extern void guestfs_set_error_handler (guestfs_h *g, guestfs_error_handler_cb cb, void *data);
extern guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *g, void **data_rtn);
extern void guestfs_set_error_handler (guestfs_h *g, guestfs_error_handler_cb cb, void *data);
extern guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *g, void **data_rtn);