linux/fs/notify/notification.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <[email protected]>
 */

/*
 * 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 = …;

/**
 * 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)
{ … }
EXPORT_SYMBOL_GPL(…);

void fsnotify_destroy_event(struct fsnotify_group *group,
			    struct fsnotify_event *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 *))
{ … }

void fsnotify_remove_queued_event(struct fsnotify_group *group,
				  struct fsnotify_event *event)
{ … }

/*
 * 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)
{ … }

/*
 * 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)
{ … }

/*
 * Called when a group is being torn down to clean up any outstanding
 * event notifications.
 */
void fsnotify_flush_notify(struct fsnotify_group *group)
{ … }