man: describe better when remount-fs.service and gpt-auto-generator are active

TODO

@@ -825,6 +825,7 @@ Features:
   - man: document the very specific env the shutdown drop-in tools live in
   - man: add more examples to man pages
   - man: maybe sort directives in man pages, and take sections from --help and apply them to man too
+  - document root=gpt-auto properly
 
 * systemctl:
   - add systemctl switch to dump transaction without executing it

man/kernel-command-line.xml

@@ -329,7 +329,7 @@
         <listitem>
           <para>Configures the root file system and its file system
           type and mount options, as well as whether it shall be
-          mounted read-only or read-writable initially. For details,
+          mounted read-only or read-write initially. For details,
           see
           <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
         </listitem>

man/systemd-gpt-auto-generator.xml

@@ -196,6 +196,45 @@
     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
   </refsect1>
 
+  <refsect1>
+    <title>Kernel Command Line</title>
+
+    <para><filename>systemd-gpt-auto-generator</filename> understands the following kernel command line
+    parameters:</para>
+
+    <variablelist class='kernel-commandline-options'>
+
+      <varlistentry>
+        <term><varname>systemd.gpt_auto</varname></term>
+        <term><varname>rd.systemd.gpt_auto</varname></term>
+
+        <listitem><para>Those options take an optional boolean argument, and default to yes.
+        The generator is enabled by default, and a negative value may be used to disable it.
+        </para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>root=</varname></term>
+
+        <listitem><para>When used with the special value <literal>gpt-auto</literal>, automatic discovery of
+        the root parition based on the GPT partition type is enabled.  Any other value disables this
+        generator.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>rw</varname></term>
+        <term><varname>ro</varname></term>
+
+        <listitem><para>Mount the root partition read-write or read-only <emphasis>initially</emphasis>.</para>
+
+        <para>Note that unlike most kernel command line options these settings do not override configuration
+        in the file system, and the file system may be remounted later. See
+        <citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+        </para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
   <refsect1>
     <title>See Also</title>
     <para>

man/systemd-remount-fs.service.xml

@@ -30,22 +30,20 @@
   <refsect1>
     <title>Description</title>
 
-    <para><filename>systemd-remount-fs.service</filename> is an
+    <para><filename>systemd-remount-fs.service</filename> is an early boot service that applies mount options
-    early boot service that applies mount options listed in
+    listed in <citerefentry
-    <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>, or
-    to the root file system, the <filename>/usr</filename> file system,
+    gathered from the partition table (when
-    and the kernel API file systems. This is required so that the
+    <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
-    mount options of these file systems — which are pre-mounted by
+    is active) to the root file system, the <filename>/usr</filename> file system, and the kernel API file
-    the kernel, the initial RAM disk, container environments or system
+    systems. This is required so that the mount options of these file systems — which are pre-mounted by the
-    manager code — are updated to those listed in
+    kernel, the initial RAM disk, container environments or system manager code — are updated to those
-    <filename>/etc/fstab</filename>. This service ignores normal file
+    configured in <filename>/etc/fstab</filename> and the other sources. This service ignores normal file
-    systems and only changes the root file system (i.e.
+    systems and only changes the root file system (i.e.  <filename>/</filename>), <filename>/usr</filename>,
-    <filename>/</filename>), <filename>/usr</filename> and the virtual
+    and the virtual kernel API file systems such as <filename>/proc</filename>, <filename>/sys</filename> or
-    kernel API file systems such as <filename>/proc</filename>,
+    <filename>/dev</filename>. This service executes no operation if no configuration is found
-    <filename>/sys</filename> or <filename>/dev</filename>. This
+    (<filename>/etc/fstab</filename> does not exist or lists no entries for the mentioned file systems, or
-    service executes no operation if <filename>/etc/fstab</filename>
+    the partition table does not contain relevant entries).</para>
-    does not exist or lists no entries for the mentioned file
-    systems.</para>
 
     <para>For a longer discussion of kernel API file systems see
     <ulink url="https://www.freedesktop.org/wiki/Software/systemd/APIFileSystems">API