Linux下連結串列的使用及探究

你好！這裡是風箏的部落格，

歡迎和我一起多多交流。

看了下Linux連結串列的實現，發現真的是把“驅動和裝置分離”的思想發揮的淋漓盡致啊！
之前我寫連結串列是這麼寫的：

Linux下連結串列是這樣：

這兩者有什麼不同呢？
當然，我不是想說雙向連結串列的事，而是指標域與資料域分離的事情。
把連結串列的底層實現封裝起來進行遮蔽，只留出資料域。這樣，當連結串列有改動時，只需修改資料域即可，底層連結串列實現不需要改動。

Linux中的list.h檔案：

#ifndef LIST_H
#define LIST_H

#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

/**
 * 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.
 *
 */
#define container_of(ptr, type, member) ({                      \
        const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
        (type *)( (char *)__mptr - offsetof(type,member) );})

/*指標域節點*/
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)
/*節點初始化*/
static inline void INIT_LIST_HEAD(struct list_head *list)
{
        list->next = list;
        list->prev = 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_head within the struct.
 */
#define list_entry(ptr, type, member) \
        container_of(ptr, type, member)

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

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

/*
 * Insert a new entry between two known consecutive entries.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
 /*連結串列底層實現*/
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_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;
}

#define LIST_POISON1  ((void *) 0x00100100)
#define LIST_POISON2  ((void *) 0x00200200)
/**
 * 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.
 */
 /*刪除節點*/
static inline void list_del(struct list_head *entry)
{
        __list_del(entry->prev, entry->next);
        entry->next = (struct list_head*)LIST_POISON1;
        entry->prev = (struct list_head*)LIST_POISON2;
}
#endif

這裡面有個很奇妙的巨集：container_of
作用是根據結構體成員的地址，得到整個結構體的地址，具體的實現方法可以自己Google下，這裡不多描述。

根據這個list.h檔案，這是連結串列的底層實現，我們不需要更改，
我們寫連結串列時，直接包含這個檔案即可：
自己寫的連結串列：
my_list.h:

#ifndef _MY_LIST_H
#define _MY_LIST_H

#include "list.h"

typedef struct list_info
{
        int  id;
        struct list_head list_node;
}list_info;

struct list_head * Create_list(void);
void Add_list_node(struct list_head * head,int id );
void list_for_each(struct list_head * head);
void Del_list_tail(struct list_head * head);
void Destroy_list(struct list_head * head);

#endif

my_list.c:

#include <stdio.h>
#include <stdlib.h>
#include "my_list.h"
#include "list.h"
struct list_head * Create_list(void)
{
         struct list_head * head = (struct list_head *)malloc( sizeof(struct list_head) );
        if(head == NULL)
                printf("create list failed !\n");
        else 
                INIT_LIST_HEAD(head);
        return head;
}

void Add_list_node(struct list_head * head,int id )
{
        list_info * node = (list_info *)malloc( sizeof(list_info) );
        if(node == NULL)
                printf("add list_node failed !\n");
        else
        {
                node->id = id;
                list_add_tail(&node->list_node,head);
        }


}

void list_for_each(struct list_head * head)
{
        list_info * pos;
        list_for_each_entry(pos, head, list_node)
                printf("list_info:%d\n",pos->id);
}

void Del_list_tail(struct list_head * head)
{
        struct list_head *pos = head->prev;
        if(list_empty(head))
        {
                printf("list is empyty,delete failed !");
                return ;
        }
        list_del(pos);
        free(container_of(pos,list_info,list_node));
}

void Destroy_list(struct list_head * head)
{
        struct list_head *pos = head->prev;
        while(pos != head)
        {
                list_del(pos);
                free(container_of(pos,list_info,list_node));
                pos = head->prev;
        }
}

main.c:

#include "my_list.h"
#include <stdio.h>
#include <stdlib.h>

int main()
{
        struct list_head * head;

        head = Create_list();
        Add_list_node(head,5 );
        Add_list_node(head,6 );
        Add_list_node(head,7 );
        printf("list node info :\n");
        list_for_each(head);
        printf("then delete list tail node info :\n");
        Del_list_tail(head);
        list_for_each(head);

        Destroy_list(head);
        return 0;
}

執行結果：