<?xml version='1.0'?> <!--*-nxml-*--> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> <!-- SPDX-License-Identifier: LGPL-2.1+ This file is part of systemd. Copyright 2013 Lennart Poettering --> <refentry id="sd_bus_request_name"> <refentryinfo> <title>sd_bus_request_name</title> <productname>systemd</productname> <authorgroup> <author> <contrib>Developer</contrib> <firstname>Lennart</firstname> <surname>Poettering</surname> <email>lennart@poettering.net</email> </author> </authorgroup> </refentryinfo> <refmeta> <refentrytitle>sd_bus_request_name</refentrytitle> <manvolnum>3</manvolnum> </refmeta> <refnamediv> <refname>sd_bus_request_name</refname> <refname>sd_bus_request_name_async</refname> <refname>sd_bus_release_name</refname> <refname>sd_bus_release_name_async</refname> <refpurpose>Request or release a well-known service name on a bus</refpurpose> </refnamediv> <refsynopsisdiv> <funcsynopsis> <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> <funcprototype> <funcdef>int <function>sd_bus_request_name</function></funcdef> <paramdef>sd_bus *<parameter>bus</parameter></paramdef> <paramdef>const char *<parameter>name</parameter></paramdef> <paramdef>uint64_t <parameter>flags</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>int <function>sd_bus_request_name_async</function></funcdef> <paramdef>sd_bus *<parameter>bus</parameter></paramdef> <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef> <paramdef>const char *<parameter>name</parameter></paramdef> <paramdef>uint64_t <parameter>flags</parameter></paramdef> <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef> <paramdef>void *<parameter>userdata</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>int <function>sd_bus_release_name</function></funcdef> <paramdef>sd_bus *<parameter>bus</parameter></paramdef> <paramdef>const char *<parameter>name</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>int <function>sd_bus_release_name_async</function></funcdef> <paramdef>sd_bus *<parameter>bus</parameter></paramdef> <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef> <paramdef>const char *<parameter>name</parameter></paramdef> <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef> <paramdef>void *<parameter>userdata</parameter></paramdef> </funcprototype> </funcsynopsis> </refsynopsisdiv> <refsect1> <title>Description</title> <para><function>sd_bus_request_name()</function> requests a well-known service name on a bus. It takes a bus connection, a valid bus name and a flags parameter. The flags parameter is a combination of the following flags:</para> <variablelist> <varlistentry> <term><varname>SD_BUS_NAME_ALLOW_REPLACEMENT</varname></term> <listitem><para>After acquiring the name successfully, permit other peers to take over the name when they try to acquire it with the <varname>SD_BUS_NAME_REPLACE_EXISTING</varname> flag set. If <varname>SD_BUS_NAME_ALLOW_REPLACEMENT</varname> is not set on the original request, such a request by other peers will be denied.</para></listitem> </varlistentry> <varlistentry> <term><varname>SD_BUS_NAME_REPLACE_EXISTING</varname></term> <listitem><para>Take over the name if it is already acquired by another peer, and that other peer has permitted takeover by setting <varname>SD_BUS_NAME_ALLOW_REPLACEMENT</varname> while acquiring it.</para></listitem> </varlistentry> <varlistentry> <term><varname>SD_BUS_NAME_QUEUE</varname></term> <listitem><para>Queue the acquisition of the name when the name is already taken.</para></listitem> </varlistentry> </variablelist> <para><function>sd_bus_request_name()</function> operates in a synchronous fashion: a message requesting the name is sent to the bus broker, and the call waits until the broker responds.</para> <para><function>sd_bus_request_name_async()</function> is an asynchronous version of of <function>sd_bus_release_name()</function>. Instead of waiting for the request to complete, the request message is enqueued. The specified <parameter>callback</parameter> will be called when the broker's response is received. If the parameter is specified as <constant>NULL</constant> a default implementation is used instead which will terminate the connection when the name cannot be acquired. The function returns a slot object in its <parameter>slot</parameter> parameter — if it is passed as non-<constant>NULL</constant> — which may be used as a reference to the name request operation. Use <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry> to destroy this reference. Note that destroying the reference will not unregister the name, but simply ensure the specified callback is no longer called.</para> <para><function>sd_bus_release_name()</function> releases an acquired well-known name. It takes a bus connection and a valid bus name as parameters. This function operates synchronously, sending a release request message to the bus broker and waiting for it to reply.</para> <para><function>sd_bus_release_name_async()</function> is an asynchronous version of <function>sd_bus_release_name()</function>. The specified <parameter>callback</parameter> function is called when the name has been released successfully. If specified as <constant>NULL</constant> a generic implementation is used that ignores the result of the operation. As above, the <parameter>slot</parameter> (if non-<constant>NULL</constant>) is set to an object that may be used to reference the operation.</para> <para>These functions are supported only on bus connections, i.e. connections to a bus broker and not on direct connections.</para> </refsect1> <refsect1> <title>Return Value</title> <para>On success, these calls return 0 or a positive integer. On failure, these calls return a negative errno-style error code.</para> <para>If <varname>SD_BUS_NAME_QUEUE</varname> is specified, <function>sd_bus_request_name()</function> will return 0 when the name is already taken by another peer and the client has been added to the queue for the name. In that case, the caller can subscribe to <literal>NameOwnerChanged</literal> signals to be notified when the name is successfully acquired. <function>sd_bus_request_name()</function> returns > 0 when the name has immediately been acquired successfully.</para> </refsect1> <refsect1> <title>Errors</title> <para>Returned errors may indicate the following problems:</para> <variablelist> <varlistentry> <term><constant>-EALREADY</constant></term> <listitem><para>The caller already is the owner of the specified name.</para></listitem> </varlistentry> <varlistentry> <term><constant>-EEXIST</constant></term> <listitem><para>The name has already been acquired by a different peer, and SD_BUS_NAME_REPLACE_EXISTING was not specified or the other peer did not specify SD_BUS_NAME_ALLOW_REPLACEMENT while acquiring the name.</para></listitem> </varlistentry> <varlistentry> <term><constant>-ESRCH</constant></term> <listitem><para>It was attempted to release a name that is currently not registered on the bus.</para></listitem> </varlistentry> <varlistentry> <term><constant>-EADDRINUSE</constant></term> <listitem><para>It was attempted to release a name that is owned by a different peer on the bus.</para></listitem> </varlistentry> <varlistentry> <term><constant>-EINVAL</constant></term> <listitem><para>A specified parameter is invalid. This is also generated when the requested name is a special service name reserved by the D-Bus specification, or when the operation is requested on a connection that does not refer to a bus.</para></listitem> </varlistentry> <varlistentry> <term><constant>-ENOTCONN</constant></term> <listitem><para>The bus connection has been disconnected.</para></listitem> </varlistentry> <varlistentry> <term><constant>-ECHILD</constant></term> <listitem><para>The bus connection has been created in a different process than the current one.</para></listitem> </varlistentry> </variablelist> </refsect1> <refsect1> <title>Notes</title> <para>The <function>sd_bus_acquire_name()</function> and the other interfaces described here are available as a shared library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para> </refsect1> <refsect1> <title>See Also</title> <para> <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry> </para> </refsect1> </refentry>