Android系统启动流程之Init说明

要写学习总结了，先将资料整理一下，以备用。
int main(int argc, char **argv){    int fd_count = 0;    struct pollfd ufds[4];    char *tmpdev;    char* debuggable;    char tmp[32];    int property_set_fd_init = 0;    int signal_fd_init = 0;    int keychord_fd_init = 0;    bool is_charger = false;//uevent 热插拔，内核和用户空间的通信机制，netlink实现。    if (!strcmp(basename(argv[0]), "ueventd"))        return ueventd_main(argc, argv);//strcmp返回0为相等，大于返回大于0，小于返回小于0.此处为电子狗    if (!strcmp(basename(argv[0]), "watchdogd"))        return watchdogd_main(argc, argv);//赋予最大的权限，即初始化权限，权限的定义为文件666-umask的值。文件夹777-umask的值。    /* clear the umask */    umask(0);//创建各种目录        /* 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. */    mkdir("/dev", 0755);    mkdir("/proc", 0755);    mkdir("/sys", 0755);//虚拟内存文件系统，用于存放一些启动中的临时文件，于外界交互    mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");    mkdir("/dev/pts", 0755);    mkdir("/dev/socket", 0755);    mount("devpts", "/dev/pts", "devpts", 0, NULL);    mount("proc", "/proc", "proc", 0, NULL);    mount("sysfs", "/sys", "sysfs", 0, NULL);//查看.booting是否为可读写和创建        /* indicate that booting is in progress to background fw loaders, etc */    close(open("/dev/.booting", O_WRONLY | O_CREAT, 0000));        /* We must have some place other than / to create the * device nodes for kmsg and null, otherwise we won't * be able to remount / read-only later on. * Now that tmpfs is mounted on /dev, we can actually * talk to the outside world. //貌似与tmpfs有关 */    open_devnull_stdio();//Klog日志初始化，内核级的log日志    klog_init();//初始化属性    property_init();//获取硬件设备名称，此机器名为trace    get_hardware_name(hardware, &revision);//处理内核命令    process_kernel_cmdline();//SElinux是linux最杰出的新安全控制子系统，是2.6版本的linux内核中提供强制访问控制（MAC）系统。包含在内核中。    union selinux_callback cb;    cb.func_log = log_callback;    selinux_set_callback(SELINUX_CB_LOG, cb);    cb.func_audit = audit_callback;    selinux_set_callback(SELINUX_CB_AUDIT, cb);    selinux_initialize();    /* These directories were necessarily created before initial policy load * and therefore need their security context restored to the proper value. * This must happen before /dev is populated by ueventd. */restorecon命令，恢复SElinux文件属性，即恢复文件的安全上下文。    restorecon("/dev");    restorecon("/dev/socket");    restorecon("/dev/__properties__");    restorecon_recursive("/sys");//是否充电？    is_charger = !strcmp(bootmode, "charger");//当前启动信息描述，属性初始化    INFO("property init\n");    property_load_boot_defaults();    INFO("reading config file\n");//重点，分析init.rc文件内容    init_parse_config_file("/init.rc");//行为触发器，early-init阶段    action_for_each_trigger("early-init", action_add_queue_tail);//执行各种创建行为    queue_builtin_action(wait_for_coldboot_done_action, "wait_for_coldboot_done");    queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");    queue_builtin_action(keychord_init_action, "keychord_init");    queue_builtin_action(console_init_action, "console_init");//执行boot action，即init阶段    /* execute all the boot actions to get us started */    action_for_each_trigger("init", action_add_queue_tail);    /* Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random * wasn't ready immediately after wait_for_coldboot_done *///再执行一遍mix-hwrng...防止/dev/hw-random或/dev/random（虚假随机的字符流）无法及时响应    queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");    queue_builtin_action(property_service_init_action, "property_service_init");    queue_builtin_action(signal_init_action, "signal_init");//充电模式下，会略过mount文件系统，开启核心服务    /* Don't mount filesystems or start core system services if in charger mode. */    if (is_charger) {        action_for_each_trigger("charger", action_add_queue_tail);    } else {        action_for_each_trigger("late-init", action_add_queue_tail);//因为充电，所以延后初始化    }//基于当前的属性配置状态，启动属性触发器。    /* run all property triggers based on current state of the properties */    queue_builtin_action(queue_property_triggers_action, "queue_property_triggers");//bootchart工具，能对系统的性能进行分析，并生成系统启动过程的图表，提供一些有价值的信息#if BOOTCHART    queue_builtin_action(bootchart_init_action, "bootchart_init");#endif//进入无限循环    for(;;) {        int nr, i, timeout = -1;//执行命令，重启死去的进程        execute_one_command();        restart_processes();//此处的几个if判断语句，2的源码在循环体的外面。现在移入到里面。每次循环都要判断，初始化状态，设备是否有效//监听来自于属性服务器事件，socket信号事件，keychord设备事件        if (!property_set_fd_init && get_property_set_fd() > 0) {            ufds[fd_count].fd = get_property_set_fd();            ufds[fd_count].events = POLLIN;            ufds[fd_count].revents = 0;            fd_count++;            property_set_fd_init = 1;        }        if (!signal_fd_init && get_signal_fd() > 0) {            ufds[fd_count].fd = get_signal_fd();            ufds[fd_count].events = POLLIN;            ufds[fd_count].revents = 0;            fd_count++;            signal_fd_init = 1;        }        if (!keychord_fd_init && get_keychord_fd() > 0) {            ufds[fd_count].fd = get_keychord_fd();            ufds[fd_count].events = POLLIN;            ufds[fd_count].revents = 0;            fd_count++;            keychord_fd_init = 1;        }        if (process_needs_restart) {            timeout = (process_needs_restart - gettime()) * 1000;            if (timeout < 0)                timeout = 0;        }        if (!action_queue_empty() || cur_action)            timeout = 0;// bootchart是一个性能统计工具，用于搜集硬件和系统的信息，并将其写入磁盘，以便其// 他程序使用#if BOOTCHART        if (bootchart_count > 0) {            if (timeout < 0 || timeout > BOOTCHART_POLLING_MS)                timeout = BOOTCHART_POLLING_MS;            if (bootchart_step() < 0 || --bootchart_count == 0) {                bootchart_finish();                bootchart_count = 0;            }        }#endif        // 等待下一个命令的提交        nr = poll(ufds, fd_count, timeout);        if (nr <= 0)            continue;        for (i = 0; i < fd_count; i++) {//处理Uevent，属性服务，keychord事件//以前是==判断，改成&。能否提速？            if (ufds[i].revents & POLLIN) {                if (ufds[i].fd == get_property_set_fd())                    handle_property_set_fd();                else if (ufds[i].fd == get_keychord_fd())                    handle_keychord();                else if (ufds[i].fd == get_signal_fd())                    handle_signal();            }        }    }    return 0;}
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