android7.1.2启动流程分析之init程序

android7.1.2启动流程分析之init程序
板子平台ROC_RK3328_CC


安卓源码树Android7.1.2-->kernel/init/main.c 文件
asmlinkage void __init start_kernel(void){
    /* Do the rest non-__init'ed, we're now alive */
    rest_init();//在start_kernel函数{BANNED}最佳后一行
}
安卓源码树Android7.1.2-->kernel/init/main.c 文件
static noinline void __init_refok rest_init(void)
{

    /*
     * We need to spawn init first so that it obtains pid 1, however
     * the init task will end up wanting to create kthreads, which, if
     * we schedule it before we create kthreadd, will OOPS.
     */
    kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
}
安卓源码树Android7.1.2-->kernel/init/main.c 文件
static int __ref kernel_init(void *unused)
{
    kernel_init_freeable();//有ramdisk_execute_command = "/init";
    /* need to finish all async __init code before freeing the memory */
    async_synchronize_full();
    free_initmem();
    mark_rodata_ro();
    system_state = SYSTEM_RUNNING;
    numa_default_policy();

    flush_delayed_fput();
/*内核启动信息“Kernel command line: root=/dev/mtdblock4 rootfstype=yaffs2 rootflags=inband-tags console=ttyS0,115200n8 rdinit=/sbin/init ro mem=64M”　而我的android 7.1.2的板子里kernel comman line 里是init=/init
   
    如果ramdisk_execute_command变量指定了要运行的程序，启动它。
　　    ramdisk_execute_command的取值分为三种情况：
　　    a.如果命令行参数中指定了“rdinit=...”，则ramdisk_execute_command等于这个参数指定的程序。
　　    b.否则，如果/init程序存在，ramdisk_execute_command就等于/init
　　    c.否则，ramdisk_execute_command为空

    本main.c文件　kernel_init_freeable(void)函数有
        if (!ramdisk_execute_command)　
        ramdisk_execute_command = "/init";
    */

    if (ramdisk_execute_command) {
        if (!run_init_process(ramdisk_execute_command))
            return 0;
        pr_err("Failed to execute %s\n", ramdisk_execute_command);
    }

    /*
     * We try each of these until one succeeds.
     *
     * The Bourne shell can be used instead of init if we are
     * trying to recover a really broken machine.
     */

    if (execute_command) {
        if (!run_init_process(execute_command))
            return 0;
        pr_err("Failed to execute %s.  Attempting defaults...\n",
            execute_command);
    }
    if (!run_init_process("/sbin/init") ||
        !run_init_process("/etc/init") ||
        !run_init_process("/bin/init") ||
        !run_init_process("/bin/sh"))
        return 0;

    panic("No init found.  Try passing init= option to kernel. "
          "See Linux Documentation/init.txt for guidance.");
}

安卓系统跟目录下的init.rc初始化脚本配置文件默认放置在android源码树的system/core/rootdir目录(类同于传统linux系统下使用busybox生成的/sbin/init程序去解析/etc/inittab文件)


android中的/init程序会通过解析/init.rc和init.rc里面包含的
import /init.${ro.hardware}.rc这两个文件中的相关的命令来完成相应的初始化流程，是当前android系统运行时所依赖的相关硬件平台的名字，/proc/cmdline命令行脚本有androidboot.hardware=rk30board,此处的ro.hardware应该就是rk30board

/init.rc初始化脚本配置文件是提供通用的相关初始化指令,/init..rc脚本配置文件是提供特定的硬件平台的机器相关的初始化指令



init.rc初始化配置脚本的语言语法规则 有说明文档android源码树system/core/init/readme.txt.


当平台启动时，kernel中的引导参数将会被设置成init=/init.从而当挂载文件系统成功后，便会开始执行/init初始化程序。init的入口点在源码树的system/core/init/init.cpp的main函数



   
   
    int main(int argc, char** argv) {
    //创建我们需要的基础文件系统/dev,/dev/pts,/dev/socket,/proc,/sys到initramdisk中的根目录，然后由*.rc脚本配置文件来解决余下的目录节点的创建
        // 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.
        if (is_first_stage) {
            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));
            mount("sysfs", "/sys", "sysfs", 0, NULL);
        }
       
 NOTICE("init %s started!\n", is_first_stage ? "first stage" : "second stage");

    if (!is_first_stage) {
    //此处是init: init second stage started! 
        // 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.
        ///操作proc/device-tree/firmware/android里面的设备树描述
        process_kernel_dt();
        //跟踪进去，发现是操作/proc/cmdline里面的内核命令行参数信息的
       
        process_kernel_cmdline();

        // Propagate the kernel variables to internal variables
        // used by init as well as the current required properties.
        export_kernel_boot_props();
    //add by xzj to set ro.rk.soc read from /proc/cpuinfo if not set
    set_soc_if_need();
    }

        // If we're in the kernel domain, re-exec init to transition to the init domain now
        // that the SELinux policy has been loaded.
        if (is_first_stage) {
            if (**restorecon("/init")** == -1) {
                ERROR("restorecon failed: %s\n", strerror(errno));
                security_failure();
            }
            char* path = argv[0];
            char* args[] = { path, const_cast("--second-stage"), nullptr };
            if (execv(path, args) == -1) {
                ERROR("execv(\"%s\") failed: %s\n", path, strerror(errno));
                security_failure();
            }
        }
   
        // 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.
        NOTICE("Running restorecon...\n");
        restorecon("/dev");
        restorecon("/dev/socket");
        restorecon("/dev/__properties__");
        restorecon("/property_contexts");
        restorecon_recursive("/sys");
   
        epoll_fd = epoll_create1(EPOLL_CLOEXEC);
        if (epoll_fd == -1) {
            ERROR("epoll_create1 failed: %s\n", strerror(errno));
            exit(1);
        }
   
        signal_handler_init();
   
        property_load_boot_defaults();
        export_oem_lock_status();
        start_property_service();
   
        const BuiltinFunctionMap function_map;
        Action::set_function_map(&function_map);
   
        Parser& parser = Parser::GetInstance();
        parser.AddSectionParser("service",std::make_unique());
        parser.AddSectionParser("on", std::make_unique());
        parser.AddSectionParser("import", std::make_unique());
//解析/init.rc配置文件
        parser.ParseConfig("/init.rc");
   
        ActionManager& am = ActionManager::GetInstance();
    //遍历链表并执行所有标志为early-init的活动Action
            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(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 = property_get("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) {
            if (!waiting_for_exec) {
                am.ExecuteOneCommand();
                restart_processes();
            }

   
        return 0;
    }
                             


/proc/cmdline  文件里信息如下
earlyprintk=uart8250-32bit,0xff130000 console=ttyFIQ0 androidboot.baseband=N/A androidboot.selinux=permissive androidboot.hardware=rk30board androidboot.console=ttyFIQ0 init=/init mtdparts=rk29xxnand:0x00002000@0x00002000(uboot),0x00004000@0x00004000(trust),0x00002000@0x00008000(misc),0x00000800@0x0000A000(baseparamer),0x00007800@0x0000A800(resource),0x00010000@0x00012000(kernel),0x00010000@0x00022000(boot),0x00010000@0x000c