drive.c

一个linux下字符设备驱动程序的编写例子

#include<linux/module.h>
#include<linux/kernel.h>
#include<linux/fs.h>         

MODULE_LICENSE("GPL");

char mybuf[1024]="SCHOOL   :     HUST                     \nSEX    :      BOY                       \nNAME   :    Zhang  Fuqiang              \nNO.   :    012004016415                 \nTEACHER  :    Pang  Lipin               \n";
int mychardrv_devnum;	

static int mychardrv_open(struct inode *inode,struct file*filp);
static int mychardrv_read(struct file * filp,char *buf,size_t count, loff_t *f_pos);
static int mychardrv_write(struct file * filp,const char *buf,size_t count,loff_t *ppos);
static int mychardrv_release(struct inode* inode,struct file * filp);
static loff_t mychardrv_lseek (struct file * file, loff_t offset,int orig);

struct file_operations mychardrv_ops=       
{   open:  mychardrv_open,
    read:  mychardrv_read,
    write: mychardrv_write,  
    release: mychardrv_release,
    llseek:mychardrv_lseek,
};

int mychardrv_read(struct file * filp,char *buf,size_t count, loff_t *f_pos)
{	
	loff_t pos;
	pos=*f_pos;
	if(pos+count>1024)
		count=1024-pos;	
	strncpy(buf,mybuf+pos,count);                             
	return count;
}

static int mychardrv_write(struct file * filp,const char *buf,size_t count,loff_t *ppos)
{	
	loff_t pos;
	pos=*ppos;
	if(pos+count>1024)
		count=1024-pos;
	strncpy(mybuf+pos,buf,count);
	return count;
}



int mychardrv_open(struct inode *inode,struct file*filp)
{	
	filp->f_op=&mychardrv_ops;
	return 0;
}

int mychardrv_release(struct inode* inode,struct file * filp)
{
	return 0;
}

loff_t mychardrv_lseek (struct file * file,loff_t offset,int orig)
{
	loff_t pos;
	pos = file->f_pos;
	switch (orig) {
	case 0:
                      	pos = offset;
		break;
	case 1:
		pos += offset;
		break;
	case 2:
		pos = 1024-offset;
		break;
	default:
		return -1;
	}
	return file->f_pos = pos;
}



int init_module(void)    
{	int result;	
	result=register_chrdev(0,"mychardrv",&mychardrv_ops);
	if(result<0)
	{	printk("Unable to get devnum!!!!!\n");
		return -1;
        	}
	if(mychardrv_devnum==0) 
		mychardrv_devnum=result;
	printk("Succeed in getting buffer!!!!\n");
	return 0;
}

void cleanup_module(void)    
{	
	unregister_chrdev(mychardrv_devnum,"mychardrv");
	printk("Succeed in unload the moudle!!!\n");
}
 
/*加载之后通过命令	mknod /dev/mychardev  c  254  0                来创建设备文件

		设备号可通过命令 cat    /proc/devices看到mychardrv所分配得到的设备号
然后编写测试程序打开该设备文件进行读写操作
*/