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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->inode)
 73                 fsnotify_recalc_inode_mask(fsn_mark->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 inode *inode,
 86                                 struct fsnotify_mark *inode_mark,
 87                                 struct fsnotify_mark *vfsmount_mark,
 88                                 u32 mask, const void *data, int data_type,
 89                                 const unsigned char *file_name, u32 cookie)
 90 {
 91         struct dnotify_mark *dn_mark;
 92         struct dnotify_struct *dn;
 93         struct dnotify_struct **prev;
 94         struct fown_struct *fown;
 95         __u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
 96 
 97         /* not a dir, dnotify doesn't care */
 98         if (!S_ISDIR(inode->i_mode))
 99                 return 0;
100 
101         BUG_ON(vfsmount_mark);
102 
103         dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
104 
105         spin_lock(&inode_mark->lock);
106         prev = &dn_mark->dn;
107         while ((dn = *prev) != NULL) {
108                 if ((dn->dn_mask & test_mask) == 0) {
109                         prev = &dn->dn_next;
110                         continue;
111                 }
112                 fown = &dn->dn_filp->f_owner;
113                 send_sigio(fown, dn->dn_fd, POLL_MSG);
114                 if (dn->dn_mask & FS_DN_MULTISHOT)
115                         prev = &dn->dn_next;
116                 else {
117                         *prev = dn->dn_next;
118                         kmem_cache_free(dnotify_struct_cache, dn);
119                         dnotify_recalc_inode_mask(inode_mark);
120                 }
121         }
122 
123         spin_unlock(&inode_mark->lock);
124 
125         return 0;
126 }
127 
128 static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
129 {
130         struct dnotify_mark *dn_mark = container_of(fsn_mark,
131                                                     struct dnotify_mark,
132                                                     fsn_mark);
133 
134         BUG_ON(dn_mark->dn);
135 
136         kmem_cache_free(dnotify_mark_cache, dn_mark);
137 }
138 
139 static struct fsnotify_ops dnotify_fsnotify_ops = {
140         .handle_event = dnotify_handle_event,
141 };
142 
143 /*
144  * Called every time a file is closed.  Looks first for a dnotify mark on the
145  * inode.  If one is found run all of the ->dn structures attached to that
146  * mark for one relevant to this process closing the file and remove that
147  * dnotify_struct.  If that was the last dnotify_struct also remove the
148  * fsnotify_mark.
149  */
150 void dnotify_flush(struct file *filp, fl_owner_t id)
151 {
152         struct fsnotify_mark *fsn_mark;
153         struct dnotify_mark *dn_mark;
154         struct dnotify_struct *dn;
155         struct dnotify_struct **prev;
156         struct inode *inode;
157         bool free = false;
158 
159         inode = file_inode(filp);
160         if (!S_ISDIR(inode->i_mode))
161                 return;
162 
163         fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode);
164         if (!fsn_mark)
165                 return;
166         dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
167 
168         mutex_lock(&dnotify_group->mark_mutex);
169 
170         spin_lock(&fsn_mark->lock);
171         prev = &dn_mark->dn;
172         while ((dn = *prev) != NULL) {
173                 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
174                         *prev = dn->dn_next;
175                         kmem_cache_free(dnotify_struct_cache, dn);
176                         dnotify_recalc_inode_mask(fsn_mark);
177                         break;
178                 }
179                 prev = &dn->dn_next;
180         }
181 
182         spin_unlock(&fsn_mark->lock);
183 
184         /* nothing else could have found us thanks to the dnotify_groups
185            mark_mutex */
186         if (dn_mark->dn == NULL) {
187                 fsnotify_detach_mark(fsn_mark);
188                 free = true;
189         }
190 
191         mutex_unlock(&dnotify_group->mark_mutex);
192 
193         if (free)
194                 fsnotify_free_mark(fsn_mark);
195         fsnotify_put_mark(fsn_mark);
196 }
197 
198 /* this conversion is done only at watch creation */
199 static __u32 convert_arg(unsigned long arg)
200 {
201         __u32 new_mask = FS_EVENT_ON_CHILD;
202 
203         if (arg & DN_MULTISHOT)
204                 new_mask |= FS_DN_MULTISHOT;
205         if (arg & DN_DELETE)
206                 new_mask |= (FS_DELETE | FS_MOVED_FROM);
207         if (arg & DN_MODIFY)
208                 new_mask |= FS_MODIFY;
209         if (arg & DN_ACCESS)
210                 new_mask |= FS_ACCESS;
211         if (arg & DN_ATTRIB)
212                 new_mask |= FS_ATTRIB;
213         if (arg & DN_RENAME)
214                 new_mask |= FS_DN_RENAME;
215         if (arg & DN_CREATE)
216                 new_mask |= (FS_CREATE | FS_MOVED_TO);
217 
218         return new_mask;
219 }
220 
221 /*
222  * If multiple processes watch the same inode with dnotify there is only one
223  * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct
224  * onto that mark.  This function either attaches the new dnotify_struct onto
225  * that list, or it |= the mask onto an existing dnofiy_struct.
226  */
227 static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,
228                      fl_owner_t id, int fd, struct file *filp, __u32 mask)
229 {
230         struct dnotify_struct *odn;
231 
232         odn = dn_mark->dn;
233         while (odn != NULL) {
234                 /* adding more events to existing dnofiy_struct? */
235                 if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
236                         odn->dn_fd = fd;
237                         odn->dn_mask |= mask;
238                         return -EEXIST;
239                 }
240                 odn = odn->dn_next;
241         }
242 
243         dn->dn_mask = mask;
244         dn->dn_fd = fd;
245         dn->dn_filp = filp;
246         dn->dn_owner = id;
247         dn->dn_next = dn_mark->dn;
248         dn_mark->dn = dn;
249 
250         return 0;
251 }
252 
253 /*
254  * When a process calls fcntl to attach a dnotify watch to a directory it ends
255  * up here.  Allocate both a mark for fsnotify to add and a dnotify_struct to be
256  * attached to the fsnotify_mark.
257  */
258 int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
259 {
260         struct dnotify_mark *new_dn_mark, *dn_mark;
261         struct fsnotify_mark *new_fsn_mark, *fsn_mark;
262         struct dnotify_struct *dn;
263         struct inode *inode;
264         fl_owner_t id = current->files;
265         struct file *f;
266         int destroy = 0, error = 0;
267         __u32 mask;
268 
269         /* we use these to tell if we need to kfree */
270         new_fsn_mark = NULL;
271         dn = NULL;
272 
273         if (!dir_notify_enable) {
274                 error = -EINVAL;
275                 goto out_err;
276         }
277 
278         /* a 0 mask means we are explicitly removing the watch */
279         if ((arg & ~DN_MULTISHOT) == 0) {
280                 dnotify_flush(filp, id);
281                 error = 0;
282                 goto out_err;
283         }
284 
285         /* dnotify only works on directories */
286         inode = file_inode(filp);
287         if (!S_ISDIR(inode->i_mode)) {
288                 error = -ENOTDIR;
289                 goto out_err;
290         }
291 
292         /* expect most fcntl to add new rather than augment old */
293         dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
294         if (!dn) {
295                 error = -ENOMEM;
296                 goto out_err;
297         }
298 
299         /* new fsnotify mark, we expect most fcntl calls to add a new mark */
300         new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
301         if (!new_dn_mark) {
302                 error = -ENOMEM;
303                 goto out_err;
304         }
305 
306         /* convert the userspace DN_* "arg" to the internal FS_* defines in fsnotify */
307         mask = convert_arg(arg);
308 
309         /* set up the new_fsn_mark and new_dn_mark */
310         new_fsn_mark = &new_dn_mark->fsn_mark;
311         fsnotify_init_mark(new_fsn_mark, dnotify_free_mark);
312         new_fsn_mark->mask = mask;
313         new_dn_mark->dn = NULL;
314 
315         /* this is needed to prevent the fcntl/close race described below */
316         mutex_lock(&dnotify_group->mark_mutex);
317 
318         /* add the new_fsn_mark or find an old one. */
319         fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode);
320         if (fsn_mark) {
321                 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
322                 spin_lock(&fsn_mark->lock);
323         } else {
324                 fsnotify_add_mark_locked(new_fsn_mark, dnotify_group, inode,
325                                          NULL, 0);
326                 spin_lock(&new_fsn_mark->lock);
327                 fsn_mark = new_fsn_mark;
328                 dn_mark = new_dn_mark;
329                 /* we used new_fsn_mark, so don't free it */
330                 new_fsn_mark = NULL;
331         }
332 
333         rcu_read_lock();
334         f = fcheck(fd);
335         rcu_read_unlock();
336 
337         /* if (f != filp) means that we lost a race and another task/thread
338          * actually closed the fd we are still playing with before we grabbed
339          * the dnotify_groups mark_mutex and fsn_mark->lock.  Since closing the
340          * fd is the only time we clean up the marks we need to get our mark
341          * off the list. */
342         if (f != filp) {
343                 /* if we added ourselves, shoot ourselves, it's possible that
344                  * the flush actually did shoot this fsn_mark.  That's fine too
345                  * since multiple calls to destroy_mark is perfectly safe, if
346                  * we found a dn_mark already attached to the inode, just sod
347                  * off silently as the flush at close time dealt with it.
348                  */
349                 if (dn_mark == new_dn_mark)
350                         destroy = 1;
351                 goto out;
352         }
353 
354         __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
355 
356         error = attach_dn(dn, dn_mark, id, fd, filp, mask);
357         /* !error means that we attached the dn to the dn_mark, so don't free it */
358         if (!error)
359                 dn = NULL;
360         /* -EEXIST means that we didn't add this new dn and used an old one.
361          * that isn't an error (and the unused dn should be freed) */
362         else if (error == -EEXIST)
363                 error = 0;
364 
365         dnotify_recalc_inode_mask(fsn_mark);
366 out:
367         spin_unlock(&fsn_mark->lock);
368 
369         if (destroy)
370                 fsnotify_detach_mark(fsn_mark);
371         mutex_unlock(&dnotify_group->mark_mutex);
372         if (destroy)
373                 fsnotify_free_mark(fsn_mark);
374         fsnotify_put_mark(fsn_mark);
375 out_err:
376         if (new_fsn_mark)
377                 fsnotify_put_mark(new_fsn_mark);
378         if (dn)
379                 kmem_cache_free(dnotify_struct_cache, dn);
380         return error;
381 }
382 
383 static int __init dnotify_init(void)
384 {
385         dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);
386         dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC);
387 
388         dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
389         if (IS_ERR(dnotify_group))
390                 panic("unable to allocate fsnotify group for dnotify\n");
391         return 0;
392 }
393 
394 module_init(dnotify_init)
395 

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