基础知识

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

初始化：

#define LIST_HEAD_INIT(name) { (name)->next = (name); (name)->prev = (name);}

相比于下面这样初始化，前面初始化的好处是，处理链表的时候，不用判空了。太厉害了。

#define LIST_HEAD_INIT(name) { (name)->next = (NULL); (name)->prev = (NULL);}

 遍历链表：

/**
 * 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)

添加节点：（表头开始添加）

/*
 * 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 inline 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 inline void list_add(struct list_head *new, struct list_head *head)
{
    __list_add(new, head, head->next);
}

添加节点：（表尾开始添加） 

/*
 * 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 inline 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_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 inline void list_add_tail(struct list_head *new, struct list_head *head)
{
	__list_add(new, head->prev, head);
}

删除节点

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

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

判空：

/**
 * 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;
}

基本功能就这些了

测试代码

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

#define _DEBUG_INFO
#ifdef _DEBUG_INFO
    #define DEBUG_INFO(format,...)	\
        printf("%s:%d -- "format"\n",\
        __func__,__LINE__,##__VA_ARGS__)
#else
    #define DEBUG_INFO(format,...)
#endif

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

struct rcu_private_data{
    struct list_head list;
};

struct my_list_node{
    struct list_head node;
    int number;
};

/**
 * 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)

#define LIST_HEAD_INIT(name) { (name)->next = (name); (name)->prev = (name);}

#define offsetof(TYPE, MEMBER)	((size_t)&((TYPE *)0)->MEMBER)
#define container_of(ptr, type, member) ({				\
	void *__mptr = (void *)(ptr);					\
	((type *)(__mptr - offsetof(type, member))); })


/**
 * 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;
}

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

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

static int list_size(struct rcu_private_data *p){
    struct list_head *pos;
    struct list_head *head = &p->list;
    int count = 0;
    if(list_empty(&p->list)){
        DEBUG_INFO("list is empty");
        return 0;
    }

    list_for_each(pos,head){count++;}
    return count;
}

static int show_list_nodes(struct rcu_private_data *p){
    struct list_head *pos;
    struct list_head *head = &p->list;
    int count = 0;
    struct my_list_node *pnode;

    if(list_empty(&p->list)){
        DEBUG_INFO("list is empty");
        return 0;
    }

    list_for_each(pos,head){
        pnode = (struct my_list_node*)container_of(pos,struct my_list_node,node);
        DEBUG_INFO("pnode->number = %d",pnode->number);
        count++;
    }
    return count;
}

int main(int argc, char **argv){

    int i = 0;
    static struct my_list_node * new[6];
    struct rcu_private_data *p = (struct rcu_private_data*)malloc(sizeof(struct rcu_private_data));
    LIST_HEAD_INIT(&p->list);
    DEBUG_INFO("list_empty(&p->list) = %d",list_empty(&p->list));

    for(i = 0;i < 3;i++){
        new[i] = (struct my_list_node*)malloc(sizeof(struct my_list_node));
        LIST_HEAD_INIT(&new[i]->node);
        new[i]->number = i;
        list_add(&new[i]->node,&p->list);
    }

    for(i = 3;i < 6;i++){
        new[i] = (struct my_list_node*)malloc(sizeof(struct my_list_node));
        LIST_HEAD_INIT(&new[i]->node);
        new[i]->number = i;
        list_add_tail(&new[i]->node,&p->list);
    }


    //输出链表节点数
    DEBUG_INFO("list_size(&p->list) = %d",list_size(p));

    //遍历链表
    show_list_nodes(p);
    //删除指定节点
    list_del(&new[3]->node);
    
    DEBUG_INFO("list_size(&p->list) = %d",list_size(p));
    //遍历链表
    show_list_nodes(p);

    
    for(i = 0;i < 6;i++){list_del(&new[i]->node);}

    DEBUG_INFO("list_size(&p->list) = %d",list_size(p));
    //遍历链表
    show_list_nodes(p);

    for(i = 0;i < 6;i++){free(new[i]);}
    free(p);
    return 0;
}

 编译

gcc -o app app.c

执行结果：

 小结