Add PXE helper

m/hut/configuration.nix

@@ -9,6 +9,7 @@
     ./nfs.nix
     ./slurm-daemon.nix
     ./ceph.nix
+    ./pxe.nix
     agenix.nixosModules.default
   ];
 

m/hut/pxe.nix

@@ -0,0 +1,26 @@
+{ theFlake, pkgs, ... }:
+
+# This module describes a script that can launch the pixiecore daemon to serve a
+# NixOS image via PXE to a node to directly boot from there, without requiring a
+# working disk.
+
+let
+  # The host config must have the netboot-minimal.nix module too
+  host = theFlake.nixosConfigurations.lake2;
+  sys = host.config.system;
+  build = sys.build;
+  kernel = "${build.kernel}/bzImage";
+  initrd = "${build.netbootRamdisk}/initrd";
+  init = "${build.toplevel}/init";
+
+  script = pkgs.writeShellScriptBin "pixiecore-helper" ''
+    #!/usr/bin/env bash -x
+
+    ${pkgs.pixiecore}/bin/pixiecore \
+      boot ${kernel} ${initrd} --cmdline "init=${init} loglevel=4" \
+      --debug --dhcp-no-bind --port 64172 --status-port 64172 "$@"
+  '';
+in
+{
+  environment.systemPackages = [ script ];
+}