linux内核链表使用

 

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)
 #endif

 struct 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;
 #endif
             return 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_test
 SRC=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)