2 * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2, or (at your option)
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; see the file COPYING. If not, write to
16 * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
20 * Basic idea behind the notification queue: An fsnotify group (like inotify)
21 * sends the userspace notification about events asynchronously some time after
22 * the event happened. When inotify gets an event it will need to add that
23 * event to the group notify queue. Since a single event might need to be on
24 * multiple group's notification queues we can't add the event directly to each
25 * queue and instead add a small "event_holder" to each queue. This event_holder
26 * has a pointer back to the original event. Since the majority of events are
27 * going to end up on one, and only one, notification queue we embed one
28 * event_holder into each event. This means we have a single allocation instead
29 * of always needing two. If the embedded event_holder is already in use by
30 * another group a new event_holder (from fsnotify_event_holder_cachep) will be
35 #include <linux/init.h>
36 #include <linux/kernel.h>
37 #include <linux/list.h>
38 #include <linux/module.h>
39 #include <linux/mount.h>
40 #include <linux/mutex.h>
41 #include <linux/namei.h>
42 #include <linux/path.h>
43 #include <linux/slab.h>
44 #include <linux/spinlock.h>
46 #include <linux/atomic.h>
48 #include <linux/fsnotify_backend.h>
51 static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
54 * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
55 * Called from fsnotify_move, which is inlined into filesystem modules.
57 u32 fsnotify_get_cookie(void)
59 return atomic_inc_return(&fsnotify_sync_cookie);
61 EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
63 /* return true if the notify queue is empty, false otherwise */
64 bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
66 BUG_ON(IS_ENABLED(CONFIG_SMP) &&
67 !spin_is_locked(&group->notification_lock));
68 return list_empty(&group->notification_list) ? true : false;
71 void fsnotify_destroy_event(struct fsnotify_group *group,
72 struct fsnotify_event *event)
74 /* Overflow events are per-group and we don't want to free them */
75 if (!event || event->mask == FS_Q_OVERFLOW)
78 * If the event is still queued, we have a problem... Do an unreliable
79 * lockless check first to avoid locking in the common case. The
80 * locking may be necessary for permission events which got removed
81 * from the list by a different CPU than the one freeing the event.
83 if (!list_empty(&event->list)) {
84 spin_lock(&group->notification_lock);
85 WARN_ON(!list_empty(&event->list));
86 spin_unlock(&group->notification_lock);
88 group->ops->free_event(event);
92 * Add an event to the group notification queue. The group can later pull this
93 * event off the queue to deal with. The function returns 0 if the event was
94 * added to the queue, 1 if the event was merged with some other queued event,
95 * 2 if the event was not queued - either the queue of events has overflown
96 * or the group is shutting down.
98 int fsnotify_add_event(struct fsnotify_group *group,
99 struct fsnotify_event *event,
100 int (*merge)(struct list_head *,
101 struct fsnotify_event *))
104 struct list_head *list = &group->notification_list;
106 pr_debug("%s: group=%p event=%p\n", __func__, group, event);
108 spin_lock(&group->notification_lock);
110 if (group->shutdown) {
111 spin_unlock(&group->notification_lock);
115 if (group->q_len >= group->max_events) {
117 /* Queue overflow event only if it isn't already queued */
118 if (!list_empty(&group->overflow_event->list)) {
119 spin_unlock(&group->notification_lock);
122 event = group->overflow_event;
126 if (!list_empty(list) && merge) {
127 ret = merge(list, event);
129 spin_unlock(&group->notification_lock);
136 list_add_tail(&event->list, list);
137 spin_unlock(&group->notification_lock);
139 wake_up(&group->notification_waitq);
140 kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
145 * Remove and return the first event from the notification list. It is the
146 * responsibility of the caller to destroy the obtained event
148 struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
150 struct fsnotify_event *event;
152 BUG_ON(IS_ENABLED(CONFIG_SMP) &&
153 !spin_is_locked(&group->notification_lock));
155 pr_debug("%s: group=%p\n", __func__, group);
157 event = list_first_entry(&group->notification_list,
158 struct fsnotify_event, list);
160 * We need to init list head for the case of overflow event so that
161 * check in fsnotify_add_event() works
163 list_del_init(&event->list);
170 * This will not remove the event, that must be done with
171 * fsnotify_remove_first_event()
173 struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
175 BUG_ON(IS_ENABLED(CONFIG_SMP) &&
176 !spin_is_locked(&group->notification_lock));
178 return list_first_entry(&group->notification_list,
179 struct fsnotify_event, list);
183 * Called when a group is being torn down to clean up any outstanding
184 * event notifications.
186 void fsnotify_flush_notify(struct fsnotify_group *group)
188 struct fsnotify_event *event;
190 spin_lock(&group->notification_lock);
191 while (!fsnotify_notify_queue_is_empty(group)) {
192 event = fsnotify_remove_first_event(group);
193 spin_unlock(&group->notification_lock);
194 fsnotify_destroy_event(group, event);
195 spin_lock(&group->notification_lock);
197 spin_unlock(&group->notification_lock);
201 * fsnotify_create_event - Allocate a new event which will be sent to each
202 * group's handle_event function if the group was interested in this
205 * @inode the inode which is supposed to receive the event (sometimes a
206 * parent of the inode to which the event happened.
207 * @mask what actually happened.
208 * @data pointer to the object which was actually affected
209 * @data_type flag indication if the data is a file, path, inode, nothing...
210 * @name the filename, if available
212 void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
215 INIT_LIST_HEAD(&event->list);
216 event->inode = inode;