linux内核链表

linux内核的链表实现

定义链表节点和初始化

LIST_HEAD_INIT宏通过将next和prev都指向自身，来对节点进行初始化

LIST_HEAD宏定义一个struct list_head类型的节点，并使用LIST_HEAD_INIT宏进行初始化

点击查看代码

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


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

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

插入节点

linux内核实现了头插法和尾插法。
__list_add函数将待插入节点，插入到prev和next之间，而不管prev和next是什么
list_add和list_add_tail，参数列表一直，但使用__list_add的方式不一致。
list_add将头结点，作为prev。
list_add_tail将头结点的prev，作为prev。
因此list_add是头插法
list_add_tail是尾插法

点击查看代码

/*
 * 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) {
  if (!__list_add_valid(new, prev, next))
    return;

  next->prev = new;
  new->next = next;
  new->prev = prev;
  WRITE_ONCE(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);
}
}

删除节点

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删除链表某个节点，使用list_del
__list_del负责将entry->next->prev 设置为 entrey -> prev。entry->prev->next 设置为 entry->next。entry自身的next指向LIST_POISON1，prev指向LIST_POISON2上。

/*
 * 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;
  WRITE_ONCE(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 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;
}

遍历

遍历链表的代码写的很漂亮，迭代地遍历所有节点。

点击查看代码

/**
 * 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_head within the struct.
  */

define list_for_each_entry(pos, head, member) \

for (pos = list_first_entry(head, typeof(*pos), member);
!list_entry_is_head(pos, head, member);
pos = list_next_entry(pos, member))