fs/notify/group.c

   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 }