Android13增加一个systemservice，并允许APP访问

1、在/frameworks/base/core/java/android/os下创建一个AIDL文件，比如IDeviceMgr.aidl

package android.os;
interface IDeviceMgr {
    int createApn(String apn);
    boolean deleteApn(int apnId);
}

编译系统，生成AIDL对应的JAVA文件。

2、在//frameworks/base/services/core/java/com/android/server创建包名devicemgr，并创建DeviceMgr，继承IDeviceMgr 

package com.android.server.devicemgr;
import android.content.Context;
import android.os.IDeviceMgr;
import android.os.RemoteException;
public class DeviceMgr extends IDeviceMgr.Stub {
    private Context mContext;
    public DeviceMgr (Context context){
        this.mContext=context;
    }
    @Override
    public int createApn(String apnInfo) throws RemoteException {
        return 0;
    }
    @Override
    public boolean deleteApn(int apnId) throws RemoteException {
        return false;
    }
}

编译，然后，然后就出错了：

Your API changes are triggering API Lint warnings or errors.
To make these errors go away, fix the code according to the
error and/or warning messages above.

If it is not possible to do so, there are workarounds:

1. You can suppress the errors with @SuppressLint("")
   where the  is given in brackets in the error message above.
2. You can update the baseline by executing the following
   command:
       (cd $ANDROID_BUILD_TOP && cp \
       "out/soong/.intermediates/frameworks/base/api-stubs-docs-non-updatable/android_common/metalava/api_lint_baseline.txt" \
       "frameworks/base/services/api/lint-baseline.txt")
   To submit the revised baseline.txt to the main Android
   repository, you will need approval.
************************************************************

服务需要APP可以调用，选择方式2，执行：

cp out/soong/.intermediates/frameworks/base/api-stubs-docs-non-updatable/android_common/metalava/api_lint_baseline.txt  frameworks/base/services/api/lint-baseline.txt

编译后继续出错：

******************************
You have tried to change the API from what has been previously approved.

To make these errors go away, you have two choices:
   1. You can add '@hide' javadoc comments (and remove @SystemApi/@TestApi/etc)
      to the new methods, etc. shown in the above diff.

   2. You can update current.txt and/or removed.txt by executing the following command:
         m api-stubs-docs-non-updatable-update-current-api

      To submit the revised current.txt to the main Android repository,
      you will need approval.
******************************

选择方法2，lunch相应product，执行：

m api-stubs-docs-non-updatable-update-current-api

这次不报错了

3、打开/frameworks/base/core/java/android/content/Context.java，添加一行对应的服务名称：

 public static final String DEVICEMGR_SERVICE = "devicemgr";

这是APP调用getSystemService对应的服务名称

4、打开/frameworks/base/services/java/com/android/server/SystemServer.java，在中间加上一行代码：

private void startOtherServices(@NonNull TimingsTraceAndSlog t) {
  .....................................
  ServiceManager.addService(Context.DEVICEMGR_SERVICE, new DeviceMgr(mSystemContext));
  .....................................
}