内核链表是双向循环链表
内核链表的实质是通过操作小结构体来实现插入、遍历、删除等功能
对于
/**
* list_for_each_entry - iterate over list of given type
* @pos: the type * to use as a loop counter.
* @head: the head for your list. //此处所指是小结构体
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry(pos, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member); \
&pos->member != (head);