将元素两次添加到Linux内核双链表 [英] Adding element twice into Linux kernel double linked list

问题描述

我正在尝试使用

I am trying to use linux kernel doubly linked-list implementation mentioned in https://github.com/torvalds/linux/blob/master/include/linux/list.h in user-space which its user-space implementation can be found in https://gist.github.com/roychen/1710968

以下是我最初使用的代码，它可以正常工作:)

following is the code which I used at first and it works fine :)

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

struct Node
{
    int data;
    char name[10];
    struct list_head mylist;
};

int main()
{
    LIST_HEAD(plist);

    struct Node node1 = {.data = 10, .name = "node1", .mylist = LIST_HEAD_INIT(node1.mylist)};
    struct Node node2;

    node2.data = 20;
    strcpy(node2.name, "node2");
    INIT_LIST_HEAD(&node2.mylist);

    list_add_tail(&node1.mylist, &plist);
    list_add_tail(&node2.mylist, &plist);

    struct Node* iter;

    list_for_each_entry(iter, &plist, mylist)
    {
        printf("name = %s, data = %d\n", iter->name, iter->data);
    }

    return 0;
}

以上代码的输出为

name = node1, data = 10
name = node2, data = 20

这是预期的.

现在假设我要添加node1 两次

方案1:

    list_add_tail(&node1.mylist, &plist);
    list_add_tail(&node1.mylist, &plist);

输出1:

name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
name = node1, data = 10
... -> non-stopping loop (to infinity)

方案2:

    list_add_tail(&node1.mylist, &plist);
    list_add_tail(&node2.mylist, &plist);
    list_add_tail(&node1.mylist, &plist);

输出2:

name = node1, data = 10 (-> just one node is added to the list instead of 3 nodes)

以上输出显示，至少在其功能宏之一中，list.h实现存在错误.

The above outputs show that the list.h implementation has bug, at least in one of its function macros.

我不知道我们无法在链接列表中添加节点两次的错误在哪里.

I don't know where is the bug which we cannot add a node twice in the linked list.

有什么主意吗?！ :|

Any idea?! :|

***** 编辑 ***** 方案3:

***** EDIT ***** Scenario 3:

    list_add_tail(&node1.mylist, &plist);
    list_add_tail(&node2.mylist, &plist);
    list_add_tail(&node1.mylist, &plist);

    struct Node* iter;

    list_for_each_entry_reverse(iter, &plist, mylist)
    {
        printf("name = %s, data = %d\n", iter->name, iter->data);
    }

输出3:

name = node2, data = 20
name = node1, data = 10
name = node2, data = 20
name = node1, data = 10
name = node2, data = 20
name = node1, data = 10
name = node2, data = 20
name = node1, data = 10
name = node2, data = 20
name = node1, data = 10
... -> non-stopping loop (to infinity)

推荐答案

Linux链表不支持多次添加节点.您不能将其两次添加到同一列表中，也不能将其添加到两个不同的列表中.

The Linux linked list does not support adding a node more than once. You can't add it twice to the same list, and you can't add it to two different lists.

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