出于对内核工作效率的好奇，最近在研究内核数据结构。
在此整理一份双向循环链表的文档，并附上相关测试代码。
（后续继续补充其它数据结构及算法）
1.代码最关键部分是my_list.h头文件，里面涉及绝大大部分对链表的处理，如添加、查找、删除、拼接，遍历等。代码整理如下：
/**********************************************************
链表跟数组的不同：
1.链表元素可实现动态创建插入，编译时不用跟数组一样确定具体需要创建多少个元素
2.链表中每个元素创建的时间各不相同，在内存中无需占用连续内存区
根据以上特性：
各元素需要通过某种方式连接到一起，于是每个元素都包含下一个元素的指针，
当有元素加入或者从链表中删除时，调整指向下一个节点的指针就可以。
链表分类：
单向链表 环形单向链表
双向链表 环形双向链表
linux内核采用环形双向链表
使用链表存放数据的理想情况：
需要遍历所有数据或需要动态加入删除数据
Author:gang.li<xfxylg@163.com>
***************************************************************/
#ifndef _LINUX_MYLIST_H
#define _LINUX_MYLIST_H
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)
#if 1
#define INIT_LIST_HEAD(ptr) do { \
(ptr)->next = (ptr); (ptr)->prev = (ptr); \
} while (0)
#else
static inline void INIT_LIST_HEAD(struct list_head *list)
{
list->next = list;
list->prev = list;
}
#endif
//------------------------------------------------------------------
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);
}
//-------------------------------------------------------------------
#define prefetch(x) __builtin_prefetch(x)
/**
* list_for_each - iterate over a list
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
* 遍历链表，pos用来指向当前项，head是提供需要遍历链表的头
*/
#define list_for_each(pos, head) \
for (pos = (head)->next; prefetch(pos->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_entry - get the struct for this entry
* @ptr: the &struct list_head pointer.
* @member: the name of the list_struct within the struct.
* 获取链表条目结构指针
*/
#define list_entry(ptr, type, member) \
container_of(ptr, type, member)
#ifndef container_of
/**
* 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) );})
#endif
#undef offsetof
#ifdef __compiler_offsetof
#define offsetof(TYPE,MEMBER) __compiler_offsetof(TYPE,MEMBER)
#else
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#endif
//-----------------------------------------------------------------------
/**
* 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.
* 遍历链表，安全删除链表条目
*/
#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.
* pos：包含list_head节点的对象指针(list_entry宏返回指针值)
* head：需要遍历的链表
* member：pos指针所指对象，成员（struct list_head）的变量名
*/
#define list_for_each_entry(pos, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member); \
prefetch(pos->member.next), &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.
* 与list_for_each_entry对应，为反向遍历
*/
#define list_for_each_entry_reverse(pos, head, member) \
for (pos = list_entry((head)->prev, typeof(*pos), member); \
prefetch(pos->member.prev), &pos->member != (head); \
pos = list_entry(pos->member.prev, 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))
#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))
/*
* Architectures might want to move the poison pointer offset
* into some well-recognized area such as 0xdead000000000000,
* that is also not mappable by user-space exploits:
*/
#ifdef CONFIG_ILLEGAL_POINTER_VALUE
# define POISON_POINTER_DELTA _AC(CONFIG_ILLEGAL_POINTER_VALUE, UL)
#else
# define POISON_POINTER_DELTA 0
#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 + POISON_POINTER_DELTA)
#define LIST_POISON2 ((void *) 0x00200200 + POISON_POINTER_DELTA)
/*
* 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.
* 删除链表特定元素
*/
static inline void list_del(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->next = LIST_POISON1;
entry->prev = LIST_POISON2;
}
/**
* 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
* 从一个链表中移除节点list项，然后将其加入到另一链表的head节点后
*/
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
* 从一个链表中移除节点list项，然后将其加入到另一链表的末尾
*/
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;
}
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.
* 合并两个链表，将list指向的链表插入到指定链表的head元素后面
*/
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);
}
}
#endif
2.编写的相关测试代码在main.c里面，如下：
#include <stdio.h>
#include <stdlib.h>
#include "./my_list.h"
typedef struct _data_node{
int data;
struct list_head list;
}data_node,*pnode;
pnode create_list()
{
/*create double dir list,init head ptr,waring:actually data section no use*/
pnode head= (pnode)malloc(sizeof(data_node));
if (head == NULL) {
printf("file,%s line,%d:malloc error!\n",__FILE__,__LINE__);
exit(1);
}
INIT_LIST_HEAD(&head->list);
return head;
}
pnode create_node(int data)
{
/*create double dir list,init head ptr,waring:actually data section no use*/
pnode node = (pnode)malloc(sizeof(data_node));
if (node == NULL) {
printf("file,%s line,%d:malloc error!\n",__FILE__,__LINE__);
exit(1);
}
memset(node,0,sizeof(data_node));
node->data = data;
return node;
}
int main(int argc , int **argv)
{
if(argc != 2){
printf("%s parm input fail!!\n",argv[0]);
}
int num = atoi(argv[1]);
srand(time(NULL));
printf("once create list :");
pnode head=create_list();
int i=0;
for(i=0; i<num; i++){
pnode new_node= create_node(rand()%500);
printf("%d ",new_node->data);
list_add(&new_node->list,&head->list);
//list_add_tail(&new_node->list, &list_2->list);
}
printf("\n\npositive traverse:");
pnode entry;
list_for_each_entry(entry,&head->list,list){
printf("%d ",entry->data);
}
printf("\nreverse traverse :");
list_for_each_entry_reverse(entry,&head->list,list){
printf("%d ",entry->data);
}
printf("\n");
#if 1
int del;
printf("delete appoint node :");
scanf("%d",&del);
/*delete list appoint node*/
struct list_head *pos=NULL,*n=NULL;
list_for_each_safe(pos,n,&head->list) {
entry = list_entry(pos, struct _data_node ,list);
if(entry->data == del){
//printf("num %d has removed from the list!\n",entry->data);
list_del(pos);
/*warning:每次安全删除链表条目后，必须free条目指针*/
free(entry);entry=NULL;
}else{
//printf("\nappoint node: %d not exist\n ",del);
printf("%d ",entry->data);
}
}
printf("\n\n");
#endif
#if 0
/*delete list all node*/
pnode entry_tmp, pnext;
list_for_each_entry_safe(entry_tmp,pnext,&head->list,list){
printf("safe iterate over del num %d has removed from the list!\n",entry_tmp->data);
free(entry_tmp);entry_tmp=NULL;
}
#endif
#if 1
printf("\ntwice create list:");
pnode head_new=create_list();
for(i=0; i<num; i++){
pnode node_new= create_node(rand()%500);
printf("%d ",node_new->data);
list_add(&node_new->list,&head_new->list);
//list_add_tail(&new_node->list, &list_2->list);
}
printf("\n\npositive traverse:");
pnode entry_new;
list_for_each_entry(entry_new,&head_new->list,list){
printf("%d ",entry_new->data);
}
printf("\n");
/*two list splice*/
list_splice(&head_new->list, &head->list);
printf("two list splice back input :");
list_for_each_entry(entry_new,&head->list,list){
printf("%d ",entry_new->data);
}
printf("\n");
#endif
}3.Makefile文件
CC = gcc
RM = rm
CFLAGS =
TARGETS := list_test
#OBJS = stu.o
OBJS = main.o
all:clean $(OBJS)
$(CC) $(CFLAGS) -o $(TARGETS) $(OBJS)
%.o:%.c
$(CC) -c -o $@ $(CFLAGS) $<
@echo "gcc" $<
clean:
-$(RM) -f *.o
-$(RM) -f $(TARGETS)在同一级目录下，添加以上三个文件，可直接编译运行，可根据个人需要添加相关测试代码。
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