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 <linux/module.h> #include <linux/init.h> #include <linux/miscdevice.h> #include <linux/interrupt.h> #include <linux/io.h> #include <linux/fs.h> #include <asm/uaccess.h> #define GPGCON 0x56000060 #define GPGDAT 0x56000064 unsigned 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 "); key_num = 0; printk("data = %lx ", 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 ", 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 ", 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 ",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 ", 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! "); } 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);