内核线程

内核线程可以用户两种方法实现：

1. 古老的方法

创建内核线程：

ret = kernel_thread(mykthread, NULL, CLONE_FS | CLONE_FILES | CLONE_SIGHAND | SIGCHLD);

 

内核线程方法的实现

static DECLARE_WAIT_QUEUE_HEAD(myevent_waitqueue);

rwlock_t myevent_lock;

extern unsigned int myevent_id;

 

static int mykthread(void *unused)

{

       unsigned int event_id = 0;

       DECLARE_WAITQUEUE(wait, current);

       //将此线程作为kthreadd的子进程，成为一个内核线程，不占用用户资源

       daemonize(“mykthread”);

 

       //daemonize()默认阻塞所有信号，所以…

       allow_signal(SIGKILL);

 

       add_wait_queue(&myevent_waitqueue, &wait);

 

       for ( ; ;)

       {

              set_current_state(TASK_INTERRUPTIBLE);

              schedule();

              if ( signal_pending(current) )

                     break;

 

              read_lock(&myevent_lock);

              if ( myevent_id)

              {

                     event_id = myevent_id;

                     read_unlock(&myevent_lock);

                     run_umode_handler(event_id);

              }

              else

              {

                     read_unlock(&myevent_lock);

              }

       }

      

       set_current_state(TASK_RUNNING);

       remove_wait_queue(&myevent_waitqueue, &wait);

       return 0;

}

 

2. 现代方法（从2.6.23起）

       创建内核线程更现代的方法是辅助函数kthread_create。

函数原型：

struct task_struct *kthread_create(int (*threadfin)(void *data),

void *data,

const char namefmt[],

…)

 

例子如下：

#include <linux/kthread.h>   // kernel thread helper interface #include <linux/completion.h> #include <linux/module.h> #include <linux/sched.h> #include <linux/init.h>   MODULE_LICENSE("Dual BSD/GPL"); MODULE_AUTHOR("[email protected]");   struct task_struct *my_task;                        /* Helper thread */ static int my_thread(void *unused) {     while (!kthread_should_stop()) {            set_current_state(TASK_INTERRUPTIBLE);        schedule();        printk("I am still running/n");     }     /* Bail out of the wait queue */   __set_current_state(TASK_RUNNING);      return 0; }   /* Module Initialization */ static int __init my_init(void) {   /* ... */    /*   my_task = kthread_create(my_thread, NULL, "%s", "my_thread");     if (my_task) wake_up_process(my_task); */      /*kthread_run会调用kthread_create函数创建新进程，并立即唤醒它*/      kthread_run(my_thread, NULL, "%s", "my_thread");*/       /* ... */       /* ... */   return 0; }   /* Module Release */ static void __exit my_release(void) {   /* ... */   kthread_stop(my_task);   /* ... */ }   module_init(my_init); module_exit(my_release);