diff --git a/authfs/src/common.rs b/authfs/src/common.rs
new file mode 100644
index 0000000..2220ae7
--- /dev/null
+++ b/authfs/src/common.rs
@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+pub const COMMON_PAGE_SIZE: u64 = 4096;
+
+pub fn divide_roundup(dividend: u64, divisor: u64) -> u64 {
+    (dividend + divisor - 1) / divisor
+}