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); 465