fs/notify/notification.c

   1 /*
   2  *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
   3  *
   4  *  This program is free software; you can redistribute it and/or modify
   5  *  it under the terms of the GNU General Public License as published by
   6  *  the Free Software Foundation; either version 2, or (at your option)
   7  *  any later version.
   8  *
   9  *  This program is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  *  GNU General Public License for more details.
  13  *
  14  *  You should have received a copy of the GNU General Public License
  15  *  along with this program; see the file COPYING.  If not, write to
  16  *  the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 /*
  20  * Basic idea behind the notification queue: An fsnotify group (like inotify)
  21  * sends the userspace notification about events asynchronously some time after
  22  * the event happened.  When inotify gets an event it will need to add that
  23  * event to the group notify queue.  Since a single event might need to be on
  24  * multiple group's notification queues we can't add the event directly to each
  25  * queue and instead add a small "event_holder" to each queue.  This event_holder
  26  * has a pointer back to the original event.  Since the majority of events are
  27  * going to end up on one, and only one, notification queue we embed one
  28  * event_holder into each event.  This means we have a single allocation instead
  29  * of always needing two.  If the embedded event_holder is already in use by
  30  * another group a new event_holder (from fsnotify_event_holder_cachep) will be
  31  * allocated and used.
  32  */
  33
  34 #include <linux/fs.h>
  35 #include <linux/init.h>
  36 #include <linux/kernel.h>
  37 #include <linux/list.h>
  38 #include <linux/module.h>
  39 #include <linux/mount.h>
  40 #include <linux/mutex.h>
  41 #include <linux/namei.h>
  42 #include <linux/path.h>
  43 #include <linux/slab.h>
  44 #include <linux/spinlock.h>
  45
  46 #include <linux/atomic.h>
  47
  48 #include <linux/fsnotify_backend.h>
  49 #include "fsnotify.h"
  50
  51 static struct kmem_cache *fsnotify_event_cachep;
  52 static struct kmem_cache *fsnotify_event_holder_cachep;
  53 /*
  54  * This is a magic event we send when the q is too full.  Since it doesn't
  55  * hold real event information we just keep one system wide and use it any time
  56  * it is needed.  It's refcnt is set 1 at kernel init time and will never
  57  * get set to 0 so it will never get 'freed'
  58  */
  59 static struct fsnotify_event *q_overflow_event;
  60 static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
  61
  62 /**
  63  * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
  64  * Called from fsnotify_move, which is inlined into filesystem modules.
  65  */
  66 u32 fsnotify_get_cookie(void)
  67 {
  68         return atomic_inc_return(&fsnotify_sync_cookie);
  69 }
  70 EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
  71
  72 /* return true if the notify queue is empty, false otherwise */
  73 bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
  74 {
  75         BUG_ON(!mutex_is_locked(&group->notification_mutex));
  76         return list_empty(&group->notification_list) ? true : false;
  77 }
  78
  79 void fsnotify_get_event(struct fsnotify_event *event)
  80 {
  81         atomic_inc(&event->refcnt);
  82 }
  83
  84 void fsnotify_put_event(struct fsnotify_event *event)
  85 {
  86         if (!event)
  87                 return;
  88
  89         if (atomic_dec_and_test(&event->refcnt)) {
  90                 pr_debug("%s: event=%p\n", __func__, event);
  91
  92                 if (event->data_type == FSNOTIFY_EVENT_PATH)
  93                         path_put(&event->path);
  94
  95                 BUG_ON(!list_empty(&event->private_data_list));
  96
  97                 kfree(event->file_name);
  98                 put_pid(event->tgid);
  99                 kmem_cache_free(fsnotify_event_cachep, event);
 100         }
 101 }
 102
 103 struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
 104 {
 105         return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
 106 }
 107
 108 void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
 109 {
 110         if (holder)
 111                 kmem_cache_free(fsnotify_event_holder_cachep, holder);
 112 }
 113
 114 /*
 115  * Find the private data that the group previously attached to this event when
 116  * the group added the event to the notification queue (fsnotify_add_notify_event)
 117  */
 118 struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
 119 {
 120         struct fsnotify_event_private_data *lpriv;
 121         struct fsnotify_event_private_data *priv = NULL;
 122
 123         assert_spin_locked(&event->lock);
 124
 125         list_for_each_entry(lpriv, &event->private_data_list, event_list) {
 126                 if (lpriv->group == group) {
 127                         priv = lpriv;
 128                         list_del(&priv->event_list);
 129                         break;
 130                 }
 131         }
 132         return priv;
 133 }
 134
 135 /*
 136  * Add an event to the group notification queue.  The group can later pull this
 137  * event off the queue to deal with.  If the event is successfully added to the
 138  * group's notification queue, a reference is taken on event.
 139  */
 140 struct fsnotify_event *fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
 141                                                  struct fsnotify_event_private_data *priv,
 142                                                  struct fsnotify_event *(*merge)(struct list_head *,
 143                                                                                  struct fsnotify_event *))
 144 {
 145         struct fsnotify_event *return_event = NULL;
 146         struct fsnotify_event_holder *holder = NULL;
 147         struct list_head *list = &group->notification_list;
 148
 149         pr_debug("%s: group=%p event=%p priv=%p\n", __func__, group, event, priv);
 150
 151         /*
 152          * There is one fsnotify_event_holder embedded inside each fsnotify_event.
 153          * Check if we expect to be able to use that holder.  If not alloc a new
 154          * holder.
 155          * For the overflow event it's possible that something will use the in
 156          * event holder before we get the lock so we may need to jump back and
 157          * alloc a new holder, this can't happen for most events...
 158          */
 159         if (!list_empty(&event->holder.event_list)) {
 160 alloc_holder:
 161                 holder = fsnotify_alloc_event_holder();
 162                 if (!holder)
 163                         return ERR_PTR(-ENOMEM);
 164         }
 165
 166         mutex_lock(&group->notification_mutex);
 167
 168         if (group->q_len >= group->max_events) {
 169                 event = q_overflow_event;
 170
 171                 /*
 172                  * we need to return the overflow event
 173                  * which means we need a ref
 174                  */
 175                 fsnotify_get_event(event);
 176                 return_event = event;
 177
 178                 /* sorry, no private data on the overflow event */
 179                 priv = NULL;
 180         }
 181
 182         if (!list_empty(list) && merge) {
 183                 struct fsnotify_event *tmp;
 184
 185                 tmp = merge(list, event);
 186                 if (tmp) {
 187                         mutex_unlock(&group->notification_mutex);
 188
 189                         if (return_event)
 190                                 fsnotify_put_event(return_event);
 191                         if (holder != &event->holder)
 192                                 fsnotify_destroy_event_holder(holder);
 193                         return tmp;
 194                 }
 195         }
 196
 197         spin_lock(&event->lock);
 198
 199         if (list_empty(&event->holder.event_list)) {
 200                 if (unlikely(holder))
 201                         fsnotify_destroy_event_holder(holder);
 202                 holder = &event->holder;
 203         } else if (unlikely(!holder)) {
 204                 /* between the time we checked above and got the lock the in
 205                  * event holder was used, go back and get a new one */
 206                 spin_unlock(&event->lock);
 207                 mutex_unlock(&group->notification_mutex);
 208
 209                 if (return_event) {
 210                         fsnotify_put_event(return_event);
 211                         return_event = NULL;
 212                 }
 213
 214                 goto alloc_holder;
 215         }
 216
 217         group->q_len++;
 218         holder->event = event;
 219
 220         fsnotify_get_event(event);
 221         list_add_tail(&holder->event_list, list);
 222         if (priv)
 223                 list_add_tail(&priv->event_list, &event->private_data_list);
 224         spin_unlock(&event->lock);
 225         mutex_unlock(&group->notification_mutex);
 226
 227         wake_up(&group->notification_waitq);
 228         kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
 229         return return_event;
 230 }
 231
 232 /*
 233  * Remove and return the first event from the notification list.  There is a
 234  * reference held on this event since it was on the list.  It is the responsibility
 235  * of the caller to drop this reference.
 236  */
 237 struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
 238 {
 239         struct fsnotify_event *event;
 240         struct fsnotify_event_holder *holder;
 241
 242         BUG_ON(!mutex_is_locked(&group->notification_mutex));
 243
 244         pr_debug("%s: group=%p\n", __func__, group);
 245
 246         holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
 247
 248         event = holder->event;
 249
 250         spin_lock(&event->lock);
 251         holder->event = NULL;
 252         list_del_init(&holder->event_list);
 253         spin_unlock(&event->lock);
 254
 255         /* event == holder means we are referenced through the in event holder */
 256         if (holder != &event->holder)
 257                 fsnotify_destroy_event_holder(holder);
 258
 259         group->q_len--;
 260
 261         return event;
 262 }
 263
 264 /*
 265  * This will not remove the event, that must be done with fsnotify_remove_notify_event()
 266  */
 267 struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
 268 {
 269         struct fsnotify_event *event;
 270         struct fsnotify_event_holder *holder;
 271
 272         BUG_ON(!mutex_is_locked(&group->notification_mutex));
 273
 274         holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
 275         event = holder->event;
 276
 277         return event;
 278 }
 279
 280 /*
 281  * Called when a group is being torn down to clean up any outstanding
 282  * event notifications.
 283  */
 284 void fsnotify_flush_notify(struct fsnotify_group *group)
 285 {
 286         struct fsnotify_event *event;
 287         struct fsnotify_event_private_data *priv;
 288
 289         mutex_lock(&group->notification_mutex);
 290         while (!fsnotify_notify_queue_is_empty(group)) {
 291                 event = fsnotify_remove_notify_event(group);
 292                 /* if they don't implement free_event_priv they better not have attached any */
 293                 if (group->ops->free_event_priv) {
 294                         spin_lock(&event->lock);
 295                         priv = fsnotify_remove_priv_from_event(group, event);
 296                         spin_unlock(&event->lock);
 297                         if (priv)
 298                                 group->ops->free_event_priv(priv);
 299                 }
 300                 fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
 301         }
 302         mutex_unlock(&group->notification_mutex);
 303 }
 304
 305 static void initialize_event(struct fsnotify_event *event)
 306 {
 307         INIT_LIST_HEAD(&event->holder.event_list);
 308         atomic_set(&event->refcnt, 1);
 309
 310         spin_lock_init(&event->lock);
 311
 312         INIT_LIST_HEAD(&event->private_data_list);
 313 }
 314
 315 /*
 316  * Caller damn well better be holding whatever mutex is protecting the
 317  * old_holder->event_list and the new_event must be a clean event which
 318  * cannot be found anywhere else in the kernel.
 319  */
 320 int fsnotify_replace_event(struct fsnotify_event_holder *old_holder,
 321                            struct fsnotify_event *new_event)
 322 {
 323         struct fsnotify_event *old_event = old_holder->event;
 324         struct fsnotify_event_holder *new_holder = &new_event->holder;
 325
 326         enum event_spinlock_class {
 327                 SPINLOCK_OLD,
 328                 SPINLOCK_NEW,
 329         };
 330
 331         pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, new_event);
 332
 333         /*
 334          * if the new_event's embedded holder is in use someone
 335          * screwed up and didn't give us a clean new event.
 336          */
 337         BUG_ON(!list_empty(&new_holder->event_list));
 338
 339         spin_lock_nested(&old_event->lock, SPINLOCK_OLD);
 340         spin_lock_nested(&new_event->lock, SPINLOCK_NEW);
 341
 342         new_holder->event = new_event;
 343         list_replace_init(&old_holder->event_list, &new_holder->event_list);
 344
 345         spin_unlock(&new_event->lock);
 346         spin_unlock(&old_event->lock);
 347
 348         /* event == holder means we are referenced through the in event holder */
 349         if (old_holder != &old_event->holder)
 350                 fsnotify_destroy_event_holder(old_holder);
 351
 352         fsnotify_get_event(new_event); /* on the list take reference */
 353         fsnotify_put_event(old_event); /* off the list, drop reference */
 354
 355         return 0;
 356 }
 357
 358 struct fsnotify_event *fsnotify_clone_event(struct fsnotify_event *old_event)
 359 {
 360         struct fsnotify_event *event;
 361
 362         event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL);
 363         if (!event)
 364                 return NULL;
 365
 366         pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, event);
 367
 368         memcpy(event, old_event, sizeof(*event));
 369         initialize_event(event);
 370
 371         if (event->name_len) {
 372                 event->file_name = kstrdup(old_event->file_name, GFP_KERNEL);
 373                 if (!event->file_name) {
 374                         kmem_cache_free(fsnotify_event_cachep, event);
 375                         return NULL;
 376                 }
 377         }
 378         event->tgid = get_pid(old_event->tgid);
 379         if (event->data_type == FSNOTIFY_EVENT_PATH)
 380                 path_get(&event->path);
 381
 382         return event;
 383 }
 384
 385 /*
 386  * fsnotify_create_event - Allocate a new event which will be sent to each
 387  * group's handle_event function if the group was interested in this
 388  * particular event.
 389  *
 390  * @to_tell the inode which is supposed to receive the event (sometimes a
 391  *      parent of the inode to which the event happened.
 392  * @mask what actually happened.
 393  * @data pointer to the object which was actually affected
 394  * @data_type flag indication if the data is a file, path, inode, nothing...
 395  * @name the filename, if available
 396  */
 397 struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
 398                                              int data_type, const unsigned char *name,
 399                                              u32 cookie, gfp_t gfp)
 400 {
 401         struct fsnotify_event *event;
 402
 403         event = kmem_cache_zalloc(fsnotify_event_cachep, gfp);
 404         if (!event)
 405                 return NULL;
 406
 407         pr_debug("%s: event=%p to_tell=%p mask=%x data=%p data_type=%d\n",
 408                  __func__, event, to_tell, mask, data, data_type);
 409
 410         initialize_event(event);
 411
 412         if (name) {
 413                 event->file_name = kstrdup(name, gfp);
 414                 if (!event->file_name) {
 415                         kmem_cache_free(fsnotify_event_cachep, event);
 416                         return NULL;
 417                 }
 418                 event->name_len = strlen(event->file_name);
 419         }
 420
 421         event->tgid = get_pid(task_tgid(current));
 422         event->sync_cookie = cookie;
 423         event->to_tell = to_tell;
 424         event->data_type = data_type;
 425
 426         switch (data_type) {
 427         case FSNOTIFY_EVENT_PATH: {
 428                 struct path *path = data;
 429                 event->path.dentry = path->dentry;
 430                 event->path.mnt = path->mnt;
 431                 path_get(&event->path);
 432                 break;
 433         }
 434         case FSNOTIFY_EVENT_INODE:
 435                 event->inode = data;
 436                 break;
 437         case FSNOTIFY_EVENT_NONE:
 438                 event->inode = NULL;
 439                 event->path.dentry = NULL;
 440                 event->path.mnt = NULL;
 441                 break;
 442         default:
 443                 BUG();
 444         }
 445
 446         event->mask = mask;
 447
 448         return event;
 449 }
 450
 451 static __init int fsnotify_notification_init(void)
 452 {
 453         fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
 454         fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);
 455
 456         q_overflow_event = fsnotify_create_event(NULL, FS_Q_OVERFLOW, NULL,
 457                                                  FSNOTIFY_EVENT_NONE, NULL, 0,
 458                                                  GFP_KERNEL);
 459         if (!q_overflow_event)
 460                 panic("unable to allocate fsnotify q_overflow_event\n");
 461
 462         return 0;
 463 }
 464 subsys_initcall(fsnotify_notification_init);