kill_fasync()异步通知

  阻塞与非阻塞访问、poll函数提供了较好的解决设备访问的机制，但是如果有了异步通知，整套机制则更加完整了。

  异步通知的意思是：一旦设备就绪，则主动通知应用程序，这样应用程序根本就不需要查询设备状态，这一点非常类似于硬件上“中断”的概念，比较准确的称谓是“信号驱动的异步I/O”。信号是在软件层次上对中断机制的一种模拟，在原理上，一个进程收到一个信号与处理器收到一个中断请求可以说是一样的。信号是异步的，一个进程不必通过任何操作来等待信号的到达，事实上，进程也不知道信号到底什么时候到达。
  阻塞I/O意味着一直等待设备可访问后再访问，非阻塞I/O中使用poll（）意味着查询设备是否可访问，而异步通知则意味着设备通知用户自身可访问，之后用户再进行I/O处理。由此可见，这几种I/O方式可以相互补充。

使用kill_fasync()异步通知实现按键处理

1、应用层

#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>
 
 
/* fifthdrvtest 
  */
int fd;
 
//信号处理函数
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;
 
	//在应用程序中捕捉SIGIO信号（由驱动程序发送）
	signal(SIGIO, my_signal_fun);
	
	fd = open("/dev/buttons", O_RDWR);
	if (fd < 0)
	{
		printf("can't open!\n");
	}
 
	//将当前进程PID设置为fd文件所对应驱动程序将要发送SIGIO,SIGUSR信号进程PID
	fcntl(fd, F_SETOWN, getpid());
	
	//获取fd的打开方式
	Oflags = fcntl(fd, F_GETFL); 
 
	//将fd的打开方式设置为FASYNC --- 即 支持异步通知
	//该行代码执行会触发 驱动程序中 file_operations->fasync 函数 ------fasync函数调用fasync_helper初始化一个fasync_struct结构体，该结构体描述了将要发送信号的进程PID (fasync_struct->fa_file->f_owner->pid)
	fcntl(fd, F_SETFL, Oflags | FASYNC);
 
 
	while (1)
	{
		sleep(1000);
	}
	
	return 0;
}

2、驱动层

#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;
 
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;
 
/*
 * K1,K2,K3,K4对应GPG0，GPG3，GPG5，GPG6
 */
 
struct pin_desc pins_desc[4] = {
	{S3C2410_GPG0, 0x01},
	{S3C2410_GPG3, 0x02},
	{S3C2410_GPG5, 0x03},
	{S3C2410_GPG6, 0x04},
};
 
 
/*
  * 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 */
	
    	//发送信号SIGIO信号给fasync_struct 结构体所描述的PID，触发应用程序的SIGIO信号处理函数
	kill_fasync (&button_async, SIGIO, POLL_IN);
	
	return IRQ_RETVAL(IRQ_HANDLED);
}
 
static int fifth_drv_open(struct inode *inode, struct file *file)
{
	/* GPG0，GPG3，GPG5，GPG6为中断引脚: EINT8,EINT11,EINT13,EINT14 */
	request_irq(IRQ_EINT8,  buttons_irq, IRQT_BOTHEDGE, "K1", &pins_desc[0]);
	request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "K2", &pins_desc[1]);
	request_irq(IRQ_EINT13, buttons_irq, IRQT_BOTHEDGE, "K3", &pins_desc[2]);
	request_irq(IRQ_EINT14, buttons_irq, IRQT_BOTHEDGE, "K4", &pins_desc[3]);	
 
	return 0;
}
 
ssize_t fifth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
	if (size != 1)
		return -EINVAL;
 
	/* 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_EINT8,  &pins_desc[0]);
	free_irq(IRQ_EINT11, &pins_desc[1]);
	free_irq(IRQ_EINT13, &pins_desc[2]);
	free_irq(IRQ_EINT14, &pins_desc[3]);
	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");
	//初始化/释放 fasync_struct 结构体 (fasync_struct->fa_file->f_owner->pid)
	return fasync_helper (fd, filp, on, &button_async);
}
 
 
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;
 
	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);
	return 0;
}
 
 
module_init(fifth_drv_init);
 
module_exit(fifth_drv_exit);
 
MODULE_LICENSE("GPL");