Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost
[cris-mirror.git] / fs / notify / notification.c
blob66f85c651c52db2e03eb3fbe440569345192e436
1 /*
2 * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
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.
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.
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.
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.
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>
46 #include <linux/atomic.h>
48 #include <linux/fsnotify_backend.h>
49 #include "fsnotify.h"
51 static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
53 /**
54 * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
55 * Called from fsnotify_move, which is inlined into filesystem modules.
57 u32 fsnotify_get_cookie(void)
59 return atomic_inc_return(&fsnotify_sync_cookie);
61 EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
63 /* return true if the notify queue is empty, false otherwise */
64 bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
66 assert_spin_locked(&group->notification_lock);
67 return list_empty(&group->notification_list) ? true : false;
70 void fsnotify_destroy_event(struct fsnotify_group *group,
71 struct fsnotify_event *event)
73 /* Overflow events are per-group and we don't want to free them */
74 if (!event || event->mask == FS_Q_OVERFLOW)
75 return;
77 * If the event is still queued, we have a problem... Do an unreliable
78 * lockless check first to avoid locking in the common case. The
79 * locking may be necessary for permission events which got removed
80 * from the list by a different CPU than the one freeing the event.
82 if (!list_empty(&event->list)) {
83 spin_lock(&group->notification_lock);
84 WARN_ON(!list_empty(&event->list));
85 spin_unlock(&group->notification_lock);
87 group->ops->free_event(event);
91 * Add an event to the group notification queue. The group can later pull this
92 * event off the queue to deal with. The function returns 0 if the event was
93 * added to the queue, 1 if the event was merged with some other queued event,
94 * 2 if the event was not queued - either the queue of events has overflown
95 * or the group is shutting down.
97 int fsnotify_add_event(struct fsnotify_group *group,
98 struct fsnotify_event *event,
99 int (*merge)(struct list_head *,
100 struct fsnotify_event *))
102 int ret = 0;
103 struct list_head *list = &group->notification_list;
105 pr_debug("%s: group=%p event=%p\n", __func__, group, event);
107 spin_lock(&group->notification_lock);
109 if (group->shutdown) {
110 spin_unlock(&group->notification_lock);
111 return 2;
114 if (group->q_len >= group->max_events) {
115 ret = 2;
116 /* Queue overflow event only if it isn't already queued */
117 if (!list_empty(&group->overflow_event->list)) {
118 spin_unlock(&group->notification_lock);
119 return ret;
121 event = group->overflow_event;
122 goto queue;
125 if (!list_empty(list) && merge) {
126 ret = merge(list, event);
127 if (ret) {
128 spin_unlock(&group->notification_lock);
129 return ret;
133 queue:
134 group->q_len++;
135 list_add_tail(&event->list, list);
136 spin_unlock(&group->notification_lock);
138 wake_up(&group->notification_waitq);
139 kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
140 return ret;
144 * Remove and return the first event from the notification list. It is the
145 * responsibility of the caller to destroy the obtained event
147 struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
149 struct fsnotify_event *event;
151 assert_spin_locked(&group->notification_lock);
153 pr_debug("%s: group=%p\n", __func__, group);
155 event = list_first_entry(&group->notification_list,
156 struct fsnotify_event, list);
158 * We need to init list head for the case of overflow event so that
159 * check in fsnotify_add_event() works
161 list_del_init(&event->list);
162 group->q_len--;
164 return event;
168 * This will not remove the event, that must be done with
169 * fsnotify_remove_first_event()
171 struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
173 assert_spin_locked(&group->notification_lock);
175 return list_first_entry(&group->notification_list,
176 struct fsnotify_event, list);
180 * Called when a group is being torn down to clean up any outstanding
181 * event notifications.
183 void fsnotify_flush_notify(struct fsnotify_group *group)
185 struct fsnotify_event *event;
187 spin_lock(&group->notification_lock);
188 while (!fsnotify_notify_queue_is_empty(group)) {
189 event = fsnotify_remove_first_event(group);
190 spin_unlock(&group->notification_lock);
191 fsnotify_destroy_event(group, event);
192 spin_lock(&group->notification_lock);
194 spin_unlock(&group->notification_lock);
198 * fsnotify_create_event - Allocate a new event which will be sent to each
199 * group's handle_event function if the group was interested in this
200 * particular event.
202 * @inode the inode which is supposed to receive the event (sometimes a
203 * parent of the inode to which the event happened.
204 * @mask what actually happened.
205 * @data pointer to the object which was actually affected
206 * @data_type flag indication if the data is a file, path, inode, nothing...
207 * @name the filename, if available
209 void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
210 u32 mask)
212 INIT_LIST_HEAD(&event->list);
213 event->inode = inode;
214 event->mask = mask;