1. 当一个设备无法立刻满足用户的读写请求时（例如调用read时，设备没有数据提供），驱动程序应当（缺省的）阻塞进程，使它进入等待（睡眠）状态，知道请求可以得到满足。
2. Linux内核等待队列：在实现阻塞驱动的过程中，需要有一个“候车室”来安排被阻塞的进程“休息”，当唤醒它们的条件成熟时，则可以从“候车室”中将这些进程唤醒。而这个“候车室”就是等待队列。
3. Linux内核等待队列的使用
（1）定义等待队列
wait_queue_head_t my_queue;
（2）初始化等待队列
init_waitqueue_head(&my_queue);
（3）定义+初始化等待队列
DECLARE_WAIT_QUEUE_HEAD(my_queue)
（4）使进程进入等待队列
① wait_event
wait_event(queue, condition)
当condition(布尔表达式)为真时，立即返回；否则让进程进入TASK_UNINTERRUPTIBLE模式的睡眠，并挂在queue参数所指定的等待队列上。
② wait_event_interruptible
wait_event_interruptible(queue, condition)
当condition(布尔表达式)为真时，立即返回；否则让进程进入TASK_INTERRUPTIBLE的睡眠，并挂在queue参数所指定的等待队列上。
③ wait_event_killable
wait_event_killable(queue, condition)
当condition(一个布尔表达式)为真时，立即返回；否则让进程进入TASK_KILLABLE的睡眠，并挂在queue参数所指定的等待队列上。
（5）从等待队列中唤醒进程
① wake_up：
wake_up(wait_queue_t *q)
从等待队列q中唤醒状态为TASK_UNINTERRUPTIBLE，TASK_INTERRUPTIBLE，TASK_KILLABLE 的所有进程。
② wake_up_interruptible
wake_up_interruptible(wait_queue_t *q)
从等待队列q中唤醒状态为TASK_INTERRUPTIBLE 的进程
4. 简单示例
#include#include #include #include #include #include #include #define GPGCON 0x56000060#define GPGDAT 0x56000064unsigned int *gpio_config;struct timer_list buttons_timer;unsigned int key_num = 0;wait_queue_head_t key_wait_queue;void keys_timer_function(unsigned long data) { printk("keys_timer_function\n"); key_num = 0; printk("data = %lx\n", data); switch(data) { case IRQ_EINT8: key_num = 1; break; case IRQ_EINT11: key_num = 2; break; case IRQ_EINT13: key_num = 3; break; case IRQ_EINT14: key_num = 4; break; case IRQ_EINT15: key_num = 5; break; case IRQ_EINT19: key_num = 6; break; default: break; } printk("key_num = %d\n", key_num); wake_up(&key_wait_queue);} irqreturn_t key_int(int irq, void *dev_id){ //1. 检测是否发生了按键中断 //2. 清除已经发生的按键中断 //3. 提交下半部 buttons_timer.data = (unsigned long)irq; mod_timer(&buttons_timer, jiffies + (HZ / 10)); //return 0; return IRQ_HANDLED;}void key_hw_init(void){ unsigned int config_data; config_data = readl(gpio_config); config_data &= 0b00111100; config_data |= 0b10000010; printk("config_data = %x\n", config_data); writel(config_data, gpio_config);}int key_open(struct inode *node,struct file *filp){ return 0; }ssize_t key_read(struct file *filp, char __user *buf, size_t size, loff_t *pos){ wait_event(key_wait_queue, key_num); printk("in kernel: key num is %d\n",key_num); copy_to_user(buf, &key_num, 4); key_num = 0; return 4;}struct file_operations key_fops = { .open = key_open, .read = key_read, };struct miscdevice key_miscdev = { .minor = 200, .name = "key", .fops = &key_fops, };static int button_init(void){ int ret; gpio_config = ioremap(GPGCON, 4); ret = misc_register(&key_miscdev); printk("ret = %d\n", ret); if (ret == 0) { //按键初始化 key_hw_init(); //注册中断处理程序 request_irq(IRQ_EINT8, key_int, IRQF_TRIGGER_LOW, "key1", 0); request_irq(IRQ_EINT11, key_int, IRQF_TRIGGER_LOW, "key2", 0); request_irq(IRQ_EINT13, key_int, IRQF_TRIGGER_LOW, "key3", 0); request_irq(IRQ_EINT14, key_int, IRQF_TRIGGER_LOW, "key4", 0); request_irq(IRQ_EINT15, key_int, IRQF_TRIGGER_LOW, "key5", 0); request_irq(IRQ_EINT19, key_int, IRQF_TRIGGER_LOW, "key6", 0); /* 初始化定时器 */ init_timer(&buttons_timer); buttons_timer.function = keys_timer_function; /* 向内核注册一个定时器 */ add_timer(&buttons_timer); /* 初始化等待队列 */ init_waitqueue_head(&key_wait_queue); } else { printk("register fail!\n"); } return ret;}static void button_exit(void){ iounmap(gpio_config); free_irq(IRQ_EINT8, 0); free_irq(IRQ_EINT11, 0); free_irq(IRQ_EINT13, 0); free_irq(IRQ_EINT14, 0); free_irq(IRQ_EINT15, 0); free_irq(IRQ_EINT19, 0); misc_deregister(&key_miscdev); }module_init(button_init);module_exit(button_exit);