#define max(a,b) \
   ({ typeof (a) _a = (a); \
       typeof (b) _b = (b); \
     _a > _b ? _a : _b; })

#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))；

struct llist_head {
        struct llist_node *first;
};

struct llist_node {
        struct llist_node *next;
};

#define LLIST_HEAD_INIT(name)        { NULL }
#define LLIST_HEAD(name)        struct llist_head name = LLIST_HEAD_INIT(name)

/**
 * init_llist_head - initialize lock-less list head
 * @head:        the head for your lock-less list
 */
static inline void init_llist_head(struct llist_head *list)
{
        list->first = NULL;
}

/**
 * llist_entry - get the struct of this entry
 * @ptr:        the &struct llist_node pointer.
 * @type:        the type of the struct this is embedded in.
 * @member:        the name of the llist_node within the struct.
 */
#define llist_entry(ptr, type, member)                \
        container_of(ptr, type, member)

/**
 * 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.
 *
 */
#define container_of(ptr, type, member) ({                        \
        const typeof( ((type *)0)->member ) *__mptr = (ptr);        \
        (type *)( (char *)__mptr - offsetof(type,member) );})

/**
 * llist_for_each - iterate over some deleted entries of a lock-less list
 * @pos:        the &struct llist_node to use as a loop cursor
 * @node:        the first entry of deleted list entries
 *
 * In general, some entries of the lock-less list can be traversed
 * safely only after being deleted from list, so start with an entry
 * instead of list head.
 *
 * If being used on entries deleted from lock-less list directly, the
 * traverse order is from the newest to the oldest added entry.  If
 * you want to traverse from the oldest to the newest, you must
 * reverse the order by yourself before traversing.
 */
#define llist_for_each(pos, node)                        \
        for ((pos) = (node); pos; (pos) = (pos)->next)

/**
 * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
 * @pos:        the type * to use as a loop cursor.
 * @node:        the fist entry of deleted list entries.
 * @member:        the name of the llist_node with the struct.
 *
 * In general, some entries of the lock-less list can be traversed
 * safely only after being removed from list, so start with an entry
 * instead of list head.
 *
 * If being used on entries deleted from lock-less list directly, the
 * traverse order is from the newest to the oldest added entry.  If
 * you want to traverse from the oldest to the newest, you must
 * reverse the order by yourself before traversing.
 */
#define llist_for_each_entry(pos, node, member)                                \
        for ((pos) = llist_entry((node), typeof(*(pos)), member);        \
             &(pos)->member != NULL;                                        \
             (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))

for ((pos) = 链表节点;
        &(pos)->next指针 != NULL; 
        (pos) = 链表下一个节点) {
    // 遍历操作
    pos.foo = bar;
}

/**
 * llist_for_each_entry_safe - iterate over some deleted entries of lock-less 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
 * @node:        the first entry of deleted list entries.
 * @member:        the name of the llist_node with the struct.
 *
 * In general, some entries of the lock-less list can be traversed
 * safely only after being removed from list, so start with an entry
 * instead of list head.
 *
 * If being used on entries deleted from lock-less list directly, the
 * traverse order is from the newest to the oldest added entry.  If
 * you want to traverse from the oldest to the newest, you must
 * reverse the order by yourself before traversing.
 */
#define llist_for_each_entry_safe(pos, n, node, member)                               \
        for (pos = llist_entry((node), typeof(*pos), member);                       \
             &pos->member != NULL &&                                               \
                (n = llist_entry(pos->member.next, typeof(*n), member), true); \
             pos = n)

static inline struct llist_node *llist_next(struct llist_node *node)
{
        return node->next;
}

/**
 * llist_add_batch - add several linked entries in batch
 * @new_first:        first entry in batch to be added
 * @new_last:        last entry in batch to be added
 * @head:        the head for your lock-less list
 *
 * Return whether list is empty before adding.
 */
bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
                     struct llist_head *head)
{
        struct llist_node *first;

        do {
                new_last->next = first = ACCESS_ONCE(head->first);
        } while (cmpxchg(&head->first, first, new_first) != first);

        return !first;
}

/**
 * llist_add - add a new entry
 * @new:        new entry to be added
 * @head:        the head for your lock-less list
 *
 * Returns true if the list was empty prior to adding this entry.
 */
static inline bool llist_add(struct llist_node *new, struct llist_head *head)
{
        return llist_add_batch(new, new, head);
}

/**
 * llist_empty - tests whether a lock-less list is empty
 * @head:        the list to test
 *
 * Not guaranteed to be accurate or up to date.  Just a quick way to
 * test whether the list is empty without deleting something from the
 * list.
 */
static inline bool llist_empty(const struct llist_head *head)
{
        return ACCESS_ONCE(head->first) == NULL;
}

/**
 * llist_del_all - delete all entries from lock-less list
 * @head:        the head of lock-less list to delete all entries
 *
 * If list is empty, return NULL, otherwise, delete all entries and
 * return the pointer to the first entry.  The order of entries
 * deleted is from the newest to the oldest added one.
 */
static inline struct llist_node *llist_del_all(struct llist_head *head)
{
        return xchg(&head->first, NULL);
}

/**
 * llist_del_first - delete the first entry of lock-less list
 * @head:        the head for your lock-less list
 *
 * If list is empty, return NULL, otherwise, return the first entry
 * deleted, this is the newest added one.
 *
 * Only one llist_del_first user can be used simultaneously with
 * multiple llist_add users without lock.  Because otherwise
 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
 * llist_add) sequence in another user may change @head->first->next,
 * but keep @head->first.  If multiple consumers are needed, please
 * use llist_del_all or use lock between consumers.
 */
struct llist_node *llist_del_first(struct llist_head *head)
{
        struct llist_node *entry, *old_entry, *next;

        entry = head->first;
        for (;;) {
                if (entry == NULL)
                        return NULL;
                old_entry = entry;
                next = entry->next;
                entry = cmpxchg(&head->first, old_entry, next);
                if (entry == old_entry)
                        break;
        }

        return entry;
}

/**
 * llist_reverse_order - reverse order of a llist chain
 * @head:        first item of the list to be reversed
 *
 * Reverse the order of a chain of llist entries and return the
 * new first entry.
 */
struct llist_node *llist_reverse_order(struct llist_node *head)
{
        struct llist_node *new_head = NULL;

        while (head) {
                struct llist_node *tmp = head;
                head = head->next;
                tmp->next = new_head;
                new_head = tmp;
        }

        return new_head;
}
EXPORT_SYMBOL_GPL(llist_reverse_order);

do {
    new_last->next = first = ACCESS_ONCE(head->first);
} while (cmpxchg(&head->first, first, new_first) != first);

entry = cmpxchg(&head->first, old_entry, next);

return xchg(&head->first, NULL);

 /*
 *           |   add    | del_first |  del_all
 * add       |    -     |     -     |     -
 * del_first |          |     L     |     L
 * del_all   |          |           |     -
 */

/*
 * The list entries deleted via llist_del_all can be traversed with
 * traversing function such as llist_for_each etc.  But the list
 * entries can not be traversed safely before deleted from the list.
 * The order of deleted entries is from the newest to the oldest added
 * one.  If you want to traverse from the oldest to the newest, you
 * must reverse the order by yourself before traversing.
 */