android 的Init进程

init进程事Linux内核启动后创建的第一个进程。init在初始化过程中会启动很多重要的守护进程。

                                                                                         |守护进程  BUD ADB

                 ---fastboot（通过USB更新手机分区映像）                            | --应用程 launcher phonebook

                                                                                         |Zygote                              | --sensorservice

                                                                                                               | ---systemserver

                         （boot.img）                                                                                     | --ActivityManager service   contentservice  Usbservwice

bootloader---Linux kernel-------------------------------------init|

                                                                                                         | --camera service 

                ----Recover                                                      |Mediaserver  

                                                                                                         |--MediaPlayer service

                                                                                        |serviceManager

    在init启动过程中会解析init.rc，根据init.rc装载android的文件系统，创建系统目录，启动android系统重要的守护进程，这些进程包括USB守护进程，ADB守护进程，Vold守护进程，rild守护进程

    Init进程的源码在system/core／init/init.c   main函数中

   

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;    if (!strcmp(basename(argv[0]), "ueventd")).  //检查启动程序文件名        return ueventd_main(argc, argv);    if (!strcmp(basename(argv[0]), "watchdogd"))        return watchdogd_main(argc, argv);    /* clear the umask */    umask(0);   ／／修改创建目录的权限        /* 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.         */    mkdir("/dev", 0755);    mkdir("/proc", 0755);    mkdir("/sys", 0755);    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);        /* indicate that booting is in progress to background fw loaders, etc */    close(open("/dev/.booting", O_WRONLY | O_CREAT, 0000));／／is_booting（）来判断是否进程处于初始化中，初始化结束后这个文件将被删除        /* 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.         */    open_devnull_stdio();／／把标准输入，标准输出和标准出错重定向到空设备文件    klog_init();／／这个函数用来创建节点／dev／_kmsg_，这样init进程可以使用kernel的log系统来输出log    memlog_init();    property_init();／／主要是创建一个共享区域来储存属性值    rk_parse_cpu();    get_hardware_name(hardware, &revision);／／通过／proc／cpuinfo文件取得系统硬件名称    process_kernel_cmdline();／／解析kernel的启动参数，启动参数通常放在／proc／cmdline    union selinux_callback cb;／／初始化SELinux    cb.func_log = klog_write;    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("/dev");    restorecon("/dev/socket");    restorecon("/dev/__properties__");    restorecon_recursive("/sys");    is_charger = !strcmp(bootmode, "charger");    INFO("property init\n");    if (!is_charger)        property_load_boot_defaults();／／解析设备根目录下的default。prop文件把文件中定义的属性值读出来设置到属性系统中    INFO("reading config file\n");
     init_parse_config_file("/init.rc");／／解析init，rc文件    action_for_each_trigger("early-init", action_add_queue_tail);／／用来将指定的action加入到执行列表action_queue    queue_builtin_action(wait_for_coldboot_done_action, "wait_for_coldboot_done");／／等待冷插拔设备初始化完成    queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");／／从硬件RNG的设备文件／dev／HW_random中读取512字节并写到Linux RNG的设备文件／dev／urandom中    queue_builtin_action(keychord_init_action, "keychord_init");／／初始化组合键监听模块    queue_builtin_action(console_init_action, "console_init");／／在屏幕上显示android 字样Logo    /* execute all the boot actions to get us started */    action_for_each_trigger("init", action_add_queue_tail);    /* skip mounting filesystems in charger mode */    if (!is_charger) {        action_for_each_trigger("early-fs", action_add_queue_tail);        action_for_each_trigger("fs", action_add_queue_tail);        action_for_each_trigger("post-fs", action_add_queue_tail);        action_for_each_trigger("post-fs-data", 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     */    queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");    queue_builtin_action(property_service_init_action, "property_service_init");／／初始化属性服务，读取系统预制的属性值    queue_builtin_action(signal_init_action, "signal_init");／／初始化信号处理模块    queue_builtin_action(check_startup_action, "check_startup");／／检查是否已经完成Init进程初始化，如果初始化完成删除.booting文件    if (is_charger) {        action_for_each_trigger("charger", action_add_queue_tail);    } else {        action_for_each_trigger("early-boot", action_add_queue_tail);        action_for_each_trigger("boot", action_add_queue_tail);    }        /* run all property triggers based on current state of the properties */    queue_builtin_action(queue_property_triggers_action, "queue_property_triggers");#if BOOTCHART    queue_builtin_action(bootchart_init_action, "bootchart_init");#endif    for(;;) {        int nr, i, timeout = -1;        execute_one_command();／／每循环执行命令列表中的一条命令        restart_processes();        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) {／／设置等待超时的时间            timeout = (process_needs_restart - gettime()) * 1000;            if (timeout < 0)                timeout = 0;        }        if (!action_queue_empty() || cur_action)            timeout = 0;#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        nr = poll(ufds, fd_count, timeout);        if (nr <= 0)            continue;        for (i = 0; i < fd_count; i++) {            if (ufds[i].revents == POLLIN) {                if (ufds[i].fd == get_property_set_fd())                    handle_property_set_fd();／／修改属性                else if (ufds[i].fd == get_keychord_fd())                    handle_keychord();／／监控组合键                else if (ufds[i].fd == get_signal_fd())                    handle_signal();／／监听到信号            }        }    }    memlog_close();    return 0;}