i>msync()</i>function should be used by programs that require a memory object to be in aknown state, for example in building transaction facilities.<p>Normal system activity can cause pages to be written to disk. Therefore,there are no guarantees that<i>msync()</i>is the only control over when pages are or are not written to disk.<p>The second form of [EINVAL] above is marked EX because it is defined as anoptional error in the POSIX Realtime Extension.</blockquote><h4><a name = "tag_000_007_842"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_843"> </a>SEE ALSO</h4><blockquote><i><a href="mmap.html">mmap()</a></i>,<i><a href="sysconf.html">sysconf()</a></i>,<i><a href="sysmman.h.html"><sys/mman.h></a></i>.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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