systemd/man/sd_bus_set_watch_bind.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<refentry id="sd_bus_set_watch_bind"
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_bus_set_watch_bind</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_set_watch_bind</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_set_watch_bind</refname>
    <refname>sd_bus_get_watch_bind</refname>

    <refpurpose>Control socket binding watching on bus connections</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_bus_set_watch_bind</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>int <parameter>b</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_get_watch_bind</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_bus_set_watch_bind()</function> may be used to enable or disable client-side watching of server
    socket binding for a bus connection object. If the <parameter>b</parameter> is true, the feature is enabled,
    otherwise disabled (which is the default). When enabled, and the selected bus address refers to an
    <filename>AF_UNIX</filename> socket in the file system which does not exist while the connection attempt is made an
    <citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry> watch is installed on
    it, waiting for the socket to appear. As soon as the socket appears the connection is made. This functionality is
    useful in particular in early-boot programs that need to run before the system bus is available, but want to
    connect to it the instant it may be connected to.</para>

    <para><function>sd_bus_get_watch_bind()</function> may be used to query the current setting of this feature. It
    returns zero when the feature is disabled, and positive if enabled.</para>

    <para>Note that no timeout is applied while we wait for the socket to appear. This means that any
    synchronous remote operation (such as
    <citerefentry><refentrytitle>sd_bus_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
    <citerefentry><refentrytitle>sd_bus_request_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>),
    that is used on a connection with this feature enabled that hasn't been established yet, might block
    forever if the socket is never created. However, asynchronous remote operations (such as
    <citerefentry><refentrytitle>sd_bus_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_bus_call_async</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_bus_add_match_async</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
    do not block in this case, and safely enqueue the requested operations to be dispatched the instant the
    connection is set up.</para>

    <para>Use <citerefentry><refentrytitle>sd_bus_is_ready</refentrytitle><manvolnum>3</manvolnum></citerefentry> to
    determine whether the connection is fully established, i.e. whether the peer socket has been bound, connected to
    and authenticated. Use
    <citerefentry><refentrytitle>sd_bus_set_connected_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry> to
    be notified when the connection is fully established.</para>

  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>On success, these functions return 0 or a positive integer. On failure, they return a negative
    errno-style error code.</para>

    <refsect2>
      <title>Errors</title>

      <para>Returned errors may indicate the following problems:</para>

      <variablelist>
        <varlistentry>
          <term><constant>-ECHILD</constant></term>

          <listitem><para>The bus connection has been created in a different process, library or module instance.</para></listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

  <xi:include href="libsystemd-pkgconfig.xml" />

  <refsect1>
    <title>Example</title>

    <example>
      <title>Create a simple system service that publishes a property on the system bus and can reconnect
      when D-Bus disconnects and reconnects</title>

      <programlisting><xi:include href="sd_bus_service_reconnect.c" parse="text"/></programlisting>

      <para>This is particularly useful for services that are configured to survive a soft-reboot, see
      <citerefentry><refentrytitle>systemd-soft-reboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
      for more details.</para>
    </example>
  </refsect1>

  <refsect1>
    <title>History</title>
    <para><function>sd_bus_set_watch_bind()</function> and
    <function>sd_bus_get_watch_bind()</function> were added in version 237.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>

    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_bus_call</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_bus_request_name</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_bus_is_ready</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_bus_set_connected_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>