struct file_operation的定义方式变了：
2.4中 一般为read:xxread
2.6改为.read=xxread
字符设备驱动的注册方法不同：
2.6内核的注册方法
(1)静态注册
int register_chrdev_region(dev_t from, unsigned count, char *name);
(2)动态注册
int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count, char *name);
2.4内核的注册方法
int register_chrdev(unsigned major, char * name, struct file_operation * fops);
2.4内核仅仅生成.o文件，2.6内核的模块扩展名是.ko
