/*
   * Directory notifications for Linux.
   *
   * Copyright (C) 2000,2001,2002 Stephen Rothwell
   *

   * Copyright (C) 2009 Eric Paris <Red Hat Inc>
   * dnotify was largly rewritten to use the new fsnotify infrastructure
   *

   * 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/fs.h>
  #include <linux/module.h>
  #include <linux/sched.h>
  #include <linux/dnotify.h>
  #include <linux/init.h>
  #include <linux/spinlock.h>
  #include <linux/slab.h>

  #include <linux/fdtable.h>

  #include <linux/fsnotify_backend.h>

  int dir_notify_enable __read_mostly = 1;

  static struct kmem_cache *dnotify_struct_cache __read_mostly;

  static struct kmem_cache *dnotify_mark_cache __read_mostly;

  static struct fsnotify_group *dnotify_group __read_mostly;
  static DEFINE_MUTEX(dnotify_mark_mutex);
  
  /*

   * dnotify will attach one of these to each inode (i_fsnotify_marks) which

   * is being watched by dnotify.  If multiple userspace applications are watching
   * the same directory with dnotify their information is chained in dn
   */

  struct dnotify_mark {
  	struct fsnotify_mark fsn_mark;

  	struct dnotify_struct *dn;
  };

  /*
   * When a process starts or stops watching an inode the set of events which
   * dnotify cares about for that inode may change.  This function runs the
   * list of everything receiving dnotify events about this directory and calculates
   * the set of all those events.  After it updates what dnotify is interested in
   * it calls the fsnotify function so it can update the set of all events relevant
   * to this inode.
   */

  static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)

  {

  	__u32 new_mask, old_mask;

  	struct dnotify_struct *dn;

  	struct dnotify_mark *dn_mark  = container_of(fsn_mark,
  						     struct dnotify_mark,
  						     fsn_mark);

  	assert_spin_locked(&fsn_mark->lock);

  	old_mask = fsn_mark->mask;

  	new_mask = 0;

  	for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)

  		new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);

  	fsnotify_set_mark_mask_locked(fsn_mark, new_mask);

  
  	if (old_mask == new_mask)
  		return;

  	if (fsn_mark->i.inode)
  		fsnotify_recalc_inode_mask(fsn_mark->i.inode);

  }

  /*
   * Mains fsnotify call where events are delivered to dnotify.
   * Find the dnotify mark on the relevant inode, run the list of dnotify structs
   * on that mark and determine which of them has expressed interest in receiving
   * events of this type.  When found send the correct process and signal and
   * destroy the dnotify struct if it was not registered to receive multiple
   * events.
   */
  static int dnotify_handle_event(struct fsnotify_group *group,

  				struct fsnotify_mark *inode_mark,
  				struct fsnotify_mark *vfsmount_mark,

  				struct fsnotify_event *event)
  {

  	struct dnotify_mark *dn_mark;

  	struct inode *to_tell;
  	struct dnotify_struct *dn;
  	struct dnotify_struct **prev;
  	struct fown_struct *fown;

  	__u32 test_mask = event->mask & ~FS_EVENT_ON_CHILD;

  	BUG_ON(vfsmount_mark);

  	to_tell = event->to_tell;

  	dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);

  	spin_lock(&inode_mark->lock);

  	prev = &dn_mark->dn;

  	while ((dn = *prev) != NULL) {

  		if ((dn->dn_mask & test_mask) == 0) {

  			prev = &dn->dn_next;
  			continue;
  		}
  		fown = &dn->dn_filp->f_owner;
  		send_sigio(fown, dn->dn_fd, POLL_MSG);
  		if (dn->dn_mask & FS_DN_MULTISHOT)
  			prev = &dn->dn_next;
  		else {
  			*prev = dn->dn_next;
  			kmem_cache_free(dnotify_struct_cache, dn);

  			dnotify_recalc_inode_mask(inode_mark);

  		}
  	}

  	spin_unlock(&inode_mark->lock);

  
  	return 0;
  }
  
  /*
   * Given an inode and mask determine if dnotify would be interested in sending
   * userspace notification for that pair.
   */
  static bool dnotify_should_send_event(struct fsnotify_group *group,

  				      struct inode *inode,

  				      struct fsnotify_mark *inode_mark,
  				      struct fsnotify_mark *vfsmount_mark,
  				      __u32 mask, void *data, int data_type)

  {

  	/* not a dir, dnotify doesn't care */
  	if (!S_ISDIR(inode->i_mode))
  		return false;

  	return true;

  }

  static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)

  {

  	struct dnotify_mark *dn_mark = container_of(fsn_mark,
  						    struct dnotify_mark,
  						    fsn_mark);

  	BUG_ON(dn_mark->dn);

  	kmem_cache_free(dnotify_mark_cache, dn_mark);

  }
  
  static struct fsnotify_ops dnotify_fsnotify_ops = {
  	.handle_event = dnotify_handle_event,
  	.should_send_event = dnotify_should_send_event,
  	.free_group_priv = NULL,

  	.freeing_mark = NULL,

  	.free_event_priv = NULL,

  };
  
  /*
   * Called every time a file is closed.  Looks first for a dnotify mark on the

   * inode.  If one is found run all of the ->dn structures attached to that

   * mark for one relevant to this process closing the file and remove that
   * dnotify_struct.  If that was the last dnotify_struct also remove the

   * fsnotify_mark.

   */

  void dnotify_flush(struct file *filp, fl_owner_t id)
  {

  	struct fsnotify_mark *fsn_mark;
  	struct dnotify_mark *dn_mark;

  	struct dnotify_struct *dn;
  	struct dnotify_struct **prev;
  	struct inode *inode;

  	inode = filp->f_path.dentry->d_inode;

  	if (!S_ISDIR(inode->i_mode))
  		return;

  	fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode);

  	if (!fsn_mark)

  		return;

  	dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);

  
  	mutex_lock(&dnotify_mark_mutex);

  	spin_lock(&fsn_mark->lock);
  	prev = &dn_mark->dn;

  	while ((dn = *prev) != NULL) {
  		if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
  			*prev = dn->dn_next;

  			kmem_cache_free(dnotify_struct_cache, dn);

  			dnotify_recalc_inode_mask(fsn_mark);

  			break;
  		}
  		prev = &dn->dn_next;
  	}

  	spin_unlock(&fsn_mark->lock);

  
  	/* nothing else could have found us thanks to the dnotify_mark_mutex */

  	if (dn_mark->dn == NULL)
  		fsnotify_destroy_mark(fsn_mark);

  	mutex_unlock(&dnotify_mark_mutex);

  	fsnotify_put_mark(fsn_mark);

  }
  
  /* this conversion is done only at watch creation */
  static __u32 convert_arg(unsigned long arg)
  {
  	__u32 new_mask = FS_EVENT_ON_CHILD;
  
  	if (arg & DN_MULTISHOT)
  		new_mask |= FS_DN_MULTISHOT;
  	if (arg & DN_DELETE)
  		new_mask |= (FS_DELETE | FS_MOVED_FROM);
  	if (arg & DN_MODIFY)
  		new_mask |= FS_MODIFY;
  	if (arg & DN_ACCESS)
  		new_mask |= FS_ACCESS;
  	if (arg & DN_ATTRIB)
  		new_mask |= FS_ATTRIB;
  	if (arg & DN_RENAME)
  		new_mask |= FS_DN_RENAME;
  	if (arg & DN_CREATE)
  		new_mask |= (FS_CREATE | FS_MOVED_TO);
  
  	return new_mask;

  }

  /*
   * If multiple processes watch the same inode with dnotify there is only one

   * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct

   * onto that mark.  This function either attaches the new dnotify_struct onto
   * that list, or it |= the mask onto an existing dnofiy_struct.
   */

  static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,

  		     fl_owner_t id, int fd, struct file *filp, __u32 mask)
  {
  	struct dnotify_struct *odn;

  	odn = dn_mark->dn;

  	while (odn != NULL) {
  		/* adding more events to existing dnofiy_struct? */
  		if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
  			odn->dn_fd = fd;
  			odn->dn_mask |= mask;
  			return -EEXIST;
  		}
  		odn = odn->dn_next;
  	}
  
  	dn->dn_mask = mask;
  	dn->dn_fd = fd;
  	dn->dn_filp = filp;
  	dn->dn_owner = id;

  	dn->dn_next = dn_mark->dn;
  	dn_mark->dn = dn;

  
  	return 0;
  }
  
  /*
   * When a process calls fcntl to attach a dnotify watch to a directory it ends
   * up here.  Allocate both a mark for fsnotify to add and a dnotify_struct to be
   * attached to the fsnotify_mark.
   */

  int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
  {

  	struct dnotify_mark *new_dn_mark, *dn_mark;
  	struct fsnotify_mark *new_fsn_mark, *fsn_mark;

  	struct dnotify_struct *dn;

  	struct inode *inode;
  	fl_owner_t id = current->files;

  	struct file *f;

  	int destroy = 0, error = 0;
  	__u32 mask;
  
  	/* we use these to tell if we need to kfree */

  	new_fsn_mark = NULL;

  	dn = NULL;

  	if (!dir_notify_enable) {
  		error = -EINVAL;
  		goto out_err;
  	}
  
  	/* a 0 mask means we are explicitly removing the watch */

  	if ((arg & ~DN_MULTISHOT) == 0) {
  		dnotify_flush(filp, id);

  		error = 0;
  		goto out_err;

  	}

  
  	/* dnotify only works on directories */

  	inode = filp->f_path.dentry->d_inode;

  	if (!S_ISDIR(inode->i_mode)) {
  		error = -ENOTDIR;
  		goto out_err;

  	}

  	/* expect most fcntl to add new rather than augment old */
  	dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
  	if (!dn) {
  		error = -ENOMEM;
  		goto out_err;
  	}

  	/* new fsnotify mark, we expect most fcntl calls to add a new mark */

  	new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
  	if (!new_dn_mark) {

  		error = -ENOMEM;
  		goto out_err;
  	}

  	/* convert the userspace DN_* "arg" to the internal FS_* defines in fsnotify */
  	mask = convert_arg(arg);

  	/* set up the new_fsn_mark and new_dn_mark */
  	new_fsn_mark = &new_dn_mark->fsn_mark;
  	fsnotify_init_mark(new_fsn_mark, dnotify_free_mark);
  	new_fsn_mark->mask = mask;
  	new_dn_mark->dn = NULL;

  	/* this is needed to prevent the fcntl/close race described below */
  	mutex_lock(&dnotify_mark_mutex);

  	/* add the new_fsn_mark or find an old one. */

  	fsn_mark = fsnotify_find_inode_mark(dnotify_group, inode);

  	if (fsn_mark) {
  		dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
  		spin_lock(&fsn_mark->lock);

  	} else {

  		fsnotify_add_mark(new_fsn_mark, dnotify_group, inode, NULL, 0);

  		spin_lock(&new_fsn_mark->lock);
  		fsn_mark = new_fsn_mark;
  		dn_mark = new_dn_mark;
  		/* we used new_fsn_mark, so don't free it */
  		new_fsn_mark = NULL;

  	}

  	rcu_read_lock();
  	f = fcheck(fd);
  	rcu_read_unlock();

  	/* if (f != filp) means that we lost a race and another task/thread
  	 * actually closed the fd we are still playing with before we grabbed

  	 * the dnotify_mark_mutex and fsn_mark->lock.  Since closing the fd is the

  	 * only time we clean up the marks we need to get our mark off

  	 * the list. */
  	if (f != filp) {
  		/* if we added ourselves, shoot ourselves, it's possible that

  		 * the flush actually did shoot this fsn_mark.  That's fine too

  		 * since multiple calls to destroy_mark is perfectly safe, if

  		 * we found a dn_mark already attached to the inode, just sod

  		 * off silently as the flush at close time dealt with it.
  		 */

  		if (dn_mark == new_dn_mark)

  			destroy = 1;
  		goto out;
  	}

  	error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
  	if (error) {
  		/* if we added, we must shoot */

  		if (dn_mark == new_dn_mark)

  			destroy = 1;
  		goto out;

  	}

  	error = attach_dn(dn, dn_mark, id, fd, filp, mask);
  	/* !error means that we attached the dn to the dn_mark, so don't free it */

  	if (!error)
  		dn = NULL;
  	/* -EEXIST means that we didn't add this new dn and used an old one.
  	 * that isn't an error (and the unused dn should be freed) */
  	else if (error == -EEXIST)
  		error = 0;

  	dnotify_recalc_inode_mask(fsn_mark);

  out:

  	spin_unlock(&fsn_mark->lock);

  
  	if (destroy)

  		fsnotify_destroy_mark(fsn_mark);

  	mutex_unlock(&dnotify_mark_mutex);

  	fsnotify_put_mark(fsn_mark);

  out_err:

  	if (new_fsn_mark)
  		fsnotify_put_mark(new_fsn_mark);

  	if (dn)
  		kmem_cache_free(dnotify_struct_cache, dn);
  	return error;

  }

  
  static int __init dnotify_init(void)
  {

  	dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);

  	dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC);

  	dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);

  	if (IS_ERR(dnotify_group))
  		panic("unable to allocate fsnotify group for dnotify
  ");

  	return 0;
  }
  
  module_init(dnotify_init)