[Android][Framework] 添加系统服务

新博客地址
http://wossoneri.github.io/2018/09/15/[android][framework]create-system-service/

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.orislink_service, demomanager.class,
       new cachedservicefetcher<demomanager>() {
           @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

1. 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。