nixos/defaults/predictable-interface-names.nix

   1 # Use predictable interface names in stage-1 and stage-2.
   2 # DOC: https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/
   3 #
   4 # Tip: names that can be given using ID_NET_NAME_* envvars
   5 # can be checked before hand with:
   6 # udevadm test-builtin net_id /sys/class/net/*
   7 { pkgs, lib, config, ... }:
   8 let
   9   udevNetSetupLinkRules = pkgs.writeTextDir "etc/udev/rules.d/79-net-setup-link.rules" ''
  10     SUBSYSTEM!="net", GOTO="net_setup_link_end"
  11
  12     IMPORT{builtin}="path_id"
  13
  14     ACTION!="add", GOTO="net_setup_link_end"
  15
  16     # Load net_setup_link to setup the ID_NET_NAME_* envvars
  17     IMPORT{builtin}="net_setup_link"
  18
  19     # Rename eth* using the "path" name policy (eg. enp1s0),
  20     # Note that in stage-1 the envvar ID_NET_NAME is not set,
  21     # hence not usable as in ''${pkgs.systemd}/lib/udev/rules.d/80-net-setup-link.rules
  22     # Because in stage-1 there is no /etc/systemd/network/*.link
  23     # nor **/systemd/network/99-default.link
  24     # to set NamePolicy= which is responsible to set ID_NET_NAME.
  25     # Not sure if ATTR{type}=="1" and KERNEL=="eth*" are equivalent or not.
  26     ATTR{type}=="1", KERNEL=="eth*", NAME="$env{ID_NET_NAME_PATH}"
  27
  28     LABEL="net_setup_link_end"
  29   '';
  30 in
  31 {
  32 networking = {
  33   # Currently no-op.
  34   # false would set boot.kernelParams = [ "net.ifnames=0" ];
  35   # to disable NamePolicy= in *.link.
  36   usePredictableInterfaceNames = true;
  37 };
  38
  39 boot.initrd = {
  40   extraUdevRulesCommands = ''
  41     # The name set here in stage-1 by 79-net-setup-link.rules
  42     # will stay in stage-2 (at least until the device is removed/added).
  43     cp -v ${udevNetSetupLinkRules}/etc/udev/rules.d/79-net-setup-link.rules $out/
  44   '';
  45 };
  46
  47 services.udev.packages = [
  48   # Only useful here in stage-2 if the device is removed and re-added
  49   # (eg. the network module is rmmod-ed then modprobe-d).
  50   # The stage-1 (or initrd) is only a pivot_root after all,
  51   # it does not reload the kernel, hence passing to stage-2
  52   # does not trigger ACTION=="add" for the net devices.
  53   udevNetSetupLinkRules
  54 ];
  55
  56 /* Useless block, only here for explanations.
  57
  58 # NixOS put this .link only in the root filesystem, not in the initrd
  59 # hence it's only active in stage-2, not stage-1.
  60 # And even in stage-2, the 80-net-setup-link.rules has priority.
  61 # DOC: https://www.freedesktop.org/software/systemd/man/systemd.link.html
  62 environment.etc."systemd/network/79-net-setup.link".text = ''
  63   [Match]
  64   OriginalName=*
  65
  66   [Link]
  67   #NamePolicy=keep kernel database onboard slot path
  68   NamePolicy=mac
  69   MACAddressPolicy=persistent
  70 '';
  71 */
  72 }