nixpkgs/modules/tasks/filesystems/unionfs-fuse.nix

{ config, pkgs, ... }:

{
  config = pkgs.lib.mkIf (pkgs.lib.any (fs: fs == "unionfs-fuse") config.boot.initrd.supportedFilesystems) {
    boot.initrd.kernelModules = [ "fuse" ];

    boot.initrd.extraUtilsCommands = ''
      cp -v ${pkgs.fuse}/lib/libfuse* $out/lib
      cp -v ${pkgs.unionfs-fuse}/bin/unionfs $out/bin
    '';

    boot.initrd.postDeviceCommands = ''
        # Hacky!!! fuse hard-codes the path to mount
        mkdir -p /nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-${pkgs.utillinux.name}/bin
        ln -s $(which mount) /nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-${pkgs.utillinux.name}/bin
        ln -s $(which umount) /nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-${pkgs.utillinux.name}/bin
      '';
  } // pkgs.lib.mkIf (pkgs.lib.any (fs: fs == "unionfs-fuse") config.boot.supportedFilesystems) {
    system.fsPackages = [ pkgs.unionfs-fuse ];
  };
}