最完美的代码

Linux kernel 中的 list api 是我见过的最完美的代码：

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

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

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

static inline void __list_add(struct list_head *new,
                  struct list_head *prev,
                  struct list_head *next) {
    next->prev = new;
    new->next = next;
    new->prev = prev;
    prev->next = new;
}

static inline void list_add(struct list_head *new, struct list_head *head) {
    __list_add(new, head, head->next);
}

static inline void list_add_tail(struct list_head *new, struct list_head *head) {
    __list_add(new, head->prev, head);
}

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

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

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;
}

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

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

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