diff --git a/binder_bindings/android/os/IUpdateEngine.aidl b/binder_bindings/android/os/IUpdateEngine.aidl
index 1305079..8a5ec71 100644
--- a/binder_bindings/android/os/IUpdateEngine.aidl
+++ b/binder_bindings/android/os/IUpdateEngine.aidl
@@ -45,4 +45,17 @@
   void resetStatus();
   /** @hide */
   boolean verifyPayloadApplicable(in String metadataFilename);
+  /**
+   * Allocate space on userdata partition.
+   *
+   * @return 0 indicates allocation is successful.
+   *   Non-zero indicates space is insufficient. The returned value is the
+   *   total required space (in bytes) on userdata partition.
+   *
+   * @throws ServiceSpecificException for other errors.
+   *
+   * @hide
+   */
+  long allocateSpaceForPayload(in String metadataFilename,
+                               in String[] headerKeyValuePairs);
 }