linux C —— 通用链表（整理自Linux内核链表）
目录
1. 简介
1.1 内核链表的思想
1.2 内核链表的技术原理：
2. 基于内核链表的通用链表
2.1 list.h
2.2 test.c
3. 内核链表
4. 文件下载
1. 简介
在Linux源代码树的include/linux/list.h文件中，采用了一种类型无关的双循环链表实现方式。其思想是将指针prev和next从具体的数据结构中提取出来构成一种通用的"双链表"数据结构list_head。如果需要构造某类对象的特定链表，则在其结构（被称为宿主数据结构）中定义一个类型为list_head类型的成员，通过这个成员将这类对象连接起来，形成所需链表，并通过通用链表函数对其进行操作。其优点是只需编写通用链表函数，即可构造和操作不同对象的链表，而无需为每类对象的每种列表编写专用函数，实现了代码的重用。
内核链表，参考：
https://blog.csdn.net/qq_26501341/article/details/53612641
https://blog.csdn.net/caihaitao2000/article/details/80556562
1.1 内核链表的思想
可以理解为：谁使用连接，就包含链表节点，通过链表节点联系数据节点。将链表操作与各种数据节点隔离开，无需因数据节点结构的变化修改链表操作。如图：
1.2 内核链表的技术原理：
数据节点结构如下：
struct person
{
int age;
int weight;
struct list_head list;
}
我们有一个指针：
struct list_head *pos;
现在有这个指针，我们怎么去获得这个指针所在的结构的变量（即是struct person变量，其实是struct
person指针）呢？看下面这样使用：
struct person *one = list_entry(pos, struct person, list);
宏展开一下（见下面源码部分说明）：
struct person *one = ((struct person *)((char *)(pos) - (size_t)(&((struct person *)0)->list)))
(size_t)(&((struct person *)0)->list)))就是成员在结构体中偏移，用offsetof宏取得。
2. 基于内核链表的通用链表
在Linux下，只需包含内核链表头文件，就可以使用内核链表，无需自己造轮子。
2.1 list.h
根据内核链表，整理通用链表（只需包含此头文件）如下：
#ifndef __C_LIST_H
#define __C_LIST_H
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
/**
* container_of - cast a member of a structure out to the containing structure
* @ptr: the pointer to the member.
* @type: the type of the container struct this is embedded in.
* @member: the name of the member within the struct.
*
*/
#define container_of(ptr, type, member) (type *)((char *)ptr -offsetof(type,member))
/*
* These are non-NULL pointers that will result in page faults
* under normal circumstances, used to verify that nobody uses
* non-initialized list entries.
*/
#define LIST_POISON1 ((void *) 0x00100100)
#define LIST_POISON2 ((void *) 0x00200200)
struct list_head {
struct list_head *next, *prev;
};
/**
* 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_struct 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_struct 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_HEAD(name) = { &(name), &(name) }
* init the struct list_head, next = prev = &name
*/
#define LIST_HEAD_INIT(name) { &(name), &(name) }
#define LIST_HEAD(name) \
struct list_head name = LIST_HEAD_INIT(name)
/**
* INIT_LIST_HEAD is a fun for init list
* LIST_HEAD_INIT is macro for init list
*/
static void INIT_LIST_HEAD(struct list_head *list)
{
list->next = list;
list->prev = list;
}
/**
* list_for_each - iterate over a list
* @pos: the &struct list_head to use as a loop counter.
* @head: the head for your list.
*/
#define list_for_each(pos, head) \
for (pos = (head)->next; pos != (head); pos = pos->next)
/**
* 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_r - iterate over a list reversely
* @pos: the &struct list_head to use as a loop counter.
* @head: the head for your list.
*/
#define list_for_each_r(pos, head) \
for (pos = (head)->prev; pos != (head); pos = pos->prev)
/*
* Insert a new entry between two known consecutive entries.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
static 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;
}
/**
* list_add - add a new entry
* @new: new entry to be added
* @head: list head to add it after
*
* Insert a new entry after the specified head.
* This is good for implementing stacks.
*/
static void list_add(struct list_head *new, struct list_head *head)
{
__list_add(new, head, head->next);
}
/**
* list_add_tail - add a new entry
* @new: new entry to be added
* @head: list head to add it before
*
* Insert a new entry before the specified head.
* This is useful for implementing queues.
*/
static void list_add_tail(struct list_head *new, struct list_head *head)
{
__list_add(new, head->prev, head);
}
/*
* Delete a list entry by making the prev/next entries
* point to each other.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
* The caller must free the memerry.
*/
static void __list_del(struct list_head * prev, struct list_head * next)
{
next->prev = prev;
prev->next = next;
}
/**
* 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 void list_del(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->next = LIST_POISON1;
entry->prev = LIST_POISON2;
}
/**
* list_del_init - deletes entry from list and reinitialize it.
* @entry: the element to delete from the list.
*/
static void list_del_init(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
INIT_LIST_HEAD(entry);
}
/**
* list_replace - replace old entry by new one
* @old : the element to be replaced
* @new : the new element to insert
*
* If @old was empty, it will be overwritten.
*/
static void list_replace(struct list_head *old,
struct list_head *new)
{
new->next = old->next;
new->next->prev = new;
new->prev = old->prev;
new->prev->next = new;
}
static void list_replace_init(struct list_head *old,
struct list_head *new)
{
list_replace(old, new);
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 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 void list_move_tail(struct list_head *list,
struct list_head *head)
{
__list_del(list->prev, list->next);
list_add_tail(list, head);
}
/**
* list_is_last - tests whether @list is the last entry in list @head
* @list: the entry to test
* @head: the head of the list
*/
static int list_is_last(const struct list_head *list,
const struct list_head *head)
{
return list->next == head;
}
/**
* list_empty - tests whether a list is empty
* @head: the list to test.
*/
static int list_empty(const struct list_head *head)
{
return head->next == head;
}
/**
* list_empty_careful - tests whether a list is empty and not being modified
* @head: the list to test
*
* Description:
* tests whether a list is empty _and_ checks that no other CPU might be
* in the process of modifying either member (next or prev)
*
* NOTE: using list_empty_careful() without synchronization
* can only be safe if the only activity that can happen
* to the list entry is list_del_init(). Eg. it cannot be used
* if another CPU could re-list_add() it.
*/
static int list_empty_careful(const struct list_head *head)
{
struct list_head *next = head->next;
return (next == head) && (next == head->prev);
}
/**
* list_is_singular - tests whether a list has just one entry.
* @head: the list to test.
*/
static int list_is_singular(const struct list_head *head)
{
return !list_empty(head) && (head->next == head->prev);
}
static void __list_cut_position(struct list_head *list,
struct list_head *head, struct list_head *entry)
{
struct list_head *new_first = entry->next;
list->next = head->next;
list->next->prev = list;
list->prev = entry;
entry->next = list;
head->next = new_first;
new_first->prev = head;
}
/**
* list_cut_position - cut a list into two
* @list: a new list to add all removed entries
* @head: a list with entries
* @entry: an entry within head, could be the head itself
* and if so we won't cut the list
*
* This helper moves the initial part of @head, up to and
* including @entry, from @head to @list. You should
* pass on @entry an element you know is on @head. @list
* should be an empty list or a list you do not care about
* losing its data.
*
*/
static void list_cut_position(struct list_head *list,
struct list_head *head, struct list_head *entry)
{
if (list_empty(head))
return;
if (list_is_singular(head) &&
(head->next != entry && head != entry))
return;
if (entry == head)
INIT_LIST_HEAD(list);
else
__list_cut_position(list, head, entry);
}
/**
* add list between prev and next
*/
static inline void __list_splice(const struct list_head *list,
struct list_head *prev,
struct list_head *next)
{
struct list_head *first = list->next;
struct list_head *last = list->prev;
first->prev = prev;
prev->next = first;
last->next = next;
next->prev = last;
}
/**
* list_splice - join two lists, this is designed for stacks
* @list: the new list to add.
* @head: the place to add it in the first list.
*/
static inline void list_splice(const struct list_head *list,
struct list_head *head)
{
if (!list_empty(list))
__list_splice(list, head, head->next);
}
/**
* list_splice_tail - join two lists, each list being a queue
* @list: the new list to add.
* @head: the place to add it in the first list.
*/
static void list_splice_tail(struct list_head *list,
struct list_head *head)
{
if (!list_empty(list))
__list_splice(list, head->prev, head);
}
/**
* list_splice_init - join two lists and reinitialise the emptied list.
* @list: the new list to add.
* @head: the place to add it in the first list.
*
* The list at @list is reinitialised
*/
static void list_splice_init(struct list_head *list,
struct list_head *head)
{
if (!list_empty(list)) {
__list_splice(list, head, head->next);
INIT_LIST_HEAD(list);
}
}
/**
* list_splice_tail_init - join two lists and reinitialise the emptied list
* @list: the new list to add.
* @head: the place to add it in the first list.
*
* Each of the lists is a queue.
* The list at @list is reinitialised
*/
static void list_splice_tail_init(struct list_head *list,
struct list_head *head)
{
if (!list_empty(list)) {
__list_splice(list, head->prev, head);
INIT_LIST_HEAD(list);
}
}
#endif // __C_LIST_H2.2 test.c
测试程序如下：
#include
#include "list.h"
struct person
{
/* data */
int age;
int weight;
/* list */
struct list_head list;
};
int main(int argc, char* argv[])
{
struct person *tmp;
struct list_head *pos;
int age_i, weight_j;
struct person person_node;
INIT_LIST_HEAD( &(person_node.list) );
for(age_i = 10, weight_j = 35; age_i < 40; age_i += 5, weight_j += 5)
{
tmp =(struct person*)malloc(sizeof(struct person));
tmp->age = age_i;
tmp->weight = weight_j;
/* 头插 */
list_add( &(tmp->list), &(person_node.list) );
}
// 下面把这个链表中各个节点的值打印出来
printf("\n");
printf("=========== print the list ===============\n");
list_for_each( pos, &(person_node.list) )
{
// 这里我们用list_entry来取得pos所在的结构的指针
tmp = list_entry(pos, struct person, list);
printf("age:%d, weight: %d \n", tmp->age, tmp->weight);
}
printf("\n");
// 下面删除一个节点中，age为20的节点
printf("========== print list after delete a node which age is 20 ==========\n");
struct list_head *del_tmp;
list_for_each_safe( pos, del_tmp, &(person_node.list) )
{
tmp = list_entry(pos, struct person, list);
if(tmp->age == 20)
{
list_del_init(pos);
free(tmp);
}
}
list_for_each( pos, &(person_node.list) )
{
tmp = list_entry(pos, struct person, list);
printf("age:%d, weight: %d \n", tmp->age, tmp->weight);
}
// 释放资源
list_for_each_safe( pos, del_tmp, &(person_node.list) )
{
tmp = list_entry(pos, struct person, list);
list_del_init(pos);
free(tmp);
}
return 0;
} 运行结果：
[root@localhost tmp]# ./a.out
=========== print the list ===============
age:35, weight: 60
age:30, weight: 55
age:25, weight: 50
age:20, weight: 45
age:15, weight: 40
age:10, weight: 35
========== print list after delete a node which age is 20 ==========
age:35, weight: 60
age:30, weight: 55
age:25, weight: 50
age:15, weight: 40
age:10, weight: 35 3. 内核链表
适合链表、栈、队列、哈希表的操作。
4. 文件下载
https://download.csdn.net/download/u011285208/11245935