【他引】代码：linux-2.4 Kernel图一 ：Linux TCP IP 协议栈分析.pdf【背景】
sk_buff{}结构是linux 网络协议栈的重要结构体，本结构描述的数据包（package）穿梭于运输层~链路层之间。每个数据包都有对应的sk_buff进行描述，而系统对这么多的sk_buff的处理时以循环双链表的形式组织的。见如下图：
图一【数据结构】
//链表表头，维护一个表，作为一个链表的标杆，不做具体数据的存储struct sk_buff_head {struct sk_buff* next;struct sk_buff* prev;__u32qlen;spinlock_tlock;};//链表数据节点struct sk_buff {/* 链表结构参数*/struct sk_buff* next;/* Next buffer in list */struct sk_buff* prev;/* Previous buffer in list */struct sk_buff_head * list;/* List we are on*//*...data...*/}
【List init】
链表的初始化…
//链表的表头的初始化static inline void skb_queue_head_init(struct sk_buff_head *list){spin_lock_init(&list->lock);list->prev = (struct sk_buff *)list;list->next = (struct sk_buff *)list;list->qlen = 0;}
【Operations】
链表的每个操作有两个函数构成，形如__fun(),fun()。而且都是在fun()中调用__fun()。主要原因是__fun()是非原子操作，在fun()中添加锁机制，确保__fun()操作的原子性。比如：__skb_quque_head()和skb_queue_head();
static inline void __skb_queue_head(struct sk_buff_head *list, struct sk_buff *newsk){struct sk_buff *prev, *next;newsk->list = list;list->qlen++;prev = (struct sk_buff *)list;next = prev->next;newsk->next = next;newsk->prev = prev;next->prev = newsk;prev->next = newsk;}/** *skb_queue_head - queue a buffer at the list head *@list: list to use *@newsk: buffer to queue * *Queue a buffer at the start of the list. This function takes the *list lock and can be used safely with other locking &sk_buff functions *safely. */ //头部添加static inline void skb_queue_head(struct sk_buff_head *list, struct sk_buff *newsk){unsigned long flags;spin_lock_irqsave(&list->lock, flags);__skb_queue_head(list, newsk);spin_unlock_irqrestore(&list->lock, flags);}
其他函数的fun()基本显示，下面就主要贴出每个链表操作的具体实现的函数__fun().
/** *__skb_queue_tail - queue a buffer at the list tail *@list: list to use *@newsk: buffer to queue * *Queue a buffer at the end of a list. This function takes no locks *and you must therefore hold required locks before calling it. * *A buffer cannot be placed on two lists at the same time. *///尾部添加static inline void __skb_queue_tail(struct sk_buff_head *list, struct sk_buff *newsk){struct sk_buff *prev, *next;newsk->list = list;list->qlen++;next = (struct sk_buff *)list;prev = next->prev;newsk->next = next;newsk->prev = prev;next->prev = newsk;prev->next = newsk;}/** *__skb_dequeue - remove from the head of the queue *@list: list to dequeue from * *Remove the head of the list. This function does not take any locks *so must be used with appropriate locks held only. The head item is *returned or %NULL if the list is empty. *///删除第一个数据节点static inline struct sk_buff *__skb_dequeue(struct sk_buff_head *list){struct sk_buff *next, *prev, *result;prev = (struct sk_buff *) list;next = prev->next;result = NULL;if (next != prev) {result = next;next = next->next;list->qlen--;next->prev = prev;prev->next = next;result->next = NULL;result->prev = NULL;result->list = NULL;}return result;}/** *__skb_dequeue_tail - remove from the tail of the queue *@list: list to dequeue from * *Remove the tail of the list. This function does not take any locks *so must be used with appropriate locks held only. The tail item is *returned or %NULL if the list is empty. *///删除最后一个数据节点static inline struct sk_buff *__skb_dequeue_tail(struct sk_buff_head *list){struct sk_buff *skb = skb_peek_tail(list); if (skb)__skb_unlink(skb, list);return skb;}/* *Insert a packet on a list. */static inline void __skb_insert(struct sk_buff *newsk,struct sk_buff * prev, struct sk_buff *next,struct sk_buff_head * list){newsk->next = next;newsk->prev = prev;next->prev = newsk;prev->next = newsk;newsk->list = list;list->qlen++;}/* *Place a packet after a given packet in a list. */static inline void __skb_append(struct sk_buff *old, struct sk_buff *newsk){__skb_insert(newsk, old, old->next, old->list);}/* * remove sk_buff from list. _Must_ be called atomically, and with * the list known.. */ static inline void __skb_unlink(struct sk_buff *skb, struct sk_buff_head *list){struct sk_buff * next, * prev;list->qlen--;next = skb->next;prev = skb->prev;skb->next = NULL;skb->prev = NULL;skb->list = NULL;next->prev = prev;prev->next = next;}
不畏不惧，不言不弃，冲破风雨的阻隔，黎明就在前方！
