fs/notify/notification.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 /*
  20  * Basic idea behind the notification queue: An fsnotify group (like inotify)
  21  * sends the userspace notification about events asynchronously some time after
  22  * the event happened.  When inotify gets an event it will need to add that
  23  * event to the group notify queue.  Since a single event might need to be on
  24  * multiple group's notification queues we can't add the event directly to each
  25  * queue and instead add a small "event_holder" to each queue.  This event_holder
  26  * has a pointer back to the original event.  Since the majority of events are
  27  * going to end up on one, and only one, notification queue we embed one
  28  * event_holder into each event.  This means we have a single allocation instead
  29  * of always needing two.  If the embedded event_holder is already in use by
  30  * another group a new event_holder (from fsnotify_event_holder_cachep) will be
  31  * allocated and used.
  32  */
  33
  34 #include <linux/fs.h>
  35 #include <linux/init.h>
  36 #include <linux/kernel.h>
  37 #include <linux/list.h>
  38 #include <linux/module.h>
  39 #include <linux/mount.h>
  40 #include <linux/mutex.h>
  41 #include <linux/namei.h>
  42 #include <linux/path.h>
  43 #include <linux/slab.h>
  44 #include <linux/spinlock.h>
  45
  46 #include <linux/atomic.h>
  47
  48 #include <linux/fsnotify_backend.h>
  49 #include "fsnotify.h"
  50
  51 static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
  52
  53 /**
  54  * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
  55  * Called from fsnotify_move, which is inlined into filesystem modules.
  56  */
  57 u32 fsnotify_get_cookie(void)
  58 {
  59         return atomic_inc_return(&fsnotify_sync_cookie);
  60 }
  61 EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
  62
  63 /* return true if the notify queue is empty, false otherwise */
  64 bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
  65 {
  66         assert_spin_locked(&group->notification_lock);
  67         return list_empty(&group->notification_list) ? true : false;
  68 }
  69
  70 void fsnotify_destroy_event(struct fsnotify_group *group,
  71                             struct fsnotify_event *event)
  72 {
  73         /* Overflow events are per-group and we don't want to free them */
  74         if (!event || event->mask == FS_Q_OVERFLOW)
  75                 return;
  76         /*
  77          * If the event is still queued, we have a problem... Do an unreliable
  78          * lockless check first to avoid locking in the common case. The
  79          * locking may be necessary for permission events which got removed
  80          * from the list by a different CPU than the one freeing the event.
  81          */
  82         if (!list_empty(&event->list)) {
  83                 spin_lock(&group->notification_lock);
  84                 WARN_ON(!list_empty(&event->list));
  85                 spin_unlock(&group->notification_lock);
  86         }
  87         group->ops->free_event(event);
  88 }
  89
  90 /*
  91  * Add an event to the group notification queue.  The group can later pull this
  92  * event off the queue to deal with.  The function returns 0 if the event was
  93  * added to the queue, 1 if the event was merged with some other queued event,
  94  * 2 if the event was not queued - either the queue of events has overflown
  95  * or the group is shutting down.
  96  */
  97 int fsnotify_add_event(struct fsnotify_group *group,
  98                        struct fsnotify_event *event,
  99                        int (*merge)(struct list_head *,
 100                                     struct fsnotify_event *))
 101 {
 102         int ret = 0;
 103         struct list_head *list = &group->notification_list;
 104
 105         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 106
 107         spin_lock(&group->notification_lock);
 108
 109         if (group->shutdown) {
 110                 spin_unlock(&group->notification_lock);
 111                 return 2;
 112         }
 113
 114         if (event == group->overflow_event ||
 115             group->q_len >= group->max_events) {
 116                 ret = 2;
 117                 /* Queue overflow event only if it isn't already queued */
 118                 if (!list_empty(&group->overflow_event->list)) {
 119                         spin_unlock(&group->notification_lock);
 120                         return ret;
 121                 }
 122                 event = group->overflow_event;
 123                 goto queue;
 124         }
 125
 126         if (!list_empty(list) && merge) {
 127                 ret = merge(list, event);
 128                 if (ret) {
 129                         spin_unlock(&group->notification_lock);
 130                         return ret;
 131                 }
 132         }
 133
 134 queue:
 135         group->q_len++;
 136         list_add_tail(&event->list, list);
 137         spin_unlock(&group->notification_lock);
 138
 139         wake_up(&group->notification_waitq);
 140         kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
 141         return ret;
 142 }
 143
 144 /*
 145  * Remove and return the first event from the notification list.  It is the
 146  * responsibility of the caller to destroy the obtained event
 147  */
 148 struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
 149 {
 150         struct fsnotify_event *event;
 151
 152         assert_spin_locked(&group->notification_lock);
 153
 154         pr_debug("%s: group=%p\n", __func__, group);
 155
 156         event = list_first_entry(&group->notification_list,
 157                                  struct fsnotify_event, list);
 158         /*
 159          * We need to init list head for the case of overflow event so that
 160          * check in fsnotify_add_event() works
 161          */
 162         list_del_init(&event->list);
 163         group->q_len--;
 164
 165         return event;
 166 }
 167
 168 /*
 169  * This will not remove the event, that must be done with
 170  * fsnotify_remove_first_event()
 171  */
 172 struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
 173 {
 174         assert_spin_locked(&group->notification_lock);
 175
 176         return list_first_entry(&group->notification_list,
 177                                 struct fsnotify_event, list);
 178 }
 179
 180 /*
 181  * Called when a group is being torn down to clean up any outstanding
 182  * event notifications.
 183  */
 184 void fsnotify_flush_notify(struct fsnotify_group *group)
 185 {
 186         struct fsnotify_event *event;
 187
 188         spin_lock(&group->notification_lock);
 189         while (!fsnotify_notify_queue_is_empty(group)) {
 190                 event = fsnotify_remove_first_event(group);
 191                 spin_unlock(&group->notification_lock);
 192                 fsnotify_destroy_event(group, event);
 193                 spin_lock(&group->notification_lock);
 194         }
 195         spin_unlock(&group->notification_lock);
 196 }
 197
 198 /*
 199  * fsnotify_create_event - Allocate a new event which will be sent to each
 200  * group's handle_event function if the group was interested in this
 201  * particular event.
 202  *
 203  * @inode the inode which is supposed to receive the event (sometimes a
 204  *      parent of the inode to which the event happened.
 205  * @mask what actually happened.
 206  * @data pointer to the object which was actually affected
 207  * @data_type flag indication if the data is a file, path, inode, nothing...
 208  * @name the filename, if available
 209  */
 210 void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
 211                          u32 mask)
 212 {
 213         INIT_LIST_HEAD(&event->list);
 214         event->inode = inode;
 215         event->mask = mask;
 216 }