417 lines
12 KiB
HTML
417 lines
12 KiB
HTML
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
||
|
|
<html>
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
||
|
|
<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
|
||
|
|
<title>mprotect()--Change Access Protection for Memory Mapping</title>
|
||
|
|
<!-- Begin Header Records -->
|
||
|
|
<!-- All rights reserved. Licensed Materials Property of IBM -->
|
||
|
|
<!-- US Government Users Restricted Rights -->
|
||
|
|
<!-- Use, duplication or disclosure restricted by -->
|
||
|
|
<!-- GSA ADP Schedule Contract with IBM Corp. -->
|
||
|
|
<!-- Change History: -->
|
||
|
|
<!-- YYMMDD USERID Change description -->
|
||
|
|
<!-- MPROTECT SCRIPT A converted by B2H R4.1 (346) (CMS) by V2CDIJAB -->
|
||
|
|
<!-- at RCHVMW2 on 19 Sep 2000 at 14:23:34 -->
|
||
|
|
<!-- Change History: -->
|
||
|
|
<!-- 011108 JTROUS Changes from CL Review 1, V5R2 -->
|
||
|
|
<!-- 0205?? JET This file has undergone html cleanup -->
|
||
|
|
<!-- 020918 Rosckes: Add ENOTAVAIL errno description, V5R3 -->
|
||
|
|
<!-- 050404 JTROUS: fix enums, no change flag, V5R4 -->
|
||
|
|
<!-- 050404 JTROUS Add note on tagged pointers, V5R4 -->
|
||
|
|
<!-- End Header Records -->
|
||
|
|
<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
|
||
|
|
</head>
|
||
|
|
<body>
|
||
|
|
<!-- Java sync-link -->
|
||
|
|
<script language="Javascript" src="../rzahg/synch.js" type="text/javascript">
|
||
|
|
</script>
|
||
|
|
|
||
|
|
<a name="Top_Of_Page"></a>
|
||
|
|
|
||
|
|
<h2>mprotect()--Change Access Protection for Memory Mapping</h2>
|
||
|
|
|
||
|
|
<div class="box" style="width: 60%;">
|
||
|
|
<br>
|
||
|
|
Syntax<br>
|
||
|
|
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
#include <sys/types.h>
|
||
|
|
#include <sys/mman.h>
|
||
|
|
|
||
|
|
int mprotect( void <em>*addr</em>,
|
||
|
|
size_t <em>len</em>,
|
||
|
|
int <em>protection</em>);
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
Service Program Name: QP0LLIB1<br>
|
||
|
|
<!-- iddvc RMBR -->
|
||
|
|
<br>
|
||
|
|
Default Public Authority: *USE<br>
|
||
|
|
<!-- iddvc RMBR -->
|
||
|
|
<br>
|
||
|
|
Threadsafe: Yes<br>
|
||
|
|
<!-- iddvc RMBR -->
|
||
|
|
<br>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<p>The <strong>mprotect()</strong> function is used to change the access
|
||
|
|
protection of a memory mapping to that specified by <em>protection</em>. All
|
||
|
|
whole pages of the process's address space, that were established by the
|
||
|
|
<strong>mmap()</strong> function, addressed from <em>addr</em> continuing for a
|
||
|
|
length of <em>len</em> will be affected by the change of access protection. You
|
||
|
|
may specify PROT_NONE, PROT_READ, PROT_WRITE, or the inclusive or of PROT_READ
|
||
|
|
and PROT_WRITE as values for the <em>protect</em> parameter.</p>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Parameters</h3>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><strong><em>addr</em></strong></dt>
|
||
|
|
|
||
|
|
<dd>(Input) The starting address of the memory region for which the access is
|
||
|
|
to be changed.
|
||
|
|
|
||
|
|
<p>The <em>addr</em> argument must be a multiple of the page size. The
|
||
|
|
<a href="sysconf.htm">sysconf()</a> function may be used to determine the system page size.<br>
|
||
|
|
<br>
|
||
|
|
</p>
|
||
|
|
</dd>
|
||
|
|
|
||
|
|
<dt><strong><em>len</em></strong></dt>
|
||
|
|
|
||
|
|
<dd>(Input) The length in bytes of the address range.<br>
|
||
|
|
<br>
|
||
|
|
</dd>
|
||
|
|
|
||
|
|
<dt><strong><em>protection</em></strong></dt>
|
||
|
|
|
||
|
|
<dd>(Input) The desired access protection. You may specify PROT_NONE,
|
||
|
|
PROT_READ, PROT_WRITE, or the inclusive or of PROT_READ AND PROT_WRITE as
|
||
|
|
values for the <em>protection</em> argument.
|
||
|
|
|
||
|
|
<p>No access through the memory mapping will be permitted if PROT_NONE is
|
||
|
|
specified.</p>
|
||
|
|
|
||
|
|
<p>Storage associated with the mapping cannot be altered unless the PROT_WRITE
|
||
|
|
value is specified.</p>
|
||
|
|
|
||
|
|
<p>For shared mappings, PROT_WRITE requires that the file descriptor used to
|
||
|
|
establish the map had been opened for write access. A shared mapping is a
|
||
|
|
mapping created with the <strong><em>MAP_SHARED</em></strong> value of the flag
|
||
|
|
parameter of the <strong>mmap()</strong> function.</p>
|
||
|
|
|
||
|
|
<p>Since private mappings do not alter the underlying file, PROT_WRITE may be
|
||
|
|
specified for a mapping that had been created MAP_PRIVATE and had been opened
|
||
|
|
for read access.</p>
|
||
|
|
|
||
|
|
<p>The following table shows the symbolic constants allowed for the protection
|
||
|
|
argument.</p>
|
||
|
|
|
||
|
|
<table border cellpadding="5" width="80%">
|
||
|
|
<tr>
|
||
|
|
<th align="left" valign="top">Symbolic Constant</th>
|
||
|
|
<th align="left" valign="top">Decimal<br>
|
||
|
|
Value</th>
|
||
|
|
<th align="left" valign="bottom">Description</th>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top" width="20%">PROT_WRITE</td>
|
||
|
|
<td align="center" valign="top" width="15%">2</td>
|
||
|
|
<td align="left" valign="top" width="65%">Write access allowed.</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top">PROT_READ</td>
|
||
|
|
<td align="center" valign="top">2</td>
|
||
|
|
<td align="left" valign="top">Read access allowed.</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top">PROT_NONE</td>
|
||
|
|
<td align="center" valign="top">8</td>
|
||
|
|
<td align="left" valign="top">No access allowed.</td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
</dd>
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Authorities</h3>
|
||
|
|
|
||
|
|
<p>No authorization is required.</p>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Return Value</h3>
|
||
|
|
|
||
|
|
<p>Upon successful completion, the <strong>mprotect()</strong> function returns
|
||
|
|
0. Upon failure, -1 is returned and errno is set to the appropriate error
|
||
|
|
number.</p>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Error Conditions</h3>
|
||
|
|
|
||
|
|
<p>When the <strong>mprotect()</strong> function fails, it returns -1 and sets
|
||
|
|
there errno variable as follows.</p>
|
||
|
|
|
||
|
|
<table cellpadding="5">
|
||
|
|
<!-- cols="25 75" -->
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<th align="left" valign="bottom">Error condition</th>
|
||
|
|
<th align="left" valign="bottom">Additional information</th>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top">
|
||
|
|
<em>[<a href="unix14.htm#EACCES">EACCES</a>]</em></td>
|
||
|
|
|
||
|
|
<td align="left" valign="top">
|
||
|
|
<p>If you are accessing a remote file through the Network File System, update
|
||
|
|
operations to file permissions at the server are not reflected at the client
|
||
|
|
until updates to data that is stored locally by the Network File System take
|
||
|
|
place. (Several options on the Add Mounted File System (ADDMFS) command
|
||
|
|
determine the time between refresh operations of local data.) Access to a
|
||
|
|
remote file may also fail due to different mappings of user IDs (UID) or group
|
||
|
|
IDs (GID) on the local and remote systems.</p>
|
||
|
|
<p>The <em>protection</em> argument specifies a protection that violates the
|
||
|
|
access permission the process has to the underlying mapped file.</p>
|
||
|
|
<p>If the QSHRMEMCTL system value was 0 at the time the mapping was created,
|
||
|
|
then this continues to limit the allowed access until the mapping is destroyed.
|
||
|
|
An attempt to change the protection of a shared mapping to PROT_WRITE when the
|
||
|
|
QSHRMEMCTL system value had been zero at the time of map creation will result
|
||
|
|
in an errno of EACCES.</p>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top">
|
||
|
|
<em>[<a href="unix14.htm#EINVAL">EINVAL</a>]</em></td>
|
||
|
|
|
||
|
|
<td align="left" valign="top">
|
||
|
|
<p>For example, the <em>addr</em> argument is not a multiple of the page size.
|
||
|
|
This error number also may indicate that the value of the <em>len</em>
|
||
|
|
argument is 0.</p>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top">
|
||
|
|
<em>[<a href="unix14.htm#ENOMEM">ENOMEM</a>]</em></td>
|
||
|
|
|
||
|
|
<td align="left" valign="top">
|
||
|
|
<p>The <em>addr</em> argument is out of the allowed range.</p>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top">
|
||
|
|
<em>[<a href="unix14.htm#ENOTAVAIL">ENOTAVAIL</a>]</em></td>
|
||
|
|
|
||
|
|
<td align="left" valign="top">
|
||
|
|
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td align="left" valign="top">
|
||
|
|
<em>[<a href="unix14.htm#ENOTSUP">ENOTSUP</a>]</em></td>
|
||
|
|
|
||
|
|
<td align="left" valign="top">
|
||
|
|
<p>For <strong>mprotect()</strong> this can be caused by an invalid combination
|
||
|
|
of access requests on the <em>protection</em> parameter.</p>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h3>Error Messages</h3>
|
||
|
|
|
||
|
|
<p>The following messages may be sent from this function.</p>
|
||
|
|
|
||
|
|
<table width="100%">
|
||
|
|
<tr>
|
||
|
|
<th align="left" valign="top">Message ID</th>
|
||
|
|
<th align="left" valign="top">Error Message Text</th>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td width="15%" valign="top">CPE3418 E</td>
|
||
|
|
<td width="85%" valign="top">Possible APAR condition or hardware failure.</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td valign="top">CPFA0D4 E</td>
|
||
|
|
<td valign="top">File system error occurred. Error number &1.</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td valign="top">CPF3CF2 E</td>
|
||
|
|
<td valign="top">Error(s) occurred during running of &1 API.</td>
|
||
|
|
</tr>
|
||
|
|
|
||
|
|
<tr>
|
||
|
|
<td valign="top">CPF9872 E</td>
|
||
|
|
<td valign="top">Program or service program &1 in library &2 ended.
|
||
|
|
Reason code &3.</td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h3>Usage Notes</h3>
|
||
|
|
|
||
|
|
<ol>
|
||
|
|
<li>The address pointer that was returned by <strong>mmap()</strong> can only
|
||
|
|
be used with the V4R4M0 or later versions of the following languages:
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>ILE COBOL</li>
|
||
|
|
|
||
|
|
<li>ILE RPG</li>
|
||
|
|
|
||
|
|
<li>ILE C if the TERASPACE parameter is used when compiling the program.</li>
|
||
|
|
</ul>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
<img src="delta.gif" alt="Start of change">
|
||
|
|
The application cannot write or store any data via the memory mapping which
|
||
|
|
includes any tagged (16-byte) pointers because the pointer attribute will be lost.
|
||
|
|
Some examples of tagged pointers include space pointers, system pointers,
|
||
|
|
invocation pointers etc..
|
||
|
|
<p>If the DTAMDL(*LLP64) parameter is used when compiling an ILE C program,
|
||
|
|
this limitation does not apply as the pointers will be 8 byte pointers, and their
|
||
|
|
pointer attribute will be preserved.
|
||
|
|
<img src="deltaend.gif" alt="End of change">
|
||
|
|
</li>
|
||
|
|
</ol>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Related Information</h3>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li><a href="creat.htm">creat()</a>--Create or Rewrite File
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="creat64.htm">creat64()</a>--Create or Rewrite a File (Large File
|
||
|
|
Enabled)
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="mmap.htm">mmap()</a>--Memory Map a Stream File
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="munmap.htm">munmap()</a>--Remove Memory Mapping
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="msync.htm">msync()</a>--Synchronize Modified Data with Mapped
|
||
|
|
File</li>
|
||
|
|
<li><a href="open.htm">open()</a>--Open File
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="open64.htm">open64()</a>--Open File (Large File Enabled)
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="sysconf.htm">sysconf()</a>--Get system configuration variables</li>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Example</h3>
|
||
|
|
|
||
|
|
<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
|
||
|
|
for information pertaining to code examples.</p>
|
||
|
|
|
||
|
|
<p>The following example creates a file, produces a memory mapping of the file
|
||
|
|
using <strong>mmap()</strong>, and then changes the protection of the file
|
||
|
|
using <strong>mprotect()</strong>.</p>
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
#include <errno.h>
|
||
|
|
#include <fcntl.h>
|
||
|
|
#include <unistd.h>
|
||
|
|
#include <stdio.h>
|
||
|
|
#include <stdlib.h>
|
||
|
|
#include <string.h>
|
||
|
|
#include <sys/types.h>
|
||
|
|
#include <sys/mman.h>
|
||
|
|
|
||
|
|
main(void) {
|
||
|
|
|
||
|
|
size_t bytesWritten =0;
|
||
|
|
int fd;
|
||
|
|
int PageSize;
|
||
|
|
char textÝ = "This is a test";
|
||
|
|
|
||
|
|
if ( (PageSize = sysconf(_SC_PAGE_SIZE)) < 0) {
|
||
|
|
perror("sysconf() Error=");
|
||
|
|
return -1;
|
||
|
|
}
|
||
|
|
|
||
|
|
fd = open("/tmp/mmprotectTest",
|
||
|
|
(O_CREAT | O_TRUNC | O_RDWR),
|
||
|
|
(S_IRWXU | S_IRWXG | S_IRWXO) );
|
||
|
|
if ( fd < 0 ) {
|
||
|
|
perror("open() error");
|
||
|
|
return fd;
|
||
|
|
}
|
||
|
|
|
||
|
|
off_t lastoffset = lseek( fd, 0, SEEK_SET);
|
||
|
|
bytesWritten = write(fd, text, strlen(text));
|
||
|
|
if (bytesWritten != strlen(text) ) {
|
||
|
|
perror("write error. ");
|
||
|
|
return -1;
|
||
|
|
}
|
||
|
|
|
||
|
|
lastoffset = lseek( fd, PageSize-1, SEEK_SET);
|
||
|
|
bytesWritten = write(fd, " ", 1); /* grow file to 1 page. */
|
||
|
|
if ( bytesWritten != 1 ) {
|
||
|
|
perror("write error. ");
|
||
|
|
return -1;
|
||
|
|
}
|
||
|
|
/* mmap the file. */
|
||
|
|
void *address;
|
||
|
|
int len;
|
||
|
|
off_t my_offset = 0;
|
||
|
|
len = PageSize; /* Map one page */
|
||
|
|
address =
|
||
|
|
mmap(NULL, len, PROT_NONE, MAP_SHARED, fd, my_offset);
|
||
|
|
|
||
|
|
if ( address == MAP_FAILED ) {
|
||
|
|
perror("mmap error. " );
|
||
|
|
return -1;
|
||
|
|
}
|
||
|
|
|
||
|
|
if ( mprotect( address, len, PROT_WRITE) < 0 ) {
|
||
|
|
perror("mprotect failed with error:");
|
||
|
|
return -1;
|
||
|
|
}
|
||
|
|
else (void) printf("%s",address);
|
||
|
|
|
||
|
|
close(fd);
|
||
|
|
unlink("/tmp/mmprotectTest");
|
||
|
|
}
|
||
|
|
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
API introduced: V5R1
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
<center>
|
||
|
|
<table cellpadding="2" cellspacing="2">
|
||
|
|
<tr align="center">
|
||
|
|
<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
|
||
|
|
"unix.htm">UNIX-Type APIs</a> | <a href="aplist.htm">APIs by category</a></td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
</center>
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
|