Bug#931130: Document that local configuration for dummy and bonding modules are getting overwritten by systemd

[Justin B Rye <justin.byam.rye@gmail.com>]

Justin B Rye wrote:
> Okay, so here's a first rough idea of what the release-notes might
> say.

Properly formatted patch attached.
-- 
JBR	with qualifications in linguistics, experience as a Debian
	sysadmin, and probably no clue about this particular package

diff --git a/en/issues.dbk b/en/issues.dbk
index 2baac7df..2fdcf7d9 100644
--- a/en/issues.dbk
+++ b/en/issues.dbk
@@ -199,6 +199,40 @@ $ sudo update-initramfs -u
     </para>
   </section>
 
+  <section id="dummy-module-config">
+    <!-- stretch to buster -->
+    <title>Module configuration for bonding and dummy interfaces/title>
+    <para>
+      Administrators who are using channel bonding and/or dummy
+      interfaces (for instance to configure a machine as a router), and
+      who have set up module parameters in a file under
+      <filename>/etc/modprobe.d</filename>, may need to change the name
+      of the local configuration file used, to avoid these parameters
+      being ignored after the upgrade to buster.
+    </para>
+    <para>
+      In buster, <systemitem role="package">udev</systemitem> ships a
+      file <filename>/lib/modprobe.d/systemd.conf</filename> designed to
+      make it easier to configure such interfaces using
+      <command>systemd-networkd</command>. This contains the lines
+    </para>
+    <screen>
+ options bonding max_bonds=0
+ options dummy numdummies=0
+    </screen>
+    <para>
+     A file in <filename>/lib/modprobe.d</filename> can be overridden by
+     one with the same name under <filename>/etc/modprobe.d</filename>,
+     but the names are processed in alphabetical order, so
+     <filename>/lib/modprobe.d/systemd.conf</filename> follows and
+     overrides (for instance)
+     <filename>/etc/modprobe.d/dummy.conf</filename>. Make sure that any
+     local configuration file has a name that sorts after
+     <quote><filename>systemd.conf</filename></quote>, such as
+     <quote><filename>/etc/modprobe.d/zz-local.conf</filename></quote>.
+    </para>
+  </section>
+
   <section id="openssl-defaults">
     <!-- stretch to buster -->
     <title>OpenSSL default version and security level raised</title>