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 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 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 */ 92 void 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 */ 111 static 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 */ 126 static 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 */ 140 void 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 */ 150 void 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 */ 178 static 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 */ 204 struct 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 } 255