183 lines
9.3 KiB
XML
183 lines
9.3 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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<!DOCTYPE refentry 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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<!--
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SPDX-License-Identifier: LGPL-2.1+
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This file is part of systemd.
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Copyright 2016 Julian Orth
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-->
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<refentry id="sd_bus_add_match">
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<refentryinfo>
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<title>sd_bus_add_match</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<firstname>Julian</firstname>
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<surname>Orth</surname>
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<email>ju.orth@gmail.com</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_add_match</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_bus_add_match</refname>
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<refname>sd_bus_add_match_async</refname>
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<refname>sd_bus_match_signal</refname>
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<refname>sd_bus_match_signal_async</refname>
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<refpurpose>Add a match rule for incoming message dispatching</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>typedef int (*<function>sd_bus_message_handler_t</function>)</funcdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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<paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_add_match</function></funcdef>
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<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
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<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
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<paramdef>const char *<parameter>match</parameter></paramdef>
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<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_add_match_async</function></funcdef>
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<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
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<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
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<paramdef>const char *<parameter>match</parameter></paramdef>
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<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
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<paramdef>sd_bus_message_handler_t <parameter>install_callback</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_match_signal</function></funcdef>
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<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
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<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
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<paramdef>const char *<parameter>sender</parameter></paramdef>
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<paramdef>const char *<parameter>path</parameter></paramdef>
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<paramdef>const char *<parameter>interface</parameter></paramdef>
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<paramdef>const char *<parameter>member</parameter></paramdef>
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<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_match_signal_async</function></funcdef>
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<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
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<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
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<paramdef>const char *<parameter>sender</parameter></paramdef>
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<paramdef>const char *<parameter>path</parameter></paramdef>
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<paramdef>const char *<parameter>interface</parameter></paramdef>
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<paramdef>const char *<parameter>member</parameter></paramdef>
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<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
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<paramdef>sd_bus_message_handler_t <parameter>install_callback</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_bus_add_match()</function> installs a match rule for messages received on the specified bus
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connection object <parameter>bus</parameter>. The syntax of the match rule expression passed in
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<parameter>match</parameter> is described in the <ulink
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url="https://dbus.freedesktop.org/doc/dbus-specification.html">D-Bus Specification</ulink>. The specified handler
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function <parameter>callback</parameter> is called for eaching incoming message matching the specified expression,
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the <parameter>userdata</parameter> parameter is passed as-is to the callback function. The match is installed
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synchronously when connected to a bus broker, i.e. the call sends a control message requested the match to be added
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to the broker and waits until the broker confirms the match has been installed successfully.</para>
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<para><function>sd_bus_add_match_async()</function> operates very similar to
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<function>sd_bus_match_signal()</function>, however it installs the match asynchronously, in a non-blocking
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fashion: a request is sent to the broker, but the call does not wait for a response. The
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<parameter>install_callback</parameter> function is called when the response is later received, with the response
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message from the broker as parameter. If this function is specified as <constant>NULL</constant> a default
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implementation is used that terminates the bus connection should installing the match fail.</para>
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<para><function>sd_bus_match_signal()</function> is very similar to <function>sd_bus_add_match()</function>, but
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only matches signals, and instead of a match expression accepts four parameters: <parameter>sender</parameter> (the
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service name of the sender), <parameter>path</parameter> (the object path of the emitting object),
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<parameter>interface</parameter> (the interface the signal belongs to), <parameter>member</parameter> (the signal
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name), from which the match string is internally generated. Optionally, these parameters may be specified as
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<constant>NULL</constant> in which case the relevant field of incoming signals is not tested.</para>
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<para><function>sd_bus_match_signal_async()</function> is combines the signal matching logic of
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<function>sd_bus_match_signal()</function> with the asynchronous behaviour of
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<function>sd_bus_add_match_async()</function>.</para>
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<para>On success, and if non-<constant>NULL</constant>, the <parameter>slot</parameter> return parameter will be
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set to a slot object that may be used as a reference to the installed match, and may be utilized to remove it again
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at a later time with
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<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If specified
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as <constant>NULL</constant> the lifetime of the match is bound to the lifetime of the bus object itself, and the
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match cannot be removed independently.</para>
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<para>The message <parameter>m</parameter> passed to the callback is only borrowed, that is, the callback should
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not call <citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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on it. If the callback wants to hold on to the message beyond the lifetime of the callback, it needs to call
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<citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry> to create a
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new reference.</para>
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<para>If an error occurs during the callback invocation, the callback should return a negative error number
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(optionally, a more precise error may be returned in <parameter>ret_error</parameter>, as well). If it wants other
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callbacks that match the same rule to be called, it should return 0. Otherwise it should return a positive integer.
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</para>
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<para>If the <parameter>bus</parameter> refers to a direct connection (i.e. not a bus connection, as set with
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<citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>) the
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match is only installed on the client side, and the synchronous and asynchronous functions operate the same.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>
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On success, <function>sd_bus_add_match()</function> and the other calls return 0 or a positive integer. On
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failure, they return a negative errno-style error code.
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</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para><function>sd_bus_add_match()</function> and the other functions described here are available as a shared
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library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
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project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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