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:

linux C —— 通用链表(整理自Linux内核链表)_第1张图片

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。

linux C —— 通用链表(整理自Linux内核链表)_第2张图片

 

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_H

2.2 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

 

你可能感兴趣的:(Linux,C语言,list,链表,通用,内核,Linux)