diff --git a/media/bufferpool/2.0/Android.bp b/media/bufferpool/2.0/Android.bp
index 405990e..1f8bbdb 100644
--- a/media/bufferpool/2.0/Android.bp
+++ b/media/bufferpool/2.0/Android.bp
@@ -11,12 +11,14 @@
         "IAccessor.hal",
         "IClientManager.hal",
         "IConnection.hal",
+        "IObserver.hal",
     ],
     interfaces: [
         "android.hidl.base@1.0",
     ],
     types: [
         "Buffer",
+        "BufferInvalidationMessage",
         "BufferStatus",
         "BufferStatusMessage",
         "ResultStatus",
diff --git a/media/bufferpool/2.0/IAccessor.hal b/media/bufferpool/2.0/IAccessor.hal
index ab7c02d..66707fe 100644
--- a/media/bufferpool/2.0/IAccessor.hal
+++ b/media/bufferpool/2.0/IAccessor.hal
@@ -17,6 +17,7 @@
 package android.hardware.media.bufferpool@2.0;
 
 import IConnection;
+import IObserver;
 /**
  * IAccessor creates IConnection which is used from IClientManager in order to
  * use functionality of the specified buffer pool.
@@ -49,6 +50,13 @@
      * made and kept private. Also part of transaction ID is a sender ID in
      * order to prevent fake transactions from other clients. This must be
      * verified with an FMQ message from a buffer pool.
+
+     * @param observer The buffer pool event observer from the client.
+     *     Observer is provided to ensure FMQ messages are processed even when
+     *     client processes are idle. Buffer invalidation caused by
+     *     reconfiguration does not call observer. Buffer invalidation caused
+     *     by termination of pipeline call observer in order to ensure
+     *     invalidation is done after pipeline completion.
      *
      * @return status The status of the call.
      *     OK               - A connection is made successfully.
@@ -64,7 +72,7 @@
      * @return fromFmqDesc FMQ descriptor. The descriptor is used to
      *     receive buffer invalidation messages from the buffer pool.
      */
-    connect()
+    connect(IObserver observer)
         generates (ResultStatus status, IConnection connection,
                    int64_t connectionId,
                    fmq_sync<BufferStatusMessage> toFmqDesc,
diff --git a/media/bufferpool/2.0/IObserver.hal b/media/bufferpool/2.0/IObserver.hal
new file mode 100644
index 0000000..a998836
--- /dev/null
+++ b/media/bufferpool/2.0/IObserver.hal
@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2018 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.
+ */
+
+package android.hardware.media.bufferpool@2.0;
+
+/**
+ * IObserver listens on notifications from the buffer pool. On receiving
+ * notifications, FMQ messages from the specific buffer pool which are already
+ * in the FMQ are processed.
+ */
+interface IObserver {
+
+    /**
+     * The specific buffer pool sent a message to the client. Calling this
+     * method from the buffer pool enforces a buffer pool client process the
+     * message.
+     *
+     * @param connectionId the connection Id of the specific buffer pool client
+     */
+    oneway onMessage(int64_t connectionId);
+};
diff --git a/media/bufferpool/2.0/types.hal b/media/bufferpool/2.0/types.hal
index 456e4aa..597e7b3 100644
--- a/media/bufferpool/2.0/types.hal
+++ b/media/bufferpool/2.0/types.hal
@@ -65,6 +65,8 @@
     TRANSFER_OK         = 7,
     /** Buffer transaction failure. */
     TRANSFER_ERROR      = 8,
+    /** Buffer invalidation ack. */
+    INVALIDATION_ACK    = 9,
 };
 
 /**
@@ -98,6 +100,7 @@
  * buffers as soon as possible upon receiving the message.
  */
 struct BufferInvalidationMessage {
+    uint32_t messageId;
     /**
      * Buffers from fromBufferId to toBufferId must be invalidated.
      * fromBufferId is inclusive, but toBufferId is not inclusive.