linux内核学习中--"list.h" del move splice 函数理解

第三篇博客，主要是针对删除，移动，合并函数的理解,很简单的，相信大家一看就明白了。

static inline void __list_del(struct list_head * prev, struct list_head * next)     //删除结点。删除链表中prev与next之间的元素{        next->prev = prev;        prev->next = next;}static inline void list_del(struct list_head *entry)               //删除一个结点entry，并将删除结点地址置为0{                                                             __list_del(entry->prev, entry->next);        entry->next = LIST_POISON1;  //指针清除0        entry->prev = LIST_POISON2;  //指针清除0}static inline void list_del_init(struct list_head *entry)      //从链表中删除元素entry,并将其初始化为新的链表。{        __list_del(entry->prev, entry->next);        INIT_LIST_HEAD(entry);        //初始化就是把指针指向自己                       }static inline void list_move(struct list_head *list, struct list_head *head) //将该结点摘除并插入到链表头部{        __list_del(list->prev, list->next);        list_add(list, head);}static inline void list_move_tail(struct list_head *list,    //将该结点摘除并插入到链表尾部部                                  struct list_head *head){        __list_del(list->prev, list->next);        list_add_tail(list, head);}static inline int list_empty(const struct list_head *head)        //测试链表是否为空{        return head->next == head;}static inline int list_empty_careful(const struct list_head *head)   {        struct list_head *next = head->next;        return (next == head) && (next == head->prev);}/*基本的list_empty()仅以头指针的next是否指向自己来判断链表是否为空，Linux链表另行提供了一个list_empty_careful()宏，它同时判断头指针的next和prev，仅当两者都指向自己时才返回真。这主要是为了应付另一个cpu正在处理同一个链表而造成next、prev不一致的情况。但代码注释也承认，这一安全保障能力有限：除非其他cpu的链表操作只有list_del_init()，否则仍然不能保证安全，也就是说，还是需要加锁保护。*/static inline void __list_splice(struct list_head *list,             //合并链表， 将链表list与head合并。                                 struct list_head *head){        struct list_head *first = list->next;        struct list_head *last = list->prev;        struct list_head *at = head->next;        first->prev = head;        head->next = first;        last->next = at;        at->prev = last;}/*** list_splice - join two lists* @list: the new list to add.* @head: the place to add it in the first list.*/static inline void list_splice(struct list_head *list, struct list_head *head) //list不为空的情况下，调用__list_splice()实现list与head的合并{        if (!list_empty(list))                __list_splice(list, 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 inline void list_splice_init(struct list_head *list,       //将两链表合并，并将list初始化。                                    struct list_head *head){        if (!list_empty(list)) {                __list_splice(list, head);                INIT_LIST_HEAD(list);        }}