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95 lines
3.9 KiB
XML
95 lines
3.9 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_slot_set_userdata" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_slot_set_userdata</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_slot_set_userdata</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_slot_set_userdata</refname>
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<refname>sd_bus_slot_get_userdata</refname>
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<refpurpose>Set and query the value in the "userdata" field</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>void* <function>sd_bus_slot_set_userdata</function></funcdef>
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<paramdef>sd_bus_slot* <parameter>slot</parameter></paramdef>
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<paramdef>void* <parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void* <function>sd_bus_slot_get_userdata</function></funcdef>
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<paramdef>sd_bus_slot* <parameter>slot</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>The userdata pointer allows data to be passed between the point where a callback is
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registered, for example when a filter is added using
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<citerefentry><refentrytitle>sd_bus_add_filter</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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or an asynchronous function call is made using
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<citerefentry><refentrytitle>sd_bus_call_async</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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and the point where the callback is called, without having any global state. The pointer has
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type <type>void*</type> and is not used by the sd-bus functions in any way, except to pass to
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the callback function.</para>
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<para>Usually, the userdata field is set when the slot object is initially
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registered. <function>sd_bus_slot_set_userdata()</function> may be used to change it later for
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the bus slot object <parameter>slot</parameter>. Previous value of the field is returned. The
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argument and returned value may be <constant>NULL</constant>. It will be passed as the
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<parameter>userdata</parameter> argument to the callback function attached to the slot.</para>
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<para><function>sd_bus_slot_set_userdata()</function> gets the value of the userdata field in
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the bus slot object <parameter>slot</parameter>.</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 the value of the userdata field before the function
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call. If the <parameter>slot</parameter> object is <constant>NULL</constant>,
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<constant>NULL</constant> will be returned to signify an error, but this is not distinguishable
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from the userdata field value being <constant>NULL</constant>.</para>
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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>History</title>
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<para><function>sd_bus_slot_set_userdata()</function> and
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<function>sd_bus_slot_get_userdata()</function> were added in version 240.</para>
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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_slot_set_destroy_callback</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_slot_get_current_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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