linux有内核级线程么

struct thread_info {

	int			preempt_count;	/* 0 => preemptable, <0 => bug */

	struct task_struct	*task;		/* main task structure */
	__u32			cpu;		/* cpu */};

struct task_struct {
	
	pid_t pid;
	
	pid_t tgid;

	void *stack;
	struct mm_struct *mm, *active_mm;
	/* filesystem information */
	struct fs_struct *fs;
	/* open file information */
	struct files_struct *files;};#define task_thread_info(task)	((struct thread_info *)(task)->stack)

pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
{
	return do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
		(unsigned long)arg, NULL, NULL);
}

pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);

#define kthread_run(threadfn, data, namefmt, ...)			   \
({									   \
	struct task_struct *__k						   \
		= kthread_create(threadfn, data, namefmt, ## __VA_ARGS__); \
	if (!IS_ERR(__k))						   \
		wake_up_process(__k);					   \
	__k;								   \
})

#define kthread_create(threadfn, data, namefmt, arg...) \
	kthread_create_on_node(threadfn, data, -1, namefmt, ##arg)


struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
					   void *data, int node,
					   const char namefmt[],
					   ...)
{
	DECLARE_COMPLETION_ONSTACK(done);
	struct task_struct *task;

	/*分配kthread_create_info空间*/
	struct kthread_create_info *create = kmalloc(sizeof(*create),
						     GFP_KERNEL);

	if (!create)
		return ERR_PTR(-ENOMEM);
	create->threadfn = threadfn;
	create->data = data;
	create->node = node;
	create->done = &done;

	/*加入到kthread_creta_list列表中，等待ktherad_add中断线程去创建改线程*/
	spin_lock(&kthread_create_lock);
	list_add_tail(&create->list, &kthread_create_list);
	spin_unlock(&kthread_create_lock);

	wake_up_process(kthreadd_task);
	/*
	* Wait for completion in killable state, for I might be chosen by
	* the OOM killer while kthreadd is trying to allocate memory for
	* new kernel thread.
	*/
	if (unlikely(wait_for_completion_killable(&done))) {
		/*
		* If I was SIGKILLed before kthreadd (or new kernel thread)
		* calls complete(), leave the cleanup of this structure to
		* that thread.
		*/
		if (xchg(&create->done, NULL))
			return ERR_PTR(-EINTR);
		/*
		* kthreadd (or new kernel thread) will call complete()
		* shortly.
		*/
		wait_for_completion(&done);
	}
	task = create->result;
	.
	.
	.
	kfree(create);
	return task;
}

int kthreadd(void *unused)
{
	struct task_struct *tsk = current;

	/* Setup a clean context for our children to inherit. */
	set_task_comm(tsk, "kthreadd");
	ignore_signals(tsk);
	set_cpus_allowed_ptr(tsk, cpu_all_mask);
	set_mems_allowed(node_states[N_MEMORY]);

	current->flags |= PF_NOFREEZE;
	
	for (;;) {
		set_current_state(TASK_INTERRUPTIBLE);
		if (list_empty(&kthread_create_list))
			schedule();
		__set_current_state(TASK_RUNNING);

		spin_lock(&kthread_create_lock);
		while (!list_empty(&kthread_create_list)) {
			struct kthread_create_info *create;

			create = list_entry(kthread_create_list.next,
					    struct kthread_create_info, list);
			list_del_init(&create->list);
			spin_unlock(&kthread_create_lock);

			create_kthread(create);

			spin_lock(&kthread_create_lock);
		}
		spin_unlock(&kthread_create_lock);
	}

	return 0;
}

static void create_kthread(struct kthread_create_info *create)
{
	int pid;


	/* We want our own signal handler (we take no signals by default). */
	pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
	if (pid < 0) {
		/* If user was SIGKILLed, I release the structure. */
		struct completion *done = xchg(&create->done, NULL);

		if (!done) {
			kfree(create);
			return;
		}
		create->result = ERR_PTR(pid);
		complete(done);
	}
}

static int kthread(void *_create)
{
	.
	.
	.
	.
	/* If user was SIGKILLed, I release the structure. */
	done = xchg(&create->done, NULL);
	if (!done) {
		kfree(create);
		do_exit(-EINTR);
	}
	/* OK, tell user we're spawned, wait for stop or wakeup */
	__set_current_state(TASK_UNINTERRUPTIBLE);
	create->result = current;
	complete(done);
	schedule();

	ret = -EINTR;

	if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) {
		__kthread_parkme(&self);
		ret = threadfn(data);
	}
	/* we can't just return, we must preserve "self" on stack */
	do_exit(ret);
}

int kthread_stop(struct task_struct *k)
{
	struct kthread *kthread;
	int ret;

	trace_sched_kthread_stop(k);

	get_task_struct(k);
	kthread = to_live_kthread(k);
	if (kthread) {
		set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
		__kthread_unpark(k, kthread);
		wake_up_process(k);
		wait_for_completion(&kthread->exited);
	}
	ret = k->exit_code;
	put_task_struct(k);

	trace_sched_kthread_stop_ret(ret);
	return ret;
}

thread_func()
{
    // do your work here
    // wait to exit
    while(!thread_could_stop())
    {
           wait();
    }
}

exit_code()
{
     kthread_stop(_task);   //发信号给task，通知其可以退出了
}

#include "test_kthread.h"
#include <linux/delay.h>
#include <linux/timer.h>

#include <linux/platform_device.h>
#include <linux/fs.h>
#include <linux/module.h>

static struct task_struct *test_thread = NULL;

unsigned int time_conut = 5;

int  test_thread_fun(void *data)
{
	int times = 0;
	while(!kthread_should_stop())
	{
		printk("\n   printk %u\r\n", times);
		times++;
		msleep_interruptible(time_conut*1000);
	}

	printk("\n   test_thread_fun exit success\r\n\n");

	return 0;
}


void register_test_thread(void)
{

	test_thread = kthread_run(test_thread_fun , NULL, "test_kthread" );
	
    if (IS_ERR(test_thread)){ 
        printk(KERN_INFO "create test_thread failed!\n"); 
    }  
    else { 
        printk(KERN_INFO "create test_thread ok!\n");  
    } 
	
}
static ssize_t kthread_debug_start(struct device *dev, struct device_attribute *attr, char *buf)
{
	register_test_thread();
	
	return 0;	
}


static ssize_t kthread_debug_stop(struct device *dev, struct device_attribute *attr, char *buf)
{
	kthread_stop(test_thread);
	
	return 0;	
}


static DEVICE_ATTR(kthread_start,  S_IRUSR,  kthread_debug_start,NULL);
static DEVICE_ATTR(kthread_stop, S_IRUSR,    kthread_debug_stop,NULL);

struct attribute * kthread_group_info_attrs[] = 
{
	&dev_attr_kthread_start.attr,
	&dev_attr_kthread_stop.attr,
	
	NULL,
};

struct attribute_group kthread_group = 
{
	.name = "kthread",
	.attrs = kthread_group_info_attrs,
};