linux内核List中关于hash链表

//双向链表对于hash表来说太浪费了//因此设计了单向链表，但是，这样在访问尾节点时间上就不再是O（1）的时间复杂度/* * Double linked lists with a single pointer list head. * Mostly useful for hash tables where the two pointer list head is * too wasteful. * You lose the ability to access the tail in O(1). */struct hlist_head {struct hlist_node *first;};//双循环链表//pprev存放的是前一个节点的next指针//对于链表头来说则是first//对于链表节点来说则是next的地址//这样做的主要目的是通过后面节点，也能修改前一个节点的值（next）//为什么不采用next和prev的结构呢（采用同一般链表的结构）？？//首先，除第一个节点（非头结点）以外的其他节点采用一般链表结构是没有问题的；//但是，对于第一个节点来说，存在着操作上与其他节点的不一致//第一个hlist_node 的next指向没有问题，但是prev是指向前一个即hlist_head的头结点//因此，此时的prev的类型是hlist_node，头结点是单链hlist_node的first//这样在访问上prev只能指向first的值，此时prev和first的值是一致的，因此失去了prev原为//指向前一个节点的意义，因此为了实现prev的功能，以及为了统一所有hash链表的操作，//采用了指向指针（双重指针）的操作，即可以通过pprev存储first的地址，起到修改和访问的作用struct hlist_node {struct hlist_node *next, **pprev;};#define HLIST_HEAD_INIT { .first = NULL }#define HLIST_HEAD(name) struct hlist_head name = {  .first = NULL }#define INIT_HLIST_HEAD(ptr) ((ptr)->first = NULL)//初始化hash链表节点static inline void INIT_HLIST_NODE(struct hlist_node *h){h->next = NULL;h->pprev = NULL;}//判断该hash是否有值？？？static inline int hlist_unhashed(const struct hlist_node *h){return !h->pprev;}//判断是否为空static inline int hlist_empty(const struct hlist_head *h){return !h->first;}//删除一个节点static inline void __hlist_del(struct hlist_node *n){struct hlist_node *next = n->next;struct hlist_node **pprev = n->pprev;*pprev = next;if (next)next->pprev = pprev;}static inline void hlist_del(struct hlist_node *n){__hlist_del(n);n->next = LIST_POISON1;n->pprev = LIST_POISON2;}static inline void hlist_del_init(struct hlist_node *n){if (!hlist_unhashed(n)) {//不为空，删除并初始化__hlist_del(n);INIT_HLIST_NODE(n);}}//插入在头结点之后的位置static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h){struct hlist_node *first = h->first;n->next = first;if (first)first->pprev = &n->next;h->first = n;n->pprev = &h->first;}//在next节点之前，加入n/* next must be != NULL */static inline void hlist_add_before(struct hlist_node *n,struct hlist_node *next){n->pprev = next->pprev;n->next = next;next->pprev = &n->next;*(n->pprev) = n;}//在节点n之后插入nextstatic inline void hlist_add_after(struct hlist_node *n,struct hlist_node *next){next->next = n->next;n->next = next;next->pprev = &n->next;if(next->next)next->next->pprev  = &next->next;}/* * Move a list from one list head to another. Fixup the pprev * reference of the first entry if it exists. */ //将一个链表从一个头结点移至另一个头结点 //并将old的节点置为nullstatic inline void hlist_move_list(struct hlist_head *old,   struct hlist_head *new){new->first = old->first;if (new->first)new->first->pprev = &new->first;old->first = NULL;}//取出指针对应的结构体成员#define hlist_entry(ptr, type, member) container_of(ptr,type,member)#define hlist_for_each(pos, head) \for (pos = (head)->first; pos && ({ prefetch(pos->next); 1; }); \     pos = pos->next)#define hlist_for_each_safe(pos, n, head) \for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \     pos = n)/** * hlist_for_each_entry- iterate over list of given type * @tpos:the type * to use as a loop cursor. * @pos:the &struct hlist_node to use as a loop cursor. * @head:the head for your list. * @member:the name of the hlist_node within the struct. */#define hlist_for_each_entry(tpos, pos, head, member) \for (pos = (head)->first; \     pos && ({ prefetch(pos->next); 1;}) && \({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \     pos = pos->next)/** * hlist_for_each_entry_continue - iterate over a hlist continuing after current point * @tpos:the type * to use as a loop cursor. * @pos:the &struct hlist_node to use as a loop cursor. * @member:the name of the hlist_node within the struct. */#define hlist_for_each_entry_continue(tpos, pos, member) \for (pos = (pos)->next; \     pos && ({ prefetch(pos->next); 1;}) && \({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \     pos = pos->next)/** * hlist_for_each_entry_from - iterate over a hlist continuing from current point * @tpos:the type * to use as a loop cursor. * @pos:the &struct hlist_node to use as a loop cursor. * @member:the name of the hlist_node within the struct. */#define hlist_for_each_entry_from(tpos, pos, member) \for (; pos && ({ prefetch(pos->next); 1;}) && \({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \     pos = pos->next)/** * hlist_for_each_entry_safe - iterate over list of given type safe against removal of list entry * @tpos:the type * to use as a loop cursor. * @pos:the &struct hlist_node to use as a loop cursor. * @n:another &struct hlist_node to use as temporary storage * @head:the head for your list. * @member:the name of the hlist_node within the struct. */#define hlist_for_each_entry_safe(tpos, pos, n, head, member)  \for (pos = (head)->first; \     pos && ({ n = pos->next; 1; }) &&  \({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \     pos = n)#endif