今年带软件08级童鞋LinuxOS试验的时候，导师让我写一个最简单的字符设备驱动，以便让从未接触过的初学者快速入门。代码参考如下。

字符设备驱动程序：

#include < linux/init.h >
#include < linux/module.h >
#include < linux/types.h >
#include < linux/fs.h >
#include < asm/uaccess.h >
#include < linux/cdev.h >

MODULE_AUTHOR("Edsionte Wu");
MODULE_LICENSE("GPL");

#define MYCDEV_MAJOR 231 /*the predefined mycdev's major devno*/
#define MYCDEV_SIZE 100

static int mycdev_open(struct inode *inode, struct file *fp)
{
	return 0;
}

static int mycdev_release(struct inode *inode, struct file *fp)
{
	return 0;
}

static ssize_t mycdev_read(struct file *fp, char __user *buf, size_t size, loff_t *pos)
{
	unsigned long p = *pos;
	unsigned int count = size;
	int i;
	char kernel_buf[MYCDEV_SIZE] = "This is mycdev!";

	if(p >= MYCDEV_SIZE)
		return -1;
	if(count > MYCDEV_SIZE)
		count = MYCDEV_SIZE - p;

	if (copy_to_user(buf, kernel_buf, count) != 0) {
		printk("read error!\n");
		return -1;
	}

	/*
	for (i = 0; i < count; i++) {
		__put_user(i, buf);//write 'i' from kernel space to user space's buf;
		buf++;
	}
	*/

	printk("edsionte's reader: %d bytes was read...\n", count);
	return count;

}

static ssize_t mycdev_write(struct file *fp, const char __user *buf, size_t size, loff_t *pos)
{
	return size;
}

/*filling the mycdev's file operation interface in the struct file_operations*/
static const struct file_operations mycdev_fops =
{
	.owner = THIS_MODULE,
	.read = mycdev_read,
	.write = mycdev_write,
	.open = mycdev_open,
	.release = mycdev_release,
};

/*module loading function*/
static int __init mycdev_init(void)
{
	int ret;

	printk("mycdev module is staring..\n");

	ret=register_chrdev(MYCDEV_MAJOR,"edsionte_cdev",&mycdev_fops);
	if(ret<0)
	{
		printk("register failed..\n");
		return 0;
	}
	else
	{
		printk("register success..\n");
	}

	return 0;
}

/*module unloading function*/
static void __exit mycdev_exit(void)
{
	printk("mycdev module is leaving..\n");
	unregister_chrdev(MYCDEV_MAJOR,"edsionte_cdev");
}

module_init(mycdev_init);
module_exit(mycdev_exit);

Makefile文件:

obj-m:=mycdev.o
PWD:=$(shell pwd)
CUR_PATH:=$(shell uname -r)
KERNEL_PATH:=/usr/src/linux-headers-$(CUR_PATH)

all:
	make -C $(KERNEL_PATH) M=$(PWD) modules
clean:
	make -C $(KERNEL_PATH) M=$(PWD) clean

用户态测试程序：

#include < stdio.h >
#include < sys/types.h >
#include < sys/stat.h >
#include < fcntl.h >
#include < stdlib.h >

int main()
{
	int testdev;
	int i, ret;
	char buf[15];

	testdev = open("/dev/mycdev", O_RDWR);

	if (-1 == testdev) {
		printf("cannot open file.\n");
		exit(1);
	}

	if (ret = read(testdev, buf, 15) < 15) {
		printf("read error!\n");
		exit(1);
	}

	printf("%s\n", buf);

	close(testdev);

	return 0;
}

使用方法：

1.make编译mycdev.c文件，并插入到内核；
2.通过cat /proc/devices 查看系统中未使用的字符设备主设备号，比如当前231未使用；
3.创建设备文件结点：sudo mknod /dev/mycdev c 231 0；具体使用方法通过man mknod命令查看；
4.修改设备文件权限：sudo chmod 777 /dev/mycdev；
5.以上成功完成后，编译本用户态测试程序；运行该程序查看结果；
6.通过dmesg查看日志信息；

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