读说rest_init&kernel_init&do_basic_setup

tatic noinline void __init_refok rest_init(void)
{
int pid;
rcu_scheduler_starting();
/*
* 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.
*/
/***********创建kernel_init进程**进程号为1********************************/
kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
numa_default_policy();
pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
rcu_read_lock();
kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
创建kthreadd内核线程，它的作用是管理和调度其它内核线程。
它循环运行一个叫做kthreadd的函数，该函数的作用是运行kthread_create_list全局链表中维护的内核线程。
调用kthread_create创建一个kthread，它会被加入到kthread_create_list 链表中；
被执行过的kthread会从kthread_create_list链表中删除；
且kthreadd会不断调用scheduler函数让出CPU。此线程不可关闭。
rcu_read_unlock();
complete(&kthreadd_done);
/*
* The boot idle thread must execute schedule()
* at least once to get things moving:
*/
init_idle_bootup_task(current);
preempt_enable_no_resched();
schedule();
preempt_disable();
/* Call into cpu_idle with preempt disabled */
cpu_idle();
}

进入kernel_init进程

tatic int __init kernel_init(void * unused)
{
    /*
     * Wait until kthreadd is all set-up.
     */
    wait_for_completion(&kthreadd_done);
    /*
     * init can allocate pages on any node
     */
    set_mems_allowed(node_states[N_HIGH_MEMORY]);
    /*
     * init can run on any cpu.
     */
    set_cpus_allowed_ptr(current, cpu_all_mask);
    /*
     * Tell the world that we're going to be the grim
     * reaper of innocent orphaned children.
     *
     * We don't want people to have to make incorrect
     * assumptions about where in the task array this
     * can be found.
     */
    init_pid_ns.child_reaper = current;

    cad_pid = task_pid(current);

    smp_prepare_cpus(setup_max_cpus);

    do_pre_smp_initcalls();
    lockup_detector_init();

    smp_init();
    sched_init_smp();
/*初始化设备驱动，完成其他驱动程序（直接编译进内核的模块）的初始化。
内核中部分的启动数据输出出自这里。
*/
    do_basic_setup();


    /* Open the /dev/console on the rootfs, this should never fail */
    if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
        printk(KERN_WARNING "Warning: unable to open an initial console.\n");
/*复制两次标准输入 一次作为输出 一次作为出错 */
    (void) sys_dup(0);
    (void) sys_dup(0);
    /*
     * check if there is an early userspace init. If yes, let it do all
     * the work
     */

    if (!ramdisk_execute_command)
        ramdisk_execute_command = "/init";

    if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
        ramdisk_execute_command = NULL;
        prepare_namespace();
    }

    /*
     * Ok, we have completed the initial bootup, and
     * we're essentially up and running. Get rid of the
     * initmem segments and start the user-mode stuff..
     */
/*准备执行用户应用程序*/
    init_post();
    return 0;
}

内核初始化过程中，通过do_base_setup来完成驱动的初始化 注册加载进内核

/*
 * Ok, the machine is now initialized. None of the devices
 * have been touched yet, but the CPU subsystem is up and
 * running, and memory and process management works.

 * Now we can finally start doing some real work..
 */
static void __init do_basic_setup(void)
{
cpuset_init_smp();
usermodehelper_init();
init_tmpfs();
driver_init();
init_irq_proc();
do_ctors();
do_initcalls();
}

driver_init()函数分析：

/**
 * driver_init - initialize driver model.
 *
 * Call the driver model init functions to initialize their
 * subsystems. Called early from init/main.c.
 */
void __init driver_init(void)
{
    /* These are the core pieces */
初始化devtmpfs文件系统，驱动核心设备将在这个文件系统中添加它们的设备节点。
这个文件系统可以由内核在挂载根文件系统之后自动挂载到/dev下，
也可以在文件系统的启动脚本中手动挂载
    devtmpfs_init();
     创建一些设备 char Blok 结点
    devices_init();
初始化驱动模型中的bus子系统
    buses_init();
    classes_init();
    firmware_init();

    hypervisor_init();

    /* These are also core pieces, but must come after the
     * core core pieces.
     */
   bus/platform子系统
    platform_bus_init();
初始化驱动模型中的system子系统
    system_bus_init();
初始化驱动模型中的devices cpu子系统
    cpu_dev_init();
    memory_dev_init();
}

do_initcalls()函数：
调用所有编译内核的驱动模块中的初始化函数。
其中按照各个内核模块初始化函数所自定义的启动级别（1～7），按顺序调用器初始化函数。
对于同一级别的初始化函数，安装编译是链接的顺序调用，也就是和内核Makefile的编写有关。
 在编写内核模块的时候需要知道这方面的知识，
 如果编写的模块必须和依赖的模块在同一级，那就必须注意内核Makefile的修改了。

static void __init do_initcalls(void)
{
    initcall_t *fn;

    for (fn = __early_initcall_end; fn < __initcall_end; fn++)
        do_one_initcall(*fn);
}
比如：board中初始化函数的调用
static int __init customize_machine(void)
{
/* customizes platform devices, or adds new ones */
if (machine_desc->init_machine)
machine_desc->init_machine();
return 0;
}
arch_initcall(customize_machine);

					
						
							
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							#define pure_initcall(fn)		__define_initcall("0",fn,0)


#define core_initcall(fn)		__define_initcall("1",fn,1)
#define core_initcall_sync(fn)		__define_initcall("1s",fn,1s)
#define postcore_initcall(fn)		__define_initcall("2",fn,2)
#define postcore_initcall_sync(fn)	__define_initcall("2s",fn,2s)
#define arch_initcall(fn)		__define_initcall("3",fn,3)
#define arch_initcall_sync(fn)		__define_initcall("3s",fn,3s)
#define subsys_initcall(fn)		__define_initcall("4",fn,4)
#define subsys_initcall_sync(fn)	__define_initcall("4s",fn,4s)
#define fs_initcall(fn)			__define_initcall("5",fn,5)
#define fs_initcall_sync(fn)		__define_initcall("5s",fn,5s)
#define rootfs_initcall(fn)		__define_initcall("rootfs",fn,rootfs)
#define device_initcall(fn)		__define_initcall("6",fn,6)
#define device_initcall_sync(fn)	__define_initcall("6s",fn,6s)
#define late_initcall(fn)		__define_initcall("7",fn,7)
#define late_initcall_sync(fn)		__define_initcall("7s",fn,7s)

#define INITCALLS                            \
    *(.initcallearly.init)                        \
    VMLINUX_SYMBOL(__early_initcall_end) = .;            \
      *(.initcall0.init)                        \
      *(.initcall0s.init)                        \
      *(.initcall1.init)                        \
      *(.initcall1s.init)                        \
      *(.initcall2.init)                        \
      *(.initcall2s.init)                        \
      *(.initcall3.init)                        \
      *(.initcall3s.init)                        \
      *(.initcall4.init)                        \
      *(.initcall4s.init)                        \
      *(.initcall5.init)                        \
      *(.initcall5s.init)                        \
    *(.initcallrootfs.init)                        \
      *(.initcall6.init)                        \
      *(.initcall6s.init)                        \
      *(.initcall7.init)                        \
      *(.initcall7s.init)

#define INIT_CALLS                            \
        VMLINUX_SYMBOL(__initcall_start) = .;            \
        INITCALLS                        \
        VMLINUX_SYMBOL(__initcall_end) = .;