1. 函数原型

内核中的链表结构如下，只有前后两个指针，没有数据项，可以很方便的构成双向链表

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

1.1. static inline void INIT_LIST_HEAD(struct list_head *list)

运行的时候初始化链表，两个指针都指向结点自己的地址

static inline void INIT_LIST_HEAD(struct list_head *list)
{
    WRITE_ONCE(list->next, list);
    list->prev = list;
}

1.2. static inline void list_add(struct list_head new, struct list_head head)；

从指定结点后面插入一个结点,new为要插入的新节点的地址，head为要插入的结点，新结点从head结点后面插入

/**
 * 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);
}

其中，__list_add()函数定义如下，在知道前后结点的情况下，插入结点

/*
 * 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);
}

1.3. static inline void list_add_tail(struct list_head new, struct list_head head)

从链表尾部插入结点

/**
 * 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);
}

1.4. static inline void list_del(struct list_head *entry)

两个宏定义，删除下来的prev、next指针指向这两个特殊值，这样设置是为了保证不在链表中的结点项不可访问--对LIST_POISON1和LIST_POISON2的访问都将引起页故障。
/*
 * These are non-NULL pointers that will result in page faults
 * under normal circumstances, used to verify that nobody uses
 * non-initialized list entries.
 */
#define LIST_POISON1  ((void *) 0x100 + POISON_POINTER_DELTA)
#define LIST_POISON2  ((void *) 0x122 + POISON_POINTER_DELTA)

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

其中__list_del_entry()函数定义如下：

/*
 * 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);
}

/*
 * Delete a list entry and clear the 'prev' pointer.
 *
 * This is a special-purpose list clearing method used in the networking code
 * for lists allocated as per-cpu, where we don't want to incur the extra
 * WRITE_ONCE() overhead of a regular list_del_init(). The code that uses this
 * needs to check the node 'prev' pointer instead of calling list_empty().
 */
static inline void __list_del_clearprev(struct list_head *entry)
{
    __list_del(entry->prev, entry->next);
    entry->prev = NULL;
}

/**
 * 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);
}

1.5. static inline void list_replace(struct list_head old,struct list_head new)

替换链表中的结点，

/**
 * list_replace - replace old entry by new one
 * @old : the element to be replaced
 * @new : the new element to insert
 *
 * If @old was empty, it will be overwritten.
 */
static inline void list_replace(struct list_head *old,
                struct list_head *new)
{
    new->next = old->next;
    new->next->prev = new;
    new->prev = old->prev;
    new->prev->next = new;
}

1.6. static inline void list_replace_init(struct list_head old,struct list_head new)

替换，将被替换的结点初始化为一个新链表

static inline void list_replace_init(struct list_head *old,
                    struct list_head *new)
{
    list_replace(old, new);
    INIT_LIST_HEAD(old);
}

1.7. static inline void list_swap(struct list_head entry1,struct list_head entry2)

交换两个结点

/**
 * list_swap - replace entry1 with entry2 and re-add entry1 at entry2's position
 * @entry1: the location to place entry2
 * @entry2: the location to place entry1
 */
static inline void list_swap(struct list_head *entry1,
                 struct list_head *entry2)
{
    struct list_head *pos = entry2->prev;

    list_del(entry2);
    list_replace(entry1, entry2);
    if (pos == entry1)
        pos = entry2;
    list_add(entry1, pos);
}

1.8. static inline void list_del_init(struct list_head *entry)

删除一项并初始化

/**
 * list_del_init - deletes entry from list and reinitialize it.
 * @entry: the element to delete from the list.
 */
static inline void list_del_init(struct list_head *entry)
{
    __list_del_entry(entry);
    INIT_LIST_HEAD(entry);
}

1.9. static inline void list_move(struct list_head list, struct list_head head)

搬移操作，将原本属于链表的一个结点移动到另一个链表的操作

/**
 * list_move - delete from one list and add as another's head
 * @list: the entry to move
 * @head: the head that will precede our entry
 */
static inline void list_move(struct list_head *list, struct list_head *head)
{
    __list_del_entry(list);
    list_add(list, head);
}

1.10. static inline void list_move_tail(struct list_head list,struct list_head head)

/**
 * list_move_tail - delete from one list and add as another's tail
 * @list: the entry to move
 * @head: the head that will follow our entry
 */
static inline void list_move_tail(struct list_head *list,
                  struct list_head *head)
{
    __list_del_entry(list);
    list_add_tail(list, head);
}

1.11. static inline void list_bulk_move_tail(struct list_head head, struct list_head first, struct list_head *last)

/**
 * list_bulk_move_tail - move a subsection of a list to its tail
 * @head: the head that will follow our entry
 * @first: first entry to move
 * @last: last entry to move, can be the same as first
 *
 * Move all entries between @first and including @last before @head.
 * All three entries must belong to the same linked list.
 */
static inline void list_bulk_move_tail(struct list_head *head,
                       struct list_head *first,
                       struct list_head *last)
{
    first->prev->next = last->next;
    last->next->prev = first->prev;

    head->prev->next = first;
    first->prev = head->prev;

    last->next = head;
    head->prev = last;
}

1.12. static inline int list_is_first(const struct list_head list,const struct list_head head)

判断结点是否为首结点

/**
 * list_is_first -- tests whether @list is the first entry in list @head
 * @list: the entry to test
 * @head: the head of the list
 */
static inline int list_is_first(const struct list_head *list,
                    const struct list_head *head)
{
    return list->prev == head;
}

1.13. static inline int list_is_last(const struct list_head list, const struct list_head head)

判断结点是否为尾结点

/**
 * list_is_last - tests whether @list is the last entry in list @head
 * @list: the entry to test
 * @head: the head of the list
 */
static inline int list_is_last(const struct list_head *list,
                const struct list_head *head)
{
    return list->next == head;
}

1.14. static inline int list_empty(const struct list_head *head)

判断是否是一个空链表

/**
 * 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;
}

1.15. static inline int list_empty_careful(const struct list_head *head)

/**
 * list_empty_careful - tests whether a list is empty and not being modified
 * @head: the list to test
 *
 * Description:
 * tests whether a list is empty _and_ checks that no other CPU might be
 * in the process of modifying either member (next or prev)
 *
 * NOTE: using list_empty_careful() without synchronization
 * can only be safe if the only activity that can happen
 * to the list entry is list_del_init(). Eg. it cannot be used
 * if another CPU could re-list_add() it.
 */
static inline int list_empty_careful(const struct list_head *head)
{
    struct list_head *next = head->next;
    return (next == head) && (next == head->prev);
}

1.16. static inline void list_rotate_left(struct list_head *head)

翻转链表

/**
 * list_rotate_left - rotate the list to the left
 * @head: the head of the list
 */
static inline void list_rotate_left(struct list_head *head)
{
    struct list_head *first;

    if (!list_empty(head)) {
        first = head->next;
        list_move_tail(first, head);
    }
}

1.17. static inline void list_rotate_to_front(struct list_head list,struct list_head head)

/**
 * list_rotate_to_front() - Rotate list to specific item.
 * @list: The desired new front of the list.
 * @head: The head of the list.
 *
 * Rotates list so that @list becomes the new front of the list.
 */
static inline void list_rotate_to_front(struct list_head *list,
                    struct list_head *head)
{
    /*
     * Deletes the list head from the list denoted by @head and
     * places it as the tail of @list, this effectively rotates the
     * list so that @list is at the front.
     */
    list_move_tail(head, list);
}

1.18. static inline int list_is_singular(const struct list_head *head)

判断一个链表是否只有一项

/**
 * list_is_singular - tests whether a list has just one entry.
 * @head: the list to test.
 */
static inline int list_is_singular(const struct list_head *head)
{
    return !list_empty(head) && (head->next == head->prev);
}

1.19. static inline void list_cut_position(struct list_head list,struct list_head head, struct list_head *entry)

将一个链表拆分为两个

/**
 * 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.
 *
 */
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);
}

1.20. static inline void list_cut_before(struct list_head list,struct list_head head,struct list_head *entry)

/**
 * list_cut_before - cut a list into two, before given entry
 * @list: a new list to add all removed entries
 * @head: a list with entries
 * @entry: an entry within head, could be the head itself
 *
 * This helper moves the initial part of @head, up to but
 * excluding @entry, from @head to @list.  You should pass
 * in @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.
 * If @entry == @head, all entries on @head are moved to
 * @list.
 */
static inline void list_cut_before(struct list_head *list,
                   struct list_head *head,
                   struct list_head *entry)
{
    if (head->next == entry) {
        INIT_LIST_HEAD(list);
        return;
    }
    list->next = head->next;
    list->next->prev = list;
    list->prev = entry->prev;
    list->prev->next = list;
    head->next = entry;
    entry->prev = head;
}

1.21. static inline void list_splice(const struct list_head list,struct list_head head)

连接两个链表

/**
 * 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.
 */
static inline void list_splice(const struct list_head *list,
                struct list_head *head)
{
    if (!list_empty(list))
        __list_splice(list, head, head->next);
}

1.22. static inline void list_splice_tail(struct list_head list,struct list_head head)

/**
 * list_splice_tail - join two lists, each list being a queue
 * @list: the new list to add.
 * @head: the place to add it in the first list.
 */
static inline void list_splice_tail(struct list_head *list,
                struct list_head *head)
{
    if (!list_empty(list))
        __list_splice(list, head->prev, head);
}

1.23. static inline void list_splice_init(struct list_head list, struct list_head 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,
                    struct list_head *head)
{
    if (!list_empty(list)) {
        __list_splice(list, head, head->next);
        INIT_LIST_HEAD(list);
    }
}

1.24. static inline void list_splice_tail_init(struct list_head list, struct list_head head)

/**
 * list_splice_tail_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.
 *
 * Each of the lists is a queue.
 * The list at @list is reinitialised
 */
static inline void list_splice_tail_init(struct list_head *list,
                     struct list_head *head)
{
    if (!list_empty(list)) {
        __list_splice(list, head->prev, head);
        INIT_LIST_HEAD(list);
    }
}

2. 使用的宏定义

2.1. LIST_HEAD_INIT

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

2.2. LIST_HEAD

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

2.3. list_entry

#define list_entry(ptr, type, member) \
    container_of(ptr, type, member)

2.4. list_first_entry

#define list_first_entry(ptr, type, member) \
    list_entry((ptr)->next, type, member)

2.5. list_last_entry

#define list_last_entry(ptr, type, member) \
    list_entry((ptr)->prev, type, member)

2.6. list_first_entry_or_null

#define list_first_entry_or_null(ptr, type, member) ({ \
    struct list_head *head__ = (ptr); \
    struct list_head *pos__ = READ_ONCE(head__->next); \
    pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
})

2.7. list_next_entry

#define list_next_entry(pos, member) \
    list_entry((pos)->member.next, typeof(*(pos)), member)

2.8. list_prev_entry

#define list_prev_entry(pos, member) \
    list_entry((pos)->member.prev, typeof(*(pos)), member)

2.9. list_for_each

#define list_for_each(pos, head) \
    for (pos = (head)->next; pos != (head); pos = pos->next)

2.10. list_for_each_prev

#define list_for_each_prev(pos, head) \
    for (pos = (head)->prev; pos != (head); pos = pos->prev)

2.11. list_for_each_safe

#define list_for_each_safe(pos, n, head) \
    for (pos = (head)->next, n = pos->next; pos != (head); \
        pos = n, n = pos->next)

2.12. list_for_each_prev_safe

#define list_for_each_prev_safe(pos, n, head) \
    for (pos = (head)->prev, n = pos->prev; \
         pos != (head); \
         pos = n, n = pos->prev)

2.13. list_for_each_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))

2.14. list_for_each_entry_reverse

#define list_for_each_entry_reverse(pos, head, member)            \
    for (pos = list_last_entry(head, typeof(*pos), member);        \
         &pos->member != (head);                     \
         pos = list_prev_entry(pos, member))

2.15. list_prepare_entry

#define list_prepare_entry(pos, head, member) \
    ((pos) ? : list_entry(head, typeof(*pos), member))

2.16. list_for_each_entry_continue

#define list_for_each_entry_continue(pos, head, member)         \
    for (pos = list_next_entry(pos, member);            \
         &pos->member != (head);                    \
         pos = list_next_entry(pos, member))

2.17. list_for_each_entry_from_reverse

#define list_for_each_entry_from_reverse(pos, head, member)        \
    for (; &pos->member != (head);                    \
         pos = list_prev_entry(pos, member))

2.18. list_for_each_entry_safe

#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))

2.19. list_for_each_entry_safe_continue

#define list_for_each_entry_safe_continue(pos, n, head, member)         \
    for (pos = list_next_entry(pos, member),                 \
        n = list_next_entry(pos, member);                \
         &pos->member != (head);                        \
         pos = n, n = list_next_entry(n, member))

2.20. list_for_each_entry_safe_from

#define list_for_each_entry_safe_from(pos, n, head, member)             \
    for (n = list_next_entry(pos, member);                    \
         &pos->member != (head);                        \
         pos = n, n = list_next_entry(n, member))

2.21. list_for_each_entry_safe_reverse

#define list_for_each_entry_safe_reverse(pos, n, head, member)        \
    for (pos = list_last_entry(head, typeof(*pos), member),        \
        n = list_prev_entry(pos, member);            \
         &pos->member != (head);                     \
         pos = n, n = list_prev_entry(n, member))

2.22. list_safe_reset_next

#define list_safe_reset_next(pos, n, member)                \
    n = list_next_entry(pos, member)