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

  int dir_notify_enable __read_mostly = 1;

  static struct kmem_cache *dn_cache __read_mostly;

  
  static void redo_inode_mask(struct inode *inode)
  {
  	unsigned long new_mask;
  	struct dnotify_struct *dn;
  
  	new_mask = 0;
  	for (dn = inode->i_dnotify; dn != NULL; dn = dn->dn_next)
  		new_mask |= dn->dn_mask & ~DN_MULTISHOT;
  	inode->i_dnotify_mask = new_mask;
  }
  
  void dnotify_flush(struct file *filp, fl_owner_t id)
  {
  	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;
  	spin_lock(&inode->i_lock);
  	prev = &inode->i_dnotify;
  	while ((dn = *prev) != NULL) {
  		if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
  			*prev = dn->dn_next;
  			redo_inode_mask(inode);
  			kmem_cache_free(dn_cache, dn);
  			break;
  		}
  		prev = &dn->dn_next;
  	}
  	spin_unlock(&inode->i_lock);
  }
  
  int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
  {
  	struct dnotify_struct *dn;
  	struct dnotify_struct *odn;
  	struct dnotify_struct **prev;
  	struct inode *inode;
  	fl_owner_t id = current->files;

  	struct file *f;

  	int error = 0;
  
  	if ((arg & ~DN_MULTISHOT) == 0) {
  		dnotify_flush(filp, id);
  		return 0;
  	}
  	if (!dir_notify_enable)
  		return -EINVAL;

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

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

  	dn = kmem_cache_alloc(dn_cache, GFP_KERNEL);

  	if (dn == NULL)
  		return -ENOMEM;
  	spin_lock(&inode->i_lock);
  	prev = &inode->i_dnotify;
  	while ((odn = *prev) != NULL) {
  		if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
  			odn->dn_fd = fd;
  			odn->dn_mask |= arg;
  			inode->i_dnotify_mask |= arg & ~DN_MULTISHOT;
  			goto out_free;
  		}
  		prev = &odn->dn_next;
  	}

  	rcu_read_lock();
  	f = fcheck(fd);
  	rcu_read_unlock();
  	/* we'd lost the race with close(), sod off silently */
  	/* note that inode->i_lock prevents reordering problems
  	 * between accesses to descriptor table and ->i_dnotify */
  	if (f != filp)
  		goto out_free;

  	error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);

  	if (error)
  		goto out_free;
  
  	dn->dn_mask = arg;
  	dn->dn_fd = fd;
  	dn->dn_filp = filp;
  	dn->dn_owner = id;
  	inode->i_dnotify_mask |= arg & ~DN_MULTISHOT;
  	dn->dn_next = inode->i_dnotify;
  	inode->i_dnotify = dn;
  	spin_unlock(&inode->i_lock);
  
  	if (filp->f_op && filp->f_op->dir_notify)
  		return filp->f_op->dir_notify(filp, arg);
  	return 0;
  
  out_free:
  	spin_unlock(&inode->i_lock);
  	kmem_cache_free(dn_cache, dn);
  	return error;
  }
  
  void __inode_dir_notify(struct inode *inode, unsigned long event)
  {
  	struct dnotify_struct *	dn;
  	struct dnotify_struct **prev;
  	struct fown_struct *	fown;
  	int			changed = 0;
  
  	spin_lock(&inode->i_lock);
  	prev = &inode->i_dnotify;
  	while ((dn = *prev) != NULL) {
  		if ((dn->dn_mask & event) == 0) {
  			prev = &dn->dn_next;
  			continue;
  		}
  		fown = &dn->dn_filp->f_owner;
  		send_sigio(fown, dn->dn_fd, POLL_MSG);
  		if (dn->dn_mask & DN_MULTISHOT)
  			prev = &dn->dn_next;
  		else {
  			*prev = dn->dn_next;
  			changed = 1;
  			kmem_cache_free(dn_cache, dn);
  		}
  	}
  	if (changed)
  		redo_inode_mask(inode);
  	spin_unlock(&inode->i_lock);
  }
  
  EXPORT_SYMBOL(__inode_dir_notify);
  
  /*
   * This is hopelessly wrong, but unfixable without API changes.  At
   * least it doesn't oops the kernel...
   *
   * To safely access ->d_parent we need to keep d_move away from it.  Use the
   * dentry's d_lock for this.
   */
  void dnotify_parent(struct dentry *dentry, unsigned long event)
  {
  	struct dentry *parent;
  
  	if (!dir_notify_enable)
  		return;
  
  	spin_lock(&dentry->d_lock);
  	parent = dentry->d_parent;
  	if (parent->d_inode->i_dnotify_mask & event) {
  		dget(parent);
  		spin_unlock(&dentry->d_lock);
  		__inode_dir_notify(parent->d_inode, event);
  		dput(parent);
  	} else {
  		spin_unlock(&dentry->d_lock);
  	}
  }
  EXPORT_SYMBOL_GPL(dnotify_parent);
  
  static int __init dnotify_init(void)
  {
  	dn_cache = kmem_cache_create("dnotify_cache",

  		sizeof(struct dnotify_struct), 0, SLAB_PANIC, NULL);

  	return 0;
  }
  
  module_init(dnotify_init)