Root/fs/notify/notification.c

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 <asm/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        if (event->data_type == FSNOTIFY_EVENT_PATH)
91            path_put(&event->path);
92
93        BUG_ON(!list_empty(&event->private_data_list));
94
95        kfree(event->file_name);
96        kmem_cache_free(fsnotify_event_cachep, event);
97    }
98}
99
100struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
101{
102    return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
103}
104
105void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
106{
107    kmem_cache_free(fsnotify_event_holder_cachep, holder);
108}
109
110/*
111 * Find the private data that the group previously attached to this event when
112 * the group added the event to the notification queue (fsnotify_add_notify_event)
113 */
114struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
115{
116    struct fsnotify_event_private_data *lpriv;
117    struct fsnotify_event_private_data *priv = NULL;
118
119    assert_spin_locked(&event->lock);
120
121    list_for_each_entry(lpriv, &event->private_data_list, event_list) {
122        if (lpriv->group == group) {
123            priv = lpriv;
124            list_del(&priv->event_list);
125            break;
126        }
127    }
128    return priv;
129}
130
131/*
132 * Check if 2 events contain the same information. We do not compare private data
133 * but at this moment that isn't a problem for any know fsnotify listeners.
134 */
135static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new)
136{
137    if ((old->mask == new->mask) &&
138        (old->to_tell == new->to_tell) &&
139        (old->data_type == new->data_type) &&
140        (old->name_len == new->name_len)) {
141        switch (old->data_type) {
142        case (FSNOTIFY_EVENT_INODE):
143            /* remember, after old was put on the wait_q we aren't
144             * allowed to look at the inode any more, only thing
145             * left to check was if the file_name is the same */
146            if (!old->name_len ||
147                !strcmp(old->file_name, new->file_name))
148                return true;
149            break;
150        case (FSNOTIFY_EVENT_PATH):
151            if ((old->path.mnt == new->path.mnt) &&
152                (old->path.dentry == new->path.dentry))
153                return true;
154            break;
155        case (FSNOTIFY_EVENT_NONE):
156            if (old->mask & FS_Q_OVERFLOW)
157                return true;
158            else if (old->mask & FS_IN_IGNORED)
159                return false;
160            return false;
161        };
162    }
163    return false;
164}
165
166/*
167 * Add an event to the group notification queue. The group can later pull this
168 * event off the queue to deal with. If the event is successfully added to the
169 * group's notification queue, a reference is taken on event.
170 */
171int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
172                  struct fsnotify_event_private_data *priv)
173{
174    struct fsnotify_event_holder *holder = NULL;
175    struct list_head *list = &group->notification_list;
176    struct fsnotify_event_holder *last_holder;
177    struct fsnotify_event *last_event;
178    int ret = 0;
179
180    /*
181     * There is one fsnotify_event_holder embedded inside each fsnotify_event.
182     * Check if we expect to be able to use that holder. If not alloc a new
183     * holder.
184     * For the overflow event it's possible that something will use the in
185     * event holder before we get the lock so we may need to jump back and
186     * alloc a new holder, this can't happen for most events...
187     */
188    if (!list_empty(&event->holder.event_list)) {
189alloc_holder:
190        holder = fsnotify_alloc_event_holder();
191        if (!holder)
192            return -ENOMEM;
193    }
194
195    mutex_lock(&group->notification_mutex);
196
197    if (group->q_len >= group->max_events) {
198        event = &q_overflow_event;
199        ret = -EOVERFLOW;
200        /* sorry, no private data on the overflow event */
201        priv = NULL;
202    }
203
204    spin_lock(&event->lock);
205
206    if (list_empty(&event->holder.event_list)) {
207        if (unlikely(holder))
208            fsnotify_destroy_event_holder(holder);
209        holder = &event->holder;
210    } else if (unlikely(!holder)) {
211        /* between the time we checked above and got the lock the in
212         * event holder was used, go back and get a new one */
213        spin_unlock(&event->lock);
214        mutex_unlock(&group->notification_mutex);
215        goto alloc_holder;
216    }
217
218    if (!list_empty(list)) {
219        last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list);
220        last_event = last_holder->event;
221        if (event_compare(last_event, event)) {
222            spin_unlock(&event->lock);
223            mutex_unlock(&group->notification_mutex);
224            if (holder != &event->holder)
225                fsnotify_destroy_event_holder(holder);
226            return -EEXIST;
227        }
228    }
229
230    group->q_len++;
231    holder->event = event;
232
233    fsnotify_get_event(event);
234    list_add_tail(&holder->event_list, list);
235    if (priv)
236        list_add_tail(&priv->event_list, &event->private_data_list);
237    spin_unlock(&event->lock);
238    mutex_unlock(&group->notification_mutex);
239
240    wake_up(&group->notification_waitq);
241    return ret;
242}
243
244/*
245 * Remove and return the first event from the notification list. There is a
246 * reference held on this event since it was on the list. It is the responsibility
247 * of the caller to drop this reference.
248 */
249struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
250{
251    struct fsnotify_event *event;
252    struct fsnotify_event_holder *holder;
253
254    BUG_ON(!mutex_is_locked(&group->notification_mutex));
255
256    holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
257
258    event = holder->event;
259
260    spin_lock(&event->lock);
261    holder->event = NULL;
262    list_del_init(&holder->event_list);
263    spin_unlock(&event->lock);
264
265    /* event == holder means we are referenced through the in event holder */
266    if (holder != &event->holder)
267        fsnotify_destroy_event_holder(holder);
268
269    group->q_len--;
270
271    return event;
272}
273
274/*
275 * This will not remove the event, that must be done with fsnotify_remove_notify_event()
276 */
277struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
278{
279    struct fsnotify_event *event;
280    struct fsnotify_event_holder *holder;
281
282    BUG_ON(!mutex_is_locked(&group->notification_mutex));
283
284    holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
285    event = holder->event;
286
287    return event;
288}
289
290/*
291 * Called when a group is being torn down to clean up any outstanding
292 * event notifications.
293 */
294void fsnotify_flush_notify(struct fsnotify_group *group)
295{
296    struct fsnotify_event *event;
297    struct fsnotify_event_private_data *priv;
298
299    mutex_lock(&group->notification_mutex);
300    while (!fsnotify_notify_queue_is_empty(group)) {
301        event = fsnotify_remove_notify_event(group);
302        /* if they don't implement free_event_priv they better not have attached any */
303        if (group->ops->free_event_priv) {
304            spin_lock(&event->lock);
305            priv = fsnotify_remove_priv_from_event(group, event);
306            spin_unlock(&event->lock);
307            if (priv)
308                group->ops->free_event_priv(priv);
309        }
310        fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
311    }
312    mutex_unlock(&group->notification_mutex);
313}
314
315static void initialize_event(struct fsnotify_event *event)
316{
317    event->holder.event = NULL;
318    INIT_LIST_HEAD(&event->holder.event_list);
319    atomic_set(&event->refcnt, 1);
320
321    spin_lock_init(&event->lock);
322
323    event->path.dentry = NULL;
324    event->path.mnt = NULL;
325    event->inode = NULL;
326    event->data_type = FSNOTIFY_EVENT_NONE;
327
328    INIT_LIST_HEAD(&event->private_data_list);
329
330    event->to_tell = NULL;
331
332    event->file_name = NULL;
333    event->name_len = 0;
334
335    event->sync_cookie = 0;
336}
337
338/*
339 * fsnotify_create_event - Allocate a new event which will be sent to each
340 * group's handle_event function if the group was interested in this
341 * particular event.
342 *
343 * @to_tell the inode which is supposed to receive the event (sometimes a
344 * parent of the inode to which the event happened.
345 * @mask what actually happened.
346 * @data pointer to the object which was actually affected
347 * @data_type flag indication if the data is a file, path, inode, nothing...
348 * @name the filename, if available
349 */
350struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
351                         int data_type, const char *name, u32 cookie,
352                         gfp_t gfp)
353{
354    struct fsnotify_event *event;
355
356    event = kmem_cache_alloc(fsnotify_event_cachep, gfp);
357    if (!event)
358        return NULL;
359
360    initialize_event(event);
361
362    if (name) {
363        event->file_name = kstrdup(name, gfp);
364        if (!event->file_name) {
365            kmem_cache_free(fsnotify_event_cachep, event);
366            return NULL;
367        }
368        event->name_len = strlen(event->file_name);
369    }
370
371    event->sync_cookie = cookie;
372    event->to_tell = to_tell;
373
374    switch (data_type) {
375    case FSNOTIFY_EVENT_FILE: {
376        struct file *file = data;
377        struct path *path = &file->f_path;
378        event->path.dentry = path->dentry;
379        event->path.mnt = path->mnt;
380        path_get(&event->path);
381        event->data_type = FSNOTIFY_EVENT_PATH;
382        break;
383    }
384    case FSNOTIFY_EVENT_PATH: {
385        struct path *path = data;
386        event->path.dentry = path->dentry;
387        event->path.mnt = path->mnt;
388        path_get(&event->path);
389        event->data_type = FSNOTIFY_EVENT_PATH;
390        break;
391    }
392    case FSNOTIFY_EVENT_INODE:
393        event->inode = data;
394        event->data_type = FSNOTIFY_EVENT_INODE;
395        break;
396    case FSNOTIFY_EVENT_NONE:
397        event->inode = NULL;
398        event->path.dentry = NULL;
399        event->path.mnt = NULL;
400        break;
401    default:
402        BUG();
403    }
404
405    event->mask = mask;
406
407    return event;
408}
409
410__init int fsnotify_notification_init(void)
411{
412    fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
413    fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);
414
415    initialize_event(&q_overflow_event);
416    q_overflow_event.mask = FS_Q_OVERFLOW;
417
418    return 0;
419}
420subsys_initcall(fsnotify_notification_init);
421
422

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