/*
   * fs/inotify.c - inode-based file event notifications
   *
   * Authors:
   *	John McCutchan	<ttb@tentacle.dhs.org>
   *	Robert Love	<rml@novell.com>
   *

   * Kernel API added by: Amy Griffis <amy.griffis@hp.com>
   *

   * Copyright (C) 2005 John McCutchan

   * Copyright 2006 Hewlett-Packard Development Company, L.P.

   *
   * 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.
   */
  
  #include <linux/module.h>
  #include <linux/kernel.h>

  #include <linux/spinlock.h>
  #include <linux/idr.h>
  #include <linux/slab.h>
  #include <linux/fs.h>

  #include <linux/init.h>
  #include <linux/list.h>
  #include <linux/writeback.h>
  #include <linux/inotify.h>

  
  static atomic_t inotify_cookie;

  /*
   * Lock ordering:
   *
   * dentry->d_lock (used to keep d_move() away from dentry->d_parent)

   * iprune_mutex (synchronize shrink_icache_memory())

   * 	inode_lock (protects the super_block->s_inodes list)

   * 	inode->inotify_mutex (protects inode->inotify_watches and watches->i_list)

   * 		inotify_handle->mutex (protects inotify_handle and watches->h_list)
   *
   * The inode->inotify_mutex and inotify_handle->mutex and held during execution
   * of a caller's event handler.  Thus, the caller must not hold any locks
   * taken in their event handler while calling any of the published inotify
   * interfaces.

   */
  
  /*

   * Lifetimes of the three main data structures--inotify_handle, inode, and

   * inotify_watch--are managed by reference count.
   *

   * inotify_handle: Lifetime is from inotify_init() to inotify_destroy().
   * Additional references can bump the count via get_inotify_handle() and drop
   * the count via put_inotify_handle().

   *

   * inotify_watch: for inotify's purposes, lifetime is from inotify_add_watch()
   * to remove_watch_no_event().  Additional references can bump the count via
   * get_inotify_watch() and drop the count via put_inotify_watch().  The caller
   * is reponsible for the final put after receiving IN_IGNORED, or when using
   * IN_ONESHOT after receiving the first event.  Inotify does the final put if
   * inotify_destroy() is called.

   *
   * inode: Pinned so long as the inode is associated with a watch, from

   * inotify_add_watch() to the final put_inotify_watch().

   */
  
  /*

   * struct inotify_handle - represents an inotify instance

   *

   * This structure is protected by the mutex 'mutex'.

   */

  struct inotify_handle {

  	struct idr		idr;		/* idr mapping wd -> watch */

  	struct mutex		mutex;		/* protects this bad boy */

  	struct list_head	watches;	/* list of watches */
  	atomic_t		count;		/* reference count */

  	u32			last_wd;	/* the last wd allocated */

  	const struct inotify_operations *in_ops; /* inotify caller operations */

  };

  static inline void get_inotify_handle(struct inotify_handle *ih)

  {

  	atomic_inc(&ih->count);

  }

  static inline void put_inotify_handle(struct inotify_handle *ih)

  {

  	if (atomic_dec_and_test(&ih->count)) {
  		idr_destroy(&ih->idr);
  		kfree(ih);

  	}
  }

  /**
   * get_inotify_watch - grab a reference to an inotify_watch
   * @watch: watch to grab
   */
  void get_inotify_watch(struct inotify_watch *watch)

  {
  	atomic_inc(&watch->count);
  }

  EXPORT_SYMBOL_GPL(get_inotify_watch);

  /**

   * put_inotify_watch - decrements the ref count on a given watch.  cleans up

   * watch references if the count reaches zero.  inotify_watch is freed by
   * inotify callers via the destroy_watch() op.
   * @watch: watch to release

   */

  void put_inotify_watch(struct inotify_watch *watch)

  {
  	if (atomic_dec_and_test(&watch->count)) {

  		struct inotify_handle *ih = watch->ih;

  		iput(watch->inode);
  		ih->in_ops->destroy_watch(watch);
  		put_inotify_handle(ih);

  	}
  }

  EXPORT_SYMBOL_GPL(put_inotify_watch);

  
  /*

   * inotify_handle_get_wd - returns the next WD for use by the given handle

   *

   * Callers must hold ih->mutex.  This function can sleep.

   */

  static int inotify_handle_get_wd(struct inotify_handle *ih,
  				 struct inotify_watch *watch)

  {
  	int ret;
  
  	do {

  		if (unlikely(!idr_pre_get(&ih->idr, GFP_KERNEL)))

  			return -ENOSPC;

  		ret = idr_get_new_above(&ih->idr, watch, ih->last_wd+1, &watch->wd);

  	} while (ret == -EAGAIN);

  	if (likely(!ret))
  		ih->last_wd = watch->wd;

  	return ret;

  }
  
  /*

   * inotify_inode_watched - returns nonzero if there are watches on this inode
   * and zero otherwise.  We call this lockless, we do not care if we race.
   */
  static inline int inotify_inode_watched(struct inode *inode)
  {
  	return !list_empty(&inode->inotify_watches);
  }
  
  /*
   * Get child dentry flag into synch with parent inode.
   * Flag should always be clear for negative dentrys.
   */
  static void set_dentry_child_flags(struct inode *inode, int watched)
  {
  	struct dentry *alias;
  
  	spin_lock(&dcache_lock);
  	list_for_each_entry(alias, &inode->i_dentry, d_alias) {
  		struct dentry *child;
  
  		list_for_each_entry(child, &alias->d_subdirs, d_u.d_child) {
  			if (!child->d_inode) {
  				WARN_ON(child->d_flags & DCACHE_INOTIFY_PARENT_WATCHED);
  				continue;
  			}
  			spin_lock(&child->d_lock);
  			if (watched) {
  				WARN_ON(child->d_flags &
  						DCACHE_INOTIFY_PARENT_WATCHED);
  				child->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
  			} else {
  				WARN_ON(!(child->d_flags &
  					DCACHE_INOTIFY_PARENT_WATCHED));
  				child->d_flags&=~DCACHE_INOTIFY_PARENT_WATCHED;
  			}
  			spin_unlock(&child->d_lock);
  		}
  	}
  	spin_unlock(&dcache_lock);
  }
  
  /*

   * inotify_find_handle - find the watch associated with the given inode and
   * handle

   *

   * Callers must hold inode->inotify_mutex.

   */

  static struct inotify_watch *inode_find_handle(struct inode *inode,
  					       struct inotify_handle *ih)

  {
  	struct inotify_watch *watch;
  
  	list_for_each_entry(watch, &inode->inotify_watches, i_list) {

  		if (watch->ih == ih)

  			return watch;
  	}
  
  	return NULL;
  }
  
  /*

   * remove_watch_no_event - remove watch without the IN_IGNORED event.

   *
   * Callers must hold both inode->inotify_mutex and ih->mutex.

   */
  static void remove_watch_no_event(struct inotify_watch *watch,

  				  struct inotify_handle *ih)

  {
  	list_del(&watch->i_list);

  	list_del(&watch->h_list);

  	if (!inotify_inode_watched(watch->inode))
  		set_dentry_child_flags(watch->inode, 0);

  	idr_remove(&ih->idr, watch->wd);

  }

  /**
   * inotify_remove_watch_locked - Remove a watch from both the handle and the
   * inode.  Sends the IN_IGNORED event signifying that the inode is no longer
   * watched.  May be invoked from a caller's event handler.
   * @ih: inotify handle associated with watch
   * @watch: watch to remove

   *

   * Callers must hold both inode->inotify_mutex and ih->mutex.

   */

  void inotify_remove_watch_locked(struct inotify_handle *ih,
  				 struct inotify_watch *watch)

  {

  	remove_watch_no_event(watch, ih);

  	ih->in_ops->handle_event(watch, watch->wd, IN_IGNORED, 0, NULL, NULL);

  }

  EXPORT_SYMBOL_GPL(inotify_remove_watch_locked);

  /* Kernel API for producing events */

  /*

   * inotify_d_instantiate - instantiate dcache entry for inode

   */

  void inotify_d_instantiate(struct dentry *entry, struct inode *inode)

  {

  	struct dentry *parent;
  
  	if (!inode)
  		return;
  
  	WARN_ON(entry->d_flags & DCACHE_INOTIFY_PARENT_WATCHED);
  	spin_lock(&entry->d_lock);
  	parent = entry->d_parent;

  	if (parent->d_inode && inotify_inode_watched(parent->d_inode))

  		entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
  	spin_unlock(&entry->d_lock);

  }

  /*
   * inotify_d_move - dcache entry has been moved
   */
  void inotify_d_move(struct dentry *entry)
  {
  	struct dentry *parent;
  
  	parent = entry->d_parent;
  	if (inotify_inode_watched(parent->d_inode))
  		entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
  	else
  		entry->d_flags &= ~DCACHE_INOTIFY_PARENT_WATCHED;
  }

  
  /**
   * inotify_inode_queue_event - queue an event to all watches on this inode
   * @inode: inode event is originating from
   * @mask: event mask describing this event
   * @cookie: cookie for synchronization, or zero
   * @name: filename, if any

   * @n_inode: inode associated with name

   */
  void inotify_inode_queue_event(struct inode *inode, u32 mask, u32 cookie,

  			       const char *name, struct inode *n_inode)

  {
  	struct inotify_watch *watch, *next;
  
  	if (!inotify_inode_watched(inode))
  		return;

  	mutex_lock(&inode->inotify_mutex);

  	list_for_each_entry_safe(watch, next, &inode->inotify_watches, i_list) {
  		u32 watch_mask = watch->mask;
  		if (watch_mask & mask) {

  			struct inotify_handle *ih= watch->ih;
  			mutex_lock(&ih->mutex);

  			if (watch_mask & IN_ONESHOT)

  				remove_watch_no_event(watch, ih);

  			ih->in_ops->handle_event(watch, watch->wd, mask, cookie,
  						 name, n_inode);

  			mutex_unlock(&ih->mutex);

  		}
  	}

  	mutex_unlock(&inode->inotify_mutex);

  }
  EXPORT_SYMBOL_GPL(inotify_inode_queue_event);
  
  /**
   * inotify_dentry_parent_queue_event - queue an event to a dentry's parent
   * @dentry: the dentry in question, we queue against this dentry's parent
   * @mask: event mask describing this event
   * @cookie: cookie for synchronization, or zero
   * @name: filename, if any
   */
  void inotify_dentry_parent_queue_event(struct dentry *dentry, u32 mask,
  				       u32 cookie, const char *name)
  {
  	struct dentry *parent;
  	struct inode *inode;

  	if (!(dentry->d_flags & DCACHE_INOTIFY_PARENT_WATCHED))

  		return;

  	spin_lock(&dentry->d_lock);
  	parent = dentry->d_parent;
  	inode = parent->d_inode;
  
  	if (inotify_inode_watched(inode)) {
  		dget(parent);
  		spin_unlock(&dentry->d_lock);

  		inotify_inode_queue_event(inode, mask, cookie, name,
  					  dentry->d_inode);

  		dput(parent);
  	} else
  		spin_unlock(&dentry->d_lock);
  }
  EXPORT_SYMBOL_GPL(inotify_dentry_parent_queue_event);
  
  /**
   * inotify_get_cookie - return a unique cookie for use in synchronizing events.
   */
  u32 inotify_get_cookie(void)
  {
  	return atomic_inc_return(&inotify_cookie);
  }
  EXPORT_SYMBOL_GPL(inotify_get_cookie);
  
  /**
   * inotify_unmount_inodes - an sb is unmounting.  handle any watched inodes.
   * @list: list of inodes being unmounted (sb->s_inodes)
   *
   * Called with inode_lock held, protecting the unmounting super block's list

   * of inodes, and with iprune_mutex held, keeping shrink_icache_memory() at bay.

   * We temporarily drop inode_lock, however, and CAN block.
   */
  void inotify_unmount_inodes(struct list_head *list)
  {
  	struct inode *inode, *next_i, *need_iput = NULL;
  
  	list_for_each_entry_safe(inode, next_i, list, i_sb_list) {
  		struct inotify_watch *watch, *next_w;
  		struct inode *need_iput_tmp;
  		struct list_head *watches;
  
  		/*
  		 * If i_count is zero, the inode cannot have any watches and
  		 * doing an __iget/iput with MS_ACTIVE clear would actually
  		 * evict all inodes with zero i_count from icache which is
  		 * unnecessarily violent and may in fact be illegal to do.
  		 */
  		if (!atomic_read(&inode->i_count))
  			continue;
  
  		/*
  		 * We cannot __iget() an inode in state I_CLEAR, I_FREEING, or
  		 * I_WILL_FREE which is fine because by that point the inode
  		 * cannot have any associated watches.
  		 */
  		if (inode->i_state & (I_CLEAR | I_FREEING | I_WILL_FREE))
  			continue;
  
  		need_iput_tmp = need_iput;
  		need_iput = NULL;

  		/* In case inotify_remove_watch_locked() drops a reference. */

  		if (inode != need_iput_tmp)
  			__iget(inode);
  		else
  			need_iput_tmp = NULL;
  		/* In case the dropping of a reference would nuke next_i. */
  		if ((&next_i->i_sb_list != list) &&
  				atomic_read(&next_i->i_count) &&
  				!(next_i->i_state & (I_CLEAR | I_FREEING |
  					I_WILL_FREE))) {
  			__iget(next_i);
  			need_iput = next_i;
  		}
  
  		/*
  		 * We can safely drop inode_lock here because we hold
  		 * references on both inode and next_i.  Also no new inodes
  		 * will be added since the umount has begun.  Finally,

  		 * iprune_mutex keeps shrink_icache_memory() away.

  		 */
  		spin_unlock(&inode_lock);
  
  		if (need_iput_tmp)
  			iput(need_iput_tmp);
  
  		/* for each watch, send IN_UNMOUNT and then remove it */

  		mutex_lock(&inode->inotify_mutex);

  		watches = &inode->inotify_watches;
  		list_for_each_entry_safe(watch, next_w, watches, i_list) {

  			struct inotify_handle *ih= watch->ih;
  			mutex_lock(&ih->mutex);
  			ih->in_ops->handle_event(watch, watch->wd, IN_UNMOUNT, 0,

  						 NULL, NULL);

  			inotify_remove_watch_locked(ih, watch);

  			mutex_unlock(&ih->mutex);

  		}

  		mutex_unlock(&inode->inotify_mutex);

  		iput(inode);		
  
  		spin_lock(&inode_lock);
  	}
  }
  EXPORT_SYMBOL_GPL(inotify_unmount_inodes);
  
  /**
   * inotify_inode_is_dead - an inode has been deleted, cleanup any watches
   * @inode: inode that is about to be removed
   */
  void inotify_inode_is_dead(struct inode *inode)
  {
  	struct inotify_watch *watch, *next;

  	mutex_lock(&inode->inotify_mutex);

  	list_for_each_entry_safe(watch, next, &inode->inotify_watches, i_list) {

  		struct inotify_handle *ih = watch->ih;
  		mutex_lock(&ih->mutex);

  		inotify_remove_watch_locked(ih, watch);

  		mutex_unlock(&ih->mutex);

  	}

  	mutex_unlock(&inode->inotify_mutex);

  }
  EXPORT_SYMBOL_GPL(inotify_inode_is_dead);

  /* Kernel Consumer API */

  /**
   * inotify_init - allocate and initialize an inotify instance
   * @ops: caller's inotify operations
   */
  struct inotify_handle *inotify_init(const struct inotify_operations *ops)

  {

  	struct inotify_handle *ih;

  	ih = kmalloc(sizeof(struct inotify_handle), GFP_KERNEL);
  	if (unlikely(!ih))
  		return ERR_PTR(-ENOMEM);

  	idr_init(&ih->idr);
  	INIT_LIST_HEAD(&ih->watches);
  	mutex_init(&ih->mutex);
  	ih->last_wd = 0;
  	ih->in_ops = ops;
  	atomic_set(&ih->count, 0);
  	get_inotify_handle(ih);

  	return ih;

  }

  EXPORT_SYMBOL_GPL(inotify_init);

  /**

   * inotify_init_watch - initialize an inotify watch
   * @watch: watch to initialize
   */
  void inotify_init_watch(struct inotify_watch *watch)
  {
  	INIT_LIST_HEAD(&watch->h_list);
  	INIT_LIST_HEAD(&watch->i_list);
  	atomic_set(&watch->count, 0);
  	get_inotify_watch(watch); /* initial get */
  }
  EXPORT_SYMBOL_GPL(inotify_init_watch);
  
  /**

   * inotify_destroy - clean up and destroy an inotify instance
   * @ih: inotify handle
   */
  void inotify_destroy(struct inotify_handle *ih)

  {

  	/*

  	 * Destroy all of the watches for this handle. Unfortunately, not very

  	 * pretty.  We cannot do a simple iteration over the list, because we
  	 * do not know the inode until we iterate to the watch.  But we need to

  	 * hold inode->inotify_mutex before ih->mutex.  The following works.

  	 */
  	while (1) {
  		struct inotify_watch *watch;
  		struct list_head *watches;
  		struct inode *inode;

  		mutex_lock(&ih->mutex);
  		watches = &ih->watches;

  		if (list_empty(watches)) {

  			mutex_unlock(&ih->mutex);

  			break;
  		}

  		watch = list_entry(watches->next, struct inotify_watch, h_list);

  		get_inotify_watch(watch);

  		mutex_unlock(&ih->mutex);

  
  		inode = watch->inode;

  		mutex_lock(&inode->inotify_mutex);

  		mutex_lock(&ih->mutex);

  
  		/* make sure we didn't race with another list removal */

  		if (likely(idr_find(&ih->idr, watch->wd))) {
  			remove_watch_no_event(watch, ih);
  			put_inotify_watch(watch);
  		}

  		mutex_unlock(&ih->mutex);

  		mutex_unlock(&inode->inotify_mutex);

  		put_inotify_watch(watch);
  	}

  	/* free this handle: the put matching the get in inotify_init() */
  	put_inotify_handle(ih);

  }

  EXPORT_SYMBOL_GPL(inotify_destroy);

  /**

   * inotify_find_watch - find an existing watch for an (ih,inode) pair
   * @ih: inotify handle
   * @inode: inode to watch
   * @watchp: pointer to existing inotify_watch
   *
   * Caller must pin given inode (via nameidata).
   */
  s32 inotify_find_watch(struct inotify_handle *ih, struct inode *inode,
  		       struct inotify_watch **watchp)
  {
  	struct inotify_watch *old;
  	int ret = -ENOENT;
  
  	mutex_lock(&inode->inotify_mutex);
  	mutex_lock(&ih->mutex);
  
  	old = inode_find_handle(inode, ih);
  	if (unlikely(old)) {
  		get_inotify_watch(old); /* caller must put watch */
  		*watchp = old;
  		ret = old->wd;
  	}
  
  	mutex_unlock(&ih->mutex);
  	mutex_unlock(&inode->inotify_mutex);
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(inotify_find_watch);
  
  /**

   * inotify_find_update_watch - find and update the mask of an existing watch
   * @ih: inotify handle
   * @inode: inode's watch to update
   * @mask: mask of events to watch

   *

   * Caller must pin given inode (via nameidata).

   */

  s32 inotify_find_update_watch(struct inotify_handle *ih, struct inode *inode,
  			      u32 mask)

  {

  	struct inotify_watch *old;
  	int mask_add = 0;
  	int ret;

  	if (mask & IN_MASK_ADD)
  		mask_add = 1;
  
  	/* don't allow invalid bits: we don't want flags set */
  	mask &= IN_ALL_EVENTS | IN_ONESHOT;
  	if (unlikely(!mask))

  		return -EINVAL;

  	mutex_lock(&inode->inotify_mutex);

  	mutex_lock(&ih->mutex);

  	/*
  	 * Handle the case of re-adding a watch on an (inode,ih) pair that we
  	 * are already watching.  We just update the mask and return its wd.
  	 */
  	old = inode_find_handle(inode, ih);
  	if (unlikely(!old)) {
  		ret = -ENOENT;
  		goto out;

  	}

  	if (mask_add)
  		old->mask |= mask;
  	else
  		old->mask = mask;
  	ret = old->wd;
  out:
  	mutex_unlock(&ih->mutex);
  	mutex_unlock(&inode->inotify_mutex);

  	return ret;
  }

  EXPORT_SYMBOL_GPL(inotify_find_update_watch);

  /**
   * inotify_add_watch - add a watch to an inotify instance
   * @ih: inotify handle
   * @watch: caller allocated watch structure
   * @inode: inode to watch
   * @mask: mask of events to watch
   *
   * Caller must pin given inode (via nameidata).
   * Caller must ensure it only calls inotify_add_watch() once per watch.
   * Calls inotify_handle_get_wd() so may sleep.
   */
  s32 inotify_add_watch(struct inotify_handle *ih, struct inotify_watch *watch,
  		      struct inode *inode, u32 mask)

  {

  	int ret = 0;

  	/* don't allow invalid bits: we don't want flags set */
  	mask &= IN_ALL_EVENTS | IN_ONESHOT;
  	if (unlikely(!mask))
  		return -EINVAL;
  	watch->mask = mask;

  	mutex_lock(&inode->inotify_mutex);
  	mutex_lock(&ih->mutex);

  	/* Initialize a new watch */
  	ret = inotify_handle_get_wd(ih, watch);

  	if (unlikely(ret))

  		goto out;
  	ret = watch->wd;

  	/* save a reference to handle and bump the count to make it official */
  	get_inotify_handle(ih);
  	watch->ih = ih;

  
  	/*

  	 * Save a reference to the inode and bump the ref count to make it
  	 * official.  We hold a reference to nameidata, which makes this safe.

  	 */

  	watch->inode = igrab(inode);

  	if (!inotify_inode_watched(inode))
  		set_dentry_child_flags(inode, 1);

  	/* Add the watch to the handle's and the inode's list */
  	list_add(&watch->h_list, &ih->watches);

  	list_add(&watch->i_list, &inode->inotify_watches);

  out:

  	mutex_unlock(&ih->mutex);

  	mutex_unlock(&inode->inotify_mutex);

  	return ret;
  }

  EXPORT_SYMBOL_GPL(inotify_add_watch);

  /**
   * inotify_rm_wd - remove a watch from an inotify instance
   * @ih: inotify handle
   * @wd: watch descriptor to remove
   *
   * Can sleep.
   */
  int inotify_rm_wd(struct inotify_handle *ih, u32 wd)

  {

  	struct inotify_watch *watch;
  	struct inode *inode;

  	mutex_lock(&ih->mutex);
  	watch = idr_find(&ih->idr, wd);
  	if (unlikely(!watch)) {
  		mutex_unlock(&ih->mutex);
  		return -EINVAL;

  	}

  	get_inotify_watch(watch);
  	inode = watch->inode;
  	mutex_unlock(&ih->mutex);

  	mutex_lock(&inode->inotify_mutex);
  	mutex_lock(&ih->mutex);

  	/* make sure that we did not race */
  	if (likely(idr_find(&ih->idr, wd) == watch))

  		inotify_remove_watch_locked(ih, watch);

  	mutex_unlock(&ih->mutex);
  	mutex_unlock(&inode->inotify_mutex);
  	put_inotify_watch(watch);

  	return 0;
  }
  EXPORT_SYMBOL_GPL(inotify_rm_wd);

  /**
   * inotify_rm_watch - remove a watch from an inotify instance
   * @ih: inotify handle
   * @watch: watch to remove
   *
   * Can sleep.
   */
  int inotify_rm_watch(struct inotify_handle *ih,
  		     struct inotify_watch *watch)
  {
  	return inotify_rm_wd(ih, watch->wd);
  }
  EXPORT_SYMBOL_GPL(inotify_rm_watch);

  /*

   * inotify_setup - core initialization function

   */

  static int __init inotify_setup(void)

  {

  	atomic_set(&inotify_cookie, 0);

  	return 0;
  }

  module_init(inotify_setup);