linux内核链表 - 技术栈

一、链表代码

下面链表代码并不完整，完整代码可以到github上linux内核下载，网址linux/include at master · torvalds/linux · GitHub，在linux目录路径为 linux-master\include\linux\list.h

注：下面链表代码只能在linux环境运行，windows运行不了

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/*
 * Copy from linux/list.h
 */

#ifndef _GCP_MISC_LIST_H_
#define _GCP_MISC_LIST_H_

#ifdef __cplusplus
extern "C" {
#endif

#include <stddef.h>

#define LIST_POISON1 NULL
#define LIST_POISON2 NULL

#define container_of(ptr, type, member)                                                            \
    ({                                                                                             \
        const typeof(((type *)0)->member) *__mptr = (ptr);                                         \
        (type *)((char *)__mptr - offsetof(type, member));                                         \
    })

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

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

#define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name)

/**
 * init_list_head - Initialize a list_head structure
 * @list: list_head structure to be initialized.
 *
 * Initializes the list_head to point to itself.  If it is a list header,
 * the result is an empty list.
 */
static inline void init_list_head(struct list_head *list) {
    list->prev = list;
    list->next = list;
}

static inline void __list_add(struct list_head *new_entry, struct list_head *prev,
                              struct list_head *next) {
    next->prev      = new_entry;
    new_entry->next = next;
    new_entry->prev = prev;
    prev->next      = new_entry;
}

/**
 * list_add - add a new_entry entry after the specified head
 * @new_entry: new_entry entry to be added
 * @head: list head to add it after
 *
 * Insert a new_entry entry after the specified head.
 * This is good for implementing stacks.
 */
static inline void list_add(struct list_head *new_entry, struct list_head *head) {
    __list_add(new_entry, head, head->next);
}

/**
 * list_add_tail - add a new_entry entry before the specified head
 * @new_entry: new_entry entry to be added
 * @head: list head to add it before
 *
 * Insert a new_entry entry before the specified head.
 * This is useful for implementing queues.
 */
static inline void list_add_tail(struct list_head *new_entry, struct list_head *head) {
    __list_add(new_entry, head->prev, head);
}

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

/**
 * list_del - deletes entry from list.
 * @entry: the element to delete from the list.
 * Note: list_empty() on entry does not return true after this, the entry is
 * in an undefined state.
 */
static inline void list_del(struct list_head *entry) {
    __list_del(entry->prev, entry->next);
    entry->next = LIST_POISON1;
    entry->prev = LIST_POISON2;
}

static inline void __list_splice(struct list_head *list, struct list_head *head) {
    struct list_head *first = list->next;
    struct list_head *last  = list->prev;
    struct list_head *at    = head->next;

    first->prev = head;
    head->next  = first;

    last->next = at;
    at->prev   = last;
}
/**
 * list_empty - tests whether a list is empty
 * @head: the list to test.
 */
static inline int list_empty(const struct list_head *head) {
    return head->next == head;
}
/**
 * list_splice - join two lists
 * @list: the new_entry list to add.
 * @head: the place to add it in the first list.
 */
static inline void list_splice(struct list_head *list, struct list_head *head) {
    if (!list_empty(list))
        __list_splice(list, head);
}
/**
 * list_replace - replace old entry by new_entry one
 * @old : the element to be replaced
 * @new_entry : the new_entry element to insert
 *
 * If @old was empty, it will be overwritten.
 */
static inline void list_replace(struct list_head *old, struct list_head *new_entry) {
    new_entry->next       = old->next;
    new_entry->next->prev = new_entry;
    new_entry->prev       = old->prev;
    new_entry->prev->next = new_entry;
}

/**
 * list_replace_init - replace old entry by new one and initialize the old one
 * @old : the element to be replaced
 * @new : the new element to insert
 *
 * If @old was empty, it will be overwritten.
 */
static inline void list_replace_init(struct list_head *old, struct list_head *new_entry) {
    list_replace(old, new_entry);
    init_list_head(old);
}
/**
 * list_move - delete from one list and add as another's head
 * @list: the entry to move
 * @head: the head that will precede our entry
 */
static inline void list_move(struct list_head *list, struct list_head *head) {
    __list_del(list->prev, list->next);
    list_add(list, head);
}

/**
 * list_move_tail - delete from one list and add as another's tail
 * @list: the entry to move
 * @head: the head that will follow our entry
 */
static inline void list_move_tail(struct list_head *list, struct list_head *head) {
    __list_del(list->prev, list->next);
    list_add_tail(list, head);
}

/**
 * list_entry - get the struct for this entry
 * @ptr:	the &struct list_head pointer.
 * @type:	the type of the struct this is embedded in.
 * @member:	the name of the list_head within the struct.
 */
#define list_entry(ptr, type, member) container_of(ptr, type, member)

/**
 * list_first_entry - get the first element from a list
 * @ptr:	the list head to take the element from.
 * @type:	the type of the struct this is embedded in.
 * @member:	the name of the list_head within the struct.
 *
 * Note, that list is expected to be not empty.
 */
#define list_first_entry(ptr, type, member) list_entry((ptr)->next, type, member)

/**
 * list_last_entry - get the last element from a list
 * @ptr:	the list head to take the element from.
 * @type:	the type of the struct this is embedded in.
 * @member:	the name of the list_head within the struct.
 *
 * Note, that list is expected to be not empty.
 */
#define list_last_entry(ptr, type, member) list_entry((ptr)->prev, type, member)

/**
 * list_for_each	-	iterate over a list
 * @pos:	the &struct list_head to use as a loop cursor.
 * @head:	the head for your list.
 */
#define list_for_each(pos, head) for (pos = (head)->next; pos != (head); pos = pos->next)
/**
 * list_for_each_entry	-	iterate over list of given type
 * @pos:	the type * to use as a loop cursor.
 * @head:	the head for your list.
 * @member:	the name of the list_struct within the struct.
 */
#define list_for_each_entry(pos, head, member)                                                     \
    for (pos = list_entry((head)->next, typeof(*pos), member); &pos->member != (head);             \
         pos = list_entry(pos->member.next, typeof(*pos), member))
/**
 * list_for_each_prev	-	iterate over a list backwards
 * @pos:	the &struct list_head to use as a loop cursor.
 * @head:	the head for your list.
 */
#define list_for_each_prev(pos, head) for (pos = (head)->prev; pos != (head); pos = pos->prev)

/**
 * list_for_each_safe - iterate over a list safe against removal of list entry
 * @pos:	the &struct list_head to use as a loop cursor.
 * @n:		another &struct list_head to use as temporary storage
 * @head:	the head for your list.
 */
#define list_for_each_safe(pos, n, head)                                                           \
    for (pos = (head)->next, n = pos->next; pos != (head); pos = n, n = pos->next)

/**
 * list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
 * @pos:	the type * to use as a loop cursor.
 * @n:		another type * to use as temporary storage
 * @head:	the head for your list.
 * @member:	the name of the list_struct within the struct.
 */
#define list_for_each_entry_safe(pos, n, head, member)                                             \
    for (pos                         = list_entry((head)->next, typeof(*pos), member),             \
        n                            = list_entry(pos->member.next, typeof(*pos), member);         \
         &pos->member != (head); pos = n, n = list_entry(n->member.next, typeof(*n), member))

#ifdef __cplusplus
}
#endif

#endif /* _GCP_MISC_LIST_H_ */

二、简单演示

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

typedef struct node{
    int id;
    struct list_head list
} Node;

int main() {
    struct list_head list_node_head;

    init_list_head(&list_node_head);               // 初始化链表

    for(int i = 0; i < 10; i ++){
        Node* newNode = (Node*)malloc(sizeof(Node));
        newNode->id = i;
        list_add(&newNode->list, &list_node_head); // 添加节点
    }

    Node* currentNode, *nextNode;                  // 临时变量
    list_for_each_entry(currentNode, &list_node_head, list){ // 遍历节点
        printf("Node ID: %d\n", currentNode->id); 
    }

    list_for_each_entry_safe(currentNode, nextNode, &list_node_head, list) { // 释放内存
        list_del(&currentNode->list);
        free(currentNode);
    }

    return 0;
}

三、详细解释

linux内核链表是其他结构体中来包含struct list_head来实现的，巧妙的运用了宏和链表元素list_head在结构体内的位置关系构。

1.该宏通过struct list_head在结构体的相对位置来确定节点头位置。

比如这样的结构体

struct node{

int id;

struct list_head list

} ; list_node_head->list，通过list与id相对位置关系来得出struct node的地址，最后获取id的值。

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#define container_of(ptr, type, member)                                                            \
    ({                                                                                             \
        const typeof(((type *)0)->member) *__mptr = (ptr);                                         \
        (type *)((char *)__mptr - offsetof(type, member));                                         \
    })

2.链表初始化，两种初始化方式

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

#define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name)

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

3.遍历

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/**
* @pos 是临时指针，记录遍历节点的，类型：你定义的结构体，如举例的 Node 结构体
* @head 是头指针，类型：struct list_head
* @member 是在结构体中，struct list_head 的名称，如举例中Node结构体的list
*/

#define list_for_each_entry(pos, head, member)                                                     \
    for (pos = list_entry((head)->next, typeof(*pos), member); &pos->member != (head);             \
         pos = list_entry(pos->member.next, typeof(*pos), member))


list_for_each_entry(currentNode, &list_node_head, list)

内容不过多说，大家自己看英文注释，都很清楚。