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  团队博客: 汽车电子社区

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一、CarService的基本架构

1.1、Android Automative整体框架

  从这幅图中我们可以看出，Android Automative是在原先Android的系统架构上增加了一些与车相关的（图中虚线框中绿色背景的）模块。
    1. Car App：包括OEM和第三方开发的App
    2. Car API：内有包含 CarSensorManager 在内的 API。位于 /platform/packages/services/Car/car-lib。
    3. CarService：系统中与车相关的服务，位于 /platform/packages/services/Car/目录。
    4. 车载 HAL：用于定义 OEM 可以实现的车辆属性的接口。包含属性元数据（例如，车辆属性是否为 int 以及允许使用哪些更改模式）。位于 hardware/libhardware/include/hardware/vehicle.h。如需了解基本参考实现，请参阅 hardware/libhardware/modules/vehicle/。

1.2、Framework CarService

  Android O/P为Automotive场景提供了一系列的服务，这些服务统被称为CarService。它们与HAL层的VehicleHAL通信，进而通过车载总线(例如CAN总线)与车身进行通讯，同时它们还为应用层的APP提供接口，从而让APP能够实现对车身的控制与状态的显示。
  CarManage位于packages/services/Car/car-lib/src/android/car/hardware目录，
  CarService位于packages/services/Car/service/src/com/android/car目录。

1.3、目录结构

1.3.1、CarService

├── Android.mk
├── apicheck.mk
├── apicheck_msg_current.txt
├── apicheck_msg_last.txt
├── car-cluster-logging-renderer    //LoggingClusterRenderingService继承InstrumentClusterRenderingService
├── car-default-input-service       //按键消息处理
├── car-lib                         //提供给汽车App特有的接口，许多定制的模块都在这里实现，包括Sensor,HVAC,Cabin,ActiveParkingAssiance,Diagnostic,Vendor等
├── car-maps-placeholder            //地图软件相关
├── car_product                     //系统编译相关
├── car-support-lib                 //android.support.car
├── car-systemtest-lib              //系统测试相关
├── car-usb-handler                 //开机自启，用于管理车机USB
├── CleanSpec.mk
├── evs  
├── obd2-lib
├── PREUPLOAD.cfg
├── procfs-inspector
├── service                         //com.android.car是一个后台运行的组件，可以长时间运行并且不需要和用户去交互的，这里即使应用被销毁，它也可以正常工作
├── tests
├── tools                           //是一系列的工具，要提到的是里面的emulator，测试需要用到的。python写的，通过adb可以连接vehicleHal的工具，用于模拟测试
├── TrustAgent
└── vehicle-hal-support-lib

1.3.2、Car APP

  Car APP的相关源码位于packages/apps/Car/目录，其中packages/services/Car/car_product/build/car.mk里面决定了需要编译哪些相关apk（system/priv-app）。
  packages/services/Car/car_product/build/car.mk内容如下：

# Common make file for all car buildsPRODUCT_PUBLIC_SEPOLICY_DIRS += packages/services/Car/car_product/sepolicy/public
PRODUCT_PRIVATE_SEPOLICY_DIRS += packages/services/Car/car_product/sepolicy/privatePRODUCT_PACKAGES += \Bluetooth \CarActivityResolver \CarDeveloperOptions \CarSettingsIntelligence \CarManagedProvisioning \OneTimeInitializer \CarProvision \StatementService \SystemUpdaterPRODUCT_PACKAGES += \clatd \pppd \screenrecord# This is for testing
ifneq (,$(filter userdebug eng, $(TARGET_BUILD_VARIANT)))
PRODUCT_PACKAGES += \DefaultStorageMonitoringCompanionApp \EmbeddedKitchenSinkApp \GarageModeTestApp \ExperimentalCarService \BugReportApp \NetworkPreferenceApp \SampleCustomInputService \AdasLocationTestApp \curl \# SEPolicy for test apps / services
BOARD_SEPOLICY_DIRS += packages/services/Car/car_product/sepolicy/test
endif# ClusterOsDouble is the testing app to test Cluster2 framework and it can handle Cluster VHAL
# and do some Cluster OS role.
ifeq ($(ENABLE_CLUSTER_OS_DOUBLE), true)
PRODUCT_PACKAGES += ClusterHomeSample ClusterOsDouble
else
# DirectRenderingCluster is the sample app for the old Cluster framework.
PRODUCT_PACKAGES += DirectRenderingCluster
endif  # ENABLE_CLUSTER_OS_DOUBLEPRODUCT_COPY_FILES += \frameworks/av/media/libeffects/data/audio_effects.conf:system/etc/audio_effects.confPRODUCT_PROPERTY_OVERRIDES += \persist.bluetooth.enablenewavrcp=false \ro.carrier=unknownPRODUCT_SYSTEM_DEFAULT_PROPERTIES += \config.disable_systemtextclassifier=true###
### Suggested values for multi-user properties - can be overridden
#### Enable headless system user mode
PRODUCT_SYSTEM_DEFAULT_PROPERTIES += \ro.fw.mu.headless_system_user?=true# Enable user pre-creation
PRODUCT_SYSTEM_DEFAULT_PROPERTIES += \android.car.number_pre_created_users?=1 \android.car.number_pre_created_guests?=1# Enable User HAL integration
# NOTE: when set to true, VHAL must also implement the user-related properties,
# otherwise CarService will ignore it
PRODUCT_SYSTEM_DEFAULT_PROPERTIES += \android.car.user_hal_enabled?=true### end of multi-user properties #### Overlay for Google network and fused location providers
$(call inherit-product, device/sample/products/location_overlay.mk)
$(call inherit-product-if-exists, frameworks/webview/chromium/chromium.mk)
$(call inherit-product, packages/services/Car/car_product/build/car_base.mk)# Overrides
PRODUCT_BRAND := generic
PRODUCT_DEVICE := generic
PRODUCT_NAME := generic_car_no_telephonyPRODUCT_IS_AUTOMOTIVE := truePRODUCT_PROPERTY_OVERRIDES := \ro.config.ringtone=Girtab.ogg \ro.config.notification_sound=Tethys.ogg \ro.config.alarm_alert=Oxygen.ogg \$(PRODUCT_PROPERTY_OVERRIDES) \PRODUCT_PROPERTY_OVERRIDES += \keyguard.no_require_sim=true# TODO(b/205189147): Remove the following change after the proper fix is landed.
# Uses the local KeyGuard animation to resolve TaskView misalignment issue after display-on.
PRODUCT_SYSTEM_PROPERTIES += \persist.wm.enable_remote_keyguard_animation=0# Automotive specific packages
PRODUCT_PACKAGES += \CarFrameworkPackageStubs \CarService \CarShell \CarDialerApp \CarRadioApp \OverviewApp \CarSystemUI \LocalMediaPlayer \CarMediaApp \CarMessengerApp \CarHTMLViewer \CarMapsPlaceholder \CarLatinIME \CarSettings \CarUsbHandler \android.car \car-frameworks-service \com.android.car.procfsinspector \libcar-framework-service-jni \ScriptExecutor \# RROs
PRODUCT_PACKAGES += \CarPermissionControllerRRO \# System Server components
# Order is important: if X depends on Y, then Y should precede X on the list.
PRODUCT_SYSTEM_SERVER_JARS += car-frameworks-service
# TODO: make the order optimal by appending 'car-frameworks-service' at the end
# after its dependency 'services'. Currently the order is violated because this
# makefile is included before AOSP makefile.
PRODUCT_BROKEN_SUBOPTIMAL_ORDER_OF_SYSTEM_SERVER_JARS := true# Boot animation
PRODUCT_COPY_FILES += \packages/services/Car/car_product/bootanimations/bootanimation-832.zip:system/media/bootanimation.zipPRODUCT_LOCALES := \en_US \af_ZA \am_ET \ar_EG ar_XB \as_IN \az_AZ \be_BY \bg_BG \bn_BD \bs_BA \ca_ES \cs_CZ \da_DK \de_DE \el_GR \en_AU en_CA en_GB en_IN en_XA \es_ES es_US \et_EE \eu_ES \fa_IR \fi_FI \fil_PH \fr_CA fr_FR \gl_ES \gu_IN \hi_IN \hr_HR \hu_HU \hy_AM \id_ID \is_IS \it_IT \iw_IL \ja_JP \ka_GE \kk_KZ \km_KH km_MH \kn_IN \ko_KR \ky_KG \lo_LA \lv_LV \lt_LT \mk_MK \ml_IN \mn_MN \mr_IN \ms_MY \my_MM \ne_NP \nl_NL \no_NO \or_IN \pa_IN \pl_PL \pt_BR pt_PT \ro_RO \ru_RU \si_LK \sk_SK \sl_SI \sq_AL \sr_RS \sv_SE \sw_TZ \ta_IN \te_IN \th_TH \tr_TR \uk_UA \ur_PK \uz_UZ \vi_VN \zh_CN zh_HK zh_TW \zu_ZAPRODUCT_BOOT_JARS += \android.carPRODUCT_HIDDENAPI_STUBS := \android.car-stubs-dexPRODUCT_HIDDENAPI_STUBS_SYSTEM := \android.car-system-stubs-dexPRODUCT_HIDDENAPI_STUBS_TEST := \android.car-test-stubs-dex# Disable Prime Shader Cache in SurfaceFlinger to make it available faster
PRODUCT_PROPERTY_OVERRIDES += \service.sf.prime_shader_cache=0

二、CarService的启动流程

2.1、系统启动后在SystemServer进程中启动CarServiceHelperService

  1. 在Android系统之后，系统首先会启动一个名为Zygote的进程，而Zygote进程又会启动SystemServer进程，这里我们先来看SystemServer的main方法。

frameworks/base/services/java/com/android/server/SystemServer.javapublic final class SystemServer implements Dumpable {public static void main(String[] args) {new SystemServer().run();}private void run(){...代码省略...// Start services.try {t.traceBegin("StartServices");startBootstrapServices(t);//启动引导服务startCoreServices(t);//启动核心服务startOtherServices(t);//启动其他服务} catch (Throwable ex) {Slog.e("System", "******************************************");Slog.e("System", "************ Failure starting system services", ex);throw ex;} finally {t.traceEnd(); // StartServices}...代码省略...}
}

  main方法里启动了run方法，而在run方法中会调用了startOtherServices() 方法。

  2. startOtherServices和CarService相关的关键代码如下所示。

public final class SystemServer implements Dumpable {private static final String CAR_SERVICE_HELPER_SERVICE_CLASS ="com.android.internal.car.CarServiceHelperService";private PackageManager mPackageManager;private void startOtherServices() {mActivityManagerService.systemReady(() -> {...代码省略...if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE)) {t.traceBegin("StartCarServiceHelperService");//如果有车机服务，则开启车机帮助服务final SystemService cshs = mSystemServiceManager.startService(CAR_SERVICE_HELPER_SERVICE_CLASS);if (cshs instanceof Dumpable) {mDumper.addDumpable((Dumpable) cshs);}if (cshs instanceof DevicePolicySafetyChecker) {dpms.setDevicePolicySafetyChecker((DevicePolicySafetyChecker) cshs);}t.traceEnd();}...代码省略...}}
}

  3. SystemServiceManager的startService方法如下所示。

frameworks/base/services/core/java/com/android/server/SystemServiceManager.javapublic class SystemServiceManager {//存储了SystemServiceManager负责启动的各种服务private final ArrayList<SystemService> mServices = new ArrayList<SystemService>();public SystemService startService(String className) {final Class<SystemService> serviceClass = loadClassFromLoader(className,this.getClass().getClassLoader());return startService(serviceClass);}@SuppressWarnings("unchecked")public <T extends SystemService> T startService(Class<T> serviceClass) {try {final String name = serviceClass.getName();...代码省略...final T service;try {Constructor<T> constructor = serviceClass.getConstructor(Context.class);service = constructor.newInstance(mContext);} ...代码省略...startService(service);return service;} finally {Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);}}public void startService(@NonNull final SystemService service) {// Register it.mServices.add(service);// Start it.long time = SystemClock.elapsedRealtime();try {service.onStart();} catch (RuntimeException ex) {throw new RuntimeException("Failed to start service " + service.getClass().getName()+ ": onStart threw an exception", ex);}warnIfTooLong(SystemClock.elapsedRealtime() - time, service, "onStart");}
}

  因为前面我们传入的参数为com.android.internal.car.CarServiceHelperService，所以这里startService方法首先会通过反射创建CarServiceHelperService对象实例，然后将其存储在类型ArrayList的mServices中，紧接着会调用CarServiceHelperService的onStart方法。
  4. CarServiceHelperService的onStart方法如下所示。

frameworks/opt/car/services/src/com/android/internal/car/CarServiceHelperService.javapublic class CarServiceHelperService extends SystemServiceimplements Dumpable, DevicePolicySafetyChecker {@Overridepublic void onStart() {EventLog.writeEvent(EventLogTags.CAR_HELPER_START);IntentFilter filter = new IntentFilter(Intent.ACTION_REBOOT);filter.addAction(Intent.ACTION_SHUTDOWN);mContext.registerReceiverForAllUsers(mShutdownEventReceiver, filter, null, null);mCarWatchdogDaemonHelper.addOnConnectionChangeListener(mConnectionListener);mCarWatchdogDaemonHelper.connect();Intent intent = new Intent();intent.setPackage("com.android.car");intent.setAction(CAR_SERVICE_INTERFACE);//通过bindService绑定车机服务CarServiceif (!mContext.bindServiceAsUser(intent, mCarServiceConnection, Context.BIND_AUTO_CREATE,mHandler, UserHandle.SYSTEM)) {Slogf.wtf(TAG, "cannot start car service");}loadNativeLibrary();}void loadNativeLibrary() {System.loadLibrary("car-framework-service-jni");}
}

packages/services/Car/car-lib/src/com/android/car/internal/common/CommonConstants.javapublic final class CommonConstants {// CarService Constantspublic static final String CAR_SERVICE_INTERFACE = "android.car.ICar";
}

  CarServiceHelperService的onStart方法首先创建一个Action为android.car.ICar，包名为com.android.car的Intent，然后通过bindService的方式启动该Intent对应的服务，而这个服务正是车机模块才有的CarService服务。

2.2、CarService启动

  1、系统关于CarService服务的声明如下所示。

packages/services/Car/service/AndroidManifest.xml<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"xmlns:androidprv="http://schemas.android.com/apk/prv/res/android"package="com.android.car"coreApp="true"android:sharedUserId="android.uid.system"><!--...代码省略...-->       <application android:label="@string/app_title"android:directBootAware="true"android:allowBackup="false"android:persistent="true"><service android:name=".CarService"android:singleUser="true"android:exported="true"><intent-filter><action android:name="android.car.ICar"/></intent-filter></service><!--...代码省略...-->       </application>
</manifest>     

结合这个配置文件我们可以知道CarServiceHelperService最终所启动的，就是CarService这个服务。
  2、CarService的onCreate方法如下所示。

public class CarService extends Service {private ICarImpl mICarImpl;@Overridepublic void onCreate() {...代码省略...mICarImpl = new ICarImpl(this,mVehicle,SystemInterface.Builder.defaultSystemInterface(this).build(),mVehicleInterfaceName);mICarImpl.init();linkToDeath(mVehicle, mVehicleDeathRecipient);//将ICarImpl存储到系统服务管理者ServiceManager中ServiceManager.addService("car_service", mICarImpl);SystemProperties.set("boot.car_service_created", "1");super.onCreate();initTiming.traceEnd(); // "CarService.onCreate"}@Overridepublic int onStartCommand(Intent intent, int flags, int startId) {// keep it alive.return START_STICKY;}@Overridepublic IBinder onBind(Intent intent) {return mICarImpl;}
}

  CarService的onCreate方法会创建一个关键对象ICarImpl的实例，并将该实例赋值给mICarImpl属性变量，然后会调用该对象的init方法，之后还会将mICarImpl存储到ServiceManager中。另外结合CarService的onBind方法我们可以知道，CarServiceHelperService通过bindService方式开启CarService，CarService会返回mICarImpl对象，通过该Binder对象使二者建立双向跨进程通信。

三、CarService源码分析

3.1、CarService框架源码分析

  当服务启动之后, 首先调用其onCreate方法. CarService的onCreate方法实现如下:

 @Overridepublic void onCreate() {Log.i(CarLog.TAG_SERVICE, "Service onCreate");//获取通知管理NotificationManager对象mCanBusErrorNotifier = new CanBusErrorNotifier(this /* context */);mVehicle = getVehicle();if (mVehicle == null) {throw new IllegalStateException("Vehicle HAL service is not available.");}try {mVehicleInterfaceName = mVehicle.interfaceDescriptor();} catch (RemoteException e) {throw new IllegalStateException("Unable to get Vehicle HAL interface descriptor", e);}Log.i(CarLog.TAG_SERVICE, "Connected to " + mVehicleInterfaceName);mICarImpl = new ICarImpl(this,mVehicle,SystemInterface.Builder.defaultSystemInterface(this).build(),mCanBusErrorNotifier,mVehicleInterfaceName);mICarImpl.init();linkToDeath(mVehicle, mVehicleDeathRecipient);ServiceManager.addService("car_service", mICarImpl);//设置SystemProperty属性  carService已创建SystemProperties.set("boot.car_service_created", "1");super.onCreate();}

  主要做了两件事情:
    1. 获取mVehicle 车辆相关的HIDL Binder远程对象。
    2. 创建了mICarImpl对象, 并将其添加到ServiceManager管理的服务列表中.
  这里的ICarImpl起着创建并管理各个服务的作用。在它的构造函数中，创建了各个服务的实例,并添加到服务列表中，源码如下:

packages/services/Car/service/src/com/android/car/ICarImpl.javapublic ICarImpl(Context serviceContext, IVehicle vehicle, SystemInterface systemInterface,CanBusErrorNotifier errorNotifier, String vehicleInterfaceName) {mContext = serviceContext;mSystemInterface = systemInterface;mHal = new VehicleHal(vehicle);mVehicleInterfaceName = vehicleInterfaceName;//创建各种重要的服务mUserManagerHelper = new CarUserManagerHelper(serviceContext);final Resources res = mContext.getResources();final int maxRunningUsers = res.getInteger(com.android.internal.R.integer.config_multiuserMaxRunningUsers);mCarUserService = new CarUserService(serviceContext, mUserManagerHelper,ActivityManager.getService(), maxRunningUsers);mSystemActivityMonitoringService = new SystemActivityMonitoringService(serviceContext);mCarPowerManagementService = new CarPowerManagementService(mContext, mHal.getPowerHal(),systemInterface, mUserManagerHelper);mCarPropertyService = new CarPropertyService(serviceContext, mHal.getPropertyHal());....//将重要的服务缓存到 CarLocalServicesCarLocalServices.addService(CarPowerManagementService.class, mCarPowerManagementService);CarLocalServices.addService(CarUserService.class, mCarUserService);CarLocalServices.addService(CarTrustedDeviceService.class, mCarTrustedDeviceService);// 将创建的服务对象依次添加到一个list中保存起来List<CarServiceBase> allServices = new ArrayList<>();allServices.add(mFeatureController);allServices.add(mCarUserService);.....
}

  这些创建的服务就是上文介绍的汽车服务.。

3.2、CarAudioService源码分析

3.2.1、构造函数

  这里读取配置文件audioUseDynamicRouting确定是否使用动态Routing。

public CarAudioService(Context context) {mContext = context;mTelephonyManager = (TelephonyManager) mContext.getSystemService(Context.TELEPHONY_SERVICE);mAudioManager = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);mUseDynamicRouting = mContext.getResources().getBoolean(R.bool.audioUseDynamicRouting);
}

3.2.2、setupDynamicRouting

  当mUseDynamicRouting为true时，将调用setupDynamicRouting函数；该函数里会创建一个AudioPolicy ，并通过mAudioManager.registerAudioPolicy函数注册该AudioPolicy。

private void setupDynamicRouting() {final IAudioControl audioControl = getAudioControl();if (audioControl == null) {return;}AudioPolicy audioPolicy = getDynamicAudioPolicy(audioControl);int r = mAudioManager.registerAudioPolicy(audioPolicy);if (r != AudioManager.SUCCESS) {throw new RuntimeException("registerAudioPolicy failed " + r);}mAudioPolicy = audioPolicy;
}

3.2.3、AudioManager::registerAudioPolicy

public int registerAudioPolicy(@NonNull AudioPolicy policy) {if (policy == null) {throw new IllegalArgumentException("Illegal null AudioPolicy argument");}final IAudioService service = getService();try {String regId = service.registerAudioPolicy(policy.getConfig(), policy.cb(),policy.hasFocusListener(), policy.isFocusPolicy(), policy.isVolumeController());if (regId == null) {return ERROR;} else {policy.setRegistration(regId);}// successful registration} catch (RemoteException e) {throw e.rethrowFromSystemServer();}return SUCCESS;
}

  【1】policy.isVolumeController()
  这里mVolCb 的值就是通过setAudioPolicyVolumeCallback函数设置进来的，因此这里的 mVolCb 就是CarAudioService的mAudioPolicyVolumeCallback
  public boolean isVolumeController() { return mVolCb != null; }

public Builder setAudioPolicyVolumeCallback(@NonNull AudioPolicyVolumeCallback vc) {if (vc == null) {throw new IllegalArgumentException("Invalid null volume callback");}mVolCb = vc;return this;
}

  【2】这里的policy.cb()为IAudioPolicyCallback ，（这个很重要，后续将会用到）

public IAudioPolicyCallback cb() { return mPolicyCb; }private final IAudioPolicyCallback mPolicyCb = new IAudioPolicyCallback.Stub() {public void notifyAudioFocusGrant(AudioFocusInfo afi, int requestResult) {sendMsg(MSG_FOCUS_GRANT, afi, requestResult);if (DEBUG) {Log.v(TAG, "notifyAudioFocusGrant: pack=" + afi.getPackageName() + " client="+ afi.getClientId() + "reqRes=" + requestResult);}}public void notifyAudioFocusLoss(AudioFocusInfo afi, boolean wasNotified) {sendMsg(MSG_FOCUS_LOSS, afi, wasNotified ? 1 : 0);if (DEBUG) {Log.v(TAG, "notifyAudioFocusLoss: pack=" + afi.getPackageName() + " client="+ afi.getClientId() + "wasNotified=" + wasNotified);}}public void notifyAudioFocusRequest(AudioFocusInfo afi, int requestResult) {sendMsg(MSG_FOCUS_REQUEST, afi, requestResult);if (DEBUG) {Log.v(TAG, "notifyAudioFocusRequest: pack=" + afi.getPackageName() + " client="+ afi.getClientId() + " gen=" + afi.getGen());}}public void notifyAudioFocusAbandon(AudioFocusInfo afi) {sendMsg(MSG_FOCUS_ABANDON, afi, 0 /* ignored */);if (DEBUG) {Log.v(TAG, "notifyAudioFocusAbandon: pack=" + afi.getPackageName() + " client="+ afi.getClientId());}}public void notifyMixStateUpdate(String regId, int state) {for (AudioMix mix : mConfig.getMixes()) {if (mix.getRegistration().equals(regId)) {mix.mMixState = state;sendMsg(MSG_MIX_STATE_UPDATE, mix, 0/*ignored*/);if (DEBUG) {Log.v(TAG, "notifyMixStateUpdate: regId=" + regId + " state=" + state);}}}}public void notifyVolumeAdjust(int adjustment) {sendMsg(MSG_VOL_ADJUST, null /* ignored */, adjustment);if (DEBUG) {Log.v(TAG, "notifyVolumeAdjust: " + adjustment);}}};

3.2.4、AudioService::registerAudioPolicy

3.2.4.1、流程图

3.2.4.2、AudioService::registerAudioPolicy代码

  AudioPolicyProxy app = new AudioPolicyProxy(policyConfig, pcb, hasFocusListener, isFocusPolicy, isVolumeController);
  这里实例化了AudioPolicyProxy，并将registerAudioPolicy参数作为AudioPolicyProxy构造函数的参数。如上所述，isVolumeController的值就是policy.isVolumeController()，因此为true。

 public String registerAudioPolicy(AudioPolicyConfig policyConfig, IAudioPolicyCallback pcb,boolean hasFocusListener, boolean isFocusPolicy, boolean isVolumeController) {AudioSystem.setDynamicPolicyCallback(mDynPolicyCallback);String regId = null;// error handlingboolean hasPermissionForPolicy =(PackageManager.PERMISSION_GRANTED == mContext.checkCallingPermission(android.Manifest.permission.MODIFY_AUDIO_ROUTING));if (!hasPermissionForPolicy) {Slog.w(TAG, "Can't register audio policy for pid " + Binder.getCallingPid() + " / uid "+ Binder.getCallingUid() + ", need MODIFY_AUDIO_ROUTING");return null;}mDynPolicyLogger.log((new AudioEventLogger.StringEvent("registerAudioPolicy for "+ pcb.asBinder() + " with config:" + policyConfig)).printLog(TAG));synchronized (mAudioPolicies) {try {if (mAudioPolicies.containsKey(pcb.asBinder())) {Slog.e(TAG, "Cannot re-register policy");return null;}AudioPolicyProxy app = new AudioPolicyProxy(policyConfig, pcb, hasFocusListener,isFocusPolicy, isVolumeController);pcb.asBinder().linkToDeath(app, 0/*flags*/);regId = app.getRegistrationId();mAudioPolicies.put(pcb.asBinder(), app);} catch (RemoteException e) {// audio policy owner has already died!Slog.w(TAG, "Audio policy registration failed, could not link to " + pcb +" binder death", e);return null;}}return regId;
}

3.2.4.3、AudioPolicyProxy构造函数

AudioPolicyProxy(AudioPolicyConfig config, IAudioPolicyCallback token,boolean hasFocusListener, boolean isFocusPolicy, boolean isVolumeController) {super(config);setRegistration(new String(config.hashCode() + ":ap:" + mAudioPolicyCounter++));mPolicyCallback = token;mHasFocusListener = hasFocusListener;mIsVolumeController = isVolumeController;if (mHasFocusListener) {mMediaFocusControl.addFocusFollower(mPolicyCallback);// can only ever be true if there is a focus listenerif (isFocusPolicy) {mIsFocusPolicy = true;mMediaFocusControl.setFocusPolicy(mPolicyCallback);}}if (mIsVolumeController) {setExtVolumeController(mPolicyCallback);}connectMixes();
}

3.2.4.4、AudioPolicyProxy::setExtVolumeController

  这里设置mExtVolumeController 的值为类AudioPolicy中的IAudioPolicyCallback mPolicyCb。

private void setExtVolumeController(IAudioPolicyCallback apc) {if (!mContext.getResources().getBoolean(com.android.internal.R.bool.config_handleVolumeKeysInWindowManager)) {Log.e(TAG, "Cannot set external volume controller: device not set for volume keys" +" handled in PhoneWindowManager");return;}synchronized (mExtVolumeControllerLock) {if (mExtVolumeController != null && !mExtVolumeController.asBinder().pingBinder()) {Log.e(TAG, "Cannot set external volume controller: existing controller");}mExtVolumeController = apc;}
}

3.2.5、CarAudioService::setupVolumeGroups

3.2.5.1、这里通过CarVolumeGroupsHelper类加载car_volume_groups.xml文件

 
private void setupVolumeGroups() {Preconditions.checkArgument(mCarAudioDeviceInfos.size() > 0,"No bus device is configured to setup volume groups");final CarVolumeGroupsHelper helper = new CarVolumeGroupsHelper(mContext, R.xml.car_volume_groups);mCarVolumeGroups = helper.loadVolumeGroups();for (CarVolumeGroup group : mCarVolumeGroups) {for (int contextNumber : group.getContexts()) {int busNumber = mContextToBus.get(contextNumber);group.bind(contextNumber, busNumber, mCarAudioDeviceInfos.get(busNumber));}// Now that we have all our contexts, ensure the HAL gets our intial valuegroup.setCurrentGainIndex(group.getCurrentGainIndex());Log.v(CarLog.TAG_AUDIO, "Processed volume group: " + group);}// Perform validation after all volume groups are processedif (!validateVolumeGroups()) {throw new RuntimeException("Invalid volume groups configuration");}
}

3.2.5.2、packages/services/Car/service/res/xml/car_volume_groups.xml文件

<volumeGroups xmlns:car="http://schemas.android.com/apk/res-auto"><group><context car:context="music"/><context car:context="call_ring"/><context car:context="notification"/><context car:context="system_sound"/></group><group><context car:context="navigation"/><context car:context="voice_command"/></group><group><context car:context="call"/></group><group><context car:context="alarm"/></group>
</volumeGroups>

3.2.5.3、USAGE、ContextNumber和volumeGroups的关系