+#define Guestfs_val(v) (*((guestfs_h **)Data_custom_val(v)))
+extern void ocaml_guestfs_raise_error (guestfs_h *g, const char *func)
+ Noreturn;
+extern char **ocaml_guestfs_strings_val (guestfs_h *g, value sv);
+extern void ocaml_guestfs_free_strings (char **r);