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}
214