1<?xml version='1.0'?>
2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
5
6<refentry id="sd_bus_message_new_signal"
7          xmlns:xi="http://www.w3.org/2001/XInclude">
8
9  <refentryinfo>
10    <title>sd_bus_message_new_signal</title>
11    <productname>systemd</productname>
12  </refentryinfo>
13
14  <refmeta>
15    <refentrytitle>sd_bus_message_new_signal</refentrytitle>
16    <manvolnum>3</manvolnum>
17  </refmeta>
18
19  <refnamediv>
20    <refname>sd_bus_message_new_signal</refname>
21
22    <refpurpose>Create a signal message</refpurpose>
23  </refnamediv>
24
25  <refsynopsisdiv>
26    <funcsynopsis>
27      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
28
29      <funcprototype>
30        <funcdef>int sd_bus_message_new_signal</funcdef>
31        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
32        <paramdef>sd_bus_message **<parameter>m</parameter></paramdef>
33        <paramdef>const char *<parameter>path</parameter></paramdef>
34        <paramdef>const char *<parameter>interface</parameter></paramdef>
35        <paramdef>const char *<parameter>member</parameter></paramdef>
36      </funcprototype>
37    </funcsynopsis>
38  </refsynopsisdiv>
39
40  <refsect1>
41    <title>Description</title>
42
43    <para>The <function>sd_bus_message_new_signal()</function> function creates a new bus message
44    object that encapsulates a D-Bus signal, and returns it in the <parameter>m</parameter> output
45    parameter. The signal will be sent to path <parameter>path</parameter>, on the interface
46    <parameter>interface</parameter>, member <parameter>member</parameter>. When this message is
47    sent, no reply is expected. See
48    <citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>1</manvolnum></citerefentry>
49    for a short description of the meaning of the <parameter>path</parameter>,
50    <parameter>interface</parameter>, and <parameter>member</parameter> parameters.
51    </para>
52  </refsect1>
53
54  <refsect1>
55    <title>Return Value</title>
56
57    <para>This function returns 0 if the message object was successfully created, and a negative
58    errno-style error code otherwise.</para>
59
60    <refsect2>
61      <title>Errors</title>
62
63      <para>Returned errors may indicate the following problems:</para>
64
65      <variablelist>
66        <varlistentry>
67          <term><constant>-EINVAL</constant></term>
68
69          <listitem><para>The output parameter <parameter>m</parameter> is
70          <constant>NULL</constant>.</para>
71
72          <para>The <parameter>path</parameter> parameter is not a valid D-Bus path
73          (<literal>/an/object/path</literal>), the <parameter>interface</parameter> parameter is not
74          a valid D-Bus interface name (<literal>an.interface.name</literal>), or the
75          <parameter>member</parameter> parameter is not a valid D-Bus member
76          (<literal>Name</literal>).</para></listitem>
77        </varlistentry>
78
79        <varlistentry>
80          <term><constant>-ENOTCONN</constant></term>
81
82          <listitem><para>The bus parameter <parameter>bus</parameter> is <constant>NULL</constant> or
83          the bus is not connected.</para></listitem>
84        </varlistentry>
85
86        <varlistentry>
87          <term><constant>-ENOMEM</constant></term>
88
89          <listitem><para>Memory allocation failed.</para></listitem>
90        </varlistentry>
91      </variablelist>
92    </refsect2>
93  </refsect1>
94
95  <xi:include href="libsystemd-pkgconfig.xml" />
96
97  <refsect1>
98    <title>Examples</title>
99
100    <example>
101      <title>Send a simple signal</title>
102
103      <programlisting><xi:include href="send-unit-files-changed.c" parse="text" /></programlisting>
104
105      <para>This function in systemd sources is used to emit the
106      <literal>UnitFilesChanged</literal> signal when the unit files have been changed.
107      </para>
108    </example>
109  </refsect1>
110
111  <refsect1>
112    <title>See Also</title>
113
114    <para>
115      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
116      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
117      <citerefentry><refentrytitle>sd_bus_emit_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>
118    </para>
119  </refsect1>
120
121</refentry>
122