1 /*
2 * Directory notifications for Linux.
3 *
4 * Copyright (C) 2000,2001,2002 Stephen Rothwell
5 *
6 * Copyright (C) 2009 Eric Paris <Red Hat Inc>
7 * dnotify was largly rewritten to use the new fsnotify infrastructure
8 *
9 * This program is free software; you can redistribute it and/or modify it
10 * under the terms of the GNU General Public License as published by the
11 * Free Software Foundation; either version 2, or (at your option) any
12 * later version.
13 *
14 * This program is distributed in the hope that it will be useful, but
15 * WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * General Public License for more details.
18 */
19 #include <linux/fs.h>
20 #include <linux/module.h>
21 #include <linux/sched.h>
22 #include <linux/dnotify.h>
23 #include <linux/init.h>
24 #include <linux/spinlock.h>
25 #include <linux/slab.h>
26 #include <linux/fdtable.h>
27 #include <linux/fsnotify_backend.h>
28
29 int dir_notify_enable __read_mostly = 1;
30
31 static struct kmem_cache *dnotify_struct_cache __read_mostly;
32 static struct kmem_cache *dnotify_mark_entry_cache __read_mostly;
33 static struct fsnotify_group *dnotify_group __read_mostly;
34 static DEFINE_MUTEX(dnotify_mark_mutex);
35
36 /*
37 * dnotify will attach one of these to each inode (i_fsnotify_mark_entries) which
38 * is being watched by dnotify. If multiple userspace applications are watching
39 * the same directory with dnotify their information is chained in dn
40 */
41 struct dnotify_mark_entry {
42 struct fsnotify_mark_entry fsn_entry;
43 struct dnotify_struct *dn;
44 };
45
46 /*
47 * When a process starts or stops watching an inode the set of events which
48 * dnotify cares about for that inode may change. This function runs the
49 * list of everything receiving dnotify events about this directory and calculates
50 * the set of all those events. After it updates what dnotify is interested in
51 * it calls the fsnotify function so it can update the set of all events relevant
52 * to this inode.
53 */
54 static void dnotify_recalc_inode_mask(struct fsnotify_mark_entry *entry)
55 {
56 __u32 new_mask, old_mask;
57 struct dnotify_struct *dn;
58 struct dnotify_mark_entry *dnentry = container_of(entry,
59 struct dnotify_mark_entry,
60 fsn_entry);
61
62 assert_spin_locked(&entry->lock);
63
64 old_mask = entry->mask;
65 new_mask = 0;
66 for (dn = dnentry->dn; dn != NULL; dn = dn->dn_next)
67 new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
68 entry->mask = new_mask;
69
70 if (old_mask == new_mask)
71 return;
72
73 if (entry->inode)
74 fsnotify_recalc_inode_mask(entry->inode);
75 }
76
77 /*
78 * Mains fsnotify call where events are delivered to dnotify.
79 * Find the dnotify mark on the relevant inode, run the list of dnotify structs
80 * on that mark and determine which of them has expressed interest in receiving
81 * events of this type. When found send the correct process and signal and
82 * destroy the dnotify struct if it was not registered to receive multiple
83 * events.
84 */
85 static int dnotify_handle_event(struct fsnotify_group *group,
86 struct fsnotify_event *event)
87 {
88 struct fsnotify_mark_entry *entry = NULL;
89 struct dnotify_mark_entry *dnentry;
90 struct inode *to_tell;
91 struct dnotify_struct *dn;
92 struct dnotify_struct **prev;
93 struct fown_struct *fown;
94 __u32 test_mask = event->mask & ~FS_EVENT_ON_CHILD;
95
96 to_tell = event->to_tell;
97
98 spin_lock(&to_tell->i_lock);
99 entry = fsnotify_find_mark_entry(group, to_tell);
100 spin_unlock(&to_tell->i_lock);
101
102 /* unlikely since we alreay passed dnotify_should_send_event() */
103 if (unlikely(!entry))
104 return 0;
105 dnentry = container_of(entry, struct dnotify_mark_entry, fsn_entry);
106
107 spin_lock(&entry->lock);
108 prev = &dnentry->dn;
109 while ((dn = *prev) != NULL) {
110 if ((dn->dn_mask & test_mask) == 0) {
111 prev = &dn->dn_next;
112 continue;
113 }
114 fown = &dn->dn_filp->f_owner;
115 send_sigio(fown, dn->dn_fd, POLL_MSG);
116 if (dn->dn_mask & FS_DN_MULTISHOT)
117 prev = &dn->dn_next;
118 else {
119 *prev = dn->dn_next;
120 kmem_cache_free(dnotify_struct_cache, dn);
121 dnotify_recalc_inode_mask(entry);
122 }
123 }
124
125 spin_unlock(&entry->lock);
126 fsnotify_put_mark(entry);
127
128 return 0;
129 }
130
131 /*
132 * Given an inode and mask determine if dnotify would be interested in sending
133 * userspace notification for that pair.
134 */
135 static bool dnotify_should_send_event(struct fsnotify_group *group,
136 struct inode *inode, __u32 mask)
137 {
138 struct fsnotify_mark_entry *entry;
139 bool send;
140
141 /* !dir_notify_enable should never get here, don't waste time checking
142 if (!dir_notify_enable)
143 return 0; */
144
145 /* not a dir, dnotify doesn't care */
146 if (!S_ISDIR(inode->i_mode))
147 return false;
148
149 spin_lock(&inode->i_lock);
150 entry = fsnotify_find_mark_entry(group, inode);
151 spin_unlock(&inode->i_lock);
152
153 /* no mark means no dnotify watch */
154 if (!entry)
155 return false;
156
157 mask = (mask & ~FS_EVENT_ON_CHILD);
158 send = (mask & entry->mask);
159
160 fsnotify_put_mark(entry); /* matches fsnotify_find_mark_entry */
161
162 return send;
163 }
164
165 static void dnotify_free_mark(struct fsnotify_mark_entry *entry)
166 {
167 struct dnotify_mark_entry *dnentry = container_of(entry,
168 struct dnotify_mark_entry,
169 fsn_entry);
170
171 BUG_ON(dnentry->dn);
172
173 kmem_cache_free(dnotify_mark_entry_cache, dnentry);
174 }
175
176 static struct fsnotify_ops dnotify_fsnotify_ops = {
177 .handle_event = dnotify_handle_event,
178 .should_send_event = dnotify_should_send_event,
179 .free_group_priv = NULL,
180 .freeing_mark = NULL,
181 .free_event_priv = NULL,
182 };
183
184 /*
185 * Called every time a file is closed. Looks first for a dnotify mark on the
186 * inode. If one is found run all of the ->dn entries attached to that
187 * mark for one relevant to this process closing the file and remove that
188 * dnotify_struct. If that was the last dnotify_struct also remove the
189 * fsnotify_mark_entry.
190 */
191 void dnotify_flush(struct file *filp, fl_owner_t id)
192 {
193 struct fsnotify_mark_entry *entry;
194 struct dnotify_mark_entry *dnentry;
195 struct dnotify_struct *dn;
196 struct dnotify_struct **prev;
197 struct inode *inode;
198
199 inode = filp->f_path.dentry->d_inode;
200 if (!S_ISDIR(inode->i_mode))
201 return;
202
203 spin_lock(&inode->i_lock);
204 entry = fsnotify_find_mark_entry(dnotify_group, inode);
205 spin_unlock(&inode->i_lock);
206 if (!entry)
207 return;
208 dnentry = container_of(entry, struct dnotify_mark_entry, fsn_entry);
209
210 mutex_lock(&dnotify_mark_mutex);
211
212 spin_lock(&entry->lock);
213 prev = &dnentry->dn;
214 while ((dn = *prev) != NULL) {
215 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
216 *prev = dn->dn_next;
217 kmem_cache_free(dnotify_struct_cache, dn);
218 dnotify_recalc_inode_mask(entry);
219 break;
220 }
221 prev = &dn->dn_next;
222 }
223
224 spin_unlock(&entry->lock);
225
226 /* nothing else could have found us thanks to the dnotify_mark_mutex */
227 if (dnentry->dn == NULL)
228 fsnotify_destroy_mark_by_entry(entry);
229
230 fsnotify_recalc_group_mask(dnotify_group);
231
232 mutex_unlock(&dnotify_mark_mutex);
233
234 fsnotify_put_mark(entry);
235 }
236
237 /* this conversion is done only at watch creation */
238 static __u32 convert_arg(unsigned long arg)
239 {
240 __u32 new_mask = FS_EVENT_ON_CHILD;
241
242 if (arg & DN_MULTISHOT)
243 new_mask |= FS_DN_MULTISHOT;
244 if (arg & DN_DELETE)
245 new_mask |= (FS_DELETE | FS_MOVED_FROM);
246 if (arg & DN_MODIFY)
247 new_mask |= FS_MODIFY;
248 if (arg & DN_ACCESS)
249 new_mask |= FS_ACCESS;
250 if (arg & DN_ATTRIB)
251 new_mask |= FS_ATTRIB;
252 if (arg & DN_RENAME)
253 new_mask |= FS_DN_RENAME;
254 if (arg & DN_CREATE)
255 new_mask |= (FS_CREATE | FS_MOVED_TO);
256
257 return new_mask;
258 }
259
260 /*
261 * If multiple processes watch the same inode with dnotify there is only one
262 * dnotify mark in inode->i_fsnotify_mark_entries but we chain a dnotify_struct
263 * onto that mark. This function either attaches the new dnotify_struct onto
264 * that list, or it |= the mask onto an existing dnofiy_struct.
265 */
266 static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark_entry *dnentry,
267 fl_owner_t id, int fd, struct file *filp, __u32 mask)
268 {
269 struct dnotify_struct *odn;
270
271 odn = dnentry->dn;
272 while (odn != NULL) {
273 /* adding more events to existing dnofiy_struct? */
274 if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
275 odn->dn_fd = fd;
276 odn->dn_mask |= mask;
277 return -EEXIST;
278 }
279 odn = odn->dn_next;
280 }
281
282 dn->dn_mask = mask;
283 dn->dn_fd = fd;
284 dn->dn_filp = filp;
285 dn->dn_owner = id;
286 dn->dn_next = dnentry->dn;
287 dnentry->dn = dn;
288
289 return 0;
290 }
291
292 /*
293 * When a process calls fcntl to attach a dnotify watch to a directory it ends
294 * up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be
295 * attached to the fsnotify_mark.
296 */
297 int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
298 {
299 struct dnotify_mark_entry *new_dnentry, *dnentry;
300 struct fsnotify_mark_entry *new_entry, *entry;
301 struct dnotify_struct *dn;
302 struct inode *inode;
303 fl_owner_t id = current->files;
304 struct file *f;
305 int destroy = 0, error = 0;
306 __u32 mask;
307
308 /* we use these to tell if we need to kfree */
309 new_entry = NULL;
310 dn = NULL;
311
312 if (!dir_notify_enable) {
313 error = -EINVAL;
314 goto out_err;
315 }
316
317 /* a 0 mask means we are explicitly removing the watch */
318 if ((arg & ~DN_MULTISHOT) == 0) {
319 dnotify_flush(filp, id);
320 error = 0;
321 goto out_err;
322 }
323
324 /* dnotify only works on directories */
325 inode = filp->f_path.dentry->d_inode;
326 if (!S_ISDIR(inode->i_mode)) {
327 error = -ENOTDIR;
328 goto out_err;
329 }
330
331 /* expect most fcntl to add new rather than augment old */
332 dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
333 if (!dn) {
334 error = -ENOMEM;
335 goto out_err;
336 }
337
338 /* new fsnotify mark, we expect most fcntl calls to add a new mark */
339 new_dnentry = kmem_cache_alloc(dnotify_mark_entry_cache, GFP_KERNEL);
340 if (!new_dnentry) {
341 error = -ENOMEM;
342 goto out_err;
343 }
344
345 /* convert the userspace DN_* "arg" to the internal FS_* defines in fsnotify */
346 mask = convert_arg(arg);
347
348 /* set up the new_entry and new_dnentry */
349 new_entry = &new_dnentry->fsn_entry;
350 fsnotify_init_mark(new_entry, dnotify_free_mark);
351 new_entry->mask = mask;
352 new_dnentry->dn = NULL;
353
354 /* this is needed to prevent the fcntl/close race described below */
355 mutex_lock(&dnotify_mark_mutex);
356
357 /* add the new_entry or find an old one. */
358 spin_lock(&inode->i_lock);
359 entry = fsnotify_find_mark_entry(dnotify_group, inode);
360 spin_unlock(&inode->i_lock);
361 if (entry) {
362 dnentry = container_of(entry, struct dnotify_mark_entry, fsn_entry);
363 spin_lock(&entry->lock);
364 } else {
365 fsnotify_add_mark(new_entry, dnotify_group, inode);
366 spin_lock(&new_entry->lock);
367 entry = new_entry;
368 dnentry = new_dnentry;
369 /* we used new_entry, so don't free it */
370 new_entry = NULL;
371 }
372
373 rcu_read_lock();
374 f = fcheck(fd);
375 rcu_read_unlock();
376
377 /* if (f != filp) means that we lost a race and another task/thread
378 * actually closed the fd we are still playing with before we grabbed
379 * the dnotify_mark_mutex and entry->lock. Since closing the fd is the
380 * only time we clean up the mark entries we need to get our mark off
381 * the list. */
382 if (f != filp) {
383 /* if we added ourselves, shoot ourselves, it's possible that
384 * the flush actually did shoot this entry. That's fine too
385 * since multiple calls to destroy_mark is perfectly safe, if
386 * we found a dnentry already attached to the inode, just sod
387 * off silently as the flush at close time dealt with it.
388 */
389 if (dnentry == new_dnentry)
390 destroy = 1;
391 goto out;
392 }
393
394 error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
395 if (error) {
396 /* if we added, we must shoot */
397 if (dnentry == new_dnentry)
398 destroy = 1;
399 goto out;
400 }
401
402 error = attach_dn(dn, dnentry, id, fd, filp, mask);
403 /* !error means that we attached the dn to the dnentry, so don't free it */
404 if (!error)
405 dn = NULL;
406 /* -EEXIST means that we didn't add this new dn and used an old one.
407 * that isn't an error (and the unused dn should be freed) */
408 else if (error == -EEXIST)
409 error = 0;
410
411 dnotify_recalc_inode_mask(entry);
412 out:
413 spin_unlock(&entry->lock);
414
415 if (destroy)
416 fsnotify_destroy_mark_by_entry(entry);
417
418 fsnotify_recalc_group_mask(dnotify_group);
419
420 mutex_unlock(&dnotify_mark_mutex);
421 fsnotify_put_mark(entry);
422 out_err:
423 if (new_entry)
424 fsnotify_put_mark(new_entry);
425 if (dn)
426 kmem_cache_free(dnotify_struct_cache, dn);
427 return error;
428 }
429
430 static int __init dnotify_init(void)
431 {
432 dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);
433 dnotify_mark_entry_cache = KMEM_CACHE(dnotify_mark_entry, SLAB_PANIC);
434
435 dnotify_group = fsnotify_obtain_group(DNOTIFY_GROUP_NUM,
436 0, &dnotify_fsnotify_ops);
437 if (IS_ERR(dnotify_group))
438 panic("unable to allocate fsnotify group for dnotify\n");
439 return 0;
440 }
441
442 module_init(dnotify_init)
443
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