三.list_head、hash_list等分析

这篇文章其实是根据xboot文件系统或者整个kernel都用到list_head而写的一个简单的示例，通过示例可以明白list_head的用法。

编写list_head.h文件，内容如下：

#ifndef _LIST_HEAD_
#define _LIST_HEAD_


struct list_head
{
    struct list_head *prev,*next;
};



#endif

编写list_head.c文件，内容如下：

#include "list_head.h"


void list_head_init(struct list_head *entry)
{
    entry->next = entry;
    entry->prev = entry;
}

void _list_add(struct list_head *new,struct list_head *prev, struct list_head *next)
{
    new->next = next;
    next->prev= new;
    new->prev= prev;
    prev->next=new;
}

void list_add(struct list_head *new,struct list_head *old)
{
    _list_add(new,old,old->next);
}

void list_add_tail(struct list_head *new,struct list_head *old)
{
    _list_add(new,old->prev,old);
}

void list_del(struct list_head *entry,struct list_head *old)
{
    entry->prev->next = entry->next;
    entry->next->prev = entry->prev;
}

接着是main.c文件，内容如下：

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

struct student{
    struct list_head stu_list;
    int age;
    char name[10];
};

struct list_head g_stu_entry;


int main(int argc, char const *argv[])
{
    struct student st1;
    struct student st2;
    struct student st3;

    struct student *st;

    struct list_head *pos;
   
    list_head_init(&g_stu_entry);

    st1.age = 10;
    memcpy(st1.name,"zhangsan",sizeof("zhangsan"));
    list_add_tail(&st1.stu_list,&g_stu_entry);

    st2.age = 20;
    memcpy(st2.name,"lisi",sizeof("lisi"));
    list_add_tail(&st2.stu_list,&g_stu_entry);

    st3.age = 30;
    memcpy(st3.name,"wangwu",sizeof("wangwu"));
    list_add_tail(&st3.stu_list,&g_stu_entry);


    printf("st1=0x%0x\r\n",&st1);

    for(pos=g_stu_entry.next;pos!=&g_stu_entry;pos=pos->next){
        st=(struct student *)((char *)pos-(char *)(&((struct student *)0)->stu_list));
        printf("st=0x%0x\r\n",st);
        printf("*st.age=%d\r\n",st->age);
        printf("*st.name=%s\r\n",st->name); 
    }

    printf("del some point...\r\n");
    list_del(&st2.stu_list,&g_stu_entry);


    for(pos=g_stu_entry.next;pos!=&g_stu_entry;pos=pos->next){
        st=(struct student *)((char *)pos-(char *)(&((struct student *)0)->stu_list));
        printf("st=0x%0x\r\n",st);
        printf("*st.age=%d\r\n",st->age);
        printf("*st.name=%s\r\n",st->name); 
    }
    return 0;
}

最后，执行文件：

$  gcc *.c -o list_head
$ ./list_head         
st1=0xf7b986f0
st=0xf7b986f0
*st.age=10
*st.name=zhangsan
st=0xf7b98710
*st.age=20
*st.name=lisi
st=0xf7b98730
*st.age=30
*st.name=wangwu
del some point...
st=0xf7b986f0
*st.age=10
*st.name=zhangsan
st=0xf7b98730
*st.age=30
*st.name=wangwu

具体分析，就不多说了。