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         BUG_ON(!mutex_is_locked(&group->notification_mutex));
  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         group->ops->free_event(event);
  78 }
  79
  80 /*
  81  * Add an event to the group notification queue.  The group can later pull this
  82  * event off the queue to deal with.  The function returns 0 if the event was
  83  * added to the queue, 1 if the event was merged with some other queued event.
  84  */
  85 int fsnotify_add_notify_event(struct fsnotify_group *group,
  86                               struct fsnotify_event *event,
  87                               int (*merge)(struct list_head *,
  88                                            struct fsnotify_event *))
  89 {
  90         int ret = 0;
  91         struct list_head *list = &group->notification_list;
  92
  93         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
  94
  95         mutex_lock(&group->notification_mutex);
  96
  97         if (group->q_len >= group->max_events) {
  98                 /* Queue overflow event only if it isn't already queued */
  99                 if (list_empty(&group->overflow_event.list))
 100                         event = &group->overflow_event;
 101                 ret = 1;
 102         }
 103
 104         if (!list_empty(list) && merge) {
 105                 ret = merge(list, event);
 106                 if (ret) {
 107                         mutex_unlock(&group->notification_mutex);
 108                         return ret;
 109                 }
 110         }
 111
 112         group->q_len++;
 113         list_add_tail(&event->list, list);
 114         mutex_unlock(&group->notification_mutex);
 115
 116         wake_up(&group->notification_waitq);
 117         kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
 118         return ret;
 119 }
 120
 121 /*
 122  * Remove and return the first event from the notification list.  It is the
 123  * responsibility of the caller to destroy the obtained event
 124  */
 125 struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
 126 {
 127         struct fsnotify_event *event;
 128
 129         BUG_ON(!mutex_is_locked(&group->notification_mutex));
 130
 131         pr_debug("%s: group=%p\n", __func__, group);
 132
 133         event = list_first_entry(&group->notification_list,
 134                                  struct fsnotify_event, list);
 135         list_del(&event->list);
 136         group->q_len--;
 137
 138         return event;
 139 }
 140
 141 /*
 142  * This will not remove the event, that must be done with fsnotify_remove_notify_event()
 143  */
 144 struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
 145 {
 146         BUG_ON(!mutex_is_locked(&group->notification_mutex));
 147
 148         return list_first_entry(&group->notification_list,
 149                                 struct fsnotify_event, list);
 150 }
 151
 152 /*
 153  * Called when a group is being torn down to clean up any outstanding
 154  * event notifications.
 155  */
 156 void fsnotify_flush_notify(struct fsnotify_group *group)
 157 {
 158         struct fsnotify_event *event;
 159
 160         mutex_lock(&group->notification_mutex);
 161         while (!fsnotify_notify_queue_is_empty(group)) {
 162                 event = fsnotify_remove_notify_event(group);
 163                 fsnotify_destroy_event(group, event);
 164         }
 165         mutex_unlock(&group->notification_mutex);
 166 }
 167
 168 /*
 169  * fsnotify_create_event - Allocate a new event which will be sent to each
 170  * group's handle_event function if the group was interested in this
 171  * particular event.
 172  *
 173  * @inode the inode which is supposed to receive the event (sometimes a
 174  *      parent of the inode to which the event happened.
 175  * @mask what actually happened.
 176  * @data pointer to the object which was actually affected
 177  * @data_type flag indication if the data is a file, path, inode, nothing...
 178  * @name the filename, if available
 179  */
 180 void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
 181                          u32 mask)
 182 {
 183         INIT_LIST_HEAD(&event->list);
 184         event->inode = inode;
 185         event->mask = mask;
 186 }