Android添加系统服务

基于android 12

添加服务

frameworks/base/services/java/com/android/server/SystemServer.java

在这两个函数中都可以添加:

startCoreServices()
startOtherServices()

比如说:

t.traceBegin("StartPowerStatsService");
// Tracks rail data to be used for power statistics.
mSystemServiceManager.startService(PowerStatsService.class);
t.traceEnd();

获取服务

frameworks/base/core/java/android/os/ServiceManager.java

比如说:

PackageManagerService pm = (PackageManagerService)ServiceManager.getService("package");

例子:

下面通过VibratorManagerService看一个完整的例子:

1. 首先aidl定义接口:

frameworks/base/core/java/android/os/IVibratorManagerService.aidl

/** {@hide} */
interface IVibratorManagerService {
    int[] getVibratorIds();
    VibratorInfo getVibratorInfo(int vibratorId);
    boolean isVibrating(int vibratorId);
    boolean registerVibratorStateListener(int vibratorId, in IVibratorStateListener listener);
    boolean unregisterVibratorStateListener(int vibratorId, in IVibratorStateListener listener);
    boolean setAlwaysOnEffect(int uid, String opPkg, int alwaysOnId,
            in CombinedVibration vibration, in VibrationAttributes attributes);
    void vibrate(int uid, String opPkg, in CombinedVibration vibration,
            in VibrationAttributes attributes, String reason, IBinder token);
    void cancelVibrate(int usageFilter, IBinder token);
}

2. VibratorManagerService 继承 IVibratorManagerService.Stub 实现aidl接口

frameworks/base/services/core/java/com/android/server/vibrator/VibratorManagerService.java

public class VibratorManagerService extends IVibratorManagerService.Stub {
    ...
    @Override // Binder call
    public int[] getVibratorIds() {
        return Arrays.copyOf(mVibratorIds, mVibratorIds.length);
    }

    @Override // Binder call
    @Nullable
    public VibratorInfo getVibratorInfo(int vibratorId) {
        VibratorController controller = mVibrators.get(vibratorId);
        return controller == null ? null : controller.getVibratorInfo();
    }

    @Override // Binder call
    public boolean isVibrating(int vibratorId) {
        mContext.enforceCallingOrSelfPermission(
                android.Manifest.permission.ACCESS_VIBRATOR_STATE,
                "isVibrating");
        VibratorController controller = mVibrators.get(vibratorId);
        return controller != null && controller.isVibrating();
    }
    ...
}

3. 客户端代理,App通过SystemVibratorManager调用, mService就是VibratorManagerService在客户端的实例

frameworks/base/core/java/android/os/SystemVibratorManager.java

public class SystemVibratorManager extends VibratorManager {
    
    public SystemVibratorManager(Context context) {
        super(context);
        mContext = context;
        mService = IVibratorManagerService.Stub.asInterface( // 通过aidl获取远程binder服务
                ServiceManager.getService(Context.VIBRATOR_MANAGER_SERVICE));
    }
	
    @NonNull
    @Override
    public int[] getVibratorIds() {
        synchronized (mLock) {
            if (mVibratorIds != null) {
                return mVibratorIds;
            }
            try {
                if (mService == null) {
                    Log.w(TAG, "Failed to retrieve vibrator ids; no vibrator manager service.");
                } else {
                    return mVibratorIds = mService.getVibratorIds();
                }
            } catch (RemoteException e) {
                e.rethrowFromSystemServer();
            }
            return new int[0];
        }
    }

    ...

}

getSystemService流程:

context.getSystemService()  -> contextImpl.getSystemService -> SystemServiceRegistry.getSystemService

从SYSTEM_SERVICE_FETCHERS获取的,put在registerService函数中.

registerService又封装了registerContextAwareService, registerStaticService,用于注册服务

frameworks/base/core/java/android/app/SystemServiceRegistry.java

    public static Object getSystemService(ContextImpl ctx, String name) {
        ...
        final ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);

        final Object ret = fetcher.getService(ctx);
        ...
    }

    private static <T> void registerService(@NonNull String serviceName,
            @NonNull Class<T> serviceClass, @NonNull ServiceFetcher<T> serviceFetcher) {
        SYSTEM_SERVICE_NAMES.put(serviceClass, serviceName);
        SYSTEM_SERVICE_FETCHERS.put(serviceName, serviceFetcher);
        SYSTEM_SERVICE_CLASS_NAMES.put(serviceName, serviceClass.getSimpleName());
    }
    // 在静态代码块中通过registerService注册服务
    static {
        // 注册VIBRATOR_MANAGER_SERVICE,实际new的SystemVibratorManager,
        // VibratorManager是个抽象类, 实现的是 SystemVibratorManager
        registerService(Context.VIBRATOR_MANAGER_SERVICE, VibratorManager.class,
                new CachedServiceFetcher<VibratorManager>() {
                    @Override
                    public VibratorManager createService(ContextImpl ctx) {
                        return new SystemVibratorManager(ctx); //
                    }});
       ...

    }
    

回到VibratorManagerService上,再看看VibratorManagerService如何通过jni到hal实现控制硬件zhendong