systemd/man/sd_bus_request_name.xml

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<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 &lt;systemd/sd-bus.h&gt;</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 &gt; 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>