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/mount.h> 39 #include <linux/mutex.h> 40 #include <linux/namei.h> 41 #include <linux/path.h> 42 #include <linux/slab.h> 43 #include <linux/spinlock.h> 44 45 #include <asm/atomic.h> 46 47 #include <linux/fsnotify_backend.h> 48 #include "fsnotify.h" 49 50 static struct kmem_cache *fsnotify_event_cachep; 51 static struct kmem_cache *fsnotify_event_holder_cachep; 52 /* 53 * This is a magic event we send when the q is too full. Since it doesn't 54 * hold real event information we just keep one system wide and use it any time 55 * it is needed. It's refcnt is set 1 at kernel init time and will never 56 * get set to 0 so it will never get 'freed' 57 */ 58 static struct fsnotify_event q_overflow_event; 59 60 /* return true if the notify queue is empty, false otherwise */ 61 bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group) 62 { 63 BUG_ON(!mutex_is_locked(&group->notification_mutex)); 64 return list_empty(&group->notification_list) ? true : false; 65 } 66 67 void fsnotify_get_event(struct fsnotify_event *event) 68 { 69 atomic_inc(&event->refcnt); 70 } 71 72 void fsnotify_put_event(struct fsnotify_event *event) 73 { 74 if (!event) 75 return; 76 77 if (atomic_dec_and_test(&event->refcnt)) { 78 if (event->data_type == FSNOTIFY_EVENT_PATH) 79 path_put(&event->path); 80 81 kfree(event->file_name); 82 kmem_cache_free(fsnotify_event_cachep, event); 83 } 84 } 85 86 struct fsnotify_event_holder *fsnotify_alloc_event_holder(void) 87 { 88 return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL); 89 } 90 91 void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder) 92 { 93 kmem_cache_free(fsnotify_event_holder_cachep, holder); 94 } 95 96 /* 97 * check if 2 events contain the same information. 98 */ 99 static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new) 100 { 101 if ((old->mask == new->mask) && 102 (old->to_tell == new->to_tell) && 103 (old->data_type == new->data_type)) { 104 switch (old->data_type) { 105 case (FSNOTIFY_EVENT_INODE): 106 if (old->inode == new->inode) 107 return true; 108 break; 109 case (FSNOTIFY_EVENT_PATH): 110 if ((old->path.mnt == new->path.mnt) && 111 (old->path.dentry == new->path.dentry)) 112 return true; 113 case (FSNOTIFY_EVENT_NONE): 114 return true; 115 }; 116 } 117 return false; 118 } 119 120 /* 121 * Add an event to the group notification queue. The group can later pull this 122 * event off the queue to deal with. If the event is successfully added to the 123 * group's notification queue, a reference is taken on event. 124 */ 125 int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event) 126 { 127 struct fsnotify_event_holder *holder = NULL; 128 struct list_head *list = &group->notification_list; 129 struct fsnotify_event_holder *last_holder; 130 struct fsnotify_event *last_event; 131 132 /* 133 * There is one fsnotify_event_holder embedded inside each fsnotify_event. 134 * Check if we expect to be able to use that holder. If not alloc a new 135 * holder. 136 * For the overflow event it's possible that something will use the in 137 * event holder before we get the lock so we may need to jump back and 138 * alloc a new holder, this can't happen for most events... 139 */ 140 if (!list_empty(&event->holder.event_list)) { 141 alloc_holder: 142 holder = fsnotify_alloc_event_holder(); 143 if (!holder) 144 return -ENOMEM; 145 } 146 147 mutex_lock(&group->notification_mutex); 148 149 if (group->q_len >= group->max_events) 150 event = &q_overflow_event; 151 152 spin_lock(&event->lock); 153 154 if (list_empty(&event->holder.event_list)) { 155 if (unlikely(holder)) 156 fsnotify_destroy_event_holder(holder); 157 holder = &event->holder; 158 } else if (unlikely(!holder)) { 159 /* between the time we checked above and got the lock the in 160 * event holder was used, go back and get a new one */ 161 spin_unlock(&event->lock); 162 mutex_unlock(&group->notification_mutex); 163 goto alloc_holder; 164 } 165 166 if (!list_empty(list)) { 167 last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list); 168 last_event = last_holder->event; 169 if (event_compare(last_event, event)) { 170 spin_unlock(&event->lock); 171 mutex_unlock(&group->notification_mutex); 172 if (holder != &event->holder) 173 fsnotify_destroy_event_holder(holder); 174 return 0; 175 } 176 } 177 178 group->q_len++; 179 holder->event = event; 180 181 fsnotify_get_event(event); 182 list_add_tail(&holder->event_list, list); 183 spin_unlock(&event->lock); 184 mutex_unlock(&group->notification_mutex); 185 186 wake_up(&group->notification_waitq); 187 return 0; 188 } 189 190 /* 191 * Remove and return the first event from the notification list. There is a 192 * reference held on this event since it was on the list. It is the responsibility 193 * of the caller to drop this reference. 194 */ 195 struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group) 196 { 197 struct fsnotify_event *event; 198 struct fsnotify_event_holder *holder; 199 200 BUG_ON(!mutex_is_locked(&group->notification_mutex)); 201 202 holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list); 203 204 event = holder->event; 205 206 spin_lock(&event->lock); 207 holder->event = NULL; 208 list_del_init(&holder->event_list); 209 spin_unlock(&event->lock); 210 211 /* event == holder means we are referenced through the in event holder */ 212 if (holder != &event->holder) 213 fsnotify_destroy_event_holder(holder); 214 215 group->q_len--; 216 217 return event; 218 } 219 220 /* 221 * This will not remove the event, that must be done with fsnotify_remove_notify_event() 222 */ 223 struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group) 224 { 225 struct fsnotify_event *event; 226 struct fsnotify_event_holder *holder; 227 228 BUG_ON(!mutex_is_locked(&group->notification_mutex)); 229 230 holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list); 231 event = holder->event; 232 233 return event; 234 } 235 236 /* 237 * Called when a group is being torn down to clean up any outstanding 238 * event notifications. 239 */ 240 void fsnotify_flush_notify(struct fsnotify_group *group) 241 { 242 struct fsnotify_event *event; 243 244 mutex_lock(&group->notification_mutex); 245 while (!fsnotify_notify_queue_is_empty(group)) { 246 event = fsnotify_remove_notify_event(group); 247 fsnotify_put_event(event); /* matches fsnotify_add_notify_event */ 248 } 249 mutex_unlock(&group->notification_mutex); 250 } 251 252 static void initialize_event(struct fsnotify_event *event) 253 { 254 event->holder.event = NULL; 255 INIT_LIST_HEAD(&event->holder.event_list); 256 atomic_set(&event->refcnt, 1); 257 258 spin_lock_init(&event->lock); 259 260 event->path.dentry = NULL; 261 event->path.mnt = NULL; 262 event->inode = NULL; 263 event->data_type = FSNOTIFY_EVENT_NONE; 264 265 event->to_tell = NULL; 266 267 event->file_name = NULL; 268 event->name_len = 0; 269 } 270 271 /* 272 * fsnotify_create_event - Allocate a new event which will be sent to each 273 * group's handle_event function if the group was interested in this 274 * particular event. 275 * 276 * @to_tell the inode which is supposed to receive the event (sometimes a 277 * parent of the inode to which the event happened. 278 * @mask what actually happened. 279 * @data pointer to the object which was actually affected 280 * @data_type flag indication if the data is a file, path, inode, nothing... 281 * @name the filename, if available 282 */ 283 struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, 284 void *data, int data_type, const char *name) 285 { 286 struct fsnotify_event *event; 287 288 event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL); 289 if (!event) 290 return NULL; 291 292 initialize_event(event); 293 294 if (name) { 295 event->file_name = kstrdup(name, GFP_KERNEL); 296 if (!event->file_name) { 297 kmem_cache_free(fsnotify_event_cachep, event); 298 return NULL; 299 } 300 event->name_len = strlen(event->file_name); 301 } 302 event->to_tell = to_tell; 303 304 switch (data_type) { 305 case FSNOTIFY_EVENT_FILE: { 306 struct file *file = data; 307 struct path *path = &file->f_path; 308 event->path.dentry = path->dentry; 309 event->path.mnt = path->mnt; 310 path_get(&event->path); 311 event->data_type = FSNOTIFY_EVENT_PATH; 312 break; 313 } 314 case FSNOTIFY_EVENT_PATH: { 315 struct path *path = data; 316 event->path.dentry = path->dentry; 317 event->path.mnt = path->mnt; 318 path_get(&event->path); 319 event->data_type = FSNOTIFY_EVENT_PATH; 320 break; 321 } 322 case FSNOTIFY_EVENT_INODE: 323 event->inode = data; 324 event->data_type = FSNOTIFY_EVENT_INODE; 325 break; 326 case FSNOTIFY_EVENT_NONE: 327 event->inode = NULL; 328 event->path.dentry = NULL; 329 event->path.mnt = NULL; 330 break; 331 default: 332 BUG(); 333 } 334 335 event->mask = mask; 336 337 return event; 338 } 339 340 __init int fsnotify_notification_init(void) 341 { 342 fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC); 343 fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC); 344 345 initialize_event(&q_overflow_event); 346 q_overflow_event.mask = FS_Q_OVERFLOW; 347 348 return 0; 349 } 350 subsys_initcall(fsnotify_notification_init); 351 352