nixos/{networkd,dhcpcd}: remove udev-settle hack

nixos/doc/manual/configuration/networking.xml

@@ -15,5 +15,6 @@
  <xi:include href="firewall.xml" />
  <xi:include href="wireless.xml" />
  <xi:include href="ad-hoc-network-config.xml" />
+ <xi:include href="renaming-interfaces.xml" />
 <!-- TODO: OpenVPN, NAT -->
 </chapter>

nixos/doc/manual/configuration/renaming-interfaces.xml

@@ -0,0 +1,67 @@
+<section xmlns="http://docbook.org/ns/docbook"
+         xmlns:xlink="http://www.w3.org/1999/xlink"
+         xmlns:xi="http://www.w3.org/2001/XInclude"
+         version="5.0"
+         xml:id="sec-rename-ifs">
+ <title>Renaming network interfaces</title>
+
+ <para>
+  NixOS uses the udev
+  <link xlink:href="https://systemd.io/PREDICTABLE_INTERFACE_NAMES/">predictable naming scheme</link>
+  to assign names to network interfaces. This means that by default
+  cards are not given the traditional names like
+  <literal>eth0</literal> or <literal>eth1</literal>, whose order can
+  change unpredictably across reboots. Instead, relying on physical
+  locations and firmware information, the scheme produces names like
+  <literal>ens1</literal>, <literal>enp2s0</literal>, etc.
+ </para>
+
+ <para>
+  These names are predictable but less memorable and not necessarily
+  stable: for example installing new hardware or changing firmware
+  settings can result in a
+  <link xlink:href="https://github.com/systemd/systemd/issues/3715#issue-165347602">name change</link>.
+  If this is undesirable, for example if you have a single ethernet
+  card, you can revert to the traditional scheme by setting
+  <xref linkend="opt-networking.usePredictableInterfaceNames"/> to
+  <literal>false</literal>.
+ </para>
+
+ <section xml:id="sec-custom-ifnames">
+  <title>Assigning custom names</title>
+  <para>
+   In case there are multiple interfaces of the same type, it’s better to
+   assign custom names based on the device hardware address. For
+   example, we assign the name <literal>wan</literal> to the interface
+   with MAC address <literal>52:54:00:12:01:01</literal> using a
+   netword link unit:
+  </para>
+  <programlisting>
+ <link linkend="opt-systemd.network.links">systemd.network.links."10-wan"</link> = {
+   matchConfig.MACAddress = "52:54:00:12:01:01";
+   linkConfig.Name = "wan";
+ };
+  </programlisting>
+  <para>
+   Note that links are directly read by udev, <emphasis>not networkd</emphasis>,
+   and will work even if networkd is disabled.
+  </para>
+  <para>
+   Alternatively, we can use a plain old udev rule:
+  </para>
+  <programlisting>
+ <link linkend="opt-services.udev.initrdRules">services.udev.initrdRules</link> = ''
+  SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", \
+  ATTR{address}=="52:54:00:12:01:01", KERNEL=="eth*", NAME="wan"
+ '';
+  </programlisting>
+
+  <warning><para>
+   The rule must be installed in the initrd using
+   <literal>services.udev.initrdRules</literal>, not the usual
+   <literal>services.udev.extraRules</literal> option. This is to avoid race
+   conditions with other programs controlling the interface.
+  </para></warning>
+ </section>
+
+</section>

nixos/doc/manual/release-notes/rl-2105.xml

@@ -91,6 +91,16 @@
   </para>
 
   <itemizedlist>
+   <listitem>
+    <para>
+     If you are using <option>services.udev.extraRules</option> to assign
+     custom names to network interfaces, this may stop working due to a change
+     in the initialisation of dhcpcd and systemd networkd. To avoid this, either
+     move them to <option>services.udev.initrdRules</option> or see the new
+     <link linkend="sec-custom-ifnames">Assigning custom names</link> section
+     of the NixOS manual for an example using networkd links.
+    </para>
+   </listitem>
     <listitem>
       <para>
         <literal>systemd-journal2gelf</literal> no longer parses json and expects the receiving system to handle it. How to achieve this with Graylog is described in this <link xlink:href="https://github.com/parse-nl/SystemdJournal2Gelf/issues/10">GitHub issue</link>.

nixos/modules/services/hardware/udev.nix

@@ -202,12 +202,26 @@ in
         '';
       };
 
-      extraRules = mkOption {
+      initrdRules = mkOption {
         default = "";
         example = ''
           SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:1D:60:B9:6D:4F", KERNEL=="eth*", NAME="my_fast_network_card"
         '';
         type = types.lines;
+        description = ''
+          <command>udev</command> rules to include in the initrd
+          <emphasis>only</emphasis>. They'll be written into file
+          <filename>99-local.rules</filename>. Thus they are read and applied
+          after the essential initrd rules.
+        '';
+      };
+
+      extraRules = mkOption {
+        default = "";
+        example = ''
+          ENV{ID_VENDOR_ID}=="046d", ENV{ID_MODEL_ID}=="0825", ENV{PULSE_IGNORE}="1"
+        '';
+        type = types.lines;
         description = ''
           Additional <command>udev</command> rules. They'll be written
           into file <filename>99-local.rules</filename>. Thus they are
@@ -284,6 +298,13 @@ in
 
     boot.kernelParams = mkIf (!config.networking.usePredictableInterfaceNames) [ "net.ifnames=0" ];
 
+    boot.initrd.extraUdevRulesCommands = optionalString (cfg.initrdRules != "")
+      ''
+        cat <<'EOF' > $out/99-local.rules
+        ${cfg.initrdRules}
+        EOF
+      '';
+
     environment.etc =
       {
         "udev/rules.d".source = udevRules;

nixos/modules/services/networking/dhcpcd.nix

@@ -191,9 +191,8 @@ in
       { description = "DHCP Client";
 
         wantedBy = [ "multi-user.target" ] ++ optional (!hasDefaultGatewaySet) "network-online.target";
-        wants = [ "network.target" "systemd-udev-settle.service" ];
+        wants = [ "network.target" ];
         before = [ "network-online.target" ];
-        after = [ "systemd-udev-settle.service" ];
 
         restartTriggers = [ exitHook ];
 

nixos/modules/system/boot/networkd.nix

@@ -1553,9 +1553,6 @@ in
         wantedBy = [ "multi-user.target" ];
         aliases = [ "dbus-org.freedesktop.network1.service" ];
         restartTriggers = map (x: x.source) (attrValues unitFiles);
-        # prevent race condition with interface renaming (#39069)
-        requires = [ "systemd-udev-settle.service" ];
-        after = [ "systemd-udev-settle.service" ];
       };
 
       systemd.services.systemd-networkd-wait-online = {

nixos/modules/system/boot/stage-1.nix

@@ -205,13 +205,22 @@ let
     ''; # */
 
 
+  # Networkd link files are used early by udev to set up interfaces early.
+  # This must be done in stage 1 to avoid race conditions between udev and
+  # network daemons.
   linkUnits = pkgs.runCommand "link-units" {
       allowedReferences = [ extraUtils ];
       preferLocalBuild = true;
-    } ''
+    } (''
       mkdir -p $out
       cp -v ${udev}/lib/systemd/network/*.link $out/
-    '';
+      '' + (
+      let
+        links = filterAttrs (n: v: hasSuffix ".link" n) config.systemd.network.units;
+        files = mapAttrsToList (n: v: "${v.unit}/${n}") links;
+      in
+        concatMapStringsSep "\n" (file: "cp -v ${file} $out/") files
+      ));
 
   udevRules = pkgs.runCommand "udev-rules" {
       allowedReferences = [ extraUtils ];

nixos/tests/networking.nix

@@ -672,6 +672,30 @@ let
             ), "The IPv6 routing table has not been properly cleaned:\n{}".format(ipv6Residue)
       '';
     };
+    rename = {
+      name = "RenameInterface";
+      machine = { pkgs, ... }: {
+        virtualisation.vlans = [ 1 ];
+        networking = {
+          useNetworkd = networkd;
+          useDHCP = false;
+        };
+      } //
+      (if networkd
+       then { systemd.network.links."10-custom_name" = {
+                matchConfig.MACAddress = "52:54:00:12:01:01";
+                linkConfig.Name = "custom_name";
+              };
+            }
+       else { services.udev.initrdRules = ''
+               SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="52:54:00:12:01:01", KERNEL=="eth*", NAME="custom_name"
+              '';
+            });
+      testScript = ''
+        machine.succeed("udevadm settle")
+        print(machine.succeed("ip link show dev custom_name"))
+      '';
+    };
     # even with disabled networkd, systemd.network.links should work
     # (as it's handled by udev, not networkd)
     link = {