linux设备驱动--等待队列实现

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include "ioctl_led.h"

#define DEV_NAME	"test-dev"
volatile bool empty = true;
//定义一个进程资源的指针变量
struct task_struct *task;

int test_open(struct inode *inode, struct file *filp)
{
	printk("test open\n");
	return 0;
}

int test_close(struct inode *inode, struct file *filp)
{
	printk("test close\n");
	return 0;
}

ssize_t test_read(struct file *filp, char __user *buf, size_t size, loff_t *off)
{
	int ret;
	//如果为真，那么就开始读
	while(empty)
	{
		//f_flags 指的是对应open调用的时候所指定的flag
		//O_NONBLOCK 非阻塞形式打开
		if(filp->f_flags & O_NONBLOCK)
		{
			return 0;
		}
		//current	(指向当前进程的task_struct)
		//(内核栈的底部thread_info.task)
		task = current;
		//设置当前进程的状态为TASK_INTERRUPTIBLE
		//TASK_INTERRUPTIBLE是阻塞态，进程当前正在等待除CPU外的其他系统资源,可以被信号唤醒.
		set_current_state(TASK_INTERRUPTIBLE);
		//通知调度器执行调度。
		schedule();
		if(signal_pending(current))
			return -ERESTARTSYS;
		//	return -EAGAIN;	

		printk("read: wake up\n");
	}

	ret = size;
	empty = true;
	return ret;
}

ssize_t test_write(struct file *filp, const char __user *buf, size_t size, loff_t *off)
{
	int ret;

	empty = false;
	wake_up_process(task);
	ret = size;

	return ret;
}

int major = 0;
struct file_operations fops = {
	.open = test_open,
	.release = test_close,
	.read = test_read,
	.write = test_write,
};

//模块;
int test_init(void)
{
	int ret;
	printk("test init\n");
	//注册一个字符设备驱动
	ret = register_chrdev(major, DEV_NAME, &fops);
	if(ret < 0)
		return ret;
	else
	{
		if(0 == major)
		{
			major = ret;
			printk("major = %d\n", major);
		}
	}

	return 0;
}

void test_exit(void)
{
	printk("test exit\n");
	//撤销字符设备
	unregister_chrdev(major, DEV_NAME);
}

module_init(test_init);
module_exit(test_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("yang.yx");
MODULE_VERSION("1.1");

Makefile

obj-m	+= test.o

ROOTFS = /rootfs
KERNEL_SRC	= /lib/modules/`uname -r`/build

all:
	make -C $(KERNEL_SRC) M=`pwd` modules

clean:
	make -C $(KERNEL_SRC) M=`pwd` clean
	rm -rf app

install:
	make -C $(KERNEL_SRC) M=`pwd` modules_install INSTALL_MOD_PATH=$(ROOTFS)

app:
	arm-linux-gcc app.c -o app

ioctl.c

#ifndef	__IOCTL_H__
#define __IOCTL_H__

#include <linux/ioctl.h>

#define LED_TYPE		0x1

#define LED_ALLON		_IO(LED_TYPE, 0)
#define LED_ALLOFF		_IO(LED_TYPE, 1)
#define LED_ON			_IOW(LED_TYPE, 2, int)
#define LED_OFF			_IOW(LED_TYPE, 3, int)

#endif