常用linux 链表分析

àì夳堔傛蜴生んèń 2022-04-10 01:40 204阅读 0赞

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本文仅仅记录比较常用的操作内核链表接口

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static inline 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.
     *
     */
     /* 该函数是将head头结点的链表切隔为两个链表，分割点为entry， list是一个
      * 新的链表头，list后面的第一个节点是原head头节点的第一个节点，list的尾节点
      * 是entry节点。原head链表的首节点变为entry的下一个节点，head链表的尾节点还是原来的尾节点。
      */
    static inline 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);
    }

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.
     */
     
    /* 将list链表中的节点添加到head的头部，此时list就只是一个空的链表头 */
    static inline void list_splice(const struct list_head *list,
    				struct list_head *head)
    {
    	if (!list_empty(list))
    		__list_splice(list, head, head->next);
    }

/**
     * 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.
     *
     */
     /* 该函数实现原理就是利用偏移 */
    #define container_of(ptr, type, member) ({			\
    	const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
    	(type *)( (char *)__mptr - offsetof(type,member) );})
    
    
    
    
    /**
     * 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_head within the struct.
     */
    
    /* 该函数的功能是根据结构体中的某个成员地址，得到该结构体的首地址，使用结构体的
     * 首地址可以访问结构体中的其他成员。
     * ptr是结构体中的成员地址，也就是member的地址
     * type是结构体的类型，member是list_head结构体类型的名字。
     */
    #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_head within the struct.
     *
     * Note, that list is expected to be not empty.
     */
     /* 获得链表头的第一个节点，ptr一般是链表头的list_head地址 */
    #define list_first_entry(ptr, type, member) \
    	list_entry((ptr)->next, type, member)
    
    /**
     * list_last_entry - get the last 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_head within the struct.
     *
     * Note, that list is expected to be not empty.
     */
     
    /* 获得链表头的最后一个节点，ptr一般是链表头的list_head地址 */
    #define list_last_entry(ptr, type, member) \
    	list_entry((ptr)->prev, type, member)
    
    
    /**
     * list_for_each	-	iterate over a list
     * @pos:	the &struct list_head to use as a loop cursor.
     * @head:	the head for your list.
     */
     /* 用于遍历head链表的所有成员，pos是中间临时变量，从链表中取出的每个节点使用pos变量临时保存 
      * 遍历过程是从head的下一个节点开始依次遍历。这种方式有一个缺点：就是在使用list_del(pos)时，
      * pos的前驱指针和后继指针都指向了非法地址，因此无法执行pos = pos->next。
      */
    #define list_for_each(pos, head) \
    	for (pos = (head)->next; pos != (head); pos = pos->next)
    
    
    /**
     * list_for_each_prev	-	iterate over a list backwards
     * @pos:	the &struct list_head to use as a loop cursor.
     * @head:	the head for your list.
     */
      /* 用于遍历head链表的所有成员，pos是中间临时变量，从链表中取出的每个节点使用pos变量临时保存 
      * 遍历过程是从head的上一个节点开始依次遍历，也就是反向遍历。
      */
    #define list_for_each_prev(pos, head) \
    	for (pos = (head)->prev; pos != (head); pos = pos->prev)
    
    
    /**
     * 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.
     */
     /* 带有safe的接口，就防止了list_for_each接口不能删除pos节点的问题，因为该接口中有两个临时节
      * 点。pos是当前使用的临时节点，n是pos的下一个节点，当删除pos节点后，依然可以得到pos的后一个节
      * 点。 因此带有safe的接口，是可以执行删除操作的。而list_for_each接口是不能执行list_del(pos)
      * 操作的。
      */
    #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_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.
     */
     /* 该接口是依次从head链表中正向取出元素，但是该接口不能删除pos，原因list_entry */
    #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_for_each_entry_safe - iterate over list of given type safe against removal of list entry
     * @pos:	the type * to use as a loop cursor.
     * @n:		another type * to use as temporary storage
     * @head:	the head for your list.
     * @member:	the name of the list_head within the struct.
     */
     /* 该接口与list_for_each_entry接口功能相同，但是此接口可以适用于删除pos节点 */
    #define list_for_each_entry_safe(pos, n, head, member)			\
    	for (pos = list_first_entry(head, typeof(*pos), member),	\
    		n = list_next_entry(pos, member);			\
    	     &pos->member != (head); 					\
    	     pos = n, n = list_next_entry(n, member))