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284806029a
Update the ARM documentation of plugin usage as the extension in the plugin library path is now optional.
88 lines
3.2 KiB
ReStructuredText
88 lines
3.2 KiB
ReStructuredText
.. Copyright (C) Internet Systems Consortium, Inc. ("ISC")
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..
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.. SPDX-License-Identifier: MPL-2.0
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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 https://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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.. _module-info:
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Plugins
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~~~~~~~
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Plugins are a mechanism to extend the functionality of :iscman:`named` using
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dynamically loadable libraries. By using plugins, core server
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functionality can be kept simple for the majority of users; more complex
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code implementing optional features need only be installed by users that
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need those features.
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The plugin interface is a work in progress, and is expected to evolve as
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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
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added in the future.
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The only plugin currently included in BIND is :iscman:`filter-aaaa.so <filter-aaaa>`, which
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replaces the ``filter-aaaa`` feature that previously existed natively as
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part of :iscman:`named`. The code for this feature has been removed from
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:iscman:`named` and can no longer be configured using standard :iscman:`named.conf`
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syntax, but linking in the :iscman:`filter-aaaa.so <filter-aaaa>` plugin provides identical
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functionality.
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Configuring Plugins
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~~~~~~~~~~~~~~~~~~~
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.. namedconf:statement:: plugin
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:tags: server
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:short: Configures plugins in :iscman:`named.conf`.
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A plugin is configured with the :any:`plugin` statement in :iscman:`named.conf`:
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::
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plugin query "library.so" {
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parameters
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};
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In this example, ``query`` indicates that this is a query plugin,
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and ``library.so`` is the name of the plugin library. Note that the
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library file extension (in this case, ``.so``) is optional, and can
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be omitted.
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Multiple :any:`plugin` statements can be specified, to load different
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plugins or multiple instances of the same plugin.
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``parameters`` are passed as an opaque string to the plugin's initialization
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routine. Configuration syntax differs depending on the module.
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Developing Plugins
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~~~~~~~~~~~~~~~~~~
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Each plugin implements four functions:
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- ``plugin_register``
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to allocate memory, configure a plugin instance, and attach to hook
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points within
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:iscman:`named`
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,
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- ``plugin_destroy``
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to tear down the plugin instance and free memory,
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- ``plugin_version``
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to check that the plugin is compatible with the current version of
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the plugin API,
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- ``plugin_check``
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to test syntactic correctness of the plugin parameters.
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At various locations within the :iscman:`named` source code, there are "hook
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points" at which a plugin may register itself. When a hook point is
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reached while :iscman:`named` is running, it is checked to see whether any
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plugins have registered themselves there; if so, the associated "hook
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action" - a function within the plugin library - is called. Hook
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actions may examine the runtime state and make changes: for example,
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modifying the answers to be sent back to a client or forcing a query to
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be aborted. More details can be found in the file
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``lib/ns/include/ns/hooks.h``.
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