Android SystemServer启动(一)

Android SystemServer启动(一)

Android小彩虹2021-08-24 4:45:20130A+A-

Android init 启动

Android Linux Zygote启动

Android Java Zygote启动

Android通过Linux启动init进程,再通过init进程forkZygote进程。在Zygote中有一个重要的步骤就是启动system_server进程,并且创建SystemServer

下面我们来深入了解一下SystemServer的创建过程。

此次分析过程基于Android 10.0

forkSystemServer

ZygoteInit中会通过forkSystemServer来创建system_server进程。

private static Runnable forkSystemServer(String abiList, String socketName,
        ZygoteServer zygoteServer) {
    long capabilities = posixCapabilitiesAsBits(
        OsConstants.CAP_IPC_LOCK,
        OsConstants.CAP_KILL,
        OsConstants.CAP_NET_ADMIN,
        OsConstants.CAP_NET_BIND_SERVICE,
        OsConstants.CAP_NET_BROADCAST,
        OsConstants.CAP_NET_RAW,
        OsConstants.CAP_SYS_MODULE,
        OsConstants.CAP_SYS_NICE,
        OsConstants.CAP_SYS_PTRACE,
        OsConstants.CAP_SYS_TIME,
        OsConstants.CAP_SYS_TTY_CONFIG,
        OsConstants.CAP_WAKE_ALARM,
        OsConstants.CAP_BLOCK_SUSPEND
    );
    /* Containers run without some capabilities, so drop any caps that are not available. */
    StructCapUserHeader header = new StructCapUserHeader(
            OsConstants._LINUX_CAPABILITY_VERSION_3, 0);
    StructCapUserData[] data;
    try {
        data = Os.capget(header);
    } catch (ErrnoException ex) {
        throw new RuntimeException("Failed to capget()", ex);
    }
    capabilities &= ((long) data[0].effective) | (((long) data[1].effective) << 32);

    // system_server 进程参数
    String args[] = {
        "--setuid=1000",
        "--setgid=1000",
        "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,1024,1032,1065,3001,3002,3003,3006,3007,3009,3010",
        "--capabilities=" + capabilities + "," + capabilities,
        "--nice-name=system_server",
        "--runtime-args",
        "--target-sdk-version=" + VMRuntime.SDK_VERSION_CUR_DEVELOPMENT,
        "com.android.server.SystemServer",
    };
    ZygoteConnection.Arguments parsedArgs = null;

    int pid;

    try {
        // 解析参数
        parsedArgs = new ZygoteConnection.Arguments(args);
        ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);
        ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);

        boolean profileSystemServer = SystemProperties.getBoolean(
                "dalvik.vm.profilesystemserver", false);
        if (profileSystemServer) {
            parsedArgs.runtimeFlags |= Zygote.PROFILE_SYSTEM_SERVER;
        }

        // fork出system_server进程
        pid = Zygote.forkSystemServer(
                parsedArgs.uid, parsedArgs.gid,
                parsedArgs.gids,
                parsedArgs.runtimeFlags,
                null,
                parsedArgs.permittedCapabilities,
                parsedArgs.effectiveCapabilities);
    } catch (IllegalArgumentException ex) {
        throw new RuntimeException(ex);
    }

    // system_server子进程
    if (pid == 0) {
        if (hasSecondZygote(abiList)) {
            waitForSecondaryZygote(socketName);
        }

        // 关闭原有进程
        zygoteServer.closeServerSocket();
        // 操作system_server进程
        return handleSystemServerProcess(parsedArgs);
    }

    return null;
}

在这里会准备fork的进程参数,从参数信息可以看出,system_server进程的uid=1000、gid=1000,进程名称为system_server,后续启动的SystemServer路径为com.android.server.SystemServer

zygote进程fork新进程之后会将原来的zygotesocket关闭,同时对于有两个zygote进程的情况,需要等待第2zygote创建完成。

public static int forkSystemServer(int uid, int gid, int[] gids, int runtimeFlags,
        int[][] rlimits, long permittedCapabilities, long effectiveCapabilities) {
    VM_HOOKS.preFork();
    // Resets nice priority for zygote process.
    resetNicePriority();
    int pid = nativeForkSystemServer(
            uid, gid, gids, runtimeFlags, rlimits, permittedCapabilities, effectiveCapabilities);
    // Enable tracing as soon as we enter the system_server.
    if (pid == 0) {
        Trace.setTracingEnabled(true, runtimeFlags);
    }
    VM_HOOKS.postForkCommon();
    return pid;
}

nativeForkSystemServer最终会通过JNI映射到com_android_internal_os_Zygote.cpp中的com_android_internal_os_Zygote_nativeForkSystemServer方法.

nativeForkSystemServer

static jint com_android_internal_os_Zygote_nativeForkSystemServer(
        JNIEnv* env, jclass, uid_t uid, gid_t gid, jintArray gids,
        jint runtime_flags, jobjectArray rlimits, jlong permitted_capabilities,
        jlong effective_capabilities) {
  std::vector<int> fds_to_close(MakeUsapPipeReadFDVector()),
                   fds_to_ignore(fds_to_close);

  fds_to_close.push_back(gUsapPoolSocketFD);

  if (gUsapPoolEventFD != -1) {
    fds_to_close.push_back(gUsapPoolEventFD);
    fds_to_ignore.push_back(gUsapPoolEventFD);
  }

  if (gSystemServerSocketFd != -1) {
      fds_to_close.push_back(gSystemServerSocketFd);
      fds_to_ignore.push_back(gSystemServerSocketFd);
  }

  // fork 子进程
  pid_t pid = ForkCommon(env, true,
                         fds_to_close,
                         fds_to_ignore,
                         true);
  if (pid == 0) {
      
      // 处理子进程
      SpecializeCommon(env, uid, gid, gids, runtime_flags, rlimits,
                       permitted_capabilities, effective_capabilities,
                       MOUNT_EXTERNAL_DEFAULT, nullptr, nullptr, true,
                       false, nullptr, nullptr, /* is_top_app= */ false,
                       /* pkg_data_info_list */ nullptr,
                       /* whitelisted_data_info_list */ nullptr, false, false);
  } else if (pid > 0) {
      gSystemServerPid = pid;
      int status;
      if (waitpid(pid, &status, WNOHANG) == pid) {
          ALOGE("System server process %d has died. Restarting Zygote!", pid);
          RuntimeAbort(env, __LINE__, "System server process has died. Restarting Zygote!");
      }

      if (UsePerAppMemcg()) {
          if (!SetTaskProfiles(pid, std::vector<std::string>{"SystemMemoryProcess"})) {
              ALOGE("couldn't add process %d into system memcg group", pid);
          }
      }
  }
  return pid;
}

在这里会通过ForkCommon来创建子进程

ForkCommon

static pid_t ForkCommon(JNIEnv* env, bool is_system_server,
                        const std::vector<int>& fds_to_close,
                        const std::vector<int>& fds_to_ignore,
                        bool is_priority_fork) {
  SetSignalHandlers();

  auto fail_fn = std::bind(ZygoteFailure, env, is_system_server ? "system_server" : "zygote",
                           nullptr, _1);

  BlockSignal(SIGCHLD, fail_fn);

  __android_log_close();
  AStatsSocket_close();

  if (gOpenFdTable == nullptr) {
    gOpenFdTable = FileDescriptorTable::Create(fds_to_ignore, fail_fn);
  } else {
    gOpenFdTable->Restat(fds_to_ignore, fail_fn);
  }

  android_fdsan_error_level fdsan_error_level = android_fdsan_get_error_level();

  mallopt(M_PURGE, 0);

  // fork子进程
  pid_t pid = fork();

  if (pid == 0) {
    // 处理子进程逻辑
    if (is_priority_fork) {
      setpriority(PRIO_PROCESS, 0, PROCESS_PRIORITY_MAX);
    } else {
      setpriority(PRIO_PROCESS, 0, PROCESS_PRIORITY_MIN);
    }

    // The child process.
    PAuthKeyChange(env);
    PreApplicationInit();

    // Clean up any descriptors which must be closed immediately
    DetachDescriptors(env, fds_to_close, fail_fn);

    // Invalidate the entries in the USAP table.
    ClearUsapTable();

    // Re-open all remaining open file descriptors so that they aren't shared
    // with the zygote across a fork.
    gOpenFdTable->ReopenOrDetach(fail_fn);

    // Turn fdsan back on.
    android_fdsan_set_error_level(fdsan_error_level);

    // Reset the fd to the unsolicited zygote socket
    gSystemServerSocketFd = -1;
  } else {
    ALOGD("Forked child process %d", pid);
  }

  // We blocked SIGCHLD prior to a fork, we unblock it here.
  UnblockSignal(SIGCHLD, fail_fn);

  return pid;
}

fork创建进程采用的是copy on write方法,这个是Linux创建进程的标准方式,会有两次返回值。

返回0时代表子进程,返回值大于0为父进程。

进程创建完毕之后,会返回Java层,并进入handleSystemServerProcess来处理system_server进程逻辑。

handleSystemServerProcess

private static Runnable handleSystemServerProcess(ZygoteConnection.Arguments parsedArgs) {
    Os.umask(S_IRWXG | S_IRWXO);

    // 设置进程名称
    if (parsedArgs.niceName != null) {
        Process.setArgV0(parsedArgs.niceName);
    }

    final String systemServerClasspath = Os.getenv("SYSTEMSERVERCLASSPATH");
    if (systemServerClasspath != null) {
        performSystemServerDexOpt(systemServerClasspath);
        boolean profileSystemServer = SystemProperties.getBoolean(
                "dalvik.vm.profilesystemserver", false);
        if (profileSystemServer && (Build.IS_USERDEBUG || Build.IS_ENG)) {
            try {
                prepareSystemServerProfile(systemServerClasspath);
            } catch (Exception e) {
                Log.wtf(TAG, "Failed to set up system server profile", e);
            }
        }
    }

    if (parsedArgs.invokeWith != null) {
        String[] args = parsedArgs.remainingArgs;
        if (systemServerClasspath != null) {
            String[] amendedArgs = new String[args.length + 2];
            amendedArgs[0] = "-cp";
            amendedArgs[1] = systemServerClasspath;
            System.arraycopy(args, 0, amendedArgs, 2, args.length);
            args = amendedArgs;
        }

        // 启动应用进程
        WrapperInit.execApplication(parsedArgs.invokeWith,
                parsedArgs.niceName, parsedArgs.targetSdkVersion,
                VMRuntime.getCurrentInstructionSet(), null, args);

        throw new IllegalStateException("Unexpected return from WrapperInit.execApplication");
    } else {
        ClassLoader cl = null;
        if (systemServerClasspath != null) {
            // 创建ClassLoader
            cl = createPathClassLoader(systemServerClasspath, parsedArgs.targetSdkVersion);

            Thread.currentThread().setContextClassLoader(cl);
        }

        return ZygoteInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);
    }
}

设置进程名称system_server,并通过zygoteInit进入。

public static final Runnable zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) {
    if (RuntimeInit.DEBUG) {
        Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote");
    }

    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");
    RuntimeInit.redirectLogStreams();

    RuntimeInit.commonInit();
    ZygoteInit.nativeZygoteInit();
    return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);
}

在这里会通过调用RuntimeInit.commonInit来初始化一些公用的东西。并通过nativeZygoteInit调用对于映射的Linux方法,即app_main.cpp中的onZygoteInit方法来初始化zygote

virtual void onZygoteInit() {
    sp<ProcessState> proc = ProcessState::self();
    proc->startThreadPool(); //启动新binder线程
}

ProcessState::self()是单例模式,主要工作是调用open()打开/dev/binder驱动设备,再利用mmap()映射内核的地址空间,将Binder驱动的fd赋值ProcessState对象中的变量mDriverFD,用于交互操作。startThreadPool()是创建一个新的binder线程,不断进行talkWithDriver()

applicationInit

继续回到Java,调用applicationInit方法:

protected static Runnable applicationInit(int targetSdkVersion, String[] argv,
        ClassLoader classLoader) {
    
    nativeSetExitWithoutCleanup(true);

    VMRuntime.getRuntime().setTargetHeapUtilization(0.75f);
    VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion);

    // 解析参数
    final Arguments args = new Arguments(argv);

    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

    return findStaticMain(args.startClass, args.startArgs, classLoader);
}

通过之前的参数列表信息,可以知道这里的startclass就是com.android.server.SystemServer

findStaticMain

最后进入findStaticMain方法来创建SystemServer

protected static Runnable findStaticMain(String className, String[] argv,
        ClassLoader classLoader) {
    Class<?> cl;

    try {
        cl = Class.forName(className, true, classLoader);
    } catch (ClassNotFoundException ex) {
        throw new RuntimeException(
                "Missing class when invoking static main " + className,
                ex);
    }

    Method m;
    try {
        m = cl.getMethod("main", new Class[] { String[].class });
    } catch (NoSuchMethodException ex) {
        throw new RuntimeException(
                "Missing static main on " + className, ex);
    } catch (SecurityException ex) {
        throw new RuntimeException(
                "Problem getting static main on " + className, ex);
    }

    int modifiers = m.getModifiers();
    if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
        throw new RuntimeException(
                "Main method is not public and static on " + className);
    }

    return new MethodAndArgsCaller(m, argv);
}

该方法也很简单,通过Java反射来获取对应的ClassMethod,这里对应的就是SystemServermain方法。

最后返回MethodAndArgsCaller

static class MethodAndArgsCaller implements Runnable {
    /** method to call */
    private final Method mMethod;

    /** argument array */
    private final String[] mArgs;

    public MethodAndArgsCaller(Method method, String[] args) {
        mMethod = method;
        mArgs = args;
    }

    public void run() {
        try {
            mMethod.invoke(null, new Object[] { mArgs });
        } catch (IllegalAccessException ex) {
            throw new RuntimeException(ex);
        } catch (InvocationTargetException ex) {
            Throwable cause = ex.getCause();
            if (cause instanceof RuntimeException) {
                throw (RuntimeException) cause;
            } else if (cause instanceof Error) {
                throw (Error) cause;
            }
            throw new RuntimeException(ex);
        }
    }
}

所以如果调用run方法就会通过反射来执行SystemServer中的main方法。

而这个Runnable最终在ZygoteInitmain方法中通过forkSystemServer创建并返回。

if (startSystemServer) {
    Runnable r = forkSystemServer(abiList, socketName, zygoteServer);

    // {@code r == null} in the parent (zygote) process, and {@code r != null} in the
    // child (system_server) process.
    if (r != null) {
        r.run();
        return;
    }
}

创建并返回Runnable之后,调用r.run()来执行SystemServermain方法。

最终进入SystemServer的流程。

现在我们已经找到了进入SystemServer的入口,后续继续分析SystemServer的作用与内部执行的逻辑。

推荐

android_startup: 提供一种在应用启动时能够更加简单、高效的方式来初始化组件。开发人员可以使用android-startup来简化启动序列,并显式地设置初始化顺序与组件之间的依赖关系。 与此同时android-startup支持同步与异步等待,并通过有向无环图拓扑排序的方式来保证内部依赖组件的初始化顺序。

AwesomeGithub: 基于Github客户端,纯练习项目,支持组件化开发,支持账户密码与认证登陆。使用Kotlin语言进行开发,项目架构是基于Jetpack&DataBindingMVVM;项目中使用了ArouterRetrofitCoroutineGlideDaggerHilt等流行开源技术。

flutter_github: 基于Flutter的跨平台版本Github客户端,与AwesomeGithub相对应。

android-api-analysis: 结合详细的Demo来全面解析Android相关的知识点, 帮助读者能够更快的掌握与理解所阐述的要点。

daily_algorithm: 每日一算法,由浅入深,欢迎加入一起共勉。

微信公众号:Android补给站,致力于Android进阶与算法分析。

点击这里复制本文地址 以上内容由权冠洲的博客整理呈现,请务必在转载分享时注明本文地址!如对内容有疑问,请联系我们,谢谢!

支持Ctrl+Enter提交

联系我们| 本站介绍| 留言建议 | 交换友链 | 域名展示
本站资源来自互联网收集,仅供用于学习和交流,请遵循相关法律法规,本站一切资源不代表本站立场,如有侵权、后门、不妥请联系本站删除

权冠洲的博客 © All Rights Reserved.  Copyright quanguanzhou.top All Rights Reserved
苏公网安备 32030302000848号   苏ICP备20033101号-1
本网站由 提供CDN/云存储服务

联系我们