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198 lines
8.7 KiB
XML
198 lines
8.7 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-or-later -->
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<refentry id="sd_bus_message_open_container"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_message_open_container</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_open_container</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_open_container</refname>
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<refname>sd_bus_message_close_container</refname>
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<refname>sd_bus_message_enter_container</refname>
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<refname>sd_bus_message_exit_container</refname>
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<refpurpose>Create and move between containers in D-Bus messages</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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<funcprototype>
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<funcdef>int sd_bus_message_open_container</funcdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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<paramdef>char <parameter>type</parameter></paramdef>
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<paramdef>const char *<parameter>contents</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int sd_bus_message_close_container</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>int sd_bus_message_enter_container</funcdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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<paramdef>char <parameter>type</parameter></paramdef>
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<paramdef>const char *<parameter>contents</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int sd_bus_message_exit_container</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_open_container()</function> appends a new container to the message
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<parameter>m</parameter>. After opening a new container, it can be filled with content using
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<citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and similar functions. Containers behave like a stack. To nest containers inside each other, call
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<function>sd_bus_message_open_container()</function> multiple times without calling
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<function>sd_bus_message_close_container()</function> in between. Each container will be nested inside the
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previous container. <parameter>type</parameter> represents the container type and should be one of
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<literal>r</literal>, <literal>a</literal>, <literal>v</literal> or <literal>e</literal> as described in
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<citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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Instead of literals, the corresponding constants <constant>SD_BUS_TYPE_STRUCT</constant>,
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<constant>SD_BUS_TYPE_ARRAY</constant>, <constant>SD_BUS_TYPE_VARIANT</constant> or
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<constant>SD_BUS_TYPE_DICT_ENTRY</constant> can also be used. <parameter>contents</parameter> describes
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the type of the container's elements and should be a D-Bus type string following the rules described in
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<citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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<para><function>sd_bus_message_close_container()</function> closes the last container opened with
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<function>sd_bus_message_open_container()</function>. On success, the write pointer of the message
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<parameter>m</parameter> is positioned after the closed container in its parent container or in
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<parameter>m</parameter> itself if there is no parent container.</para>
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<para><function>sd_bus_message_enter_container()</function> enters the next container of the message
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<parameter>m</parameter> for reading. It behaves mostly the same as
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<function>sd_bus_message_open_container()</function>. Entering a container allows reading its contents
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with
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<citerefentry><refentrytitle>sd_bus_message_read</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and similar functions. <parameter>type</parameter> and <parameter>contents</parameter> are the same as in
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<function>sd_bus_message_open_container()</function>.</para>
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<para><function>sd_bus_message_exit_container()</function> exits the scope of the last container entered
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with <function>sd_bus_message_enter_container()</function>. It behaves mostly the same as
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<function>sd_bus_message_close_container()</function>. Note that
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<function>sd_bus_message_exit_container()</function> may only be called after iterating through all
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members of the container, i.e. reading or skipping over them. Use
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<citerefentry><refentrytitle>sd_bus_message_skip</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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to skip over fields of a container in order to be able to exit the container with
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<function>sd_bus_message_exit_container()</function> without reading all members.</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, these functions return a non-negative integer.
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<function>sd_bus_message_open_container()</function> and <function>sd_bus_message_close_container()</function>
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return 0.
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<function>sd_bus_message_enter_container()</function> returns 1 if it successfully opened a new container, and 0 if
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that was not possible because the end of the currently open container or message was reached.
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<function>sd_bus_message_exit_container()</function> returns 1 on success.
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On failure, all of these functions return a negative errno-style error code.</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><parameter>m</parameter> or <parameter>contents</parameter> are
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<constant>NULL</constant> or <parameter>type</parameter> is invalid.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EBADMSG</constant></term>
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<listitem><para>Message <parameter>m</parameter> has invalid structure.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENXIO</constant></term>
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<listitem><para>Message <parameter>m</parameter> does not have a container of type
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<parameter>type</parameter> at the current position, or the contents do not match
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<parameter>contents</parameter>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EPERM</constant></term>
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<listitem><para>The message <parameter>m</parameter> is already sealed.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ESTALE</constant></term>
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<listitem><para>The message <parameter>m</parameter> is in an invalid state.</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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<varlistentry>
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<term><constant>-EBUSY</constant></term>
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<listitem><para><function>sd_bus_message_exit_container()</function> was called but there are
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unread members left in the container.</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>Examples</title>
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<example>
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<title>Append an array of strings to a message</title>
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<programlisting><xi:include href="sd-bus-container-append.c" parse="text" /></programlisting>
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</example>
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<example>
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<title>Read an array of strings from a message</title>
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<programlisting><xi:include href="sd-bus-container-read.c" parse="text" /></programlisting>
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</example>
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</refsect1>
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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_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_read</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_skip</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<ulink url="https://dbus.freedesktop.org/doc/dbus-specification.html">The D-Bus specification</ulink>
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</para>
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</refsect1>
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</refentry>
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