linux字符驱动insmod出现错误

[birdthree]

linux字符驱动insmod出现如下错误：

BUG: unable to handle kernel NULL pointer dereference at 00000014

关键代码：

struct mem_dev

{ 

	char *data;

	unsigned long size;

};



/*include semaphore ,cdev

*/

struct scull_dev   //我自己定义的一种字符设备，问题出自在各个？
但LDD上面写的可以将cdev结构嵌入到自己的设备特定结构中啊

{

	struct mem_dev *mem_devp;

	struct semaphore sem;	

	struct cdev cdev;

};

struct scull_dev *dev;


	/*setup cdev*/
printk("1111\n");     //执行完这一行后出错

	cdev_init(&dev->cdev, &scull_fops);	//问题就出现在这一行
printk("2222\n");

	dev->cdev.owner = THIS_MODULE;
printk("3333\n");

	dev->cdev.ops = &scull_fops;	//relate file_operations
printk("4444\n");

	if ((ret = cdev_add(&dev->cdev, devt, 1)))	//acknowledge kernel

	{

		printk(KERN_NOTICE "Error %d adding scull.\n", ret);

		return -1;

	}

	else

		printk("scull register success.\n");

dmesg调试结果：

[ 210.151746] alloc register successfully.
[ 210.160767] 1111
[ 210.161425] BUG: unable to handle kernel NULL pointer dereference at 00000014
[ 210.161655] IP: [<c020d503>] cdev_init+0x23/0x50


其他信息:

[birdthree]

独立的cdev结构我是能成功的，所用系统为ubuntu10.04

[nevil]

struct scull_dev *dev这行错了，应该是声明个结构struct scull_dev dev;

[birdthree]

[Quote=引用 2 楼 的回复:]

struct scull_dev *dev这行错了，应该是声明个结构struct scull_dev dev;
[/Quote]

如果只改这行，->这样的引用方式也是错的

这有什么区别呢

[nevil]

[Quote=引用 3 楼 的回复:]

引用 2 楼 的回复:

struct scull_dev *dev这行错了，应该是声明个结构struct scull_dev dev;


如果只改这行，->这样的引用方式也是错的

这有什么区别呢
[/Quote]

因为你没有为struct scull_dev *dev分配空间，要么你就用kmalloc分配

struct scull_dev *dev = kmalloc(sizeof(struct scull_dev ), GFP_KERNEL)
cdev_init(&dev->cdev, &scull_fops);