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<?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>
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