systemd/man/sd_varlink_send.xml

<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="sd_varlink_send" xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_varlink_send</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_varlink_send</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_varlink_send</refname>
    <refname>sd_varlink_sendb</refname>
    <refname>sd_varlink_sendbo</refname>

    <refpurpose>Enqueues a Varlink method call, not expecting a reply</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_varlink_send</function></funcdef>
        <paramdef>sd_varlink *<parameter>link</parameter></paramdef>
        <paramdef>const char *<parameter>method</parameter></paramdef>
        <paramdef>sd_json_variant *<parameter>parameters</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_varlink_sendb</function></funcdef>
        <paramdef>sd_varlink *<parameter>link</parameter></paramdef>
        <paramdef>const char *<parameter>method</parameter></paramdef>
        <paramdef>…</paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_varlink_sendbo</function></funcdef>
        <paramdef>sd_varlink *<parameter>link</parameter></paramdef>
        <paramdef>const char *<parameter>method</parameter></paramdef>
        <paramdef>…</paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_varlink_send()</function> submits a method call via a Varlink connection. It takes the
    Varlink connection object, a method name as string parameter, and a JSON object containing the parameters
    to pass as function parameters. This call is asynchronous: the message will not be delivered immediately
    but only once
    <citerefentry><refentrytitle>sd_varlink_process</refentrytitle><manvolnum>3</manvolnum></citerefentry> is
    invoked (which will happen automatically in one of the following event loop iterations if the Varlink
    connection is attached to an even loop).</para>

    <para><function>sd_varlink_sendb()</function> is similar to <function>sd_varlink_send()</function>, but
    instead of expecting a fully constructed <type>sd_json_variant</type> object carrying the parameters,
    this object is constructed on-the-fly directly from the parameter list, in a style identical to
    <citerefentry><refentrytitle>sd_json_build</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

    <para><function>sd_varlink_sendbo()</function> is identical to <function>sd_varlink_sendb()</function>,
    but an enclosing object is implicitly added, so that the parameter list is expected to consist of field
    pairs only. For details about the expected argument list, see
    <citerefentry><refentrytitle>sd_json_buildo</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

    <para>Use <function>sd_varlink_send()</function>, <function>sd_varlink_sendb()</function> and
    <function>sd_varlink_sendbo()</function> only if no method call results are required, as they neither
    provide return parameters nor success/failure information. Use
    <citerefentry><refentrytitle>sd_varlink_call</refentrytitle><manvolnum>3</manvolnum></citerefentry> (and
    related calls) to submit a method call synchronously, returning the server's response.</para>
  </refsect1>

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

    <para>On success, <function>sd_varlink_send()</function>, <function>sd_varlink_sendb()</function> and
    <function>sd_varlink_sendbo()</function> return a non-negative 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>-EINVAL</constant></term>

          <listitem><para>An argument is invalid.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOMEM</constant></term>

          <listitem><para>Memory allocation failed.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOTCONN</constant></term>

          <listitem><para>The Varlink connection object is not connected.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-EBUSY</constant></term>

          <listitem><para>The Varlink connection object is already used for other purposes, i.e. executing a
          method call or similar.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOBUFS</constant></term>

          <listitem><para>The internal limit of queued messages for the Varlink connection has been
          reached. This limit is set very high, and hitting it typically indicates that the Varlink
          connection object is stalled — possibly because <function>sd_varlink_process()</function> has not
          been called regularly enough, or because the peer is not processing any queued messages. This limit
          is a safety precaution to ensure a stalled peer will not result in unbounded memory allocations on
          the client side.</para></listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

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

  <refsect1>
    <title>History</title>
    <para><function>sd_varlink_send()</function>, <function>sd_varlink_sendb()</function>,
    <function>sd_varlink_sendbo()</function> were added in version 257.</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-varlink</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_varlink_call</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_varlink_build</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>
</refentry>