linux kernel_init

Kernel:

asmlinkage __visible void __init start_kernel(void)
{
        ....
   	trap_init();
	sched_init();
	rest_init();
}

static noinline void __init_refok rest_init(void)
{
    kernel_thread(kernel_init, NULL, CLONE_FS);
    pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);

}

static int __ref kernel_init(void *unused)
{
        int ret;

        kernel_init_freeable();
        /* 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();

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

        if (!try_to_run_init_process("/sbin/init") ||
            !try_to_run_init_process("/etc/init") ||
            !try_to_run_init_process("/bin/init") ||
            !try_to_run_init_process("/bin/sh"))
                return 0;

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

static noinline void __init kernel_init_freeable(void)
{
        if (!ramdisk_execute_command)
                ramdisk_execute_command = "/init";
}

內核系統調用：

static int run_init_process(const char *init_filename)
{
        argv_init[0] = init_filename;
        return do_execve(getname_kernel(init_filename),
                (const char __user *const __user *)argv_init,
                (const char __user *const __user *)envp_init);
}

Userspace：init進程啓動

int main(int argc, char** argv) {
    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<char*>("--second-stage"), nullptr };
        if (execv(path, args) == -1) {
            ERROR("execv(\"%s\") failed: %s\n", path, strerror(errno));
            security_failure();
        }
    }

    restorecon("/dev/__properties__");
    signal_handler_init();

    property_load_boot_defaults();
    start_property_service();

    init_parse_config_file("/init.rc");
}