xref: /linux/fs/notify/group.c (revision bfd5bb6f90af092aa345b15cd78143956a13c2a8)
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 #include <linux/list.h>
20 #include <linux/mutex.h>
21 #include <linux/slab.h>
22 #include <linux/srcu.h>
23 #include <linux/rculist.h>
24 #include <linux/wait.h>
25 
26 #include <linux/fsnotify_backend.h>
27 #include "fsnotify.h"
28 
29 #include <linux/atomic.h>
30 
31 /*
32  * Final freeing of a group
33  */
34 static void fsnotify_final_destroy_group(struct fsnotify_group *group)
35 {
36 	if (group->ops->free_group_priv)
37 		group->ops->free_group_priv(group);
38 
39 	kfree(group);
40 }
41 
42 /*
43  * Stop queueing new events for this group. Once this function returns
44  * fsnotify_add_event() will not add any new events to the group's queue.
45  */
46 void fsnotify_group_stop_queueing(struct fsnotify_group *group)
47 {
48 	spin_lock(&group->notification_lock);
49 	group->shutdown = true;
50 	spin_unlock(&group->notification_lock);
51 }
52 
53 /*
54  * Trying to get rid of a group. Remove all marks, flush all events and release
55  * the group reference.
56  * Note that another thread calling fsnotify_clear_marks_by_group() may still
57  * hold a ref to the group.
58  */
59 void fsnotify_destroy_group(struct fsnotify_group *group)
60 {
61 	/*
62 	 * Stop queueing new events. The code below is careful enough to not
63 	 * require this but fanotify needs to stop queuing events even before
64 	 * fsnotify_destroy_group() is called and this makes the other callers
65 	 * of fsnotify_destroy_group() to see the same behavior.
66 	 */
67 	fsnotify_group_stop_queueing(group);
68 
69 	/* Clear all marks for this group and queue them for destruction */
70 	fsnotify_clear_marks_by_group(group, FSNOTIFY_OBJ_ALL_TYPES_MASK);
71 
72 	/*
73 	 * Some marks can still be pinned when waiting for response from
74 	 * userspace. Wait for those now. fsnotify_prepare_user_wait() will
75 	 * not succeed now so this wait is race-free.
76 	 */
77 	wait_event(group->notification_waitq, !atomic_read(&group->user_waits));
78 
79 	/*
80 	 * Wait until all marks get really destroyed. We could actually destroy
81 	 * them ourselves instead of waiting for worker to do it, however that
82 	 * would be racy as worker can already be processing some marks before
83 	 * we even entered fsnotify_destroy_group().
84 	 */
85 	fsnotify_wait_marks_destroyed();
86 
87 	/*
88 	 * Since we have waited for fsnotify_mark_srcu in
89 	 * fsnotify_mark_destroy_list() there can be no outstanding event
90 	 * notification against this group. So clearing the notification queue
91 	 * of all events is reliable now.
92 	 */
93 	fsnotify_flush_notify(group);
94 
95 	/*
96 	 * Destroy overflow event (we cannot use fsnotify_destroy_event() as
97 	 * that deliberately ignores overflow events.
98 	 */
99 	if (group->overflow_event)
100 		group->ops->free_event(group->overflow_event);
101 
102 	fsnotify_put_group(group);
103 }
104 
105 /*
106  * Get reference to a group.
107  */
108 void fsnotify_get_group(struct fsnotify_group *group)
109 {
110 	refcount_inc(&group->refcnt);
111 }
112 
113 /*
114  * Drop a reference to a group.  Free it if it's through.
115  */
116 void fsnotify_put_group(struct fsnotify_group *group)
117 {
118 	if (refcount_dec_and_test(&group->refcnt))
119 		fsnotify_final_destroy_group(group);
120 }
121 
122 /*
123  * Create a new fsnotify_group and hold a reference for the group returned.
124  */
125 struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
126 {
127 	struct fsnotify_group *group;
128 
129 	group = kzalloc(sizeof(struct fsnotify_group), GFP_KERNEL);
130 	if (!group)
131 		return ERR_PTR(-ENOMEM);
132 
133 	/* set to 0 when there a no external references to this group */
134 	refcount_set(&group->refcnt, 1);
135 	atomic_set(&group->num_marks, 0);
136 	atomic_set(&group->user_waits, 0);
137 
138 	spin_lock_init(&group->notification_lock);
139 	INIT_LIST_HEAD(&group->notification_list);
140 	init_waitqueue_head(&group->notification_waitq);
141 	group->max_events = UINT_MAX;
142 
143 	mutex_init(&group->mark_mutex);
144 	INIT_LIST_HEAD(&group->marks_list);
145 
146 	group->ops = ops;
147 
148 	return group;
149 }
150 
151 int fsnotify_fasync(int fd, struct file *file, int on)
152 {
153 	struct fsnotify_group *group = file->private_data;
154 
155 	return fasync_helper(fd, file, on, &group->fsn_fa) >= 0 ? 0 : -EIO;
156 }
157