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dnotify.c
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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_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_marks) 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 {
42  struct fsnotify_mark fsn_mark;
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 *fsn_mark)
55 {
56  __u32 new_mask, old_mask;
57  struct dnotify_struct *dn;
58  struct dnotify_mark *dn_mark = container_of(fsn_mark,
59  struct dnotify_mark,
60  fsn_mark);
61 
62  assert_spin_locked(&fsn_mark->lock);
63 
64  old_mask = fsn_mark->mask;
65  new_mask = 0;
66  for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
67  new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
68  fsnotify_set_mark_mask_locked(fsn_mark, new_mask);
69 
70  if (old_mask == new_mask)
71  return;
72 
73  if (fsn_mark->i.inode)
74  fsnotify_recalc_inode_mask(fsn_mark->i.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_mark *inode_mark,
87  struct fsnotify_mark *vfsmount_mark,
88  struct fsnotify_event *event)
89 {
90  struct dnotify_mark *dn_mark;
91  struct inode *to_tell;
92  struct dnotify_struct *dn;
93  struct dnotify_struct **prev;
94  struct fown_struct *fown;
95  __u32 test_mask = event->mask & ~FS_EVENT_ON_CHILD;
96 
97  BUG_ON(vfsmount_mark);
98 
99  to_tell = event->to_tell;
100 
101  dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
102 
103  spin_lock(&inode_mark->lock);
104  prev = &dn_mark->dn;
105  while ((dn = *prev) != NULL) {
106  if ((dn->dn_mask & test_mask) == 0) {
107  prev = &dn->dn_next;
108  continue;
109  }
110  fown = &dn->dn_filp->f_owner;
111  send_sigio(fown, dn->dn_fd, POLL_MSG);
112  if (dn->dn_mask & FS_DN_MULTISHOT)
113  prev = &dn->dn_next;
114  else {
115  *prev = dn->dn_next;
116  kmem_cache_free(dnotify_struct_cache, dn);
117  dnotify_recalc_inode_mask(inode_mark);
118  }
119  }
120 
121  spin_unlock(&inode_mark->lock);
122 
123  return 0;
124 }
125 
126 /*
127  * Given an inode and mask determine if dnotify would be interested in sending
128  * userspace notification for that pair.
129  */
130 static bool dnotify_should_send_event(struct fsnotify_group *group,
131  struct inode *inode,
132  struct fsnotify_mark *inode_mark,
133  struct fsnotify_mark *vfsmount_mark,
134  __u32 mask, void *data, int data_type)
135 {
136  /* not a dir, dnotify doesn't care */
137  if (!S_ISDIR(inode->i_mode))
138  return false;
139 
140  return true;
141 }
142 
143 static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
144 {
145  struct dnotify_mark *dn_mark = container_of(fsn_mark,
146  struct dnotify_mark,
147  fsn_mark);
148 
149  BUG_ON(dn_mark->dn);
150 
151  kmem_cache_free(dnotify_mark_cache, dn_mark);
152 }
153 
154 static struct fsnotify_ops dnotify_fsnotify_ops = {
155  .handle_event = dnotify_handle_event,
156  .should_send_event = dnotify_should_send_event,
157  .free_group_priv = NULL,
158  .freeing_mark = NULL,
159  .free_event_priv = NULL,
160 };
161 
162 /*
163  * Called every time a file is closed. Looks first for a dnotify mark on the
164  * inode. If one is found run all of the ->dn structures attached to that
165  * mark for one relevant to this process closing the file and remove that
166  * dnotify_struct. If that was the last dnotify_struct also remove the
167  * fsnotify_mark.
168  */
169 void dnotify_flush(struct file *filp, fl_owner_t id)
170 {
171  struct fsnotify_mark *fsn_mark;
172  struct dnotify_mark *dn_mark;
173  struct dnotify_struct *dn;
174  struct dnotify_struct **prev;
175  struct inode *inode;
176 
177  inode = filp->f_path.dentry->d_inode;
178  if (!S_ISDIR(inode->i_mode))
179  return;
180 
181  fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode);
182  if (!fsn_mark)
183  return;
184  dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
185 
186  mutex_lock(&dnotify_mark_mutex);
187 
188  spin_lock(&fsn_mark->lock);
189  prev = &dn_mark->dn;
190  while ((dn = *prev) != NULL) {
191  if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
192  *prev = dn->dn_next;
193  kmem_cache_free(dnotify_struct_cache, dn);
194  dnotify_recalc_inode_mask(fsn_mark);
195  break;
196  }
197  prev = &dn->dn_next;
198  }
199 
200  spin_unlock(&fsn_mark->lock);
201 
202  /* nothing else could have found us thanks to the dnotify_mark_mutex */
203  if (dn_mark->dn == NULL)
204  fsnotify_destroy_mark(fsn_mark);
205 
206  mutex_unlock(&dnotify_mark_mutex);
207 
208  fsnotify_put_mark(fsn_mark);
209 }
210 
211 /* this conversion is done only at watch creation */
212 static __u32 convert_arg(unsigned long arg)
213 {
214  __u32 new_mask = FS_EVENT_ON_CHILD;
215 
216  if (arg & DN_MULTISHOT)
217  new_mask |= FS_DN_MULTISHOT;
218  if (arg & DN_DELETE)
219  new_mask |= (FS_DELETE | FS_MOVED_FROM);
220  if (arg & DN_MODIFY)
221  new_mask |= FS_MODIFY;
222  if (arg & DN_ACCESS)
223  new_mask |= FS_ACCESS;
224  if (arg & DN_ATTRIB)
225  new_mask |= FS_ATTRIB;
226  if (arg & DN_RENAME)
227  new_mask |= FS_DN_RENAME;
228  if (arg & DN_CREATE)
229  new_mask |= (FS_CREATE | FS_MOVED_TO);
230 
231  return new_mask;
232 }
233 
234 /*
235  * If multiple processes watch the same inode with dnotify there is only one
236  * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct
237  * onto that mark. This function either attaches the new dnotify_struct onto
238  * that list, or it |= the mask onto an existing dnofiy_struct.
239  */
240 static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,
241  fl_owner_t id, int fd, struct file *filp, __u32 mask)
242 {
243  struct dnotify_struct *odn;
244 
245  odn = dn_mark->dn;
246  while (odn != NULL) {
247  /* adding more events to existing dnofiy_struct? */
248  if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
249  odn->dn_fd = fd;
250  odn->dn_mask |= mask;
251  return -EEXIST;
252  }
253  odn = odn->dn_next;
254  }
255 
256  dn->dn_mask = mask;
257  dn->dn_fd = fd;
258  dn->dn_filp = filp;
259  dn->dn_owner = id;
260  dn->dn_next = dn_mark->dn;
261  dn_mark->dn = dn;
262 
263  return 0;
264 }
265 
266 /*
267  * When a process calls fcntl to attach a dnotify watch to a directory it ends
268  * up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be
269  * attached to the fsnotify_mark.
270  */
271 int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
272 {
273  struct dnotify_mark *new_dn_mark, *dn_mark;
274  struct fsnotify_mark *new_fsn_mark, *fsn_mark;
275  struct dnotify_struct *dn;
276  struct inode *inode;
277  fl_owner_t id = current->files;
278  struct file *f;
279  int destroy = 0, error = 0;
280  __u32 mask;
281 
282  /* we use these to tell if we need to kfree */
283  new_fsn_mark = NULL;
284  dn = NULL;
285 
286  if (!dir_notify_enable) {
287  error = -EINVAL;
288  goto out_err;
289  }
290 
291  /* a 0 mask means we are explicitly removing the watch */
292  if ((arg & ~DN_MULTISHOT) == 0) {
293  dnotify_flush(filp, id);
294  error = 0;
295  goto out_err;
296  }
297 
298  /* dnotify only works on directories */
299  inode = filp->f_path.dentry->d_inode;
300  if (!S_ISDIR(inode->i_mode)) {
301  error = -ENOTDIR;
302  goto out_err;
303  }
304 
305  /* expect most fcntl to add new rather than augment old */
306  dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
307  if (!dn) {
308  error = -ENOMEM;
309  goto out_err;
310  }
311 
312  /* new fsnotify mark, we expect most fcntl calls to add a new mark */
313  new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
314  if (!new_dn_mark) {
315  error = -ENOMEM;
316  goto out_err;
317  }
318 
319  /* convert the userspace DN_* "arg" to the internal FS_* defines in fsnotify */
320  mask = convert_arg(arg);
321 
322  /* set up the new_fsn_mark and new_dn_mark */
323  new_fsn_mark = &new_dn_mark->fsn_mark;
324  fsnotify_init_mark(new_fsn_mark, dnotify_free_mark);
325  new_fsn_mark->mask = mask;
326  new_dn_mark->dn = NULL;
327 
328  /* this is needed to prevent the fcntl/close race described below */
329  mutex_lock(&dnotify_mark_mutex);
330 
331  /* add the new_fsn_mark or find an old one. */
332  fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode);
333  if (fsn_mark) {
334  dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
335  spin_lock(&fsn_mark->lock);
336  } else {
337  fsnotify_add_mark(new_fsn_mark, dnotify_group, inode, NULL, 0);
338  spin_lock(&new_fsn_mark->lock);
339  fsn_mark = new_fsn_mark;
340  dn_mark = new_dn_mark;
341  /* we used new_fsn_mark, so don't free it */
342  new_fsn_mark = NULL;
343  }
344 
345  rcu_read_lock();
346  f = fcheck(fd);
347  rcu_read_unlock();
348 
349  /* if (f != filp) means that we lost a race and another task/thread
350  * actually closed the fd we are still playing with before we grabbed
351  * the dnotify_mark_mutex and fsn_mark->lock. Since closing the fd is the
352  * only time we clean up the marks we need to get our mark off
353  * the list. */
354  if (f != filp) {
355  /* if we added ourselves, shoot ourselves, it's possible that
356  * the flush actually did shoot this fsn_mark. That's fine too
357  * since multiple calls to destroy_mark is perfectly safe, if
358  * we found a dn_mark already attached to the inode, just sod
359  * off silently as the flush at close time dealt with it.
360  */
361  if (dn_mark == new_dn_mark)
362  destroy = 1;
363  goto out;
364  }
365 
366  error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
367  if (error) {
368  /* if we added, we must shoot */
369  if (dn_mark == new_dn_mark)
370  destroy = 1;
371  goto out;
372  }
373 
374  error = attach_dn(dn, dn_mark, id, fd, filp, mask);
375  /* !error means that we attached the dn to the dn_mark, so don't free it */
376  if (!error)
377  dn = NULL;
378  /* -EEXIST means that we didn't add this new dn and used an old one.
379  * that isn't an error (and the unused dn should be freed) */
380  else if (error == -EEXIST)
381  error = 0;
382 
383  dnotify_recalc_inode_mask(fsn_mark);
384 out:
385  spin_unlock(&fsn_mark->lock);
386 
387  if (destroy)
388  fsnotify_destroy_mark(fsn_mark);
389 
390  mutex_unlock(&dnotify_mark_mutex);
391  fsnotify_put_mark(fsn_mark);
392 out_err:
393  if (new_fsn_mark)
394  fsnotify_put_mark(new_fsn_mark);
395  if (dn)
396  kmem_cache_free(dnotify_struct_cache, dn);
397  return error;
398 }
399 
400 static int __init dnotify_init(void)
401 {
402  dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);
403  dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC);
404 
405  dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
406  if (IS_ERR(dnotify_group))
407  panic("unable to allocate fsnotify group for dnotify\n");
408  return 0;
409 }
410 
411 module_init(dnotify_init)