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  * 2 if the queue of events has overflown.
  85  */
  86 int fsnotify_add_notify_event(struct fsnotify_group *group,
  87                               struct fsnotify_event *event,
  88                               int (*merge)(struct list_head *,
  89                                            struct fsnotify_event *))
  90 {
  91         int ret = 0;
  92         struct list_head *list = &group->notification_list;
  93
  94         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
  95
  96         mutex_lock(&group->notification_mutex);
  97
  98         if (group->q_len >= group->max_events) {
  99                 ret = 2;
 100                 /* Queue overflow event only if it isn't already queued */
 101                 if (!list_empty(&group->overflow_event->list)) {
 102                         mutex_unlock(&group->notification_mutex);
 103                         return ret;
 104                 }
 105                 event = group->overflow_event;
 106                 goto queue;
 107         }
 108
 109         if (!list_empty(list) && merge) {
 110                 ret = merge(list, event);
 111                 if (ret) {
 112                         mutex_unlock(&group->notification_mutex);
 113                         return ret;
 114                 }
 115         }
 116
 117 queue:
 118         group->q_len++;
 119         list_add_tail(&event->list, list);
 120         mutex_unlock(&group->notification_mutex);
 121
 122         wake_up(&group->notification_waitq);
 123         kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
 124         return ret;
 125 }
 126
 127 /*
 128  * Remove and return the first event from the notification list.  It is the
 129  * responsibility of the caller to destroy the obtained event
 130  */
 131 struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
 132 {
 133         struct fsnotify_event *event;
 134
 135         BUG_ON(!mutex_is_locked(&group->notification_mutex));
 136
 137         pr_debug("%s: group=%p\n", __func__, group);
 138
 139         event = list_first_entry(&group->notification_list,
 140                                  struct fsnotify_event, list);
 141         /*
 142          * We need to init list head for the case of overflow event so that
 143          * check in fsnotify_add_notify_events() works
 144          */
 145         list_del_init(&event->list);
 146         group->q_len--;
 147
 148         return event;
 149 }
 150
 151 /*
 152  * This will not remove the event, that must be done with fsnotify_remove_notify_event()
 153  */
 154 struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
 155 {
 156         BUG_ON(!mutex_is_locked(&group->notification_mutex));
 157
 158         return list_first_entry(&group->notification_list,
 159                                 struct fsnotify_event, list);
 160 }
 161
 162 /*
 163  * Called when a group is being torn down to clean up any outstanding
 164  * event notifications.
 165  */
 166 void fsnotify_flush_notify(struct fsnotify_group *group)
 167 {
 168         struct fsnotify_event *event;
 169
 170         mutex_lock(&group->notification_mutex);
 171         while (!fsnotify_notify_queue_is_empty(group)) {
 172                 event = fsnotify_remove_notify_event(group);
 173                 fsnotify_destroy_event(group, event);
 174         }
 175         mutex_unlock(&group->notification_mutex);
 176 }
 177
 178 /*
 179  * fsnotify_create_event - Allocate a new event which will be sent to each
 180  * group's handle_event function if the group was interested in this
 181  * particular event.
 182  *
 183  * @inode the inode which is supposed to receive the event (sometimes a
 184  *      parent of the inode to which the event happened.
 185  * @mask what actually happened.
 186  * @data pointer to the object which was actually affected
 187  * @data_type flag indication if the data is a file, path, inode, nothing...
 188  * @name the filename, if available
 189  */
 190 void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
 191                          u32 mask)
 192 {
 193         INIT_LIST_HEAD(&event->list);
 194         event->inode = inode;
 195         event->mask = mask;
 196 }