驱动中的同步互斥阻塞之原子量

目的：只能有一个app打开驱动程序

1.原子操作

原子操作指的是在执行过程中不会被别的代码路径所中断的操作

常用原子操作函数举例

atomic_v  v=ATOMIC_INIT(0);  //定义原子变量v并初始化为0

atomic_read(atomic_t *v); //返回原子变量的值

void atomic_inc(atomic_t *v);//原子变量增加1

void atomic_dec(atomic_t *v);//原子变量减少1

int atomic_dec_and_test(atomic_t *v);//自减操作后测试其是否为0，为0返回true，否则返回false

范例代码如下

#include <linux/device.h>#include <linux/interrupt.h>#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 <mach/gpio.h>#include<linux/cdev.h>#include <linux/poll.h>int key_id;struct cdev cdev;dev_t devno;static atomic_t canopen=ATOMIC_INIT(1); //定义原子变量，并初始化为1static DECLARE_WAIT_QUEUE_HEAD(key_qaq);/*等待队列头*//*中断事件标志，中断服务程序将它置为1，read函数将它置为0*/unsigned int wait_val=0;struct class *my_class;static irqreturn_t key_func(int irq,void *dev_id){key_id=(int)dev_id;/*唤醒*/wait_val=1;wake_up_interruptible(&key_qaq);return 0;}static int key_open(struct inode *inode,struct file *file){if(!atomic_dec_and_test(&canopen)){atomic_inc(&canopen);return -EBUSY;}request_irq(IRQ_EINT(16),key_func,IRQF_TRIGGER_FALLING,"k1",1);request_irq(IRQ_EINT(17),key_func,IRQF_TRIGGER_FALLING,"k2",2);request_irq(IRQ_EINT(18),key_func,IRQF_TRIGGER_FALLING,"k3",3);request_irq(IRQ_EINT(19),key_func,IRQF_TRIGGER_FALLING,"k4",4);request_irq(IRQ_EINT(24),key_func,IRQF_TRIGGER_FALLING,"k5",5);request_irq(IRQ_EINT(25),key_func,IRQF_TRIGGER_FALLING,"k6",6);request_irq(IRQ_EINT(26),key_func,IRQF_TRIGGER_FALLING,"k7",7);request_irq(IRQ_EINT(27),key_func,IRQF_TRIGGER_FALLING,"k8",8);return 0;}static int key_close(struct inode *inode,struct file *file){atomic_inc(&canopen);free_irq(IRQ_EINT(16),1);free_irq(IRQ_EINT(17),2);free_irq(IRQ_EINT(18),3);free_irq(IRQ_EINT(19),4);free_irq(IRQ_EINT(24),5);free_irq(IRQ_EINT(25),6);free_irq(IRQ_EINT(26),7);free_irq(IRQ_EINT(27),8);return 0;}ssize_t key_read(struct file *filp, char __user *buf, size_t size,loff_t *pos){/*如果没有按键按下，休眠，让出CPU*/wait_event_interruptible(key_qaq,wait_val);/*如果有按键按下*/copy_to_user(buf,&key_id,sizeof(key_id)); wait_val=0;return 0;}static unsigned key_poll(struct file *file, poll_table *wait){unsigned int mask=0;poll_wait(file,&key_qaq,wait);/*不会立即休眠，只是挂在那个队列上面去*/if(wait_val)mask |= POLLIN | POLLRDNORM;return mask;}static struct file_Operations key_fops ={.owner = THIS_MODULE,.open = key_open,.release = key_close,.read = key_read,.poll = key_poll,};static int __init key_atomic_init(void){cdev_init(&cdev,&key_fops);alloc_chrdev_region(&devno, 0 , 1 , "mykey_atomic");cdev_add(&cdev, devno, 1);my_class = class_create(THIS_MODULE, "key_atomic_class");if(IS_ERR(my_class)){PRintk("Err: failed in creating class./n");return -1;}device_create(my_class, NULL, devno,NULL,"key_atomic_driver");return 0;}static void key_atomic_exit(void){device_destroy(my_class,devno);class_destroy(my_class);cdev_del(&cdev);unregister_chrdev_region(devno,1);}module_init(key_atomic_init);module_exit(key_atomic_exit);MODULE_LICENSE("GPL");MODULE_AUTHOR("EIGHT_FIVE");

测试程序如下

#include<stdio.h>#include<sys/ioctl.h>#include<sys/types.h>#include<sys/stat.h>#include<fcntl.h>int main(int argv,char **argc){int fd,buf;fd=open("/dev/key_atomic_driver",0x666);if(fd<0){printf("can't open/n");return -1;}while(1){read(fd,&buf,4);printf("key_val =%d/n",buf);}close(fd);return 0;}