/// Expected output hash.
    pub output_hash: Option<String>,

    let newnet = if r.output_hash.is_some() {
        0
    } else {
        libc::CLONE_NEWNET
    };

                flags: (libc::CLONE_NEWPID | libc::CLONE_NEWNET | libc::CLONE_NEWNS) as u64,

                flags: (libc::CLONE_NEWPID | newnet | libc::CLONE_NEWNS) as u64,

  optional string output_hash = 5;

let derivation connection ~name ~builder ~paths ~target =
  let req = Elpegrpc.Elpe.DerivationRequest.make ~name ~builder ~paths ~target () in

let derivation connection ~name ~builder ~paths ~target ~output_hash =
  let req =
    match output_hash with
    | None ->
        Elpegrpc.Elpe.DerivationRequest.make ~name ~builder ~paths ~target ()
    | Some output_hash ->
        Elpegrpc.Elpe.DerivationRequest.make ~name ~builder ~paths ~target
          ~output_hash ()
  in

    method output_hash : string option Lwt.t = Lwt.return None

      | pre :: post :: _ -> Lwt.return (pre ^ "\nif [[ -e Makefile ]]; then make; fi\n" ^ post)

      | pre :: post :: _ ->
          Lwt.return (pre ^ "\nif [[ -e Makefile ]]; then make; fi\n" ^ post)

      | pre :: post :: _ -> Lwt.return (pre ^ "\nif [[ -e Makefile ]]; then make install; fi\n" ^ post)

      | pre :: post :: _ ->
          Lwt.return
            (pre ^ "\nif [[ -e Makefile ]]; then make install; fi\n" ^ post)

      let* res = derivation c ~name:self#name ~builder ~paths:!extra_paths ~target:self#target in

      let* output_hash = self#output_hash in
      let* res =
        derivation c ~name:self#name ~builder ~paths:!extra_paths
          ~target:self#target ~output_hash
      in