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TOMOYO Linux Cross Reference
Linux/fs/notify/notification.c

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  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 (group->q_len >= group->max_events) {
115                 ret = 2;
116                 /* Queue overflow event only if it isn't already queued */
117                 if (!list_empty(&group->overflow_event->list)) {
118                         spin_unlock(&group->notification_lock);
119                         return ret;
120                 }
121                 event = group->overflow_event;
122                 goto queue;
123         }
124 
125         if (!list_empty(list) && merge) {
126                 ret = merge(list, event);
127                 if (ret) {
128                         spin_unlock(&group->notification_lock);
129                         return ret;
130                 }
131         }
132 
133 queue:
134         group->q_len++;
135         list_add_tail(&event->list, list);
136         spin_unlock(&group->notification_lock);
137 
138         wake_up(&group->notification_waitq);
139         kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
140         return ret;
141 }
142 
143 /*
144  * Remove and return the first event from the notification list.  It is the
145  * responsibility of the caller to destroy the obtained event
146  */
147 struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
148 {
149         struct fsnotify_event *event;
150 
151         assert_spin_locked(&group->notification_lock);
152 
153         pr_debug("%s: group=%p\n", __func__, group);
154 
155         event = list_first_entry(&group->notification_list,
156                                  struct fsnotify_event, list);
157         /*
158          * We need to init list head for the case of overflow event so that
159          * check in fsnotify_add_event() works
160          */
161         list_del_init(&event->list);
162         group->q_len--;
163 
164         return event;
165 }
166 
167 /*
168  * This will not remove the event, that must be done with
169  * fsnotify_remove_first_event()
170  */
171 struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
172 {
173         assert_spin_locked(&group->notification_lock);
174 
175         return list_first_entry(&group->notification_list,
176                                 struct fsnotify_event, list);
177 }
178 
179 /*
180  * Called when a group is being torn down to clean up any outstanding
181  * event notifications.
182  */
183 void fsnotify_flush_notify(struct fsnotify_group *group)
184 {
185         struct fsnotify_event *event;
186 
187         spin_lock(&group->notification_lock);
188         while (!fsnotify_notify_queue_is_empty(group)) {
189                 event = fsnotify_remove_first_event(group);
190                 spin_unlock(&group->notification_lock);
191                 fsnotify_destroy_event(group, event);
192                 spin_lock(&group->notification_lock);
193         }
194         spin_unlock(&group->notification_lock);
195 }
196 
197 /*
198  * fsnotify_create_event - Allocate a new event which will be sent to each
199  * group's handle_event function if the group was interested in this
200  * particular event.
201  *
202  * @inode the inode which is supposed to receive the event (sometimes a
203  *      parent of the inode to which the event happened.
204  * @mask what actually happened.
205  * @data pointer to the object which was actually affected
206  * @data_type flag indication if the data is a file, path, inode, nothing...
207  * @name the filename, if available
208  */
209 void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode,
210                          u32 mask)
211 {
212         INIT_LIST_HEAD(&event->list);
213         event->inode = inode;
214         event->mask = mask;
215 }
216 

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