diff --git a/camera/device/3.6/ICameraOfflineSession.hal b/camera/device/3.6/ICameraOfflineSession.hal
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+/*
+ * Copyright (C) 2019 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.camera.device@3.6;
+
+import @3.5::ICameraDeviceCallback;
+
+/**
+ * Camera device offline session interface.
+ *
+ * Obtained via ICameraDeviceSession::switchToOffline(), this interface contains
+ * the methods and callback interfaces that define how camera service interacts
+ * with an offline session.
+ *
+ * An offline session contains some unfinished capture requests that were submitted
+ * to the parent ICameraDeviceSession before calling switchToOffline, and is
+ * responsible for delivering these capture results back to camera service regardless
+ * of whether the parent camera device is still opened or not. An offline session must
+ * not have access to the camera device's image sensor. During switchToOffline
+ * call, camera HAL must capture all necessary frames from the image sensor that
+ * is needed for completing the requests offline later.
+ */
+interface ICameraOfflineSession {
+    /**
+     * Set the callbacks for offline session to communicate with camera service.
+     *
+     * Offline session is responsible to store all callbacks the camera HAL
+     * generated after the return of ICameraDeviceSession::switchToOffline, and
+     * send them to camera service once this method is called.
+     *
+     * Camera service must not call this method more than once, so these
+     * callbacks can be assumed to be constant after the first setCallback call.
+     */
+    setCallback(ICameraDeviceCallback cb);
+
+    /**
+     * getCaptureResultMetadataQueue:
+     *
+     * Retrieves the queue used along with
+     * ICameraDeviceCallback#processCaptureResult.
+     *
+     * Clients to ICameraOfflineSession must:
+     * - Call getCaptureRequestMetadataQueue to retrieve the fast message queue;
+     * - In implementation of ICameraDeviceCallback, test whether
+     *   .fmqResultSize field is zero.
+     *     - If .fmqResultSize != 0, read result metadata from the fast message
+     *       queue;
+     *     - otherwise, read result metadata in CaptureResult.result.
+     *
+     * @return queue the queue that implementation writes result metadata to.
+     */
+    getCaptureResultMetadataQueue() generates (fmq_sync<uint8_t> queue);
+
+    /**
+     * Close the offline session and release all resources.
+     *
+     * Camera service may call this method before or after the offline session
+     * has finished all requests it needs to handle. If there are still unfinished
+     * requests when close is called, camera HAL must send ERROR_REQUEST for
+     * all unfinished requests and return all buffers via
+     * ICameraDeviceCallback#processCaptureResult or
+     * ICameraDeviceCallback#returnStreamBuffers.
+     * Also, all buffer caches maintained by the offline session must be erased
+     * before the close call returns.
+     */
+    close();
+};