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