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_method_call" 7 xmlns:xi="http://www.w3.org/2001/XInclude"> 8 9 <refentryinfo> 10 <title>sd_bus_message_new_method_call</title> 11 <productname>systemd</productname> 12 </refentryinfo> 13 14 <refmeta> 15 <refentrytitle>sd_bus_message_new_method_call</refentrytitle> 16 <manvolnum>3</manvolnum> 17 </refmeta> 18 19 <refnamediv> 20 <refname>sd_bus_message_new_method_call</refname> 21 <refname>sd_bus_message_new_method_return</refname> 22 23 <refpurpose>Create a method call message</refpurpose> 24 </refnamediv> 25 26 <refsynopsisdiv> 27 <funcsynopsis> 28 <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> 29 30 <funcprototype> 31 <funcdef>int <function>sd_bus_message_new_method_call</function></funcdef> 32 <paramdef>sd_bus *<parameter>bus</parameter></paramdef> 33 <paramdef>sd_bus_message **<parameter>m</parameter></paramdef> 34 <paramdef>const char *<parameter>destination</parameter></paramdef> 35 <paramdef>const char *<parameter>path</parameter></paramdef> 36 <paramdef>const char *<parameter>interface</parameter></paramdef> 37 <paramdef>const char *<parameter>member</parameter></paramdef> 38 </funcprototype> 39 40 <funcprototype> 41 <funcdef>int <function>sd_bus_message_new_method_return</function></funcdef> 42 <paramdef>sd_bus_message *<parameter>call</parameter></paramdef> 43 <paramdef>sd_bus_message **<parameter>m</parameter></paramdef> 44 </funcprototype> 45 </funcsynopsis> 46 </refsynopsisdiv> 47 48 <refsect1> 49 <title>Description</title> 50 51 <para>The <function>sd_bus_message_new_method_call()</function> function creates a new bus 52 message object that encapsulates a D-Bus method call, and returns it in the 53 <parameter>m</parameter> output parameter. The call will be made on the destination 54 <parameter>destination</parameter>, path <parameter>path</parameter>, on the interface 55 <parameter>interface</parameter>, member <parameter>member</parameter>.</para> 56 57 <para>Briefly, the <emphasis>destination</emphasis> is a dot-separated name that identifies a 58 service connected to the bus. The <emphasis>path</emphasis> is a slash-separated identifier of 59 an object within the destination that resembles a file system path. The meaning of this path is 60 defined by the destination. The <emphasis>interface</emphasis> is a dot-separated name that 61 resembles a Java interface name that identifies a group of methods and signals supported by the 62 object identified by path. Methods and signals are collectively called 63 <emphasis>members</emphasis> and are identified by a simple name composed of ASCII letters, 64 numbers, and underscores. See the <ulink 65 url="https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts">D-Bus Tutorial</ulink> for an 66 in-depth explanation.</para> 67 68 <para>The <parameter>destination</parameter> parameter may be <constant>NULL</constant>. The 69 <parameter>interface</parameter> parameter may be <constant>NULL</constant>, if the destination 70 has only a single member with the given name and there is no ambiguity if the interface name is 71 omitted.</para> 72 73 <para>Note that this is a low level interface. See 74 <citerefentry><refentrytitle>sd_bus_call_method</refentrytitle><manvolnum>3</manvolnum></citerefentry> 75 for a more convenient way of calling D-Bus methods.</para> 76 77 <para>The <function>sd_bus_message_new_method_return()</function> function creates a new bus 78 message object that is a reply to the method call <parameter>call</parameter> and returns it in 79 the <parameter>m</parameter> output parameter. The <parameter>call</parameter> parameter must be 80 a method call message. The sender of <parameter>call</parameter> is used as the destination. 81 </para> 82 </refsect1> 83 84 <refsect1> 85 <title>Return Value</title> 86 87 <para>On success, these functions return a non-negative integer. On failure, they return a 88 negative errno-style error code.</para> 89 90 <refsect2 id='errors'> 91 <title>Errors</title> 92 93 <para>Returned errors may indicate the following problems:</para> 94 95 <variablelist> 96 <varlistentry> 97 <term><constant>-EINVAL</constant></term> 98 99 <listitem><para>The output parameter <parameter>m</parameter> is 100 <constant>NULL</constant>.</para> 101 102 <para>The <parameter>destination</parameter> parameter is non-null and is not a valid D-Bus 103 service name (<literal>org.somewhere.Something</literal>), the <parameter>path</parameter> 104 parameter is not a valid D-Bus path (<literal>/an/object/path</literal>), the 105 <parameter>interface</parameter> parameter is non-null and is not a valid D-Bus interface 106 name (<literal>an.interface.name</literal>), or the <parameter>member</parameter> parameter 107 is not a valid D-Bus member (<literal>Name</literal>).</para> 108 109 <para>The <parameter>call</parameter> parameter is not a method call object.</para> 110 </listitem> 111 </varlistentry> 112 113 <varlistentry> 114 <term><constant>-ENOTCONN</constant></term> 115 116 <listitem><para>The bus parameter <parameter>bus</parameter> is <constant>NULL</constant> or 117 the bus is not connected.</para></listitem> 118 </varlistentry> 119 120 <varlistentry> 121 <term><constant>-ENOMEM</constant></term> 122 123 <listitem><para>Memory allocation failed.</para></listitem> 124 </varlistentry> 125 126 <varlistentry> 127 <term><constant>-EPERM</constant></term> 128 129 <listitem> 130 <para>The <parameter>call</parameter> parameter is not sealed.</para> 131 </listitem> 132 </varlistentry> 133 134 <varlistentry> 135 <term><constant>-EOPNOTSUPP</constant></term> 136 137 <listitem> 138 <para>The <parameter>call</parameter> message does not have a cookie.</para> 139 </listitem> 140 </varlistentry> 141 </variablelist> 142 </refsect2> 143 </refsect1> 144 145 <xi:include href="libsystemd-pkgconfig.xml" /> 146 147 <refsect1> 148 <title>Examples</title> 149 150 <example> 151 <title>Make a call to a D-Bus method that takes a single parameter</title> 152 153 <programlisting><xi:include href="print-unit-path.c" parse="text" /></programlisting> 154 <para>This defines a minimally useful program that will open a connection to the bus, create a 155 message object, send it, wait for the reply, and finally extract and print the answer. It does 156 error handling and proper memory management.</para> 157 </example> 158 </refsect1> 159 160 <refsect1> 161 <title>See Also</title> 162 163 <para> 164 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, 165 <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 166 <citerefentry><refentrytitle>sd_bus_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 167 <citerefentry><refentrytitle>sd_bus_call_method</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 168 <citerefentry><refentrytitle>sd_bus_path_encode</refentrytitle><manvolnum>3</manvolnum></citerefentry> 169 </para> 170 </refsect1> 171 172</refentry> 173