[Android][Framework] 添加系统服务

做系统开发，有时候需要自己定义一些接口供App使用， 同时为了方便维护管理，就会需要自己建立一个服务，把新的功能集中在一起。下面就是新建一个系统服务的基本步骤。

1. 添加接口

   frameworks/base/core/java/android/app/IDemoManager.aidl

   package android.app;
   
   interface IDemoManager
   {
       int getCpuTemperature();
   }
   

2. 添加服务，实现aidl文件定义的接口

   frameworks/base/services/core/java/com/android/server/DemoManagerService.java

   package com.android.server;
   
   import android.app.IDemoManager;
   import android.content.Context;
   import android.util.Slog;
   
   public class DemoManagerService extends IDemoManager.Stub {
       private Context mContext;
   
       public DemoManagerService(Context context) {
           mContext = context;
           Slog.d("Demo", "Construct");
       }
   
       @Override
       public int getCpuTemperature() {
           return 100; // Test code
       }
   }
   

3. 添加对应的Manager

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

   package android.app;
   
   import android.content.Context;
   import android.os.RemoteException;
   import android.util.Slog;
   
   public class DemoManager {
       Context mContext;
       IDemoManager mService;
   
       public DemoManager(Context context, IDemoManager service) {
           mContext = context;
           mService = service;
       }
   
       public int getCpuTemperature() {
           if (mService != null) {
               try {
                   return mService.getCpuTemperature();
               } catch (RemoteException e) {
                   Slog.e("Demo", "RemoteException " + e);
               }
           }
           return -1;
       }
   }
   

4. 添加aidl到Makefile src

   frameworks/base/Android.mk

   LOCAL_SRC_FILES += \
       core/java/android/app/IDemoManager.aidl \
   

5. 添加DEMO_SERVICE常量

   frameworks/base/core/java/android/content/Context.java

   public static final String DEMO_SERVICE = "demo";
   

6. 注册系统服务

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

   registerService(Context.DEMO_SERVICE, DemoManager.class,
       new CachedServiceFetcher() {
           @Override
           public DemoManager createService(ContextImpl ctx) {
               IBinder b = ServiceManager.getService(Context.DEMO_SERVICE);
               return new DemoManager(ctx, IDemoManager.Stub.asInterface(b));
   }});
   

7. 开机启动服务

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

   try {
       ServiceManager.addService(Context.DEMO_SERVICE, new DemoManagerService(context));
   } catch (Throwable e) {
       Slog.e("Demo", "Failed to start Demo Service " + e);
   }
   

8. 编译源码，因为添加了接口，所以需要

   make update-api
   

   更新接口。然后再整编刷机。

9. service list 查看服务，不存在，这是因为selinux权限没加。

10. 添加sepolicy权限

    device/qcom/sepolicy/msm8937/service.te

    type demo_service, system_api_service, system_server_service, service_manager_type;
    

    device/qcom/sepolicy/msm8937/service_contexts

    demo  u:object_r:demo_service:s0
    

11. 重新编译代码，使用下面测试代码验证

    import android.app.DemoManager;
    
    DemoManager om = (DemoManager) getSystemService(Context.DEMO_SERVICE);
    Log.d(TAG, "Current temperature is " + om.getCpuTemperature());
    

    最终log打印出100，服务添加完成。