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 queue of events has overflown. 86 */ 87 int fsnotify_add_event(struct fsnotify_group *group, 88 struct fsnotify_event *event, 89 int (*merge)(struct list_head *, 90 struct fsnotify_event *)) 91 { 92 int ret = 0; 93 struct list_head *list = &group->notification_list; 94 95 pr_debug("%s: group=%p event=%p\n", __func__, group, event); 96 97 mutex_lock(&group->notification_mutex); 98 99 if (group->q_len >= group->max_events) { 100 ret = 2; 101 /* Queue overflow event only if it isn't already queued */ 102 if (!list_empty(&group->overflow_event->list)) { 103 mutex_unlock(&group->notification_mutex); 104 return ret; 105 } 106 event = group->overflow_event; 107 goto queue; 108 } 109 110 if (!list_empty(list) && merge) { 111 ret = merge(list, event); 112 if (ret) { 113 mutex_unlock(&group->notification_mutex); 114 return ret; 115 } 116 } 117 118 queue: 119 group->q_len++; 120 list_add_tail(&event->list, list); 121 mutex_unlock(&group->notification_mutex); 122 123 wake_up(&group->notification_waitq); 124 kill_fasync(&group->fsn_fa, SIGIO, POLL_IN); 125 return ret; 126 } 127 128 /* 129 * Remove @event from group's notification queue. It is the responsibility of 130 * the caller to destroy the event. 131 */ 132 void fsnotify_remove_event(struct fsnotify_group *group, 133 struct fsnotify_event *event) 134 { 135 mutex_lock(&group->notification_mutex); 136 if (!list_empty(&event->list)) { 137 list_del_init(&event->list); 138 group->q_len--; 139 } 140 mutex_unlock(&group->notification_mutex); 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 BUG_ON(!mutex_is_locked(&group->notification_mutex)); 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 BUG_ON(!mutex_is_locked(&group->notification_mutex)); 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 mutex_lock(&group->notification_mutex); 188 while (!fsnotify_notify_queue_is_empty(group)) { 189 event = fsnotify_remove_first_event(group); 190 fsnotify_destroy_event(group, event); 191 } 192 mutex_unlock(&group->notification_mutex); 193 } 194 195 /* 196 * fsnotify_create_event - Allocate a new event which will be sent to each 197 * group's handle_event function if the group was interested in this 198 * particular event. 199 * 200 * @inode the inode which is supposed to receive the event (sometimes a 201 * parent of the inode to which the event happened. 202 * @mask what actually happened. 203 * @data pointer to the object which was actually affected 204 * @data_type flag indication if the data is a file, path, inode, nothing... 205 * @name the filename, if available 206 */ 207 void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode, 208 u32 mask) 209 { 210 INIT_LIST_HEAD(&event->list); 211 event->inode = inode; 212 event->mask = mask; 213 } 214