aboutsummaryrefslogtreecommitdiff
path: root/fs/notify/notification.c
blob: a95d8e037aebe24ba36421861d3abaad6f7dfc89 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
/*
 *  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.
 */

/*
 * Basic idea behind the notification queue: An fsnotify group (like inotify)
 * sends the userspace notification about events asynchronously 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.
 */

#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/module.h>
#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 <linux/atomic.h>

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

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);

/* 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;
}

void fsnotify_destroy_event(struct fsnotify_group *group,
			    struct fsnotify_event *event)
{
	/* Overflow events are per-group and we don't want to free them */
	if (!event || event->mask == FS_Q_OVERFLOW)
		return;
	/* If the event is still queued, we have a problem... */
	WARN_ON(!list_empty(&event->list));
	group->ops->free_event(event);
}

/*
 * Add an event to the group notification queue.  The group can later pull this
 * event off the queue to deal with.  The function returns 0 if the event was
 * added to the queue, 1 if the event was merged with some other queued event,
 * 2 if the queue of events has overflown.
 */
int fsnotify_add_event(struct fsnotify_group *group,
		       struct fsnotify_event *event,
		       int (*merge)(struct list_head *,
				    struct fsnotify_event *))
{
	int ret = 0;
	struct list_head *list = &group->notification_list;

	pr_debug("%s: group=%p event=%p\n", __func__, group, event);

	mutex_lock(&group->notification_mutex);

	if (group->q_len >= group->max_events) {
		ret = 2;
		/* Queue overflow event only if it isn't already queued */
		if (!list_empty(&group->overflow_event->list)) {
			mutex_unlock(&group->notification_mutex);
			return ret;
		}
		event = group->overflow_event;
		goto queue;
	}

	if (!list_empty(list) && merge) {
		ret = merge(list, event);
		if (ret) {
			mutex_unlock(&group->notification_mutex);
			return ret;
		}
	}

queue:
	group->q_len++;
	list_add_tail(&event->list, list);
	mutex_unlock(&group->notification_mutex);

	wake_up(&group->notification_waitq);
	kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
	return ret;
}

/*
 * Remove @event from group's notification queue. It is the responsibility of
 * the caller to destroy the event.
 */
void fsnotify_remove_event(struct fsnotify_group *group,
			   struct fsnotify_event *event)
{
	mutex_lock(&group->notification_mutex);
	if (!list_empty(&event->list)) {
		list_del_init(&event->list);
		group->q_len--;
	}
	mutex_unlock(&group->notification_mutex);
}

/*
 * Remove and return the first event from the notification list.  It is the
 * responsibility of the caller to destroy the obtained event
 */
struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
{
	struct fsnotify_event *event;

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

	pr_debug("%s: group=%p\n", __func__, group);

	event = list_first_entry(&group->notification_list,
				 struct fsnotify_event, list);
	/*
	 * We need to init list head for the case of overflow event so that
	 * check in fsnotify_add_event() works
	 */
	list_del_init(&event->list);
	group->q_len--;

	return event;
}

/*
 * This will not remove the event, that must be done with
 * fsnotify_remove_first_event()
 */
struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
{
	BUG_ON(!mutex_is_locked(&group->notification_mutex));

	return list_first_entry(&group->notification_list,
				struct fsnotify_event, list);
}

/*
 * 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;

	mutex_lock(&group->notification_mutex);
	while (!fsnotify_notify_queue_is_empty(group)) {
		event = fsnotify_remove_first_event(group);
		fsnotify_destroy_event(group, event);
	}
	mutex_unlock(&group->notification_mutex);
}

/*
 * 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.
 *
 * @inode 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...
 * @name the filename, if available
 */
void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
			 u32 mask)
{
	INIT_LIST_HEAD(&event->list);
	event->inode = inode;
	event->mask = mask;
}