1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
7 * Basic idea behind the notification queue: An fsnotify group (like inotify)
8 * sends the userspace notification about events asynchronously some time after
9 * the event happened. When inotify gets an event it will need to add that
10 * event to the group notify queue. Since a single event might need to be on
11 * multiple group's notification queues we can't add the event directly to each
12 * queue and instead add a small "event_holder" to each queue. This event_holder
13 * has a pointer back to the original event. Since the majority of events are
14 * going to end up on one, and only one, notification queue we embed one
15 * event_holder into each event. This means we have a single allocation instead
16 * of always needing two. If the embedded event_holder is already in use by
17 * another group a new event_holder (from fsnotify_event_holder_cachep) will be
22 #include <linux/init.h>
23 #include <linux/kernel.h>
24 #include <linux/list.h>
25 #include <linux/module.h>
26 #include <linux/mount.h>
27 #include <linux/mutex.h>
28 #include <linux/namei.h>
29 #include <linux/path.h>
30 #include <linux/slab.h>
31 #include <linux/spinlock.h>
33 #include <linux/atomic.h>
35 #include <linux/fsnotify_backend.h>
38 static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
41 * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
42 * Called from fsnotify_move, which is inlined into filesystem modules.
44 u32 fsnotify_get_cookie(void)
46 return atomic_inc_return(&fsnotify_sync_cookie);
48 EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
50 void fsnotify_destroy_event(struct fsnotify_group *group,
51 struct fsnotify_event *event)
53 /* Overflow events are per-group and we don't want to free them */
54 if (!event || event == group->overflow_event)
57 * If the event is still queued, we have a problem... Do an unreliable
58 * lockless check first to avoid locking in the common case. The
59 * locking may be necessary for permission events which got removed
60 * from the list by a different CPU than the one freeing the event.
62 if (!list_empty(&event->list)) {
63 spin_lock(&group->notification_lock);
64 WARN_ON(!list_empty(&event->list));
65 spin_unlock(&group->notification_lock);
67 group->ops->free_event(event);
71 * Add an event to the group notification queue. The group can later pull this
72 * event off the queue to deal with. The function returns 0 if the event was
73 * added to the queue, 1 if the event was merged with some other queued event,
74 * 2 if the event was not queued - either the queue of events has overflown
75 * or the group is shutting down.
77 int fsnotify_add_event(struct fsnotify_group *group,
78 struct fsnotify_event *event,
79 int (*merge)(struct list_head *,
80 struct fsnotify_event *))
83 struct list_head *list = &group->notification_list;
85 pr_debug("%s: group=%p event=%p\n", __func__, group, event);
87 spin_lock(&group->notification_lock);
89 if (group->shutdown) {
90 spin_unlock(&group->notification_lock);
94 if (event == group->overflow_event ||
95 group->q_len >= group->max_events) {
97 /* Queue overflow event only if it isn't already queued */
98 if (!list_empty(&group->overflow_event->list)) {
99 spin_unlock(&group->notification_lock);
102 event = group->overflow_event;
106 if (!list_empty(list) && merge) {
107 ret = merge(list, event);
109 spin_unlock(&group->notification_lock);
116 list_add_tail(&event->list, list);
117 spin_unlock(&group->notification_lock);
119 wake_up(&group->notification_waitq);
120 kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
124 void fsnotify_remove_queued_event(struct fsnotify_group *group,
125 struct fsnotify_event *event)
127 assert_spin_locked(&group->notification_lock);
129 * We need to init list head for the case of overflow event so that
130 * check in fsnotify_add_event() works
132 list_del_init(&event->list);
137 * Return the first event on the notification list without removing it.
138 * Returns NULL if the list is empty.
140 struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
142 assert_spin_locked(&group->notification_lock);
144 if (fsnotify_notify_queue_is_empty(group))
147 return list_first_entry(&group->notification_list,
148 struct fsnotify_event, list);
152 * Remove and return the first event from the notification list. It is the
153 * responsibility of the caller to destroy the obtained event
155 struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
157 struct fsnotify_event *event = fsnotify_peek_first_event(group);
162 pr_debug("%s: group=%p event=%p\n", __func__, group, event);
164 fsnotify_remove_queued_event(group, event);
170 * Called when a group is being torn down to clean up any outstanding
171 * event notifications.
173 void fsnotify_flush_notify(struct fsnotify_group *group)
175 struct fsnotify_event *event;
177 spin_lock(&group->notification_lock);
178 while (!fsnotify_notify_queue_is_empty(group)) {
179 event = fsnotify_remove_first_event(group);
180 spin_unlock(&group->notification_lock);
181 fsnotify_destroy_event(group, event);
182 spin_lock(&group->notification_lock);
184 spin_unlock(&group->notification_lock);