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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 <asm/atomic.h>
30
31/* protects writes to fsnotify_groups and fsnotify_mask */
32static DEFINE_MUTEX(fsnotify_grp_mutex);
33/* protects reads while running the fsnotify_groups list */
34struct srcu_struct fsnotify_grp_srcu;
35/* all groups registered to receive filesystem notifications */
36LIST_HEAD(fsnotify_groups);
37/* bitwise OR of all events (FS_*) interesting to some group on this system */
38__u32 fsnotify_mask;
39
40/*
41 * When a new group registers or changes it's set of interesting events
42 * this function updates the fsnotify_mask to contain all interesting events
43 */
44void fsnotify_recalc_global_mask(void)
45{
46 struct fsnotify_group *group;
47 __u32 mask = 0;
48 int idx;
49
50 idx = srcu_read_lock(&fsnotify_grp_srcu);
51 list_for_each_entry_rcu(group, &fsnotify_groups, group_list)
52 mask |= group->mask;
53 srcu_read_unlock(&fsnotify_grp_srcu, idx);
54 fsnotify_mask = mask;
55}
56
57/*
58 * Update the group->mask by running all of the marks associated with this
59 * group and finding the bitwise | of all of the mark->mask. If we change
60 * the group->mask we need to update the global mask of events interesting
61 * to the system.
62 */
63void fsnotify_recalc_group_mask(struct fsnotify_group *group)
64{
65 __u32 mask = 0;
66 __u32 old_mask = group->mask;
67 struct fsnotify_mark_entry *entry;
68
69 spin_lock(&group->mark_lock);
70 list_for_each_entry(entry, &group->mark_entries, g_list)
71 mask |= entry->mask;
72 spin_unlock(&group->mark_lock);
73
74 group->mask = mask;
75
76 if (old_mask != mask)
77 fsnotify_recalc_global_mask();
78}
79
80/*
81 * Take a reference to a group so things found under the fsnotify_grp_mutex
82 * can't get freed under us
83 */
84static void fsnotify_get_group(struct fsnotify_group *group)
85{
86 atomic_inc(&group->refcnt);
87}
88
89/*
90 * Final freeing of a group
91 */
92void fsnotify_final_destroy_group(struct fsnotify_group *group)
93{
94 /* clear the notification queue of all events */
95 fsnotify_flush_notify(group);
96
97 if (group->ops->free_group_priv)
98 group->ops->free_group_priv(group);
99
100 kfree(group);
101}
102
103/*
104 * Trying to get rid of a group. We need to first get rid of any outstanding
105 * allocations and then free the group. Remember that fsnotify_clear_marks_by_group
106 * could miss marks that are being freed by inode and those marks could still
107 * hold a reference to this group (via group->num_marks) If we get into that
108 * situtation, the fsnotify_final_destroy_group will get called when that final
109 * mark is freed.
110 */
111static void fsnotify_destroy_group(struct fsnotify_group *group)
112{
113 /* clear all inode mark entries for this group */
114 fsnotify_clear_marks_by_group(group);
115
116 /* past the point of no return, matches the initial value of 1 */
117 if (atomic_dec_and_test(&group->num_marks))
118 fsnotify_final_destroy_group(group);
119}
120
121/*
122 * Remove this group from the global list of groups that will get events
123 * this can be done even if there are still references and things still using
124 * this group. This just stops the group from getting new events.
125 */
126static void __fsnotify_evict_group(struct fsnotify_group *group)
127{
128 BUG_ON(!mutex_is_locked(&fsnotify_grp_mutex));
129
130 if (group->on_group_list)
131 list_del_rcu(&group->group_list);
132 group->on_group_list = 0;
133}
134
135/*
136 * Called when a group is no longer interested in getting events. This can be
137 * used if a group is misbehaving or if for some reason a group should no longer
138 * get any filesystem events.
139 */
140void fsnotify_evict_group(struct fsnotify_group *group)
141{
142 mutex_lock(&fsnotify_grp_mutex);
143 __fsnotify_evict_group(group);
144 mutex_unlock(&fsnotify_grp_mutex);
145}
146
147/*
148 * Drop a reference to a group. Free it if it's through.
149 */
150void fsnotify_put_group(struct fsnotify_group *group)
151{
152 if (!atomic_dec_and_mutex_lock(&group->refcnt, &fsnotify_grp_mutex))
153 return;
154
155 /*
156 * OK, now we know that there's no other users *and* we hold mutex,
157 * so no new references will appear
158 */
159 __fsnotify_evict_group(group);
160
161 /*
162 * now it's off the list, so the only thing we might care about is
163 * srcu access....
164 */
165 mutex_unlock(&fsnotify_grp_mutex);
166 synchronize_srcu(&fsnotify_grp_srcu);
167
168 /* and now it is really dead. _Nothing_ could be seeing it */
169 fsnotify_recalc_global_mask();
170 fsnotify_destroy_group(group);
171}
172
173/*
174 * Simply run the fsnotify_groups list and find a group which matches
175 * the given parameters. If a group is found we take a reference to that
176 * group.
177 */
178static struct fsnotify_group *fsnotify_find_group(unsigned int group_num, __u32 mask,
179 const struct fsnotify_ops *ops)
180{
181 struct fsnotify_group *group_iter;
182 struct fsnotify_group *group = NULL;
183
184 BUG_ON(!mutex_is_locked(&fsnotify_grp_mutex));
185
186 list_for_each_entry_rcu(group_iter, &fsnotify_groups, group_list) {
187 if (group_iter->group_num == group_num) {
188 if ((group_iter->mask == mask) &&
189 (group_iter->ops == ops)) {
190 fsnotify_get_group(group_iter);
191 group = group_iter;
192 } else
193 group = ERR_PTR(-EEXIST);
194 }
195 }
196 return group;
197}
198
199/*
200 * Either finds an existing group which matches the group_num, mask, and ops or
201 * creates a new group and adds it to the global group list. In either case we
202 * take a reference for the group returned.
203 */
204struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num, __u32 mask,
205 const struct fsnotify_ops *ops)
206{
207 struct fsnotify_group *group, *tgroup;
208
209 /* very low use, simpler locking if we just always alloc */
210 group = kmalloc(sizeof(struct fsnotify_group), GFP_KERNEL);
211 if (!group)
212 return ERR_PTR(-ENOMEM);
213
214 atomic_set(&group->refcnt, 1);
215
216 group->on_group_list = 0;
217 group->group_num = group_num;
218 group->mask = mask;
219
220 mutex_init(&group->notification_mutex);
221 INIT_LIST_HEAD(&group->notification_list);
222 init_waitqueue_head(&group->notification_waitq);
223 group->q_len = 0;
224 group->max_events = UINT_MAX;
225
226 spin_lock_init(&group->mark_lock);
227 atomic_set(&group->num_marks, 0);
228 INIT_LIST_HEAD(&group->mark_entries);
229
230 group->ops = ops;
231
232 mutex_lock(&fsnotify_grp_mutex);
233 tgroup = fsnotify_find_group(group_num, mask, ops);
234 if (tgroup) {
235 /* group already exists */
236 mutex_unlock(&fsnotify_grp_mutex);
237 /* destroy the new one we made */
238 fsnotify_put_group(group);
239 return tgroup;
240 }
241
242 /* group not found, add a new one */
243 list_add_rcu(&group->group_list, &fsnotify_groups);
244 group->on_group_list = 1;
245 /* being on the fsnotify_groups list holds one num_marks */
246 atomic_inc(&group->num_marks);
247
248 mutex_unlock(&fsnotify_grp_mutex);
249
250 if (mask)
251 fsnotify_recalc_global_mask();
252
253 return group;
254}