man: add more references for extensions to portablectl

Link in systemd.io and systemd-sysext

Fixes #22146

diff --git a/man/portablectl.xml b/man/portablectl.xml
index c5404db0bae59d6de07b4a47b978433beb69bca6..f58275b1585b537223da58bfc5683821d735cb33 100644 (file)
--- a/man/portablectl.xml
+++ b/man/portablectl.xml
@@ -47,7 +47,8 @@
     <para>Portable service images are an efficient way to bundle multiple related services and other units together,
     and transfer them as a whole between systems. When these images are attached the local system the contained units
     may run in most ways like regular system-provided units, either with full privileges or inside strict sandboxing,
-    depending on the selected configuration.</para>
+    depending on the selected configuration. For more details, see
+    <ulink url="https://systemd.io/PORTABLE_SERVICES">Portable Services</ulink>.</para>
 
     <para>Specifically portable service images may be of the following kind:</para>
 
@@ -359,10 +360,13 @@
         top of <replaceable>IMAGE</replaceable> when attaching/detaching. This argument can be specified
         multiple times, in which case the order in which images are laid down follows the rules specified in
         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
-        for the <varname>ExtensionImages=</varname> directive. The image(s) must contain an
-        <filename>extension-release</filename> file with metadata that matches what is defined in the
-        <filename>os-release</filename> of <replaceable>IMAGE</replaceable>. See:
+        for the <varname>ExtensionImages=</varname> directive and for the
+        <citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>8</manvolnum></citerefentry> tool.
+        The image(s) must contain an <filename>extension-release</filename> file with metadata that matches
+        what is defined in the <filename>os-release</filename> of <replaceable>IMAGE</replaceable>. See:
         <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+        For more information on portable services with extensions, see the <literal>Extension Images</literal>
+        paragraph on <ulink url="https://systemd.io/PORTABLE_SERVICES">Portable Services</ulink>.
         </para>
 
         <para>Note that the same extensions have to be specified, in the same order, when attaching
@@ -451,6 +455,7 @@
     <title>See Also</title>
     <para>
       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>org.freedesktop.portable1</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>systemd-portabled.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
     </para>