Evan Hunt
87997fdcbf
- dns64 implementation has been moved from query.c to the dns64 module. - the code in lib/dns/dns64.c has not yet been moved. - the module does not yet parse dns64 options in named.conf; that's still done by named. - the module does not have persistent storage; we still use the client object. - made more functions globally accessible so they can be called from modules: ns_query_lookup(), ns_query_addsoa(), ns_query_nodata(), ns_query_ncache(), ns_query_setorder().
97 lines
4.1 KiB
XML
97 lines
4.1 KiB
XML
<!--
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- Copyright (C) Internet Systems Consortium, Inc. ("ISC")
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-
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- This Source Code Form is subject to the terms of the Mozilla Public
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- License, v. 2.0. If a copy of the MPL was not distributed with this
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- file, You can obtain one at http://mozilla.org/MPL/2.0/.
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-
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- See the COPYRIGHT file distributed with this work for additional
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- information regarding copyright ownership.
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-->
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<!-- Converted by db4-upgrade version 1.0 -->
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<section xmlns:db="http://docbook.org/ns/docbook" version="5.0" xml:id="module-info"><info><title>Plugins</title></info>
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<para>
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Plugins are a mechanism to extend the functionality of
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<command>named</command> using dynamically loadable libraries.
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By using plugins, core server functionality can be kept simple
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for the majority of users; more complex code implementing optional
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features need only be installed by users that need those features.
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</para>
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<para>
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The plugin interface is a work in progress, and is expected to evolve
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as more plugins are added. Currently, only "query plugins" are supported;
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these modify the name server query logic. Other plugin types may be added
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in the future.
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</para>
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<para>
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The only plugins currently included in BIND are
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<filename>filter-aaaa.so</filename> and <filename>dns64.so</filename>,
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which replace the <command>filter-aaaa</command> and
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<command>dns64</command> features that previously existed natively
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as part of <command>named</command>.
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The code for these features has been removed from <command>named</command>,
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and they can no longer be configured using standard
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<filename>named.conf</filename> syntax, but linking in the
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<filename>filter-aaaa.so</filename> or <filename>dns64.so</filename>
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plugins provides identical functionality.
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</para>
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<section><info><title>Configuring Plugins</title></info>
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<para>
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A plugin is configured with the <command>plugin</command>
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statement in <filename>named.conf</filename>:
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</para>
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<screen>
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plugin query "library.so" {
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<replaceable>parameters</replaceable>
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};
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</screen>
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<para>
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In this example, file <filename>library.so</filename> is the plugin
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library. <literal>query</literal> indicates that this is a query
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plugin.
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<para>
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</para>
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Multiple <command>plugin</command> statements can be specified, to load
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different plugins or multiple instances of the same plugin.
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</para>
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<para>
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<replaceable>parameters</replaceable> are passed as an opaque
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string to the plugin's initialization routine. Configuration
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syntax will differ depending on the module.
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</para>
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</section>
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<section><info><title>Developing Plugins</title></info>
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<para>
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Each plugin implements four functions:
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<itemizedlist>
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<listitem><command>plugin_register</command> to allocate memory,
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configure a plugin instance, and attach to hook points within
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<command>named</command>,</listitem>
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<listitem><command>plugin_destroy</command> to tear down the plugin
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instance and free memory,</listitem>
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<listitem><command>plugin_version</command> to check that the plugin
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is compatible with the current version of the plugin API,</listitem>
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<listitem><command>plugin_check</command> to test syntactic
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correctness of the plugin parameters.</listitem>
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</itemizedlist>
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</para>
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<para>
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At various locations within the <command>named</command> source code,
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there are "hook points" at which a plugin may register itself.
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When a hook point is reached while <command>named</command> is
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running, it is checked to see whether any plugins have registered
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themselves there; if so, the associated "hook action" is called -
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this is a function within the plugin library. Hook actions may
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examine the runtime state and make changes - for example, modifying
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the answers to be sent back to a client or forcing a query to be
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aborted. More details can be found in the file
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<filename>lib/ns/include/ns/hooks.h</filename>.
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</para>
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</section>
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</section>
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