Linux内核代码拾遗：双向链表接口

    Linux内核代码中使用的双向链表接口，简单、扩展性好，简化代码实现；
本人实际使用中，裁剪出一个简化版本接口文件（第3部分，可直接移植），可
满足基本的增、删、查功能，算法效率随元素个数线性增长-O(n)。

一、接口定义

1. list_add - 新增链表元素
2. list_del - 删除链表元素
3. list_move - 移动链表元素
4. list_splice - 合并链表
5. list_for_each_entry - 遍历链表
6. list_for_each_entry_reverse - 反向遍历链表

二、应用示例

    以下示例代码，关键之处在于：在目标结构体中内嵌 struct list_head。
代码演示了链表静态创建、插入、查找、删除，简单方便。

 /* 数组元素个数. @weifan */
#define NELEM(plist) (sizeof(plist)/sizeof(typeof(*plist))))

typedef struct {
    int dwStar;    /* Put some stars in this box! @weifan */
    struct list_head list;    /* 关键之处: 在目标结构体中内嵌 struct list_head. @weifan */
} 
LIST_SAMPLE_BOX_T;

/** @fn : list_if_coding_sample
  * @brief : list接口应用示例
  * @param  : None 
  * @return : # 
  * @author : [e-mail] 
*/
void list_if_coding_sample(void)
{
    int i = 0;
    
    /* box list head. @weifan */
    LIST_SAMPLE_BOX_T stBoxHead = {0, LIST_HEAD_INIT(stBoxHead)};

    /* boxes to add, with 1,2,3... stars for these boxes. @weifan */
    LIST_SAMPLE_BOX_T stBox1 = {1, LIST_HEAD_INIT(stBox1)};
    LIST_SAMPLE_BOX_T stBox2 = {2, LIST_HEAD_INIT(stBox2)};
    LIST_SAMPLE_BOX_T stBox3 = {3, LIST_HEAD_INIT(stBox3)};

    LIST_SAMPLE_BOX_T *pstBoxArray[] = {&stBox1, &stBox2, &stBox3};

    LIST_SAMPLE_BOX_T pstBoxPtr = NULL;

    /* Add boxes, with different stars, to box head list. @weifan */
    for (i = 0; i < NELEM(pstBoxArray); i++)
    {
        list_add(&(pstBoxArray[i].list), &(stBoxHead->list));
    }
    
    /* Find the box with 2 stars in the box head list, and remove it. @weifan */
    list_for_each_entry(pstBoxPtr, stBoxHead, list)
    {
        if (2 == pstBoxPtr->dwStar)
        {
            printf("Box with 2 stars FOUND!\n");
            printf("Then Remove it!\n");
            list_del(&(pstBoxPtr->list));
        }
    }

    /* Re-find the box with 2 stars. @weifan */
    list_for_each_entry(pstBoxPtr, stBoxHead, list)
    {
        if (2 == pstBoxPtr->dwStar)
        {
            printf("Box with 2 stars Not Removed!\n");
        }
    }

    printf("Sample Ends.\n");

    return ;
}

三、接口实现

以下链表实现头文件可直接移植引用，代码源自Linux内核 list.h 文件。

/******************************************************************************

  @note Author [e-mail]. All Right Reserved.

 ******************************************************************************
  @file: list.h
  @version: v1.0.0
  @author: [e-mail]
  @date: Sunday, January 21, 2018
  @note:
  @brief: minimum list interface, copy from linux kernel.
  @func:
  @history:
  @date: Sunday, January 21, 2018
  @note: Create

******************************************************************************/
#ifndef __LIST_H__
#define __LIST_H__
/*----------------------------------------------*
 * Included Header                              *
 *----------------------------------------------*/

/*----------------------------------------------*
 * Macros                                        *
 *----------------------------------------------*/

/**
 * container_of - cast a member of a structure out to the containing structure
 *
 * @ptr:    the pointer to the member.
 * @type:    the type of the container struct this is embedded in.
 * @member:    the name of the member within the struct.
 *
 */
#ifndef container_of
#define container_of(ptr, type, member) ({            \
        const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
        (type *)( (char *)__mptr - offsetof(type,member) );})
#endif

/*
 * These are non-NULL pointers that will result in page faults
 * under normal circumstances, used to verify that nobody uses
 * non-initialized list entries.
 */
#define LIST_POISON1  ((void *) 0x00100100)
#define LIST_POISON2  ((void *) 0x00200200)


/*
 * Simple doubly linked list implementation.
 *
 * Some of the internal functions ("__xxx") are useful when
 * manipulating whole lists rather than single entries, as
 * sometimes we already know the next/prev entries and we can
 * generate better code by using them directly rather than
 * using the generic single-entry routines.
 */

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

#define LIST_HEAD_INIT(name) { &(name), &(name) }

#define LIST_HEAD(name) \
    struct list_head name = LIST_HEAD_INIT(name)

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

/*
 * Insert a new entry between two known consecutive entries.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
static inline void __list_add(struct list_head *new,
                  struct list_head *prev,
                  struct list_head *next)
{
    next->prev = new;
    new->next = next;
    new->prev = prev;
    prev->next = new;
}

/**
 * list_add - add a new entry
 * @new: new entry to be added
 * @head: list head to add it after
 *
 * Insert a new entry after the specified head.
 * This is good for implementing stacks.
 */
static inline void list_add(struct list_head *new, struct list_head *head)
{
    __list_add(new, head, head->next);
}

/**
 * list_add_tail - add a new entry
 * @new: new entry to be added
 * @head: list head to add it before
 *
 * Insert a new entry before the specified head.
 * This is useful for implementing queues.
 */
static inline void list_add_tail(struct list_head *new, struct list_head *head)
{
    __list_add(new, head->prev, head);
}

/*
 * Delete a list entry by making the prev/next entries
 * point to each other.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
static inline void __list_del(struct list_head * prev, struct list_head * next)
{
    next->prev = prev;
    prev->next = next;
}

/**
 * list_del - deletes entry from list.
 * @entry: the element to delete from the list.
 * Note: list_empty on entry does not return true after this, the entry is
 * in an undefined state.
 */
static inline void list_del(struct list_head *entry)
{
    __list_del(entry->prev, entry->next);
    entry->next = LIST_POISON1;
    entry->prev = LIST_POISON2;
}

/**
 * list_del_init - deletes entry from list and reinitialize it.
 * @entry: the element to delete from the list.
 */
static inline void list_del_init(struct list_head *entry)
{
    __list_del(entry->prev, entry->next);
    INIT_LIST_HEAD(entry);
}

/**
 * list_move - delete from one list and add as another's head
 * @list: the entry to move
 * @head: the head that will precede our entry
 */
static inline void list_move(struct list_head *list, struct list_head *head)
{
        __list_del(list->prev, list->next);
        list_add(list, head);
}

/**
 * list_move_tail - delete from one list and add as another's tail
 * @list: the entry to move
 * @head: the head that will follow our entry
 */
static inline void list_move_tail(struct list_head *list,
                  struct list_head *head)
{
        __list_del(list->prev, list->next);
        list_add_tail(list, head);
}

/**
 * list_empty - tests whether a list is empty
 * @head: the list to test.
 */
static inline int list_empty(const struct list_head *head)
{
    return head->next == head;
}

/**
 * list_empty_careful - tests whether a list is
 * empty _and_ checks that no other CPU might be
 * in the process of still modifying either member
 *
 * NOTE: using list_empty_careful() without synchronization
 * can only be safe if the only activity that can happen
 * to the list entry is list_del_init(). Eg. it cannot be used
 * if another CPU could re-list_add() it.
 *
 * @head: the list to test.
 */
static inline int list_empty_careful(const struct list_head *head)
{
    struct list_head *next = head->next;
    return (next == head) && (next == head->prev);
}

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);
}

/**
 * list_splice_init - join two lists and reinitialise the emptied list.
 * @list: the new list to add.
 * @head: the place to add it in the first list.
 *
 * The list at @list is reinitialised
 */
static inline void list_splice_init(struct list_head *list,
                    struct list_head *head)
{
    if (!list_empty(list)) {
        __list_splice(list, head);
        INIT_LIST_HEAD(list);
    }
}

/**
 * list_entry - get the struct for this entry
 * @ptr:    the &struct list_head pointer.
 * @type:    the type of the struct this is embedded in.
 * @member:    the name of the list_struct within the struct.
 */
#define list_entry(ptr, type, member) \
    container_of(ptr, type, member)

/**
 * __list_for_each    -    iterate over a list
 * @pos:    the &struct list_head to use as a loop counter.
 * @head:    the head for your list.
 *
 * This variant differs from list_for_each() in that it's the
 * simplest possible list iteration code, no prefetching is done.
 * Use this for code that knows the list to be very short (empty
 * or 1 entry) most of the time.
 */
#define __list_for_each(pos, head) \
    for (pos = (head)->next; pos != (head); pos = pos->next)

/**
 * list_for_each_prev    -    iterate over a list backwards
 * @pos:    the &struct list_head to use as a loop counter.
 * @head:    the head for your list.
 */
#define list_for_each_prev(pos, head) \
    for (pos = (head)->prev; prefetch(pos->prev), pos != (head); \
            pos = pos->prev)

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


/**
 * 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.
 * @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);     \
         pos = list_entry(pos->member.next, typeof(*pos), member))

/**
 * list_for_each_entry_reverse - iterate backwards over list of given type.
 * @pos:    the type * to use as a loop counter.
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 */
#define list_for_each_entry_reverse(pos, head, member)            \
    for (pos = list_entry((head)->prev, typeof(*pos), member);    \
         &pos->member != (head);     \
         pos = list_entry(pos->member.prev, typeof(*pos), member))
/*----------------------------------------------*
 * Type Definition                              *
 *----------------------------------------------*/

/*----------------------------------------------*
 * Constant                                     *
 *----------------------------------------------*/

/*----------------------------------------------*
 * External Varible                             *
 *----------------------------------------------*/

/*----------------------------------------------*
 * Gobal Varible                                *
 *----------------------------------------------*/

/*----------------------------------------------*
 * Module Varible                               *
 *----------------------------------------------*/

/*----------------------------------------------*
 * External Function                            *
 *----------------------------------------------*/

/*----------------------------------------------*
 * Internal Function                            *
 *----------------------------------------------*/

/*----------------------------------------------*
 * Routines' Implementations                    *
 *----------------------------------------------*/


#endif