/*
 * 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@1.0;

import IConnection;
/**
 * IAccessor creates IConnection which is used from IClientManager in order to
 * use functionality of the specified buffer pool.
 */
interface IAccessor {

    /**
     * Registers a new client and creates IConnection to the buffer pool for
     * the client. IConnection and FMQ are used by IClientManager in order to
     * communicate with the buffer pool. Via FMQ IClientManager sends
     * BufferStatusMesage(s) to the buffer pool.
     *
     * FMQ is used to send buffer ownership status changes to a buffer pool
     * from a buffer pool client. A buffer pool synchronizes FMQ messages when
     * there is a hidl request from the clients. Every client has its own
     * connection and FMQ to communicate with the buffer pool. So sending an
     * FMQ message on behalf of other clients is not possible.
     *
     * FMQ messages are sent when a buffer is acquired or released. Also, FMQ
     * messages are sent when a buffer is transferred from a client to another
     * client. FMQ has its own ID from a buffer pool. A client is specified
     * with the ID.
     *
     * To transfer a buffer, a sender must send an FMQ message. The message
     * must include a receiver's ID and a transaction ID. A receiver must send
     * the transaction ID to fetch a buffer from a buffer pool. Since the
     * sender already registered the receiver via an FMQ message, The buffer
     * pool must verify the receiver with the transaction ID. In order to
     * prevent faking a receiver, a connection to a buffer pool from client is
     * 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.
     *
     * @return status The status of the call.
     *     OK               - A connection is made successfully.
     *     NO_MEMORY        - Memory allocation failure occurred.
     *     ALREADY_EXISTS   - A connection was already made.
     *     CRITICAL_ERROR   - Other errors.
     * @return connection The IConnection have interfaces
     *     to get shared buffers from the buffer pool.
     * @return connectionId Id of IConnection. The Id identifies
     *     sender and receiver in FMQ messages during buffer transfer.
     * @return mqDesc FMQ descriptor. The descriptor can be used to
     *     send/receive FMQ messages.
     */
    connect()
        generates (ResultStatus status, IConnection connection,
                   int64_t connectionId, fmq_sync<BufferStatusMessage> mqDesc);
};