转自:http://blog.csdn.net/moyu123456789/article/details/50573358
1.SystemServer简介
Android系统中的好多功能能够运行起来,在代码层面好多都是以服务的方式实现的。而几乎所有的服务都是在SystemServer中创建的。SystemServer作为Android系统的一个核心进程,它是在zygote进程中孕育出来的。
那么zygote进程是怎么来的呢?再次我稍作解释。
我们知道,Android系统是以Linux为内核的,在Linux系统中,所有的进程无一例外的都是由init进程直接或者间接创建的,也就是说所有的进程都是init进程的后代(这个和我们现在所讲的,中国人都是炎黄子孙一个道理,炎黄相当于是init进程,我们这些人都是其子孙进程)。那么zygote进程也不例外,它就是在系统启动过程中由init进程创建的。在系统启动脚本system/core/rootdir/init.rc文件中,我们可以看到启动Zygote进程的脚本命令:
- import /init.${ro.zygote}.rc
- service servicemanager /system/bin/servicemanager
- class core
- user system
- group system
- critical
- onrestart restart healthd
- onrestart restart zygote
- onrestart restart media
- onrestart restart surfaceflinger
- onrestart restart drm
-
- service surfaceflinger /system/bin/surfaceflinger
- class core
- user system
- group graphics drmrpc
- onrestart restart zygote
在rootdir中还有4个和zygote相关的脚本:init.zygote32.rc、init.zygote32_64.rc、init.zygote64.rc、init.zygote64_32.rc,这个是为了区分64位和32才这么做的。
我们可以看一下init.zygote32.rc中的内容:
- service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
- class main
- socket zygote stream 660 root system
- onrestart write /sys/android_power/request_state wake
- onrestart write /sys/power/state on
- onrestart restart media
- onrestart restart netd
那么SystemServer又是怎样创建的呢?答案是:在ZygoteInit中创建的,看下边的代码。
- public class ZygoteInit {
- private static final String TAG = "Zygote";
-
- public static void main(String argv[]) {
- try {
- // Start profiling the zygote initialization.
- SamplingProfilerIntegration.start();
-
- boolean startSystemServer = false;
- String socketName = "zygote";
- String abiList = null;
- for (int i = 1; i < argv.length; i++) {
- if ("start-system-server".equals(argv[i])) {
- startSystemServer = true;
- } else if (argv[i].startsWith(ABI_LIST_ARG)) {
- abiList = argv[i].substring(ABI_LIST_ARG.length());
- } else if (argv[i].startsWith(SOCKET_NAME_ARG)) {
- socketName = argv[i].substring(SOCKET_NAME_ARG.length());
- } else {
- throw new RuntimeException("Unknown command line argument: " + argv[i]);
- }
- }
-
- if (abiList == null) {
- throw new RuntimeException("No ABI list supplied.");
- }
-
- registerZygoteSocket(socketName);
- EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
- SystemClock.uptimeMillis());
- preload();
- EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
- SystemClock.uptimeMillis());
-
- // Finish profiling the zygote initialization.
- SamplingProfilerIntegration.writeZygoteSnapshot();
-
- // Do an initial gc to clean up after startup
- gc();
-
- // Disable tracing so that forked processes do not inherit stale tracing tags from
- // Zygote.
- Trace.setTracingEnabled(false);
-
- if (startSystemServer) {
- startSystemServer(abiList, socketName);/*启动SystemServer的地方*/
- }
-
- Log.i(TAG, "Accepting command socket connections");
- runSelectLoop(abiList);
-
- closeServerSocket();
- } catch (MethodAndArgsCaller caller) {
- caller.run();
- } catch (RuntimeException ex) {
- Log.e(TAG, "Zygote died with exception", ex);
- closeServerSocket();
- throw ex;
- }
- }
我们在来看看startSystemServer方法的代码实现:
- /*
- * Prepare the arguments and fork for the system server process.
- */
- private static boolean startSystemServer(String abiList, String socketName)
- int pid;
-
- try {
- parsedArgs = new ZygoteConnection.Arguments(args);
- ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);
- ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);
-
- /* Request to fork the system server process */
- pid = Zygote.forkSystemServer(/*这里fork了SystemServer*/
- parsedArgs.uid, parsedArgs.gid,
- parsedArgs.gids,
- parsedArgs.debugFlags,
- null,
- parsedArgs.permittedCapabilities,
- parsedArgs.effectiveCapabilities);
- } catch (IllegalArgumentException ex) {
- throw new RuntimeException(ex);
- }
-
- /* For child process */
- if (pid == 0) {
- if (hasSecondZygote(abiList)) {
- waitForSecondaryZygote(socketName);
- }
-
- handleSystemServerProcess(parsedArgs);
- }
-
- return true;
- }
2.以太网服务的启动
以太网在Android中能够运行,也是作为一个系统级服务来执行的,那么自然我们能联想到它是在SystemServer中启动的。代码路径如下:
frameworks/base/services/java/com/android/server/SystemServer.java
- public final class SystemServer {
- private static final String TAG = "SystemServer";
- .......................
- private static final String ETHERNET_SERVICE_CLASS =
- "com.android.server.ethernet.EthernetService";
- /**
- * The main entry point from zygote.
- */
- public static void main(String[] args) {
- new SystemServer().run();
- }
-
- private void run() {
- // Create the system service manager.
- mSystemServiceManager = new SystemServiceManager(mSystemContext);
- LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
-
- // Start services.
- /* SystemServer中启动服务的三个方法 */
- try {
- startBootstrapServices();
- startCoreServices();
- startOtherServices(); /* 这个方法里启动了以太网服务进程 */
- } catch (Throwable ex) {
- Slog.e("System", "******************************************");
- Slog.e("System", "************ Failure starting system services", ex);
- throw ex;
- }
- }
- }
-
- private void startOtherServices() {
- if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_ETHERNET)) {
- mSystemServiceManager.startService(ETHERNET_SERVICE_CLASS);
- }
- }
至此,Android以太网服务进程就算启动起来了
以太网服务启动后,以太网卡对应的端口又是怎样up起来的呢?又是怎样分配到地址的呢?我的另一篇博文《Android5.1系统启动过程中启动有线网卡并为其分配静态IP地址》http://blog.csdn.net/moyu123456789/article/details/50002099中有比较明确的解释。