man/sd_bus_request_name.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   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   </refentryinfo>
  15
  16   <refmeta>
  17     <refentrytitle>sd_bus_request_name</refentrytitle>
  18     <manvolnum>3</manvolnum>
  19   </refmeta>
  20
  21   <refnamediv>
  22     <refname>sd_bus_request_name</refname>
  23     <refname>sd_bus_request_name_async</refname>
  24     <refname>sd_bus_release_name</refname>
  25     <refname>sd_bus_release_name_async</refname>
  26     <refpurpose>Request or release a well-known service name on a bus</refpurpose>
  27   </refnamediv>
  28
  29   <refsynopsisdiv>
  30     <funcsynopsis>
  31       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  32
  33       <funcprototype>
  34         <funcdef>int <function>sd_bus_request_name</function></funcdef>
  35         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  36         <paramdef>const char *<parameter>name</parameter></paramdef>
  37         <paramdef>uint64_t <parameter>flags</parameter></paramdef>
  38       </funcprototype>
  39
  40       <funcprototype>
  41         <funcdef>int <function>sd_bus_request_name_async</function></funcdef>
  42         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  43         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  44         <paramdef>const char *<parameter>name</parameter></paramdef>
  45         <paramdef>uint64_t <parameter>flags</parameter></paramdef>
  46         <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
  47         <paramdef>void *<parameter>userdata</parameter></paramdef>
  48       </funcprototype>
  49
  50       <funcprototype>
  51         <funcdef>int <function>sd_bus_release_name</function></funcdef>
  52         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  53         <paramdef>const char *<parameter>name</parameter></paramdef>
  54       </funcprototype>
  55
  56       <funcprototype>
  57         <funcdef>int <function>sd_bus_release_name_async</function></funcdef>
  58         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  59         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  60         <paramdef>const char *<parameter>name</parameter></paramdef>
  61         <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
  62         <paramdef>void *<parameter>userdata</parameter></paramdef>
  63       </funcprototype>
  64     </funcsynopsis>
  65   </refsynopsisdiv>
  66
  67   <refsect1>
  68     <title>Description</title>
  69
  70     <para><function>sd_bus_request_name()</function> requests a well-known service name on a bus. It takes a bus
  71     connection, a valid bus name and a flags parameter. The flags parameter is a combination of the following
  72     flags:</para>
  73
  74     <variablelist>
  75       <varlistentry>
  76         <term><varname>SD_BUS_NAME_ALLOW_REPLACEMENT</varname></term>
  77
  78         <listitem><para>After acquiring the name successfully, permit other peers to take over the name when they try
  79         to acquire it with the <varname>SD_BUS_NAME_REPLACE_EXISTING</varname> flag set. If
  80         <varname>SD_BUS_NAME_ALLOW_REPLACEMENT</varname> is not set on the original request, such a request by other
  81         peers will be denied.</para></listitem>
  82       </varlistentry>
  83
  84       <varlistentry>
  85         <term><varname>SD_BUS_NAME_REPLACE_EXISTING</varname></term>
  86
  87         <listitem><para>Take over the name if it is already acquired by another peer, and that other peer has permitted
  88         takeover by setting <varname>SD_BUS_NAME_ALLOW_REPLACEMENT</varname> while acquiring it.</para></listitem>
  89       </varlistentry>
  90
  91       <varlistentry>
  92         <term><varname>SD_BUS_NAME_QUEUE</varname></term>
  93
  94         <listitem><para>Queue the acquisition of the name when the name is already taken.</para></listitem>
  95       </varlistentry>
  96     </variablelist>
  97
  98     <para><function>sd_bus_request_name()</function> operates in a synchronous fashion: a message requesting the name
  99     is sent to the bus broker, and the call waits until the broker responds.</para>
 100
 101     <para><function>sd_bus_request_name_async()</function> is an asynchronous version of
 102     <function>sd_bus_release_name()</function>. Instead of waiting for the request to complete, the request message is
 103     enqueued. The specified <parameter>callback</parameter> will be called when the broker's response is received. If
 104     the parameter is specified as <constant>NULL</constant> a default implementation is used instead which will
 105     terminate the connection when the name cannot be acquired. The function returns a slot object in its
 106     <parameter>slot</parameter> parameter — if it is passed as non-<constant>NULL</constant> — which may be used as a
 107     reference to the name request operation. Use
 108     <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry> to destroy
 109     this reference. Note that destroying the reference will not unregister the name, but simply ensure the specified
 110     callback is no longer called.</para>
 111
 112     <para><function>sd_bus_release_name()</function> releases an acquired well-known name. It takes a bus connection
 113     and a valid bus name as parameters. This function operates synchronously, sending a release request message to the
 114     bus broker and waiting for it to reply.</para>
 115
 116     <para><function>sd_bus_release_name_async()</function> is an asynchronous version of
 117     <function>sd_bus_release_name()</function>. The specified <parameter>callback</parameter> function is called when
 118     the name has been released successfully. If specified as <constant>NULL</constant> a generic implementation is used
 119     that ignores the result of the operation. As above, the <parameter>slot</parameter> (if
 120     non-<constant>NULL</constant>) is set to an object that may be used to reference the operation.</para>
 121
 122     <para>These functions are supported only on bus connections, i.e. connections to a bus broker and not on direct
 123     connections.</para>
 124   </refsect1>
 125
 126   <refsect1>
 127     <title>Return Value</title>
 128
 129     <para>On success, these calls return 0 or a positive integer. On failure, these calls return a negative errno-style
 130     error code.</para>
 131
 132     <para>If <varname>SD_BUS_NAME_QUEUE</varname> is specified, <function>sd_bus_request_name()</function> will return
 133     0 when the name is already taken by another peer and the client has been added to the queue for the name. In that
 134     case, the caller can subscribe to <literal>NameOwnerChanged</literal> signals to be notified when the name is
 135     successfully acquired.  <function>sd_bus_request_name()</function> returns &gt; 0 when the name has immediately
 136     been acquired successfully.</para>
 137   </refsect1>
 138
 139   <refsect1>
 140     <title>Errors</title>
 141
 142     <para>Returned errors may indicate the following problems:</para>
 143
 144     <variablelist>
 145       <varlistentry>
 146         <term><constant>-EALREADY</constant></term>
 147
 148         <listitem><para>The caller already is the owner of the specified name.</para></listitem>
 149       </varlistentry>
 150
 151       <varlistentry>
 152         <term><constant>-EEXIST</constant></term>
 153
 154         <listitem><para>The name has already been acquired by a different peer, and SD_BUS_NAME_REPLACE_EXISTING was
 155         not specified or the other peer did not specify SD_BUS_NAME_ALLOW_REPLACEMENT while acquiring the
 156         name.</para></listitem>
 157       </varlistentry>
 158
 159       <varlistentry>
 160         <term><constant>-ESRCH</constant></term>
 161
 162         <listitem><para>It was attempted to release a name that is currently not registered on the
 163         bus.</para></listitem>
 164       </varlistentry>
 165
 166       <varlistentry>
 167         <term><constant>-EADDRINUSE</constant></term>
 168
 169         <listitem><para>It was attempted to release a name that is owned by a different peer on the
 170         bus.</para></listitem>
 171       </varlistentry>
 172
 173       <varlistentry>
 174         <term><constant>-EINVAL</constant></term>
 175
 176         <listitem><para>A specified parameter is invalid. This is also generated when the requested name is a special
 177         service name reserved by the D-Bus specification, or when the operation is requested on a connection that does
 178         not refer to a bus.</para></listitem>
 179       </varlistentry>
 180
 181       <varlistentry>
 182         <term><constant>-ENOTCONN</constant></term>
 183
 184         <listitem><para>The bus connection has been disconnected.</para></listitem>
 185       </varlistentry>
 186
 187       <varlistentry>
 188         <term><constant>-ECHILD</constant></term>
 189
 190         <listitem><para>The bus connection has been created in a different process than the current
 191         one.</para></listitem>
 192       </varlistentry>
 193     </variablelist>
 194   </refsect1>
 195
 196   <refsect1>
 197     <title>Notes</title>
 198
 199     <para>The <function>sd_bus_acquire_name()</function> and the other interfaces described here are available as a
 200     shared library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
 201     project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
 202   </refsect1>
 203
 204   <refsect1>
 205     <title>See Also</title>
 206
 207     <para>
 208       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 209       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 210       <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 211       <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 212     </para>
 213   </refsect1>
 214
 215 </refentry>