man: document db_persist udev rules OPTION

Fixes #1551

diff --git a/man/udev.xml b/man/udev.xml
index 08fedfc86cf120564f1948830fa175829d28a3fc..74aab8e024fb7d62d8c1fdbe94a99c98f0426b01 100644 (file)
--- a/man/udev.xml
+++ b/man/udev.xml
@@ -566,6 +566,18 @@
                   <para>Disable the watching of a device node with inotify.</para>
                 </listitem>
               </varlistentry>
+              <varlistentry>
+                <term><option>db_persist</option></term>
+                <listitem>
+                  <para>Set the flag (sticky bit) on the udev database entry
+                  of the event device. Device properties are then kept in the
+                  database even when
+                  <command>udevadm info --cleanup-db</command> is called.
+                  This option can be useful in certain cases
+                  (e.g. Device Mapper devices) for persisting device state
+                  on the transition from initramfs.</para>
+                </listitem>
+              </varlistentry>
             </variablelist>
           </listitem>
         </varlistentry>