博客地址：http://blog.csdn.net/muyang_ren
内核链表示意图
关于内核链表与简单的双向连表，是否有过疑惑
内核链表定义：
struct list_head{
struct list_head *next,*prev;
};
struct doublelist{
datatype data;
struct list_head list;
}double_list;struct doublelist{
datatype data;
struct doublelist *next, *prior;
}double_list;不同：双向链表：大结构体内包含两个个与自身类型相同的结构体指针
可见内核链表是将两个指针变量封装在一个小结构体内，那么问题来了。
问题1、
被封装的指针指向的地址是堆中对应的大结构体地址还是指向小结构体内的地址呢？这个问题想想就模糊了，来看看内核是怎么做的吧。
链表初始化时：
static inline void INIT_LIST_HEAD(struct list_head *list)
{
list->next = list;
list->prev = list;
}
是的，你看到的没错，它指向的只是小结构体的地址！
问题2、
那么当你新增节点的时候会不会实现将链表与下一个大结构体的起始位置相关联呢？
static inline void list_add(struct list_head *new, struct list_head *head)
{
__list_add(new, head, head->next);
}
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;
我嘞个呵呵，看到new的数据类型没，是不是对应的list_head类型？看到没有，内核他在搞什么鬼，指向小结构体地址那我的大结构体数据是怎么读取？使用指针，我还没那么神吧。关于怎么通过小结构体变量来读取到大结构体的地址我就不深入探讨了，这个内核有相应的处理。
只研究下我们该怎么使用内核链表这种机制实现自己的数据读取。
对比：
使用内核历遍链表代码：
double_plist p;
list_for_each_entry(p, &H->list,list){
}
使用简单双链表历遍链表：
double_plist p;
for(p=list->next; p!=list; p=p->next){
<span style="white-space:pre"> </span>......
}list_for_each_entry定义
/**内核里的list_for_each_entry的定义
************历遍链表****************
*
* @pos: 临时的H类型的指针变量
* @head: 表头H内存放的list结构体地址
* @member H内的小结构体变量名，我的就是list
*
*/
#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))
#define container_of(ptr, type, member) ({ const typeof( ((type *)0)->member ) *__mptr = (ptr); (type *)( (char *)__mptr - offsetof(type,member) );})#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)看懂了这个宏定义没？我是没看太懂，只是自己太概猜测的他应该要实现的功能：
pos是个临时大结构体的指针变量，head则是表头的list地址，而最后一个则是list变量，从list所指向的下一个小结构体地址开时历遍，终止条件是不等于表头list的地址每指向下一个节点的同时使用指针运算等我还不清楚的东西通过小结构体的地址和小结构体的空间大小与大结构体内的空间换算出大结构体的起始地址赋予临时的指针变量pos（p），这样就可以通过p实现简单的链表里的运算啦！
内核链表为什么要搞的这么复杂呢，我们是不是应该这样想想，对于一个系统，所面对的肯定不是小数据是吧，面对每个结构体都对应这这么庞大的数据，将指针变量封装也比较好实现不同的大结构体的数据处理，再说我猜测的一个想法，使用指针运算的时候是不是还会计算数据空间，使用小结构体这种封装机制是不是可以实现继续计算相对较小的空间大小从而实现指针运算？要是数据诺大，你说省出了多少时间？
对此，内核链表为何要加个小结构体变量的探讨先到此吧！
程序实现：
使用内核链表实现增删查改
1、主函数
main.c(有些文件我改名了，没改头文件的宏定义，那个没关系的)
#include "head.h"
//@使用系统的内核链表来完成数据的 增 删 查 改
//
int main(void)
{
int num, i;
double_plist list;
doublelist_init(&list); //初始化双向链表
printf("\n请输入链表长度：");
scanf("%d",&num);
//增
printf("---------------- ① ----------------\n");
printf("----------------增加----------------\n");
for(i=1;i<=num;i++){
printf(">>> 增加 %d\n", i);
doublelist_addnum(list,i); //加入数据到双向链表
}
//查
printf("---------------- ② ----------------\n");
printf("----------------显示----------------\n");
doublelist_show(list); //显示双向链表内数据
//删
printf("---------------- ③ ----------------\n");
printf("----------------删除----------------\n");
printf("请输入要删除的数据\n");
scanf("%d",&num);
doublelist_del(list,num);
//再查
printf("----------------显示----------------\n");
doublelist_show(list); //显示双向链表内数据
//修改
printf("\n---------------- ④ ----------------\n");
printf("----------------增加----------------\n");
printf(">>>: n m ,则将 n 修改为 m\n");
scanf("%d %d", &i, &num);
doublelist_revise(list, i, num); //显示双向链表内数据
//再再查
printf("----------------显示----------------\n");
doublelist_show(list); //显示双向链表内数据
return 0;
}
2、头文件
head.h
#ifndef __doubleLIST_H__
#define __doubleLIST_H__
#include <stdio.h>
#include <stdlib.h>
#include "kernellist.h"
typedef int datatype;
typedef struct doublelist{
datatype data;
struct list_head list;
#if 0
list成员是两个list_head类型的指针，在内核定义，
struct list_head{
list_headstruct list_head *next,*prev;
};
#endif
}double_list,*double_plist;
extern void doublelist_new(double_plist * );
extern void doublelist_init(double_plist * );//初始化表头
extern void doublelist_show(double_plist );//查
extern void doublelist_addnum(double_plist, int);//增
extern void doublelist_del(double_plist ,int);//删
extern void doublelist_revise(double_plist ,int , int );//改
#endif
kernellist.c
#include "head.h"
//开辟新的节点空间
void doublelist_new(double_plist *list){
*list=(double_plist)malloc(sizeof(double_list));
if(NULL == *list){
perror("malloc\n");
exit(-1);
}
}
//双向链表初始化
void doublelist_init(double_plist *H){
*H=(double_plist)malloc(sizeof(double_list));
if(NULL == *H){
perror("malloc\n");
exit(-1);
}
//(*list)->next=(*list)->prior=(*list);
INIT_LIST_HEAD(&(*H)->list);
#if 0
调用内核链表头文件函数，INIT_LIST_HEAD使得大结构体H的小结构体list的prev和next都指向小结构体本身的地址；
讲解：malloc申请一个大的结构体空间的时候，包含了小结构体list两个指针变量的空间，内核链表初始化时H保存
的任然是个表头，表头存放数据，list内的指针变量也和双向链表一样只指向大结构体内的小结构体list的地址空间
的起始地址。
static inline void INIT_LIST_HEAD(struct list_head *list)
{
list->next = list;
list->prev = list;
}
#endif
}
//------------------------------增-------------------------------------
//将新值放到链表表头之后
//比如 依次存放 1 2 3 4 5
//链表则为： 表头 5 4 3 2 1
void doublelist_addnum(double_plist H,int num)
{
double_plist new;
doublelist_new(&new); //开辟新的空间给new
new->data = num;
list_add(&new->list,&H->list);
#if 0
内核链表list_add函数是将新的节点内的list指针成员与之前H的list的
内的list指针成员相互指向，而并非是指向大结构体的起始地址。通过
以下的内核定义可以看出。
static inline void list_add(struct list_head *new, struct list_head *head)
{
__list_add(new, head, head->next);
}
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;
#endif
}
//将新值放到链表表尾之后
//比如 依次存放 1 2 3 4 5
//链表则为： 旧表尾 1 2 3 4 5
void doublelist_addnum_tail(double_plist H,int num)
{
double_plist new;
doublelist_new(&new); //开辟新的空间给new
new->data = num;
list_add_tail(&new->list,&H->list);
}
//------------------------------查-------------------------------------
//显示双向链表内数据
void doublelist_show(double_plist H)
{
int i=1;
double_plist p;
//for(p=list->next; p!=list; p=p->next){
list_for_each_entry(p, &H->list,list){
#if 0
/**内核里的list_for_each_entry的定义
************历遍链表****************
*
* @pos: 临时的H类型的指针变量
* @head: 表头H内存放的list结构体地址
* @member H内的小结构体变量名，我的就是list
*
*/
#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))
#endif
while(i++%6==0){
printf("\n");
}
printf("%d\t",p->data);
}
printf("\n");
}
//------------------------------删-------------------------------------
#if 0
/**
* list_del - 删除对应的节点.
* @entry: 参数是对应的结构体list变量的地址
*/
static inline void list_del(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->next = LIST_POISON1;
entry->prev = LIST_POISON2;
}
#endif
void doublelist_del(double_plist H,int num)
{
int flag=0; //flag 找到删除点的标志位
double_plist p;
//for(p=list->next; p!=list; p=p->next){
list_for_each_entry(p, &(H->list),list){
//如果找到了链表对应的值
if(num == p->data){
list_del(&p->list);
free(p);
flag=1; //标志位置1；
break;
}
}
//如果没找到链表对应的值
if(flag==0){
printf("***在链表中没有找到对应的值***\n");
}
}
//------------------------------改-------------------------------------
void doublelist_revise(double_plist H,int old_num, int new_num)
{
int flag=0; //flag 找到删除点的标志位
double_plist p;
list_for_each_entry(p, &H->list,list){
//for(p=list->next; p!=list; p=p->next){
//如果找到了链表对应的值
if(old_num == p->data){
p->data = new_num;
flag=1; //标志位置1；
}
}
//如果没修改链表对应的值
if(flag==0){
printf("***在链表中没有找到对应的值***\n");
}
}
kernellist.h
#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H
/*
* 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_POISON1 ((void *) 0x00100100 + 0)
#define LIST_POISON2 ((void *) 0x00200200 + 0)
#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) );})
#define LIST_HEAD_INIT(name) { &(name), &(name) }
#define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name)
static inline void INIT_LIST_HEAD(struct list_head *list)
{
list->next = list;
list->prev = list;
}
/*
* Insert a new entry between two known consecutive entries.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
#ifndef CONFIG_DEBUG_LIST
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;
}
#else
extern void __list_add(struct list_head *new,
struct list_head *prev,
struct list_head *next);
#endif
/**
* 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.
*/
#ifndef CONFIG_DEBUG_LIST
static inline void __list_del_entry(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
}
static inline void list_del(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->next = LIST_POISON1;
entry->prev = LIST_POISON2;
}
#else
extern void __list_del_entry(struct list_head *entry);
extern void list_del(struct list_head *entry);
#endif
/**
* list_replace - replace old entry by new one
* @old : the element to be replaced
* @new : the new element to insert
*
* If @old was empty, it will be overwritten.
*/
static inline void list_replace(struct list_head *old,
struct list_head *new)
{
new->next = old->next;
new->next->prev = new;
new->prev = old->prev;
new->prev->next = new;
}
static inline void list_replace_init(struct list_head *old,
struct list_head *new)
{
list_replace(old, new);
INIT_LIST_HEAD(old);
}
/**
* 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(entry);
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_entry(list);
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_entry(list);
list_add_tail(list, head);
}
/**
* list_is_last - tests whether @list is the last entry in list @head
* @list: the entry to test
* @head: the head of the list
*/
static inline int list_is_last(const struct list_head *list,
const struct list_head *head)
{
return list->next == 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 not being modified
* @head: the list to test
*
* Description:
* tests whether a list is empty _and_ checks that no other CPU might be
* in the process of modifying either member (next or prev)
*
* 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.
*/
static inline int list_empty_careful(const struct list_head *head)
{
struct list_head *next = head->next;
return (next == head) && (next == head->prev);
}
/**
* list_rotate_left - rotate the list to the left
* @head: the head of the list
*/
static inline void list_rotate_left(struct list_head *head)
{
struct list_head *first;
if (!list_empty(head)) {
first = head->next;
list_move_tail(first, head);
}
}
/**
* list_is_singular - tests whether a list has just one entry.
* @head: the list to test.
*/
static inline int list_is_singular(const struct list_head *head)
{
return !list_empty(head) && (head->next == head->prev);
}
static inline void __list_cut_position(struct list_head *list,
struct list_head *head, struct list_head *entry)
{
struct list_head *new_first = entry->next;
list->next = head->next;
list->next->prev = list;
list->prev = entry;
entry->next = list;
head->next = new_first;
new_first->prev = head;
}
/**
* list_cut_position - cut a list into two
* @list: a new list to add all removed entries
* @head: a list with entries
* @entry: an entry within head, could be the head itself
* and if so we won't cut the list
*
* This helper moves the initial part of @head, up to and
* including @entry, from @head to @list. You should
* pass on @entry an element you know is on @head. @list
* should be an empty list or a list you do not care about
* losing its data.
*
*/
static inline void list_cut_position(struct list_head *list,
struct list_head *head, struct list_head *entry)
{
if (list_empty(head))
return;
if (list_is_singular(head) &&
(head->next != entry && head != entry))
return;
if (entry == head)
INIT_LIST_HEAD(list);
else
__list_cut_position(list, head, entry);
}
static inline void __list_splice(const struct list_head *list,
struct list_head *prev,
struct list_head *next)
{
struct list_head *first = list->next;
struct list_head *last = list->prev;
first->prev = prev;
prev->next = first;
last->next = next;
next->prev = last;
}
/**
* list_splice - join two lists, this is designed for stacks
* @list: the new list to add.
* @head: the place to add it in the first list.
*/
static inline void list_splice(const struct list_head *list,
struct list_head *head)
{
if (!list_empty(list))
__list_splice(list, head, head->next);
}
/**
* list_splice_tail - join two lists, each list being a queue
* @list: the new list to add.
* @head: the place to add it in the first list.
*/
static inline void list_splice_tail(struct list_head *list,
struct list_head *head)
{
if (!list_empty(list))
__list_splice(list, head->prev, 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, head->next);
INIT_LIST_HEAD(list);
}
}
/**
* list_splice_tail_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.
*
* Each of the lists is a queue.
* The list at @list is reinitialised
*/
static inline void list_splice_tail_init(struct list_head *list,
struct list_head *head)
{
if (!list_empty(list)) {
__list_splice(list, head->prev, 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_first_entry - get the first element from a list
* @ptr: the list head to take the element from.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_struct within the struct.
*
* Note, that list is expected to be not empty.
*/
#define list_first_entry(ptr, type, member) list_entry((ptr)->next, type, member)
/**
* list_for_each - iterate over a list
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
*/
#define list_for_each(pos, head) for (pos = (head)->next; pos != (head); pos = pos->next)
/**
* __list_for_each - iterate over a list
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
*
* This variant doesn't differ from list_for_each() any more.
* We don't do prefetching in either case.
*/
#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 cursor.
* @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 cursor.
* @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_prev_safe - iterate over a list backwards safe against removal of list entry
* @pos: the &struct list_head to use as a loop cursor.
* @n: another &struct list_head to use as temporary storage
* @head: the head for your list.
*/
#define list_for_each_prev_safe(pos, n, head) for (pos = (head)->prev, n = pos->prev; pos != (head); pos = n, n = pos->prev)
/**
* 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_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 cursor.
* @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))
/**
* list_prepare_entry - prepare a pos entry for use in list_for_each_entry_continue()
* @pos: the type * to use as a start point
* @head: the head of the list
* @member: the name of the list_struct within the struct.
*
* Prepares a pos entry for use as a start point in list_for_each_entry_continue().
*/
#define list_prepare_entry(pos, head, member) ((pos) ? : list_entry(head, typeof(*pos), member))
/**
* list_for_each_entry_continue - continue iteration 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_struct within the struct.
*
* Continue to iterate over list of given type, continuing after
* the current position.
*/
#define list_for_each_entry_continue(pos, head, member) for (pos = list_entry(pos->member.next, typeof(*pos), member); &pos->member != (head); pos = list_entry(pos->member.next, typeof(*pos), member))
/**
* list_for_each_entry_continue_reverse - iterate backwards from the given point
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*
* Start to iterate over list of given type backwards, continuing after
* the current position.
*/
#define list_for_each_entry_continue_reverse(pos, head, member) for (pos = list_entry(pos->member.prev, typeof(*pos), member); &pos->member != (head); pos = list_entry(pos->member.prev, typeof(*pos), member))
/**
* list_for_each_entry_from - iterate over list of given type from the current point
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*
* Iterate over list of given type, continuing from current position.
*/
#define list_for_each_entry_from(pos, head, member) for (; &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_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))
/**
* list_for_each_entry_safe_continue - continue list iteration safe against removal
* @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_struct within the struct.
*
* Iterate over list of given type, continuing after current point,
* safe against removal of list entry.
*/
#define list_for_each_entry_safe_continue(pos, n, head, member) for (pos = list_entry(pos->member.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_for_each_entry_safe_from - iterate over list from current point safe against removal
* @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_struct within the struct.
*
* Iterate over list of given type from current point, safe against
* removal of list entry.
*/
#define list_for_each_entry_safe_from(pos, n, head, member) for (n = list_entry(pos->member.next, typeof(*pos), member); &pos->member != (head); pos = n, n = list_entry(n->member.next, typeof(*n), member))
/**
* list_for_each_entry_safe_reverse - iterate backwards over list safe against removal
* @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_struct within the struct.
*
* Iterate backwards over list of given type, safe against removal
* of list entry.
*/
#define list_for_each_entry_safe_reverse(pos, n, head, member) for (pos = list_entry((head)->prev, typeof(*pos), member), n = list_entry(pos->member.prev, typeof(*pos), member); &pos->member != (head); pos = n, n = list_entry(n->member.prev, typeof(*n), member))
/**
* list_safe_reset_next - reset a stale list_for_each_entry_safe loop
* @pos: the loop cursor used in the list_for_each_entry_safe loop
* @n: temporary storage used in list_for_each_entry_safe
* @member: the name of the list_struct within the struct.
*
* list_safe_reset_next is not safe to use in general if the list may be
* modified concurrently (eg. the lock is dropped in the loop body). An
* exception to this is if the cursor element (pos) is pinned in the list,
* and list_safe_reset_next is called after re-taking the lock and before
* completing the current iteration of the loop body.
*/
#define list_safe_reset_next(pos, n, member) n = list_entry(pos->member.next, typeof(*pos), member)
/*
* Double linked lists with a single pointer list head.
* Mostly useful for hash tables where the two pointer list head is
* too wasteful.
* You lose the ability to access the tail in O(1).
*/
#endif
原文地址：http://blog.csdn.net/muyang_ren/article/details/44994817
