鏈表操作與管理

在程序開發中，經常需要用到鏈表處理數據，其具有靈活、動態增長、動態分配、動態釋放等特點。
一般在模塊化，結構化或者解耦合編程中經常需要使用它，可以讓其任務具有隊列的特點而形成生產-消費模型。
本文介紹的這種鏈表模型的單個節點（結構體）可以分爲鏈表的數據體與連接點的兩個數據塊，且鏈表連接節點需要放在鏈表節點結構體的最尾端，巧妙的利用了從結構體局部元素來獲取整個結構體的數據首地址。

1. 鏈表的結構定義

鏈表的單個節點定義如下：

struct list_node {
	struct list_data data; //數據體
	struct list_head node; //連接點
};

struct list_head {
	struct list_head * next; 
	struct list_head * prev;
};

圖像結構如下：

2. 鏈表的初始化

#define LIST_HEAD_INIT(name) { &(name), &(name) }
#define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name)

INIT_LIST_HEAD與LIST_HEAD_INIT宏的效果一樣，只不過一個接受結構體，一個接受結構體指針

#define INIT_LIST_HEAD(ptr) do { \
	(ptr)->next = (ptr); (ptr)->prev = (ptr); \
} while (0)

static LIST_HEAD(m_request_list);

初始化後的圖像結構：

3. 判斷鏈表是否空

/**
* 判斷list是否爲空，傳入的是鏈表的首節點(也稱爲0節點)
*/
__inline int list_empty(struct list_head *head)
{
	return head->next == head;
}

4. 刪除鏈表節點

/**
* 從鏈表中刪除list的一個節點，傳入需要刪除的目標節點
*/
__inline void list_del(struct list_head * entry)
{
	__list_del(entry->prev, entry->next);
	entry->next = NULL;
	entry->prev = NULL;
}

__inline void __list_del(struct list_head * prev, struct list_head * next)
{
	next->prev = prev;
	prev->next = next;
}

5. 獲取鏈表的第一個有效節點

/**
* 獲取鏈表的第一個節點(非首節點)
*/
#define list_first_entry(ptr, type, member) list_entry((ptr)->next, type, member)
//局部訪問整體，也是整個鏈表結構的精髓所在
#define list_entry(ptr, type, member) ((type *)((char *)(ptr)-(unsigned long)(&((type *)0)->member))) 

eg. struct list_node evt = list_first_entry(&m_request_list, struct list_node, node);

6. 向鏈表尾部添加節點

/**
* 在鏈表結尾添加一個節點
*/
 __inline void list_add_tail(struct list_head * newitem, struct list_head * head)
{
	__list_add(newitem, head->prev, head);
}

__inline void __list_add(struct list_head * newitem,
    struct list_head * prev, struct list_head * next)
{
	next->prev    = newitem;
	newitem->next = next;
	newitem->prev = prev;
	prev->next    = newitem;
}

eg. struct list_node * olditem;
list_add_tail(&(olditem->node), &m_request_list);
添加一個元素的效果圖：

添加兩個節點後的效果圖：

7. 向鏈表首部添加節點

/**
* 在鏈表首部添加一個節點
*/
__inline void list_add(struct list_head * newitem,
    struct list_head * head)
{
	__list_add(newitem, head, head->next);
}

__inline void __list_add(struct list_head * newitem,
    struct list_head * prev, struct list_head * next)
{
	next->prev    = newitem;
	newitem->next = next;
	newitem->prev = prev;
	prev->next    = newitem;
}

8. 遍歷鏈表的節點

/**
* 遍歷鏈表的所有節點
*/
#define list_for_each_entry(pos, head, member, type)            \
	for (pos = list_entry((head)->next, type, member); &pos->member != (head); pos = list_entry(pos->member.next, type, member))

/**
 * list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
 * @pos:	the type * to use as a loop counter.
 * @n:		another type * to use as temporary storage
 * @head:	the head for your list.
 * @member:	the name of the list_struct within the struct.
 */
#define list_for_each_entry_safe(pos, n, head, member, type)            \
	for (pos = list_entry((head)->next, type, member),              \
	       n = list_entry(pos->member.next, type, member);          \
	     &pos->member != (head);                                    \
	     pos = n, n = list_entry(n->member.next, type, member))

eg. struct list_node * i;
list_for_each_entry(i, &m_request_list, node, struct list_node)

9. 鏈表的拼接

static __inline void __list_splice(struct list_head * list,
    struct list_head * head)
{
	struct list_head * first = list->next;
	struct list_head * last  = list->prev;
	struct list_head * at    = head->next;

	first->prev = head;
	head->next  = first;
	last->next  = at;
	at->prev    = last;
}

/**
 * list_splice - join two lists
 * @list: the new list to add.
 * @head: the place to add it in the first list.
 */
static __inline void list_splice(struct list_head * list,
    struct list_head * head)
{
	if (!list_empty(list))
		__list_splice(list, head);
}