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 asyncronously 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 <asm/atomic.h>
48 #include <linux/fsnotify_backend.h>
51 static struct kmem_cache *fsnotify_event_cachep;
52 static struct kmem_cache *fsnotify_event_holder_cachep;
54 * This is a magic event we send when the q is too full. Since it doesn't
55 * hold real event information we just keep one system wide and use it any time
56 * it is needed. It's refcnt is set 1 at kernel init time and will never
57 * get set to 0 so it will never get 'freed'
59 static struct fsnotify_event *q_overflow_event;
60 static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
63 * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
64 * Called from fsnotify_move, which is inlined into filesystem modules.
66 u32 fsnotify_get_cookie(void)
68 return atomic_inc_return(&fsnotify_sync_cookie);
70 EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
72 /* return true if the notify queue is empty, false otherwise */
73 bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
75 BUG_ON(!mutex_is_locked(&group->notification_mutex));
76 return list_empty(&group->notification_list) ? true : false;
79 void fsnotify_get_event(struct fsnotify_event *event)
81 atomic_inc(&event->refcnt);
84 void fsnotify_put_event(struct fsnotify_event *event)
89 if (atomic_dec_and_test(&event->refcnt)) {
90 pr_debug("%s: event=%p\n", __func__, event);
92 if (event->data_type == FSNOTIFY_EVENT_PATH)
93 path_put(&event->path);
95 BUG_ON(!list_empty(&event->private_data_list));
97 kfree(event->file_name);
99 kmem_cache_free(fsnotify_event_cachep, event);
103 struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
105 return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
108 void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
111 kmem_cache_free(fsnotify_event_holder_cachep, holder);
115 * Find the private data that the group previously attached to this event when
116 * the group added the event to the notification queue (fsnotify_add_notify_event)
118 struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
120 struct fsnotify_event_private_data *lpriv;
121 struct fsnotify_event_private_data *priv = NULL;
123 assert_spin_locked(&event->lock);
125 list_for_each_entry(lpriv, &event->private_data_list, event_list) {
126 if (lpriv->group == group) {
128 list_del(&priv->event_list);
136 * Add an event to the group notification queue. The group can later pull this
137 * event off the queue to deal with. If the event is successfully added to the
138 * group's notification queue, a reference is taken on event.
140 int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
141 struct fsnotify_event_private_data *priv,
142 int (*merge)(struct list_head *,
143 struct fsnotify_event *,
147 struct fsnotify_event_holder *holder = NULL;
148 struct list_head *list = &group->notification_list;
151 pr_debug("%s: group=%p event=%p priv=%p\n", __func__, group, event, priv);
154 * There is one fsnotify_event_holder embedded inside each fsnotify_event.
155 * Check if we expect to be able to use that holder. If not alloc a new
157 * For the overflow event it's possible that something will use the in
158 * event holder before we get the lock so we may need to jump back and
159 * alloc a new holder, this can't happen for most events...
161 if (!list_empty(&event->holder.event_list)) {
163 holder = fsnotify_alloc_event_holder();
168 mutex_lock(&group->notification_mutex);
170 if (group->q_len >= group->max_events) {
171 event = q_overflow_event;
173 /* sorry, no private data on the overflow event */
177 if (!list_empty(list) && merge) {
180 ret = merge(list, event, arg);
182 mutex_unlock(&group->notification_mutex);
183 if (holder != &event->holder)
184 fsnotify_destroy_event_holder(holder);
189 spin_lock(&event->lock);
191 if (list_empty(&event->holder.event_list)) {
192 if (unlikely(holder))
193 fsnotify_destroy_event_holder(holder);
194 holder = &event->holder;
195 } else if (unlikely(!holder)) {
196 /* between the time we checked above and got the lock the in
197 * event holder was used, go back and get a new one */
198 spin_unlock(&event->lock);
199 mutex_unlock(&group->notification_mutex);
204 holder->event = event;
206 fsnotify_get_event(event);
207 list_add_tail(&holder->event_list, list);
209 list_add_tail(&priv->event_list, &event->private_data_list);
210 spin_unlock(&event->lock);
211 mutex_unlock(&group->notification_mutex);
213 wake_up(&group->notification_waitq);
218 * Remove and return the first event from the notification list. There is a
219 * reference held on this event since it was on the list. It is the responsibility
220 * of the caller to drop this reference.
222 struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
224 struct fsnotify_event *event;
225 struct fsnotify_event_holder *holder;
227 BUG_ON(!mutex_is_locked(&group->notification_mutex));
229 pr_debug("%s: group=%p\n", __func__, group);
231 holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
233 event = holder->event;
235 spin_lock(&event->lock);
236 holder->event = NULL;
237 list_del_init(&holder->event_list);
238 spin_unlock(&event->lock);
240 /* event == holder means we are referenced through the in event holder */
241 if (holder != &event->holder)
242 fsnotify_destroy_event_holder(holder);
250 * This will not remove the event, that must be done with fsnotify_remove_notify_event()
252 struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
254 struct fsnotify_event *event;
255 struct fsnotify_event_holder *holder;
257 BUG_ON(!mutex_is_locked(&group->notification_mutex));
259 holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
260 event = holder->event;
266 * Called when a group is being torn down to clean up any outstanding
267 * event notifications.
269 void fsnotify_flush_notify(struct fsnotify_group *group)
271 struct fsnotify_event *event;
272 struct fsnotify_event_private_data *priv;
274 mutex_lock(&group->notification_mutex);
275 while (!fsnotify_notify_queue_is_empty(group)) {
276 event = fsnotify_remove_notify_event(group);
277 /* if they don't implement free_event_priv they better not have attached any */
278 if (group->ops->free_event_priv) {
279 spin_lock(&event->lock);
280 priv = fsnotify_remove_priv_from_event(group, event);
281 spin_unlock(&event->lock);
283 group->ops->free_event_priv(priv);
285 fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
287 mutex_unlock(&group->notification_mutex);
290 static void initialize_event(struct fsnotify_event *event)
292 INIT_LIST_HEAD(&event->holder.event_list);
293 atomic_set(&event->refcnt, 1);
295 spin_lock_init(&event->lock);
297 INIT_LIST_HEAD(&event->private_data_list);
301 * Caller damn well better be holding whatever mutex is protecting the
302 * old_holder->event_list and the new_event must be a clean event which
303 * cannot be found anywhere else in the kernel.
305 int fsnotify_replace_event(struct fsnotify_event_holder *old_holder,
306 struct fsnotify_event *new_event)
308 struct fsnotify_event *old_event = old_holder->event;
309 struct fsnotify_event_holder *new_holder = &new_event->holder;
311 enum event_spinlock_class {
316 pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, new_event);
319 * if the new_event's embedded holder is in use someone
320 * screwed up and didn't give us a clean new event.
322 BUG_ON(!list_empty(&new_holder->event_list));
324 spin_lock_nested(&old_event->lock, SPINLOCK_OLD);
325 spin_lock_nested(&new_event->lock, SPINLOCK_NEW);
327 new_holder->event = new_event;
328 list_replace_init(&old_holder->event_list, &new_holder->event_list);
330 spin_unlock(&new_event->lock);
331 spin_unlock(&old_event->lock);
333 /* event == holder means we are referenced through the in event holder */
334 if (old_holder != &old_event->holder)
335 fsnotify_destroy_event_holder(old_holder);
337 fsnotify_get_event(new_event); /* on the list take reference */
338 fsnotify_put_event(old_event); /* off the list, drop reference */
343 struct fsnotify_event *fsnotify_clone_event(struct fsnotify_event *old_event)
345 struct fsnotify_event *event;
347 event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL);
351 pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, event);
353 memcpy(event, old_event, sizeof(*event));
354 initialize_event(event);
356 if (event->name_len) {
357 event->file_name = kstrdup(old_event->file_name, GFP_KERNEL);
358 if (!event->file_name) {
359 kmem_cache_free(fsnotify_event_cachep, event);
363 event->tgid = get_pid(old_event->tgid);
364 if (event->data_type == FSNOTIFY_EVENT_PATH)
365 path_get(&event->path);
371 * fsnotify_create_event - Allocate a new event which will be sent to each
372 * group's handle_event function if the group was interested in this
375 * @to_tell the inode which is supposed to receive the event (sometimes a
376 * parent of the inode to which the event happened.
377 * @mask what actually happened.
378 * @data pointer to the object which was actually affected
379 * @data_type flag indication if the data is a file, path, inode, nothing...
380 * @name the filename, if available
382 struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
383 int data_type, const unsigned char *name,
384 u32 cookie, gfp_t gfp)
386 struct fsnotify_event *event;
388 event = kmem_cache_zalloc(fsnotify_event_cachep, gfp);
392 pr_debug("%s: event=%p to_tell=%p mask=%x data=%p data_type=%d\n",
393 __func__, event, to_tell, mask, data, data_type);
395 initialize_event(event);
398 event->file_name = kstrdup(name, gfp);
399 if (!event->file_name) {
400 kmem_cache_free(fsnotify_event_cachep, event);
403 event->name_len = strlen(event->file_name);
406 event->tgid = get_pid(task_tgid(current));
407 event->sync_cookie = cookie;
408 event->to_tell = to_tell;
409 event->data_type = data_type;
412 case FSNOTIFY_EVENT_PATH: {
413 struct path *path = data;
414 event->path.dentry = path->dentry;
415 event->path.mnt = path->mnt;
416 path_get(&event->path);
419 case FSNOTIFY_EVENT_INODE:
422 case FSNOTIFY_EVENT_NONE:
424 event->path.dentry = NULL;
425 event->path.mnt = NULL;
436 __init int fsnotify_notification_init(void)
438 fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
439 fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);
441 q_overflow_event = fsnotify_create_event(NULL, FS_Q_OVERFLOW, NULL,
442 FSNOTIFY_EVENT_NONE, NULL, 0,
444 if (!q_overflow_event)
445 panic("unable to allocate fsnotify q_overflow_event\n");
449 subsys_initcall(fsnotify_notification_init);