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 /* If the event is still queued, we have a problem... */ 77 WARN_ON(!list_empty(&event->list)); 78 group->ops->free_event(event); 79 } 80 81 /* 82 * Add an event to the group notification queue. The group can later pull this 83 * event off the queue to deal with. The function returns 0 if the event was 84 * added to the queue, 1 if the event was merged with some other queued event, 85 * 2 if the event was not queued - either the queue of events has overflown 86 * or the group is shutting down. 87 */ 88 int fsnotify_add_event(struct fsnotify_group *group, 89 struct fsnotify_event *event, 90 int (*merge)(struct list_head *, 91 struct fsnotify_event *)) 92 { 93 int ret = 0; 94 struct list_head *list = &group->notification_list; 95 96 pr_debug("%s: group=%p event=%p\n", __func__, group, event); 97 98 mutex_lock(&group->notification_mutex); 99 100 if (group->shutdown) { 101 mutex_unlock(&group->notification_mutex); 102 return 2; 103 } 104 105 if (group->q_len >= group->max_events) { 106 ret = 2; 107 /* Queue overflow event only if it isn't already queued */ 108 if (!list_empty(&group->overflow_event->list)) { 109 mutex_unlock(&group->notification_mutex); 110 return ret; 111 } 112 event = group->overflow_event; 113 goto queue; 114 } 115 116 if (!list_empty(list) && merge) { 117 ret = merge(list, event); 118 if (ret) { 119 mutex_unlock(&group->notification_mutex); 120 return ret; 121 } 122 } 123 124 queue: 125 group->q_len++; 126 list_add_tail(&event->list, list); 127 mutex_unlock(&group->notification_mutex); 128 129 wake_up(&group->notification_waitq); 130 kill_fasync(&group->fsn_fa, SIGIO, POLL_IN); 131 return ret; 132 } 133 134 /* 135 * Remove and return the first event from the notification list. It is the 136 * responsibility of the caller to destroy the obtained event 137 */ 138 struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group) 139 { 140 struct fsnotify_event *event; 141 142 BUG_ON(!mutex_is_locked(&group->notification_mutex)); 143 144 pr_debug("%s: group=%p\n", __func__, group); 145 146 event = list_first_entry(&group->notification_list, 147 struct fsnotify_event, list); 148 /* 149 * We need to init list head for the case of overflow event so that 150 * check in fsnotify_add_event() works 151 */ 152 list_del_init(&event->list); 153 group->q_len--; 154 155 return event; 156 } 157 158 /* 159 * This will not remove the event, that must be done with 160 * fsnotify_remove_first_event() 161 */ 162 struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group) 163 { 164 BUG_ON(!mutex_is_locked(&group->notification_mutex)); 165 166 return list_first_entry(&group->notification_list, 167 struct fsnotify_event, list); 168 } 169 170 /* 171 * Called when a group is being torn down to clean up any outstanding 172 * event notifications. 173 */ 174 void fsnotify_flush_notify(struct fsnotify_group *group) 175 { 176 struct fsnotify_event *event; 177 178 mutex_lock(&group->notification_mutex); 179 while (!fsnotify_notify_queue_is_empty(group)) { 180 event = fsnotify_remove_first_event(group); 181 fsnotify_destroy_event(group, event); 182 } 183 mutex_unlock(&group->notification_mutex); 184 } 185 186 /* 187 * fsnotify_create_event - Allocate a new event which will be sent to each 188 * group's handle_event function if the group was interested in this 189 * particular event. 190 * 191 * @inode the inode which is supposed to receive the event (sometimes a 192 * parent of the inode to which the event happened. 193 * @mask what actually happened. 194 * @data pointer to the object which was actually affected 195 * @data_type flag indication if the data is a file, path, inode, nothing... 196 * @name the filename, if available 197 */ 198 void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode, 199 u32 mask) 200 { 201 INIT_LIST_HEAD(&event->list); 202 event->inode = inode; 203 event->mask = mask; 204 } 205