man: udev - add section about hwdb

man/udev.xml

@@ -30,7 +30,7 @@
 
   <refnamediv>
     <refname>udev</refname>
-    <refpurpose>Linux dynamic device management</refpurpose>
+    <refpurpose>Dynamic device management</refpurpose>
   </refnamediv>
 
   <refsect1><title>Description</title>
@@ -54,7 +54,7 @@
     sources is provided by the library libudev.</para>
   </refsect1>
 
-  <refsect1><title>Rules files</title>
+  <refsect1><title>Rules Files</title>
       <para>The udev rules are read from the files located in the
       system rules directory <filename>/usr/lib/udev/rules.d</filename>,
       the volatile runtime directory <filename>/run/udev/rules.d</filename>
@@ -67,10 +67,8 @@
       used to override a system-supplied rules file with a local file if needed;
       a symlink in <filename>/etc</filename> with the same name as a rules file in
       <filename>/lib</filename>, pointing to <filename>/dev/null</filename>,
-      disables the rules file entirely.</para>
-
-      <para>Rule files must have the extension <filename>.rules</filename>; other
-      extensions are ignored.</para>
+      disables the rules file entirely. Rule files must have the extension
+      <filename>.rules</filename>; other extensions are ignored.</para>
 
       <para>Every line in the rules file contains at least one key-value pair.
       Except for empty lines or lines beginning with <literal>#</literal>, which are ignored.
@@ -273,7 +271,7 @@
         </varlistentry>
       </variablelist>
 
-      <para>Most of the fields support shell-style pattern matching. The following
+      <para>Most of the fields support shell glob pattern matching. The following
       pattern characters are supported:</para>
       <variablelist>
         <varlistentry>
@@ -471,7 +469,7 @@
                   <para>Import the stored keys from the parent device by reading
                   the database entry of the parent device. The value assigned to
                   <option>IMPORT{parent}</option> is used as a filter of key names
-                  to import (with the same shell-style pattern matching used for
+                  to import (with the same shell glob pattern matching used for
                   comparisons).</para>
                 </listitem>
               </varlistentry>
@@ -701,6 +699,41 @@
       </variablelist>
   </refsect1>
 
+  <refsect1><title>Hardware Database Files</title>
+      <para>The hwdb files are read from the files located in the
+      system hwdb directory <filename>/usr/lib/udev/hwdb.d</filename>,
+      the volatile runtime directory <filename>/run/udev/hwdb.d</filename>
+      and the local administration directory <filename>/etc/udev/hwdb.d</filename>.
+      All rules files are collectively sorted and processed in lexical order,
+      regardless of the directories in which they live. However, files with
+      identical filenames replace each other. Files in <filename>/etc</filename>
+      have the highest priority, files in <filename>/run</filename> take precedence
+      over files with the same name in <filename>/lib</filename>. This can be
+      used to override a system-supplied hwdb file with a local file if needed;
+      a symlink in <filename>/etc</filename> with the same name as a rules file in
+      <filename>/lib</filename>, pointing to <filename>/dev/null</filename>,
+      disables the rules file entirely. Hwdb files must have the extension
+      <filename>.hwdb</filename>; other extensions are ignored.</para>
+
+      <para>The hwdb file contains data records consisting of matches and
+      associated key-value pairs. Every record in the hwdb starts with one or
+      more match string, specifying a shell glob to compare the database
+      lookup string against. Multiple match lines are specified in additional
+      consecutive lines. Every match line is compared indivdually, they are
+      combined by OR. Every match line must start at the first character of
+      the line.</para>
+
+      <para>The match lines are followed by one or more key-value pair lines, which
+      are recognized by a leading space character. The key name and value are separated
+      by <literal>=</literal>. An empty line signifies the end
+      of a record. Lines beginning with <literal>#</literal> are ignored.</para>
+
+      <para>The content of all hwdb files is read by
+      <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+      and compiled to a binary database located at <filename>/etc/udev/hwdb.bin</filename>.
+      During runtime only the binary database is used.</para>
+  </refsect1>
+
   <refsect1>
     <title>See Also</title>
     <para><citerefentry>