1 <?xml version='1.0'?> <!--*-nxml-*-->
2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
6 SPDX-License-Identifier: LGPL-2.1+
9 <refentry id="sd_bus_request_name">
12 <title>sd_bus_request_name</title>
13 <productname>systemd</productname>
17 <contrib>Developer</contrib>
18 <firstname>Lennart</firstname>
19 <surname>Poettering</surname>
20 <email>lennart@poettering.net</email>
26 <refentrytitle>sd_bus_request_name</refentrytitle>
27 <manvolnum>3</manvolnum>
31 <refname>sd_bus_request_name</refname>
32 <refname>sd_bus_request_name_async</refname>
33 <refname>sd_bus_release_name</refname>
34 <refname>sd_bus_release_name_async</refname>
35 <refpurpose>Request or release a well-known service name on a bus</refpurpose>
40 <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
43 <funcdef>int <function>sd_bus_request_name</function></funcdef>
44 <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
45 <paramdef>const char *<parameter>name</parameter></paramdef>
46 <paramdef>uint64_t <parameter>flags</parameter></paramdef>
50 <funcdef>int <function>sd_bus_request_name_async</function></funcdef>
51 <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
52 <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
53 <paramdef>const char *<parameter>name</parameter></paramdef>
54 <paramdef>uint64_t <parameter>flags</parameter></paramdef>
55 <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
56 <paramdef>void *<parameter>userdata</parameter></paramdef>
60 <funcdef>int <function>sd_bus_release_name</function></funcdef>
61 <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
62 <paramdef>const char *<parameter>name</parameter></paramdef>
66 <funcdef>int <function>sd_bus_release_name_async</function></funcdef>
67 <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
68 <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
69 <paramdef>const char *<parameter>name</parameter></paramdef>
70 <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
71 <paramdef>void *<parameter>userdata</parameter></paramdef>
77 <title>Description</title>
79 <para><function>sd_bus_request_name()</function> requests a well-known service name on a bus. It takes a bus
80 connection, a valid bus name and a flags parameter. The flags parameter is a combination of the following
85 <term><varname>SD_BUS_NAME_ALLOW_REPLACEMENT</varname></term>
87 <listitem><para>After acquiring the name successfully, permit other peers to take over the name when they try
88 to acquire it with the <varname>SD_BUS_NAME_REPLACE_EXISTING</varname> flag set. If
89 <varname>SD_BUS_NAME_ALLOW_REPLACEMENT</varname> is not set on the original request, such a request by other
90 peers will be denied.</para></listitem>
94 <term><varname>SD_BUS_NAME_REPLACE_EXISTING</varname></term>
96 <listitem><para>Take over the name if it is already acquired by another peer, and that other peer has permitted
97 takeover by setting <varname>SD_BUS_NAME_ALLOW_REPLACEMENT</varname> while acquiring it.</para></listitem>
101 <term><varname>SD_BUS_NAME_QUEUE</varname></term>
103 <listitem><para>Queue the acquisition of the name when the name is already taken.</para></listitem>
107 <para><function>sd_bus_request_name()</function> operates in a synchronous fashion: a message requesting the name
108 is sent to the bus broker, and the call waits until the broker responds.</para>
110 <para><function>sd_bus_request_name_async()</function> is an asynchronous version of
111 <function>sd_bus_release_name()</function>. Instead of waiting for the request to complete, the request message is
112 enqueued. The specified <parameter>callback</parameter> will be called when the broker's response is received. If
113 the parameter is specified as <constant>NULL</constant> a default implementation is used instead which will
114 terminate the connection when the name cannot be acquired. The function returns a slot object in its
115 <parameter>slot</parameter> parameter — if it is passed as non-<constant>NULL</constant> — which may be used as a
116 reference to the name request operation. Use
117 <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry> to destroy
118 this reference. Note that destroying the reference will not unregister the name, but simply ensure the specified
119 callback is no longer called.</para>
121 <para><function>sd_bus_release_name()</function> releases an acquired well-known name. It takes a bus connection
122 and a valid bus name as parameters. This function operates synchronously, sending a release request message to the
123 bus broker and waiting for it to reply.</para>
125 <para><function>sd_bus_release_name_async()</function> is an asynchronous version of
126 <function>sd_bus_release_name()</function>. The specified <parameter>callback</parameter> function is called when
127 the name has been released successfully. If specified as <constant>NULL</constant> a generic implementation is used
128 that ignores the result of the operation. As above, the <parameter>slot</parameter> (if
129 non-<constant>NULL</constant>) is set to an object that may be used to reference the operation.</para>
131 <para>These functions are supported only on bus connections, i.e. connections to a bus broker and not on direct
136 <title>Return Value</title>
138 <para>On success, these calls return 0 or a positive integer. On failure, these calls return a negative errno-style
141 <para>If <varname>SD_BUS_NAME_QUEUE</varname> is specified, <function>sd_bus_request_name()</function> will return
142 0 when the name is already taken by another peer and the client has been added to the queue for the name. In that
143 case, the caller can subscribe to <literal>NameOwnerChanged</literal> signals to be notified when the name is
144 successfully acquired. <function>sd_bus_request_name()</function> returns > 0 when the name has immediately
145 been acquired successfully.</para>
149 <title>Errors</title>
151 <para>Returned errors may indicate the following problems:</para>
155 <term><constant>-EALREADY</constant></term>
157 <listitem><para>The caller already is the owner of the specified name.</para></listitem>
161 <term><constant>-EEXIST</constant></term>
163 <listitem><para>The name has already been acquired by a different peer, and SD_BUS_NAME_REPLACE_EXISTING was
164 not specified or the other peer did not specify SD_BUS_NAME_ALLOW_REPLACEMENT while acquiring the
165 name.</para></listitem>
169 <term><constant>-ESRCH</constant></term>
171 <listitem><para>It was attempted to release a name that is currently not registered on the
172 bus.</para></listitem>
176 <term><constant>-EADDRINUSE</constant></term>
178 <listitem><para>It was attempted to release a name that is owned by a different peer on the
179 bus.</para></listitem>
183 <term><constant>-EINVAL</constant></term>
185 <listitem><para>A specified parameter is invalid. This is also generated when the requested name is a special
186 service name reserved by the D-Bus specification, or when the operation is requested on a connection that does
187 not refer to a bus.</para></listitem>
191 <term><constant>-ENOTCONN</constant></term>
193 <listitem><para>The bus connection has been disconnected.</para></listitem>
197 <term><constant>-ECHILD</constant></term>
199 <listitem><para>The bus connection has been created in a different process than the current
200 one.</para></listitem>
208 <para>The <function>sd_bus_acquire_name()</function> and the other interfaces described here are available as a
209 shared library, which can be compiled and linked to with the <constant>libelogind</constant> <citerefentry
210 project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
214 <title>See Also</title>
217 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
218 <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
219 <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
220 <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>