Function wal_reservation_response 

pub fn wal_reservation_response(
    request_matches: bool,
    request_epoch: i64,
    observed_epoch: i64,
    response_epoch: i64,
    base: i64,
    count: i64,
) -> Option<i64>

Admit a controller reservation response bound to the exact request and leader epoch.

-1 means the caller cannot observe the controller epoch; the response must still carry a nonnegative epoch committed by the leader.