关于设备驱动模型的一个问题，谢谢

我们知道cdev表示的是字符设备，而block_device表示的是块设备，但似乎都没看见他们内嵌device结构，2.6里面不是利用device结构来使得这些设备被包含在各种各样的subsystem里面的吗？似乎gendisk 结构里面还有一个device的指针，但是为什么不内嵌在里面，而使用指针呢？在cdev里面就找不到device的影子了：

struct block_device {
dev_t bd_dev; /* not a kdev_t - it's a search key */
struct inode * bd_inode; /* will die */
int bd_openers;
struct semaphore bd_sem; /* open/close mutex */
struct semaphore bd_mount_sem; /* mount mutex */
struct list_head bd_inodes;
void * bd_holder;
int bd_holders;
struct block_device * bd_contains;
unsigned bd_block_size;
struct hd_struct * bd_part;
unsigned bd_part_count;
int bd_invalidated;
struct gendisk * bd_disk;
struct list_head bd_list;
/*
* Private data. You must have bd_claim'ed the block_device
* to use this. NOTE: bd_claim allows an owner to claim
* the same device multiple times, the owner must take special
* care to not mess up bd_private for that case.
*/
unsigned long bd_private;
};

struct cdev {
struct kobject kobj;
struct module *owner;
struct file_operations *ops;
struct list_head list;
dev_t dev;
unsigned int count;
};


struct device {
int dev_type; // PCICA, PCICC, or PCIXCC
enum devstat dev_stat; // current device status
int dev_self_x; // Index in array
int disabled; // Set when device is in error
int user_disabled; // Set when device is disabled by user
int dev_q_depth; // q depth
unsigned char * dev_resp_p; // Response buffer address
int dev_resp_l; // Response Buffer length
int dev_caller_count; // Number of callers
int dev_total_req_cnt; // # requests for device since load
struct list_head dev_caller_list; // List of callers
};

那么像device这样的通用设备结构和具体的设备结构到底是个什么关系呢？谢谢。