ops/nixos: add netboot for netbooting a basic system with my defaults

ops/nixos/default.nix

@@ -52,8 +52,12 @@ let
       stockExporters ++ customExporters;
   in
     builtins.listToAttrs (builtins.concatLists (lib.mapAttrsToList exportersForSystem evaledSystems));
+
+  netbootSystem = systemFor "netboot" (import ./netboot);
 in systemDrvs // {
   systems = systemDrvs;
   systemExporters = systemExporters;
   tailscaleIPs = systemTailscaleIPs;
+
+  netboot = netbootSystem.config.system.build.pixiecore;
 }

ops/nixos/netboot/default.nix

@@ -0,0 +1,38 @@
+# SPDX-FileCopyrightText: 2020 Luke Granger-Brown <depot@lukegb.com>
+#
+# SPDX-License-Identifier: Apache-2.0
+
+{ depot, lib, pkgs, rebuilder, config, ... }:
+let
+  inherit (depot.ops) secrets;
+in {
+  imports = [
+    ../../../third_party/nixpkgs/nixos/modules/installer/netboot/netboot-minimal.nix
+  ];
+
+  environment.noXlibs = false;
+  services.getty.autologinUser = lib.mkForce "root";
+  systemd.services.sshd.wantedBy = lib.mkOverride 0 [ "multi-user.target" ];
+  boot.kernelPackages = pkgs.linuxPackages_latest;
+
+  system.build.netbootWrap = pkgs.symlinkJoin {
+    name = "netboot";
+    paths = with config.system.build; [
+      netbootRamdisk
+      kernel
+      netbootIpxeScript
+    ];
+  };
+  system.build.pixiecore = pkgs.writeScript "netboot-pixiecore.sh" ''
+    n="$(realpath ${config.system.build.netbootWrap})"
+    init="$(grep -ohP 'init=\S+' "$n/netboot.ipxe")"
+    pixiecore="${pkgs.pixiecore}"
+
+    exec "$pixiecore/bin/pixiecore" \
+      boot "$n/bzImage" "$n/initrd" \
+      --cmdline "$init loglevel=4" \
+      --debug --dhcp-no-bind --port 64172 --status-port 64172
+  '';
+
+  system.stateVersion = "21.05";
+}