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b1de39dec8
Logically, this is better, because we're describing a subset of possible return values. Visually this also looks quite good because groff renders refsect2 much less prominently. Also rewrap things, add <constant> in various places, fix some typos.
190 lines
8.4 KiB
XML
190 lines
8.4 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="sd_bus_message_new" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_message_new</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_message_new</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_message_new</refname>
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<refname>sd_bus_message_ref</refname>
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<refname>sd_bus_message_unref</refname>
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<refname>sd_bus_message_unrefp</refname>
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<refname>SD_BUS_MESSAGE_METHOD_CALL</refname>
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<refname>SD_BUS_MESSAGE_METHOD_RETURN</refname>
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<refname>SD_BUS_MESSAGE_METHOD_ERROR</refname>
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<refname>SD_BUS_MESSAGE_SIGNAL</refname>
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<refname>sd_bus_message_get_bus</refname>
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<refpurpose>Create a new bus message object and create or destroy references to it</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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<funcsynopsisinfo><token>enum</token> {
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<constant>SD_BUS_MESSAGE_METHOD_CALL</constant>,
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<constant>SD_BUS_MESSAGE_METHOD_RETURN</constant>,
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<constant>SD_BUS_MESSAGE_METHOD_ERROR</constant>,
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<constant>SD_BUS_MESSAGE_SIGNAL</constant>,
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};</funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_bus_message_new</function></funcdef>
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<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
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<paramdef>sd_bus_message **<parameter>m</parameter></paramdef>
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<paramdef>uint8_t <parameter>type</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_bus_message *<function>sd_bus_message_ref</function></funcdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_bus_message *<function>sd_bus_message_unref</function></funcdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void <function>sd_bus_message_unrefp</function></funcdef>
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<paramdef>sd_bus_message **<parameter>mp</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_bus *<function>sd_bus_message_get_bus</function></funcdef>
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<paramdef>sd_bus_message *<parameter>m</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_message_new()</function> creates a new bus message object attached to the
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bus <parameter>bus</parameter> and returns it in the output parameter <parameter>m</parameter>.
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This object is reference-counted, and will be destroyed when all references are gone. Initially,
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the caller of this function owns the sole reference to the message object. Note that the message
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object holds a reference to the bus object, so the bus object will not be destroyed as long as
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the message exists.</para>
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<para>Note: this is a low-level call. In most cases functions like
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<citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_new_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_new_method_return</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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and <citerefentry><refentrytitle>sd_bus_message_new_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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that create a message of a certain type and initialize various fields are easier to use.</para>
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<para>The <parameter>type</parameter> parameter specifies the type of the message. It must be
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one of <constant>SD_BUS_MESSAGE_METHOD_CALL</constant> — a method call,
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<constant>SD_BUS_MESSAGE_METHOD_RETURN</constant> — a method call reply,
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<constant>SD_BUS_MESSAGE_METHOD_ERROR</constant> — an error reply to a method call,
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<constant>SD_BUS_MESSAGE_SIGNAL</constant> — a broadcast message with no reply.
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</para>
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<para>The flag to allow interactive authorization is initialized based on the current value set
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in the bus object, see
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<citerefentry><refentrytitle>sd_bus_set_allow_interactive_authorization</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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This may be changed using
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<citerefentry><refentrytitle>sd_bus_message_set_allow_interactive_authorization</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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<para><function>sd_bus_message_ref()</function> increases the reference counter of
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<parameter>m</parameter> by one.</para>
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<para><function>sd_bus_message_unref()</function> decreases the reference counter of
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<parameter>m</parameter> by one. Once the reference count has dropped to zero, message object is
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destroyed and cannot be used anymore, so further calls to
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<function>sd_bus_message_ref()</function> or <function>sd_bus_message_unref()</function> are
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illegal.</para>
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<para><function>sd_bus_message_unrefp()</function> is similar to
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<function>sd_bus_message_unref()</function> but takes a pointer to a
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pointer to an <type>sd_bus_message</type> object. This call is useful in
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conjunction with GCC's and LLVM's <ulink
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url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
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Variable Attribute</ulink>. See
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<citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for an example how to use the cleanup attribute.</para>
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<para><function>sd_bus_message_ref()</function> and <function>sd_bus_message_unref()</function>
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execute no operation if the passed in bus object address is
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<constant>NULL</constant>. <function>sd_bus_message_unrefp()</function> will first dereference
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its argument, which must not be <constant>NULL</constant>, and will execute no operation if
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<emphasis>that</emphasis> is <constant>NULL</constant>.
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</para>
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<para><function>sd_bus_message_get_bus()</function> returns the bus object that message
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<parameter>m</parameter> is attached to.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, <function>sd_bus_message_new()</function> returns 0 or a positive integer. On
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failure, it returns a negative errno-style error code.</para>
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<para><function>sd_bus_message_ref()</function> always returns the argument.
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</para>
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<para><function>sd_bus_message_unref()</function> always returns
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<constant>NULL</constant>.</para>
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<para><function>sd_bus_message_get_bus()</function> always returns the bus object.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>Specified <parameter>type</parameter> is invalid.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOTCONN</constant></term>
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<listitem><para>The bus parameter <parameter>bus</parameter> is <constant>NULL</constant> or
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the bus is not connected.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Memory allocation failed.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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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_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_new_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_new_method_return</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_new_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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