external strings : t -> string -> string array = "ocaml_guestfs_strings"
external strings_e : t -> string -> string -> string array = "ocaml_guestfs_strings_e"
external hexdump : t -> string -> string = "ocaml_guestfs_hexdump"
+external zerofree : t -> string -> unit = "ocaml_guestfs_zerofree"