fs/notify/dnotify/dnotify.c - linux/torvalds/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * 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
  */
 #include <linux/fs.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/sched/signal.h>
 #include <linux/dnotify.h>
 #include <linux/init.h>
 #include <linux/security.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;

 /*
  * 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 = 0;
 	struct dnotify_struct *dn;
 	struct dnotify_mark *dn_mark  = container_of(fsn_mark,
 						     struct dnotify_mark,
 						     fsn_mark);

 	assert_spin_locked(&fsn_mark->lock);

 	for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
 		new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
 	if (fsn_mark->mask == new_mask)
 		return;
 	fsn_mark->mask = new_mask;

 	fsnotify_recalc_mask(fsn_mark->connector);
 }

 /*
  * 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 inode *inode,
 				u32 mask, const void *data, int data_type,
 				const struct qstr *file_name, u32 cookie,
 				struct fsnotify_iter_info *iter_info)
 {
 	struct fsnotify_mark *inode_mark = fsnotify_iter_inode_mark(iter_info);
 	struct dnotify_mark *dn_mark;
 	struct dnotify_struct *dn;
 	struct dnotify_struct **prev;
 	struct fown_struct *fown;
 	__u32 test_mask = mask & ~FS_EVENT_ON_CHILD;

 	/* not a dir, dnotify doesn't care */
 	if (!S_ISDIR(inode->i_mode))
 		return 0;

 	if (WARN_ON(fsnotify_iter_vfsmount_mark(iter_info)))
 		return 0;

 	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;
 }

 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 const struct fsnotify_ops dnotify_fsnotify_ops = {
 	.handle_event = dnotify_handle_event,
 	.free_mark = dnotify_free_mark,
 };

 /*
  * 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;
 	bool free = false;

 	inode = file_inode(filp);
 	if (!S_ISDIR(inode->i_mode))
 		return;

 	fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
 	if (!fsn_mark)
 		return;
 	dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);

 	mutex_lock(&dnotify_group->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_groups
 	   mark_mutex */
 	if (dn_mark->dn == NULL) {
 		fsnotify_detach_mark(fsn_mark);
 		free = true;
 	}

 	mutex_unlock(&dnotify_group->mark_mutex);

 	if (free)
 		fsnotify_free_mark(fsn_mark);
 	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 = file_inode(filp);
 	if (!S_ISDIR(inode->i_mode)) {
 		error = -ENOTDIR;
 		goto out_err;
 	}

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

 	error = security_path_notify(&filp->f_path, mask,
 			FSNOTIFY_OBJ_TYPE_INODE);
 	if (error)
 		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;
 	}

 	/* 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_group);
 	new_fsn_mark->mask = mask;
 	new_dn_mark->dn = NULL;

 	/* this is needed to prevent the fcntl/close race described below */
 	mutex_lock(&dnotify_group->mark_mutex);

 	/* add the new_fsn_mark or find an old one. */
 	fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
 	if (fsn_mark) {
 		dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
 		spin_lock(&fsn_mark->lock);
 	} else {
 		error = fsnotify_add_inode_mark_locked(new_fsn_mark, inode, 0);
 		if (error) {
 			mutex_unlock(&dnotify_group->mark_mutex);
 			goto out_err;
 		}
 		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_groups 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;
 		error = 0;
 		goto out;
 	}

 	__f_setown(filp, task_pid(current), PIDTYPE_TGID, 0);

 	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_detach_mark(fsn_mark);
 	mutex_unlock(&dnotify_group->mark_mutex);
 	if (destroy)
 		fsnotify_free_mark(fsn_mark);
 	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|SLAB_ACCOUNT);
 	dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT);

 	dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
 	if (IS_ERR(dnotify_group))
 		panic("unable to allocate fsnotify group for dnotify\n");
 	return 0;
 }

 module_init(dnotify_init)
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* 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
	*/
	#include <linux/fs.h>
	#include <linux/module.h>
	#include <linux/sched.h>
	#include <linux/sched/signal.h>
	#include <linux/dnotify.h>
	#include <linux/init.h>
	#include <linux/security.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;

	/*
	* 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 = 0;
	struct dnotify_struct *dn;
	struct dnotify_mark *dn_mark = container_of(fsn_mark,
	struct dnotify_mark,
	fsn_mark);

	assert_spin_locked(&fsn_mark->lock);

	for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
	new_mask \|= (dn->dn_mask & ~FS_DN_MULTISHOT);
	if (fsn_mark->mask == new_mask)
	return;
	fsn_mark->mask = new_mask;

	fsnotify_recalc_mask(fsn_mark->connector);
	}

	/*
	* 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 inode *inode,
	u32 mask, const void *data, int data_type,
	const struct qstr *file_name, u32 cookie,
	struct fsnotify_iter_info *iter_info)
	{
	struct fsnotify_mark *inode_mark = fsnotify_iter_inode_mark(iter_info);
	struct dnotify_mark *dn_mark;
	struct dnotify_struct *dn;
	struct dnotify_struct **prev;
	struct fown_struct *fown;
	__u32 test_mask = mask & ~FS_EVENT_ON_CHILD;

	/* not a dir, dnotify doesn't care */
	if (!S_ISDIR(inode->i_mode))
	return 0;

	if (WARN_ON(fsnotify_iter_vfsmount_mark(iter_info)))
	return 0;

	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;
	}

	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 const struct fsnotify_ops dnotify_fsnotify_ops = {
	.handle_event = dnotify_handle_event,
	.free_mark = dnotify_free_mark,
	};

	/*
	* 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;
	bool free = false;

	inode = file_inode(filp);
	if (!S_ISDIR(inode->i_mode))
	return;

	fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
	if (!fsn_mark)
	return;
	dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);

	mutex_lock(&dnotify_group->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_groups
	mark_mutex */
	if (dn_mark->dn == NULL) {
	fsnotify_detach_mark(fsn_mark);
	free = true;
	}

	mutex_unlock(&dnotify_group->mark_mutex);

	if (free)
	fsnotify_free_mark(fsn_mark);
	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 = file_inode(filp);
	if (!S_ISDIR(inode->i_mode)) {
	error = -ENOTDIR;
	goto out_err;
	}

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

	error = security_path_notify(&filp->f_path, mask,
	FSNOTIFY_OBJ_TYPE_INODE);
	if (error)
	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;
	}

	/* 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_group);
	new_fsn_mark->mask = mask;
	new_dn_mark->dn = NULL;

	/* this is needed to prevent the fcntl/close race described below */
	mutex_lock(&dnotify_group->mark_mutex);

	/* add the new_fsn_mark or find an old one. */
	fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
	if (fsn_mark) {
	dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
	spin_lock(&fsn_mark->lock);
	} else {
	error = fsnotify_add_inode_mark_locked(new_fsn_mark, inode, 0);
	if (error) {
	mutex_unlock(&dnotify_group->mark_mutex);
	goto out_err;
	}
	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_groups 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;
	error = 0;
	goto out;
	}

	__f_setown(filp, task_pid(current), PIDTYPE_TGID, 0);

	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_detach_mark(fsn_mark);
	mutex_unlock(&dnotify_group->mark_mutex);
	if (destroy)
	fsnotify_free_mark(fsn_mark);
	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\|SLAB_ACCOUNT);
	dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC\|SLAB_ACCOUNT);

	dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
	if (IS_ERR(dnotify_group))
	panic("unable to allocate fsnotify group for dnotify\n");
	return 0;
	}

	module_init(dnotify_init)