<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>General plugin concepts — MIT Kerberos Documentation</title> <link rel="stylesheet" href="../_static/agogo.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <link rel="stylesheet" type="text/css" href="../_static/kerb.css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/language_data.js"></script> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="Client preauthentication interface (clpreauth)" href="clpreauth.html" /> <link rel="prev" title="For plugin module developers" href="index.html" /> </head><body> <div class="header-wrapper"> <div class="header"> <h1><a href="../index.html">MIT Kerberos Documentation</a></h1> <div class="rel"> <a href="../index.html" title="Full Table of Contents" accesskey="C">Contents</a> | <a href="index.html" title="For plugin module developers" accesskey="P">previous</a> | <a href="clpreauth.html" title="Client preauthentication interface (clpreauth)" accesskey="N">next</a> | <a href="../genindex.html" title="General Index" accesskey="I">index</a> | <a href="../search.html" title="Enter search criteria" accesskey="S">Search</a> | <a href="mailto:krb5-bugs@mit.edu?subject=Documentation__General plugin concepts">feedback</a> </div> </div> </div> <div class="content-wrapper"> <div class="content"> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="general-plugin-concepts"> <h1>General plugin concepts<a class="headerlink" href="#general-plugin-concepts" title="Permalink to this headline">¶</a></h1> <p>A krb5 dynamic plugin module is a Unix shared object or Windows DLL. Typically, the source code for a dynamic plugin module should live in its own project with a build system using <a class="reference external" href="https://www.gnu.org/software/automake/">automake</a> and <a class="reference external" href="https://www.gnu.org/software/libtool/">libtool</a>, or tools with similar functionality.</p> <p>A plugin module must define a specific symbol name, which depends on the pluggable interface and module name. For most pluggable interfaces, the exported symbol is a function named <code class="docutils literal notranslate"><span class="pre">INTERFACE_MODULE_initvt</span></code>, where <em>INTERFACE</em> is the name of the pluggable interface and <em>MODULE</em> is the name of the module. For these interfaces, it is possible for one shared object or DLL to implement multiple plugin modules, either for the same pluggable interface or for different ones. For example, a shared object could implement both KDC and client preauthentication mechanisms, by exporting functions named <code class="docutils literal notranslate"><span class="pre">kdcpreauth_mymech_initvt</span></code> and <code class="docutils literal notranslate"><span class="pre">clpreauth_mymech_initvt</span></code>.</p> <p>A plugin module implementation should include the header file <code class="docutils literal notranslate"><span class="pre"><krb5/INTERFACE_plugin.h></span></code>, where <em>INTERFACE</em> is the name of the pluggable interface. For instance, a ccselect plugin module implementation should use <code class="docutils literal notranslate"><span class="pre">#include</span> <span class="pre"><krb5/ccselect_plugin.h></span></code>.</p> <p>initvt functions have the following prototype:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">krb5_error_code</span> <span class="n">interface_modname_initvt</span><span class="p">(</span><span class="n">krb5_context</span> <span class="n">context</span><span class="p">,</span> <span class="nb">int</span> <span class="n">maj_ver</span><span class="p">,</span> <span class="nb">int</span> <span class="n">min_ver</span><span class="p">,</span> <span class="n">krb5_plugin_vtable</span> <span class="n">vtable</span><span class="p">);</span> </pre></div> </div> <p>and should do the following:</p> <ol class="arabic simple"> <li>Check that the supplied maj_ver argument is supported by the module. If it is not supported, the function should return KRB5_PLUGIN_VER_NOTSUPP.</li> <li>Cast the supplied vtable pointer to the structure type corresponding to the major version, as documented in the pluggable interface header file.</li> <li>Fill in the structure fields with pointers to method functions and static data, stopping at the field indicated by the supplied minor version. Fields for unimplemented optional methods can be left alone; it is not necessary to initialize them to NULL.</li> </ol> <p>In most cases, the context argument will not be used. The initvt function should not allocate memory; think of it as a glorified structure initializer. Each pluggable interface defines methods for allocating and freeing module state if doing so is necessary for the interface.</p> <p>Pluggable interfaces typically include a <strong>name</strong> field in the vtable structure, which should be filled in with a pointer to a string literal containing the module name.</p> <p>Here is an example of what an initvt function might look like for a fictional pluggable interface named fences, for a module named “wicker”:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">krb5_error_code</span> <span class="n">fences_wicker_initvt</span><span class="p">(</span><span class="n">krb5_context</span> <span class="n">context</span><span class="p">,</span> <span class="nb">int</span> <span class="n">maj_ver</span><span class="p">,</span> <span class="nb">int</span> <span class="n">min_ver</span><span class="p">,</span> <span class="n">krb5_plugin_vtable</span> <span class="n">vtable</span><span class="p">)</span> <span class="p">{</span> <span class="n">krb5_ccselect_vtable</span> <span class="n">vt</span><span class="p">;</span> <span class="k">if</span> <span class="p">(</span><span class="n">maj_ver</span> <span class="o">==</span> <span class="mi">1</span><span class="p">)</span> <span class="p">{</span> <span class="n">krb5_fences_vtable</span> <span class="n">vt</span> <span class="o">=</span> <span class="p">(</span><span class="n">krb5_fences_vtable</span><span class="p">)</span><span class="n">vtable</span><span class="p">;</span> <span class="n">vt</span><span class="o">-></span><span class="n">name</span> <span class="o">=</span> <span class="s2">"wicker"</span><span class="p">;</span> <span class="n">vt</span><span class="o">-></span><span class="n">slats</span> <span class="o">=</span> <span class="n">wicker_slats</span><span class="p">;</span> <span class="n">vt</span><span class="o">-></span><span class="n">braces</span> <span class="o">=</span> <span class="n">wicker_braces</span><span class="p">;</span> <span class="p">}</span> <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">maj_ver</span> <span class="o">==</span> <span class="mi">2</span><span class="p">)</span> <span class="p">{</span> <span class="n">krb5_fences_vtable_v2</span> <span class="n">vt</span> <span class="o">=</span> <span class="p">(</span><span class="n">krb5_fences_vtable_v2</span><span class="p">)</span><span class="n">vtable</span><span class="p">;</span> <span class="n">vt</span><span class="o">-></span><span class="n">name</span> <span class="o">=</span> <span class="s2">"wicker"</span><span class="p">;</span> <span class="n">vt</span><span class="o">-></span><span class="n">material</span> <span class="o">=</span> <span class="n">wicker_material</span><span class="p">;</span> <span class="n">vt</span><span class="o">-></span><span class="n">construction</span> <span class="o">=</span> <span class="n">wicker_construction</span><span class="p">;</span> <span class="k">if</span> <span class="p">(</span><span class="n">min_ver</span> <span class="o"><</span> <span class="mi">2</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span> <span class="n">vt</span><span class="o">-></span><span class="n">footing</span> <span class="o">=</span> <span class="n">wicker_footing</span><span class="p">;</span> <span class="k">if</span> <span class="p">(</span><span class="n">min_ver</span> <span class="o"><</span> <span class="mi">3</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span> <span class="n">vt</span><span class="o">-></span><span class="n">appearance</span> <span class="o">=</span> <span class="n">wicker_appearance</span><span class="p">;</span> <span class="p">}</span> <span class="k">else</span> <span class="p">{</span> <span class="k">return</span> <span class="n">KRB5_PLUGIN_VER_NOTSUPP</span><span class="p">;</span> <span class="p">}</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span> <span class="p">}</span> </pre></div> </div> <div class="section" id="logging-from-kdc-and-kadmind-plugin-modules"> <h2>Logging from KDC and kadmind plugin modules<a class="headerlink" href="#logging-from-kdc-and-kadmind-plugin-modules" title="Permalink to this headline">¶</a></h2> <p>Plugin modules for the KDC or kadmind daemons can write to the configured logging outputs (see <a class="reference internal" href="../admin/conf_files/kdc_conf.html#logging"><span class="std std-ref">[logging]</span></a>) by calling the <strong>com_err</strong> function. The first argument (<em>whoami</em>) is ignored. If the second argument (<em>code</em>) is zero, the formatted message is logged at informational severity; otherwise, the formatted message is logged at error severity and includes the error message for the supplied code. Here are examples:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">com_err</span><span class="p">(</span><span class="s2">""</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="s2">"Client message contains </span><span class="si">%d</span><span class="s2"> items"</span><span class="p">,</span> <span class="n">nitems</span><span class="p">);</span> <span class="n">com_err</span><span class="p">(</span><span class="s2">""</span><span class="p">,</span> <span class="n">retval</span><span class="p">,</span> <span class="s2">"while decoding client message"</span><span class="p">);</span> </pre></div> </div> <p>(The behavior described above is new in release 1.17. In prior releases, the <em>whoami</em> argument is included for some logging output types, the logged message does not include the usual header for some output types, and the severity for syslog outputs is configured as part of the logging specification, defaulting to error severity.)</p> </div> </div> </div> </div> </div> </div> <div class="sidebar"> <h2>On this page</h2> <ul> <li><a class="reference internal" href="#">General plugin concepts</a><ul> <li><a class="reference internal" href="#logging-from-kdc-and-kadmind-plugin-modules">Logging from KDC and kadmind plugin modules</a></li> </ul> </li> </ul> <br/> <h2>Table of contents</h2> <ul class="current"> <li class="toctree-l1"><a class="reference internal" href="../user/index.html">For users</a></li> <li class="toctree-l1"><a class="reference internal" href="../admin/index.html">For administrators</a></li> <li class="toctree-l1"><a class="reference internal" href="../appdev/index.html">For application developers</a></li> <li class="toctree-l1 current"><a class="reference internal" href="index.html">For plugin module developers</a><ul class="current"> <li class="toctree-l2 current"><a class="current reference internal" href="#">General plugin concepts</a></li> <li class="toctree-l2"><a class="reference internal" href="clpreauth.html">Client preauthentication interface (clpreauth)</a></li> <li class="toctree-l2"><a class="reference internal" href="kdcpreauth.html">KDC preauthentication interface (kdcpreauth)</a></li> <li class="toctree-l2"><a class="reference internal" href="ccselect.html">Credential cache selection interface (ccselect)</a></li> <li class="toctree-l2"><a class="reference internal" href="pwqual.html">Password quality interface (pwqual)</a></li> <li class="toctree-l2"><a class="reference internal" href="kadm5_hook.html">KADM5 hook interface (kadm5_hook)</a></li> <li class="toctree-l2"><a class="reference internal" href="kadm5_auth.html">kadmin authorization interface (kadm5_auth)</a></li> <li class="toctree-l2"><a class="reference internal" href="hostrealm.html">Host-to-realm interface (hostrealm)</a></li> <li class="toctree-l2"><a class="reference internal" href="localauth.html">Local authorization interface (localauth)</a></li> <li class="toctree-l2"><a class="reference internal" href="locate.html">Server location interface (locate)</a></li> <li class="toctree-l2"><a class="reference internal" href="profile.html">Configuration interface (profile)</a></li> <li class="toctree-l2"><a class="reference internal" href="gssapi.html">GSSAPI mechanism interface</a></li> <li class="toctree-l2"><a class="reference internal" href="internal.html">Internal pluggable interfaces</a></li> <li class="toctree-l2"><a class="reference internal" href="certauth.html">PKINIT certificate authorization interface (certauth)</a></li> <li class="toctree-l2"><a class="reference internal" href="kdcpolicy.html">KDC policy interface (kdcpolicy)</a></li> </ul> </li> <li class="toctree-l1"><a class="reference internal" href="../build/index.html">Building Kerberos V5</a></li> <li class="toctree-l1"><a class="reference internal" href="../basic/index.html">Kerberos V5 concepts</a></li> <li class="toctree-l1"><a class="reference internal" href="../formats/index.html">Protocols and file formats</a></li> <li class="toctree-l1"><a class="reference internal" href="../mitK5features.html">MIT Kerberos features</a></li> <li class="toctree-l1"><a class="reference internal" href="../build_this.html">How to build this documentation from the source</a></li> <li class="toctree-l1"><a class="reference internal" href="../about.html">Contributing to the MIT Kerberos Documentation</a></li> <li class="toctree-l1"><a class="reference internal" href="../resources.html">Resources</a></li> </ul> <br/> <h4><a href="../index.html">Full Table of Contents</a></h4> <h4>Search</h4> <form class="search" action="../search.html" method="get"> <input type="text" name="q" size="18" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <div class="clearer"></div> </div> </div> <div class="footer-wrapper"> <div class="footer" > <div class="right" ><i>Release: 1.17</i><br /> © <a href="../copyright.html">Copyright</a> 1985-2019, MIT. </div> <div class="left"> <a href="../index.html" title="Full Table of Contents" >Contents</a> | <a href="index.html" title="For plugin module developers" >previous</a> | <a href="clpreauth.html" title="Client preauthentication interface (clpreauth)" >next</a> | <a href="../genindex.html" title="General Index" >index</a> | <a href="../search.html" title="Enter search criteria" >Search</a> | <a href="mailto:krb5-bugs@mit.edu?subject=Documentation__General plugin concepts">feedback</a> </div> </div> </div> </body> </html>