在帕美尔省后面有一座金刚山，它有一小时路程高，一小时路程宽，一小时路程深。有一只鸟每隔一百年飞到这里来一次，在这座山上磨一磨它的小嘴。要等到这座山完全磨平，那么永恒的第一秒钟才算过去。 ----------- 坚持

Android操作系统已经成为全球最重要的操作系统，系统的开放性为他的发展带来了无数的可能性，由Android系统衍生出来的物联网系统AndroidThings简化了嵌入式设备开发的难度，专为低端用户服务的AndroidGo进一步开拓了低端用户市场，随着Android系统的不断发展完善，迎来更好的用户体验；同时Kotlin , 即时应用的新技术使得Android越发得老当益壮。不得不说对于Google即将推出的Fuchsia(灯笼海棠系统)目前来说不足也为惧，它对Android应用的支持也为新一代中端系统提供了过渡的空间; 技术是为了提供更好的服务而发展出的手段；

1.系统孵化准备第一阶段

int main(int argc, char** argv) {if (!strcmp(basename(argv[0]), "ueventd")) {return ueventd_main(argc, argv); //1.1uevent message 监听}if (!strcmp(basename(argv[0]), "watchdogd")) {return watchdogd_main(argc, argv); //1.2系统看门狗设置}if (REBOOT_BOOTLOADER_ON_PANIC) {InstallRebootSignalHandlers(); //设置系统重启Signal Action}add_environment("PATH", _PATH_DEFPATH); //注册环境PATHbool is_first_stage = (getenv("INIT_SECOND_STAGE") == nullptr); //检查环境变量if (is_first_stage) {boot_clock::time_point start_time = boot_clock::now();// Clear the umask.umask(0); //清空文件权限// 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.//挂在文件系统，创建文件并设置文件权限mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");mkdir("/dev/pts", 0755);mkdir("/dev/socket", 0755);mount("devpts", "/dev/pts", "devpts", 0, NULL);#define MAKE_STR(x) __STRING(x)mount("proc", "/proc", "proc", 0, "hidepid=2,gid=" MAKE_STR(AID_READPROC));// Don't expose the raw commandline to unprivileged processes.chmod("/proc/cmdline", 0440);gid_t groups[] = { AID_READPROC };setgroups(arraysize(groups), groups);mount("sysfs", "/sys", "sysfs", 0, NULL);mount("selinuxfs", "/sys/fs/selinux", "selinuxfs", 0, NULL);mknod("/dev/kmsg", S_IFCHR | 0600, makedev(1, 11));mknod("/dev/random", S_IFCHR | 0666, makedev(1, 8));mknod("/dev/urandom", S_IFCHR | 0666, makedev(1, 9));// Now that tmpfs is mounted on /dev and we have /dev/kmsg, we can actually// talk to the outside world...InitKernelLogging(argv); //1.3初始化系统日志系统LOG(INFO) << "init first stage started!";if (!DoFirstStageMount()) {LOG(ERROR) << "Failed to mount required partitions early ...";panic();}SetInitAvbVersionInRecovery(); //刷机模式avb版本// Set up SELinux, loading the SELinux policy.selinux_initialize(true); //1.4设置Selinux安全策略// We're in the kernel domain, so re-exec init to transition to the init domain now// that the SELinux policy has been loaded.if (selinux_android_restorecon("/init", 0) == -1) {PLOG(ERROR) << "restorecon failed";security_failure();}setenv("INIT_SECOND_STAGE", "true", 1); //设置环境变量static constexpr uint32_t kNanosecondsPerMillisecond = 1e6;uint64_t start_ms = start_time.time_since_epoch().count() / kNanosecondsPerMillisecond;setenv("INIT_STARTED_AT", std::to_string(start_ms).c_str(), 1);char* path = argv[0];char* args[] = { path, nullptr };execv(path, args); //重新执行main，进行二次初始化// execv() only returns if an error happened, in which case we// panic and never fall through this conditional.PLOG(ERROR) << "execv(\"" << path << "\") failed";security_failure();}
}

1.1 ueventd_main

通过linux提供的epoll机制监听系统的启动

int ueventd_main(int argc, char** argv) {/** init sets the umask to 077 for forked processes. We need to* create files with exact permissions, without modification by* the umask.*/umask(000);InitKernelLogging(argv);LOG(INFO) << "ueventd started!";//设置selinux会调selinux_callback cb; cb.func_log = selinux_klog_callback;selinux_set_callback(SELINUX_CB_LOG, cb);//设置冷启动 uevent 句柄DeviceHandler device_handler = CreateDeviceHandler();UeventListener uevent_listener;if (access(COLDBOOT_DONE, F_OK) != 0) {ColdBoot cold_boot(uevent_listener, device_handler);cold_boot.Run();}//epoll 冷启动 循环等待// We use waitpid() in ColdBoot, so we can't ignore SIGCHLD until now.signal(SIGCHLD, SIG_IGN);// Reap and pending children that exited between the last call to waitpid() and setting SIG_IGN// for SIGCHLD above.while (waitpid(-1, nullptr, WNOHANG) > 0) {}uevent_listener.Poll([&device_handler](const Uevent& uevent) {HandleFirmwareEvent(uevent);device_handler.HandleDeviceEvent(uevent);return ListenerAction::kContinue;});return 0;
}

1.2 watchdogd_main

通过定时喂狗的方式看门

int watchdogd_main(int argc, char **argv) {InitKernelLogging(argv);int interval = 10;if (argc >= 2) interval = atoi(argv[1]);int margin = 10;if (argc >= 3) margin = atoi(argv[2]);LOG(INFO) << "watchdogd started (interval " << interval << ", margin " << margin << ")!";int fd = open(DEV_NAME, O_RDWR|O_CLOEXEC);if (fd == -1) {PLOG(ERROR) << "Failed to open " << DEV_NAME;return 1;}//超时检测int timeout = interval + margin;int ret = ioctl(fd, WDIOC_SETTIMEOUT, &timeout); // ioctl linux内核函数if (ret) {PLOG(ERROR) << "Failed to set timeout to " << timeout;ret = ioctl(fd, WDIOC_GETTIMEOUT, &timeout);if (ret) {PLOG(ERROR) << "Failed to get timeout";} else {if (timeout > margin) {interval = timeout - margin; //计算超时时间差值} else {interval = 1;}LOG(WARNING) << "Adjusted interval to timeout returned by driver: "<< "timeout " << timeout<< ", interval " << interval<< ", margin " << margin;}}while (true) {  //循环喂狗write(fd, "", 1);sleep(interval);}
}

1.3 InitKernelLogging

void InitKernelLogging(char* argv[]) {// Make stdin/stdout/stderr all point to /dev/null.int fd = open("/sys/fs/selinux/null", O_RDWR);if (fd == -1) {int saved_errno = errno;android::base::InitLogging(argv, &android::base::KernelLogger); //写入日志errno = saved_errno;PLOG(FATAL) << "Couldn't open /sys/fs/selinux/null";}dup2(fd, 0);dup2(fd, 1);dup2(fd, 2);if (fd > 2) close(fd);android::base::InitLogging(argv, &android::base::KernelLogger);
}

##1.4 selinux_initialize

Android使用Selinux安全策略来保护系统安全，即使设备被root以后仍然能保护系统安全，除了selinux外，还有mac等保护机制。

static void selinux_initialize(bool in_kernel_domain) {Timer t;//selinux 安全上下文回调selinux_callback cb;cb.func_log = selinux_klog_callback;selinux_set_callback(SELINUX_CB_LOG, cb);cb.func_audit = audit_callback;selinux_set_callback(SELINUX_CB_AUDIT, cb);if (in_kernel_domain) {LOG(INFO) << "Loading SELinux policy";if (!selinux_load_policy()) {  //载入 selinux 安全策略panic();}bool kernel_enforcing = (security_getenforce() == 1);bool is_enforcing = selinux_is_enforcing();if (kernel_enforcing != is_enforcing) {if (security_setenforce(is_enforcing)) {PLOG(ERROR) << "security_setenforce(%s) failed" << (is_enforcing ? "true" : "false");security_failure();}}std::string err;if (!WriteFile("/sys/fs/selinux/checkreqprot", "0", &err)) {LOG(ERROR) << err;security_failure();}// init's first stage can't set properties, so pass the time to the second stage.setenv("INIT_SELINUX_TOOK", std::to_string(t.duration().count()).c_str(), 1);} else {selinux_init_all_handles(); // 处理回调}
}

2.系统孵化准备第二阶段

 // At this point we're in the second stage of init.InitKernelLogging(argv); //第二阶段日志系统初始化LOG(INFO) << "init second stage started!";// Set up a session keyring that all processes will have access to. It// will hold things like FBE encryption keys. No process should override// its session keyring.keyctl_get_keyring_ID(KEY_SPEC_SESSION_KEYRING, 1); //初始化进程会话密钥// Indicate that booting is in progress to background fw loaders, etc.close(open("/dev/.booting", O_WRONLY | O_CREAT | O_CLOEXEC, 0000)); //创建启动文件//文件属性读取配置property_init(); 2.1初始化属性系统// If arguments are passed both on the command line and in DT,// properties set in DT always have priority over the command-line ones.process_kernel_dt(); //2.2处理DT属性process_kernel_cmdline(); //处理命令行属性// Propagate the kernel variables to internal variables// used by init as well as the current required properties.export_kernel_boot_props(); //处理其他的一些属性// Make the time that init started available for bootstat to log.property_set("ro.boottime.init", getenv("INIT_STARTED_AT"));property_set("ro.boottime.init.selinux", getenv("INIT_SELINUX_TOOK"));// Set libavb version for Framework-only OTA match in Treble build.const char* avb_version = getenv("INIT_AVB_VERSION");if (avb_version) property_set("ro.boot.avb_version", avb_version);// Clean up our environment.//清空这些之前都已经存入到系统属性中去的环境变量unsetenv("INIT_SECOND_STAGE");unsetenv("INIT_STARTED_AT");unsetenv("INIT_SELINUX_TOOK");unsetenv("INIT_AVB_VERSION");// Now set up SELinux for second stage.selinux_initialize(false); //初始化SELINUXselinux_restore_context(); //重置 selinux上下文epoll_fd = epoll_create1(EPOLL_CLOEXEC); //创建Epoll文件句柄if (epoll_fd == -1) {PLOG(ERROR) << "epoll_create1 failed";exit(1);}signal_handler_init(); //2.3系统重启信号句柄初始化property_load_boot_defaults(); //加载默认启动属性export_oem_lock_status(); // ODM,即Original design manufacture(原始设计商)的缩写start_property_service(); //启动系统属性服务set_usb_controller(); //设置 usb 控制器

##2.1 property_init

void property_init() {if (__system_property_area_init()) { //系统属性初始化LOG(ERROR) << "Failed to initialize property area";exit(1);}
}

2.2 process_kernel_dt

Linux内核在启动的时候会加载dts(读取内核设备树结构)文件，此处将dt写入到系统属性中

static void process_kernel_dt() {if (!is_android_dt_value_expected("compatible", "android,firmware")) {return;}std::unique_ptr<DIR, int (*)(DIR*)> dir(opendir(get_android_dt_dir().c_str()), closedir);if (!dir) return;std::string dt_file;struct dirent *dp;while ((dp = readdir(dir.get())) != NULL) { //读取内核设备树结构if (dp->d_type != DT_REG || !strcmp(dp->d_name, "compatible") || !strcmp(dp->d_name, "name")) {continue;}std::string file_name = get_android_dt_dir() + dp->d_name;android::base::ReadFileToString(file_name, &dt_file);std::replace(dt_file.begin(), dt_file.end(), ',', '.');property_set("ro.boot."s + dp->d_name, dt_file); //写入属性}
}

2.3 signal_handler_init

通过创建socket对和设置触发动作，以及epoll监听来处理系统重启

void signal_handler_init() {// Create a signalling mechanism for SIGCHLD.//创建套接对int s[2];if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0, s) == -1) {PLOG(ERROR) << "socketpair failed";exit(1);}signal_write_fd = s[0];signal_read_fd = s[1];// Write to signal_write_fd if we catch SIGCHLD.struct sigaction act;memset(&act, 0, sizeof(act));act.sa_handler = SIGCHLD_handler;act.sa_flags = SA_NOCLDSTOP;sigaction(SIGCHLD, &act, 0); //设置触发actionServiceManager::GetInstance().ReapAnyOutstandingChildren(); //系统重启处理register_epoll_handler(signal_read_fd, handle_signal); //注册处理函数
}

3.系统孵化准备第三阶段

系统孵化前第三个阶段是对init.rc文件的解析，其中包括对.rc文件中 service, on, import 的解析触发以及执行，最主要的是对zygote.rc文件的解析，此外还包括一些服务的启动比如 MediaService 。

//init.rc文件解析const BuiltinFunctionMap function_map; //内建函数跳转表Action::set_function_map(&function_map); //设置表到ActionActionManager& am = ActionManager::GetInstance(); //Action解析管理ServiceManager& sm = ServiceManager::GetInstance(); //Service解析管理Parser& parser = Parser::GetInstance(); //rc文件解析parser.AddSectionParser("service", std::make_unique<ServiceParser>(&sm));parser.AddSectionParser("on", std::make_unique<ActionParser>(&am));parser.AddSectionParser("import", std::make_unique<ImportParser>(&parser));std::string bootscript = GetProperty("ro.boot.init_rc", "");if (bootscript.empty()) { //是否已存在解析脚本parser.ParseConfig("/init.rc");parser.set_is_system_etc_init_loaded(parser.ParseConfig("/system/etc/init"));parser.set_is_vendor_etc_init_loaded(parser.ParseConfig("/vendor/etc/init"));parser.set_is_odm_etc_init_loaded(parser.ParseConfig("/odm/etc/init"));} else {parser.ParseConfig(bootscript);parser.set_is_system_etc_init_loaded(true);parser.set_is_vendor_etc_init_loaded(true);parser.set_is_odm_etc_init_loaded(true);}// Turning this on and letting the INFO logging be discarded adds 0.2s to// Nexus 9 boot time, so it's disabled by default.if (false) DumpState();//触发系列动作am.QueueEventTrigger("early-init"); // Queue an action that waits for coldboot done so we know ueventd has set up all of /dev...am.QueueBuiltinAction(wait_for_coldboot_done_action, "wait_for_coldboot_done");// ... so that we can start queuing up actions that require stuff from /dev.am.QueueBuiltinAction(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");am.QueueBuiltinAction(set_mmap_rnd_bits_action, "set_mmap_rnd_bits");am.QueueBuiltinAction(set_kptr_restrict_action, "set_kptr_restrict");am.QueueBuiltinAction(keychord_init_action, "keychord_init");am.QueueBuiltinAction(console_init_action, "console_init");// Trigger all the boot actions to get us started.am.QueueEventTrigger("init");// Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random// wasn't ready immediately after wait_for_coldboot_doneam.QueueBuiltinAction(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");// charger 模式不挂在文件系统std::string bootmode = GetProperty("ro.bootmode", "");if (bootmode == "charger") {am.QueueEventTrigger("charger");} else {am.QueueEventTrigger("late-init");}// Run all property triggers based on current state of the properties.am.QueueBuiltinAction(queue_property_triggers_action, "queue_property_triggers");while (true) { //进入循环等待// By default, sleep until something happens.int epoll_timeout_ms = -1;if (do_shutdown && !shutting_down) { //关机状态do_shutdown = false;if (HandlePowerctlMessage(shutdown_command)) {shutting_down = true;}}if (!(waiting_for_prop || sm.IsWaitingForExec())) {am.ExecuteOneCommand(); //执行command}//是否执行进程重启if (!(waiting_for_prop || sm.IsWaitingForExec())) {if (!shutting_down) restart_processes();// If there's a process that needs restarting, wake up in time for that.if (process_needs_restart_at != 0) {epoll_timeout_ms = (process_needs_restart_at - time(nullptr)) * 1000;if (epoll_timeout_ms < 0) epoll_timeout_ms = 0;}// If there's more work to do, wake up again immediately.if (am.HasMoreCommands()) epoll_timeout_ms = 0;}// epoll 事件处理epoll_event ev;int nr = TEMP_FAILURE_RETRY(epoll_wait(epoll_fd, &ev, 1, epoll_timeout_ms));if (nr == -1) {PLOG(ERROR) << "epoll_wait failed";} else if (nr == 1) {((void (*)()) ev.data.ptr)();}}return 0;

3.1 BuiltinFunctionMap

内建函数表用于解析后 InvockFunc 函数回调

const BuiltinFunctionMap::Map& BuiltinFunctionMap::map() const { //内建函数跳转表constexpr std::size_t kMax = std::numeric_limits<std::size_t>::max();// clang-format offstatic const Map builtin_functions = {{"bootchart",               {1,     1,    do_bootchart}},{"chmod",                   {2,     2,    do_chmod}},{"chown",                   {2,     3,    do_chown}},{"class_reset",             {1,     1,    do_class_reset}},{"class_restart",           {1,     1,    do_class_restart}},{"class_start",             {1,     1,    do_class_start}},{"class_stop",              {1,     1,    do_class_stop}},{"copy",                    {2,     2,    do_copy}},{"domainname",              {1,     1,    do_domainname}},{"enable",                  {1,     1,    do_enable}},{"exec",                    {1,     kMax, do_exec}},{"exec_start",              {1,     1,    do_exec_start}},{"export",                  {2,     2,    do_export}},{"hostname",                {1,     1,    do_hostname}},{"ifup",                    {1,     1,    do_ifup}},{"init_user0",              {0,     0,    do_init_user0}},{"insmod",                  {1,     kMax, do_insmod}},{"installkey",              {1,     1,    do_installkey}},{"load_persist_props",      {0,     0,    do_load_persist_props}},{"load_system_props",       {0,     0,    do_load_system_props}},{"loglevel",                {1,     1,    do_loglevel}},{"mkdir",                   {1,     4,    do_mkdir}},{"mount_all",               {1,     kMax, do_mount_all}},{"mount",                   {3,     kMax, do_mount}},{"umount",                  {1,     1,    do_umount}},{"restart",                 {1,     1,    do_restart}},{"restorecon",              {1,     kMax, do_restorecon}},{"restorecon_recursive",    {1,     kMax, do_restorecon_recursive}},{"rm",                      {1,     1,    do_rm}},{"rmdir",                   {1,     1,    do_rmdir}},{"setprop",                 {2,     2,    do_setprop}},{"setrlimit",               {3,     3,    do_setrlimit}},{"start",                   {1,     1,    do_start}},{"stop",                    {1,     1,    do_stop}},{"swapon_all",              {1,     1,    do_swapon_all}},{"symlink",                 {2,     2,    do_symlink}},{"sysclktz",                {1,     1,    do_sysclktz}},{"trigger",                 {1,     1,    do_trigger}},{"verity_load_state",       {0,     0,    do_verity_load_state}},{"verity_update_state",     {0,     0,    do_verity_update_state}},{"wait",                    {1,     2,    do_wait}},{"wait_for_prop",           {2,     2,    do_wait_for_prop}},{"write",                   {2,     2,    do_write}},};// clang-format onreturn builtin_functions;
}

3.2 AddSectionParser

section_parsers_数组包含 service , on , import 分别对应 servie解析，action解析，import解析

Parser& Parser::GetInstance() {static Parser instance;return instance;
}void Parser::AddSectionParser(const std::string& name,std::unique_ptr<SectionParser> parser) {section_parsers_[name] = std::move(parser); //service,on,import 加入解析数组
}void Parser::AddSingleLineParser(const std::string& prefix, LineCallback callback) {line_callbacks_.emplace_back(prefix, callback);
}

3.3 ParseConfig

bool Parser::ParseConfig(const std::string& path) {if (is_dir(path.c_str())) {return ParseConfigDir(path); //查找dir}return ParseConfigFile(path); //解析文件
}

解析文件

bool Parser::ParseConfigFile(const std::string& path) {LOG(INFO) << "Parsing file " << path << "...";android::base::Timer t;std::string data;std::string err;if (!ReadFile(path, &data, &err)) {LOG(ERROR) << err;return false;}data.push_back('\n'); // TODO: fix parse_config.ParseData(path, data); //解析文件数据for (const auto& [section_name, section_parser] : section_parsers_) {section_parser->EndFile();}LOG(VERBOSE) << "(Parsing " << path << " took " << t << ".)";return true;
}

调用具体解析

void Parser::ParseData(const std::string& filename, const std::string& data) {//TODO: Use a parser with const input and remove this copystd::vector<char> data_copy(data.begin(), data.end());data_copy.push_back('\0');parse_state state; //解析状态结构state.line = 0;state.ptr = &data_copy[0];state.nexttoken = 0;SectionParser* section_parser = nullptr;std::vector<std::string> args;for (;;) {switch (next_token(&state)) {case T_EOF:if (section_parser) {section_parser->EndSection();}return;case T_NEWLINE:state.line++;if (args.empty()) {break;}// If we have a line matching a prefix we recognize, call its callback and unset any// current section parsers.  This is meant for /sys/ and /dev/ line entries for uevent.for (const auto& [prefix, callback] : line_callbacks_) {if (android::base::StartsWith(args[0], prefix.c_str())) {if (section_parser) section_parser->EndSection(); // 结束std::string ret_err;if (!callback(std::move(args), &ret_err)) {LOG(ERROR) << filename << ": " << state.line << ": " << ret_err;}section_parser = nullptr;break;}}if (section_parsers_.count(args[0])) { if (section_parser) {section_parser->EndSection();}section_parser = section_parsers_[args[0]].get();std::string ret_err;//执行段解析if (!section_parser->ParseSection(std::move(args), filename, state.line, &ret_err)) {LOG(ERROR) << filename << ": " << state.line << ": " << ret_err;section_parser = nullptr;}} else if (section_parser) {std::string ret_err;//执行行解析if (!section_parser->ParseLineSection(std::move(args), state.line, &ret_err)) {LOG(ERROR) << filename << ": " << state.line << ": " << ret_err;}}args.clear();break;case T_TEXT:args.emplace_back(state.text);break;}}
}

按字符解析.rc文件


int next_token(struct parse_state *state)
{char *x = state->ptr;char *s;if (state->nexttoken) {int t = state->nexttoken; //取下一tokenstate->nexttoken = 0;return t;}for (;;) {switch (*x) {case 0:state->ptr = x;return T_EOF; //文件结束case '\n':x++;state->ptr = x;return T_NEWLINE; //下一行case ' ':case '\t':case '\r':x++;continue; //空格继续case '#':while (*x && (*x != '\n')) x++;if (*x == '\n') {state->ptr = x+1;return T_NEWLINE;} else {state->ptr = x;return T_EOF;}default:goto text;}}textdone:state->ptr = x;*s = 0;return T_TEXT;
text:state->text = s = x;
textresume:for (;;) {switch (*x) {case 0:goto textdone;case ' ':case '\t':case '\r':x++;goto textdone;case '\n':state->nexttoken = T_NEWLINE;x++;goto textdone;case '"':x++;for (;;) {switch (*x) {case 0:/* unterminated quoted thing */state->ptr = x;return T_EOF;case '"':x++;goto textresume;default:*s++ = *x++;}}break;case '\\': //注释x++;switch (*x) {case 0:goto textdone;case 'n':*s++ = '\n';break;case 'r':*s++ = '\r';break;case 't':*s++ = '\t';break;case '\\':*s++ = '\\';break;case '\r':/* \ <cr> <lf> -> line continuation */if (x[1] != '\n') {x++;continue;}case '\n':/* \ <lf> -> line continuation */state->line++;x++;/* eat any extra whitespace */while((*x == ' ') || (*x == '\t')) x++;continue;default:/* unknown escape -- just copy */*s++ = *x++;}continue;default:*s++ = *x++;}}return T_EOF;
}

解析Action

bool ActionParser::ParseSection(std::vector<std::string>&& args, const std::string& filename,int line, std::string* err) {std::vector<std::string> triggers(args.begin() + 1, args.end());if (triggers.size() < 1) {*err = "actions must have a trigger";return false;}auto action = std::make_unique<Action>(false, filename, line);if (!action->InitTriggers(triggers, err)) { //触发解析return false;}action_ = std::move(action);return true;
}

3.3 ExecuteOneCommand

执行解析命令

void Action::ExecuteOneCommand(std::size_t command) const {// We need a copy here since some Command execution may result in// changing commands_ vector by importing .rc files through parserCommand cmd = commands_[command];ExecuteCommand(cmd);
}

InvokeFunc()函数回调

void Action::ExecuteCommand(const Command& command) const {android::base::Timer t;int result = command.InvokeFunc(); //执行函数表跳转auto duration = t.duration();// Any action longer than 50ms will be warned to user as slow operationif (duration > 50ms || android::base::GetMinimumLogSeverity() <= android::base::DEBUG) {std::string trigger_name = BuildTriggersString();std::string cmd_str = command.BuildCommandString();LOG(INFO) << "Command '" << cmd_str << "' action=" << trigger_name << " (" << filename_<< ":" << command.line() << ") returned " << result << " took "<< duration.count() << "ms.";}
}

执行类启动

static int do_class_start(const std::vector<std::string>& args) {/* Starting a class does not start services* which are explicitly disabled.  They must* be started individually.*/ServiceManager::GetInstance().ForEachServiceInClass(args[1], [] (Service* s) { s->StartIfNotDisabled(); });return 0;
}

函数do_class_start函数在表中的位置

static const Map builtin_functions = {{"bootchart",               {1,     1,    do_bootchart}},{"chmod",                   {2,     2,    do_chmod}},{"chown",                   {2,     3,    do_chown}},{"class_reset",             {1,     1,    do_class_reset}},{"class_restart",           {1,     1,    do_class_restart}},{"class_start",             {1,     1,    do_class_start}},......

3.4 .rc文件

import /init.environ.rc
import /init.usb.rc
import /init.${ro.hardware}.rc
import /vendor/etc/init/hw/init.${ro.hardware}.rc
import /init.usb.configfs.rc
import /init.${ro.zygote}.rc

zygote.rc文件

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-serverclass mainpriority -20user rootgroup root readprocsocket zygote stream 660 root systemonrestart write /sys/android_power/request_state wakeonrestart write /sys/power/state ononrestart restart audioserveronrestart restart cameraserveronrestart restart mediaonrestart restart netdonrestart restart wificondwritepid /dev/cpuset/foreground/tasks

4 .进入系统孵化阶段

int main(int argc, char* const argv[])
{if (!LOG_NDEBUG) {String8 argv_String;for (int i = 0; i < argc; ++i) { //参数处理argv_String.append("\"");argv_String.append(argv[i]);argv_String.append("\" ");}ALOGV("app_process main with argv: %s", argv_String.string());}AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv)); //初始化运行时// Process command line arguments// ignore argv[0]//忽略argv[0]argc--;argv++;//解析规则// --zygote : Start in zygote mode 孵化器类型// --start-system-server : Start the system server. 系统服务// --application : Start in application (stand alone, non zygote) mode. 应用模式// --nice-name : The nice name for this process. 进程优先级const char* spaced_commands[] = { "-cp", "-classpath" };// Allow "spaced commands" to be succeeded by exactly 1 argument (regardless of -s).bool known_command = false;......
}

至此，系统孵化准备工作完毕，接下来是系统将进入孵化阶段，孵化阶段将会启动Zygote, AndroidRuntime, SystemServer, JVM环境初始化等等，孵化阶段将提供JAVA运行环境，为后续启动系统服务提供基本保障，孵化阶段还为应用的创建提供高效的措施。

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Android8.0 系统启动之孵化准备