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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<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 <systemd/sd-hwdb.h></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></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ENOENT</constant></term>
<listitem><para>An entry for the specified <parameter>modalias</parameter> was not found.
</para></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></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>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-hwdb</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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