man/sd_bus_request_name.xml

   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">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7 -->
   8
   9 <refentry id="sd_bus_request_name">
  10
  11   <refentryinfo>
  12     <title>sd_bus_request_name</title>
  13     <productname>systemd</productname>
  14
  15     <authorgroup>
  16       <author>
  17         <contrib>Developer</contrib>
  18         <firstname>Lennart</firstname>
  19         <surname>Poettering</surname>
  20         <email>lennart@poettering.net</email>
  21       </author>
  22     </authorgroup>
  23   </refentryinfo>
  24
  25   <refmeta>
  26     <refentrytitle>sd_bus_request_name</refentrytitle>
  27     <manvolnum>3</manvolnum>
  28   </refmeta>
  29
  30   <refnamediv>
  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>
  36   </refnamediv>
  37
  38   <refsynopsisdiv>
  39     <funcsynopsis>
  40       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  41
  42       <funcprototype>
  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>
  47       </funcprototype>
  48
  49       <funcprototype>
  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>
  57       </funcprototype>
  58
  59       <funcprototype>
  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>
  63       </funcprototype>
  64
  65       <funcprototype>
  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>
  72       </funcprototype>
  73     </funcsynopsis>
  74   </refsynopsisdiv>
  75
  76   <refsect1>
  77     <title>Description</title>
  78
  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
  81     flags:</para>
  82
  83     <variablelist>
  84       <varlistentry>
  85         <term><varname>SD_BUS_NAME_ALLOW_REPLACEMENT</varname></term>
  86
  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>
  91       </varlistentry>
  92
  93       <varlistentry>
  94         <term><varname>SD_BUS_NAME_REPLACE_EXISTING</varname></term>
  95
  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>
  98       </varlistentry>
  99
 100       <varlistentry>
 101         <term><varname>SD_BUS_NAME_QUEUE</varname></term>
 102
 103         <listitem><para>Queue the acquisition of the name when the name is already taken.</para></listitem>
 104       </varlistentry>
 105     </variablelist>
 106
 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>
 109
 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>
 120
 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>
 124
 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>
 130
 131     <para>These functions are supported only on bus connections, i.e. connections to a bus broker and not on direct
 132     connections.</para>
 133   </refsect1>
 134
 135   <refsect1>
 136     <title>Return Value</title>
 137
 138     <para>On success, these calls return 0 or a positive integer. On failure, these calls return a negative errno-style
 139     error code.</para>
 140
 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 &gt; 0 when the name has immediately
 145     been acquired successfully.</para>
 146   </refsect1>
 147
 148   <refsect1>
 149     <title>Errors</title>
 150
 151     <para>Returned errors may indicate the following problems:</para>
 152
 153     <variablelist>
 154       <varlistentry>
 155         <term><constant>-EALREADY</constant></term>
 156
 157         <listitem><para>The caller already is the owner of the specified name.</para></listitem>
 158       </varlistentry>
 159
 160       <varlistentry>
 161         <term><constant>-EEXIST</constant></term>
 162
 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>
 166       </varlistentry>
 167
 168       <varlistentry>
 169         <term><constant>-ESRCH</constant></term>
 170
 171         <listitem><para>It was attempted to release a name that is currently not registered on the
 172         bus.</para></listitem>
 173       </varlistentry>
 174
 175       <varlistentry>
 176         <term><constant>-EADDRINUSE</constant></term>
 177
 178         <listitem><para>It was attempted to release a name that is owned by a different peer on the
 179         bus.</para></listitem>
 180       </varlistentry>
 181
 182       <varlistentry>
 183         <term><constant>-EINVAL</constant></term>
 184
 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>
 188       </varlistentry>
 189
 190       <varlistentry>
 191         <term><constant>-ENOTCONN</constant></term>
 192
 193         <listitem><para>The bus connection has been disconnected.</para></listitem>
 194       </varlistentry>
 195
 196       <varlistentry>
 197         <term><constant>-ECHILD</constant></term>
 198
 199         <listitem><para>The bus connection has been created in a different process than the current
 200         one.</para></listitem>
 201       </varlistentry>
 202     </variablelist>
 203   </refsect1>
 204
 205   <refsect1>
 206     <title>Notes</title>
 207
 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>libsystemd</constant> <citerefentry
 210     project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
 211   </refsect1>
 212
 213   <refsect1>
 214     <title>See Also</title>
 215
 216     <para>
 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>
 221     </para>
 222   </refsect1>
 223
 224 </refentry>