/* * Copyright (C) 2008 Red Hat, Inc., Eric Paris * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2, or (at your option) * any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; see the file COPYING. If not, write to * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */ /* * Basic idea behind the notification queue: An fsnotify group (like inotify) * sends the userspace notification about events asyncronously some time after * the event happened. When inotify gets an event it will need to add that * event to the group notify queue. Since a single event might need to be on * multiple group's notification queues we can't add the event directly to each * queue and instead add a small "event_holder" to each queue. This event_holder * has a pointer back to the original event. Since the majority of events are * going to end up on one, and only one, notification queue we embed one * event_holder into each event. This means we have a single allocation instead * of always needing two. If the embedded event_holder is already in use by * another group a new event_holder (from fsnotify_event_holder_cachep) will be * allocated and used. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include "fsnotify.h" static struct kmem_cache *fsnotify_event_cachep; static struct kmem_cache *fsnotify_event_holder_cachep; /* * This is a magic event we send when the q is too full. Since it doesn't * hold real event information we just keep one system wide and use it any time * it is needed. It's refcnt is set 1 at kernel init time and will never * get set to 0 so it will never get 'freed' */ static struct fsnotify_event q_overflow_event; static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0); /** * fsnotify_get_cookie - return a unique cookie for use in synchronizing events. * Called from fsnotify_move, which is inlined into filesystem modules. */ u32 fsnotify_get_cookie(void) { return atomic_inc_return(&fsnotify_sync_cookie); } EXPORT_SYMBOL_GPL(fsnotify_get_cookie); /* return true if the notify queue is empty, false otherwise */ bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group) { BUG_ON(!mutex_is_locked(&group->notification_mutex)); return list_empty(&group->notification_list) ? true : false; } void fsnotify_get_event(struct fsnotify_event *event) { atomic_inc(&event->refcnt); } void fsnotify_put_event(struct fsnotify_event *event) { if (!event) return; if (atomic_dec_and_test(&event->refcnt)) { if (event->data_type == FSNOTIFY_EVENT_PATH) path_put(&event->path); kfree(event->file_name); kmem_cache_free(fsnotify_event_cachep, event); } } struct fsnotify_event_holder *fsnotify_alloc_event_holder(void) { return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL); } void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder) { kmem_cache_free(fsnotify_event_holder_cachep, holder); } /* * check if 2 events contain the same information. */ static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new) { if ((old->mask == new->mask) && (old->to_tell == new->to_tell) && (old->data_type == new->data_type)) { switch (old->data_type) { case (FSNOTIFY_EVENT_INODE): if (old->inode == new->inode) return true; break; case (FSNOTIFY_EVENT_PATH): if ((old->path.mnt == new->path.mnt) && (old->path.dentry == new->path.dentry)) return true; case (FSNOTIFY_EVENT_NONE): return true; }; } return false; } /* * Add an event to the group notification queue. The group can later pull this * event off the queue to deal with. If the event is successfully added to the * group's notification queue, a reference is taken on event. */ int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event) { struct fsnotify_event_holder *holder = NULL; struct list_head *list = &group->notification_list; struct fsnotify_event_holder *last_holder; struct fsnotify_event *last_event; /* * There is one fsnotify_event_holder embedded inside each fsnotify_event. * Check if we expect to be able to use that holder. If not alloc a new * holder. * For the overflow event it's possible that something will use the in * event holder before we get the lock so we may need to jump back and * alloc a new holder, this can't happen for most events... */ if (!list_empty(&event->holder.event_list)) { alloc_holder: holder = fsnotify_alloc_event_holder(); if (!holder) return -ENOMEM; } mutex_lock(&group->notification_mutex); if (group->q_len >= group->max_events) event = &q_overflow_event; spin_lock(&event->lock); if (list_empty(&event->holder.event_list)) { if (unlikely(holder)) fsnotify_destroy_event_holder(holder); holder = &event->holder; } else if (unlikely(!holder)) { /* between the time we checked above and got the lock the in * event holder was used, go back and get a new one */ spin_unlock(&event->lock); mutex_unlock(&group->notification_mutex); goto alloc_holder; } if (!list_empty(list)) { last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list); last_event = last_holder->event; if (event_compare(last_event, event)) { spin_unlock(&event->lock); mutex_unlock(&group->notification_mutex); if (holder != &event->holder) fsnotify_destroy_event_holder(holder); return 0; } } group->q_len++; holder->event = event; fsnotify_get_event(event); list_add_tail(&holder->event_list, list); spin_unlock(&event->lock); mutex_unlock(&group->notification_mutex); wake_up(&group->notification_waitq); return 0; } /* * Remove and return the first event from the notification list. There is a * reference held on this event since it was on the list. It is the responsibility * of the caller to drop this reference. */ struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group) { struct fsnotify_event *event; struct fsnotify_event_holder *holder; BUG_ON(!mutex_is_locked(&group->notification_mutex)); holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list); event = holder->event; spin_lock(&event->lock); holder->event = NULL; list_del_init(&holder->event_list); spin_unlock(&event->lock); /* event == holder means we are referenced through the in event holder */ if (holder != &event->holder) fsnotify_destroy_event_holder(holder); group->q_len--; return event; } /* * This will not remove the event, that must be done with fsnotify_remove_notify_event() */ struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group) { struct fsnotify_event *event; struct fsnotify_event_holder *holder; BUG_ON(!mutex_is_locked(&group->notification_mutex)); holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list); event = holder->event; return event; } /* * Called when a group is being torn down to clean up any outstanding * event notifications. */ void fsnotify_flush_notify(struct fsnotify_group *group) { struct fsnotify_event *event; mutex_lock(&group->notification_mutex); while (!fsnotify_notify_queue_is_empty(group)) { event = fsnotify_remove_notify_event(group); fsnotify_put_event(event); /* matches fsnotify_add_notify_event */ } mutex_unlock(&group->notification_mutex); } static void initialize_event(struct fsnotify_event *event) { event->holder.event = NULL; INIT_LIST_HEAD(&event->holder.event_list); atomic_set(&event->refcnt, 1); spin_lock_init(&event->lock); event->path.dentry = NULL; event->path.mnt = NULL; event->inode = NULL; event->data_type = FSNOTIFY_EVENT_NONE; event->to_tell = NULL; event->file_name = NULL; event->name_len = 0; event->sync_cookie = 0; } /* * fsnotify_create_event - Allocate a new event which will be sent to each * group's handle_event function if the group was interested in this * particular event. * * @to_tell the inode which is supposed to receive the event (sometimes a * parent of the inode to which the event happened. * @mask what actually happened. * @data pointer to the object which was actually affected * @data_type flag indication if the data is a file, path, inode, nothing... * @name the filename, if available */ struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data, int data_type, const char *name, u32 cookie) { struct fsnotify_event *event; event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL); if (!event) return NULL; initialize_event(event); if (name) { event->file_name = kstrdup(name, GFP_KERNEL); if (!event->file_name) { kmem_cache_free(fsnotify_event_cachep, event); return NULL; } event->name_len = strlen(event->file_name); } event->sync_cookie = cookie; event->to_tell = to_tell; switch (data_type) { case FSNOTIFY_EVENT_FILE: { struct file *file = data; struct path *path = &file->f_path; event->path.dentry = path->dentry; event->path.mnt = path->mnt; path_get(&event->path); event->data_type = FSNOTIFY_EVENT_PATH; break; } case FSNOTIFY_EVENT_PATH: { struct path *path = data; event->path.dentry = path->dentry; event->path.mnt = path->mnt; path_get(&event->path); event->data_type = FSNOTIFY_EVENT_PATH; break; } case FSNOTIFY_EVENT_INODE: event->inode = data; event->data_type = FSNOTIFY_EVENT_INODE; break; case FSNOTIFY_EVENT_NONE: event->inode = NULL; event->path.dentry = NULL; event->path.mnt = NULL; break; default: BUG(); } event->mask = mask; return event; } __init int fsnotify_notification_init(void) { fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC); fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC); initialize_event(&q_overflow_event); q_overflow_event.mask = FS_Q_OVERFLOW; return 0; } subsys_initcall(fsnotify_notification_init);