C语言链表结构（4）——内核链表

一.内核链表的概念

1. 什么是内核链表？
         内核链表与传统链表不一样，传统链表的数据域与指针域都是用户自定义，但是内核链表数据域是用户自定义，但指针域是在内核链表的头文件中已经定义好了。内核链表是一种双向循环，头节点无效的链表。

2. 内核链表模型与传统链表差异？
内核链表头文件： kernel_list.h

#ifndef __DLIST_H
#define __DLIST_H

/* This file is from Linux Kernel (include/linux/list.h)
* and modified by simply removing hardware prefetching of list items.
* Here by copyright, credits attributed to wherever they belong.
* Kulesh Shanmugasundaram (kulesh [squiggly] isis.poly.edu)
*/

/*
* 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.
*/
/**
 * 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 offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

#define container_of(ptr, type, member) ({            \
        const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
        (type *)( (char *)__mptr - offsetof(type,member) );})
/*
 * 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 *) 0x00200)

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 = (void *) 0;
    entry->prev = (void *) 0;
}

/**
* 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(struct list_head *head)
{
    return head->next == head;
}

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) \
((type *)((char *)(ptr)-(unsigned long)(&((type *)0)->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.
*/
#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; 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_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)            \
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))

#endif

既然内核链表指针域已经定义好，那么究竟这个指针域是长什么样子？
该指针域是一个结构体来的：
struct list_head{

　　struct list_head *next; -> 后继指针
　　struct list_head *prev; -> 前驱指针 
};

3. 设计内核链表模型？
struct list_node{
　　/* 自定义数据域 */
　　int a;

　　/* 头文件中已经定义好的指针域 */
　　struct list_head list;
}

二.内核链表的增删改查

实例编程：

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

//设计节点
struct list_node{
    int a;
    struct list_head list; //指针域，里面已经包含了两个指针
};

struct list_node *init_list_head(struct list_node *head)
{
    head = (struct list_node *)malloc(sizeof(struct list_node));
    if(head == NULL)
        printf("malloc head error!\n");
    
    INIT_LIST_HEAD(&(head->list));
    
    return head;
}

int tail_add_list(struct list_node *head,int num)
{
    struct list_node *Node = NULL;
    Node = (struct list_node *)malloc(sizeof(struct list_node));
    if(Node == NULL)
        printf("malloc Node error!\n");
    
    Node->a = num;
    
    list_add_tail(&(Node->list),&(head->list));
    
    return 0;
}

int head_add_list(struct list_node *head,int num)
{
    struct list_node *Node = NULL;
    Node = (struct list_node *)malloc(sizeof(struct list_node));
    if(Node == NULL)
        printf("malloc Node error!\n");
    
    Node->a = num;
    
    list_add(&(Node->list),&(head->list));
    
    return 0;
}

int forward_show_list(struct list_node *head)
{
    struct list_node *p = NULL;
    
    list_for_each_entry(p,&(head->list),list)
    {
        printf("p->a:%d\n",p->a);
    }
    
    return 0;
}

int backward_show_list(struct list_node *head)
{
    struct list_head *p = NULL;
    struct list_node *tmp = NULL;
    
    list_for_each_prev(p,&(head->list))
    {
        tmp = list_entry(p,struct list_node,list);
        printf("tmp->a:%d\n",tmp->a);
    }
    
    return 0;
}

int delete_list_node(struct list_node *head,int num)
{
    struct list_node *p = NULL;
    struct list_node *q = NULL;
    
    list_for_each_entry_safe(p,q,&(head->list),list)
    {
        if(p->a == num)
        {
            list_del(&(p->list));
            free(p);
        }
    }
    
    return 0;
}

int delete_list(struct list_node *head)
{
    struct list_node *p = NULL;
    struct list_node *q = NULL;
    
    list_for_each_entry_safe(p,q,&(head->list),list)
    {
        list_del(&(p->list));
        free(p);
    }
    
    list_del(&(head->list));
    free(head);
    
    return 0;
}

int main(int argc,char *argv[])
{
    //1. 初始化链表
    struct list_node *head = NULL;
    head = init_list_head(head);
    
    //2. 尾插数据
    tail_add_list(head,10);
    tail_add_list(head,20);
    tail_add_list(head,30);
    
    //3. 头插数据
    head_add_list(head,8);
    head_add_list(head,5);
    head_add_list(head,3);
    
    //4. 往后遍历链表
    forward_show_list(head);
    
    //5. 往前遍历链表
    backward_show_list(head);
    
    //6. 删除链表的节点
    delete_list_node(head,20);
    
    //7. 删除整条链表的空间
    delete_list(head);
}