struct wakelock {	char			*name;  //wakelock名字	struct rb_node		node; //红黑树节点，所有wakelock以红黑树的方式组织在该模块里，便于管理	struct wakeup_source	*ws; //wakelock对应的ws#ifdef CONFIG_PM_WAKELOCKS_GC	struct list_head	lru; //与wakelock的回收机制有关，见后续介绍#endif};

@ kernel/power/wakelock.cstatic struct rb_root wakelocks_tree = RB_ROOT; //红黑树根节点，所有wakelock都会挂在这上面，便于管理
static LIST_HEAD(wakelocks_lru_list); //该链表用于管理已生成的wakelock，便于回收机制处理，后续称其为回收链表
//当 CONFIG_PM_WAKELOCKS_LIMIT 配置大于0时，保存已存在的wakelock数量，用于限制存在的wakelock数量不超过CONFIG_PM_WAKELOCKS_LIMITstatic unsigned int number_of_wakelocks; 
//当 CONFIG_PM_WAKELOCKS_GC 配置时，表示启动wakelock回收机制。该变量用于累计已解锁的wakelock的数量，当该变量超过WL_GC_COUNT_MAX（100）时，会触发回收workstatic unsigned int wakelocks_gc_count; 

/* call by wake_lock_store()*/int pm_wake_lock(const char *buf){	const char *str = buf;	struct wakelock *wl;	u64 timeout_ns = 0;	size_t len;	int ret = 0;
	//解析传入的字符串，第一个参数为wakelock名称，第二个参数（可选）则是wakelock超时时间	while (*str && !isspace(*str))		str++;
	len = str - buf;	if (!len)		return -EINVAL;
	if (*str && *str != '\n') {		/* Find out if there's a valid timeout string appended. */		ret = kstrtou64(skip_spaces(str), 10, &timeout_ns);		if (ret)			return -EINVAL;	}
	mutex_lock(&wakelocks_lock);	//查找wakelock，找不到时创建	wl = wakelock_lookup_add(buf, len, true);	if (IS_ERR(wl)) {		ret = PTR_ERR(wl);		goto out;	}	if (timeout_ns) {  //如果传入了超时参数，则持锁，超时后会自动释放该锁		u64 timeout_ms = timeout_ns + NSEC_PER_MSEC - 1;		do_div(timeout_ms, NSEC_PER_MSEC);		__pm_wakeup_event(wl->ws, timeout_ms);	} else { //否则直接持锁		__pm_stay_awake(wl->ws);	}
	wakelocks_lru_most_recent(wl); //将该wakelock移到回收链表前端，使得回收机制触发时靠后处理
 out:	mutex_unlock(&wakelocks_lock);	return ret;}static struct wakelock *wakelock_lookup_add(const char *name, size_t len,					    bool add_if_not_found){	struct rb_node **node = &wakelocks_tree.rb_node;	struct rb_node *parent = *node;	struct wakelock *wl;		//根据名称在红黑树上查找是否已经存在该wakelock	while (*node) {		int diff;
		parent = *node;		wl = rb_entry(*node, struct wakelock, node);		diff = strncmp(name, wl->name, len);		if (diff == 0) {			if (wl->name[len])				diff = -1;			else				return wl; //找到同名wakelock，返回		}		if (diff < 0)			node = &(*node)->rb_left;		else			node = &(*node)->rb_right;	}	if (!add_if_not_found)		return ERR_PTR(-EINVAL);
	//配置CONFIG_PM_WAKELOCKS_LIMIT>0的情况下，会检测已创建的wakelock数量是否已经超过该配置	if (wakelocks_limit_exceeded())		return ERR_PTR(-ENOSPC);
	/* 未找到同名wakelock的情况下，开始创建wakelock */	wl = kzalloc(sizeof(*wl), GFP_KERNEL);	if (!wl)		return ERR_PTR(-ENOMEM);
	wl->name = kstrndup(name, len, GFP_KERNEL);	if (!wl->name) {		kfree(wl);		return ERR_PTR(-ENOMEM);	}	//本质wakelock是通过wakeup_source机制实现的	wl->ws = wakeup_source_register(NULL, wl->name);	if (!wl->ws) {		kfree(wl->name);		kfree(wl);		return ERR_PTR(-ENOMEM);	}	wl->ws->last_time = ktime_get();	//将该wakelock挂到红黑树上	rb_link_node(&wl->node, parent, node);	rb_insert_color(&wl->node, &wakelocks_tree);	wakelocks_lru_add(wl); //添加到回收链表	increment_wakelocks_number(); //wakelock数量+1	return wl;}

/* call by wake_unlock_store()*/int pm_wake_unlock(const char *buf){	struct wakelock *wl;	size_t len;	int ret = 0;
	len = strlen(buf);	if (!len)		return -EINVAL;
	if (buf[len-1] == '\n')		len--;
	if (!len)		return -EINVAL;
	mutex_lock(&wakelocks_lock);	//查找wakelock，找不到时直接返回错误	wl = wakelock_lookup_add(buf, len, false);	if (IS_ERR(wl)) {		ret = PTR_ERR(wl);		goto out;	}	__pm_relax(wl->ws); //释放锁
	wakelocks_lru_most_recent(wl); //将该wakelock移到回收链表前端，使得回收机制触发时靠后处理	wakelocks_gc();  //已解锁的wakelock加1，并判断是否超过上限，触发回收处理work
 out:	mutex_unlock(&wakelocks_lock);	return ret;}

static void __wakelocks_gc(struct work_struct *work){	struct wakelock *wl, *aux;	ktime_t now;
	mutex_lock(&wakelocks_lock);
	now = ktime_get();	 //从回收链表尾部开始倒序遍历（越靠近链表头部的wakelock，越是最近才操作的wakelock）	list_for_each_entry_safe_reverse(wl, aux, &wakelocks_lru_list, lru) {		u64 idle_time_ns;		bool active;
		spin_lock_irq(&wl->ws->lock);		idle_time_ns = ktime_to_ns(ktime_sub(now, wl->ws->last_time)); //计算该锁有多长时间未被操作过		active = wl->ws->active; //获取锁的激活状态		spin_unlock_irq(&wl->ws->lock);
		if (idle_time_ns < ((u64)WL_GC_TIME_SEC * NSEC_PER_SEC)) //如果锁空闲时间小于300s，则不再继续回收			break;
		//如果锁已经失活，则注销该锁，从红黑树中移除，并移除出回收链表，释放空间，wakelock数量-1		if (!active) {			wakeup_source_unregister(wl->ws);			rb_erase(&wl->node, &wakelocks_tree);			list_del(&wl->lru);			kfree(wl->name);			kfree(wl);			decrement_wakelocks_number();		}	}	wakelocks_gc_count = 0; //重置回收锁计数
	mutex_unlock(&wakelocks_lock);}