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  * Final freeing of a group
  82  */
  83 void fsnotify_final_destroy_group(struct fsnotify_group *group)
  84 {
  85         /* clear the notification queue of all events */
  86         fsnotify_flush_notify(group);
  87
  88         if (group->ops->free_group_priv)
  89                 group->ops->free_group_priv(group);
  90
  91         kfree(group);
  92 }
  93
  94 /*
  95  * Trying to get rid of a group.  We need to first get rid of any outstanding
  96  * allocations and then free the group.  Remember that fsnotify_clear_marks_by_group
  97  * could miss marks that are being freed by inode and those marks could still
  98  * hold a reference to this group (via group->num_marks)  If we get into that
  99  * situtation, the fsnotify_final_destroy_group will get called when that final
 100  * mark is freed.
 101  */
 102 static void fsnotify_destroy_group(struct fsnotify_group *group)
 103 {
 104         /* clear all inode mark entries for this group */
 105         fsnotify_clear_marks_by_group(group);
 106
 107         /* past the point of no return, matches the initial value of 1 */
 108         if (atomic_dec_and_test(&group->num_marks))
 109                 fsnotify_final_destroy_group(group);
 110 }
 111
 112 /*
 113  * Remove this group from the global list of groups that will get events
 114  * this can be done even if there are still references and things still using
 115  * this group.  This just stops the group from getting new events.
 116  */
 117 static void __fsnotify_evict_group(struct fsnotify_group *group)
 118 {
 119         BUG_ON(!mutex_is_locked(&fsnotify_grp_mutex));
 120
 121         if (group->on_group_list)
 122                 list_del_rcu(&group->group_list);
 123         group->on_group_list = 0;
 124 }
 125
 126 /*
 127  * Called when a group is no longer interested in getting events.  This can be
 128  * used if a group is misbehaving or if for some reason a group should no longer
 129  * get any filesystem events.
 130  */
 131 void fsnotify_evict_group(struct fsnotify_group *group)
 132 {
 133         mutex_lock(&fsnotify_grp_mutex);
 134         __fsnotify_evict_group(group);
 135         mutex_unlock(&fsnotify_grp_mutex);
 136 }
 137
 138 /*
 139  * Drop a reference to a group.  Free it if it's through.
 140  */
 141 void fsnotify_put_group(struct fsnotify_group *group)
 142 {
 143         if (!atomic_dec_and_mutex_lock(&group->refcnt, &fsnotify_grp_mutex))
 144                 return;
 145
 146         /*
 147          * OK, now we know that there's no other users *and* we hold mutex,
 148          * so no new references will appear
 149          */
 150         __fsnotify_evict_group(group);
 151
 152         /*
 153          * now it's off the list, so the only thing we might care about is
 154          * srcu access....
 155          */
 156         mutex_unlock(&fsnotify_grp_mutex);
 157         synchronize_srcu(&fsnotify_grp_srcu);
 158
 159         /* and now it is really dead. _Nothing_ could be seeing it */
 160         fsnotify_recalc_global_mask();
 161         fsnotify_destroy_group(group);
 162 }
 163
 164 /*
 165  * Either finds an existing group which matches the group_num, mask, and ops or
 166  * creates a new group and adds it to the global group list.  In either case we
 167  * take a reference for the group returned.
 168  */
 169 struct fsnotify_group *fsnotify_obtain_group(__u32 mask,
 170                                              const struct fsnotify_ops *ops)
 171 {
 172         struct fsnotify_group *group;
 173
 174         /* very low use, simpler locking if we just always alloc */
 175         group = kzalloc(sizeof(struct fsnotify_group), GFP_KERNEL);
 176         if (!group)
 177                 return ERR_PTR(-ENOMEM);
 178
 179         atomic_set(&group->refcnt, 1);
 180
 181         group->on_group_list = 0;
 182         group->mask = mask;
 183
 184         mutex_init(&group->notification_mutex);
 185         INIT_LIST_HEAD(&group->notification_list);
 186         init_waitqueue_head(&group->notification_waitq);
 187         group->q_len = 0;
 188         group->max_events = UINT_MAX;
 189
 190         spin_lock_init(&group->mark_lock);
 191         atomic_set(&group->num_marks, 0);
 192         INIT_LIST_HEAD(&group->mark_entries);
 193
 194         group->ops = ops;
 195
 196         mutex_lock(&fsnotify_grp_mutex);
 197
 198         /* group not found, add a new one */
 199         list_add_rcu(&group->group_list, &fsnotify_groups);
 200         group->on_group_list = 1;
 201         /* being on the fsnotify_groups list holds one num_marks */
 202         atomic_inc(&group->num_marks);
 203
 204         mutex_unlock(&fsnotify_grp_mutex);
 205
 206         if (mask)
 207                 fsnotify_recalc_global_mask();
 208
 209         return group;
 210 }