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6d4a5182 | 1 | <?xml version='1.0'?> |
3a54a157 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
6d4a5182 ZJS |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> | |
5 | ||
6 | <refentry id="sd_bus_slot_set_userdata" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
7 | ||
8 | <refentryinfo> | |
9 | <title>sd_bus_slot_set_userdata</title> | |
10 | <productname>systemd</productname> | |
11 | </refentryinfo> | |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>sd_bus_slot_set_userdata</refentrytitle> | |
15 | <manvolnum>3</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>sd_bus_slot_set_userdata</refname> | |
20 | <refname>sd_bus_slot_get_userdata</refname> | |
21 | ||
22 | <refpurpose>Set and query the value in the "userdata" field</refpurpose> | |
23 | </refnamediv> | |
24 | ||
25 | <refsynopsisdiv> | |
26 | <funcsynopsis> | |
27 | <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> | |
28 | ||
29 | <funcprototype> | |
30 | <funcdef>void* <function>sd_bus_slot_set_userdata</function></funcdef> | |
31 | <paramdef>sd_bus_slot* <parameter>slot</parameter></paramdef> | |
32 | <paramdef>void* <parameter>userdata</parameter></paramdef> | |
33 | </funcprototype> | |
34 | ||
35 | <funcprototype> | |
36 | <funcdef>void* <function>sd_bus_slot_get_userdata</function></funcdef> | |
37 | <paramdef>sd_bus_slot* <parameter>slot</parameter></paramdef> | |
38 | </funcprototype> | |
39 | ||
40 | </funcsynopsis> | |
41 | </refsynopsisdiv> | |
42 | ||
43 | <refsect1> | |
44 | <title>Description</title> | |
45 | ||
46 | <para>The userdata pointer allows data to be passed between the point where a callback is | |
47 | registered, for example when a filter is added using | |
48 | <citerefentry><refentrytitle>sd_bus_add_filter</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
49 | or an asynchronous function call is made using | |
50 | <citerefentry><refentrytitle>sd_bus_call_async</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
51 | and the point where the callback is called, without having any global state. The pointer has | |
52 | type <type>void*</type> and is not used by the sd-bus functions in any way, except to pass to | |
53 | the callback function.</para> | |
54 | ||
55 | <para>Usually, the userdata field is set when the slot object is initially | |
56 | registered. <function>sd_bus_slot_set_userdata()</function> may be used to change it later for | |
57 | the bus slot object <parameter>slot</parameter>. Previous value of the field is returned. The | |
58 | argument and returned value may be <constant>NULL</constant>. It will be passed as the | |
59 | <parameter>userdata</parameter> argument to the callback function attached to the slot.</para> | |
60 | ||
61 | <para><function>sd_bus_slot_set_userdata()</function> gets the value of the userdata field in | |
62 | the bus slot object <parameter>slot</parameter>.</para> | |
63 | </refsect1> | |
64 | ||
65 | <refsect1> | |
66 | <title>Return Value</title> | |
67 | ||
68 | <para>On success, these functions return the value of the userdata field before the function | |
69 | call. If the <parameter>slot</parameter> object is <constant>NULL</constant>, | |
70 | <constant>NULL</constant> will be returned to signify an error, but this is not distinguishable | |
71 | from the userdata field value being <constant>NULL</constant>.</para> | |
72 | </refsect1> | |
73 | ||
74 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
75 | ||
76 | <refsect1> | |
77 | <title>See Also</title> | |
78 | ||
79 | <para> | |
80 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
81 | <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
82 | <citerefentry><refentrytitle>sd_bus_slot_set_destroy_callback</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
83 | <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
84 | <citerefentry><refentrytitle>sd_bus_slot_get_current_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
85 | </para> | |
86 | </refsect1> | |
87 | ||
88 | </refentry> |