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158 lines
6.3 KiB
XML
158 lines
6.3 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="sd_hwdb_get" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_hwdb_get</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_hwdb_get</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_hwdb_get</refname>
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<refname>sd_hwdb_seek</refname>
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<refname>sd_hwdb_enumerate</refname>
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<refname>SD_HWDB_FOREACH_PROPERTY</refname>
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<refpurpose>Seek to a location in hwdb or access entries</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-hwdb.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_hwdb_get</function></funcdef>
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<paramdef>sd_hwdb *<parameter>hwdb</parameter></paramdef>
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<paramdef>const char *<parameter>modalias</parameter></paramdef>
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<paramdef>const char *<parameter>key</parameter></paramdef>
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<paramdef>const char **<parameter>value</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_hwdb_seek</function></funcdef>
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<paramdef>sd_hwdb *<parameter>hwdb</parameter></paramdef>
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<paramdef>const char *<parameter>modalias</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_hwdb_enumerate</function></funcdef>
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<paramdef>sd_hwdb *<parameter>hwdb</parameter></paramdef>
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<paramdef>const char **<parameter>key</parameter></paramdef>
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<paramdef>const char **<parameter>value</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef><function>SD_HWDB_FOREACH_PROPERTY</function></funcdef>
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<paramdef>hwdb</paramdef>
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<paramdef>modalias</paramdef>
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<paramdef>key</paramdef>
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<paramdef>value</paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_hwdb_get()</function> queries the <parameter>hwdb</parameter> object created earlier
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with <citerefentry><refentrytitle>sd_hwdb_new</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
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entries matching the specified string <parameter>modalias</parameter>, and returns the value
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corresponding to the the key <parameter>key</parameter>. The value is returned as a
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<constant>NUL</constant>-terminated string in <parameter>value</parameter>. It must not be modified by
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the caller and is valid as long as a reference to <parameter>hwdb</parameter> is kept. When multiple
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patterns in the database match <parameter>modalias</parameter>, the one with the highest priority is
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used. See <citerefentry><refentrytitle>hwdb</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
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details.</para>
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<para><function>sd_hwdb_seek()</function> selects entries matching the specified string
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<parameter>modalias</parameter>. Subsequent queries with <function>sd_hwdb_enumerate()</function> will
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access the key-value pairs for that string.</para>
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<para><function>sd_hwdb_enumerate()</function> returns (in turn) all the key-value pairs defined for the
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string used with <function>sd_hwdb_seek()</function>. Each pair is returned as
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<constant>NUL</constant>-terminated strings in <parameter>key</parameter> and
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<parameter>value</parameter>. The strings must not be modified by the caller and are valid as long as a
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reference to <parameter>hwdb</parameter> is kept. When multiple patterns in the database match
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<parameter>modalias</parameter>, the combination of all matching key-value pairs is used. See
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<citerefentry><refentrytitle>hwdb</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
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details.</para>
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<para>The <function>SD_HWDB_FOREACH_PROPERTY</function> macro combines
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<function>sd_hwdb_seek()</function> and <function>sd_hwdb_enumerate()</function>. No error handling is
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performed and iteration simply stops on error. See the example below.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, <function>sd_hwdb_get()</function> and <function>sd_hwdb_seek()</function> return a
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non-negative integer. On failure, they return a negative errno-style error code.</para>
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<para><function>sd_hwdb_enumerate()</function> returns a positive integer if another key-value pair was found or zero if
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all entries have already been enumerated. On failure, it returns a negative errno-style error code.
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</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>A parameter is <constant>NULL</constant>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOENT</constant></term>
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<listitem><para>An entry for the specified <parameter>modalias</parameter> was not found.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EAGAIN</constant></term>
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<listitem><para><function>sd_hwdb_seek()</function> was not called before
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<function>sd_hwdb_enumerate()</function>.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>Examples</title>
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<example>
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<title>Look up hwdb entries for a USB device</title>
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<programlisting><xi:include href="hwdb-usb-device.c" parse="text" /></programlisting>
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<para>The effect is similar to calling <command>systemd-hwdb query usb:v046DpC534</command>.
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</para>
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</example>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-udev.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-hwdb</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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