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_inode_groups);
  37 /* bitwise OR of all events (FS_*) interesting to some group on this system */
  38 __u32 fsnotify_inode_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_inode_groups, inode_group_list)
  52                 mask |= group->mask;
  53         srcu_read_unlock(&fsnotify_grp_srcu, idx);
  54         fsnotify_inode_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 void fsnotify_add_inode_group(struct fsnotify_group *group)
  81 {
  82         mutex_lock(&fsnotify_grp_mutex);
  83
  84         if (!group->on_inode_group_list)
  85                 list_add_tail_rcu(&group->inode_group_list, &fsnotify_inode_groups);
  86         group->on_inode_group_list = 1;
  87
  88         mutex_unlock(&fsnotify_grp_mutex);
  89 }
  90
  91 /*
  92  * Final freeing of a group
  93  */
  94 void fsnotify_final_destroy_group(struct fsnotify_group *group)
  95 {
  96         /* clear the notification queue of all events */
  97         fsnotify_flush_notify(group);
  98
  99         if (group->ops->free_group_priv)
 100                 group->ops->free_group_priv(group);
 101
 102         kfree(group);
 103 }
 104
 105 /*
 106  * Trying to get rid of a group.  We need to first get rid of any outstanding
 107  * allocations and then free the group.  Remember that fsnotify_clear_marks_by_group
 108  * could miss marks that are being freed by inode and those marks could still
 109  * hold a reference to this group (via group->num_marks)  If we get into that
 110  * situtation, the fsnotify_final_destroy_group will get called when that final
 111  * mark is freed.
 112  */
 113 static void fsnotify_destroy_group(struct fsnotify_group *group)
 114 {
 115         /* clear all inode mark entries for this group */
 116         fsnotify_clear_marks_by_group(group);
 117
 118         /* past the point of no return, matches the initial value of 1 */
 119         if (atomic_dec_and_test(&group->num_marks))
 120                 fsnotify_final_destroy_group(group);
 121 }
 122
 123 /*
 124  * Remove this group from the global list of groups that will get events
 125  * this can be done even if there are still references and things still using
 126  * this group.  This just stops the group from getting new events.
 127  */
 128 static void __fsnotify_evict_group(struct fsnotify_group *group)
 129 {
 130         BUG_ON(!mutex_is_locked(&fsnotify_grp_mutex));
 131
 132         if (group->on_inode_group_list)
 133                 list_del_rcu(&group->inode_group_list);
 134         group->on_inode_group_list = 0;
 135 }
 136
 137 /*
 138  * Called when a group is no longer interested in getting events.  This can be
 139  * used if a group is misbehaving or if for some reason a group should no longer
 140  * get any filesystem events.
 141  */
 142 void fsnotify_evict_group(struct fsnotify_group *group)
 143 {
 144         mutex_lock(&fsnotify_grp_mutex);
 145         __fsnotify_evict_group(group);
 146         mutex_unlock(&fsnotify_grp_mutex);
 147 }
 148
 149 /*
 150  * Drop a reference to a group.  Free it if it's through.
 151  */
 152 void fsnotify_put_group(struct fsnotify_group *group)
 153 {
 154         if (!atomic_dec_and_mutex_lock(&group->refcnt, &fsnotify_grp_mutex))
 155                 return;
 156
 157         /*
 158          * OK, now we know that there's no other users *and* we hold mutex,
 159          * so no new references will appear
 160          */
 161         __fsnotify_evict_group(group);
 162
 163         /*
 164          * now it's off the list, so the only thing we might care about is
 165          * srcu access....
 166          */
 167         mutex_unlock(&fsnotify_grp_mutex);
 168         synchronize_srcu(&fsnotify_grp_srcu);
 169
 170         /* and now it is really dead. _Nothing_ could be seeing it */
 171         fsnotify_recalc_global_mask();
 172         fsnotify_destroy_group(group);
 173 }
 174
 175 /*
 176  * Create a new fsnotify_group and hold a reference for the group returned.
 177  */
 178 struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
 179 {
 180         struct fsnotify_group *group;
 181
 182         group = kzalloc(sizeof(struct fsnotify_group), GFP_KERNEL);
 183         if (!group)
 184                 return ERR_PTR(-ENOMEM);
 185
 186         /* set to 0 when there a no external references to this group */
 187         atomic_set(&group->refcnt, 1);
 188         /*
 189          * hits 0 when there are no external references AND no marks for
 190          * this group
 191          */
 192         atomic_set(&group->num_marks, 1);
 193
 194         mutex_init(&group->notification_mutex);
 195         INIT_LIST_HEAD(&group->notification_list);
 196         init_waitqueue_head(&group->notification_waitq);
 197         group->max_events = UINT_MAX;
 198
 199         INIT_LIST_HEAD(&group->inode_group_list);
 200
 201         spin_lock_init(&group->mark_lock);
 202         INIT_LIST_HEAD(&group->mark_entries);
 203
 204         group->ops = ops;
 205
 206         return group;
 207 }