Linux 中的 list_entry [英] list_entry in Linux

问题描述

user/include/linux/list.h

本声明:

#define list_entry(ptr, type, member) ((type *)((char *)(ptr) – (unsigned long)(&((type *)0)->member)))

谁能解释一下这是什么以及它是如何工作的，在此先感谢

附言请尽可能简化您的答案，我了解 Linux 中的线程和进程，现在我正在探索各种可能性，但我对这个问题有点困惑.

解决方案

考虑两个这样的结构:

结构数据{输入一些东西；};结构容器{int something_before;结构数据data_item;int something_after;};

假设您有一个指向 struct data 值的指针:

struct data *data_ptr;

list_entry() 宏可帮助您将 data_ptr 转换为指向保存 struct 数据的 struct 容器 值的指针 值，由 ptr 指向:

struct container *cont_ptr = list_entry(data_ptr, struct container, data_item);

宏的工作原理是计算 struct 容器 中 data_item 的偏移量，然后从 data_ptr 指针中减去那么多字节.当转换为 struct container * 时，它会给出一个指向 struct container 的有效指针，该指针包含这个特定的 struct data inside".>

宏也可以通过使用内置的 offsetof() 宏来简化:

#define list_entry(ptr, type, member) ((type *)((char *)(ptr) – offsetof(type, member)))

user/include/linux/list.h

this declaration:

#define list_entry(ptr, type, member) 
((type *)((char *)(ptr) – (unsigned long)(&((type *)0)->member)))

can somebody please explain what is this and how does it work, thanks in advance

P.S. please simplify your answer as much as possible, I know about threads, processes in Linux, now I'm exploring possibilities and I'm a little bit stuck with this one.

解决方案

Consider two structs like this:

struct data {
    int something;
};

struct container {
    int something_before;
    struct data data_item;
    int something_after;
};

Assume you have a pointer to a struct data value:

struct data *data_ptr;

The list_entry() macro helps you to convert data_ptr to a pointer to the struct container value that holds the struct data value, pointed to by ptr:

struct container *cont_ptr = list_entry(data_ptr, struct container, data_item);

The macro works by computing the offset of data_item inside the struct container, and subtracting that many bytes from the data_ptr pointer. This, when cast to struct container *, gives a valid pointer to the struct container that holds this particular struct data "inside".

The macro can also be simplified a bit by using the builtin offsetof() macro:

#define list_entry(ptr, type, member) 
    ((type *)((char *)(ptr) – offsetof(type, member)))

这篇关于Linux 中的 list_entry的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！