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