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 asyncronously 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 <asm/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                 if (event->data_type == FSNOTIFY_EVENT_PATH)
  91                         path_put(&event->path);
  92
  93                 BUG_ON(!list_empty(&event->private_data_list));
  94
  95                 kfree(event->file_name);
  96                 kmem_cache_free(fsnotify_event_cachep, event);
  97         }
  98 }
  99
 100 struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
 101 {
 102         return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
 103 }
 104
 105 void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
 106 {
 107         kmem_cache_free(fsnotify_event_holder_cachep, holder);
 108 }
 109
 110 /*
 111  * Find the private data that the group previously attached to this event when
 112  * the group added the event to the notification queue (fsnotify_add_notify_event)
 113  */
 114 struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
 115 {
 116         struct fsnotify_event_private_data *lpriv;
 117         struct fsnotify_event_private_data *priv = NULL;
 118
 119         assert_spin_locked(&event->lock);
 120
 121         list_for_each_entry(lpriv, &event->private_data_list, event_list) {
 122                 if (lpriv->group == group) {
 123                         priv = lpriv;
 124                         list_del(&priv->event_list);
 125                         break;
 126                 }
 127         }
 128         return priv;
 129 }
 130
 131 /*
 132  * Check if 2 events contain the same information.  We do not compare private data
 133  * but at this moment that isn't a problem for any know fsnotify listeners.
 134  */
 135 static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new)
 136 {
 137         if ((old->mask == new->mask) &&
 138             (old->to_tell == new->to_tell) &&
 139             (old->data_type == new->data_type) &&
 140             (old->name_len == new->name_len)) {
 141                 switch (old->data_type) {
 142                 case (FSNOTIFY_EVENT_INODE):
 143                         /* remember, after old was put on the wait_q we aren't
 144                          * allowed to look at the inode any more, only thing
 145                          * left to check was if the file_name is the same */
 146                         if (old->name_len &&
 147                             !strcmp(old->file_name, new->file_name))
 148                                 return true;
 149                         break;
 150                 case (FSNOTIFY_EVENT_PATH):
 151                         if ((old->path.mnt == new->path.mnt) &&
 152                             (old->path.dentry == new->path.dentry))
 153                                 return true;
 154                         break;
 155                 case (FSNOTIFY_EVENT_NONE):
 156                         if (old->mask & FS_Q_OVERFLOW)
 157                                 return true;
 158                         else if (old->mask & FS_IN_IGNORED)
 159                                 return false;
 160                         return false;
 161                 };
 162         }
 163         return false;
 164 }
 165
 166 /*
 167  * Add an event to the group notification queue.  The group can later pull this
 168  * event off the queue to deal with.  If the event is successfully added to the
 169  * group's notification queue, a reference is taken on event.
 170  */
 171 int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
 172                               struct fsnotify_event_private_data *priv)
 173 {
 174         struct fsnotify_event_holder *holder = NULL;
 175         struct list_head *list = &group->notification_list;
 176         struct fsnotify_event_holder *last_holder;
 177         struct fsnotify_event *last_event;
 178         int ret = 0;
 179
 180         /*
 181          * There is one fsnotify_event_holder embedded inside each fsnotify_event.
 182          * Check if we expect to be able to use that holder.  If not alloc a new
 183          * holder.
 184          * For the overflow event it's possible that something will use the in
 185          * event holder before we get the lock so we may need to jump back and
 186          * alloc a new holder, this can't happen for most events...
 187          */
 188         if (!list_empty(&event->holder.event_list)) {
 189 alloc_holder:
 190                 holder = fsnotify_alloc_event_holder();
 191                 if (!holder)
 192                         return -ENOMEM;
 193         }
 194
 195         mutex_lock(&group->notification_mutex);
 196
 197         if (group->q_len >= group->max_events) {
 198                 event = &q_overflow_event;
 199                 ret = -EOVERFLOW;
 200                 /* sorry, no private data on the overflow event */
 201                 priv = NULL;
 202         }
 203
 204         spin_lock(&event->lock);
 205
 206         if (list_empty(&event->holder.event_list)) {
 207                 if (unlikely(holder))
 208                         fsnotify_destroy_event_holder(holder);
 209                 holder = &event->holder;
 210         } else if (unlikely(!holder)) {
 211                 /* between the time we checked above and got the lock the in
 212                  * event holder was used, go back and get a new one */
 213                 spin_unlock(&event->lock);
 214                 mutex_unlock(&group->notification_mutex);
 215                 goto alloc_holder;
 216         }
 217
 218         if (!list_empty(list)) {
 219                 last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list);
 220                 last_event = last_holder->event;
 221                 if (event_compare(last_event, event)) {
 222                         spin_unlock(&event->lock);
 223                         mutex_unlock(&group->notification_mutex);
 224                         if (holder != &event->holder)
 225                                 fsnotify_destroy_event_holder(holder);
 226                         return -EEXIST;
 227                 }
 228         }
 229
 230         group->q_len++;
 231         holder->event = event;
 232
 233         fsnotify_get_event(event);
 234         list_add_tail(&holder->event_list, list);
 235         if (priv)
 236                 list_add_tail(&priv->event_list, &event->private_data_list);
 237         spin_unlock(&event->lock);
 238         mutex_unlock(&group->notification_mutex);
 239
 240         wake_up(&group->notification_waitq);
 241         return ret;
 242 }
 243
 244 /*
 245  * Remove and return the first event from the notification list.  There is a
 246  * reference held on this event since it was on the list.  It is the responsibility
 247  * of the caller to drop this reference.
 248  */
 249 struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
 250 {
 251         struct fsnotify_event *event;
 252         struct fsnotify_event_holder *holder;
 253
 254         BUG_ON(!mutex_is_locked(&group->notification_mutex));
 255
 256         holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
 257
 258         event = holder->event;
 259
 260         spin_lock(&event->lock);
 261         holder->event = NULL;
 262         list_del_init(&holder->event_list);
 263         spin_unlock(&event->lock);
 264
 265         /* event == holder means we are referenced through the in event holder */
 266         if (holder != &event->holder)
 267                 fsnotify_destroy_event_holder(holder);
 268
 269         group->q_len--;
 270
 271         return event;
 272 }
 273
 274 /*
 275  * This will not remove the event, that must be done with fsnotify_remove_notify_event()
 276  */
 277 struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
 278 {
 279         struct fsnotify_event *event;
 280         struct fsnotify_event_holder *holder;
 281
 282         BUG_ON(!mutex_is_locked(&group->notification_mutex));
 283
 284         holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
 285         event = holder->event;
 286
 287         return event;
 288 }
 289
 290 /*
 291  * Called when a group is being torn down to clean up any outstanding
 292  * event notifications.
 293  */
 294 void fsnotify_flush_notify(struct fsnotify_group *group)
 295 {
 296         struct fsnotify_event *event;
 297         struct fsnotify_event_private_data *priv;
 298
 299         mutex_lock(&group->notification_mutex);
 300         while (!fsnotify_notify_queue_is_empty(group)) {
 301                 event = fsnotify_remove_notify_event(group);
 302                 /* if they don't implement free_event_priv they better not have attached any */
 303                 if (group->ops->free_event_priv) {
 304                         spin_lock(&event->lock);
 305                         priv = fsnotify_remove_priv_from_event(group, event);
 306                         spin_unlock(&event->lock);
 307                         if (priv)
 308                                 group->ops->free_event_priv(priv);
 309                 }
 310                 fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
 311         }
 312         mutex_unlock(&group->notification_mutex);
 313 }
 314
 315 static void initialize_event(struct fsnotify_event *event)
 316 {
 317         event->holder.event = NULL;
 318         INIT_LIST_HEAD(&event->holder.event_list);
 319         atomic_set(&event->refcnt, 1);
 320
 321         spin_lock_init(&event->lock);
 322
 323         event->path.dentry = NULL;
 324         event->path.mnt = NULL;
 325         event->inode = NULL;
 326         event->data_type = FSNOTIFY_EVENT_NONE;
 327
 328         INIT_LIST_HEAD(&event->private_data_list);
 329
 330         event->to_tell = NULL;
 331
 332         event->file_name = NULL;
 333         event->name_len = 0;
 334
 335         event->sync_cookie = 0;
 336 }
 337
 338 /*
 339  * fsnotify_create_event - Allocate a new event which will be sent to each
 340  * group's handle_event function if the group was interested in this
 341  * particular event.
 342  *
 343  * @to_tell the inode which is supposed to receive the event (sometimes a
 344  *      parent of the inode to which the event happened.
 345  * @mask what actually happened.
 346  * @data pointer to the object which was actually affected
 347  * @data_type flag indication if the data is a file, path, inode, nothing...
 348  * @name the filename, if available
 349  */
 350 struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
 351                                              int data_type, const char *name, u32 cookie,
 352                                              gfp_t gfp)
 353 {
 354         struct fsnotify_event *event;
 355
 356         event = kmem_cache_alloc(fsnotify_event_cachep, gfp);
 357         if (!event)
 358                 return NULL;
 359
 360         initialize_event(event);
 361
 362         if (name) {
 363                 event->file_name = kstrdup(name, gfp);
 364                 if (!event->file_name) {
 365                         kmem_cache_free(fsnotify_event_cachep, event);
 366                         return NULL;
 367                 }
 368                 event->name_len = strlen(event->file_name);
 369         }
 370
 371         event->sync_cookie = cookie;
 372         event->to_tell = to_tell;
 373
 374         switch (data_type) {
 375         case FSNOTIFY_EVENT_FILE: {
 376                 struct file *file = data;
 377                 struct path *path = &file->f_path;
 378                 event->path.dentry = path->dentry;
 379                 event->path.mnt = path->mnt;
 380                 path_get(&event->path);
 381                 event->data_type = FSNOTIFY_EVENT_PATH;
 382                 break;
 383         }
 384         case FSNOTIFY_EVENT_PATH: {
 385                 struct path *path = data;
 386                 event->path.dentry = path->dentry;
 387                 event->path.mnt = path->mnt;
 388                 path_get(&event->path);
 389                 event->data_type = FSNOTIFY_EVENT_PATH;
 390                 break;
 391         }
 392         case FSNOTIFY_EVENT_INODE:
 393                 event->inode = data;
 394                 event->data_type = FSNOTIFY_EVENT_INODE;
 395                 break;
 396         case FSNOTIFY_EVENT_NONE:
 397                 event->inode = NULL;
 398                 event->path.dentry = NULL;
 399                 event->path.mnt = NULL;
 400                 break;
 401         default:
 402                 BUG();
 403         }
 404
 405         event->mask = mask;
 406
 407         return event;
 408 }
 409
 410 __init int fsnotify_notification_init(void)
 411 {
 412         fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
 413         fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);
 414
 415         initialize_event(&q_overflow_event);
 416         q_overflow_event.mask = FS_Q_OVERFLOW;
 417
 418         return 0;
 419 }
 420 subsys_initcall(fsnotify_notification_init);
 421