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As some incompatible changes have already been made to the hooks interface (removal of the setSkip method), it seems pointless to support both old and new hoos-libraries syntax. These modifications remove support for the old syntax.
96 lines
3.7 KiB
XML
96 lines
3.7 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
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<!ENTITY mdash "—" >
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]>
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<chapter id="hooks-libraries">
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<title>Hooks Libraries</title>
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<section id="hooks-libraries-introduction">
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<title>Introduction</title>
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<para>
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Although Kea offers a lot of flexibility, there may be cases where
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its behavior needs customisation. To accommodate this possibility,
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Kea includes the idea of "Hooks". This feature lets Kea load one
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or more dynamically-linked libraries (known as "hooks libraries")
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and, at various points in its processing ("hook points"), call
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functions in them. Those functions perform whatever custom
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processing is required.
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</para>
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<para>
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Hooks libraries are attached to individual Kea processes, not to
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Kea as a whole. This means (for example) that it is possible
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to associate one set of libraries with the DHCP4 server and a
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different set to the DHCP6 server.
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</para>
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<para>
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Another point to note is that it is possible for a process to
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load multiple libraries. When processing reaches a hook point,
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Kea calls the hooks library functions attached to it. If multiple
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libraries have attached a function to a given hook point, Kea calls
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all of them, in the order in which the libraries are specified in
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the configuration file. The order may be important: consult the
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documentation of the libraries to see if this is the case.
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</para>
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<para>
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The next section describes how to configure hooks libraries. If you
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are interested in writing your own hooks library, information can be
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found in the <ulink url="http://git.kea.isc.org/~tester/kea/doxygen">Kea
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Developer's Guide</ulink>.
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</para>
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</section> <!-- end Introduction -->
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<section>
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<title>Configuring Hooks Libraries</title>
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<para>
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The hooks libraries for a given process are configured using the
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<command>hooks-libraries</command> keyword in the
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configuration for that process. (Note that
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the word "hooks" is plural). The value of the keyword
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is an array of map structures, each structure corresponding to a hooks
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library. For example, to set up two hooks libraries for the DHCPv4
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server, the configuration would be:
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<screen>
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<userinput>"Dhcp4": {
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:
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"hooks-libraries": [
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{
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"library": "/opt/charging.so"
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},
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{
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"library": "/opt/local/notification.so"
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}
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]
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:
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}</userinput>
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</screen>
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</para>
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<note><para>
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This is a change to the syntax used in Kea 0.9.2 and earlier, where
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hooks-libraries was a list of strings, each string being the name of
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a library. The change has been made in Kea 1.0 to facilitate the
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specification of library-specific parameters, a feature that will be
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added to a future version of Kea.
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</para></note>
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<para>
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Notes:
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<itemizedlist mark='bullet'>
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<listitem><para>
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The full path to each library should be given.
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</para></listitem>
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<listitem><para>
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As noted above, order may be important - consult the documentation for
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each library.
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</para></listitem>
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<listitem><para>
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An empty list has the same effect as omitting the
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<command>hooks-libraries</command> configuration element all together.
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</para></listitem>
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</itemizedlist>
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</para>
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<para>
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At the present time, only the kea-dhcp4 and kea-dhcp6 processes support
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hooks libraries.
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</para>
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</section>
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</chapter> <!-- hooks-libraries -->
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