notification.c 12.2 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
/*
 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2, or (at your option)
 *  any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; see the file COPYING.  If not, write to
 *  the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
 */

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
/*
 * Basic idea behind the notification queue: An fsnotify group (like inotify)
 * sends the userspace notification about events asyncronously some time after
 * the event happened.  When inotify gets an event it will need to add that
 * event to the group notify queue.  Since a single event might need to be on
 * multiple group's notification queues we can't add the event directly to each
 * queue and instead add a small "event_holder" to each queue.  This event_holder
 * has a pointer back to the original event.  Since the majority of events are
 * going to end up on one, and only one, notification queue we embed one
 * event_holder into each event.  This means we have a single allocation instead
 * of always needing two.  If the embedded event_holder is already in use by
 * another group a new event_holder (from fsnotify_event_holder_cachep) will be
 * allocated and used.
 */

34 35 36 37
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/list.h>
38
#include <linux/module.h>
39 40 41 42 43 44 45 46 47 48 49 50 51
#include <linux/mount.h>
#include <linux/mutex.h>
#include <linux/namei.h>
#include <linux/path.h>
#include <linux/slab.h>
#include <linux/spinlock.h>

#include <asm/atomic.h>

#include <linux/fsnotify_backend.h>
#include "fsnotify.h"

static struct kmem_cache *fsnotify_event_cachep;
52 53 54 55 56 57 58 59
static struct kmem_cache *fsnotify_event_holder_cachep;
/*
 * This is a magic event we send when the q is too full.  Since it doesn't
 * hold real event information we just keep one system wide and use it any time
 * it is needed.  It's refcnt is set 1 at kernel init time and will never
 * get set to 0 so it will never get 'freed'
 */
static struct fsnotify_event q_overflow_event;
60 61 62 63 64 65 66 67 68 69 70
static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);

/**
 * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
 * Called from fsnotify_move, which is inlined into filesystem modules.
 */
u32 fsnotify_get_cookie(void)
{
	return atomic_inc_return(&fsnotify_sync_cookie);
}
EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
71 72 73 74 75 76 77

/* return true if the notify queue is empty, false otherwise */
bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
{
	BUG_ON(!mutex_is_locked(&group->notification_mutex));
	return list_empty(&group->notification_list) ? true : false;
}
78 79 80 81 82 83 84 85 86 87 88 89 90 91 92

void fsnotify_get_event(struct fsnotify_event *event)
{
	atomic_inc(&event->refcnt);
}

void fsnotify_put_event(struct fsnotify_event *event)
{
	if (!event)
		return;

	if (atomic_dec_and_test(&event->refcnt)) {
		if (event->data_type == FSNOTIFY_EVENT_PATH)
			path_put(&event->path);

93 94
		BUG_ON(!list_empty(&event->private_data_list));

95
		kfree(event->file_name);
96 97 98 99
		kmem_cache_free(fsnotify_event_cachep, event);
	}
}

100 101 102 103 104 105 106 107 108 109 110
struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
{
	return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
}

void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
{
	kmem_cache_free(fsnotify_event_holder_cachep, holder);
}

/*
111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133
 * Find the private data that the group previously attached to this event when
 * the group added the event to the notification queue (fsnotify_add_notify_event)
 */
struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
{
	struct fsnotify_event_private_data *lpriv;
	struct fsnotify_event_private_data *priv = NULL;

	assert_spin_locked(&event->lock);

	list_for_each_entry(lpriv, &event->private_data_list, event_list) {
		if (lpriv->group == group) {
			priv = lpriv;
			list_del(&priv->event_list);
			break;
		}
	}
	return priv;
}

/*
 * Check if 2 events contain the same information.  We do not compare private data
 * but at this moment that isn't a problem for any know fsnotify listeners.
134 135 136 137 138
 */
static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new)
{
	if ((old->mask == new->mask) &&
	    (old->to_tell == new->to_tell) &&
139 140
	    (old->data_type == new->data_type) &&
	    (old->name_len == new->name_len)) {
141 142
		switch (old->data_type) {
		case (FSNOTIFY_EVENT_INODE):
143 144 145
			/* remember, after old was put on the wait_q we aren't
			 * allowed to look at the inode any more, only thing
			 * left to check was if the file_name is the same */
146
			if (!old->name_len ||
147
			    !strcmp(old->file_name, new->file_name))
148 149 150 151 152 153
				return true;
			break;
		case (FSNOTIFY_EVENT_PATH):
			if ((old->path.mnt == new->path.mnt) &&
			    (old->path.dentry == new->path.dentry))
				return true;
154
			break;
155
		case (FSNOTIFY_EVENT_NONE):
156 157 158 159
			if (old->mask & FS_Q_OVERFLOW)
				return true;
			else if (old->mask & FS_IN_IGNORED)
				return false;
160
			return false;
161 162 163 164 165
		};
	}
	return false;
}

166
/*
167 168 169
 * Add an event to the group notification queue.  The group can later pull this
 * event off the queue to deal with.  If the event is successfully added to the
 * group's notification queue, a reference is taken on event.
170
 */
171 172
int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
			      struct fsnotify_event_private_data *priv)
173 174 175 176 177
{
	struct fsnotify_event_holder *holder = NULL;
	struct list_head *list = &group->notification_list;
	struct fsnotify_event_holder *last_holder;
	struct fsnotify_event *last_event;
Eric Paris's avatar
Eric Paris committed
178
	int ret = 0;
179

180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196
	/*
	 * There is one fsnotify_event_holder embedded inside each fsnotify_event.
	 * Check if we expect to be able to use that holder.  If not alloc a new
	 * holder.
	 * For the overflow event it's possible that something will use the in
	 * event holder before we get the lock so we may need to jump back and
	 * alloc a new holder, this can't happen for most events...
	 */
	if (!list_empty(&event->holder.event_list)) {
alloc_holder:
		holder = fsnotify_alloc_event_holder();
		if (!holder)
			return -ENOMEM;
	}

	mutex_lock(&group->notification_mutex);

197
	if (group->q_len >= group->max_events) {
198
		event = &q_overflow_event;
Eric Paris's avatar
Eric Paris committed
199
		ret = -EOVERFLOW;
200 201 202
		/* sorry, no private data on the overflow event */
		priv = NULL;
	}
203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225

	spin_lock(&event->lock);

	if (list_empty(&event->holder.event_list)) {
		if (unlikely(holder))
			fsnotify_destroy_event_holder(holder);
		holder = &event->holder;
	} else if (unlikely(!holder)) {
		/* between the time we checked above and got the lock the in
		 * event holder was used, go back and get a new one */
		spin_unlock(&event->lock);
		mutex_unlock(&group->notification_mutex);
		goto alloc_holder;
	}

	if (!list_empty(list)) {
		last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list);
		last_event = last_holder->event;
		if (event_compare(last_event, event)) {
			spin_unlock(&event->lock);
			mutex_unlock(&group->notification_mutex);
			if (holder != &event->holder)
				fsnotify_destroy_event_holder(holder);
226
			return -EEXIST;
227 228 229 230 231 232 233 234
		}
	}

	group->q_len++;
	holder->event = event;

	fsnotify_get_event(event);
	list_add_tail(&holder->event_list, list);
235 236
	if (priv)
		list_add_tail(&priv->event_list, &event->private_data_list);
237 238 239 240
	spin_unlock(&event->lock);
	mutex_unlock(&group->notification_mutex);

	wake_up(&group->notification_waitq);
Eric Paris's avatar
Eric Paris committed
241
	return ret;
242 243 244 245 246 247 248 249
}

/*
 * Remove and return the first event from the notification list.  There is a
 * reference held on this event since it was on the list.  It is the responsibility
 * of the caller to drop this reference.
 */
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

256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296
	holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);

	event = holder->event;

	spin_lock(&event->lock);
	holder->event = NULL;
	list_del_init(&holder->event_list);
	spin_unlock(&event->lock);

	/* event == holder means we are referenced through the in event holder */
	if (holder != &event->holder)
		fsnotify_destroy_event_holder(holder);

	group->q_len--;

	return event;
}

/*
 * This will not remove the event, that must be done with fsnotify_remove_notify_event()
 */
struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
{
	struct fsnotify_event *event;
	struct fsnotify_event_holder *holder;

	BUG_ON(!mutex_is_locked(&group->notification_mutex));

	holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
	event = holder->event;

	return event;
}

/*
 * Called when a group is being torn down to clean up any outstanding
 * event notifications.
 */
void fsnotify_flush_notify(struct fsnotify_group *group)
{
	struct fsnotify_event *event;
297
	struct fsnotify_event_private_data *priv;
298 299 300 301

	mutex_lock(&group->notification_mutex);
	while (!fsnotify_notify_queue_is_empty(group)) {
		event = fsnotify_remove_notify_event(group);
302 303 304 305 306 307 308 309
		/* if they don't implement free_event_priv they better not have attached any */
		if (group->ops->free_event_priv) {
			spin_lock(&event->lock);
			priv = fsnotify_remove_priv_from_event(group, event);
			spin_unlock(&event->lock);
			if (priv)
				group->ops->free_event_priv(priv);
		}
310 311 312 313 314 315 316 317 318
		fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
	}
	mutex_unlock(&group->notification_mutex);
}

static void initialize_event(struct fsnotify_event *event)
{
	event->holder.event = NULL;
	INIT_LIST_HEAD(&event->holder.event_list);
319 320 321 322 323 324 325
	atomic_set(&event->refcnt, 1);

	spin_lock_init(&event->lock);

	event->path.dentry = NULL;
	event->path.mnt = NULL;
	event->inode = NULL;
326
	event->data_type = FSNOTIFY_EVENT_NONE;
327

328 329
	INIT_LIST_HEAD(&event->private_data_list);

330
	event->to_tell = NULL;
331 332 333

	event->file_name = NULL;
	event->name_len = 0;
334 335

	event->sync_cookie = 0;
336 337 338 339 340 341 342 343 344 345 346 347
}

/*
 * fsnotify_create_event - Allocate a new event which will be sent to each
 * group's handle_event function if the group was interested in this
 * particular event.
 *
 * @to_tell the inode which is supposed to receive the event (sometimes a
 *	parent of the inode to which the event happened.
 * @mask what actually happened.
 * @data pointer to the object which was actually affected
 * @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,
351 352
					     int data_type, const char *name, u32 cookie,
					     gfp_t gfp)
353 354 355
{
	struct fsnotify_event *event;

356
	event = kmem_cache_alloc(fsnotify_event_cachep, gfp);
357 358 359 360
	if (!event)
		return NULL;

	initialize_event(event);
361 362

	if (name) {
363
		event->file_name = kstrdup(name, gfp);
364 365 366 367 368 369
		if (!event->file_name) {
			kmem_cache_free(fsnotify_event_cachep, event);
			return NULL;
		}
		event->name_len = strlen(event->file_name);
	}
370 371

	event->sync_cookie = cookie;
372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412
	event->to_tell = to_tell;

	switch (data_type) {
	case FSNOTIFY_EVENT_FILE: {
		struct file *file = data;
		struct path *path = &file->f_path;
		event->path.dentry = path->dentry;
		event->path.mnt = path->mnt;
		path_get(&event->path);
		event->data_type = FSNOTIFY_EVENT_PATH;
		break;
	}
	case FSNOTIFY_EVENT_PATH: {
		struct path *path = data;
		event->path.dentry = path->dentry;
		event->path.mnt = path->mnt;
		path_get(&event->path);
		event->data_type = FSNOTIFY_EVENT_PATH;
		break;
	}
	case FSNOTIFY_EVENT_INODE:
		event->inode = data;
		event->data_type = FSNOTIFY_EVENT_INODE;
		break;
	case FSNOTIFY_EVENT_NONE:
		event->inode = NULL;
		event->path.dentry = NULL;
		event->path.mnt = NULL;
		break;
	default:
		BUG();
	}

	event->mask = mask;

	return event;
}

__init int fsnotify_notification_init(void)
{
	fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
413 414 415 416
	fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);

	initialize_event(&q_overflow_event);
	q_overflow_event.mask = FS_Q_OVERFLOW;
417 418 419 420 421

	return 0;
}
subsys_initcall(fsnotify_notification_init);