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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
51static 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 */
57u32 fsnotify_get_cookie(void)
58{
59 return atomic_inc_return(&fsnotify_sync_cookie);
60}
61EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
62
63/* return true if the notify queue is empty, false otherwise */
64bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
65{
66 BUG_ON(!mutex_is_locked(&group->notification_mutex));
67 return list_empty(&group->notification_list) ? true : false;
68}
69
70void 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 /* If the event is still queued, we have a problem... */
77 WARN_ON(!list_empty(&event->list));
78 group->ops->free_event(event);
79}
80
81/*
82 * Add an event to the group notification queue. The group can later pull this
83 * event off the queue to deal with. The function returns 0 if the event was
84 * added to the queue, 1 if the event was merged with some other queued event,
85 * 2 if the queue of events has overflown.
86 */
87int fsnotify_add_event(struct fsnotify_group *group,
88 struct fsnotify_event *event,
89 int (*merge)(struct list_head *,
90 struct fsnotify_event *))
91{
92 int ret = 0;
93 struct list_head *list = &group->notification_list;
94
95 pr_debug("%s: group=%p event=%p\n", __func__, group, event);
96
97 mutex_lock(&group->notification_mutex);
98
99 if (group->q_len >= group->max_events) {
100 ret = 2;
101 /* Queue overflow event only if it isn't already queued */
102 if (!list_empty(&group->overflow_event->list)) {
103 mutex_unlock(&group->notification_mutex);
104 return ret;
105 }
106 event = group->overflow_event;
107 goto queue;
108 }
109
110 if (!list_empty(list) && merge) {
111 ret = merge(list, event);
112 if (ret) {
113 mutex_unlock(&group->notification_mutex);
114 return ret;
115 }
116 }
117
118queue:
119 group->q_len++;
120 list_add_tail(&event->list, list);
121 mutex_unlock(&group->notification_mutex);
122
123 wake_up(&group->notification_waitq);
124 kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
125 return ret;
126}
127
128/*
129 * Remove @event from group's notification queue. It is the responsibility of
130 * the caller to destroy the event.
131 */
132void fsnotify_remove_event(struct fsnotify_group *group,
133 struct fsnotify_event *event)
134{
135 mutex_lock(&group->notification_mutex);
136 if (!list_empty(&event->list)) {
137 list_del_init(&event->list);
138 group->q_len--;
139 }
140 mutex_unlock(&group->notification_mutex);
141}
142
143/*
144 * Remove and return the first event from the notification list. It is the
145 * responsibility of the caller to destroy the obtained event
146 */
147struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
148{
149 struct fsnotify_event *event;
150
151 BUG_ON(!mutex_is_locked(&group->notification_mutex));
152
153 pr_debug("%s: group=%p\n", __func__, group);
154
155 event = list_first_entry(&group->notification_list,
156 struct fsnotify_event, list);
157 /*
158 * We need to init list head for the case of overflow event so that
159 * check in fsnotify_add_event() works
160 */
161 list_del_init(&event->list);
162 group->q_len--;
163
164 return event;
165}
166
167/*
168 * This will not remove the event, that must be done with
169 * fsnotify_remove_first_event()
170 */
171struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
172{
173 BUG_ON(!mutex_is_locked(&group->notification_mutex));
174
175 return list_first_entry(&group->notification_list,
176 struct fsnotify_event, list);
177}
178
179/*
180 * Called when a group is being torn down to clean up any outstanding
181 * event notifications.
182 */
183void fsnotify_flush_notify(struct fsnotify_group *group)
184{
185 struct fsnotify_event *event;
186
187 mutex_lock(&group->notification_mutex);
188 while (!fsnotify_notify_queue_is_empty(group)) {
189 event = fsnotify_remove_first_event(group);
190 fsnotify_destroy_event(group, event);
191 }
192 mutex_unlock(&group->notification_mutex);
193}
194
195/*
196 * fsnotify_create_event - Allocate a new event which will be sent to each
197 * group's handle_event function if the group was interested in this
198 * particular event.
199 *
200 * @inode the inode which is supposed to receive the event (sometimes a
201 * parent of the inode to which the event happened.
202 * @mask what actually happened.
203 * @data pointer to the object which was actually affected
204 * @data_type flag indication if the data is a file, path, inode, nothing...
205 * @name the filename, if available
206 */
207void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
208 u32 mask)
209{
210 INIT_LIST_HEAD(&event->list);
211 event->inode = inode;
212 event->mask = mask;
213}
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
51static 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 */
57u32 fsnotify_get_cookie(void)
58{
59 return atomic_inc_return(&fsnotify_sync_cookie);
60}
61EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
62
63/* return true if the notify queue is empty, false otherwise */
64bool 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
70void 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 */
97int 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
134queue:
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 */
148struct 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 */
172struct 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 */
184void 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 */
210void 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}