static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
{
	int pwake = 0;
	unsigned int revents;

	/*
	 * Set the new event interest mask before calling f_op->poll();
	 * otherwise we might miss an event that happens between the
	 * f_op->poll() call and the new event set registering.
	 */
	epi->event.events = event->events;
	epi->event.data = event->data; /* protected by mtx */

	/*
	 * Get current event bits. We can safely use the file* here because
	 * its usage count has been increased by the caller of this function.
	 */
	revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);

	/*
	 * If the item is "hot" and it is not registered inside the ready
	 * list, push it inside.
	 */
	if (revents & event->events) {
		spin_lock_irq(&ep->lock);
		if (!ep_is_linked(&epi->rdllink)) {
			list_add_tail(&epi->rdllink, &ep->rdllist);

			/* Notify waiting tasks that events are available */
			if (waitqueue_active(&ep->wq))
				wake_up_locked(&ep->wq);
			if (waitqueue_active(&ep->poll_wait))
				pwake++;
		}
		spin_unlock_irq(&ep->lock);
	}

	/* We have to call this outside the lock */
	if (pwake)
		ep_poll_safewake(&ep->poll_wait);

	return 0;
}
static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
{
	int pwake = 0;
	unsigned int revents;

	 
	epi->event.events = event->events;
	epi->event.data = event->data;  

	 
	revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);

	 
	if (revents & event->events) {
		spin_lock_irq(&ep->lock);
		if (!ep_is_linked(&epi->rdllink)) {
			list_add_tail(&epi->rdllink, &ep->rdllist);

			 
			if (waitqueue_active(&ep->wq))
				wake_up_locked(&ep->wq);
			if (waitqueue_active(&ep->poll_wait))
				pwake++;
		}
		spin_unlock_irq(&ep->lock);
	}

	 
	if (pwake)
		ep_poll_safewake(&ep->poll_wait);

	return 0;
}