static ssize_t inotify_read(struct file *file, char __user *buf,
			    size_t count, loff_t *pos)
{
	struct fsnotify_group *group;
	struct fsnotify_event *kevent;
	char __user *start;
	int ret;
	DEFINE_WAIT_FUNC(wait, woken_wake_function);

	start = buf;
	group = file->private_data;

	add_wait_queue(&group->notification_waitq, &wait);
	while (1) {
		spin_lock(&group->notification_lock);
		kevent = get_one_event(group, count);
		spin_unlock(&group->notification_lock);

		pr_debug("%s: group=%p kevent=%p\n", __func__, group, kevent);

		if (kevent) {
			ret = PTR_ERR(kevent);
			if (IS_ERR(kevent))
				break;
			ret = copy_event_to_user(group, kevent, buf);
			fsnotify_destroy_event(group, kevent);
			if (ret < 0)
				break;
			buf += ret;
			count -= ret;
			continue;
		}

		ret = -EAGAIN;
		if (file->f_flags & O_NONBLOCK)
			break;
		ret = -ERESTARTSYS;
		if (signal_pending(current))
			break;

		if (start != buf)
			break;

		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
	}
	remove_wait_queue(&group->notification_waitq, &wait);

	if (start != buf && ret != -EFAULT)
		ret = buf - start;
	return ret;
}

#define DEFINE_WAIT_FUNC(name, function)					\
	struct wait_queue_entry name = {					\
		.private	= current,					\
		.func		= function,					\
		.entry		= LIST_HEAD_INIT((name).entry),			\
	}

int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
{
	/* Pairs with the smp_store_mb() in wait_woken(). */
	smp_mb(); /* C */
	wq_entry->flags |= WQ_FLAG_WOKEN;

	return default_wake_function(wq_entry, mode, sync, key);
}

int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flags, void *key)
{
	WARN_ON_ONCE(IS_ENABLED(CONFIG_SCHED_DEBUG) && wake_flags & ~(WF_SYNC|WF_CURRENT_CPU));
	return try_to_wake_up(curr->private, mode, wake_flags);
}

long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
{
	/*
	 * The below executes an smp_mb(), which matches with the full barrier
	 * executed by the try_to_wake_up() in woken_wake_function() such that
	 * either we see the store to wq_entry->flags in woken_wake_function()
	 * or woken_wake_function() sees our store to current->state.
	 */
	set_current_state(mode); /* A */
	if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !kthread_should_stop_or_park())
		timeout = schedule_timeout(timeout);
	__set_current_state(TASK_RUNNING);

	/*
	 * The below executes an smp_mb(), which matches with the smp_mb() (C)
	 * in woken_wake_function() such that either we see the wait condition
	 * being true or the store to wq_entry->flags in woken_wake_function()
	 * follows ours in the coherence order.
	 */
	smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */

	return timeout;
}

#include <stdio.h>  
#include <sys/inotify.h>  
#include <unistd.h>  
  
#define EVENT_SIZE  (sizeof(struct inotify_event))  
#define BUF_LEN     (1024 * (EVENT_SIZE + 16))  
  
int main(void){  
    int fd = inotify_init();  
    int wd = inotify_add_watch(fd, ".", IN_MODIFY|IN_CREATE|IN_DELETE);  
  
    int pid = fork();  
    printf("pid %d created\n", pid);  
  
    char buffer[BUF_LEN];  
  
    printf("pid %d before_read\n", pid);  
    int len = read(fd, buffer, BUF_LEN);  
    printf("pid %d after_read\n", pid);  
  
    for (int i=0; i<len;){  
        struct inotify_event *event = (struct inotify_event *) &buffer[i];  
        if (event->len){  
            if (event->mask & IN_CREATE) {  
                printf("The file %s was created.\n", event->name);  
            } else if (event->mask & IN_DELETE) {  
                printf("The file %s was deleted.\n", event->name);  
            } else if (event->mask & IN_MODIFY) {  
                printf("The file %s was modified.\n", event->name);  
            }  
        }  
        i += EVENT_SIZE + event->len;  
    }  
}