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diff --git a/rubbos/app/apache2/manual/dso.html.en b/rubbos/app/apache2/manual/dso.html.en deleted file mode 100644 index f37d73a0..00000000 --- a/rubbos/app/apache2/manual/dso.html.en +++ /dev/null @@ -1,318 +0,0 @@ -<?xml version="1.0" encoding="ISO-8859-1"?> -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> -<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX - This file is generated from xml source: DO NOT EDIT - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX - --> -<title>Dynamic Shared Object (DSO) Support - Apache HTTP Server</title> -<link href="./style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> -<link href="./style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> -<link href="./style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /> -<link href="./images/favicon.ico" rel="shortcut icon" /></head> -<body id="manual-page"><div id="page-header"> -<p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.html">Directives</a> | <a href="./faq/">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p> -<p class="apache">Apache HTTP Server Version 2.0</p> -<img alt="" src="./images/feather.gif" /></div> -<div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div> -<div id="path"> -<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.0</a></div><div id="page-content"><div id="preamble"><h1>Dynamic Shared Object (DSO) Support</h1> -<div class="toplang"> -<p><span>Available Languages: </span><a href="./en/dso.html" title="English"> en </a> | -<a href="./es/dso.html" hreflang="es" rel="alternate" title="Español"> es </a> | -<a href="./fr/dso.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | -<a href="./ja/dso.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | -<a href="./ko/dso.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | -<a href="./tr/dso.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p> -</div> - - <p>The Apache HTTP Server is a modular program where the - administrator can choose the functionality to include in the - server by selecting a set of modules. The modules can be - statically compiled into the <code class="program"><a href="./programs/httpd.html">httpd</a></code> binary when the - server is built. Alternatively, modules can be compiled as - Dynamic Shared Objects (DSOs) that exist separately from the - main <code class="program"><a href="./programs/httpd.html">httpd</a></code> binary file. DSO modules may be - compiled at the time the server is built, or they may be - compiled and added at a later time using the Apache Extension - Tool (<code class="program"><a href="./programs/apxs.html">apxs</a></code>).</p> - - <p>This document describes how to use DSO modules as well as - the theory behind their use.</p> - </div> -<div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#implementation">Implementation</a></li> -<li><img alt="" src="./images/down.gif" /> <a href="#usage">Usage Summary</a></li> -<li><img alt="" src="./images/down.gif" /> <a href="#background">Background</a></li> -<li><img alt="" src="./images/down.gif" /> <a href="#advantages">Advantages and Disadvantages</a></li> -</ul></div> -<div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> -<div class="section"> -<h2><a name="implementation" id="implementation">Implementation</a></h2> - -<table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_so.html">mod_so</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code></li></ul></td></tr></table> - - <p>The DSO support for loading individual Apache modules is based - on a module named <code class="module"><a href="./mod/mod_so.html">mod_so</a></code> which must be statically - compiled into the Apache core. It is the only module besides - <code class="module"><a href="./mod/core.html">core</a></code> which cannot be put into a DSO - itself. Practically all other distributed Apache modules can then - be placed into a DSO by individually enabling the DSO build for - them via <code class="program"><a href="./programs/configure.html">configure</a></code>'s - <code>--enable-<em>module</em>=shared</code> option as discussed - in the <a href="install.html">install documentation</a>. After a - module is compiled into a DSO named <code>mod_foo.so</code> you - can use <code class="module"><a href="./mod/mod_so.html">mod_so</a></code>'s <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> command in your - <code>httpd.conf</code> file to load this module at server startup - or restart.</p> - - <p>To simplify this creation of DSO files for Apache modules - (especially for third-party modules) a new support program - named <code class="program"><a href="./programs/apxs.html">apxs</a></code> (<dfn>APache - eXtenSion</dfn>) is available. It can be used to build DSO based - modules <em>outside of</em> the Apache source tree. The idea is - simple: When installing Apache the <code class="program"><a href="./programs/configure.html">configure</a></code>'s - <code>make install</code> procedure installs the Apache C - header files and puts the platform-dependent compiler and - linker flags for building DSO files into the <code class="program"><a href="./programs/apxs.html">apxs</a></code> - program. This way the user can use <code class="program"><a href="./programs/apxs.html">apxs</a></code> to compile - his Apache module sources without the Apache distribution - source tree and without having to fiddle with the - platform-dependent compiler and linker flags for DSO - support.</p> -</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> -<div class="section"> -<h2><a name="usage" id="usage">Usage Summary</a></h2> - - <p>To give you an overview of the DSO features of Apache 2.x, - here is a short and concise summary:</p> - - <ol> - <li> - Build and install a <em>distributed</em> Apache module, say - <code>mod_foo.c</code>, into its own DSO - <code>mod_foo.so</code>: - -<div class="example"><p><code> -$ ./configure --prefix=/path/to/install --enable-foo=shared<br /> -$ make install -</code></p></div> - </li> - - <li> - Build and install a <em>third-party</em> Apache module, say - <code>mod_foo.c</code>, into its own DSO - <code>mod_foo.so</code>: - -<div class="example"><p><code> -$ ./configure --add-module=module_type:/path/to/3rdparty/mod_foo.c --enable-foo=shared<br /> -$ make install -</code></p></div> - </li> - - <li> - Configure Apache for <em>later installation</em> of shared - modules: - -<div class="example"><p><code> -$ ./configure --enable-so<br /> -$ make install -</code></p></div> - </li> - - <li> - Build and install a <em>third-party</em> Apache module, say - <code>mod_foo.c</code>, into its own DSO - <code>mod_foo.so</code> <em>outside of</em> the Apache - source tree using <code class="program"><a href="./programs/apxs.html">apxs</a></code>: - -<div class="example"><p><code> -$ cd /path/to/3rdparty<br /> -$ apxs -c mod_foo.c<br /> -$ apxs -i -a -n foo mod_foo.la -</code></p></div> - </li> - </ol> - - <p>In all cases, once the shared module is compiled, you must - use a <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> - directive in <code>httpd.conf</code> to tell Apache to activate - the module.</p> -</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> -<div class="section"> -<h2><a name="background" id="background">Background</a></h2> - - <p>On modern Unix derivatives there exists a nifty mechanism - usually called dynamic linking/loading of <em>Dynamic Shared - Objects</em> (DSO) which provides a way to build a piece of - program code in a special format for loading it at run-time - into the address space of an executable program.</p> - - <p>This loading can usually be done in two ways: Automatically - by a system program called <code>ld.so</code> when an - executable program is started or manually from within the - executing program via a programmatic system interface to the - Unix loader through the system calls - <code>dlopen()/dlsym()</code>.</p> - - <p>In the first way the DSO's are usually called <em>shared - libraries</em> or <em>DSO libraries</em> and named - <code>libfoo.so</code> or <code>libfoo.so.1.2</code>. They - reside in a system directory (usually <code>/usr/lib</code>) - and the link to the executable program is established at - build-time by specifying <code>-lfoo</code> to the linker - command. This hard-codes library references into the executable - program file so that at start-time the Unix loader is able to - locate <code>libfoo.so</code> in <code>/usr/lib</code>, in - paths hard-coded via linker-options like <code>-R</code> or in - paths configured via the environment variable - <code>LD_LIBRARY_PATH</code>. It then resolves any (yet - unresolved) symbols in the executable program which are - available in the DSO.</p> - - <p>Symbols in the executable program are usually not referenced - by the DSO (because it's a reusable library of general code) - and hence no further resolving has to be done. The executable - program has no need to do anything on its own to use the - symbols from the DSO because the complete resolving is done by - the Unix loader. (In fact, the code to invoke - <code>ld.so</code> is part of the run-time startup code which - is linked into every executable program which has been bound - non-static). The advantage of dynamic loading of common library - code is obvious: the library code needs to be stored only once, - in a system library like <code>libc.so</code>, saving disk - space for every program.</p> - - <p>In the second way the DSO's are usually called <em>shared - objects</em> or <em>DSO files</em> and can be named with an - arbitrary extension (although the canonical name is - <code>foo.so</code>). These files usually stay inside a - program-specific directory and there is no automatically - established link to the executable program where they are used. - Instead the executable program manually loads the DSO at - run-time into its address space via <code>dlopen()</code>. At - this time no resolving of symbols from the DSO for the - executable program is done. But instead the Unix loader - automatically resolves any (yet unresolved) symbols in the DSO - from the set of symbols exported by the executable program and - its already loaded DSO libraries (especially all symbols from - the ubiquitous <code>libc.so</code>). This way the DSO gets - knowledge of the executable program's symbol set as if it had - been statically linked with it in the first place.</p> - - <p>Finally, to take advantage of the DSO's API the executable - program has to resolve particular symbols from the DSO via - <code>dlsym()</code> for later use inside dispatch tables - <em>etc.</em> In other words: The executable program has to - manually resolve every symbol it needs to be able to use it. - The advantage of such a mechanism is that optional program - parts need not be loaded (and thus do not spend memory) until - they are needed by the program in question. When required, - these program parts can be loaded dynamically to extend the - base program's functionality.</p> - - <p>Although this DSO mechanism sounds straightforward there is - at least one difficult step here: The resolving of symbols from - the executable program for the DSO when using a DSO to extend a - program (the second way). Why? Because "reverse resolving" DSO - symbols from the executable program's symbol set is against the - library design (where the library has no knowledge about the - programs it is used by) and is neither available under all - platforms nor standardized. In practice the executable - program's global symbols are often not re-exported and thus not - available for use in a DSO. Finding a way to force the linker - to export all global symbols is the main problem one has to - solve when using DSO for extending a program at run-time.</p> - - <p>The shared library approach is the typical one, because it - is what the DSO mechanism was designed for, hence it is used - for nearly all types of libraries the operating system - provides. On the other hand using shared objects for extending - a program is not used by a lot of programs.</p> - - <p>As of 1998 there are only a few software packages available - which use the DSO mechanism to actually extend their - functionality at run-time: Perl 5 (via its XS mechanism and the - DynaLoader module), Netscape Server, <em>etc.</em> Starting - with version 1.3, Apache joined the crew, because Apache - already uses a module concept to extend its functionality and - internally uses a dispatch-list-based approach to link external - modules into the Apache core functionality. So, Apache is - really predestined for using DSO to load its modules at - run-time.</p> -</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> -<div class="section"> -<h2><a name="advantages" id="advantages">Advantages and Disadvantages</a></h2> - - <p>The above DSO based features have the following - advantages:</p> - - <ul> - <li>The server package is more flexible at run-time because - the actual server process can be assembled at run-time via - <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> - <code>httpd.conf</code> configuration commands instead of - <code class="program"><a href="./programs/configure.html">configure</a></code> options at build-time. For instance - this way one is able to run different server instances - (standard & SSL version, minimalistic & powered up - version [mod_perl, PHP3], <em>etc.</em>) with only one Apache - installation.</li> - - <li>The server package can be easily extended with - third-party modules even after installation. This is at least - a great benefit for vendor package maintainers who can create - a Apache core package and additional packages containing - extensions like PHP3, mod_perl, mod_fastcgi, - <em>etc.</em></li> - - <li>Easier Apache module prototyping because with the - DSO/<code class="program"><a href="./programs/apxs.html">apxs</a></code> pair you can both work outside the - Apache source tree and only need an <code>apxs -i</code> - command followed by an <code>apachectl restart</code> to - bring a new version of your currently developed module into - the running Apache server.</li> - </ul> - - <p>DSO has the following disadvantages:</p> - - <ul> - <li>The DSO mechanism cannot be used on every platform - because not all operating systems support dynamic loading of - code into the address space of a program.</li> - - <li>The server is approximately 20% slower at startup time - because of the symbol resolving overhead the Unix loader now - has to do.</li> - - <li>The server is approximately 5% slower at execution time - under some platforms because position independent code (PIC) - sometimes needs complicated assembler tricks for relative - addressing which are not necessarily as fast as absolute - addressing.</li> - - <li>Because DSO modules cannot be linked against other - DSO-based libraries (<code>ld -lfoo</code>) on all platforms - (for instance a.out-based platforms usually don't provide - this functionality while ELF-based platforms do) you cannot - use the DSO mechanism for all types of modules. Or in other - words, modules compiled as DSO files are restricted to only - use symbols from the Apache core, from the C library - (<code>libc</code>) and all other dynamic or static libraries - used by the Apache core, or from static library archives - (<code>libfoo.a</code>) containing position independent code. - The only chances to use other code is to either make sure the - Apache core itself already contains a reference to it or - loading the code yourself via <code>dlopen()</code>.</li> - </ul> - -</div></div> -<div class="bottomlang"> -<p><span>Available Languages: </span><a href="./en/dso.html" title="English"> en </a> | -<a href="./es/dso.html" hreflang="es" rel="alternate" title="Español"> es </a> | -<a href="./fr/dso.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | -<a href="./ja/dso.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | -<a href="./ko/dso.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | -<a href="./tr/dso.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p> -</div><div id="footer"> -<p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p> -<p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.html">Directives</a> | <a href="./faq/">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p></div> -</body></html>
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