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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
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19/*
20 * Basic idea behind the notification queue: An fsnotify group (like inotify)
b3834be5 21 * sends the userspace notification about events asynchronously some time after
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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
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34#include <linux/fs.h>
35#include <linux/init.h>
36#include <linux/kernel.h>
37#include <linux/list.h>
47882c6f 38#include <linux/module.h>
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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
60063497 46#include <linux/atomic.h>
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47
48#include <linux/fsnotify_backend.h>
49#include "fsnotify.h"
50
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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);
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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}
90586523 69
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70void fsnotify_destroy_event(struct fsnotify_group *group,
71 struct fsnotify_event *event)
90586523 72{
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73 /* Overflow events are per-group and we don't want to free them */
74 if (!event || event->mask == FS_Q_OVERFLOW)
90586523 75 return;
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76 /* If the event is still queued, we have a problem... */
77 WARN_ON(!list_empty(&event->list));
7053aee2 78 group->ops->free_event(event);
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79}
80
90586523 81/*
a2d8bc6c 82 * Add an event to the group notification queue. The group can later pull this
83c0e1b4 83 * event off the queue to deal with. The function returns 0 if the event was
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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.
90586523 86 */
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87int fsnotify_add_event(struct fsnotify_group *group,
88 struct fsnotify_event *event,
89 int (*merge)(struct list_head *,
90 struct fsnotify_event *))
a2d8bc6c 91{
83c0e1b4 92 int ret = 0;
a2d8bc6c 93 struct list_head *list = &group->notification_list;
e4aff117 94
7053aee2 95 pr_debug("%s: group=%p event=%p\n", __func__, group, event);
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96
97 mutex_lock(&group->notification_mutex);
98
e4aff117 99 if (group->q_len >= group->max_events) {
482ef06c 100 ret = 2;
7053aee2 101 /* Queue overflow event only if it isn't already queued */
ff57cd58 102 if (!list_empty(&group->overflow_event->list)) {
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103 mutex_unlock(&group->notification_mutex);
104 return ret;
105 }
ff57cd58 106 event = group->overflow_event;
482ef06c 107 goto queue;
e4aff117 108 }
a2d8bc6c 109
74766bbf 110 if (!list_empty(list) && merge) {
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111 ret = merge(list, event);
112 if (ret) {
7053aee2 113 mutex_unlock(&group->notification_mutex);
83c0e1b4 114 return ret;
f70ab54c 115 }
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116 }
117
482ef06c 118queue:
a2d8bc6c 119 group->q_len++;
7053aee2 120 list_add_tail(&event->list, list);
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121 mutex_unlock(&group->notification_mutex);
122
123 wake_up(&group->notification_waitq);
0a6b6bd5 124 kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
83c0e1b4 125 return ret;
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126}
127
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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
a2d8bc6c 143/*
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144 * Remove and return the first event from the notification list. It is the
145 * responsibility of the caller to destroy the obtained event
a2d8bc6c 146 */
8ba8fa91 147struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
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148{
149 struct fsnotify_event *event;
150
a2d8bc6c 151 BUG_ON(!mutex_is_locked(&group->notification_mutex));
90586523 152
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153 pr_debug("%s: group=%p\n", __func__, group);
154
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155 event = list_first_entry(&group->notification_list,
156 struct fsnotify_event, list);
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157 /*
158 * We need to init list head for the case of overflow event so that
8ba8fa91 159 * check in fsnotify_add_event() works
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160 */
161 list_del_init(&event->list);
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162 group->q_len--;
163
164 return event;
165}
166
167/*
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168 * This will not remove the event, that must be done with
169 * fsnotify_remove_first_event()
a2d8bc6c 170 */
8ba8fa91 171struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
a2d8bc6c 172{
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173 BUG_ON(!mutex_is_locked(&group->notification_mutex));
174
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175 return list_first_entry(&group->notification_list,
176 struct fsnotify_event, list);
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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)) {
8ba8fa91 189 event = fsnotify_remove_first_event(group);
7053aee2 190 fsnotify_destroy_event(group, event);
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191 }
192 mutex_unlock(&group->notification_mutex);
193}
194
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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 *
7053aee2 200 * @inode the inode which is supposed to receive the event (sometimes a
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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...
62ffe5df 205 * @name the filename, if available
a2d8bc6c 206 */
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207void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
208 u32 mask)
a2d8bc6c 209{
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210 INIT_LIST_HEAD(&event->list);
211 event->inode = inode;
90586523 212 event->mask = mask;
90586523 213}