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TOMOYO Linux Cross Reference
Linux/fs/notify/dnotify/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 
 35 /*
 36  * dnotify will attach one of these to each inode (i_fsnotify_marks) which
 37  * is being watched by dnotify.  If multiple userspace applications are watching
 38  * the same directory with dnotify their information is chained in dn
 39  */
 40 struct dnotify_mark {
 41         struct fsnotify_mark fsn_mark;
 42         struct dnotify_struct *dn;
 43 };
 44 
 45 /*
 46  * When a process starts or stops watching an inode the set of events which
 47  * dnotify cares about for that inode may change.  This function runs the
 48  * list of everything receiving dnotify events about this directory and calculates
 49  * the set of all those events.  After it updates what dnotify is interested in
 50  * it calls the fsnotify function so it can update the set of all events relevant
 51  * to this inode.
 52  */
 53 static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
 54 {
 55         __u32 new_mask, old_mask;
 56         struct dnotify_struct *dn;
 57         struct dnotify_mark *dn_mark  = container_of(fsn_mark,
 58                                                      struct dnotify_mark,
 59                                                      fsn_mark);
 60 
 61         assert_spin_locked(&fsn_mark->lock);
 62 
 63         old_mask = fsn_mark->mask;
 64         new_mask = 0;
 65         for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
 66                 new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
 67         fsnotify_set_mark_mask_locked(fsn_mark, new_mask);
 68 
 69         if (old_mask == new_mask)
 70                 return;
 71 
 72         if (fsn_mark->i.inode)
 73                 fsnotify_recalc_inode_mask(fsn_mark->i.inode);
 74 }
 75 
 76 /*
 77  * Mains fsnotify call where events are delivered to dnotify.
 78  * Find the dnotify mark on the relevant inode, run the list of dnotify structs
 79  * on that mark and determine which of them has expressed interest in receiving
 80  * events of this type.  When found send the correct process and signal and
 81  * destroy the dnotify struct if it was not registered to receive multiple
 82  * events.
 83  */
 84 static int dnotify_handle_event(struct fsnotify_group *group,
 85                                 struct fsnotify_mark *inode_mark,
 86                                 struct fsnotify_mark *vfsmount_mark,
 87                                 struct fsnotify_event *event)
 88 {
 89         struct dnotify_mark *dn_mark;
 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         BUG_ON(vfsmount_mark);
 97 
 98         to_tell = event->to_tell;
 99 
100         dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
101 
102         spin_lock(&inode_mark->lock);
103         prev = &dn_mark->dn;
104         while ((dn = *prev) != NULL) {
105                 if ((dn->dn_mask & test_mask) == 0) {
106                         prev = &dn->dn_next;
107                         continue;
108                 }
109                 fown = &dn->dn_filp->f_owner;
110                 send_sigio(fown, dn->dn_fd, POLL_MSG);
111                 if (dn->dn_mask & FS_DN_MULTISHOT)
112                         prev = &dn->dn_next;
113                 else {
114                         *prev = dn->dn_next;
115                         kmem_cache_free(dnotify_struct_cache, dn);
116                         dnotify_recalc_inode_mask(inode_mark);
117                 }
118         }
119 
120         spin_unlock(&inode_mark->lock);
121 
122         return 0;
123 }
124 
125 /*
126  * Given an inode and mask determine if dnotify would be interested in sending
127  * userspace notification for that pair.
128  */
129 static bool dnotify_should_send_event(struct fsnotify_group *group,
130                                       struct inode *inode,
131                                       struct fsnotify_mark *inode_mark,
132                                       struct fsnotify_mark *vfsmount_mark,
133                                       __u32 mask, void *data, int data_type)
134 {
135         /* not a dir, dnotify doesn't care */
136         if (!S_ISDIR(inode->i_mode))
137                 return false;
138 
139         return true;
140 }
141 
142 static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
143 {
144         struct dnotify_mark *dn_mark = container_of(fsn_mark,
145                                                     struct dnotify_mark,
146                                                     fsn_mark);
147 
148         BUG_ON(dn_mark->dn);
149 
150         kmem_cache_free(dnotify_mark_cache, dn_mark);
151 }
152 
153 static struct fsnotify_ops dnotify_fsnotify_ops = {
154         .handle_event = dnotify_handle_event,
155         .should_send_event = dnotify_should_send_event,
156         .free_group_priv = NULL,
157         .freeing_mark = NULL,
158         .free_event_priv = NULL,
159 };
160 
161 /*
162  * Called every time a file is closed.  Looks first for a dnotify mark on the
163  * inode.  If one is found run all of the ->dn structures attached to that
164  * mark for one relevant to this process closing the file and remove that
165  * dnotify_struct.  If that was the last dnotify_struct also remove the
166  * fsnotify_mark.
167  */
168 void dnotify_flush(struct file *filp, fl_owner_t id)
169 {
170         struct fsnotify_mark *fsn_mark;
171         struct dnotify_mark *dn_mark;
172         struct dnotify_struct *dn;
173         struct dnotify_struct **prev;
174         struct inode *inode;
175 
176         inode = file_inode(filp);
177         if (!S_ISDIR(inode->i_mode))
178                 return;
179 
180         fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode);
181         if (!fsn_mark)
182                 return;
183         dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
184 
185         mutex_lock(&dnotify_group->mark_mutex);
186 
187         spin_lock(&fsn_mark->lock);
188         prev = &dn_mark->dn;
189         while ((dn = *prev) != NULL) {
190                 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
191                         *prev = dn->dn_next;
192                         kmem_cache_free(dnotify_struct_cache, dn);
193                         dnotify_recalc_inode_mask(fsn_mark);
194                         break;
195                 }
196                 prev = &dn->dn_next;
197         }
198 
199         spin_unlock(&fsn_mark->lock);
200 
201         /* nothing else could have found us thanks to the dnotify_groups
202            mark_mutex */
203         if (dn_mark->dn == NULL)
204                 fsnotify_destroy_mark_locked(fsn_mark, dnotify_group);
205 
206         mutex_unlock(&dnotify_group->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 = file_inode(filp);
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_group->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_locked(new_fsn_mark, dnotify_group, inode,
338                                          NULL, 0);
339                 spin_lock(&new_fsn_mark->lock);
340                 fsn_mark = new_fsn_mark;
341                 dn_mark = new_dn_mark;
342                 /* we used new_fsn_mark, so don't free it */
343                 new_fsn_mark = NULL;
344         }
345 
346         rcu_read_lock();
347         f = fcheck(fd);
348         rcu_read_unlock();
349 
350         /* if (f != filp) means that we lost a race and another task/thread
351          * actually closed the fd we are still playing with before we grabbed
352          * the dnotify_groups mark_mutex and fsn_mark->lock.  Since closing the
353          * fd is the only time we clean up the marks we need to get our mark
354          * off the list. */
355         if (f != filp) {
356                 /* if we added ourselves, shoot ourselves, it's possible that
357                  * the flush actually did shoot this fsn_mark.  That's fine too
358                  * since multiple calls to destroy_mark is perfectly safe, if
359                  * we found a dn_mark already attached to the inode, just sod
360                  * off silently as the flush at close time dealt with it.
361                  */
362                 if (dn_mark == new_dn_mark)
363                         destroy = 1;
364                 goto out;
365         }
366 
367         error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
368         if (error) {
369                 /* if we added, we must shoot */
370                 if (dn_mark == new_dn_mark)
371                         destroy = 1;
372                 goto out;
373         }
374 
375         error = attach_dn(dn, dn_mark, id, fd, filp, mask);
376         /* !error means that we attached the dn to the dn_mark, so don't free it */
377         if (!error)
378                 dn = NULL;
379         /* -EEXIST means that we didn't add this new dn and used an old one.
380          * that isn't an error (and the unused dn should be freed) */
381         else if (error == -EEXIST)
382                 error = 0;
383 
384         dnotify_recalc_inode_mask(fsn_mark);
385 out:
386         spin_unlock(&fsn_mark->lock);
387 
388         if (destroy)
389                 fsnotify_destroy_mark_locked(fsn_mark, dnotify_group);
390 
391         mutex_unlock(&dnotify_group->mark_mutex);
392         fsnotify_put_mark(fsn_mark);
393 out_err:
394         if (new_fsn_mark)
395                 fsnotify_put_mark(new_fsn_mark);
396         if (dn)
397                 kmem_cache_free(dnotify_struct_cache, dn);
398         return error;
399 }
400 
401 static int __init dnotify_init(void)
402 {
403         dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);
404         dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC);
405 
406         dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
407         if (IS_ERR(dnotify_group))
408                 panic("unable to allocate fsnotify group for dnotify\n");
409         return 0;
410 }
411 
412 module_init(dnotify_init)
413 

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