Loading...
1/*
2 * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
3 *
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)
7 * any later version.
8 *
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.
13 *
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.
17 */
18
19/*
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
31 * allocated and used.
32 */
33
34#include <linux/fs.h>
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>
45
46#include <linux/atomic.h>
47
48#include <linux/fsnotify_backend.h>
49#include "fsnotify.h"
50
51static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
52
53/**
54 * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
55 * Called from fsnotify_move, which is inlined into filesystem modules.
56 */
57u32 fsnotify_get_cookie(void)
58{
59 return atomic_inc_return(&fsnotify_sync_cookie);
60}
61EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
62
63/* return true if the notify queue is empty, false otherwise */
64bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
65{
66 assert_spin_locked(&group->notification_lock);
67 return list_empty(&group->notification_list) ? true : false;
68}
69
70void fsnotify_destroy_event(struct fsnotify_group *group,
71 struct fsnotify_event *event)
72{
73 /* Overflow events are per-group and we don't want to free them */
74 if (!event || event->mask == FS_Q_OVERFLOW)
75 return;
76 /*
77 * If the event is still queued, we have a problem... Do an unreliable
78 * lockless check first to avoid locking in the common case. The
79 * locking may be necessary for permission events which got removed
80 * from the list by a different CPU than the one freeing the event.
81 */
82 if (!list_empty(&event->list)) {
83 spin_lock(&group->notification_lock);
84 WARN_ON(!list_empty(&event->list));
85 spin_unlock(&group->notification_lock);
86 }
87 group->ops->free_event(event);
88}
89
90/*
91 * Add an event to the group notification queue. The group can later pull this
92 * event off the queue to deal with. The function returns 0 if the event was
93 * added to the queue, 1 if the event was merged with some other queued event,
94 * 2 if the event was not queued - either the queue of events has overflown
95 * or the group is shutting down.
96 */
97int fsnotify_add_event(struct fsnotify_group *group,
98 struct fsnotify_event *event,
99 int (*merge)(struct list_head *,
100 struct fsnotify_event *))
101{
102 int ret = 0;
103 struct list_head *list = &group->notification_list;
104
105 pr_debug("%s: group=%p event=%p\n", __func__, group, event);
106
107 spin_lock(&group->notification_lock);
108
109 if (group->shutdown) {
110 spin_unlock(&group->notification_lock);
111 return 2;
112 }
113
114 if (event == group->overflow_event ||
115 group->q_len >= group->max_events) {
116 ret = 2;
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);
120 return ret;
121 }
122 event = group->overflow_event;
123 goto queue;
124 }
125
126 if (!list_empty(list) && merge) {
127 ret = merge(list, event);
128 if (ret) {
129 spin_unlock(&group->notification_lock);
130 return ret;
131 }
132 }
133
134queue:
135 group->q_len++;
136 list_add_tail(&event->list, list);
137 spin_unlock(&group->notification_lock);
138
139 wake_up(&group->notification_waitq);
140 kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
141 return ret;
142}
143
144/*
145 * Remove and return the first event from the notification list. It is the
146 * responsibility of the caller to destroy the obtained event
147 */
148struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
149{
150 struct fsnotify_event *event;
151
152 assert_spin_locked(&group->notification_lock);
153
154 pr_debug("%s: group=%p\n", __func__, group);
155
156 event = list_first_entry(&group->notification_list,
157 struct fsnotify_event, list);
158 /*
159 * We need to init list head for the case of overflow event so that
160 * check in fsnotify_add_event() works
161 */
162 list_del_init(&event->list);
163 group->q_len--;
164
165 return event;
166}
167
168/*
169 * This will not remove the event, that must be done with
170 * fsnotify_remove_first_event()
171 */
172struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
173{
174 assert_spin_locked(&group->notification_lock);
175
176 return list_first_entry(&group->notification_list,
177 struct fsnotify_event, list);
178}
179
180/*
181 * Called when a group is being torn down to clean up any outstanding
182 * event notifications.
183 */
184void fsnotify_flush_notify(struct fsnotify_group *group)
185{
186 struct fsnotify_event *event;
187
188 spin_lock(&group->notification_lock);
189 while (!fsnotify_notify_queue_is_empty(group)) {
190 event = fsnotify_remove_first_event(group);
191 spin_unlock(&group->notification_lock);
192 fsnotify_destroy_event(group, event);
193 spin_lock(&group->notification_lock);
194 }
195 spin_unlock(&group->notification_lock);
196}
197
198/*
199 * fsnotify_create_event - Allocate a new event which will be sent to each
200 * group's handle_event function if the group was interested in this
201 * particular event.
202 *
203 * @inode the inode which is supposed to receive the event (sometimes a
204 * parent of the inode to which the event happened.
205 * @mask what actually happened.
206 * @data pointer to the object which was actually affected
207 * @data_type flag indication if the data is a file, path, inode, nothing...
208 * @name the filename, if available
209 */
210void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
211 u32 mask)
212{
213 INIT_LIST_HEAD(&event->list);
214 event->inode = inode;
215 event->mask = mask;
216}
1/*
2 * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
3 *
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)
7 * any later version.
8 *
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.
13 *
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.
17 */
18
19/*
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
31 * allocated and used.
32 */
33
34#include <linux/fs.h>
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>
45
46#include <linux/atomic.h>
47
48#include <linux/fsnotify_backend.h>
49#include "fsnotify.h"
50
51static struct kmem_cache *fsnotify_event_cachep;
52static struct kmem_cache *fsnotify_event_holder_cachep;
53/*
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'
58 */
59static struct fsnotify_event *q_overflow_event;
60static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
61
62/**
63 * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
64 * Called from fsnotify_move, which is inlined into filesystem modules.
65 */
66u32 fsnotify_get_cookie(void)
67{
68 return atomic_inc_return(&fsnotify_sync_cookie);
69}
70EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
71
72/* return true if the notify queue is empty, false otherwise */
73bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
74{
75 BUG_ON(!mutex_is_locked(&group->notification_mutex));
76 return list_empty(&group->notification_list) ? true : false;
77}
78
79void fsnotify_get_event(struct fsnotify_event *event)
80{
81 atomic_inc(&event->refcnt);
82}
83
84void fsnotify_put_event(struct fsnotify_event *event)
85{
86 if (!event)
87 return;
88
89 if (atomic_dec_and_test(&event->refcnt)) {
90 pr_debug("%s: event=%p\n", __func__, event);
91
92 if (event->data_type == FSNOTIFY_EVENT_PATH)
93 path_put(&event->path);
94
95 BUG_ON(!list_empty(&event->private_data_list));
96
97 kfree(event->file_name);
98 put_pid(event->tgid);
99 kmem_cache_free(fsnotify_event_cachep, event);
100 }
101}
102
103struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
104{
105 return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
106}
107
108void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
109{
110 if (holder)
111 kmem_cache_free(fsnotify_event_holder_cachep, holder);
112}
113
114/*
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)
117 */
118struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
119{
120 struct fsnotify_event_private_data *lpriv;
121 struct fsnotify_event_private_data *priv = NULL;
122
123 assert_spin_locked(&event->lock);
124
125 list_for_each_entry(lpriv, &event->private_data_list, event_list) {
126 if (lpriv->group == group) {
127 priv = lpriv;
128 list_del(&priv->event_list);
129 break;
130 }
131 }
132 return priv;
133}
134
135/*
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.
139 */
140struct fsnotify_event *fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
141 struct fsnotify_event_private_data *priv,
142 struct fsnotify_event *(*merge)(struct list_head *,
143 struct fsnotify_event *))
144{
145 struct fsnotify_event *return_event = NULL;
146 struct fsnotify_event_holder *holder = NULL;
147 struct list_head *list = &group->notification_list;
148
149 pr_debug("%s: group=%p event=%p priv=%p\n", __func__, group, event, priv);
150
151 /*
152 * There is one fsnotify_event_holder embedded inside each fsnotify_event.
153 * Check if we expect to be able to use that holder. If not alloc a new
154 * holder.
155 * For the overflow event it's possible that something will use the in
156 * event holder before we get the lock so we may need to jump back and
157 * alloc a new holder, this can't happen for most events...
158 */
159 if (!list_empty(&event->holder.event_list)) {
160alloc_holder:
161 holder = fsnotify_alloc_event_holder();
162 if (!holder)
163 return ERR_PTR(-ENOMEM);
164 }
165
166 mutex_lock(&group->notification_mutex);
167
168 if (group->q_len >= group->max_events) {
169 event = q_overflow_event;
170
171 /*
172 * we need to return the overflow event
173 * which means we need a ref
174 */
175 fsnotify_get_event(event);
176 return_event = event;
177
178 /* sorry, no private data on the overflow event */
179 priv = NULL;
180 }
181
182 if (!list_empty(list) && merge) {
183 struct fsnotify_event *tmp;
184
185 tmp = merge(list, event);
186 if (tmp) {
187 mutex_unlock(&group->notification_mutex);
188
189 if (return_event)
190 fsnotify_put_event(return_event);
191 if (holder != &event->holder)
192 fsnotify_destroy_event_holder(holder);
193 return tmp;
194 }
195 }
196
197 spin_lock(&event->lock);
198
199 if (list_empty(&event->holder.event_list)) {
200 if (unlikely(holder))
201 fsnotify_destroy_event_holder(holder);
202 holder = &event->holder;
203 } else if (unlikely(!holder)) {
204 /* between the time we checked above and got the lock the in
205 * event holder was used, go back and get a new one */
206 spin_unlock(&event->lock);
207 mutex_unlock(&group->notification_mutex);
208
209 if (return_event) {
210 fsnotify_put_event(return_event);
211 return_event = NULL;
212 }
213
214 goto alloc_holder;
215 }
216
217 group->q_len++;
218 holder->event = event;
219
220 fsnotify_get_event(event);
221 list_add_tail(&holder->event_list, list);
222 if (priv)
223 list_add_tail(&priv->event_list, &event->private_data_list);
224 spin_unlock(&event->lock);
225 mutex_unlock(&group->notification_mutex);
226
227 wake_up(&group->notification_waitq);
228 return return_event;
229}
230
231/*
232 * Remove and return the first event from the notification list. There is a
233 * reference held on this event since it was on the list. It is the responsibility
234 * of the caller to drop this reference.
235 */
236struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
237{
238 struct fsnotify_event *event;
239 struct fsnotify_event_holder *holder;
240
241 BUG_ON(!mutex_is_locked(&group->notification_mutex));
242
243 pr_debug("%s: group=%p\n", __func__, group);
244
245 holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
246
247 event = holder->event;
248
249 spin_lock(&event->lock);
250 holder->event = NULL;
251 list_del_init(&holder->event_list);
252 spin_unlock(&event->lock);
253
254 /* event == holder means we are referenced through the in event holder */
255 if (holder != &event->holder)
256 fsnotify_destroy_event_holder(holder);
257
258 group->q_len--;
259
260 return event;
261}
262
263/*
264 * This will not remove the event, that must be done with fsnotify_remove_notify_event()
265 */
266struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
267{
268 struct fsnotify_event *event;
269 struct fsnotify_event_holder *holder;
270
271 BUG_ON(!mutex_is_locked(&group->notification_mutex));
272
273 holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
274 event = holder->event;
275
276 return event;
277}
278
279/*
280 * Called when a group is being torn down to clean up any outstanding
281 * event notifications.
282 */
283void fsnotify_flush_notify(struct fsnotify_group *group)
284{
285 struct fsnotify_event *event;
286 struct fsnotify_event_private_data *priv;
287
288 mutex_lock(&group->notification_mutex);
289 while (!fsnotify_notify_queue_is_empty(group)) {
290 event = fsnotify_remove_notify_event(group);
291 /* if they don't implement free_event_priv they better not have attached any */
292 if (group->ops->free_event_priv) {
293 spin_lock(&event->lock);
294 priv = fsnotify_remove_priv_from_event(group, event);
295 spin_unlock(&event->lock);
296 if (priv)
297 group->ops->free_event_priv(priv);
298 }
299 fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
300 }
301 mutex_unlock(&group->notification_mutex);
302}
303
304static void initialize_event(struct fsnotify_event *event)
305{
306 INIT_LIST_HEAD(&event->holder.event_list);
307 atomic_set(&event->refcnt, 1);
308
309 spin_lock_init(&event->lock);
310
311 INIT_LIST_HEAD(&event->private_data_list);
312}
313
314/*
315 * Caller damn well better be holding whatever mutex is protecting the
316 * old_holder->event_list and the new_event must be a clean event which
317 * cannot be found anywhere else in the kernel.
318 */
319int fsnotify_replace_event(struct fsnotify_event_holder *old_holder,
320 struct fsnotify_event *new_event)
321{
322 struct fsnotify_event *old_event = old_holder->event;
323 struct fsnotify_event_holder *new_holder = &new_event->holder;
324
325 enum event_spinlock_class {
326 SPINLOCK_OLD,
327 SPINLOCK_NEW,
328 };
329
330 pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, new_event);
331
332 /*
333 * if the new_event's embedded holder is in use someone
334 * screwed up and didn't give us a clean new event.
335 */
336 BUG_ON(!list_empty(&new_holder->event_list));
337
338 spin_lock_nested(&old_event->lock, SPINLOCK_OLD);
339 spin_lock_nested(&new_event->lock, SPINLOCK_NEW);
340
341 new_holder->event = new_event;
342 list_replace_init(&old_holder->event_list, &new_holder->event_list);
343
344 spin_unlock(&new_event->lock);
345 spin_unlock(&old_event->lock);
346
347 /* event == holder means we are referenced through the in event holder */
348 if (old_holder != &old_event->holder)
349 fsnotify_destroy_event_holder(old_holder);
350
351 fsnotify_get_event(new_event); /* on the list take reference */
352 fsnotify_put_event(old_event); /* off the list, drop reference */
353
354 return 0;
355}
356
357struct fsnotify_event *fsnotify_clone_event(struct fsnotify_event *old_event)
358{
359 struct fsnotify_event *event;
360
361 event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL);
362 if (!event)
363 return NULL;
364
365 pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, event);
366
367 memcpy(event, old_event, sizeof(*event));
368 initialize_event(event);
369
370 if (event->name_len) {
371 event->file_name = kstrdup(old_event->file_name, GFP_KERNEL);
372 if (!event->file_name) {
373 kmem_cache_free(fsnotify_event_cachep, event);
374 return NULL;
375 }
376 }
377 event->tgid = get_pid(old_event->tgid);
378 if (event->data_type == FSNOTIFY_EVENT_PATH)
379 path_get(&event->path);
380
381 return event;
382}
383
384/*
385 * fsnotify_create_event - Allocate a new event which will be sent to each
386 * group's handle_event function if the group was interested in this
387 * particular event.
388 *
389 * @to_tell the inode which is supposed to receive the event (sometimes a
390 * parent of the inode to which the event happened.
391 * @mask what actually happened.
392 * @data pointer to the object which was actually affected
393 * @data_type flag indication if the data is a file, path, inode, nothing...
394 * @name the filename, if available
395 */
396struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
397 int data_type, const unsigned char *name,
398 u32 cookie, gfp_t gfp)
399{
400 struct fsnotify_event *event;
401
402 event = kmem_cache_zalloc(fsnotify_event_cachep, gfp);
403 if (!event)
404 return NULL;
405
406 pr_debug("%s: event=%p to_tell=%p mask=%x data=%p data_type=%d\n",
407 __func__, event, to_tell, mask, data, data_type);
408
409 initialize_event(event);
410
411 if (name) {
412 event->file_name = kstrdup(name, gfp);
413 if (!event->file_name) {
414 kmem_cache_free(fsnotify_event_cachep, event);
415 return NULL;
416 }
417 event->name_len = strlen(event->file_name);
418 }
419
420 event->tgid = get_pid(task_tgid(current));
421 event->sync_cookie = cookie;
422 event->to_tell = to_tell;
423 event->data_type = data_type;
424
425 switch (data_type) {
426 case FSNOTIFY_EVENT_PATH: {
427 struct path *path = data;
428 event->path.dentry = path->dentry;
429 event->path.mnt = path->mnt;
430 path_get(&event->path);
431 break;
432 }
433 case FSNOTIFY_EVENT_INODE:
434 event->inode = data;
435 break;
436 case FSNOTIFY_EVENT_NONE:
437 event->inode = NULL;
438 event->path.dentry = NULL;
439 event->path.mnt = NULL;
440 break;
441 default:
442 BUG();
443 }
444
445 event->mask = mask;
446
447 return event;
448}
449
450__init int fsnotify_notification_init(void)
451{
452 fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
453 fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);
454
455 q_overflow_event = fsnotify_create_event(NULL, FS_Q_OVERFLOW, NULL,
456 FSNOTIFY_EVENT_NONE, NULL, 0,
457 GFP_KERNEL);
458 if (!q_overflow_event)
459 panic("unable to allocate fsnotify q_overflow_event\n");
460
461 return 0;
462}
463subsys_initcall(fsnotify_notification_init);
464