实现的功能是在读取按键信息的时候，如果没有产生按键，则程序休眠在read函数中，利用poll机制，可以在没有退出的情况下让程序自动退出。
下面的程序就是在读取按键信息的时候，如果5000ms内没有按键信息，则自己退出。
首先应用程序执行poll函数
kernel中的sys_poll
do_sys_poll
init_poll_funcptr-->do_poll
do_poll
for(;;)
{
if(do_pollfd(pfd,pt))
{
count++; //如果驱动的poll返回非0值，那么count++
//把进程挂到队列中休眠
pt=null;}
if( count || !*timeout || signal_pending(current))
break; //如果count非0 超时， 有信号等待处理
}
__timeout = schedule_timeout(__time_out); //休眠 下次执行到上面的判断时，就会超时退出
驱动代码：
#include <linux/sched.h>
#include <linux/signal.h>
#include <linux/spinlock.h>
#include <linux/errno.h>
#include <linux/random.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/wait.h>
#include <linux/mutex.h>
#include <linux/io.h>
#include <asm/irq.h>
#include <linux/irq.h>
#include <linux/fs.h>
#include <asm/arch/regs-gpio.h>
#include <linux/interrupt.h>
#include <linux/poll.h> static struct class *key_class; //创建类
static struct class_device *key_class_devs; //创建类对应的设备 struct pin_desc{
unsigned int pin;
unsigned int key_val;
};
struct pin_desc pins_desc[] = {
{S3C2410_GPF0,0X01},
{S3C2410_GPF2,0X02},
{S3C2410_GPG3,0X03},
{S3C2410_GPG11,0X04},
};
unsigned char keyvals=; static volatile int ev_press = ;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq); static irqreturn_t keys_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)
{
keyvals = pindesc->key_val|0x80;
}
else
{
keyvals = pindesc->key_val;
}
ev_press = ;
wake_up_interruptible(&button_waitq);
return IRQ_HANDLED;
} int key_open(struct inode *inode, struct file *fp)
{
request_irq( IRQ_EINT0, keys_irq, IRQT_BOTHEDGE, "key2", &pins_desc[]);
request_irq( IRQ_EINT2, keys_irq, IRQT_BOTHEDGE, "key3", &pins_desc[]);
request_irq( IRQ_EINT11, keys_irq, IRQT_BOTHEDGE, "key4", &pins_desc[]);
request_irq( IRQ_EINT19, keys_irq, IRQT_BOTHEDGE, "key5", &pins_desc[]);
return ;
} ssize_t key_read(struct file *fp, char __user *buff, size_t count, loff_t *offp){ if(count != )
{
return -EINVAL;
}
wait_event_interruptible(button_waitq,ev_press); copy_to_user(buff,&keyvals,);
ev_press = ;
return ;
} ssize_t key_write(struct file *fp, const char __user *buf, size_t count, loff_t *ppos){
} int key_close(struct inode *inode, struct file *file)
{
free_irq(IRQ_EINT0,&pins_desc[]);
free_irq(IRQ_EINT2,&pins_desc[]);
free_irq(IRQ_EINT11,&pins_desc[]);
free_irq(IRQ_EINT19,&pins_desc[]);
} static unsigned int key_poll(struct file *file, struct poll_table_struct *wait)
{
unsigned int mask = ;
poll_wait(file, &button_waitq,wait);
if(ev_press)
mask |= POLLIN|POLLRDNORM;
return mask;
} struct file_operations led_fops={
.owner = THIS_MODULE,
.open = key_open,
.write = key_write,
.read = key_read,
.release = key_close,
.poll = key_poll,
}; int major;
static int key_init(void)
{
major = register_chrdev( ,"key_drv", &led_fops );
key_class = class_create(THIS_MODULE,"key_class");
key_class_devs = class_device_create(key_class,NULL,MKDEV(major,),NULL,"my_keys"); printk("key install Module\n");
return ;
} static void key_exit(void)
{
unregister_chrdev( major, "key_drv" );
class_device_unregister(key_class_devs);
class_destroy(key_class);
printk("key Module exit\n");
} module_init(key_init);
module_exit(key_exit);
MODULE_LICENSE("GPL");
应用测试代码：
#include <stdio.h>
#include <fcntl.h>
#include <poll.h> int main()
{
int fd;
int ret;
struct pollfd pfd[];
unsigned char key_val;
fd = open("/dev/my_keys",O_RDWR);
if(fd<)
{
printf("open failed\n");
return ;
}
pfd[].fd = fd;
pfd[].events = POLLIN;
while()
{
ret = poll(pfd, , ); //如果在5000ms之内没有按下按键 这自动退出
// read(fd, &key_val,1);
if(ret==)
printf("time out\n");
else
{
read(fd, &key_val,);
printf("key:%x\n",key_val);
}
}
}
sd