车载之-自定义系统服务
源码梳理
- SystemServer的启动,SystemServer是由Zygote启动的。
/**
* The main entry point from zygote.
*/
public static void main(String[] args) {
new SystemServer().run();
}
- 继续看run()方法,看关键代码，开启服务。
startBootstrapServices主要是针对底层相关的服务；
startCoreServices主要针对用户相关的服务；
startOtherServices主要针对应用相关的服务，而对于我们应用的开发，百分之99都是修改此方法。
private void run() {
...
// Start services.
try {
traceBeginAndSlog("StartServices");
startBootstrapServices();
startCoreServices();
startOtherServices();
SystemServerInitThreadPool.shutdown();
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
traceEnd();
}
...
}
- 我们关注一下服务 的启动形式，我们进入startBootstrapServices方法内，我们发现规律，基本上服务都是由mSystemServiceManager.startService这个方法启动的。
// Wait for installd to finish starting up so that it has a chance to
// create critical directories such as /data/user with the appropriate
// permissions. We need this to complete before we initialize other services.
traceBeginAndSlog("StartInstaller");
Installer installer = mSystemServiceManager.startService(Installer.class);
traceEnd();
// In some cases after launching an app we need to access device identifiers,
// therefore register the device identifier policy before the activity manager.
traceBeginAndSlog("DeviceIdentifiersPolicyService");
mSystemServiceManager.startService(DeviceIdentifiersPolicyService.class);
traceEnd();
// Uri Grants Manager.
traceBeginAndSlog("UriGrantsManagerService");
mSystemServiceManager.startService(UriGrantsManagerService.Lifecycle.class);
traceEnd();
- 并且启动的所有服务都是集成自SystemService这个类，例如：Installer，DeviceIdentifiersPolicyService，UriGrantsManagerService.Lifecycle等，其可以监听系统的启动流程
其对于我们比较重要的方法有，onStart与onBootPhase方法。
onStart在启动时回；
onBootPhase在启动过程中回调，其携带的参数时SystemService中的常量，比如PHASE_WAIT_FOR_DEFAULT_DISPLAY，PHASE_LOCK_SETTINGS_READY，PHASE_SYSTEM_SERVICES_READY等。
收到PHASE_ACTIVITY_MANAGER_READY消息，就可以做发送广播等操作。
收到PHASE_THIRD_PARTY_APPS_CAN_START消息，其表示其启动第三方引用。
收到PHASE_BOOT_COMPLETED表示应用程序与用户可以进行交互了。
//com.android.server.SystemService
/**
* Called when the dependencies listed in the @Service class-annotation are available
* and after the chosen start phase.
* When this method returns, the service should be published.
*/
public abstract void onStart();
/**
* Called on each phase of the boot process. Phases before the service's start phase
* (as defined in the @Service annotation) are never received.
*
* @param phase The current boot phase.
*/
public void onBootPhase(int phase) {}
- 还有设计比较巧妙的地方是，Java只支持单继承，而如果ActivityManagerService是需要进程间通讯的，需要集成Binder，这样就不能集成SystemService，所以其增加了内部类LifeCycle来创建ActivityManagerService，从而持有其实例。
public static final class Lifecycle extends SystemService {
private final ActivityManagerService mService;
private static ActivityTaskManagerService sAtm;
public Lifecycle(Context context) {
super(context);
mService = new ActivityManagerService(context, sAtm);
}
public static ActivityManagerService startService(
SystemServiceManager ssm, ActivityTaskManagerService atm) {
sAtm = atm;
return ssm.startService(ActivityManagerService.Lifecycle.class).getService();
}
@Override
public void onStart() {
mService.start();
}
@Override
public void onBootPhase(int phase) {
mService.mBootPhase = phase;
if (phase == PHASE_SYSTEM_SERVICES_READY) {
mService.mBatteryStatsService.systemServicesReady();
mService.mServices.systemServicesReady();
} else if (phase == PHASE_ACTIVITY_MANAGER_READY) {
mService.startBroadcastObservers();
} else if (phase == PHASE_THIRD_PARTY_APPS_CAN_START) {
mService.mPackageWatchdog.onPackagesReady();
}
}
@Override
public void onCleanupUser(int userId) {
mService.mBatteryStatsService.onCleanupUser(userId);
}
public ActivityManagerService getService() {
return mService;
}
}
- 服务创建后需要将服务注册到ServiceManager中，调用ServiceManager.addService()方法进行注册。
public void setSystemProcess() {
try {
ServiceManager.addService(Context.ACTIVITY_SERVICE, this, /* allowIsolated= */ true,
DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PRIORITY_NORMAL | DUMP_FLAG_PROTO);
ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
ServiceManager.addService("meminfo", new MemBinder(this), /* allowIsolated= */ false,
DUMP_FLAG_PRIORITY_HIGH);
ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
ServiceManager.addService("dbinfo", new DbBinder(this));
if (MONITOR_CPU_USAGE) {
ServiceManager.addService("cpuinfo", new CpuBinder(this),
/* allowIsolated= */ false, DUMP_FLAG_PRIORITY_CRITICAL);
}
ServiceManager.addService("permission", new PermissionController(this));
ServiceManager.addService("processinfo", new ProcessInfoService(this));
ApplicationInfo info = mContext.getPackageManager().getApplicationInfo(
"android", STOCK_PM_FLAGS | MATCH_SYSTEM_ONLY);
mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader());
synchronized (this) {
ProcessRecord app = mProcessList.newProcessRecordLocked(info, info.processName,
false,
0,
new HostingRecord("system"));
app.setPersistent(true);
app.pid = MY_PID;
app.getWindowProcessController().setPid(MY_PID);
app.maxAdj = ProcessList.SYSTEM_ADJ;
app.makeActive(mSystemThread.getApplicationThread(), mProcessStats);
mPidsSelfLocked.put(app);
mProcessList.updateLruProcessLocked(app, false, null);
updateOomAdjLocked(OomAdjuster.OOM_ADJ_REASON_NONE);
}
} catch (PackageManager.NameNotFoundException e) {
throw new RuntimeException(
"Unable to find android system package", e);
}
// Start watching app ops after we and the package manager are up and running.
mAppOpsService.startWatchingMode(AppOpsManager.OP_RUN_IN_BACKGROUND, null,
new IAppOpsCallback.Stub() {
@Override public void opChanged(int op, int uid, String packageName) {
if (op == AppOpsManager.OP_RUN_IN_BACKGROUND && packageName != null) {
if (mAppOpsService.checkOperation(op, uid, packageName)
!= AppOpsManager.MODE_ALLOWED) {
runInBackgroundDisabled(uid);
}
}
}
});
}
实践
- 创建AIDL接口
/frameworks/base/core/java/android/app/IToolManager.aidl
//android.app
interfadce IToolManager{
String handler();
}
- 服务端
//frameworks/base/services/core/java/com/android/server/tool/ToolManagerService.java
package com.android.server.tool;
import android.app.IToolManager;
import android.os.RemoteException;
/**
* 服务端 AMS PMS WMS
*/
public class ToolManagerService extends IToolManager.Stub {
@Override
public String request(String msg) throws RemoteException {
return "ToolManagerService接收数据:"+msg;
}
- 客户端
//frameworks/base/core/java/android/app/ToolManager.java
package android.app;
import android.annotation.SystemService;
import android.compat.annotation.UnsupportedAppUsage;
import android.content.Context;
import android.os.IBinder;
import android.os.RemoteException;
import android.util.Singleton;
import android.os.ServiceManager;
import android.annotation.Nullable;
/**
* 客户端
*/
@SystemService(Context.TOOL_SERVICE)
public class ToolManager {
/**
* @hide
*/
public ToolManager() {
}
/**
* @hide
*/
public static IToolManager getServerice(){
return I_TOOL_MANAGER_SINGLETON.get();
}
@UnsupportedAppUsage
private static final Singleton<IToolManager> I_TOOL_MANAGER_SINGLETON =
new Singleton<IToolManager>() {
@Override
protected IToolManager create() {
final IBinder b= ServiceManager.getService(Context.TOOL_SERVICE);
final IToolManager im=IToolManager.Stub.asInterface(b);
return im;
}
};
@Nullable
public String handle(@Nullable String msg){
try{
return getServerice().request(msg);
}catch (RemoteException e){
throw e.rethrowFromSystemServer();
}
}
}
- 添加常量
/frameworks/base/core/java/android/context/Context.java
添加 public static final String TOOL_SERVICE = "tool";
- 注册Binder
frameworks/base/services/java/com/android/server/SystemServer.java
//在startOtherServices方法中
ServiceManager.addService(Context.TOOL_SERVICE,new ToolManagerService());
SystemServiceRegistry用于给客户端获取服务的类,有一个static块 执行了registerService用于注册.
frameworks/base/core/java/android/app/SystemServiceRegistry.java
registerService(Context.TOOL_SERVICE, ToolManager.class,
new CachedServiceFetcher<ToolManager>() {
@Override
public ToolManager createService(ContextImpl ctx) {
return new ToolManager();
}});
- 修改SeLinux安全权限
system/sepolicy/prebuilts/api/32.0/private/
与 system/sepolicy/private/ 目录下，
分别修改以下三个文件
-
service_contexts
#配置自定义服务selinux角色
chen u:object_r:tool_service:s0
用户:角色:类型:安全级别 -
service.te
#配置自定义服务类型的权限
type tool_service, app_api_service, ephemeral_app_api_service, system_server_service,
service_manager_type; -
untrusted_app_all.te
#允许所有app使用自定义服务
allow untrusted_app_all tool_service:service_manager find;
- 更新编译
- 更新api
make update-api - 编译
m - 运行模拟器
emulator