/*
   *  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 <linux/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
  ", __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
  ", __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
  ", __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
  ", __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
  ", __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
  ",
  		 __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
  ");

  
  	return 0;
  }
  subsys_initcall(fsnotify_notification_init);