Linux 内核 hlist 详解

标签：style   blog   http   color   使用   os   

在Linux内核中，hlist（哈希链表）使用非常广泛。本文将对其数据结构和核心函数进行分析。

和hlist相关的数据结构有两个：hlist_head 和 hlist_node

//hash桶的头结点
struct hlist_head {
	struct hlist_node *first;//指向每一个hash桶的第一个结点的指针
};
//hash桶的普通结点
struct hlist_node {
	struct hlist_node *next;//指向下一个结点的指针
	struct hlist_node **pprev;//指向上一个结点的next指针的地址
};

对应的程序代码如下：

static inline void __hlist_del(struct hlist_node *n) 
{ 
 struct hlist_node *next = n->next;//获取指向第二个普通结点的指针 
 struct hlist_node **pprev = n->pprev;//保留待删除的第一个结点的pprev域（即头结点first域的地址），此时 pprev = &first 
 *pprev = next; 
 /*
 因为pprev = &first，所以*pprev = next，相当于 first = next
 即将hash桶的头结点指针指向原来的第二个结点，如上图中的黑线1
 */
 if (next) //如果第二个结点不为空
  next->pprev = pprev;//将第二个结点的pprev域设置为头结点first域的地址，如上图中的黑线2 
}

对应的程序代码如下：

static inline void __hlist_del(struct hlist_node *n) 
{ 
 struct hlist_node *next = n->next;//获取指向待删除结点的下一个普通结点的指针 
 struct hlist_node **pprev = n->pprev;//获取待删除结点的pprev域 
 *pprev = next; //修改待删除结点的pprev域，逻辑上使待删除结点的前驱结点指向待删除结点的后继结点，如上图中的黑线1

 if (next) //如果待删除结点的下一个普通结点不为空
      next->pprev = pprev;//设置下一个结点的pprev域，如上图中的黑线2，保持hlist的结构 
}

很明显删除hash桶对应链表中的非第一个普通结点，只需要如下两行代码：

n->next->prev = n->prev;
n->prev->next = n->next;

#define list_for_each(pos, head)         for (pos = (head)->next; prefetch(pos->next), pos != (head);                 pos = pos->next)
 
#define hlist_for_each(pos, head)         for (pos = (head)->first; pos && ({ prefetch(pos->next); 1; });              pos = pos->next)

#define list_for_each_entry(pos, head, member)         for (pos = list_entry((head)->next, typeof(*pos), member);              prefetch(pos->member.next), &pos->member != (head);              pos = list_entry(pos->member.next, typeof(*pos), member))
 
#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)

#define list_for_each_safe(pos, n, head)         for (pos = (head)->next, n = pos->next; pos != (head);                 pos = n, n = pos->next)
 
#define hlist_for_each_safe(pos, n, head)         for (pos = (head)->first; pos && ({ n = pos->next; 1; });              pos = n)

//hash桶的头结点 
struct hlist_head { 
     struct hlist_node *first;//指向每一个hash桶的第一个结点的指针 
}; 
//hash桶的普通结点 
struct hlist_node { 
 struct hlist_node *next;//指向下一个结点的指针 
 struct hlist_node **pprev;//指向上一个结点的next指针的地址 
}; 
//以下三种方法都是初始化hash桶的头结点 
#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桶的普通结点 
static inline void INIT_HLIST_NODE(struct hlist_node *h) 
{ 
 h->next = NULL; 
 h->pprev = NULL; 
} 

//判断一个结点是否已经存在于hash桶中 
static inline int hlist_unhashed(const struct hlist_node *h) 
{ 
     return !h->pprev; 
} 

//判断一个hash桶是否为空 
static inline int hlist_empty(const struct hlist_head *h) 
{ 
     return !h->first; 
} 

static inline void __hlist_del(struct hlist_node *n) 
{ 
 struct hlist_node *next = n->next;//获取指向待删除结点的下一个结点的指针 
 struct hlist_node **pprev = n->pprev;//保留待删除结点的pprev域 
 *pprev = next;//修改待删除结点的pprev域，逻辑上使待删除结点的前驱结点指向待删除结点的后继结点 
 if (next) 
  next->pprev = pprev;//设置待删除结点的下一个结点的pprev域，保持hlist的结构 
} 

static inline void hlist_del(struct hlist_node *n) 
{ 
 __hlist_del(n);//删除结点之后，需要将其next域和pprev域设置为无用值 
 n->next = LIST_POISON1; 
 n->pprev = LIST_POISON2; 
} 

static inline void hlist_del_init(struct hlist_node *n) 
{ 
 if (!hlist_unhashed(n)) 
 { 
  __hlist_del(n); 
  INIT_HLIST_NODE(n); 
 } 
} 

//将普通结点n插入到头结点h对应的hash桶的第一个结点的位置 
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; 
} 

/* next must be != NULL */ 
//在next结点之前插入结点n，即使next结点是hash桶中的第一个结点也可以 
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; 
} 

//在结点n之后插入结点next 
static 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. 
 */ 
static 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; 
} 

//通过一个结构体内部一个成员的地址获取结构体的首地址 
#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)

Linux 内核 hlist 详解,码迷,mamicode.com

Linux 内核 hlist 详解

标签：style   blog   http   color   使用   os   

原文地址：http://blog.csdn.net/hs794502825/article/details/24597773