/* * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com> * * 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 <linux/fs.h> #include <linux/init.h> #include <linux/kernel.h> #include <linux/list.h> #include <linux/module.h> #include <linux/mount.h> #include <linux/mutex.h> #include <linux/namei.h> #include <linux/path.h> #include <linux/slab.h> #include <linux/spinlock.h> #include <asm/atomic.h> #include <linux/fsnotify_backend.h> #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)) { pr_debug("%s: event=%p\n", __func__, event); if (event->data_type == FSNOTIFY_EVENT_PATH) path_put(&event->path); BUG_ON(!list_empty(&event->private_data_list)); kfree(event->file_name); put_pid(event->tgid); 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) { if (holder) kmem_cache_free(fsnotify_event_holder_cachep, holder); } /* * Find the private data that the group previously attached to this event when * the group added the event to the notification queue (fsnotify_add_notify_event) */ struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event) { struct fsnotify_event_private_data *lpriv; struct fsnotify_event_private_data *priv = NULL; assert_spin_locked(&event->lock); list_for_each_entry(lpriv, &event->private_data_list, event_list) { if (lpriv->group == group) { priv = lpriv; list_del(&priv->event_list); break; } } return priv; } /* * 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. */ struct fsnotify_event *fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event, struct fsnotify_event_private_data *priv, struct fsnotify_event *(*merge)(struct list_head *, struct fsnotify_event *)) { struct fsnotify_event *return_event = NULL; struct fsnotify_event_holder *holder = NULL; struct list_head *list = &group->notification_list; pr_debug("%s: group=%p event=%p priv=%p\n", __func__, group, event, priv); /* * 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 ERR_PTR(-ENOMEM); } mutex_lock(&group->notification_mutex); if (group->q_len >= group->max_events) { event = q_overflow_event; /* * we need to return the overflow event * which means we need a ref */ fsnotify_get_event(event); return_event = event; /* sorry, no private data on the overflow event */ priv = NULL; } if (!list_empty(list) && merge) { struct fsnotify_event *tmp; tmp = merge(list, event); if (tmp) { mutex_unlock(&group->notification_mutex); if (return_event) fsnotify_put_event(return_event); if (holder != &event->holder) fsnotify_destroy_event_holder(holder); return tmp; } } 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); if (return_event) { fsnotify_put_event(return_event); return_event = NULL; } goto alloc_holder; } group->q_len++; holder->event = event; fsnotify_get_event(event); list_add_tail(&holder->event_list, list); if (priv) list_add_tail(&priv->event_list, &event->private_data_list); spin_unlock(&event->lock); mutex_unlock(&group->notification_mutex); wake_up(&group->notification_waitq); return return_event; } /* * 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)); pr_debug("%s: group=%p\n", __func__, group); 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; struct fsnotify_event_private_data *priv; mutex_lock(&group->notification_mutex); while (!fsnotify_notify_queue_is_empty(group)) { event = fsnotify_remove_notify_event(group); /* if they don't implement free_event_priv they better not have attached any */ if (group->ops->free_event_priv) { spin_lock(&event->lock); priv = fsnotify_remove_priv_from_event(group, event); spin_unlock(&event->lock); if (priv) group->ops->free_event_priv(priv); } fsnotify_put_event(event); /* matches fsnotify_add_notify_event */ } mutex_unlock(&group->notification_mutex); } static void initialize_event(struct fsnotify_event *event) { INIT_LIST_HEAD(&event->holder.event_list); atomic_set(&event->refcnt, 1); spin_lock_init(&event->lock); INIT_LIST_HEAD(&event->private_data_list); } /* * Caller damn well better be holding whatever mutex is protecting the * old_holder->event_list and the new_event must be a clean event which * cannot be found anywhere else in the kernel. */ int fsnotify_replace_event(struct fsnotify_event_holder *old_holder, struct fsnotify_event *new_event) { struct fsnotify_event *old_event = old_holder->event; struct fsnotify_event_holder *new_holder = &new_event->holder; enum event_spinlock_class { SPINLOCK_OLD, SPINLOCK_NEW, }; pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, new_event); /* * if the new_event's embedded holder is in use someone * screwed up and didn't give us a clean new event. */ BUG_ON(!list_empty(&new_holder->event_list)); spin_lock_nested(&old_event->lock, SPINLOCK_OLD); spin_lock_nested(&new_event->lock, SPINLOCK_NEW); new_holder->event = new_event; list_replace_init(&old_holder->event_list, &new_holder->event_list); spin_unlock(&new_event->lock); spin_unlock(&old_event->lock); /* event == holder means we are referenced through the in event holder */ if (old_holder != &old_event->holder) fsnotify_destroy_event_holder(old_holder); fsnotify_get_event(new_event); /* on the list take reference */ fsnotify_put_event(old_event); /* off the list, drop reference */ return 0; } struct fsnotify_event *fsnotify_clone_event(struct fsnotify_event *old_event) { struct fsnotify_event *event; event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL); if (!event) return NULL; pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, event); memcpy(event, old_event, sizeof(*event)); initialize_event(event); if (event->name_len) { event->file_name = kstrdup(old_event->file_name, GFP_KERNEL); if (!event->file_name) { kmem_cache_free(fsnotify_event_cachep, event); return NULL; } } event->tgid = get_pid(old_event->tgid); if (event->data_type == FSNOTIFY_EVENT_PATH) path_get(&event->path); return event; } /* * 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 unsigned char *name, u32 cookie, gfp_t gfp) { struct fsnotify_event *event; event = kmem_cache_zalloc(fsnotify_event_cachep, gfp); if (!event) return NULL; pr_debug("%s: event=%p to_tell=%p mask=%x data=%p data_type=%d\n", __func__, event, to_tell, mask, data, data_type); initialize_event(event); if (name) { event->file_name = kstrdup(name, gfp); if (!event->file_name) { kmem_cache_free(fsnotify_event_cachep, event); return NULL; } event->name_len = strlen(event->file_name); } event->tgid = get_pid(task_tgid(current)); event->sync_cookie = cookie; event->to_tell = to_tell; event->data_type = data_type; switch (data_type) { case FSNOTIFY_EVENT_PATH: { struct path *path = data; event->path.dentry = path->dentry; event->path.mnt = path->mnt; path_get(&event->path); break; } case FSNOTIFY_EVENT_INODE: event->inode = data; 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); q_overflow_event = fsnotify_create_event(NULL, FS_Q_OVERFLOW, NULL, FSNOTIFY_EVENT_NONE, NULL, 0, GFP_KERNEL); if (!q_overflow_event) panic("unable to allocate fsnotify q_overflow_event\n"); return 0; } subsys_initcall(fsnotify_notification_init);