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[thirdparty/systemd.git] / man / sd_hwdb_get.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">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="sd_hwdb_get" xmlns:xi="http://www.w3.org/2001/XInclude">
  <refentryinfo>
    <title>sd_hwdb_get</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_hwdb_get</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_hwdb_get</refname>
    <refname>sd_hwdb_seek</refname>
    <refname>sd_hwdb_enumerate</refname>
    <refname>SD_HWDB_FOREACH_PROPERTY</refname>

    <refpurpose>Seek to a location in hwdb or access entries</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_hwdb_get</function></funcdef>
        <paramdef>sd_hwdb *<parameter>hwdb</parameter></paramdef>
        <paramdef>const char *<parameter>modalias</parameter></paramdef>
        <paramdef>const char *<parameter>key</parameter></paramdef>
        <paramdef>const char **<parameter>value</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_hwdb_seek</function></funcdef>
        <paramdef>sd_hwdb *<parameter>hwdb</parameter></paramdef>
        <paramdef>const char *<parameter>modalias</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_hwdb_enumerate</function></funcdef>
        <paramdef>sd_hwdb *<parameter>hwdb</parameter></paramdef>
        <paramdef>const char **<parameter>key</parameter></paramdef>
        <paramdef>const char **<parameter>value</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef><function>SD_HWDB_FOREACH_PROPERTY</function></funcdef>
        <paramdef>hwdb</paramdef>
        <paramdef>modalias</paramdef>
        <paramdef>key</paramdef>
        <paramdef>value</paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_hwdb_get()</function> queries the <parameter>hwdb</parameter> object created earlier
    with <citerefentry><refentrytitle>sd_hwdb_new</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
    entries matching the specified string <parameter>modalias</parameter>, and returns the value
    corresponding to the key <parameter>key</parameter>. The value is returned as a
    <constant>NUL</constant>-terminated string in <parameter>value</parameter>. It must not be modified by
    the caller and is valid as long as a reference to <parameter>hwdb</parameter> is kept. When multiple
    patterns in the database match <parameter>modalias</parameter>, the one with the highest priority is
    used. See <citerefentry><refentrytitle>hwdb</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
    details.</para>

    <para><function>sd_hwdb_seek()</function> selects entries matching the specified string
    <parameter>modalias</parameter>. Subsequent queries with <function>sd_hwdb_enumerate()</function> will
    access the key-value pairs for that string.</para>

    <para><function>sd_hwdb_enumerate()</function> returns (in turn) all the key-value pairs defined for the
    string used with <function>sd_hwdb_seek()</function>. Each pair is returned as
    <constant>NUL</constant>-terminated strings in <parameter>key</parameter> and
    <parameter>value</parameter>. The strings must not be modified by the caller and are valid as long as a
    reference to <parameter>hwdb</parameter> is kept. When multiple patterns in the database match
    <parameter>modalias</parameter>, the combination of all matching key-value pairs is used. See
    <citerefentry><refentrytitle>hwdb</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
    details.</para>

    <para>The <function>SD_HWDB_FOREACH_PROPERTY()</function> macro combines
    <function>sd_hwdb_seek()</function> and <function>sd_hwdb_enumerate()</function>. No error handling is
    performed and iteration simply stops on error. See the example below.</para>
  </refsect1>

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

    <para>On success, <function>sd_hwdb_get()</function> and <function>sd_hwdb_seek()</function> return a
    non-negative integer. On failure, they return a negative errno-style error code.</para>

    <para><function>sd_hwdb_enumerate()</function> returns a positive integer if another key-value pair was found or zero if
    all entries have already been enumerated. On failure, it returns 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>A parameter is <constant>NULL</constant>.</para>

          <xi:include href="version-info.xml" xpointer="v246"/></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOENT</constant></term>

          <listitem><para>An entry for the specified <parameter>modalias</parameter> was not found.
          </para>

          <xi:include href="version-info.xml" xpointer="v246"/></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-EAGAIN</constant></term>

          <listitem><para><function>sd_hwdb_seek()</function> was not called before
          <function>sd_hwdb_enumerate()</function>.</para>

          <xi:include href="version-info.xml" xpointer="v246"/></listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

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

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Look up hwdb entries for a USB device</title>

      <programlisting><xi:include href="hwdb-usb-device.c" parse="text" /></programlisting>

      <para>The effect is similar to calling <command>systemd-hwdb query usb:v046DpC534</command>.
      </para>
    </example>
  </refsect1>

  <refsect1>
    <title>History</title>
    <para><function>sd_hwdb_get()</function>,
    <function>sd_hwdb_seek()</function>,
    <function>sd_hwdb_enumerate()</function>, and
    <function>SD_HWDB_FOREACH_PROPERTY()</function> were added in version 246.</para>
  </refsect1>

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

    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd-hwdb</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>