宋宝华《Linux设备驱动开发详解》示例代码之fifo字符设备驱动

最新推荐文章于 2025-01-10 09:17:40 发布

bg2bkk

最新推荐文章于 2025-01-10 09:17:40 发布

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分类专栏： LDD3学习

本文链接：https://blog.youkuaiyun.com/bg2bkk/article/details/8946345

本文展示了宋宝华《Linux设备驱动开发详解》中的fifo字符设备驱动代码，包括scull.c、load_scull.sh、unload_scull.sh和test.sh四个部分。在运行测试脚本后，通过echo命令向/dev/scull写入数据，当超过设备缓冲区16B限制时，只能读取，无法再写入。

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驱动代码如下：

scull.c

#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/cdev.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/gfp.h>
#include <linux/poll.h>
#include <asm/uaccess.h>

#define	SCULL_MAJOR	252
#define SCULL_NAME	"scull"
#define MAX_DATA	0x10

static	int scull_major = SCULL_MAJOR;
struct scull_dev {
	struct cdev cdev;
	unsigned char data[MAX_DATA];
	struct semaphore sem;
	unsigned int current_len;
	wait_queue_head_t r_wait;
	wait_queue_head_t w_wait;
};

MODULE_LICENSE("GPL");
MODULE_AUTHOR("BG2BKK");

struct	scull_dev *scull_devp;

int	scull_open(struct inode *inode, struct file *filp)
{
	struct scull_dev *dev = container_of(inode->i_cdev, struct scull_dev, cdev);
	filp->private_data = dev;
	printk(KERN_ALERT "open the scull device\n");
	return 0;
}

int	scull_release(struct inode *inode, struct file *filp)
{
	printk(KERN_ALERT "close the scull device\n");
	return 0;
}

ssize_t	scull_read(struct file *filp, char __user *buf, size_t count, loff_t *f_ops)
{
	struct scull_dev *dev = filp->private_data;
	int ret = 0;
	DECLARE_WAITQUEUE(wait, current);

	down(&dev->sem);
	add_wait_queue(&dev->r_wait, &wait);
	while(dev->current_len == 0)
	{
		if(filp->f_flags & O_NONBLOCK)
		{
			ret = -EAGAIN;
			goto out;
		}
		__set_current_state(TASK_INTERRUP