man: document the newly acquired cryptsetup features

man/crypttab.xml

@@ -41,7 +41,7 @@
     character are ignored. Each of the remaining lines describes one
     encrypted block device. Fields are delimited by white space.</para>
 
-    <para>Each line is in the form<programlisting><replaceable>name</replaceable> <replaceable>encrypted-device</replaceable> <replaceable>password</replaceable> <replaceable>options</replaceable></programlisting>
+    <para>Each line is in the form<programlisting><replaceable>volume-name</replaceable> <replaceable>encrypted-device</replaceable> <replaceable>key-file</replaceable> <replaceable>options</replaceable></programlisting>
     The first two fields are mandatory, the remaining two are
     optional.</para>
 
@@ -53,24 +53,20 @@
     it is opened as a LUKS device; otherwise, it is assumed to be in
     raw dm-crypt (plain mode) format.</para>
 
-    <para>The first field contains the name of the resulting encrypted
-    block device; the device is set up within
-    <filename>/dev/mapper/</filename>.</para>
+    <para>The first field contains the name of the resulting encrypted volume; its block device is set up
+    below <filename>/dev/mapper/</filename>.</para>
 
     <para>The second field contains a path to the underlying block
     device or file, or a specification of a block device via
     <literal>UUID=</literal> followed by the UUID.</para>
 
-    <para>The third field specifies the encryption password. If the
-    field is not present or the password is set to
-    <literal>none</literal> or <literal>-</literal>, the password has
-    to be manually entered during system boot. Otherwise, the field is
-    interpreted as an absolute path to a file containing the encryption
-    password. For swap encryption, <filename>/dev/urandom</filename>
-    or the hardware device <filename>/dev/hw_random</filename> can be
-    used as the password file; using <filename>/dev/random</filename>
-    may prevent boot completion if the system does not have enough
-    entropy to generate a truly random encryption key.</para>
+    <para>The third field specifies an absolute path to a file to read the encryption key from. If the field
+    is not present or set to <literal>none</literal> or <literal>-</literal>, a key file named after the
+    volume to unlock (i.e. the first column of the line), suffixed with <filename>.key</filename> is
+    automatically loaded from the <filename>/etc/cryptsetup-keys.d/</filename> and
+    <filename>/run/cryptsetup-keys.d/</filename> directories, if present. Otherwise, the password has to be
+    manually entered during system boot. For swap encryption, <filename>/dev/urandom</filename> may be used
+    as key file.</para>
 
     <para>The fourth field, if present, is a comma-delimited list of
     options. The following options are recognized:</para>
@@ -138,6 +134,15 @@
         size is then given by the key size.</para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><option>keyfile-erase</option></term>
+
+        <listitem><para>If enabled, the specified key file is erased after the volume is activated or when
+        activation fails. This is in particular useful when the key file is only acquired transiently before
+        activation (e.g. via a file in <filename>/run/</filename>, generated by a service running before
+        activation), and shall be removed after use. Defaults to off.</para></listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><option>key-slot=</option></term>
 
@@ -431,6 +436,15 @@
         before it is used to unlock the LUKS volume.</para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><option>try-empty-password=</option></term>
+
+        <listitem><para>Takes a boolean argument. If enabled, right before asking the user for a password it
+        is first attempted to unlock the volume with an empty password. This is useful for systems that are
+        initialized with an encrypted volume with only an empty password set, which shall be replaced with a
+        suitable password during first boot, but after activation.</para></listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><option>x-systemd.device-timeout=</option></term>