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90586523 EP |
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 */ | |
32 | static DEFINE_MUTEX(fsnotify_grp_mutex); | |
33 | /* protects reads while running the fsnotify_groups list */ | |
34 | struct srcu_struct fsnotify_grp_srcu; | |
35 | /* all groups registered to receive filesystem notifications */ | |
36 | LIST_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 | */ | |
44 | void 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 | ||
3be25f49 EP |
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 | */ | |
63 | void 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 | ||
90586523 EP |
80 | /* |
81 | * Take a reference to a group so things found under the fsnotify_grp_mutex | |
82 | * can't get freed under us | |
83 | */ | |
84 | static void fsnotify_get_group(struct fsnotify_group *group) | |
85 | { | |
86 | atomic_inc(&group->refcnt); | |
87 | } | |
88 | ||
89 | /* | |
90 | * Final freeing of a group | |
91 | */ | |
3be25f49 | 92 | void fsnotify_final_destroy_group(struct fsnotify_group *group) |
90586523 EP |
93 | { |
94 | if (group->ops->free_group_priv) | |
95 | group->ops->free_group_priv(group); | |
96 | ||
97 | kfree(group); | |
98 | } | |
99 | ||
3be25f49 EP |
100 | /* |
101 | * Trying to get rid of a group. We need to first get rid of any outstanding | |
102 | * allocations and then free the group. Remember that fsnotify_clear_marks_by_group | |
103 | * could miss marks that are being freed by inode and those marks could still | |
104 | * hold a reference to this group (via group->num_marks) If we get into that | |
105 | * situtation, the fsnotify_final_destroy_group will get called when that final | |
106 | * mark is freed. | |
107 | */ | |
108 | static void fsnotify_destroy_group(struct fsnotify_group *group) | |
109 | { | |
110 | /* clear all inode mark entries for this group */ | |
111 | fsnotify_clear_marks_by_group(group); | |
112 | ||
113 | /* past the point of no return, matches the initial value of 1 */ | |
114 | if (atomic_dec_and_test(&group->num_marks)) | |
115 | fsnotify_final_destroy_group(group); | |
116 | } | |
117 | ||
90586523 EP |
118 | /* |
119 | * Remove this group from the global list of groups that will get events | |
120 | * this can be done even if there are still references and things still using | |
121 | * this group. This just stops the group from getting new events. | |
122 | */ | |
123 | static void __fsnotify_evict_group(struct fsnotify_group *group) | |
124 | { | |
125 | BUG_ON(!mutex_is_locked(&fsnotify_grp_mutex)); | |
126 | ||
127 | if (group->on_group_list) | |
128 | list_del_rcu(&group->group_list); | |
129 | group->on_group_list = 0; | |
130 | } | |
131 | ||
132 | /* | |
133 | * Called when a group is no longer interested in getting events. This can be | |
134 | * used if a group is misbehaving or if for some reason a group should no longer | |
135 | * get any filesystem events. | |
136 | */ | |
137 | void fsnotify_evict_group(struct fsnotify_group *group) | |
138 | { | |
139 | mutex_lock(&fsnotify_grp_mutex); | |
140 | __fsnotify_evict_group(group); | |
141 | mutex_unlock(&fsnotify_grp_mutex); | |
142 | } | |
143 | ||
144 | /* | |
145 | * Drop a reference to a group. Free it if it's through. | |
146 | */ | |
147 | void fsnotify_put_group(struct fsnotify_group *group) | |
148 | { | |
149 | if (!atomic_dec_and_mutex_lock(&group->refcnt, &fsnotify_grp_mutex)) | |
150 | return; | |
151 | ||
152 | /* | |
153 | * OK, now we know that there's no other users *and* we hold mutex, | |
154 | * so no new references will appear | |
155 | */ | |
156 | __fsnotify_evict_group(group); | |
157 | ||
158 | /* | |
159 | * now it's off the list, so the only thing we might care about is | |
160 | * srcu access.... | |
161 | */ | |
162 | mutex_unlock(&fsnotify_grp_mutex); | |
163 | synchronize_srcu(&fsnotify_grp_srcu); | |
164 | ||
165 | /* and now it is really dead. _Nothing_ could be seeing it */ | |
166 | fsnotify_recalc_global_mask(); | |
167 | fsnotify_destroy_group(group); | |
168 | } | |
169 | ||
170 | /* | |
171 | * Simply run the fsnotify_groups list and find a group which matches | |
172 | * the given parameters. If a group is found we take a reference to that | |
173 | * group. | |
174 | */ | |
175 | static struct fsnotify_group *fsnotify_find_group(unsigned int group_num, __u32 mask, | |
176 | const struct fsnotify_ops *ops) | |
177 | { | |
178 | struct fsnotify_group *group_iter; | |
179 | struct fsnotify_group *group = NULL; | |
180 | ||
181 | BUG_ON(!mutex_is_locked(&fsnotify_grp_mutex)); | |
182 | ||
183 | list_for_each_entry_rcu(group_iter, &fsnotify_groups, group_list) { | |
184 | if (group_iter->group_num == group_num) { | |
185 | if ((group_iter->mask == mask) && | |
186 | (group_iter->ops == ops)) { | |
187 | fsnotify_get_group(group_iter); | |
188 | group = group_iter; | |
189 | } else | |
190 | group = ERR_PTR(-EEXIST); | |
191 | } | |
192 | } | |
193 | return group; | |
194 | } | |
195 | ||
196 | /* | |
197 | * Either finds an existing group which matches the group_num, mask, and ops or | |
198 | * creates a new group and adds it to the global group list. In either case we | |
199 | * take a reference for the group returned. | |
200 | */ | |
201 | struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num, __u32 mask, | |
202 | const struct fsnotify_ops *ops) | |
203 | { | |
204 | struct fsnotify_group *group, *tgroup; | |
205 | ||
206 | /* very low use, simpler locking if we just always alloc */ | |
207 | group = kmalloc(sizeof(struct fsnotify_group), GFP_KERNEL); | |
208 | if (!group) | |
209 | return ERR_PTR(-ENOMEM); | |
210 | ||
211 | atomic_set(&group->refcnt, 1); | |
212 | ||
213 | group->on_group_list = 0; | |
214 | group->group_num = group_num; | |
215 | group->mask = mask; | |
216 | ||
3be25f49 EP |
217 | spin_lock_init(&group->mark_lock); |
218 | atomic_set(&group->num_marks, 0); | |
219 | INIT_LIST_HEAD(&group->mark_entries); | |
220 | ||
90586523 EP |
221 | group->ops = ops; |
222 | ||
223 | mutex_lock(&fsnotify_grp_mutex); | |
224 | tgroup = fsnotify_find_group(group_num, mask, ops); | |
225 | if (tgroup) { | |
226 | /* group already exists */ | |
227 | mutex_unlock(&fsnotify_grp_mutex); | |
228 | /* destroy the new one we made */ | |
229 | fsnotify_put_group(group); | |
230 | return tgroup; | |
231 | } | |
232 | ||
233 | /* group not found, add a new one */ | |
234 | list_add_rcu(&group->group_list, &fsnotify_groups); | |
235 | group->on_group_list = 1; | |
3be25f49 EP |
236 | /* being on the fsnotify_groups list holds one num_marks */ |
237 | atomic_inc(&group->num_marks); | |
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238 | |
239 | mutex_unlock(&fsnotify_grp_mutex); | |
240 | ||
241 | if (mask) | |
242 | fsnotify_recalc_global_mask(); | |
243 | ||
244 | return group; | |
245 | } |