Android 源码分析（九） Init 启动分析
一.前言:
init进程 –> Zygote进程 –> SystemServer进程 –> Launcher桌面程序 -> 我们的App应用
init进程：linux的根进程，android系统是基于linux系统的，因此可以算作是整个android操作系统的第一个进程；
Zygote进程：android系统的根进程，主要作用：可以作用Zygote进程fork出SystemServer进程和各种应用进程；
SystemService进程：主要是在这个进程中启动系统的各项服务，比如ActivityManagerService，PackageManagerService，WindowManagerService服务等等；
Launcher桌面程序:就是我们平时看到的桌面程序，它其实也是一个android应用程序，只不过这个应用程序是系统默认第一个启动的应用程序.
二. init 进程分析
linux的根进程,同样也是守护进程，usb连接电脑后，cmd窗口，输入：adb shell ps 命令，能看到手机系统中当前跑的所有进程，有一个init进程。
init进程主要任务：
源码：
//system/core/init/init.cpp //1.创建目录 //2.将log重定向 //3.初始化环境变量 //4.得到硬件信息和版本 //5.解析内核启动参数 //6.导入默认环境变量 //7.得到系统分区 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 (REBOOT_BOOTLOADER_ON_PANIC) { install_reboot_signal_handlers(); } add_environment("PATH", _PATH_DEFPATH); 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); // 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)); 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); LOG(INFO) << "init first stage started!"; if (!DoFirstStageMount()) { LOG(ERROR) << "Failed to mount required partitions early ..."; panic(); } SetInitAvbVersionInRecovery(); // Set up SELinux, loading the SELinux policy. selinux_initialize(true); // 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 (restorecon("/init") == -1) { PLOG(ERROR) << "restorecon failed"; security_failure(); } 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", StringPrintf("%" PRIu64, 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(ERROR) << "execv(\"" << path << "\") failed"; security_failure(); } // 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(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. selinux_initialize(false); selinux_restore_context(); epoll_fd = epoll_create1(EPOLL_CLOEXEC); if (epoll_fd == -1) { PLOG(ERROR) << "epoll_create1 failed"; exit(1); } signal_handler_init(); property_load_boot_defaults(); export_oem_lock_status(); start_property_service(); set_usb_controller(); const BuiltinFunctionMap function_map; Action::set_function_map(&function_map); Parser& parser = Parser::GetInstance(); parser.AddSectionParser("service",std::make_unique<ServiceParser>()); parser.AddSectionParser("on", std::make_unique<ActionParser>()); parser.AddSectionParser("import", std::make_unique<ImportParser>()); std::string bootscript = GetProperty("ro.boot.init_rc", ""); if (bootscript.empty()) { 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) parser.DumpState(); ActionManager& am = ActionManager::GetInstance(); 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_done am.QueueBuiltinAction(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng"); // 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"); while (true) { // By default, sleep until something happens. int epoll_timeout_ms = -1; if (!(waiting_for_prop || ServiceManager::GetInstance().IsWaitingForExec())) { am.ExecuteOneCommand(); } if (!(waiting_for_prop || ServiceManager::GetInstance().IsWaitingForExec())) { 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_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; }
