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90586523 EP |
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 | ||
a2d8bc6c EP |
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 | ||
90586523 EP |
34 | #include <linux/fs.h> |
35 | #include <linux/init.h> | |
36 | #include <linux/kernel.h> | |
37 | #include <linux/list.h> | |
38 | #include <linux/mount.h> | |
39 | #include <linux/mutex.h> | |
40 | #include <linux/namei.h> | |
41 | #include <linux/path.h> | |
42 | #include <linux/slab.h> | |
43 | #include <linux/spinlock.h> | |
44 | ||
45 | #include <asm/atomic.h> | |
46 | ||
47 | #include <linux/fsnotify_backend.h> | |
48 | #include "fsnotify.h" | |
49 | ||
50 | static struct kmem_cache *fsnotify_event_cachep; | |
a2d8bc6c EP |
51 | static struct kmem_cache *fsnotify_event_holder_cachep; |
52 | /* | |
53 | * This is a magic event we send when the q is too full. Since it doesn't | |
54 | * hold real event information we just keep one system wide and use it any time | |
55 | * it is needed. It's refcnt is set 1 at kernel init time and will never | |
56 | * get set to 0 so it will never get 'freed' | |
57 | */ | |
58 | static struct fsnotify_event q_overflow_event; | |
59 | ||
60 | /* return true if the notify queue is empty, false otherwise */ | |
61 | bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group) | |
62 | { | |
63 | BUG_ON(!mutex_is_locked(&group->notification_mutex)); | |
64 | return list_empty(&group->notification_list) ? true : false; | |
65 | } | |
90586523 EP |
66 | |
67 | void fsnotify_get_event(struct fsnotify_event *event) | |
68 | { | |
69 | atomic_inc(&event->refcnt); | |
70 | } | |
71 | ||
72 | void fsnotify_put_event(struct fsnotify_event *event) | |
73 | { | |
74 | if (!event) | |
75 | return; | |
76 | ||
77 | if (atomic_dec_and_test(&event->refcnt)) { | |
78 | if (event->data_type == FSNOTIFY_EVENT_PATH) | |
79 | path_put(&event->path); | |
80 | ||
81 | kmem_cache_free(fsnotify_event_cachep, event); | |
82 | } | |
83 | } | |
84 | ||
a2d8bc6c EP |
85 | struct fsnotify_event_holder *fsnotify_alloc_event_holder(void) |
86 | { | |
87 | return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL); | |
88 | } | |
89 | ||
90 | void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder) | |
91 | { | |
92 | kmem_cache_free(fsnotify_event_holder_cachep, holder); | |
93 | } | |
94 | ||
95 | /* | |
96 | * check if 2 events contain the same information. | |
97 | */ | |
98 | static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new) | |
99 | { | |
100 | if ((old->mask == new->mask) && | |
101 | (old->to_tell == new->to_tell) && | |
102 | (old->data_type == new->data_type)) { | |
103 | switch (old->data_type) { | |
104 | case (FSNOTIFY_EVENT_INODE): | |
105 | if (old->inode == new->inode) | |
106 | return true; | |
107 | break; | |
108 | case (FSNOTIFY_EVENT_PATH): | |
109 | if ((old->path.mnt == new->path.mnt) && | |
110 | (old->path.dentry == new->path.dentry)) | |
111 | return true; | |
112 | case (FSNOTIFY_EVENT_NONE): | |
113 | return true; | |
114 | }; | |
115 | } | |
116 | return false; | |
117 | } | |
118 | ||
90586523 | 119 | /* |
a2d8bc6c EP |
120 | * Add an event to the group notification queue. The group can later pull this |
121 | * event off the queue to deal with. If the event is successfully added to the | |
122 | * group's notification queue, a reference is taken on event. | |
90586523 | 123 | */ |
a2d8bc6c EP |
124 | int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event) |
125 | { | |
126 | struct fsnotify_event_holder *holder = NULL; | |
127 | struct list_head *list = &group->notification_list; | |
128 | struct fsnotify_event_holder *last_holder; | |
129 | struct fsnotify_event *last_event; | |
130 | ||
131 | /* | |
132 | * There is one fsnotify_event_holder embedded inside each fsnotify_event. | |
133 | * Check if we expect to be able to use that holder. If not alloc a new | |
134 | * holder. | |
135 | * For the overflow event it's possible that something will use the in | |
136 | * event holder before we get the lock so we may need to jump back and | |
137 | * alloc a new holder, this can't happen for most events... | |
138 | */ | |
139 | if (!list_empty(&event->holder.event_list)) { | |
140 | alloc_holder: | |
141 | holder = fsnotify_alloc_event_holder(); | |
142 | if (!holder) | |
143 | return -ENOMEM; | |
144 | } | |
145 | ||
146 | mutex_lock(&group->notification_mutex); | |
147 | ||
148 | if (group->q_len >= group->max_events) | |
149 | event = &q_overflow_event; | |
150 | ||
151 | spin_lock(&event->lock); | |
152 | ||
153 | if (list_empty(&event->holder.event_list)) { | |
154 | if (unlikely(holder)) | |
155 | fsnotify_destroy_event_holder(holder); | |
156 | holder = &event->holder; | |
157 | } else if (unlikely(!holder)) { | |
158 | /* between the time we checked above and got the lock the in | |
159 | * event holder was used, go back and get a new one */ | |
160 | spin_unlock(&event->lock); | |
161 | mutex_unlock(&group->notification_mutex); | |
162 | goto alloc_holder; | |
163 | } | |
164 | ||
165 | if (!list_empty(list)) { | |
166 | last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list); | |
167 | last_event = last_holder->event; | |
168 | if (event_compare(last_event, event)) { | |
169 | spin_unlock(&event->lock); | |
170 | mutex_unlock(&group->notification_mutex); | |
171 | if (holder != &event->holder) | |
172 | fsnotify_destroy_event_holder(holder); | |
173 | return 0; | |
174 | } | |
175 | } | |
176 | ||
177 | group->q_len++; | |
178 | holder->event = event; | |
179 | ||
180 | fsnotify_get_event(event); | |
181 | list_add_tail(&holder->event_list, list); | |
182 | spin_unlock(&event->lock); | |
183 | mutex_unlock(&group->notification_mutex); | |
184 | ||
185 | wake_up(&group->notification_waitq); | |
186 | return 0; | |
187 | } | |
188 | ||
189 | /* | |
190 | * Remove and return the first event from the notification list. There is a | |
191 | * reference held on this event since it was on the list. It is the responsibility | |
192 | * of the caller to drop this reference. | |
193 | */ | |
194 | struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group) | |
90586523 EP |
195 | { |
196 | struct fsnotify_event *event; | |
a2d8bc6c | 197 | struct fsnotify_event_holder *holder; |
90586523 | 198 | |
a2d8bc6c | 199 | BUG_ON(!mutex_is_locked(&group->notification_mutex)); |
90586523 | 200 | |
a2d8bc6c EP |
201 | holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list); |
202 | ||
203 | event = holder->event; | |
204 | ||
205 | spin_lock(&event->lock); | |
206 | holder->event = NULL; | |
207 | list_del_init(&holder->event_list); | |
208 | spin_unlock(&event->lock); | |
209 | ||
210 | /* event == holder means we are referenced through the in event holder */ | |
211 | if (holder != &event->holder) | |
212 | fsnotify_destroy_event_holder(holder); | |
213 | ||
214 | group->q_len--; | |
215 | ||
216 | return event; | |
217 | } | |
218 | ||
219 | /* | |
220 | * This will not remove the event, that must be done with fsnotify_remove_notify_event() | |
221 | */ | |
222 | struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group) | |
223 | { | |
224 | struct fsnotify_event *event; | |
225 | struct fsnotify_event_holder *holder; | |
226 | ||
227 | BUG_ON(!mutex_is_locked(&group->notification_mutex)); | |
228 | ||
229 | holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list); | |
230 | event = holder->event; | |
231 | ||
232 | return event; | |
233 | } | |
234 | ||
235 | /* | |
236 | * Called when a group is being torn down to clean up any outstanding | |
237 | * event notifications. | |
238 | */ | |
239 | void fsnotify_flush_notify(struct fsnotify_group *group) | |
240 | { | |
241 | struct fsnotify_event *event; | |
242 | ||
243 | mutex_lock(&group->notification_mutex); | |
244 | while (!fsnotify_notify_queue_is_empty(group)) { | |
245 | event = fsnotify_remove_notify_event(group); | |
246 | fsnotify_put_event(event); /* matches fsnotify_add_notify_event */ | |
247 | } | |
248 | mutex_unlock(&group->notification_mutex); | |
249 | } | |
250 | ||
251 | static void initialize_event(struct fsnotify_event *event) | |
252 | { | |
253 | event->holder.event = NULL; | |
254 | INIT_LIST_HEAD(&event->holder.event_list); | |
90586523 EP |
255 | atomic_set(&event->refcnt, 1); |
256 | ||
257 | spin_lock_init(&event->lock); | |
258 | ||
259 | event->path.dentry = NULL; | |
260 | event->path.mnt = NULL; | |
261 | event->inode = NULL; | |
a2d8bc6c | 262 | event->data_type = FSNOTIFY_EVENT_NONE; |
90586523 | 263 | |
a2d8bc6c EP |
264 | event->to_tell = NULL; |
265 | } | |
266 | ||
267 | /* | |
268 | * fsnotify_create_event - Allocate a new event which will be sent to each | |
269 | * group's handle_event function if the group was interested in this | |
270 | * particular event. | |
271 | * | |
272 | * @to_tell the inode which is supposed to receive the event (sometimes a | |
273 | * parent of the inode to which the event happened. | |
274 | * @mask what actually happened. | |
275 | * @data pointer to the object which was actually affected | |
276 | * @data_type flag indication if the data is a file, path, inode, nothing... | |
277 | */ | |
278 | struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, | |
279 | void *data, int data_type) | |
280 | { | |
281 | struct fsnotify_event *event; | |
282 | ||
283 | event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL); | |
284 | if (!event) | |
285 | return NULL; | |
286 | ||
287 | initialize_event(event); | |
90586523 EP |
288 | event->to_tell = to_tell; |
289 | ||
290 | switch (data_type) { | |
291 | case FSNOTIFY_EVENT_FILE: { | |
292 | struct file *file = data; | |
293 | struct path *path = &file->f_path; | |
294 | event->path.dentry = path->dentry; | |
295 | event->path.mnt = path->mnt; | |
296 | path_get(&event->path); | |
297 | event->data_type = FSNOTIFY_EVENT_PATH; | |
298 | break; | |
299 | } | |
300 | case FSNOTIFY_EVENT_PATH: { | |
301 | struct path *path = data; | |
302 | event->path.dentry = path->dentry; | |
303 | event->path.mnt = path->mnt; | |
304 | path_get(&event->path); | |
305 | event->data_type = FSNOTIFY_EVENT_PATH; | |
306 | break; | |
307 | } | |
308 | case FSNOTIFY_EVENT_INODE: | |
309 | event->inode = data; | |
310 | event->data_type = FSNOTIFY_EVENT_INODE; | |
311 | break; | |
312 | case FSNOTIFY_EVENT_NONE: | |
313 | event->inode = NULL; | |
314 | event->path.dentry = NULL; | |
315 | event->path.mnt = NULL; | |
316 | break; | |
317 | default: | |
318 | BUG(); | |
319 | } | |
320 | ||
321 | event->mask = mask; | |
322 | ||
323 | return event; | |
324 | } | |
325 | ||
326 | __init int fsnotify_notification_init(void) | |
327 | { | |
328 | fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC); | |
a2d8bc6c EP |
329 | fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC); |
330 | ||
331 | initialize_event(&q_overflow_event); | |
332 | q_overflow_event.mask = FS_Q_OVERFLOW; | |
90586523 EP |
333 | |
334 | return 0; | |
335 | } | |
336 | subsys_initcall(fsnotify_notification_init); | |
337 |