1. Android开机过程

system/core/init/  -main.cpp  -init.cpp  -parser.cpp/system/core/rootdir/  -init.rc

// system/core/init/main.cppint main(int argc, char** argv) {#if __has_feature(address_sanitizer)     __asan_set_error_report_callback(AsanReportCallback);#endif// 创建设备节点、权限设定等if(!strcmp(basename(argv[0]), "ueventd")) {return ueventd_main(argc, argv);    }if(argc > 1){// 初始化日志系统if(!strcmp(argv[1], "subcontext")){            android::base::InitLogging(argv, &android::base::KernelLogger);const BuiltinFunctionMap function_map;return SubcontextMain(argc, argv, &function_map);        }// 2.创建安全增强型Linux（SELinux）if(!strcmp(argv[1], "selinux_setup")){return SetupSelinux(argv);        }// 3.解析init.rc文件、提供服务、创建epoll与处理子进程的终止等if (!strcmp(argv[1], "second_stage")){return SecondStageMain(argc, argv);        }    }// 1.挂载相关文件系统return FirstStageMain(argc, argv);}

// system/core/init/first_stage_init.cppint FirstStageMain(int argc, char** argv){if(REBOOT_BOOTLOADER_ON_PANIC){        InstallRebootSignalHandlers();    }    boot_clock::time_point start_time = boot_clock::now();std::vector<std::pair<std::string, int>> errors;#define CHECKCALL(x) \if (x != 0) errors.emplace_back(#x " failed", errno);    umask(0);// 创建于挂载相关文件系统    CHECKCALL(clearenv());    CHECKCALL(setenv("PATH", _PATH_DEFPATH, 1));// Get the basic filesystem setup we need put together in the initramdisk// on / and then we'll let the rc file figure out the rest.    CHECKCALL(mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755"));    CHECKCALL(mkdir("/dev/pts", 0755));    CHECKCALL(mkdir("/dev/socket", 0755));    CHECKCALL(mount("devpts", "/dev/pts", "devpts", 0, NULL));#define MAKE_STR(x) __STRING(x)    CHECKCALL(mount("proc", "/proc", "proc", 0, "hidepid=2,gid=" MAKE_STR(AID_READPROC)));#undef MAKE_STR// 原始命令不可暴露给没有特权的进程    CHECKCALL(chmod("/proc/cmdline", 0440));gid_t groups[] = {AID_READPROC};    CHECKCALL(setgroups(arraysize(groups), groups));    CHECKCALL(mount("sysfs", "/sys", "sysfs", 0, NULL));    CHECKCALL(mount("selinuxfs", "/sys/fs/selinux", "selinuxfs", 0, NULL));// tmpfs已经挂载在/dev下，并且已生成/dev/kmsg，故可以与外界通信// 初始化日志系统    InitKernelLogging(argv);// 进入下一步const char* path = "/system/bin/init";const char* args[] = {path, "selinux_setup", nullptr};    execv(path, const_cast<char**>(args));
// 只有在错误发生的情况下execv()函数才会返回    PLOG(FATAL) << "execv(\"" << path << "\") failed";
return 1;}

// system/core/init/selinux.cppint SetupSelinux(char** argv) {//初始化本阶段内核日志    InitKernelLogging(argv);
if (REBOOT_BOOTLOADER_ON_PANIC) {        InstallRebootSignalHandlers();    }
//  初始化 SELinux，加载 SELinux 策略    SelinuxSetupKernelLogging();    SelinuxInitialize();//  再次调用 main 函数，并传入 second_stage 进入第二阶段//  而且此次启动就已经在 SELinux 上下文中运行if (selinux_android_restorecon("/system/bin/init", 0) == -1) {        PLOG(FATAL) << "restorecon failed of /system/bin/init failed";    }
// 进入下一步const char* path = "/system/bin/init";const char* args[] = {path, "second_stage", nullptr};    execv(path, const_cast<char**>(args));
// execv() only returns if an error happened, in which case we// panic and never return from this function.    PLOG(FATAL) << "execv(\"" << path << "\") failed";
return 1;}

//  system/core/init/init.cppint SecondStageMain(int argc, char** argv) {    SetStdioToDevNull(argv);// 初始化本阶段内核日志    InitKernelLogging(argv);//  系统属性初始化    property_init();//  建立 Epoll    Epoll epoll;//  注册信号处理    InstallSignalFdHandler(&epoll);//  加载默认的系统属性    property_load_boot_defaults(load_debug_prop);//  启动属性服务    StartPropertyService(&epoll);       subcontexts = InitializeSubcontexts();//加载系统启动脚本"/init.rc"       ActionManager& am = ActionManager::GetInstance();    ServiceList& sm = ServiceList::GetInstance();    LoadBootScripts(am, sm);
// 触发early-init，，init，late-init流程    am.QueueEventTrigger("early-init");    am.QueueEventTrigger("init");    am.QueueBuiltinAction(InitBinder, "InitBinder");    am.QueueEventTrigger("late-init");
//解析启动脚本while (true) {//  执行 Action        am.ExecuteOneCommand();//  还有就是重启死掉的子进程auto next_process_action_time = HandleProcessActions();    }}

//system/core/init/init.cppstatic void LoadBootScripts(ActionManager& action_manager, ServiceList& service_list) {    Parser parser = CreateParser(action_manager, service_list);std::string bootscript = GetProperty("ro.boot.init_rc", "");if (bootscript.empty()) {        parser.ParseConfig("/init.rc");if (!parser.ParseConfig("/system/etc/init")) {            late_import_paths.emplace_back("/system/etc/init");        }if (!parser.ParseConfig("/product/etc/init")) {            late_import_paths.emplace_back("/product/etc/init");        }if (!parser.ParseConfig("/product_services/etc/init")) {            late_import_paths.emplace_back("/product_services/etc/init");        }if (!parser.ParseConfig("/odm/etc/init")) {            late_import_paths.emplace_back("/odm/etc/init");        }if (!parser.ParseConfig("/vendor/etc/init")) {            late_import_paths.emplace_back("/vendor/etc/init");        }    } else {        parser.ParseConfig(bootscript);    }}

// system/core/rootdir/init.rcimport /init.environ.rcimport /init.usb.rcimport /init.${ro.hardware}.rcimport /init.${ro.zygote}.rcimport /init.trace.rc
on early-initstart ueventdmkdir /mnt 0775 root systemon initmount tmpfs none /sys/fs/cgroup mode=0750,uid=0,gid=1000mkdir /sys/fs/cgroup/memory 0750 root systemmount cgroup none /sys/fs/cgroup/memory memoryon property:sys.boot_from_charger_mode=1class_stop chargertrigger late-init
service ueventd /sbin/ueventdclass corecriticalseclabel u:r:ueventd:s0
service logd /system/bin/logdclass coresocket logd stream 0666 logd logdsocket logdr seqpacket 0666 logd logdsocket logdw dgram 0222 logd logdseclabel u:r:logd:s0
service console /system/bin/shclass coreconsoledisableduser shellseclabel u:r:shell:s0
service adbd /sbin/adbd --root_seclabel=u:r:su:s0class coresocket adbd stream 660 system systemdisabledseclabel u:r:adbd:s0
service servicemanager /system/bin/servicemanagerclass coreuser systemgroup systemcriticalonrestart restart healthdonrestart restart zygoteonrestart restart mediaonrestart restart surfaceflingeronrestart restart drm
on late-inittrigger early-fstrigger fstrigger post-fstrigger late-fstrigger post-fs-datatrigger load_persist_props_action// 这里启动zygote-starttrigger zygote-starttrigger firmware_mounts_completetrigger early-boottrigger boot

// system/core/rootdir/init.zygote64.rcservice zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-serverclass mainpriority -20user rootgroup root readproc reserved_disksocket zygote stream 660 root systemsocket usap_pool_primary stream 660 root systemonrestart exec_background - system system -- /ssystem/bin/vdc volume abort_fuseonrestart write /sys/power/state ononrestart restart audioserveronrestart restart cmeraserveronrestart restart mediaonrestart restart netdonrestart setprop sys.android.reboot 1writepid /dev/cpuset/foreground/taskscritical window=${zygote.critical_window.minute:-off} target=zygote-fatal

// frameworks/base/cmds/app_process/app_main.cppint main(int argc, char* const argv[])    {if(zygote){         runtime.start("com.android.internal.os.ZygoteInit", args, zygote);         }    }

// frameworks/base/core/jni/AndroidRuntime.cppvoid AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote){        ALOGD(">>>>>> START %s uid %d <<<<<<\n",class Name！= NULL？class Name："(unknown)", getuid() );// 打印LOG_BOOT_PROGRESS_START日志        LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START, ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));if(startVm(&mJavaVM, &env, zygote, primaryZygote) != 0){return;        }        onVmCreated(env);// 调用ZygoteInit类的main()方法        env.CallStaticVoidMethod(startClass, startMeth, strArray)    }

//frameworks/base/core/java/com/android/internal/os/ZygoteInit.java@UnsupportedAppUsagepublic static void main(String argv[]) {//zygote进程会fork出system_server进程if (startSystemServer) {        Runnable r = forkSystemServer(abiList, socketName, zygoteServer);// zygote进程中，r == null；zygote子进程（如system_server进程）中， r != nullif (r != null) {          r.run();return;        }    }    Log.i(TAG, "Accepting command socket connections");// zygote进程会在select loop死循环；而非zygote进程中之前已return。// loops forever in the zygote.    caller = zygoteServer.runSelectLoop(abiList);if (caller != null) {        caller.run();    }}

// frameworks/base/services/java/com/android/server/SystemServer.javapublic static void main(String[] args) {new SystemServer().run();}
private void run() {try {        Looper.prepareMainLooper();// 初始化本地服务        System.loadLibrary("android_servers");// 初始化系统上下文        createSystemContext();// 创建SystemServiceManager        mSystemServiceManager = new SystemServiceManager(mSystemContext);        mSystemServiceManager.setStartInfo(mRuntimeRestart,                mRuntimeStartElapsedTime, mRuntimeStartUptime);        LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);// 构建线程池，以便并行执行一些初始化任务        SystemServerInitThreadPool.get();    } finally {        traceEnd();  // InitBeforeStartServices    }
// 开启服务try {        traceBeginAndSlog("StartServices");        startBootstrapServices();// 启动引导服务        startCoreServices();// 启动核心服务        startOtherServices();// 启动其他服务        SystemServerInitThreadPool.shutdown();    } catch (Throwable ex) {        Slog.e("System", "******************************************");        Slog.e("System", "************ Failure starting system services", ex);throw ex;    } finally {        traceEnd();    }    Looper.loop();throw new RuntimeException("Main thread loop unexpectedly exited");}

2. 分析开机时间

// frameworks/base/core/jni/AndroidRuntime.cppvoid AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote){for (size_t i = 0; i < options.size(); ++i) {if (options[i] == startSystemServer) {            primary_zygote = true;/* track our progress through the boot sequence */const int LOG_BOOT_PROGRESS_START = 3000;           LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START,  ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));        }    }}

// frameworks/base/core/java/com/android/internal/os/ZygoteInit.javapublic static void main(String[] argv){if(!enableLazyPreload){        bootTimingsTraceLog.traceBegin("ZygotePreload");        EventLog.writeEvent(BOOT_PROGRESS_PRELOAD_START, SystemClock.uptimeMillis());        preload(bootTimingsTraceLog);        EventLog.writeEvent(BOOT_PROGRESS_PRELOAD_END, SystemClock.uptimeMillis());        bootTimingsTraceLog.traceEnd();    }}

// frameworks/base/services/java/com/android/server/SystemServer.javaprivate void run() {   Slog.i(TAG, "Entered the Android system server!");final long uptimeMillis = SystemClock.elapsedRealtime();   EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN, uptimeMillis);if (!mRuntimeRestart){            FrameworkStatsLog.write(FrameworkStatsLog.BOOT_TIME_EVENT_ELAPSED_TIME_REPORTED,FrameworkStatsLog.BOOT_TIME_EVENT_ELAPSED_TIME__EVENT__SYSTEM_SERVER_INIT_START,uptimeMillis);      }    }

// frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.javapublic PackageManagerService(Injector injector, boolean onlyCore, boolean factoryTest) {    LockGuard.installLock(mLock, LockGuard.INDEX_PACKAGES);    EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_START,SystemClock.uptimeMillis()    );}

// frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.javapublic PackageManagerService(Injector injector, boolean onlyCore, boolean factoryTest) {long startTime = SystemClock.uptimeMillis();   EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_SYSTEM_SCAN_START, startTime);}

// frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.javapublic PackageManagerService(Injector injector, boolean onlyCore, boolean factoryTest) {final long systemScanTime = SystemClock.uptimeMillis() - startTime;final int systemPackagesCount = mPackages.size();        Slog.i(TAG, "Finished scanning system apps. Time: " + systemScanTime                    + " ms, packageCount: " + systemPackagesCount                    + " , timePerPackage: "                    + (systemPackagesCount == 0 ? 0 : systemScanTime / systemPackagesCount)                    + " , cached: " + cachedSystemApps);if (mIsUpgrade && systemPackagesCount > 0) {            FrameworkStatsLog.write(FrameworkStatsLog.BOOT_TIME_EVENT_DURATION_REPORTED,                BOOT_TIME_EVENT_DURATION__EVENT__OTA_PACKAGE_MANAGER_SYSTEM_APP_AVG_SCAN_TIME,     systemScanTime / systemPackagesCount);            }if (!mOnlyCore) {            EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_DATA_SCAN_START,            SystemClock.uptimeMillis());            scanDirTracedLI(sAppInstallDir, 0, scanFlags | SCAN_REQUIRE_KNOWN, 0,                        packageParser, executorService);            }}

// frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.javapublic PackageManagerService(Injector injector, boolean onlyCore, boolean factoryTest) {        mPackageUsage.read(mSettings.mPackages);        mCompilerStats.read();        EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_SCAN_END,                    SystemClock.uptimeMillis());            Slog.i(TAG, "Time to scan packages: "                    + ((SystemClock.uptimeMillis()-startTime)/1000f)                    + " seconds");}

// frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.javapublic PackageManagerService(Injector injector, boolean onlyCore, boolean factoryTest) {        t.traceBegin("write settings");        mSettings.writeLPr();        t.traceEnd();        EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_READY, SystemClock.uptimeMillis());    }

// frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.javapublic void systemReady(final Runnable goingCallback, @NonNull TimingsTraceAndSlog t) {        t.traceEnd();        EventLog.writeBootProgressAmsReady(SystemClock.uptimeMillis());    }

// frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java@Overridepublic void enableScreenAfterBoot(boolean booted) {        writeBootProgressEnableScreen(SystemClock.uptimeMillis());        mWindowManager.enableScreenAfterBoot();synchronized (mGlobalLock) {            updateEventDispatchingLocked(booted);        } }

// frameworks/native/services/surfaceflinger/SurfaceFlinger.cppvoid SurfaceFlinger::bootFinished(){         property_set("service.bootanim.exit", "1");         LOG_EVENT_LONG(LOGTAG_SF_STOP_BOOTANIM, ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));}

// frameworks/base/services/core/java/com/android/server/wm/WindowManagerService.javaprivate void performEnableScreen() {        EventLogTags.writeWmBootAnimationDone(SystemClock.uptimeMillis());        Trace.asyncTraceEnd(TRACE_TAG_WINDOW_MANAGER,   "Stop bootanim");}

// frameworks/base/services/core/java/com/android/server/SystemServiceManager.javapublic <T extends SystemService> T startService(Class<T> serviceClass)    {try {            final String name = serviceClass.getName();            Slog.i(TAG, "Starting " + name);            Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartService " + name);try {                Constructor<T> constructor = serviceClass . getConstructor (Context.class);                service = constructor.newInstance(mContext);            } catch ...                startService(service);            return service;        } finally {            Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);        }    }

// system/core/init/bootchart.cppstatic int do_bootchart_start() {// 只要存在/data/bootchart/enabled文件，即抓取bootchart数据std::string start;if (!android::base::ReadFileToString("/data/bootchart/enabled", &start)) {       LOG(VERBOSE) << "Not bootcharting";return 0; }   g_bootcharting_thread = new std::thread(bootchart_thread_main);return 0;}

adb shell touch /data/bootchart/enabledadb reboot

adb  pull /data/bootchart

tar -czf bootchart.tgz *

java -jar bootchart.jar bootchart.tgz

adb pull /system/etc/init/atrace.rc

 on property:persist.debug.atrace.boottrace=1start boottrace    service boottrace /system/bin/atrace --async_start -b 30720 gfx input view webview wm am sm audio video binder_lock binder_driver camera hal res dalvik rs bionic power pm ss database network adb vibrator aidl sched      disabled    oneshot

 adb push atrace.rc /system/etc/init/

adb  shell setprop persist.debug.atrace.boottrace 1

adb  shell setprop persist.debug.atrace.boottrace 0

 adb shell atrace --async_stop -z -c -o /data/local/tmp/boot_trace

 adb  pull /data/local/tmp/boot_trace

3. 开机速度优化实践

07-15 04:13:35.244 I/boot_progress_start( 1059): 404007-15 04:13:35.934 I/boot_progress_preload_start( 1059): 473007-15 04:13:37.255 I/boot_progress_preload_end( 1059): 605107-15 04:13:37.636 I/boot_progress_system_run( 2221): 643207-15 04:13:38.260 I/boot_progress_pms_start( 2221): 705607-15 04:13:38.473 I/boot_progress_pms_system_scan_start( 2221): 726907-15 04:13:38.797 I/boot_progress_pms_data_scan_start( 2221): 759307-15 04:13:38.803 I/boot_progress_pms_scan_end( 2221): 759907-15 04:13:38.894 I/boot_progress_pms_ready( 2221): 769007-15 04:13:58.006 I/boot_progress_ams_ready( 2221): 2680207-15 04:13:59.164 I/boot_progress_enable_screen( 2221): 27960

作者:努比亚技术团队链接:https://www.jianshu.com/p/3f23e027b591