// SPDX-License-Identifier: GPL-2.0-or-later/* *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com> */ /* * Basic idea behind the notification queue: An fsnotify group (like inotify) * sends the userspace notification about events asynchronously some time after * the event happened.  When inotify gets an event it will need to add that * event to the group notify queue.  Since a single event might need to be on * multiple group's notification queues we can't add the event directly to each * queue and instead add a small "event_holder" to each queue.  This event_holder * has a pointer back to the original event.  Since the majority of events are * going to end up on one, and only one, notification queue we embed one * event_holder into each event.  This means we have a single allocation instead * of always needing two.  If the embedded event_holder is already in use by * another group a new event_holder (from fsnotify_event_holder_cachep) will be * allocated and used. */ #include <linux/fs.h>#include <linux/init.h>#include <linux/kernel.h>#include <linux/list.h>#include <linux/module.h>#include <linux/mount.h>#include <linux/mutex.h>#include <linux/namei.h>#include <linux/path.h>#include <linux/slab.h>#include <linux/spinlock.h> #include <linux/atomic.h> #include <linux/fsnotify_backend.h>#include "fsnotify.h" static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0); /** * fsnotify_get_cookie - return a unique cookie for use in synchronizing events. * Called from fsnotify_move, which is inlined into filesystem modules. */u32 fsnotify_get_cookie(void){	return atomic_inc_return(&fsnotify_sync_cookie);}EXPORT_SYMBOL_GPL(fsnotify_get_cookie); void fsnotify_destroy_event(struct fsnotify_group *group,			    struct fsnotify_event *event){	/* Overflow events are per-group and we don't want to free them */	if (!event || event == group->overflow_event)		return;	/*	 * If the event is still queued, we have a problem... Do an unreliable	 * lockless check first to avoid locking in the common case. The	 * locking may be necessary for permission events which got removed	 * from the list by a different CPU than the one freeing the event.	 */	if (!list_empty(&event->list)) {		spin_lock(&group->notification_lock);		WARN_ON(!list_empty(&event->list));		spin_unlock(&group->notification_lock);	}	group->ops->free_event(group, event);} /* * Try to add an event to the notification queue. * The group can later pull this event off the queue to deal with. * The group can use the @merge hook to merge the event with a queued event. * The group can use the @insert hook to insert the event into hash table. * The function returns: * 0 if the event was added to a queue * 1 if the event was merged with some other queued event * 2 if the event was not queued - either the queue of events has overflown *   or the group is shutting down. */int fsnotify_insert_event(struct fsnotify_group *group,			  struct fsnotify_event *event,			  int (*merge)(struct fsnotify_group *,				       struct fsnotify_event *),			  void (*insert)(struct fsnotify_group *,					 struct fsnotify_event *)){	int ret = 0;	struct list_head *list = &group->notification_list; 	pr_debug("%s: group=%p event=%p\n", __func__, group, event); 	spin_lock(&group->notification_lock); 	if (group->shutdown) {		spin_unlock(&group->notification_lock);		return 2;	} 	if (event == group->overflow_event ||	    group->q_len >= group->max_events) {		ret = 2;		/* Queue overflow event only if it isn't already queued */		if (!list_empty(&group->overflow_event->list)) {			spin_unlock(&group->notification_lock);			return ret;		}		event = group->overflow_event;		goto queue;	} 	if (!list_empty(list) && merge) {		ret = merge(group, event);		if (ret) {			spin_unlock(&group->notification_lock);			return ret;		}	} queue:	group->q_len++;	list_add_tail(&event->list, list);	if (insert)		insert(group, event);	spin_unlock(&group->notification_lock); 	wake_up(&group->notification_waitq);	kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);	return ret;} void fsnotify_remove_queued_event(struct fsnotify_group *group,				  struct fsnotify_event *event){	assert_spin_locked(&group->notification_lock);	/*	 * We need to init list head for the case of overflow event so that	 * check in fsnotify_add_event() works	 */	list_del_init(&event->list);	group->q_len--;} /* * Return the first event on the notification list without removing it. * Returns NULL if the list is empty. */struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group){	assert_spin_locked(&group->notification_lock); 	if (fsnotify_notify_queue_is_empty(group))		return NULL; 	return list_first_entry(&group->notification_list,				struct fsnotify_event, list);} /* * Remove and return the first event from the notification list.  It is the * responsibility of the caller to destroy the obtained event */struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group){	struct fsnotify_event *event = fsnotify_peek_first_event(group); 	if (!event)		return NULL; 	pr_debug("%s: group=%p event=%p\n", __func__, group, event); 	fsnotify_remove_queued_event(group, event); 	return event;} /* * Called when a group is being torn down to clean up any outstanding * event notifications. */void fsnotify_flush_notify(struct fsnotify_group *group){	struct fsnotify_event *event; 	spin_lock(&group->notification_lock);	while (!fsnotify_notify_queue_is_empty(group)) {		event = fsnotify_remove_first_event(group);		spin_unlock(&group->notification_lock);		fsnotify_destroy_event(group, event);		spin_lock(&group->notification_lock);	}	spin_unlock(&group->notification_lock);}