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 atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
52
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.
56 */
fsnotify_get_cookie(void)57 u32 fsnotify_get_cookie(void)
58 {
59 return atomic_inc_return(&fsnotify_sync_cookie);
60 }
61 EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
62
63 /* return true if the notify queue is empty, false otherwise */
fsnotify_notify_queue_is_empty(struct fsnotify_group * group)64 bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
65 {
66 assert_spin_locked(&group->notification_lock);
67 return list_empty(&group->notification_list) ? true : false;
68 }
69
fsnotify_destroy_event(struct fsnotify_group * group,struct fsnotify_event * event)70 void fsnotify_destroy_event(struct fsnotify_group *group,
71 struct fsnotify_event *event)
72 {
73 /* Overflow events are per-group and we don't want to free them */
74 if (!event || event->mask == FS_Q_OVERFLOW)
75 return;
76 /*
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.
81 */
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);
86 }
87 group->ops->free_event(event);
88 }
89
90 /*
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.
96 */
fsnotify_add_event(struct fsnotify_group * group,struct fsnotify_event * event,int (* merge)(struct list_head *,struct fsnotify_event *))97 int fsnotify_add_event(struct fsnotify_group *group,
98 struct fsnotify_event *event,
99 int (*merge)(struct list_head *,
100 struct fsnotify_event *))
101 {
102 int ret = 0;
103 struct list_head *list = &group->notification_list;
104
105 pr_debug("%s: group=%p event=%p\n", __func__, group, event);
106
107 spin_lock(&group->notification_lock);
108
109 if (group->shutdown) {
110 spin_unlock(&group->notification_lock);
111 return 2;
112 }
113
114 if (event == group->overflow_event ||
115 group->q_len >= group->max_events) {
116 ret = 2;
117 /* Queue overflow event only if it isn't already queued */
118 if (!list_empty(&group->overflow_event->list)) {
119 spin_unlock(&group->notification_lock);
120 return ret;
121 }
122 event = group->overflow_event;
123 goto queue;
124 }
125
126 if (!list_empty(list) && merge) {
127 ret = merge(list, event);
128 if (ret) {
129 spin_unlock(&group->notification_lock);
130 return ret;
131 }
132 }
133
134 queue:
135 group->q_len++;
136 list_add_tail(&event->list, list);
137 spin_unlock(&group->notification_lock);
138
139 wake_up(&group->notification_waitq);
140 kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
141 return ret;
142 }
143
144 /*
145 * Remove and return the first event from the notification list. It is the
146 * responsibility of the caller to destroy the obtained event
147 */
fsnotify_remove_first_event(struct fsnotify_group * group)148 struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
149 {
150 struct fsnotify_event *event;
151
152 assert_spin_locked(&group->notification_lock);
153
154 pr_debug("%s: group=%p\n", __func__, group);
155
156 event = list_first_entry(&group->notification_list,
157 struct fsnotify_event, list);
158 /*
159 * We need to init list head for the case of overflow event so that
160 * check in fsnotify_add_event() works
161 */
162 list_del_init(&event->list);
163 group->q_len--;
164
165 return event;
166 }
167
168 /*
169 * This will not remove the event, that must be done with
170 * fsnotify_remove_first_event()
171 */
fsnotify_peek_first_event(struct fsnotify_group * group)172 struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
173 {
174 assert_spin_locked(&group->notification_lock);
175
176 return list_first_entry(&group->notification_list,
177 struct fsnotify_event, list);
178 }
179
180 /*
181 * Called when a group is being torn down to clean up any outstanding
182 * event notifications.
183 */
fsnotify_flush_notify(struct fsnotify_group * group)184 void fsnotify_flush_notify(struct fsnotify_group *group)
185 {
186 struct fsnotify_event *event;
187
188 spin_lock(&group->notification_lock);
189 while (!fsnotify_notify_queue_is_empty(group)) {
190 event = fsnotify_remove_first_event(group);
191 spin_unlock(&group->notification_lock);
192 fsnotify_destroy_event(group, event);
193 spin_lock(&group->notification_lock);
194 }
195 spin_unlock(&group->notification_lock);
196 }
197
198 /*
199 * fsnotify_create_event - Allocate a new event which will be sent to each
200 * group's handle_event function if the group was interested in this
201 * particular event.
202 *
203 * @inode the inode which is supposed to receive the event (sometimes a
204 * parent of the inode to which the event happened.
205 * @mask what actually happened.
206 * @data pointer to the object which was actually affected
207 * @data_type flag indication if the data is a file, path, inode, nothing...
208 * @name the filename, if available
209 */
fsnotify_init_event(struct fsnotify_event * event,struct inode * inode,u32 mask)210 void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
211 u32 mask)
212 {
213 INIT_LIST_HEAD(&event->list);
214 event->inode = inode;
215 event->mask = mask;
216 }
217