pxescript: add helper

pkgs/default.nix

@@ -8,6 +8,8 @@
     nix = nixUnstable;
   };
 
+  makePxeScript = callPackage ./pxescript {};
+
   makeSquashfsManifest = callPackage ./squashfs-recursive {
     # nixUnstable may not be required. Todo: revisit (2020-05-25)
     nix = nixUnstable;

pkgs/pxescript/default.nix

@@ -0,0 +1,39 @@
+{ stdenv, runCommand }:
+{ config
+, initrds ? {}
+, pkgs
+,
+}:
+runCommand "netboot" {
+  pxe = ''
+    #!ipxe
+    kernel ${pkgs.stdenv.hostPlatform.platform.kernelTarget} init=${config.system.build.toplevel}/init initrd=initrd ${toString config.boot.kernelParams}
+    ${builtins.concatStringsSep "\n" (builtins.attrValues (builtins.mapAttrs (name: path: "initrd ${name}") initrds))}
+    initrd initrd
+    boot
+  '';
+} ''
+  mkdir stage
+  cd stage
+  ln -s "${config.system.build.kernel}/${pkgs.stdenv.hostPlatform.platform.kernelTarget}" ./
+
+  set -x
+  ${builtins.concatStringsSep "\n"
+  (
+    builtins.attrValues
+      (
+        builtins.mapAttrs
+          (
+            name: path: ''
+              test -f "$(realpath "${path}")"
+              ln -s ${path} ./${name}
+            ''
+          ) initrds
+      )
+  )}
+  set +x
+  echo "$pxe" > netboot.ipxe
+
+  cd ..
+  mv stage $out
+''