嵌入式驱动之阻塞操作、非阻塞操作

阻塞
阻塞操作    
是指在执行设备操作时若不能获得资源则挂起进程，直到满足可操作的条件后再进行操作。
被挂起的进程进入休眠状态，被从调度器的运行队列移走，直到等待的条件被满足。

非阻塞操作  
进程在不能进行设备操作时并不挂起，它或者放弃，或者不停地查询，直至可以进行操作为止。

fd = open("...", O_RDWR | O_NONBLOCK); 

比如：想要读取一个按键值，如果一直没有按键按下，程序就一直等待直到有按键按下，这叫阻塞操作。非阻塞操作就是想要读取一个按键值，如果没有按键值可读，就立即返回。

驱动程序：

#include <linux/module.h>#include <linux/kernel.h>#include <linux/fs.h>#include <linux/init.h>#include <linux/delay.h>#include <linux/irq.h>#include <asm/uaccess.h>#include <asm/irq.h>#include <asm/io.h>#include <asm/arch/regs-gpio.h>#include <asm/hardware.h>#include <linux/poll.h>static struct class *fifthdrv_class;static struct class_device*fifthdrv_class_dev;volatile unsigned long *gpfcon;volatile unsigned long *gpfdat;volatile unsigned long *gpgcon;volatile unsigned long *gpgdat;static DECLARE_WAIT_QUEUE_HEAD(button_waitq);/* 中断事件标志, 中断服务程序将它置1，fifth_drv_read将它清0 */static volatile int ev_press = 0;static struct fasync_struct *button_async;struct pin_desc{unsigned int pin;unsigned int key_val;};/* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 *//* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */static unsigned char key_val;struct pin_desc pins_desc[4] = {{S3C2410_GPF0, 0x01},{S3C2410_GPF2, 0x02},{S3C2410_GPG3, 0x03},{S3C2410_GPG11, 0x04},};static DECLARE_MUTEX(button_lock);     //定义互斥锁   定义信号量/*  * 确定按键值  */static irqreturn_t buttons_irq(int irq, void *dev_id){struct pin_desc * pindesc = (struct pin_desc *)dev_id;unsigned int pinval;pinval = s3c2410_gpio_getpin(pindesc->pin);if (pinval){/* 松开 */key_val = 0x80 | pindesc->key_val;}else{/* 按下 */key_val = pindesc->key_val;}    ev_press = 1;                  /* 表示中断发生了 */    wake_up_interruptible(&button_waitq);   /* 唤醒休眠的进程 */kill_fasync (&button_async, SIGIO, POLL_IN);  //return IRQ_RETVAL(IRQ_HANDLED);}static int fifth_drv_open(struct inode *inode, struct file *file){if (file->f_flags & O_NONBLOCK)  //非阻塞操作  如果无法获取信号量，就立即返回{if (down_trylock(&button_lock))return -EBUSY;}else    //阻塞操作  陷入休眠，一直等待{/* 获取信号量 */down(&button_lock);  //如果无法获取信号量，应用程序就会陷入休眠}/* 配置GPF0,2为输入引脚 *//* 配置GPG3,11为输入引脚 */request_irq(IRQ_EINT0,  buttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]);request_irq(IRQ_EINT2,  buttons_irq, IRQT_BOTHEDGE, "S3", &pins_desc[1]);request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "S4", &pins_desc[2]);request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "S5", &pins_desc[3]);return 0;}ssize_t sixth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos){if (size != 1)return -EINVAL;if (file->f_flags & O_NONBLOCK)  //如果是非阻塞操作{if (!ev_press)   //如果没有按键按下，即ev_press=0，就立即返回return -EAGAIN;}else     //是阻塞操作{/* 如果没有按键动作, 休眠 */wait_event_interruptible(button_waitq, ev_press);}/* 如果有按键动作, 返回键值 */copy_to_user(buf, &key_val, 1);ev_press = 0;return 1;}int fifth_drv_close(struct inode *inode, struct file *file){free_irq(IRQ_EINT0, &pins_desc[0]);free_irq(IRQ_EINT2, &pins_desc[1]);free_irq(IRQ_EINT11, &pins_desc[2]);free_irq(IRQ_EINT19, &pins_desc[3]);up(&button_lock);  //释放信号量return 0;}static unsigned fifth_drv_poll(struct file *file, poll_table *wait){unsigned int mask = 0;poll_wait(file, &button_waitq, wait); // 不会立即休眠if (ev_press)mask |= POLLIN | POLLRDNORM;return mask;}static int fifth_drv_fasync (int fd, struct file *filp, int on){printk("driver: fifth_drv_fasync\n");return fasync_helper (fd, filp, on, &button_async);  //初始化&button_async结构体，给此结构体分配内存，此结构体包含了应用进程ID}static struct file_operations sencod_drv_fops = {    .owner   =  THIS_MODULE,    /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */    .open    =  fifth_drv_open,     .read =fifth_drv_read,   .release =  fifth_drv_close,.poll    =  fifth_drv_poll,.fasync =  fifth_drv_fasync,};int major;static int fifth_drv_init(void){major = register_chrdev(0, "fifth_drv", &sencod_drv_fops);fifthdrv_class = class_create(THIS_MODULE, "fifth_drv");fifthdrv_class_dev = class_device_create(fifthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);gpfdat = gpfcon + 1;gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);gpgdat = gpgcon + 1;return 0;}static void fifth_drv_exit(void){unregister_chrdev(major, "fifth_drv");class_device_unregister(fifthdrv_class_dev);class_destroy(fifthdrv_class);iounmap(gpfcon);iounmap(gpgcon);return 0;}module_init(fifth_drv_init);module_exit(fifth_drv_exit);MODULE_LICENSE("GPL");

修改的地方有：

1.83行，在fifth_drv_open()函数里，添加了阻塞与非阻塞的判断。并执行相应程序。

if (file->f_flags & O_NONBLOCK)  //非阻塞操作  如果无法获取信号量，就立即返回{if (down_trylock(&button_lock))return -EBUSY;}else    //阻塞操作  陷入休眠，一直等待{/* 获取信号量 */down(&button_lock);  //如果无法获取信号量，应用程序就会陷入休眠}

阻塞方式还是非阻塞方式，是由应用程序传入的。

2.109行，在sixth_drv_read()函数里，添加了阻塞与非阻塞的判断。

if (file->f_flags & O_NONBLOCK)  //如果是非阻塞操作{if (!ev_press)   //如果没有按键按下，即ev_press=0，就立即返回return -EAGAIN;}else     //是阻塞操作{/* 如果没有按键动作, 休眠 */wait_event_interruptible(button_waitq, ev_press);}

以阻塞方式打开的测试程序：

#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <stdio.h>#include <poll.h>#include <signal.h>#include <sys/types.h>#include <unistd.h>#include <fcntl.h>/* sixthdrvtest   */int fd;void my_signal_fun(int signum){unsigned char key_val;read(fd, &key_val, 1);printf("key_val: 0x%x\n", key_val);}int main(int argc, char **argv){unsigned char key_val;int ret;int Oflags;//fd = open("/dev/buttons", O_RDWR | O_NONBLOCK); //非阻塞的方式fd = open("/dev/buttons", O_RDWR); //阻塞的方式if (fd < 0){printf("can't open!\n");return -1;}while (1){ret = read(fd, &key_val, 1);printf("key_val: 0x%x, ret = %d\n", key_val, ret);//sleep(5);}return 0;}

主函数里死循环ret = read(fd, &key_val, 1)，对应到驱动程序里sixth_drv_read(),当没有按键按下时，会在

/* 如果没有按键动作, 休眠 */wait_event_interruptible(button_waitq, ev_press);

这里陷入休眠，然后有按键按下，调用中断服务函数，修改ev_press = 1;唤醒休眠状态，接着执行后面的程序：

/* 如果有按键动作, 返回键值 */copy_to_user(buf, &key_val, 1);ev_press = 0;return 1;

回到主函数，打印key_val的值。

以非阻塞方式打开的测试程序：

#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <stdio.h>#include <poll.h>#include <signal.h>#include <sys/types.h>#include <unistd.h>#include <fcntl.h>/* sixthdrvtest   */int fd;void my_signal_fun(int signum){unsigned char key_val;read(fd, &key_val, 1);printf("key_val: 0x%x\n", key_val);}int main(int argc, char **argv){unsigned char key_val;int ret;int Oflags;//fd = open("/dev/buttons", O_RDWR); //阻塞的方式fd = open("/dev/buttons", O_RDWR | O_NONBLOCK); //非阻塞的方式if (fd < 0){printf("can't open!\n");return -1;}while (1){ret = read(fd, &key_val, 1);printf("key_val: 0x%x, ret = %d\n", key_val, ret);sleep(5);   //延时5s}return 0;}

终端会每5秒输出一次。