lua_pushcfunction
lua_pushcfunction(L, openf);
lua_pushcfunction(L, iter); /* will return generator, */
#define lua_register(L,n,f) (lua_pushcfunction(L, (f)), lua_setglobal(L, (n)))
(lua_pushcfunction(L, (f)), \
lua_pushcfunction(state, zcp_error_handler);
lua_pushcfunction(state, zcp_lua_to_nvlist_helper);
lua_pushcfunction(state, info->gc);