<?xml version='1.0'?> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> <refentry id="sd_bus_message_new" xmlns:xi="http://www.w3.org/2001/XInclude"> <refentryinfo> <title>sd_bus_message_new</title> <productname>systemd</productname> </refentryinfo> <refmeta> <refentrytitle>sd_bus_message_new</refentrytitle> <manvolnum>3</manvolnum> </refmeta> <refnamediv> <refname>sd_bus_message_new</refname> <refname>sd_bus_message_ref</refname> <refname>sd_bus_message_unref</refname> <refname>sd_bus_message_unrefp</refname> <refname>SD_BUS_MESSAGE_METHOD_CALL</refname> <refname>SD_BUS_MESSAGE_METHOD_RETURN</refname> <refname>SD_BUS_MESSAGE_METHOD_ERROR</refname> <refname>SD_BUS_MESSAGE_SIGNAL</refname> <refname>sd_bus_message_get_bus</refname> <refpurpose>Create a new bus message object and create or destroy references to it</refpurpose> </refnamediv> <refsynopsisdiv> <funcsynopsis> <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> <funcsynopsisinfo><token>enum</token> { <constant>SD_BUS_MESSAGE_METHOD_CALL</constant>, <constant>SD_BUS_MESSAGE_METHOD_RETURN</constant>, <constant>SD_BUS_MESSAGE_METHOD_ERROR</constant>, <constant>SD_BUS_MESSAGE_SIGNAL</constant>, };</funcsynopsisinfo> <funcprototype> <funcdef>int <function>sd_bus_message_new</function></funcdef> <paramdef>sd_bus *<parameter>bus</parameter></paramdef> <paramdef>sd_bus_message **<parameter>m</parameter></paramdef> <paramdef>uint8_t <parameter>type</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>sd_bus_message *<function>sd_bus_message_ref</function></funcdef> <paramdef>sd_bus_message *<parameter>m</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>sd_bus_message *<function>sd_bus_message_unref</function></funcdef> <paramdef>sd_bus_message *<parameter>m</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>void <function>sd_bus_message_unrefp</function></funcdef> <paramdef>sd_bus_message **<parameter>mp</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>sd_bus *<function>sd_bus_message_get_bus</function></funcdef> <paramdef>sd_bus_message *<parameter>m</parameter></paramdef> </funcprototype> </funcsynopsis> </refsynopsisdiv> <refsect1> <title>Description</title> <para><function>sd_bus_message_new()</function> creates a new bus message object attached to the bus <parameter>bus</parameter> and returns it in the output parameter <parameter>m</parameter>. This object is reference-counted, and will be destroyed when all references are gone. Initially, the caller of this function owns the sole reference to the message object. Note that the message object holds a reference to the bus object, so the bus object will not be destroyed as long as the message exists.</para> <para>Note: this is a low-level call. In most cases functions like <citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_message_new_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_message_new_method_return</refentrytitle><manvolnum>3</manvolnum></citerefentry>, and <citerefentry><refentrytitle>sd_bus_message_new_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry> that create a message of a certain type and initialize various fields are easier to use.</para> <para>The <parameter>type</parameter> parameter specifies the type of the message. It must be one of <constant>SD_BUS_MESSAGE_METHOD_CALL</constant> — a method call, <constant>SD_BUS_MESSAGE_METHOD_RETURN</constant> — a method call reply, <constant>SD_BUS_MESSAGE_METHOD_ERROR</constant> — an error reply to a method call, <constant>SD_BUS_MESSAGE_SIGNAL</constant> — a broadcast message with no reply. </para> <para>The flag to allow interactive authorization is initialized based on the current value set in the bus object, see <citerefentry><refentrytitle>sd_bus_set_allow_interactive_authorization</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This may be changed using <citerefentry><refentrytitle>sd_bus_message_set_allow_interactive_authorization</refentrytitle><manvolnum>3</manvolnum></citerefentry>. </para> <para><function>sd_bus_message_ref()</function> increases the internal reference counter of <parameter>m</parameter> by one.</para> <para><function>sd_bus_message_unref()</function> decreases the internal reference counter of <parameter>m</parameter> by one. Once the reference count has dropped to zero, message object is destroyed and cannot be used anymore, so further calls to <function>sd_bus_message_ref()</function> or <function>sd_bus_message_unref()</function> are illegal.</para> <para><function>sd_bus_message_unrefp()</function> is similar to <function>sd_bus_message_unref()</function> but takes a pointer to a pointer to an <type>sd_bus_message</type> object. This call is useful in conjunction with GCC's and LLVM's <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up Variable Attribute</ulink>. See <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry> for an example how to use the cleanup attribute.</para> <para><function>sd_bus_message_ref()</function> and <function>sd_bus_message_unref()</function> execute no operation if the passed in bus message object address is <constant>NULL</constant>. <function>sd_bus_message_unrefp()</function> will first dereference its argument, which must not be <constant>NULL</constant>, and will execute no operation if <emphasis>that</emphasis> is <constant>NULL</constant>. </para> <para><function>sd_bus_message_get_bus()</function> returns the bus object that message <parameter>m</parameter> is attached to.</para> </refsect1> <refsect1> <title>Return Value</title> <para>On success, <function>sd_bus_message_new()</function> returns 0 or a positive integer. On failure, it returns a negative errno-style error code.</para> <para><function>sd_bus_message_ref()</function> always returns the argument. </para> <para><function>sd_bus_message_unref()</function> always returns <constant>NULL</constant>.</para> <para><function>sd_bus_message_get_bus()</function> always returns the bus object.</para> <refsect2> <title>Errors</title> <para>Returned errors may indicate the following problems:</para> <variablelist> <varlistentry> <term><constant>-EINVAL</constant></term> <listitem><para>Specified <parameter>type</parameter> is invalid.</para></listitem> </varlistentry> <varlistentry> <term><constant>-ENOTCONN</constant></term> <listitem><para>The bus parameter <parameter>bus</parameter> is <constant>NULL</constant> or the bus is not connected.</para></listitem> </varlistentry> <varlistentry> <term><constant>-ENOMEM</constant></term> <listitem><para>Memory allocation failed.</para></listitem> </varlistentry> </variablelist> </refsect2> </refsect1> <xi:include href="libsystemd-pkgconfig.xml" /> <refsect1> <title>See Also</title> <para> <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_message_new_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_message_new_method_return</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_message_new_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry> </para> </refsect1> </refentry>