pub unsafe extern "C" fn rrd_fetch_r(
filename: *const c_char,
cf: *const c_char,
start: *mut time_t,
end: *mut time_t,
step: *mut c_ulong,
ds_cnt: *mut c_ulong,
ds_namv: *mut *mut *mut c_char,
data: *mut *mut rrd_value_t,
) -> c_int