Linux kernel 中的轮询操作-select poll

轮询操作：应用程序通常会使用select()系统调用查询是否可对设备进行无阻塞的访问。

该函数通过系统调用最终会引发设备驱动中的poll()函数被执行

该机制还可以实现一个用户进程对多个设备驱动文件的监测

轮询操作应用层接口函数介绍：

文件描述符集合的基本操作：

文件描述符集合的变量的定义

fd_set fds；

清空描述符集合

FD_ZERO(fd_set *set);

加入一个文件描述符到集合中

FD_SET(int fd, fd_set *set);

文件描述符集合的辅助操作：

从集合中清除一个文件描述符

FD_CLR(int fd, fd_set *set);

判断文件描述符是否被置位

FD_ISSET(int fd, fd_set *set);

返回非0，表示置位

（该文件描述集合中有文件可进行读写操作，或产

生错误）

#include <sys/select.h>

在应用程序中调用的文件描述符监测函数

int select(int numfds,

fd_set *readfds,

fd_set *writefds,

fd_set *exceptfds,

struct timeval *timeout);

参数1 numfds： 待监听中最大描述符值加一

参数2 readfds： 监听读操作的文件描述符集合

参数3 writefds： 监听写操作的文件描述符集合

参数4 exceptfds：监听异常处理的文件描述符集合

参数5 timeout: 监听等待超时退出select()

轮询操作驱动层接口函数介绍：

poll()函数：为file_operation成员之一

static unsigned int poll(struct file *file,

struct poll_table_struct *wait)

参数file:是文件结构指针

参数wait:轮询表指针，管理着一系列等待列表

注：以上两个参数是由内核传递给poll函数

//添加等待队列到wait参数指定的轮询列表中

void poll_wait(struct file *filp,

wait_queue_heat_t *wq, poll_table *wait);

poll_wait()将可能引起文件状态变化的进程添加到轮询列

表，由内核去监听进程状态的变化，不会阻塞进程

一旦进程有变化(wake_up)，内核就会自动去调用poll()而poll()是返回给select()的，所以当进程被唤醒poll(应该将状态掩码返回给select()，从而select()退出阻塞。完成一次监测，poll函数被调用一次或两次

第一次为用户执行select函数时被执行

第二次调用poll为内核监测到进程的wake_up操作时或进程休眠时间到唤醒再或被信号唤醒时

poll函数返回的状态掩码

可读状态掩码

POLLIN:有数据可读

POLLRDNORM:有普通数据可读

POLLRDBAND:有优先数据可读

POLLPRI:有紧迫数据可读

可写状态掩码

POLLOUT:写数据不会导致阻塞

POLLWRNORM:写普通数据不会导致阻塞

POLLWRBAND:写优先数据不会导致阻塞

POLLMSG/SIGPOLL:消息可用

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/select.h>

int main()
{
	char *devname1 = "/dev/key8_eint";
	char *devname2 = "/dev/key2_eint";

	int fd1,fd2,fd_max;
	unsigned char key;
	int retval;
	
	fd1 = open(devname1, O_RDONLY);
	if (fd1 < 0){
		perror("open key_eint2_poll");
		exit(1);
	}
	
	fd2 = open(devname2, O_RDONLY);
	if (fd2 < 0){
		perror("open key_eint3_poll");
		exit(1);
	}
	
	while(1){
		fd_set rds;
		int ret;
		
		FD_ZERO(&rds);
		FD_SET(fd1, &rds);
		FD_SET(fd2, &rds);
		
		if(fd1 > fd2)
			fd_max = fd1;
		else
			fd_max = fd2;
	
		/*使用select监听设备描述符是否有变化*/
		retval = select(fd_max + 1, &rds, NULL,NULL, NULL);
		
		switch(retval){
			case -1 :
				perror("select");
				exit(1); 
				break;
			case 0 :
				printf("Timeout.\n"); 
				break;
			default:
				printf("the ret is %d\n",ret);
				if (FD_ISSET(fd1, &rds)) /*检查是否有数据可读*/
				{
					ret = read(fd1,&key, sizeof(key));
					printf("the key = %d\n",key);
				}
				else if (FD_ISSET(fd2, &rds)) /*检查是否有数据可读*/
				{
					ret = read(fd2,&key, sizeof(key));
					printf("the key = %d\n",key);
				}	
		}			
	}
	close(fd1);
	close(fd2);
}

#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 <mach/regs-gpio.h>  

#include <linux/poll.h>  //poll_wait()

#define EINT_DEVICE_ID			1

#define DRIVER_NAME				"key8_eint"
#define err(msg) 				printk(KERN_ERR "%s: " msg "\n", DRIVER_NAME)
#define __debug(fmt, arg...)	printk(KERN_DEBUG fmt, ##arg)

#define GPH3CON					(unsigned long)(S5PV210_GPH3_BASE+ 0x00)
#define GPH3DAT					(unsigned long)(S5PV210_GPH3_BASE + 0x04)

#define GPH2UP					(unsigned long)(S5PV210_GPH2_BASE + 0x08)

static int major = 0;		
static int minor = 0;		
struct class *key_class;
static struct device *key_device;

/*定义等待队列头，该等待队列头属于该驱动程序*/
static wait_queue_head_t wait_queue;
static unsigned char key;

irqreturn_t buttons_interrupt(int irq, void *dev_id)
{	
	key = (unsigned int)dev_id;

	wake_up_interruptible(&wait_queue);			//唤醒等待队列
	return IRQ_HANDLED;
}

static void key_io_port_init(void)
{
	unsigned long reg_val;
	
	reg_val = readl(GPH3CON);
	reg_val &= ~((0x0f<<0) | (0x0f<<4));
	reg_val |= ((0x01<<0) | (0x01<<4));
	writel(reg_val, GPH3CON);

	reg_val = readl(GPH3DAT);
	reg_val &= ~((0x01<<0) | (0x01<<1));
	writel(reg_val, GPH3DAT);

	reg_val = readl(GPH2UP);
	reg_val &= ~(0x03<<8);
	reg_val |= 0x02<<8;
	writel(reg_val, GPH2UP);
}

static ssize_t key_read(struct file *filp, char *buf, size_t count, loff_t *f_pos)
{
	int key_num;
	int cpy_len;
	int retval;

	key_num = key;		//读取键值
	key = 0;
	cpy_len = min(sizeof(key_num), count);
	retval = copy_to_user(buf, &key_num, cpy_len);
	
	return (cpy_len - retval);
}

static unsigned int key_poll(struct file *file, struct poll_table_struct *wait)
{
	/*将当前进程添加到队列列表中，但不挂起该进程*/
	poll_wait(file, &wait_queue, wait);
	/*根据当前的键值返回适当的状态掩码*/
	return key==0 ? 0 : POLLIN | POLLRDNORM;
}

/* Driver Operation structure */
static struct file_operations key_fops = {
	.owner = THIS_MODULE,
	.read = key_read,
	.poll = key_poll,
};


static int __init key_eint_init(void)
{
	int retval;
	

	key_io_port_init();

	init_waitqueue_head(&wait_queue);			//初始化等待队列头
	
	retval = set_irq_type(IRQ_EINT(20),IRQ_TYPE_EDGE_FALLING);
	if(retval){
		err("IRQ_EINT20 set irq type failed");
		goto error;
	}
	
	retval = request_irq(IRQ_EINT(20), buttons_interrupt, IRQF_DISABLED, 
			"KEY1", (void *)EINT_DEVICE_ID);
	if(retval){
		err("request eint20 failed");
		goto error;
	}
	
	
	major = register_chrdev(major, DRIVER_NAME, &key_fops);
	if(major < 0){
		err("register char device fail");
		retval = major;
		goto error_register;
	}
	key_class=class_create(THIS_MODULE,DRIVER_NAME);
	if(IS_ERR(key_class)){
		err("class create failed!");
		retval =  PTR_ERR(key_class);
		goto error_class;
	}
	key_device=device_create(key_class,NULL, MKDEV(major, minor), NULL,DRIVER_NAME);
	if(IS_ERR(key_device)){
		err("device create failed!");
		retval = PTR_ERR(key_device);
		goto error_device;
	}
	__debug("register myDriver OK! Major = %d\n", major);
	return 0;

error_device:
	class_destroy(key_class);
error_class:
	unregister_chrdev(major, DRIVER_NAME);
error_register:
	free_irq(IRQ_EINT(20), (void *)EINT_DEVICE_ID);
error:
	return retval;
}

static void __exit key_eint_exit(void)
{
	//__debug("in key_eint_exit\n");
	
	free_irq(IRQ_EINT(20), (void *)EINT_DEVICE_ID);

	unregister_chrdev(major, DRIVER_NAME);
	device_destroy(key_class,MKDEV(major, minor));
	class_destroy(key_class);

	return;
}

module_init(key_eint_init);
module_exit(key_eint_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Eric");

 
#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 <mach/regs-gpio.h>  

#include <linux/poll.h>  //poll_wait()

#define EINT_DEVICE_ID			2

#define DRIVER_NAME			"key2_eint"
#define err(msg) 					printk(KERN_ERR "%s: " msg "\n", DRIVER_NAME)
#define __debug(fmt, arg...)		printk(KERN_DEBUG fmt, ##arg)

#define GPH3CON					(unsigned long)(S5PV210_GPH3_BASE+ 0x00)
#define GPH3DAT					(unsigned long)(S5PV210_GPH3_BASE + 0x04)

#define GPH2UP					(unsigned long)(S5PV210_GPH2_BASE + 0x08)

static int major = 0;		
static int minor = 0;		
struct class *key_class;
static struct device *key_device;

/*定义等待队列头，该等待队列头属于该驱动程序*/
static wait_queue_head_t wait_queue;
static unsigned char key;

irqreturn_t buttons_interrupt(int irq, void *dev_id)
{	
	key = (unsigned int)dev_id;

	wake_up_interruptible(&wait_queue);			//唤醒等待队列
	return IRQ_HANDLED;
}

static void key_io_port_init(void)
{
	unsigned long reg_val;
	
	reg_val = readl(GPH3CON);
	reg_val &= ~((0x0f<<0) | (0x0f<<4));
	reg_val |= ((0x01<<0) | (0x01<<4));
	writel(reg_val, GPH3CON);

	reg_val = readl(GPH3DAT);
	reg_val &= ~((0x01<<0) | (0x01<<1));
	writel(reg_val, GPH3DAT);

	reg_val = readl(GPH2UP);
	reg_val &= ~(0x03<<6);
	reg_val |= 0x02<<6;
	writel(reg_val, GPH2UP);
}

static ssize_t key_read(struct file *filp, char *buf, size_t count, loff_t *f_pos)
{
	int key_num;
	int cpy_len;
	int retval;

	key_num = key;		//读取键值
	key = 0;
	cpy_len = min(sizeof(key_num), count);
	retval = copy_to_user(buf, &key_num, cpy_len);
	
	return (cpy_len - retval);
}

static unsigned int key_poll(struct file *file, struct poll_table_struct *wait)
{
	/*将当前进程添加到队列列表中，但不挂起该进程*/
	poll_wait(file, &wait_queue, wait);
	/*根据当前的键值返回适当的状态掩码*/
	return key==0 ? 0 : POLLIN | POLLRDNORM;
}

/* Driver Operation structure */
static struct file_operations key_fops = {
	.owner = THIS_MODULE,
	.read = key_read,
	.poll = key_poll,
};


static int __init key_eint_init(void)
{
	int retval;
	

	key_io_port_init();

	init_waitqueue_head(&wait_queue);			//初始化等待队列头
	
	retval = set_irq_type(IRQ_EINT(19),IRQ_TYPE_EDGE_FALLING);
	if(retval){
		err("IRQ_EINT20 set irq type failed");
		goto error;
	}
	
	retval = request_irq(IRQ_EINT(19), buttons_interrupt, IRQF_DISABLED, 
			"KEY1", (void *)EINT_DEVICE_ID);
	if(retval){
		err("request eint20 failed");
		goto error;
	}
	
	
	major = register_chrdev(major, DRIVER_NAME, &key_fops);
	if(major < 0){
		err("register char device fail");
		retval = major;
		goto error_register;
	}
	key_class=class_create(THIS_MODULE,DRIVER_NAME);
	if(IS_ERR(key_class)){
		err("class create failed!");
		retval =  PTR_ERR(key_class);
		goto error_class;
	}
	key_device=device_create(key_class,NULL, MKDEV(major, minor), NULL,DRIVER_NAME);
	if(IS_ERR(key_device)){
		err("device create failed!");
		retval = PTR_ERR(key_device);
		goto error_device;
	}
	__debug("register myDriver OK! Major = %d\n", major);
	return 0;

error_device:
	class_destroy(key_class);
error_class:
	unregister_chrdev(major, DRIVER_NAME);
error_register:
	free_irq(IRQ_EINT(19), (void *)EINT_DEVICE_ID);
error:
	return retval;
}

static void __exit key_eint_exit(void)
{
	//__debug("in key_eint_exit\n");
	
	free_irq(IRQ_EINT(19), (void *)EINT_DEVICE_ID);

	unregister_chrdev(major, DRIVER_NAME);
	device_destroy(key_class,MKDEV(major, minor));
	class_destroy(key_class);

	return;
}

module_init(key_eint_init);
module_exit(key_eint_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("eric");