modprobe.d: ship drop-in to set bonding max_bonds to 0 (#6448)

This allows networkd to correctly manage bond0 using networkd, when requested
by the user.

Fixes #5971 #6184

NEWS

@@ -1,5 +1,16 @@
 systemd System and Service Manager
 
+CHANGES WITH 235:
+
+        * modprobe.d drop-in is now shipped by default that sets bonding module
+          option max_bonds=0. This overrides the kernel default, to avoid
+          conflicts and ambigiuty as to whether or not bond0 should be managed
+          by networkd or not. This resolves multiple bugs of bond0 properties
+          not being applied, when bond0 is configured with
+          networkd. Distributors may choose to not package this, however in
+          that case users will be prevented from correctly managing bond0
+          interface using networkd.
+
 CHANGES WITH 234:
 
         * Meson is now supported as build system in addition to Automake. It is

README

@@ -110,11 +110,10 @@ REQUIREMENTS:
         It's a good idea to disable the implicit creation of networking bonding
         devices by the kernel networking bonding module, so that the
         automatically created "bond0" interface doesn't conflict with any such
-        device created by systemd-networkd (or other tools). Please make sure
-        that the kernel module bonding.ko is shipped with max_bonds=0 set by
-        default. Ideally there would be a kernel compile-time option for this,
-        but there currently isn't. The next best thing is to make this change
-        through a modprobe.d drop-in.
+        device created by systemd-networkd (or other tools). Ideally there
+        would be a kernel compile-time option for this, but there currently
+        isn't. The next best thing is to make this change through a modprobe.d
+        drop-in. This is shipped by default, see modprobe.d/systemd.conf.
 
         Note that kernel auditing is broken when used with systemd's
         container code. When using systemd in conjunction with

meson.build

@@ -81,6 +81,7 @@ polkitpkladir = join_paths(localstatedir, 'lib/polkit-1/localauthority/10-vendor
 varlogdir = join_paths(localstatedir, 'log')
 xinitrcdir = join_paths(sysconfdir, 'X11/xinit/xinitrc.d')
 rpmmacrosdir = get_option('rpmmacrosdir')
+modprobedir = join_paths(rootlibdir, 'modprobe.d')
 
 # Our own paths
 pkgdatadir = join_paths(datadir, 'systemd')
@@ -2307,6 +2308,8 @@ install_data('xorg/50-systemd-user.sh',
              install_dir : xinitrcdir)
 install_data('system-preset/90-systemd.preset',
              install_dir : systempresetdir)
+install_data('modprobe.d/systemd.conf',
+             install_dir : modprobedir)
 install_data('README',
              'NEWS',
              'CODING_STYLE',
@@ -2393,6 +2396,7 @@ status = [
         'PAM modules dir:                   @0@'.format(pamlibdir),
         'PAM configuration dir:             @0@'.format(pamconfdir),
         'RPM macros dir:                    @0@'.format(rpmmacrosdir),
+        'modprobe.d dir:                    @0@'.format(modprobedir),
         'D-Bus policy dir:                  @0@'.format(dbuspolicydir),
         'D-Bus session dir:                 @0@'.format(dbussessionservicedir),
         'D-Bus system dir:                  @0@'.format(dbussystemservicedir),

modprobe.d/systemd.conf

@@ -0,0 +1,14 @@
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+#
+# When bonding module is loaded, it creates bond0 by default due to max_bonds
+# option default value 1. This interferes with the network configuration
+# management / networkd, as it is not possible to detect whether this bond0 was
+# intentionally configured by the user, or should be managed by
+# networkd/NM/etc. Therefore disable bond0 creation.
+
+options bonding max_bonds=0