diff --git a/core/src/layers/logging.rs b/core/src/layers/logging.rs
index d65797f555cb..04ad1b604a53 100644
--- a/core/src/layers/logging.rs
+++ b/core/src/layers/logging.rs
@@ -27,7 +27,7 @@ use futures::TryFutureExt;
 use log::debug;
 use log::log;
 use log::trace;
-use log::Level;
+pub use log::Level;
 
 use crate::ops::*;
 use crate::raw::oio::ReadOperation;
@@ -45,6 +45,8 @@ use crate::*;
 ///   - `finished`: the operation is successful.
 ///   - `errored`: the operation returns an expected error like `NotFound`.
 ///   - `failed`: the operation returns an unexpected error.
+/// - The default log level while expected error happened is `Warn`.
+/// - The default log level while unexpected failure happened is `Error`.
 ///
 /// # Todo
 ///