linux内核链表使用

Linux内核链表的核心思想是：在用户自定义的结构A中声明list_head类型的成员p，这样每个结构类型为A的变量a中，都拥有同样的成员p，如下：

struct A{

int property;

struct list_head p;

}

其中，list_head结构类型定义如下：

struct list_head {

struct list_head *next,*prev;

};

list_head拥有两个指针成员，其类型都为list_head，分别为前驱指针prev和后驱指针next。

假设：

（1）多个结构类型为A的变量a1...an，其list_head结构类型的成员为p1...pn

（2）一个list_head结构类型的变量head，代表头节点

使：

（1）head.next= p1 ; head.prev = pn

（2）p1.prev = head，p1.next = p2;

（3）p2.prev= p1 , p2.next = p3;

…

（n）pn.prev= pn-1 , pn.next = head

以上，则构成了一个循环链表。

因p是嵌入到a中的，p与a的地址偏移量可知，又因为head的地址可知，所以每个结构类型为A的链表节点a1...an的地址也是可以计算出的，从而可实现链表的遍历，在此基础上，则可以实现链表的各种操作。

下面是从linux内核中移植出来的简单链表，list.h和list.c:

list.h:

#ifndef _INIT_LIST_H_#define _INIT_LIST_H_#ifndef offsetof/* Offset of member MEMBER in a struct of type TYPE. */#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)#endifstruct listnode{    struct listnode *next;    struct listnode *prev;};#define node_to_item(node, container, member) \    (container *) (((char*) (node)) - offsetof(container, member))#define list_declare(name) \    struct listnode name = { \        .next = &name, \        .prev = &name, \    }#define list_for_each(node, list) \    for (node = (list)->next; node != (list); node = node->next)#define list_for_each_reverse(node, list) \    for (node = (list)->prev; node != (list); node = node->prev)void list_init(struct listnode *list);void list_add_tail(struct listnode *list, struct listnode *item);void list_remove(struct listnode *item);#define list_empty(list) ((list) == (list)->next)#define list_head(list) ((list)->next)#define list_tail(list) ((list)->prev)#endif

list.c：

#include "list.h"void list_init(struct listnode *node){    node->next = node;    node->prev = node;}void list_add_tail(struct listnode *head, struct listnode *item){    item->next = head;    item->prev = head->prev;    head->prev->next = item;    head->prev = item;}void list_remove(struct listnode *item){    item->next->prev = item->prev;    item->prev->next = item->next;}

测试代码list_test.c:

#include<stdio.h>#include<stdlib.h>#include "list.h"#define STUDENT_FREE_MEMORY//声明链表节点typedef struct {int id;char *name;struct listnode _list;}student;//遍历函数指针typedef void (*student_foreach_fun)(student *stu,void *data);//声明链表static list_declare(student_list);//添加节点int student_add(struct listnode *list,student *stu){list_init(&stu->_list);list_add_tail(list,&stu->_list);}//删除节点，释放节点空间int student_del(struct listnode *list,int id){struct listnode *node;student *stu;list_for_each(node,list){stu = node_to_item(node,student,_list);if(id == stu->id){printf("list_del, id:%d,name:%s\n",stu->id,stu->name);list_remove(node);#ifdef STUDENT_FREE_MEMORY//释放节点空间free(stu);stu = NULL;#endifreturn 1;}}return 0;}//节点遍历void student_foreach(struct listnode *list,student_foreach_fun fun,void *data){struct listnode *node;student *stu;list_for_each(node,list){stu = node_to_item(node,student,_list);fun(stu,data);}}//打印节点信息void student_print(student *stu,void *data){printf("id:%d,name:%s\n",stu->id,stu->name);}int main(){int i,len;student *stu;char *stu_name[]={"tonny","andy","michael","leslie","john"};len = sizeof(stu_name)/sizeof(stu_name[0]);//添加节点for(i=0;i<len;i++){stu = calloc(1,sizeof(student));stu->id = i + 1;stu->name = stu_name[i];student_add(&student_list,stu);}//打印所有节点student_foreach(&student_list,student_print,(void *)0);//删除节点student_del(&student_list,1);student_foreach(&student_list,student_print,(void *)0);//删除节点student_del(&student_list,5);student_foreach(&student_list,student_print,(void *)0);return 0;}

Makefile:

TARGET=list_testSRC=list_test.c list.c#SRC=$(wildcard *.c)OBJ=$(SRC:.c=.o)CFLAGS=-g -Wall -o$(TARGET):$(SRC)gcc $(SRC) $(CFLAGS) $(TARGET)clean:rm $(OBJ) $(TARGET)