Linux内核list_head学习（二）

前一篇文章讨论了list_head 结构的基本结构和实现原理，本文主要介绍一下实例代码。

自己如果想在应用程序中使用list_head 的相应操作（当然应该没人使用了，C++ STL提供了list 用起来貌似更方便）， 在应用程序中需要包含自己的 "list.h" 头文件：

/*
注：这个list.h 是为了配合示例程序而建的，内容来自：linux/include/linux/list.h 和相关文件
*/
#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H
 
struct list_head {
         struct list_head *next, *prev;
};

#define LIST_HEAD_INIT(name) { &(name), &(name) }

#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) );})


static inline void INIT_LIST_HEAD(struct list_head *list)
{
        list->next = list;
        list->prev = 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;
}


static inline void list_add(struct list_head *new, struct list_head *head)
{
        __list_add(new, head, head->next);
}
 
 
static inline void __list_del(struct list_head * prev, struct list_head * next)
{
        next->prev = prev;
        prev->next = next;
}
 
static inline void list_del(struct list_head *entry)
{
        __list_del(entry->prev, entry->next);
        entry->next = NULL;
        entry->prev = NULL;
}


#define prefetch(x) __builtin_prefetch(x)


//注：这里prefetch 是gcc的一个优化，也可以不要
#define list_for_each(pos, head) \
         for (pos = (head)->next; prefetch(pos->next), pos != (head); \
                 pos = pos->next)

#define list_entry(ptr, type, member) \
         container_of(ptr, type, member)

#endif

写了一个简单的应用程序：

#include "list.h" 
#include <stdio.h> 
#include <string.h>

#define MAX_NAME_LEN 32
#define MAX_ID_LEN 10

typedef struct stud
{
    struct list_head list;
    char name[MAX_NAME_LEN];
    char stu_number[MAX_ID_LEN];
}num_n_stu;

int main(void)
{
    struct list_head head;
    num_n_stu stu_1;
    num_n_stu stu_2;
    num_n_stu *entry;

    struct list_head *p;
    INIT_LIST_HEAD(&head);
    strcpy(stu_1.name,"lisi");
    strcpy(stu_1.stu_number,"10000000");

    strcpy(stu_2.name,"zhangsan");
    strcpy(stu_2.stu_number,"10000001");
    list_add(&stu_1.list,&head);
    list_add(&stu_2.list,&head);
    list_del(&stu_2.list);
    list_for_each(p,&head)
    {
        entry=list_entry(p,struct stud,list);
        printf("name: %s\n",entry->name);
        printf("stu_number: %s\n",entry->stu_number);
    }
    list_del(&stu_1.list);
    return 0;
}

在Linux内核中可以使用这个以类似驱动模块的形式加载到内核：（这里就不用使用自定义的list.h了）

#include <linux/list.h>
#include <linux/init.h>
#include <linux/module.h>

MODULE_LICENSE("GPL");

#define MAX_NAME_LEN 32
#define MAX_ID_LEN 10


typedef struct stud
{
    struct list_head list;
    char name[MAX_NAME_LEN];
    char stu_number[MAX_ID_LEN];
}num_n_stu;

static int my_main(void)
{

    struct list_head head;
    num_n_stu stu_1;
    num_n_stu stu_2;
    num_n_stu *entry;

    struct list_head *p;
    INIT_LIST_HEAD(&head);

    strcpy(stu_1.name,"lisi");
    strcpy(stu_1.stu_number,"10000000");

    strcpy(stu_2.name,"zhangsan");
    strcpy(stu_2.stu_number,"10000001");

    list_add(&stu_1.list,&head);
    list_add(&stu_2.list,&head);

    list_del(&stu_2.list);

    list_for_each(p,&head)
    {

        entry=list_entry(p,struct stud,list);

        printk("name: %s\n",entry->name);

        printk("stu_number: %s\n",entry->stu_number);

    }
    
    list_del(&stu_1.list);
    
    return 0;

}

static void my_exit(void)
{
    printk("my_exit ! \n");
}


module_init(my_main);
module_exit(my_exit);