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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 | ||
62ffe5df | 81 | kfree(event->file_name); |
90586523 EP |
82 | kmem_cache_free(fsnotify_event_cachep, event); |
83 | } | |
84 | } | |
85 | ||
a2d8bc6c EP |
86 | struct fsnotify_event_holder *fsnotify_alloc_event_holder(void) |
87 | { | |
88 | return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL); | |
89 | } | |
90 | ||
91 | void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder) | |
92 | { | |
93 | kmem_cache_free(fsnotify_event_holder_cachep, holder); | |
94 | } | |
95 | ||
96 | /* | |
97 | * check if 2 events contain the same information. | |
98 | */ | |
99 | static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new) | |
100 | { | |
101 | if ((old->mask == new->mask) && | |
102 | (old->to_tell == new->to_tell) && | |
103 | (old->data_type == new->data_type)) { | |
104 | switch (old->data_type) { | |
105 | case (FSNOTIFY_EVENT_INODE): | |
106 | if (old->inode == new->inode) | |
107 | return true; | |
108 | break; | |
109 | case (FSNOTIFY_EVENT_PATH): | |
110 | if ((old->path.mnt == new->path.mnt) && | |
111 | (old->path.dentry == new->path.dentry)) | |
112 | return true; | |
113 | case (FSNOTIFY_EVENT_NONE): | |
114 | return true; | |
115 | }; | |
116 | } | |
117 | return false; | |
118 | } | |
119 | ||
90586523 | 120 | /* |
a2d8bc6c EP |
121 | * Add an event to the group notification queue. The group can later pull this |
122 | * event off the queue to deal with. If the event is successfully added to the | |
123 | * group's notification queue, a reference is taken on event. | |
90586523 | 124 | */ |
a2d8bc6c EP |
125 | int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event) |
126 | { | |
127 | struct fsnotify_event_holder *holder = NULL; | |
128 | struct list_head *list = &group->notification_list; | |
129 | struct fsnotify_event_holder *last_holder; | |
130 | struct fsnotify_event *last_event; | |
131 | ||
132 | /* | |
133 | * There is one fsnotify_event_holder embedded inside each fsnotify_event. | |
134 | * Check if we expect to be able to use that holder. If not alloc a new | |
135 | * holder. | |
136 | * For the overflow event it's possible that something will use the in | |
137 | * event holder before we get the lock so we may need to jump back and | |
138 | * alloc a new holder, this can't happen for most events... | |
139 | */ | |
140 | if (!list_empty(&event->holder.event_list)) { | |
141 | alloc_holder: | |
142 | holder = fsnotify_alloc_event_holder(); | |
143 | if (!holder) | |
144 | return -ENOMEM; | |
145 | } | |
146 | ||
147 | mutex_lock(&group->notification_mutex); | |
148 | ||
149 | if (group->q_len >= group->max_events) | |
150 | event = &q_overflow_event; | |
151 | ||
152 | spin_lock(&event->lock); | |
153 | ||
154 | if (list_empty(&event->holder.event_list)) { | |
155 | if (unlikely(holder)) | |
156 | fsnotify_destroy_event_holder(holder); | |
157 | holder = &event->holder; | |
158 | } else if (unlikely(!holder)) { | |
159 | /* between the time we checked above and got the lock the in | |
160 | * event holder was used, go back and get a new one */ | |
161 | spin_unlock(&event->lock); | |
162 | mutex_unlock(&group->notification_mutex); | |
163 | goto alloc_holder; | |
164 | } | |
165 | ||
166 | if (!list_empty(list)) { | |
167 | last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list); | |
168 | last_event = last_holder->event; | |
169 | if (event_compare(last_event, event)) { | |
170 | spin_unlock(&event->lock); | |
171 | mutex_unlock(&group->notification_mutex); | |
172 | if (holder != &event->holder) | |
173 | fsnotify_destroy_event_holder(holder); | |
174 | return 0; | |
175 | } | |
176 | } | |
177 | ||
178 | group->q_len++; | |
179 | holder->event = event; | |
180 | ||
181 | fsnotify_get_event(event); | |
182 | list_add_tail(&holder->event_list, list); | |
183 | spin_unlock(&event->lock); | |
184 | mutex_unlock(&group->notification_mutex); | |
185 | ||
186 | wake_up(&group->notification_waitq); | |
187 | return 0; | |
188 | } | |
189 | ||
190 | /* | |
191 | * Remove and return the first event from the notification list. There is a | |
192 | * reference held on this event since it was on the list. It is the responsibility | |
193 | * of the caller to drop this reference. | |
194 | */ | |
195 | struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group) | |
90586523 EP |
196 | { |
197 | struct fsnotify_event *event; | |
a2d8bc6c | 198 | struct fsnotify_event_holder *holder; |
90586523 | 199 | |
a2d8bc6c | 200 | BUG_ON(!mutex_is_locked(&group->notification_mutex)); |
90586523 | 201 | |
a2d8bc6c EP |
202 | holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list); |
203 | ||
204 | event = holder->event; | |
205 | ||
206 | spin_lock(&event->lock); | |
207 | holder->event = NULL; | |
208 | list_del_init(&holder->event_list); | |
209 | spin_unlock(&event->lock); | |
210 | ||
211 | /* event == holder means we are referenced through the in event holder */ | |
212 | if (holder != &event->holder) | |
213 | fsnotify_destroy_event_holder(holder); | |
214 | ||
215 | group->q_len--; | |
216 | ||
217 | return event; | |
218 | } | |
219 | ||
220 | /* | |
221 | * This will not remove the event, that must be done with fsnotify_remove_notify_event() | |
222 | */ | |
223 | struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group) | |
224 | { | |
225 | struct fsnotify_event *event; | |
226 | struct fsnotify_event_holder *holder; | |
227 | ||
228 | BUG_ON(!mutex_is_locked(&group->notification_mutex)); | |
229 | ||
230 | holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list); | |
231 | event = holder->event; | |
232 | ||
233 | return event; | |
234 | } | |
235 | ||
236 | /* | |
237 | * Called when a group is being torn down to clean up any outstanding | |
238 | * event notifications. | |
239 | */ | |
240 | void fsnotify_flush_notify(struct fsnotify_group *group) | |
241 | { | |
242 | struct fsnotify_event *event; | |
243 | ||
244 | mutex_lock(&group->notification_mutex); | |
245 | while (!fsnotify_notify_queue_is_empty(group)) { | |
246 | event = fsnotify_remove_notify_event(group); | |
247 | fsnotify_put_event(event); /* matches fsnotify_add_notify_event */ | |
248 | } | |
249 | mutex_unlock(&group->notification_mutex); | |
250 | } | |
251 | ||
252 | static void initialize_event(struct fsnotify_event *event) | |
253 | { | |
254 | event->holder.event = NULL; | |
255 | INIT_LIST_HEAD(&event->holder.event_list); | |
90586523 EP |
256 | atomic_set(&event->refcnt, 1); |
257 | ||
258 | spin_lock_init(&event->lock); | |
259 | ||
260 | event->path.dentry = NULL; | |
261 | event->path.mnt = NULL; | |
262 | event->inode = NULL; | |
a2d8bc6c | 263 | event->data_type = FSNOTIFY_EVENT_NONE; |
90586523 | 264 | |
a2d8bc6c | 265 | event->to_tell = NULL; |
62ffe5df EP |
266 | |
267 | event->file_name = NULL; | |
268 | event->name_len = 0; | |
a2d8bc6c EP |
269 | } |
270 | ||
271 | /* | |
272 | * fsnotify_create_event - Allocate a new event which will be sent to each | |
273 | * group's handle_event function if the group was interested in this | |
274 | * particular event. | |
275 | * | |
276 | * @to_tell the inode which is supposed to receive the event (sometimes a | |
277 | * parent of the inode to which the event happened. | |
278 | * @mask what actually happened. | |
279 | * @data pointer to the object which was actually affected | |
280 | * @data_type flag indication if the data is a file, path, inode, nothing... | |
62ffe5df | 281 | * @name the filename, if available |
a2d8bc6c EP |
282 | */ |
283 | struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, | |
62ffe5df | 284 | void *data, int data_type, const char *name) |
a2d8bc6c EP |
285 | { |
286 | struct fsnotify_event *event; | |
287 | ||
288 | event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL); | |
289 | if (!event) | |
290 | return NULL; | |
291 | ||
292 | initialize_event(event); | |
62ffe5df EP |
293 | |
294 | if (name) { | |
295 | event->file_name = kstrdup(name, GFP_KERNEL); | |
296 | if (!event->file_name) { | |
297 | kmem_cache_free(fsnotify_event_cachep, event); | |
298 | return NULL; | |
299 | } | |
300 | event->name_len = strlen(event->file_name); | |
301 | } | |
90586523 EP |
302 | event->to_tell = to_tell; |
303 | ||
304 | switch (data_type) { | |
305 | case FSNOTIFY_EVENT_FILE: { | |
306 | struct file *file = data; | |
307 | struct path *path = &file->f_path; | |
308 | event->path.dentry = path->dentry; | |
309 | event->path.mnt = path->mnt; | |
310 | path_get(&event->path); | |
311 | event->data_type = FSNOTIFY_EVENT_PATH; | |
312 | break; | |
313 | } | |
314 | case FSNOTIFY_EVENT_PATH: { | |
315 | struct path *path = data; | |
316 | event->path.dentry = path->dentry; | |
317 | event->path.mnt = path->mnt; | |
318 | path_get(&event->path); | |
319 | event->data_type = FSNOTIFY_EVENT_PATH; | |
320 | break; | |
321 | } | |
322 | case FSNOTIFY_EVENT_INODE: | |
323 | event->inode = data; | |
324 | event->data_type = FSNOTIFY_EVENT_INODE; | |
325 | break; | |
326 | case FSNOTIFY_EVENT_NONE: | |
327 | event->inode = NULL; | |
328 | event->path.dentry = NULL; | |
329 | event->path.mnt = NULL; | |
330 | break; | |
331 | default: | |
332 | BUG(); | |
333 | } | |
334 | ||
335 | event->mask = mask; | |
336 | ||
337 | return event; | |
338 | } | |
339 | ||
340 | __init int fsnotify_notification_init(void) | |
341 | { | |
342 | fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC); | |
a2d8bc6c EP |
343 | fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC); |
344 | ||
345 | initialize_event(&q_overflow_event); | |
346 | q_overflow_event.mask = FS_Q_OVERFLOW; | |
90586523 EP |
347 | |
348 | return 0; | |
349 | } | |
350 | subsys_initcall(fsnotify_notification_init); | |
351 |