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<h1><a href="../index.html">MIT Kerberos Documentation</a></h1>
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<section id="general-plugin-concepts">
<h1>General plugin concepts<a class="headerlink" href="#general-plugin-concepts" title="Link to this heading">¶</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><p>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.</p></li>
<li><p>Cast the supplied vtable pointer to the structure type
corresponding to the major version, as documented in the pluggable
interface header file.</p></li>
<li><p>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.</p></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>
<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="Link to this heading">¶</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>
</section>
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<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>
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<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>
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<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>
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<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>
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