summaryrefslogtreecommitdiffstats
path: root/fs/notify/notification.c
blob: 9022ae650cf863ea5276027204fcae754024cf62 (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
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
 */

/*
 * 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);

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 == group->overflow_event)
		return;
	/*
	 * If the event is still queued, we have a problem... Do an unreliable
	 * lockless check first to avoid locking in the common case. The
	 * locking may be necessary for permission events which got removed
	 * from the list by a different CPU than the one freeing the event.
	 */
	if (!list_empty(&event->list)) {
		spin_lock(&group->notification_lock);
		WARN_ON(!list_empty(&event->list));
		spin_unlock(&group->notification_lock);
	}
	group->ops->free_event(group, event);
}

/*
 * Try to add an event to the notification queue.
 * The group can later pull this event off the queue to deal with.
 * The group can use the @merge hook to merge the event with a queued event.
 * The group can use the @insert hook to insert the event into hash table.
 * The function returns:
 * 0 if the event was added to a queue
 * 1 if the event was merged with some other queued event
 * 2 if the event was not queued - either the queue of events has overflown
 *   or the group is shutting down.
 */
int fsnotify_insert_event(struct fsnotify_group *group,
			  struct fsnotify_event *event,
			  int (*merge)(struct fsnotify_group *,
				       struct fsnotify_event *),
			  void (*insert)(struct fsnotify_group *,
					 struct fsnotify_event *))
{
	int ret = 0;
	struct list_head *list = &group->notification_list;

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

	spin_lock(&group->notification_lock);

	if (group->shutdown) {
		spin_unlock(&group->notification_lock);
		return 2;
	}

	if (event == group->overflow_event ||
	    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)) {
			spin_unlock(&group->notification_lock);
			return ret;
		}
		event = group->overflow_event;
		goto queue;
	}

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

queue:
	group->q_len++;
	list_add_tail(&event->list, list);
	if (insert)
		insert(group, event);
	spin_unlock(&group->notification_lock);

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

void fsnotify_remove_queued_event(struct fsnotify_group *group,
				  struct fsnotify_event *event)
{
	assert_spin_locked(&group->notification_lock);
	/*
	 * 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 the first event on the notification list without removing it.
 * Returns NULL if the list is empty.
 */
struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
{
	assert_spin_locked(&group->notification_lock);

	if (fsnotify_notify_queue_is_empty(group))
		return NULL;

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

/*
 * 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 = fsnotify_peek_first_event(group);

	if (!event)
		return NULL;

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

	fsnotify_remove_queued_event(group, event);

	return event;
}

/*
 * 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;

	spin_lock(&group->notification_lock);
	while (!fsnotify_notify_queue_is_empty(group)) {
		event = fsnotify_remove_first_event(group);
		spin_unlock(&group->notification_lock);
		fsnotify_destroy_event(group, event);
		spin_lock(&group->notification_lock);
	}
	spin_unlock(&group->notification_lock);
}