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 true; 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 { 350 struct fsnotify_event *event; 351 352 event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL); 353 if (!event) 354 return NULL; 355 356 initialize_event(event); 357 358 if (name) { 359 event->file_name = kstrdup(name, GFP_KERNEL); 360 if (!event->file_name) { 361 kmem_cache_free(fsnotify_event_cachep, event); 362 return NULL; 363 } 364 event->name_len = strlen(event->file_name); 365 } 366 367 event->sync_cookie = cookie; 368 event->to_tell = to_tell; 369 370 switch (data_type) { 371 case FSNOTIFY_EVENT_FILE: { 372 struct file *file = data; 373 struct path *path = &file->f_path; 374 event->path.dentry = path->dentry; 375 event->path.mnt = path->mnt; 376 path_get(&event->path); 377 event->data_type = FSNOTIFY_EVENT_PATH; 378 break; 379 } 380 case FSNOTIFY_EVENT_PATH: { 381 struct path *path = data; 382 event->path.dentry = path->dentry; 383 event->path.mnt = path->mnt; 384 path_get(&event->path); 385 event->data_type = FSNOTIFY_EVENT_PATH; 386 break; 387 } 388 case FSNOTIFY_EVENT_INODE: 389 event->inode = data; 390 event->data_type = FSNOTIFY_EVENT_INODE; 391 break; 392 case FSNOTIFY_EVENT_NONE: 393 event->inode = NULL; 394 event->path.dentry = NULL; 395 event->path.mnt = NULL; 396 break; 397 default: 398 BUG(); 399 } 400 401 event->mask = mask; 402 403 return event; 404 } 405 406 __init int fsnotify_notification_init(void) 407 { 408 fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC); 409 fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC); 410 411 initialize_event(&q_overflow_event); 412 q_overflow_event.mask = FS_Q_OVERFLOW; 413 414 return 0; 415 } 416 subsys_initcall(fsnotify_notification_init); 417 418