利用 Linux 内核提供的链表机制创建一个链表

linux 内核提供的链表接口函数定义在 include/linux/list.h 中

main.c

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

#include "list.h"

struct num { // 封装的自己的数据结构
  int i;
  struct list_head list; // 将链表的操作以及组织完全交由内核提供的工具
};

int main(int argc, char **argv) {
  LIST_HEAD(test_list); // 链表头结点 test_list
  /*
  #define LIST_HEAD_INIT(name) { &(name), &(name) }
  #define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name)
  */
  int i;
  struct num *num; // 声明变量
  struct num *num1;

  srand((unsigned)time(NULL));

  /* Add */ 
  printf("add 100 element into list\n");
  for (i = 0; i < 100; i++) {
    num = (struct num*)malloc(sizeof(struct num)); // 创建了一个节点
    num->i = i;
    list_add_tail(&num->list, &test_list); // new entry to be added，list head to add it before 头插法
  }

  i = 0;
  /* print list */
  printf("printf the list\n");
  list_for_each_entry(num, &test_list, list) {
    printf("%2d ", num->i);
    if ((i+1)%10 == 0)
      printf("\n");
    i++;
  }
  printf("\n");

  /* Delete */
  list_for_each_entry_safe(num, num1, &test_list, list) {
    list_del(&num->list);
    free(num);
  }

  if (list_empty(&test_list))
    printf("Free test_list successfully\n");

  return 0;
}

list.h

static inline void __list_add(struct list_head *new,
            struct list_head *prev,
            struct list_head *next)
{
  if (!__list_add_valid(new, prev, next))
    return;

  next->prev = new;
  new->next = next;
  new->prev = prev;
  WRITE_ONCE(prev->next, new);
}
static inline void list_add(struct list_head *new, struct list_head *head)
{
  __list_add(new, head, head->next);
}
static inline void list_add_tail(struct list_head *new, struct list_head *head) // 新节点，头结点
{
  __list_add(new, head->prev, head);
}

static inline void __list_del(struct list_head * prev, struct list_head * next)
{
  next->prev = prev;
  WRITE_ONCE(prev->next, next);
}
static inline void __list_del_entry(struct list_head *entry)
{
  if (!__list_del_entry_valid(entry))
    return;

  __list_del(entry->prev, entry->next);
}
static inline void list_del(struct list_head *entry)
{
  __list_del_entry(entry);
  entry->next = LIST_POISON1;
  entry->prev = LIST_POISON2;
}

/**
 * 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_head within the struct.
 */
#define list_for_each_entry(pos, head, member)        \
  for (pos = list_first_entry(head, typeof(*pos), member);  \
       &pos->member != (head);          \
       pos = list_next_entry(pos, member))

/**
 * list_empty - tests whether a list is empty
 * @head: the list to test.
 */
static inline int list_empty(const struct list_head *head)
{
  return READ_ONCE(head->next) == head;
}