前言:

 

内核在启动用户空间程序时会创建两个线程,kthread() 和 kernel_init()线程,在前一篇介绍了kthread()线程 点击打开链接,本文不在赘述,这里主要是对kernel_init()线程创建init=1号进程,并完成驱动模块的注册(这里的驱动模块是编译进内核的模块)。

 

1. kthreadd()

路径:linux-3.10.x\init\main.c

 

static 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.
	 */
	kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND); //init=1 号进程的创建
	numa_default_policy();
	pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES); //内核进程kthread的创建,用来管理内核层线程
	rcu_read_lock();
	kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
	rcu_read_unlock();
	complete(&kthreadd_done); //唤醒完成量

	/*
	 * The boot idle thread must execute schedule()
	 * at least once to get things moving:
	 */
	init_idle_bootup_task(current);
	schedule_preempt_disabled();
	/* Call into cpu_idle with preempt disabled */
	cpu_startup_entry(CPUHP_ONLINE);
}

 

2. kernel_init()

 路径:linux-3.10.x\init\main.c

功能:init=1号进程创建、内核驱动模块注册、启动默认控制台/dev/console

static int __ref kernel_init(void *unused)
{
	//kernel_init_freeable内部使用了等待完成量“kthreadd_done”,通过内核启动的报文我们得知,该线程虽然先创建
	//但却是在“kthreadd”线程创建完才执行的,原因是kthreadd执行完后才唤醒完成量的,所以这里会等待完成量!!!
	kernel_init_freeable();
	/* need to finish all async __init code before freeing the memory */
	async_synchronize_full();
	free_initmem(); //释放init初始化数据段,见下面
	mark_rodata_ro(); //标记只读数据段为只读,arm平台不影响
	system_state = SYSTEM_RUNNING;//设置系统为运行状态
	numa_default_policy(); //numa即非一致性内存访问,设置默认策略

	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”
	
	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
  	韦老师书中所用的命令没有设定“rdinit=...”,根文件系统中也没有"/init"。所以ramdisk_execute_command为空。if下的那块程序不会执行。
	*/
	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);
	}

	/*
		分析文件系统中init源码,里面主要是1号进程创建,环境设置,还有文件系统的console,
	*/
	
	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.");
}
即非一致性内存访问,设置默认策略

	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”
	
	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
  	韦老师书中所用的命令没有设定“rdinit=...”,根文件系统中也没有"/init"。所以ramdisk_execute_command为空。if下的那块程序不会执行。
	*/
	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);
	}

	/*
		分析文件系统中init源码,里面主要是1号进程创建,环境设置,还有文件系统的console,
	*/
	
	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.");
}

 

void free_initmem(void)
{
#ifdef CONFIG_HAVE_TCM
	extern char __tcm_start, __tcm_end;

	poison_init_mem(&__tcm_start, &__tcm_end - &__tcm_start);
	free_reserved_area(&__tcm_start, &__tcm_end, 0, "TCM link");
#endif

	poison_init_mem(__init_begin, __init_end - __init_begin); //释放init段
	if (!machine_is_integrator() && !machine_is_cintegrator())
		free_initmem_default(0);
}
/*
 * Poison init memory with an undefined instruction (ARM) or a branch to an
 * undefined instruction (Thumb).
 */
static inline void poison_init_mem(void *s, size_t count)
{
	u32 *p = (u32 *)s;
	for (; count != 0; count -= 4)
		*p++ = 0xe7fddef0;
		/*
		内核初始化时把这些内存区域初始化为0xe7fddef0 (an undefined instruction (ARM) or 
		a branch to an undefined instruction (Thumb)),如果运行时函数非法访问到了这些区域,
		会触发一个undef instruction的异常并打印相应的回调,从而辅助开发人员更快地解决相关
		问题。
		*/
}

 

 

3. kernel_init_freeable()

路径:linux-3.10.x\init\main.c

功能:kernel_init_freeable主要功能是,等待内核线程创建完wait_for_completion(&kthreadd_done)、注册内核驱动模块do_basic_setup()、启动默认控制台/dev/console

 

static noinline void __init kernel_init_freeable(void)
{
	/*
	 * Wait until kthreadd is all set-up.
	 */
	wait_for_completion(&kthreadd_done); //等待完成量,即等待kthreadd线程完成

	/* Now the scheduler is fully set up and can do blocking allocations */
	gfp_allowed_mask = __GFP_BITS_MASK;

	/*
	 * init can allocate pages on any node
	 */
	set_mems_allowed(node_states[N_MEMORY]);
	/*
	 * init can run on any cpu.
	 */
	set_cpus_allowed_ptr(current, cpu_all_mask);

	cad_pid = task_pid(current);

	smp_prepare_cpus(setup_max_cpus);

	do_pre_smp_initcalls();
	lockup_detector_init();

	smp_init();
	sched_init_smp();

	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)
		pr_err("Warning: unable to open an initial console.\n");

	(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..
	 */

	/* rootfs is available now, try loading default modules */
	load_default_modules();
}

 

 

4. do_basic_setup()

路径:linux-3.10.x\init\main.c

功能:初始化cpuset子系统、创建khelper线程队列、内核模块驱动注册、

 

static void __init do_basic_setup(void)
{
	cpuset_init_smp(); //初始化内核control group的cpuset子系统
	usermodehelper_init();//创建khelper单线程工作队列,用于协助新建和运行用户空间程序
	shmem_init(); //初始化共享内存
	driver_init(); //驱动模块总线、文件系统注册,包括bus、devtmpfs、platform
	init_irq_proc(); //创建/proc/irq目录, 并初始化系统中所有中断对应的子目录
	do_ctors(); //执行内核的构造函数
	usermodehelper_enable(); //使能usermodehelper
	do_initcalls(); //调用level 0到level 7的initcall函数,依次的level名称是"early", "core", "postcore", "arch", "subsys", "fs", "device", “late”,需要注意的kernel在这块的命名有些问题,early_initcall对应的level小于0,pure_initcall对应level才是0
	random_int_secret_init(); //初始化随机数生成池
}

 

 

void __init driver_init(void)
{
	/* These are the core pieces */
	devtmpfs_init();
	devices_init();
	buses_init();
	classes_init();
	firmware_init();
	hypervisor_init();

	/* These are also core pieces, but must come after the
	 * core core pieces.
	 */
	platform_bus_init(); //见此文分析:http://blog.csdn.net/xichangbao/article/details/52938240
	cpu_dev_init();
	memory_dev_init();
}

 

 

 

5. do_initcalls()路径:linux-3.10.x\init\main.c

 

 

功能:初始化initcall_levels,完成编译进内核的驱动模块注册

 

static void __init do_initcalls(void)
{
	int level;

	for (level = 0; level < ARRAY_SIZE(initcall_levels) - 1; level++)
		do_initcall_level(level);
}

由于这里涉及到的东西比较多,可以见之前写的一篇博客点击打开链接,本文不再赘述!

至此,内核的初始化结束,正式进入了用户空间的初始化过程至此,内核的初始化结束,正式进入了用户空间的初始化过程至此,内核的初始化结束,正式进入了用户空间的初始化过程,在kernel_init线程中调用的do_basic_setup()函数会去初始化设备驱动,完成其他驱动程序(直接编译进内核的模块)的初始化。内核中大部分的启动数据输出(都是各设备的驱动模块输出)都是这里产生的。是我们驱动工程师需要重点关注的函数。




 

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