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

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