//init进程的三大功能：属性服务、处理子进程终止、解析与运行init.rc文件
int main(int argc, char** argv) {if (!strcmp(basename(argv[0]), "ueventd")) {return ueventd_main(argc, argv);}if (!strcmp(basename(argv[0]), "watchdogd")) {return watchdogd_main(argc, argv);}if (argc > 1 && !strcmp(argv[1], "subcontext")) {InitKernelLogging(argv);const BuiltinFunctionMap function_map;return SubcontextMain(argc, argv, &function_map);}if (REBOOT_BOOTLOADER_ON_PANIC) {InstallRebootSignalHandlers();}bool is_first_stage = (getenv("INIT_SECOND_STAGE") == nullptr);if (is_first_stage) {boot_clock::time_point start_time = boot_clock::now();// Clear the umask.umask(0);clearenv();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.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));if constexpr (WORLD_WRITABLE_KMSG) {mknod("/dev/kmsg_debug", S_IFCHR | 0622, makedev(1, 11));}mknod("/dev/random", S_IFCHR | 0666, makedev(1, 8));mknod("/dev/urandom", S_IFCHR | 0666, makedev(1, 9));// Mount staging areas for devices managed by vold// See storage config details at http://source.android.com/devices/storage/mount("tmpfs", "/mnt", "tmpfs", MS_NOEXEC | MS_NOSUID | MS_NODEV,"mode=0755,uid=0,gid=1000");// /mnt/vendor is used to mount vendor-specific partitions that can not be// part of the vendor partition, e.g. because they are mounted read-write.mkdir("/mnt/vendor", 0755);// Now that tmpfs is mounted on /dev and we have /dev/kmsg, we can actually// talk to the outside world...InitKernelLogging(argv);LOG(INFO) << "init first stage started!";if (!DoFirstStageMount()) {LOG(FATAL) << "Failed to mount required partitions early ...";}SetInitAvbVersionInRecovery();// Enable seccomp if global boot option was passed (otherwise it is enabled in zygote).global_seccomp();// Set up SELinux, loading the SELinux policy.SelinuxSetupKernelLogging();SelinuxInitialize();// 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(FATAL) << "restorecon failed of /init failed";}setenv("INIT_SECOND_STAGE", "true", 1);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);// execv() only returns if an error happened, in which case we// panic and never fall through this conditional.PLOG(FATAL) << "execv(\"" << path << "\") failed";}// At this point we're in the second stage of init.InitKernelLogging(argv);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);// Indicate that booting is in progress to background fw loaders, etc.close(open("/dev/.booting", O_WRONLY | O_CREAT | O_CLOEXEC, 0000));property_init();// 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();process_kernel_cmdline();// Propagate the kernel variables to internal variables// used by init as well as the current required properties.export_kernel_boot_props();// 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.unsetenv("INIT_SECOND_STAGE");unsetenv("INIT_STARTED_AT");unsetenv("INIT_SELINUX_TOOK");unsetenv("INIT_AVB_VERSION");// Now set up SELinux for second stage.SelinuxSetupKernelLogging();SelabelInitialize();SelinuxRestoreContext();epoll_fd = epoll_create1(EPOLL_CLOEXEC);if (epoll_fd == -1) {PLOG(FATAL) << "epoll_create1 failed";}sigchld_handler_init();//注册子进程死亡监听socketif (!IsRebootCapable()) {// If init does not have the CAP_SYS_BOOT capability, it is running in a container.// In that case, receiving SIGTERM will cause the system to shut down.InstallSigtermHandler();}property_load_boot_defaults();export_oem_lock_status();start_property_service();set_usb_controller();const BuiltinFunctionMap function_map;Action::set_function_map(&function_map);subcontexts = InitializeSubcontexts();//am中的actions_成员变量用来保存action list(动作列表)ActionManager& am = ActionManager::GetInstance();//sm中的service_成员变量用来保存service list(服务列表)ServiceList& sm = ServiceList::GetInstance();//解析rc文件，并将动作和服务分别添加到am和sm中LoadBootScripts(am, sm);// 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();// ① 触发early-init Actionam.QueueEventTrigger("early-init");// Queue an action that waits for coldboot done so we know ueventd has set up all of /dev...// ② 新建一个"wait_for_coldboot_done"触发器，并且触发该触发器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(MixHwrngIntoLinuxRngAction, "MixHwrngIntoLinuxRng");am.QueueBuiltinAction(SetMmapRndBitsAction, "SetMmapRndBits");am.QueueBuiltinAction(SetKptrRestrictAction, "SetKptrRestrict");am.QueueBuiltinAction(keychord_init_action, "keychord_init");am.QueueBuiltinAction(console_init_action, "console_init");// Trigger all the boot actions to get us started.// ③ 触发"init"，触发器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(MixHwrngIntoLinuxRngAction, "MixHwrngIntoLinuxRng");// Don't mount filesystems or start core system services in charger mode.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");//继续向下分析，就是依次执行已经触发的触发器action对象的command命令，并且监听属性服务和子进程的终止。while (true) {// By default, sleep until something happens.int epoll_timeout_ms = -1;if (do_shutdown && !shutting_down) {do_shutdown = false;if (HandlePowerctlMessage(shutdown_command)) {shutting_down = true;}}if (!(waiting_for_prop || Service::is_exec_service_running())) {am.ExecuteOneCommand();//依次执行已触发aciton的command命令}if (!(waiting_for_prop || Service::is_exec_service_running())) {if (!shutting_down) {auto next_process_restart_time = RestartProcesses();//重启需要重启的子进程// If there's a process that needs restarting, wake up in time for that.if (next_process_restart_time) {epoll_timeout_ms = std::chrono::ceil<std::chrono::milliseconds>(*next_process_restart_time - boot_clock::now()).count();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_event ev;//上面通过epoll_ctl注册了属性服务和子进程终止，现在通过epoll_wait来真正的监听。当有属性申请和子进程终止时，就执行前面分析的对应的处理函数。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;
}