307 lines
8.5 KiB
HTML
307 lines
8.5 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>munmap()--Remove Memory Mapping</title>
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<!-- Begin Header Records -->
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<!-- Change History: -->
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<!-- YYMMDD USERID Change description -->
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<!-- MUNMAP SCRIPT A converted by B2H R4.1 (346) (CMS) by V2CDIJAB at -->
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<!-- RCHVMW2 on 19 Sep 2000 at 14:19:56 -->
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<!-- 011108 JTROUS Changes from CL Review 1, V5R2 -->
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<!-- 0205?? JET This file has undergone html cleanup -->
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<!-- 020918 Rosckes: Add ENOTAVAIL errno description, V5R3 -->
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<!-- 050404 JTROUS: fix enums, no change flag, V5R4 -->
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<!-- 050404 JTROUS Add note on tagged pointers, V5R4 -->
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<!-- End Header Records -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<!-- Java sync-link -->
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<script language="Javascript" src="../rzahg/synch.js" type="text/javascript">
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</script>
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<a name="Top_Of_Page"></a>
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<h2>munmap()--Remove Memory Mapping</h2>
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<div class="box" style="width: 60%;">
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<br>
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Syntax<br>
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<pre>
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#include <sys/types.h>
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#include <sys/mman.h>
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int munmap ( void <em>*addr</em>,
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size_t <em>len</em> );
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</pre>
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Service Program Name: QP0LLIB1<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE<br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <strong>munmap()</strong> function removes addressability to a range of
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memory mapped pages of a process's address space. All pages starting with <em>
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addr</em> and continuing for a length of <em>len</em> bytes are removed.</p>
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<p>The address range specified must begin on a page boundary. Portions of the
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specified address range which are not mapped, or were not established by the
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<strong>mmap()</strong> function, are not affected by the <strong>
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munmap()</strong> function.</p>
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<p>If the mapping was created <strong><em>MAP_PRIVATE</em></strong> then any
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private altered pages are discarded and the system storage associated with the
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copies are returned to the system free space.</p>
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<p>When the mapping is removed, the reference associated with the pages mapped
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over the file is removed. If the file has no references other than those due to
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memory mapping and the remaining memory mappings are removed by the <strong>
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munmap()</strong> function, then the file becomes unreferenced. If the file
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becomes unreferenced due to an <strong>munmap()</strong> function call and the
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file is no longer linked, then the file will be deleted.</p>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong><em>addr</em></strong></dt>
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<dd>The starting address of the memory region being removed.
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<p>The <em>addr</em> parameter must be a multiple of the page size. The value
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zero or NULL is not a valid starting address. The <strong>sysconf()</strong>
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function may be used to determine the system page size.<br>
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<br>
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</p>
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</dd>
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<dt><strong><em>len</em></strong></dt>
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<dd>(Input) The length of the address range. All whole pages beginning with
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<em>addr</em> for a length of <em>len</em> are included in the address
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range.</dd>
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</dl>
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<br>
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<h3>Authorities</h3>
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<p>No authorization is required.</p>
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<br>
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<h3>Return Value</h3>
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<p>Upon successful completion, the <strong>munmap()</strong> function returns
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0. Upon failure, -1 is returned and errno is set to the appropriate error
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number.</p>
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<br>
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<h3>Error Conditions</h3>
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<p>When the <strong>munmap()</strong> function fails, it returns -1 and sets
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errno as follows.</p>
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<table cellpadding="5">
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<!-- cols="25 75" -->
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<tr>
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<th align="left" valign="bottom">Error condition</th>
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<th align="left" valign="bottom">Additional information</th>
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</tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#EINVAL">EINVAL</a>]</em></td>
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<td align="left" valign="top">
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<p>For example, for <strong>munmap()</strong> this may mean that the address range from <em>
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addr</em> and continuing for a length of <em>len</em> is outside the valid
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range allowed for a process. This error may also indicate that the value for
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the <em>addr</em> parameter is not a multiple of the page size. A value of 0
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for parameter <em>len</em> also will result in this error number.</p>
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</td></tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#ENOTAVAIL">ENOTAVAIL</a>]</em></td>
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<td align="left" valign="top">
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</td>
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</tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#EUNKNOWN">EUNKNOWN</a>]</em></td>
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<td align="left" valign="top">
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</td>
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</tr>
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</table>
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<br>
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<br>
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<h3>Error Messages</h3>
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<p>The following messages may be sent from this function.</p>
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<table width="100%">
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<tr>
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<th align="left" valign="top">Message ID</th>
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<th align="left" valign="top">Error Message Text</th>
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</tr>
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<tr>
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<td width="15%" valign="top">CPE3418 E</td>
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<td width="85%" valign="top">Possible APAR condition or hardware failure.</td>
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</tr>
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<tr>
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<td valign="top">CPFA0D4 E</td>
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<td valign="top">File system error occurred. Error number &1.</td>
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</tr>
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<tr>
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<td valign="top">CPF3CF2 E</td>
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<td valign="top">Error(s) occurred during running of &1 API.</td>
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</tr>
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<tr>
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<td valign="top">CPF9872 E</td>
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<td valign="top">Program or service program &1 in library &2 ended.
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Reason code &3.</td>
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</tr>
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</table>
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<br>
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<h3>Usage Notes</h3>
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<ol>
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<li>The address pointer that was returned by <strong>mmap()</strong> can only
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be used with the V4R4M0 or later versions of the following languages:
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<ul>
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<li>ILE COBOL</li>
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<li>ILE RPG</li>
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<li>ILE C if the TERASPACE parameter is used when compiling the program.</li>
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</ul>
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<br>
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</li>
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<li>
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<img src="delta.gif" alt="Start of change">
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The application cannot write or store any data via the memory mapping which
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includes any tagged (16-byte) pointers because the pointer attribute will be lost.
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Some examples of tagged pointers include space pointers, system pointers,
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invocation pointers etc..
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<p>If the DTAMDL(*LLP64) parameter is used when compiling an ILE C program,
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this limitation does not apply as the pointers will be 8 byte pointers, and their
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pointer attribute will be preserved.
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<img src="deltaend.gif" alt="End of change">
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</li>
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</ol>
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<br>
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<h3>Related Information</h3>
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<ul>
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<li><a href="open.htm">open()</a>--Open File
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</li>
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<li><a href="open64.htm">open64()</a>--Open File (Large File Enabled)
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</li>
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<li><a href="mmap.htm">mmap()</a>--Memory Map a Stream File
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</li>
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<li><a href="mprotect.htm">mprotect()</a>--Change Access Protection for Memory
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Mapping
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</li>
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<li><a href="msync.htm">msync()</a>--Synchronize Modified Data with Mapped
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File</li>
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</ul>
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<br>
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<h3>Example</h3>
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<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
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for information pertaining to code examples.</p>
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<p>The following example creates a file, produces a memory mapping of the file
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using mmap(), and then removes the mapping using the <strong>munmap()</strong>
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function.</p>
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<pre>
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#include <stdio.h>
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#include <fcntl.h>
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#include <sys/types.h>
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#include <sys/mman.h>
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main() {
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char fn[]="creat.file";
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char text[]="This is a test";
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int fd;
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int PageSize;
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if ((fd =
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open(fn, O_CREAT | O_RDWR | O_APPEND,S_IRWXU) < 0)
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perror("open() error");
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else if (write(fd, text, strlen(text)) < 0;
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error("write() error=");
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else if ( (PageSize=sysconf(_SC_PAGESIZE)) < 0 )
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error("sysconf() Error=");
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else {
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off_t lastoffset = lseek( fd, PageSize-1, SEEK_SET);
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write(fd, " ", 1); /* grow file to 1 page. */
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/* mmap the file. */
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void *address;
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int len;
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my_offset = 0;
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len = 4096; /* Map one page */
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address =
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mmap(NULL, len, PROT_READ, MAP_SHARED, fd, my_offset)
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if ( address != MAP_FAILED ) {
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if ( munmap( address, len ) ) == -1) {
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error("munmap failed with error:");
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}
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}
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close(fd);
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unlink(fn);
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}
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}
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</pre>
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<hr>
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API introduced: V5R1
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<hr>
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<center>
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<table cellpadding="2" cellspacing="2">
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<tr align="center">
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<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
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"unix.htm">UNIX-Type APIs</a> | <a href="aplist.htm">APIs by category</a></td>
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</tr>
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</table>
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</center>
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</body>
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</html>
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