/*
   * fs/kernfs/dir.c - kernfs directory implementation
   *
   * Copyright (c) 2001-3 Patrick Mochel
   * Copyright (c) 2007 SUSE Linux Products GmbH
   * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
   *
   * This file is released under the GPLv2.
   */

  #include <linux/sched.h>

  #include <linux/fs.h>
  #include <linux/namei.h>
  #include <linux/idr.h>
  #include <linux/slab.h>
  #include <linux/security.h>
  #include <linux/hash.h>
  
  #include "kernfs-internal.h"

  DEFINE_MUTEX(kernfs_mutex);

  static DEFINE_SPINLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
  static char kernfs_pr_cont_buf[PATH_MAX];	/* protected by rename_lock */

  #define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)

  static bool kernfs_active(struct kernfs_node *kn)
  {
  	lockdep_assert_held(&kernfs_mutex);
  	return atomic_read(&kn->active) >= 0;
  }

  static bool kernfs_lockdep(struct kernfs_node *kn)
  {
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  	return kn->flags & KERNFS_LOCKDEP;
  #else
  	return false;
  #endif
  }

  static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
  {
  	return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
  }

  /* kernfs_node_depth - compute depth from @from to @to */
  static size_t kernfs_depth(struct kernfs_node *from, struct kernfs_node *to)

  {

  	size_t depth = 0;

  	while (to->parent && to != from) {
  		depth++;
  		to = to->parent;
  	}
  	return depth;
  }

  static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a,
  						  struct kernfs_node *b)
  {
  	size_t da, db;
  	struct kernfs_root *ra = kernfs_root(a), *rb = kernfs_root(b);
  
  	if (ra != rb)
  		return NULL;
  
  	da = kernfs_depth(ra->kn, a);
  	db = kernfs_depth(rb->kn, b);
  
  	while (da > db) {
  		a = a->parent;
  		da--;
  	}
  	while (db > da) {
  		b = b->parent;
  		db--;
  	}
  
  	/* worst case b and a will be the same at root */
  	while (b != a) {
  		b = b->parent;
  		a = a->parent;
  	}
  
  	return a;
  }
  
  /**
   * kernfs_path_from_node_locked - find a pseudo-absolute path to @kn_to,
   * where kn_from is treated as root of the path.
   * @kn_from: kernfs node which should be treated as root for the path
   * @kn_to: kernfs node to which path is needed
   * @buf: buffer to copy the path into
   * @buflen: size of @buf
   *
   * We need to handle couple of scenarios here:
   * [1] when @kn_from is an ancestor of @kn_to at some level
   * kn_from: /n1/n2/n3
   * kn_to:   /n1/n2/n3/n4/n5
   * result:  /n4/n5
   *
   * [2] when @kn_from is on a different hierarchy and we need to find common
   * ancestor between @kn_from and @kn_to.
   * kn_from: /n1/n2/n3/n4
   * kn_to:   /n1/n2/n5
   * result:  /../../n5
   * OR
   * kn_from: /n1/n2/n3/n4/n5   [depth=5]
   * kn_to:   /n1/n2/n3         [depth=3]
   * result:  /../..
   *

   * Returns the length of the full path.  If the full length is equal to or
   * greater than @buflen, @buf contains the truncated path with the trailing
   * '\0'.  On error, -errno is returned.

   */
  static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
  					struct kernfs_node *kn_from,
  					char *buf, size_t buflen)
  {
  	struct kernfs_node *kn, *common;
  	const char parent_str[] = "/..";

  	size_t depth_from, depth_to, len = 0;
  	int i, j;

  
  	if (!kn_from)
  		kn_from = kernfs_root(kn_to)->kn;
  
  	if (kn_from == kn_to)
  		return strlcpy(buf, "/", buflen);
  
  	common = kernfs_common_ancestor(kn_from, kn_to);
  	if (WARN_ON(!common))

  		return -EINVAL;

  
  	depth_to = kernfs_depth(common, kn_to);
  	depth_from = kernfs_depth(common, kn_from);
  
  	if (buf)
  		buf[0] = '\0';
  
  	for (i = 0; i < depth_from; i++)
  		len += strlcpy(buf + len, parent_str,
  			       len < buflen ? buflen - len : 0);
  
  	/* Calculate how many bytes we need for the rest */

  	for (i = depth_to - 1; i >= 0; i--) {
  		for (kn = kn_to, j = 0; j < i; j++)
  			kn = kn->parent;
  		len += strlcpy(buf + len, "/",
  			       len < buflen ? buflen - len : 0);
  		len += strlcpy(buf + len, kn->name,
  			       len < buflen ? buflen - len : 0);

  	}

  	return len;

  }
  
  /**
   * kernfs_name - obtain the name of a given node
   * @kn: kernfs_node of interest
   * @buf: buffer to copy @kn's name into
   * @buflen: size of @buf
   *
   * Copies the name of @kn into @buf of @buflen bytes.  The behavior is
   * similar to strlcpy().  It returns the length of @kn's name and if @buf
   * isn't long enough, it's filled upto @buflen-1 and nul terminated.
   *
   * This function can be called from any context.
   */
  int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
  {
  	unsigned long flags;
  	int ret;
  
  	spin_lock_irqsave(&kernfs_rename_lock, flags);
  	ret = kernfs_name_locked(kn, buf, buflen);
  	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
  	return ret;
  }
  
  /**

   * kernfs_path_from_node - build path of node @to relative to @from.
   * @from: parent kernfs_node relative to which we need to build the path
   * @to: kernfs_node of interest
   * @buf: buffer to copy @to's path into
   * @buflen: size of @buf
   *
   * Builds @to's path relative to @from in @buf. @from and @to must
   * be on the same kernfs-root. If @from is not parent of @to, then a relative
   * path (which includes '..'s) as needed to reach from @from to @to is
   * returned.
   *

   * Returns the length of the full path.  If the full length is equal to or
   * greater than @buflen, @buf contains the truncated path with the trailing
   * '\0'.  On error, -errno is returned.

   */
  int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
  			  char *buf, size_t buflen)
  {
  	unsigned long flags;
  	int ret;
  
  	spin_lock_irqsave(&kernfs_rename_lock, flags);
  	ret = kernfs_path_from_node_locked(to, from, buf, buflen);
  	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(kernfs_path_from_node);
  
  /**

   * pr_cont_kernfs_name - pr_cont name of a kernfs_node
   * @kn: kernfs_node of interest
   *
   * This function can be called from any context.
   */
  void pr_cont_kernfs_name(struct kernfs_node *kn)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&kernfs_rename_lock, flags);
  
  	kernfs_name_locked(kn, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf));
  	pr_cont("%s", kernfs_pr_cont_buf);
  
  	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
  }
  
  /**
   * pr_cont_kernfs_path - pr_cont path of a kernfs_node
   * @kn: kernfs_node of interest
   *
   * This function can be called from any context.
   */
  void pr_cont_kernfs_path(struct kernfs_node *kn)
  {
  	unsigned long flags;

  	int sz;

  
  	spin_lock_irqsave(&kernfs_rename_lock, flags);

  	sz = kernfs_path_from_node_locked(kn, NULL, kernfs_pr_cont_buf,
  					  sizeof(kernfs_pr_cont_buf));
  	if (sz < 0) {
  		pr_cont("(error)");
  		goto out;
  	}
  
  	if (sz >= sizeof(kernfs_pr_cont_buf)) {
  		pr_cont("(name too long)");
  		goto out;
  	}
  
  	pr_cont("%s", kernfs_pr_cont_buf);

  out:

  	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
  }
  
  /**
   * kernfs_get_parent - determine the parent node and pin it
   * @kn: kernfs_node of interest
   *
   * Determines @kn's parent, pins and returns it.  This function can be
   * called from any context.
   */
  struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
  {
  	struct kernfs_node *parent;
  	unsigned long flags;
  
  	spin_lock_irqsave(&kernfs_rename_lock, flags);
  	parent = kn->parent;
  	kernfs_get(parent);
  	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
  
  	return parent;
  }

  /**

   *	kernfs_name_hash

   *	@name: Null terminated string to hash
   *	@ns:   Namespace tag to hash
   *
   *	Returns 31 bit hash of ns + name (so it fits in an off_t )
   */

  static unsigned int kernfs_name_hash(const char *name, const void *ns)

  {

  	unsigned long hash = init_name_hash(ns);

  	unsigned int len = strlen(name);
  	while (len--)
  		hash = partial_name_hash(*name++, hash);

  	hash = end_name_hash(hash);

  	hash &= 0x7fffffffU;
  	/* Reserve hash numbers 0, 1 and INT_MAX for magic directory entries */

  	if (hash < 2)

  		hash += 2;
  	if (hash >= INT_MAX)
  		hash = INT_MAX - 1;
  	return hash;
  }

  static int kernfs_name_compare(unsigned int hash, const char *name,
  			       const void *ns, const struct kernfs_node *kn)

  {

  	if (hash < kn->hash)
  		return -1;
  	if (hash > kn->hash)
  		return 1;
  	if (ns < kn->ns)
  		return -1;
  	if (ns > kn->ns)
  		return 1;

  	return strcmp(name, kn->name);

  }

  static int kernfs_sd_compare(const struct kernfs_node *left,
  			     const struct kernfs_node *right)

  {

  	return kernfs_name_compare(left->hash, left->name, left->ns, right);

  }
  
  /**

   *	kernfs_link_sibling - link kernfs_node into sibling rbtree

   *	@kn: kernfs_node of interest

   *

   *	Link @kn into its sibling rbtree which starts from

   *	@kn->parent->dir.children.

   *
   *	Locking:

   *	mutex_lock(kernfs_mutex)

   *
   *	RETURNS:
   *	0 on susccess -EEXIST on failure.
   */

  static int kernfs_link_sibling(struct kernfs_node *kn)

  {

  	struct rb_node **node = &kn->parent->dir.children.rb_node;

  	struct rb_node *parent = NULL;

  	while (*node) {

  		struct kernfs_node *pos;

  		int result;

  		pos = rb_to_kn(*node);

  		parent = *node;

  		result = kernfs_sd_compare(kn, pos);

  		if (result < 0)

  			node = &pos->rb.rb_left;

  		else if (result > 0)

  			node = &pos->rb.rb_right;

  		else
  			return -EEXIST;
  	}

  	/* add new node and rebalance the tree */

  	rb_link_node(&kn->rb, parent, node);
  	rb_insert_color(&kn->rb, &kn->parent->dir.children);

  
  	/* successfully added, account subdir number */
  	if (kernfs_type(kn) == KERNFS_DIR)
  		kn->parent->dir.subdirs++;

  	return 0;
  }
  
  /**

   *	kernfs_unlink_sibling - unlink kernfs_node from sibling rbtree

   *	@kn: kernfs_node of interest

   *

   *	Try to unlink @kn from its sibling rbtree which starts from
   *	kn->parent->dir.children.  Returns %true if @kn was actually
   *	removed, %false if @kn wasn't on the rbtree.

   *
   *	Locking:

   *	mutex_lock(kernfs_mutex)

   */

  static bool kernfs_unlink_sibling(struct kernfs_node *kn)

  {

  	if (RB_EMPTY_NODE(&kn->rb))
  		return false;

  	if (kernfs_type(kn) == KERNFS_DIR)

  		kn->parent->dir.subdirs--;

  	rb_erase(&kn->rb, &kn->parent->dir.children);

  	RB_CLEAR_NODE(&kn->rb);
  	return true;

  }
  
  /**

   *	kernfs_get_active - get an active reference to kernfs_node

   *	@kn: kernfs_node to get an active reference to

   *

   *	Get an active reference of @kn.  This function is noop if @kn

   *	is NULL.
   *
   *	RETURNS:

   *	Pointer to @kn on success, NULL on failure.

   */

  struct kernfs_node *kernfs_get_active(struct kernfs_node *kn)

  {

  	if (unlikely(!kn))

  		return NULL;

  	if (!atomic_inc_unless_negative(&kn->active))
  		return NULL;

  	if (kernfs_lockdep(kn))

  		rwsem_acquire_read(&kn->dep_map, 0, 1, _RET_IP_);
  	return kn;

  }
  
  /**

   *	kernfs_put_active - put an active reference to kernfs_node

   *	@kn: kernfs_node to put an active reference to

   *

   *	Put an active reference to @kn.  This function is noop if @kn

   *	is NULL.
   */

  void kernfs_put_active(struct kernfs_node *kn)

  {

  	struct kernfs_root *root = kernfs_root(kn);

  	int v;

  	if (unlikely(!kn))

  		return;

  	if (kernfs_lockdep(kn))

  		rwsem_release(&kn->dep_map, 1, _RET_IP_);

  	v = atomic_dec_return(&kn->active);

  	if (likely(v != KN_DEACTIVATED_BIAS))

  		return;

  	wake_up_all(&root->deactivate_waitq);

  }
  
  /**

   * kernfs_drain - drain kernfs_node
   * @kn: kernfs_node to drain

   *

   * Drain existing usages and nuke all existing mmaps of @kn.  Mutiple
   * removers may invoke this function concurrently on @kn and all will
   * return after draining is complete.

   */

  static void kernfs_drain(struct kernfs_node *kn)

  	__releases(&kernfs_mutex) __acquires(&kernfs_mutex)

  {

  	struct kernfs_root *root = kernfs_root(kn);

  	lockdep_assert_held(&kernfs_mutex);

  	WARN_ON_ONCE(kernfs_active(kn));

  	mutex_unlock(&kernfs_mutex);

  	if (kernfs_lockdep(kn)) {

  		rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
  		if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
  			lock_contended(&kn->dep_map, _RET_IP_);
  	}

  	/* but everyone should wait for draining */

  	wait_event(root->deactivate_waitq,
  		   atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);

  	if (kernfs_lockdep(kn)) {

  		lock_acquired(&kn->dep_map, _RET_IP_);
  		rwsem_release(&kn->dep_map, 1, _RET_IP_);
  	}

  	kernfs_unmap_bin_file(kn);

  	mutex_lock(&kernfs_mutex);

  }

  /**

   * kernfs_get - get a reference count on a kernfs_node
   * @kn: the target kernfs_node

   */

  void kernfs_get(struct kernfs_node *kn)

  {

  	if (kn) {

  		WARN_ON(!atomic_read(&kn->count));
  		atomic_inc(&kn->count);

  	}
  }
  EXPORT_SYMBOL_GPL(kernfs_get);
  
  /**

   * kernfs_put - put a reference count on a kernfs_node
   * @kn: the target kernfs_node

   *

   * Put a reference count of @kn and destroy it if it reached zero.

   */

  void kernfs_put(struct kernfs_node *kn)

  {

  	struct kernfs_node *parent;

  	struct kernfs_root *root;

  	if (!kn || !atomic_dec_and_test(&kn->count))

  		return;

  	root = kernfs_root(kn);

   repeat:

  	/*
  	 * Moving/renaming is always done while holding reference.

  	 * kn->parent won't change beneath us.

  	 */

  	parent = kn->parent;

  	WARN_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS,
  		  "kernfs_put: %s/%s: released with incorrect active_ref %d
  ",
  		  parent ? parent->name : "", kn->name, atomic_read(&kn->active));

  	if (kernfs_type(kn) == KERNFS_LINK)

  		kernfs_put(kn->symlink.target_kn);

  
  	kfree_const(kn->name);

  	if (kn->iattr) {
  		if (kn->iattr->ia_secdata)
  			security_release_secctx(kn->iattr->ia_secdata,
  						kn->iattr->ia_secdata_len);
  		simple_xattrs_free(&kn->iattr->xattrs);

  	}

  	kfree(kn->iattr);
  	ida_simple_remove(&root->ino_ida, kn->ino);

  	kmem_cache_free(kernfs_node_cache, kn);

  	kn = parent;
  	if (kn) {

  		if (atomic_dec_and_test(&kn->count))

  			goto repeat;
  	} else {

  		/* just released the root kn, free @root too */

  		ida_destroy(&root->ino_ida);

  		kfree(root);
  	}

  }
  EXPORT_SYMBOL_GPL(kernfs_put);

  static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)

  {

  	struct kernfs_node *kn;

  
  	if (flags & LOOKUP_RCU)
  		return -ECHILD;

  	/* Always perform fresh lookup for negatives */

  	if (d_really_is_negative(dentry))

  		goto out_bad_unlocked;

  	kn = dentry->d_fsdata;

  	mutex_lock(&kernfs_mutex);

  	/* The kernfs node has been deactivated */
  	if (!kernfs_active(kn))

  		goto out_bad;

  	/* The kernfs node has been moved? */

  	if (dentry->d_parent->d_fsdata != kn->parent)

  		goto out_bad;

  	/* The kernfs node has been renamed */

  	if (strcmp(dentry->d_name.name, kn->name) != 0)

  		goto out_bad;

  	/* The kernfs node has been moved to a different namespace */

  	if (kn->parent && kernfs_ns_enabled(kn->parent) &&

  	    kernfs_info(dentry->d_sb)->ns != kn->ns)

  		goto out_bad;

  	mutex_unlock(&kernfs_mutex);

  	return 1;
  out_bad:

  	mutex_unlock(&kernfs_mutex);

  out_bad_unlocked:

  	return 0;
  }

  static void kernfs_dop_release(struct dentry *dentry)

  {
  	kernfs_put(dentry->d_fsdata);
  }

  const struct dentry_operations kernfs_dops = {

  	.d_revalidate	= kernfs_dop_revalidate,

  	.d_release	= kernfs_dop_release,

  };

  /**
   * kernfs_node_from_dentry - determine kernfs_node associated with a dentry
   * @dentry: the dentry in question
   *
   * Return the kernfs_node associated with @dentry.  If @dentry is not a
   * kernfs one, %NULL is returned.
   *
   * While the returned kernfs_node will stay accessible as long as @dentry
   * is accessible, the returned node can be in any state and the caller is
   * fully responsible for determining what's accessible.
   */
  struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
  {

  	if (dentry->d_sb->s_op == &kernfs_sops)

  		return dentry->d_fsdata;
  	return NULL;
  }

  static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
  					     const char *name, umode_t mode,
  					     unsigned flags)

  {

  	struct kernfs_node *kn;

  	int ret;

  	name = kstrdup_const(name, GFP_KERNEL);
  	if (!name)
  		return NULL;

  	kn = kmem_cache_zalloc(kernfs_node_cache, GFP_KERNEL);

  	if (!kn)

  		goto err_out1;

  	ret = ida_simple_get(&root->ino_ida, 1, 0, GFP_KERNEL);

  	if (ret < 0)

  		goto err_out2;

  	kn->ino = ret;

  	atomic_set(&kn->count, 1);

  	atomic_set(&kn->active, KN_DEACTIVATED_BIAS);

  	RB_CLEAR_NODE(&kn->rb);

  	kn->name = name;
  	kn->mode = mode;

  	kn->flags = flags;

  	return kn;

  
   err_out2:

  	kmem_cache_free(kernfs_node_cache, kn);

   err_out1:

  	kfree_const(name);

  	return NULL;
  }

  struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
  				    const char *name, umode_t mode,
  				    unsigned flags)
  {
  	struct kernfs_node *kn;
  
  	kn = __kernfs_new_node(kernfs_root(parent), name, mode, flags);
  	if (kn) {
  		kernfs_get(parent);
  		kn->parent = parent;
  	}
  	return kn;
  }

  /**

   *	kernfs_add_one - add kernfs_node to parent without warning

   *	@kn: kernfs_node to be added

   *

   *	The caller must already have initialized @kn->parent.  This
   *	function increments nlink of the parent's inode if @kn is a
   *	directory and link into the children list of the parent.

   *

   *	RETURNS:
   *	0 on success, -EEXIST if entry with the given name already
   *	exists.
   */

  int kernfs_add_one(struct kernfs_node *kn)

  {

  	struct kernfs_node *parent = kn->parent;

  	struct kernfs_iattrs *ps_iattr;

  	bool has_ns;

  	int ret;

  	mutex_lock(&kernfs_mutex);
  
  	ret = -EINVAL;
  	has_ns = kernfs_ns_enabled(parent);
  	if (WARN(has_ns != (bool)kn->ns, KERN_WARNING "kernfs: ns %s in '%s' for '%s'
  ",
  		 has_ns ? "required" : "invalid", parent->name, kn->name))
  		goto out_unlock;

  	if (kernfs_type(parent) != KERNFS_DIR)

  		goto out_unlock;

  	ret = -ENOENT;

  	if (parent->flags & KERNFS_EMPTY_DIR)
  		goto out_unlock;

  	if ((parent->flags & KERNFS_ACTIVATED) && !kernfs_active(parent))

  		goto out_unlock;

  	kn->hash = kernfs_name_hash(kn->name, kn->ns);

  	ret = kernfs_link_sibling(kn);

  	if (ret)

  		goto out_unlock;

  
  	/* Update timestamps on the parent */

  	ps_iattr = parent->iattr;

  	if (ps_iattr) {
  		struct iattr *ps_iattrs = &ps_iattr->ia_iattr;

  		ktime_get_real_ts(&ps_iattrs->ia_ctime);
  		ps_iattrs->ia_mtime = ps_iattrs->ia_ctime;

  	}

  	mutex_unlock(&kernfs_mutex);
  
  	/*
  	 * Activate the new node unless CREATE_DEACTIVATED is requested.
  	 * If not activated here, the kernfs user is responsible for
  	 * activating the node with kernfs_activate().  A node which hasn't
  	 * been activated is not visible to userland and its removal won't
  	 * trigger deactivation.
  	 */
  	if (!(kernfs_root(kn)->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
  		kernfs_activate(kn);
  	return 0;

  out_unlock:

  	mutex_unlock(&kernfs_mutex);

  	return ret;

  }
  
  /**

   * kernfs_find_ns - find kernfs_node with the given name
   * @parent: kernfs_node to search under

   * @name: name to look for
   * @ns: the namespace tag to use
   *

   * Look for kernfs_node with name @name under @parent.  Returns pointer to
   * the found kernfs_node on success, %NULL on failure.

   */

  static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
  					  const unsigned char *name,
  					  const void *ns)

  {

  	struct rb_node *node = parent->dir.children.rb_node;

  	bool has_ns = kernfs_ns_enabled(parent);

  	unsigned int hash;

  	lockdep_assert_held(&kernfs_mutex);

  
  	if (has_ns != (bool)ns) {

  		WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'
  ",

  		     has_ns ? "required" : "invalid", parent->name, name);

  		return NULL;
  	}

  	hash = kernfs_name_hash(name, ns);

  	while (node) {

  		struct kernfs_node *kn;

  		int result;

  		kn = rb_to_kn(node);

  		result = kernfs_name_compare(hash, name, ns, kn);

  		if (result < 0)
  			node = node->rb_left;
  		else if (result > 0)
  			node = node->rb_right;
  		else

  			return kn;

  	}
  	return NULL;
  }

  static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
  					  const unsigned char *path,
  					  const void *ns)
  {

  	size_t len;
  	char *p, *name;

  
  	lockdep_assert_held(&kernfs_mutex);

  	/* grab kernfs_rename_lock to piggy back on kernfs_pr_cont_buf */
  	spin_lock_irq(&kernfs_rename_lock);
  
  	len = strlcpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf));
  
  	if (len >= sizeof(kernfs_pr_cont_buf)) {
  		spin_unlock_irq(&kernfs_rename_lock);

  		return NULL;

  	}
  
  	p = kernfs_pr_cont_buf;

  
  	while ((name = strsep(&p, "/")) && parent) {
  		if (*name == '\0')
  			continue;
  		parent = kernfs_find_ns(parent, name, ns);
  	}

  	spin_unlock_irq(&kernfs_rename_lock);

  	return parent;
  }

  /**

   * kernfs_find_and_get_ns - find and get kernfs_node with the given name
   * @parent: kernfs_node to search under

   * @name: name to look for
   * @ns: the namespace tag to use
   *

   * Look for kernfs_node with name @name under @parent and get a reference

   * if found.  This function may sleep and returns pointer to the found

   * kernfs_node on success, %NULL on failure.

   */

  struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
  					   const char *name, const void *ns)

  {

  	struct kernfs_node *kn;

  	mutex_lock(&kernfs_mutex);

  	kn = kernfs_find_ns(parent, name, ns);
  	kernfs_get(kn);

  	mutex_unlock(&kernfs_mutex);

  	return kn;

  }
  EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
  
  /**

   * kernfs_walk_and_get_ns - find and get kernfs_node with the given path
   * @parent: kernfs_node to search under
   * @path: path to look for
   * @ns: the namespace tag to use
   *
   * Look for kernfs_node with path @path under @parent and get a reference
   * if found.  This function may sleep and returns pointer to the found
   * kernfs_node on success, %NULL on failure.
   */
  struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
  					   const char *path, const void *ns)
  {
  	struct kernfs_node *kn;
  
  	mutex_lock(&kernfs_mutex);
  	kn = kernfs_walk_ns(parent, path, ns);
  	kernfs_get(kn);
  	mutex_unlock(&kernfs_mutex);
  
  	return kn;
  }
  
  /**

   * kernfs_create_root - create a new kernfs hierarchy

   * @scops: optional syscall operations for the hierarchy

   * @flags: KERNFS_ROOT_* flags

   * @priv: opaque data associated with the new directory
   *
   * Returns the root of the new hierarchy on success, ERR_PTR() value on
   * failure.
   */

  struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,

  				       unsigned int flags, void *priv)

  {
  	struct kernfs_root *root;

  	struct kernfs_node *kn;

  
  	root = kzalloc(sizeof(*root), GFP_KERNEL);
  	if (!root)
  		return ERR_PTR(-ENOMEM);

  	ida_init(&root->ino_ida);

  	INIT_LIST_HEAD(&root->supers);

  	kn = __kernfs_new_node(root, "", S_IFDIR | S_IRUGO | S_IXUGO,
  			       KERNFS_DIR);

  	if (!kn) {

  		ida_destroy(&root->ino_ida);

  		kfree(root);
  		return ERR_PTR(-ENOMEM);
  	}

  	kn->priv = priv;

  	kn->dir.root = root;

  	root->syscall_ops = scops;

  	root->flags = flags;

  	root->kn = kn;

  	init_waitqueue_head(&root->deactivate_waitq);

  	if (!(root->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
  		kernfs_activate(kn);

  	return root;
  }
  
  /**
   * kernfs_destroy_root - destroy a kernfs hierarchy
   * @root: root of the hierarchy to destroy
   *
   * Destroy the hierarchy anchored at @root by removing all existing
   * directories and destroying @root.
   */
  void kernfs_destroy_root(struct kernfs_root *root)
  {

  	kernfs_remove(root->kn);	/* will also free @root */

  }
  
  /**

   * kernfs_create_dir_ns - create a directory
   * @parent: parent in which to create a new directory
   * @name: name of the new directory

   * @mode: mode of the new directory

   * @priv: opaque data associated with the new directory
   * @ns: optional namespace tag of the directory
   *
   * Returns the created node on success, ERR_PTR() value on failure.
   */

  struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,

  					 const char *name, umode_t mode,
  					 void *priv, const void *ns)

  {

  	struct kernfs_node *kn;

  	int rc;
  
  	/* allocate */

  	kn = kernfs_new_node(parent, name, mode | S_IFDIR, KERNFS_DIR);

  	if (!kn)

  		return ERR_PTR(-ENOMEM);

  	kn->dir.root = parent->dir.root;
  	kn->ns = ns;

  	kn->priv = priv;

  
  	/* link in */

  	rc = kernfs_add_one(kn);

  	if (!rc)

  		return kn;

  	kernfs_put(kn);

  	return ERR_PTR(rc);
  }

  /**
   * kernfs_create_empty_dir - create an always empty directory
   * @parent: parent in which to create a new directory
   * @name: name of the new directory
   *
   * Returns the created node on success, ERR_PTR() value on failure.
   */
  struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
  					    const char *name)
  {
  	struct kernfs_node *kn;
  	int rc;
  
  	/* allocate */
  	kn = kernfs_new_node(parent, name, S_IRUGO|S_IXUGO|S_IFDIR, KERNFS_DIR);
  	if (!kn)
  		return ERR_PTR(-ENOMEM);
  
  	kn->flags |= KERNFS_EMPTY_DIR;
  	kn->dir.root = parent->dir.root;
  	kn->ns = NULL;
  	kn->priv = NULL;
  
  	/* link in */
  	rc = kernfs_add_one(kn);
  	if (!rc)
  		return kn;
  
  	kernfs_put(kn);
  	return ERR_PTR(rc);
  }

  static struct dentry *kernfs_iop_lookup(struct inode *dir,
  					struct dentry *dentry,
  					unsigned int flags)

  {

  	struct dentry *ret;

  	struct kernfs_node *parent = dentry->d_parent->d_fsdata;
  	struct kernfs_node *kn;

  	struct inode *inode;
  	const void *ns = NULL;

  	mutex_lock(&kernfs_mutex);

  	if (kernfs_ns_enabled(parent))

  		ns = kernfs_info(dir->i_sb)->ns;

  	kn = kernfs_find_ns(parent, dentry->d_name.name, ns);

  
  	/* no such entry */

  	if (!kn || !kernfs_active(kn)) {

  		ret = NULL;

  		goto out_unlock;
  	}

  	kernfs_get(kn);
  	dentry->d_fsdata = kn;

  
  	/* attach dentry and inode */

  	inode = kernfs_get_inode(dir->i_sb, kn);

  	if (!inode) {
  		ret = ERR_PTR(-ENOMEM);
  		goto out_unlock;
  	}
  
  	/* instantiate and hash dentry */

  	ret = d_splice_alias(inode, dentry);

   out_unlock:

  	mutex_unlock(&kernfs_mutex);

  	return ret;
  }

  static int kernfs_iop_mkdir(struct inode *dir, struct dentry *dentry,
  			    umode_t mode)
  {
  	struct kernfs_node *parent = dir->i_private;

  	struct kernfs_syscall_ops *scops = kernfs_root(parent)->syscall_ops;

  	int ret;

  	if (!scops || !scops->mkdir)

  		return -EPERM;

  	if (!kernfs_get_active(parent))
  		return -ENODEV;

  	ret = scops->mkdir(parent, dentry->d_name.name, mode);

  
  	kernfs_put_active(parent);
  	return ret;

  }
  
  static int kernfs_iop_rmdir(struct inode *dir, struct dentry *dentry)
  {
  	struct kernfs_node *kn  = dentry->d_fsdata;

  	struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;

  	int ret;

  	if (!scops || !scops->rmdir)

  		return -EPERM;

  	if (!kernfs_get_active(kn))
  		return -ENODEV;

  	ret = scops->rmdir(kn);

  
  	kernfs_put_active(kn);
  	return ret;

  }
  
  static int kernfs_iop_rename(struct inode *old_dir, struct dentry *old_dentry,

  			     struct inode *new_dir, struct dentry *new_dentry,
  			     unsigned int flags)

  {
  	struct kernfs_node *kn  = old_dentry->d_fsdata;
  	struct kernfs_node *new_parent = new_dir->i_private;

  	struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;

  	int ret;

  	if (flags)
  		return -EINVAL;

  	if (!scops || !scops->rename)

  		return -EPERM;

  	if (!kernfs_get_active(kn))
  		return -ENODEV;
  
  	if (!kernfs_get_active(new_parent)) {
  		kernfs_put_active(kn);
  		return -ENODEV;
  	}

  	ret = scops->rename(kn, new_parent, new_dentry->d_name.name);

  
  	kernfs_put_active(new_parent);
  	kernfs_put_active(kn);
  	return ret;

  }

  const struct inode_operations kernfs_dir_iops = {

  	.lookup		= kernfs_iop_lookup,
  	.permission	= kernfs_iop_permission,
  	.setattr	= kernfs_iop_setattr,
  	.getattr	= kernfs_iop_getattr,

  	.listxattr	= kernfs_iop_listxattr,

  
  	.mkdir		= kernfs_iop_mkdir,
  	.rmdir		= kernfs_iop_rmdir,
  	.rename		= kernfs_iop_rename,

  };

  static struct kernfs_node *kernfs_leftmost_descendant(struct kernfs_node *pos)

  {

  	struct kernfs_node *last;

  
  	while (true) {
  		struct rb_node *rbn;
  
  		last = pos;

  		if (kernfs_type(pos) != KERNFS_DIR)

  			break;

  		rbn = rb_first(&pos->dir.children);

  		if (!rbn)
  			break;

  		pos = rb_to_kn(rbn);

  	}
  
  	return last;
  }
  
  /**

   * kernfs_next_descendant_post - find the next descendant for post-order walk

   * @pos: the current position (%NULL to initiate traversal)

   * @root: kernfs_node whose descendants to walk

   *
   * Find the next descendant to visit for post-order traversal of @root's
   * descendants.  @root is included in the iteration and the last node to be
   * visited.
   */

  static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
  						       struct kernfs_node *root)

  {
  	struct rb_node *rbn;

  	lockdep_assert_held(&kernfs_mutex);

  
  	/* if first iteration, visit leftmost descendant which may be root */
  	if (!pos)

  		return kernfs_leftmost_descendant(root);

  
  	/* if we visited @root, we're done */
  	if (pos == root)
  		return NULL;
  
  	/* if there's an unvisited sibling, visit its leftmost descendant */

  	rbn = rb_next(&pos->rb);

  	if (rbn)

  		return kernfs_leftmost_descendant(rb_to_kn(rbn));

  
  	/* no sibling left, visit parent */

  	return pos->parent;

  }

  /**
   * kernfs_activate - activate a node which started deactivated
   * @kn: kernfs_node whose subtree is to be activated
   *
   * If the root has KERNFS_ROOT_CREATE_DEACTIVATED set, a newly created node
   * needs to be explicitly activated.  A node which hasn't been activated
   * isn't visible to userland and deactivation is skipped during its
   * removal.  This is useful to construct atomic init sequences where
   * creation of multiple nodes should either succeed or fail atomically.
   *
   * The caller is responsible for ensuring that this function is not called
   * after kernfs_remove*() is invoked on @kn.
   */
  void kernfs_activate(struct kernfs_node *kn)
  {
  	struct kernfs_node *pos;
  
  	mutex_lock(&kernfs_mutex);
  
  	pos = NULL;
  	while ((pos = kernfs_next_descendant_post(pos, kn))) {
  		if (!pos || (pos->flags & KERNFS_ACTIVATED))
  			continue;
  
  		WARN_ON_ONCE(pos->parent && RB_EMPTY_NODE(&pos->rb));
  		WARN_ON_ONCE(atomic_read(&pos->active) != KN_DEACTIVATED_BIAS);
  
  		atomic_sub(KN_DEACTIVATED_BIAS, &pos->active);
  		pos->flags |= KERNFS_ACTIVATED;
  	}
  
  	mutex_unlock(&kernfs_mutex);
  }

  static void __kernfs_remove(struct kernfs_node *kn)

  {

  	struct kernfs_node *pos;
  
  	lockdep_assert_held(&kernfs_mutex);

  	/*
  	 * Short-circuit if non-root @kn has already finished removal.
  	 * This is for kernfs_remove_self() which plays with active ref
  	 * after removal.
  	 */
  	if (!kn || (kn->parent && RB_EMPTY_NODE(&kn->rb)))

  		return;

  	pr_debug("kernfs %s: removing
  ", kn->name);

  	/* prevent any new usage under @kn by deactivating all nodes */

  	pos = NULL;
  	while ((pos = kernfs_next_descendant_post(pos, kn)))

  		if (kernfs_active(pos))
  			atomic_add(KN_DEACTIVATED_BIAS, &pos->active);

  
  	/* deactivate and unlink the subtree node-by-node */

  	do {

  		pos = kernfs_leftmost_descendant(kn);
  
  		/*

  		 * kernfs_drain() drops kernfs_mutex temporarily and @pos's
  		 * base ref could have been put by someone else by the time
  		 * the function returns.  Make sure it doesn't go away
  		 * underneath us.

  		 */
  		kernfs_get(pos);

  		/*
  		 * Drain iff @kn was activated.  This avoids draining and
  		 * its lockdep annotations for nodes which have never been
  		 * activated and allows embedding kernfs_remove() in create
  		 * error paths without worrying about draining.
  		 */
  		if (kn->flags & KERNFS_ACTIVATED)
  			kernfs_drain(pos);
  		else
  			WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS);

  
  		/*
  		 * kernfs_unlink_sibling() succeeds once per node.  Use it
  		 * to decide who's responsible for cleanups.
  		 */
  		if (!pos->parent || kernfs_unlink_sibling(pos)) {
  			struct kernfs_iattrs *ps_iattr =
  				pos->parent ? pos->parent->iattr : NULL;
  
  			/* update timestamps on the parent */
  			if (ps_iattr) {

  				ktime_get_real_ts(&ps_iattr->ia_iattr.ia_ctime);
  				ps_iattr->ia_iattr.ia_mtime =
  					ps_iattr->ia_iattr.ia_ctime;

  			}

  			kernfs_put(pos);

  		}
  
  		kernfs_put(pos);
  	} while (pos != kn);

  }
  
  /**

   * kernfs_remove - remove a kernfs_node recursively
   * @kn: the kernfs_node to remove

   *

   * Remove @kn along with all its subdirectories and files.

   */

  void kernfs_remove(struct kernfs_node *kn)

  {

  	mutex_lock(&kernfs_mutex);
  	__kernfs_remove(kn);
  	mutex_unlock(&kernfs_mutex);

  }
  
  /**

   * kernfs_break_active_protection - break out of active protection
   * @kn: the self kernfs_node
   *
   * The caller must be running off of a kernfs operation which is invoked
   * with an active reference - e.g. one of kernfs_ops.  Each invocation of
   * this function must also be matched with an invocation of
   * kernfs_unbreak_active_protection().
   *
   * This function releases the active reference of @kn the caller is
   * holding.  Once this function is called, @kn may be removed at any point
   * and the caller is solely responsible for ensuring that the objects it
   * dereferences are accessible.
   */
  void kernfs_break_active_protection(struct kernfs_node *kn)
  {
  	/*
  	 * Take out ourself out of the active ref dependency chain.  If
  	 * we're called without an active ref, lockdep will complain.
  	 */
  	kernfs_put_active(kn);
  }
  
  /**
   * kernfs_unbreak_active_protection - undo kernfs_break_active_protection()
   * @kn: the self kernfs_node
   *
   * If kernfs_break_active_protection() was called, this function must be
   * invoked before finishing the kernfs operation.  Note that while this
   * function restores the active reference, it doesn't and can't actually
   * restore the active protection - @kn may already or be in the process of
   * being removed.  Once kernfs_break_active_protection() is invoked, that
   * protection is irreversibly gone for the kernfs operation instance.
   *
   * While this function may be called at any point after
   * kernfs_break_active_protection() is invoked, its most useful location
   * would be right before the enclosing kernfs operation returns.
   */
  void kernfs_unbreak_active_protection(struct kernfs_node *kn)
  {
  	/*
  	 * @kn->active could be in any state; however, the increment we do
  	 * here will be undone as soon as the enclosing kernfs operation
  	 * finishes and this temporary bump can't break anything.  If @kn
  	 * is alive, nothing changes.  If @kn is being deactivated, the
  	 * soon-to-follow put will either finish deactivation or restore
  	 * deactivated state.  If @kn is already removed, the temporary
  	 * bump is guaranteed to be gone before @kn is released.
  	 */
  	atomic_inc(&kn->active);
  	if (kernfs_lockdep(kn))
  		rwsem_acquire(&kn->dep_map, 0, 1, _RET_IP_);
  }
  
  /**
   * kernfs_remove_self - remove a kernfs_node from its own method
   * @kn: the self kernfs_node to remove
   *
   * The caller must be running off of a kernfs operation which is invoked
   * with an active reference - e.g. one of kernfs_ops.  This can be used to
   * implement a file operation which deletes itself.
   *
   * For example, the "delete" file for a sysfs device directory can be
   * implemented by invoking kernfs_remove_self() on the "delete" file
   * itself.  This function breaks the circular dependency of trying to
   * deactivate self while holding an active ref itself.  It isn't necessary
   * to modify the usual removal path to use kernfs_remove_self().  The
   * "delete" implementation can simply invoke kernfs_remove_self() on self
   * before proceeding with the usual removal path.  kernfs will ignore later
   * kernfs_remove() on self.
   *
   * kernfs_remove_self() can be called multiple times concurrently on the
   * same kernfs_node.  Only the first one actually performs removal and
   * returns %true.  All others will wait until the kernfs operation which
   * won self-removal finishes and return %false.  Note that the losers wait
   * for the completion of not only the winning kernfs_remove_self() but also
   * the whole kernfs_ops which won the arbitration.  This can be used to
   * guarantee, for example, all concurrent writes to a "delete" file to
   * finish only after the whole operation is complete.
   */
  bool kernfs_remove_self(struct kernfs_node *kn)
  {
  	bool ret;
  
  	mutex_lock(&kernfs_mutex);
  	kernfs_break_active_protection(kn);
  
  	/*
  	 * SUICIDAL is used to arbitrate among competing invocations.  Only
  	 * the first one will actually perform removal.  When the removal
  	 * is complete, SUICIDED is set and the active ref is restored
  	 * while holding kernfs_mutex.  The ones which lost arbitration
  	 * waits for SUICDED && drained which can happen only after the
  	 * enclosing kernfs operation which executed the winning instance
  	 * of kernfs_remove_self() finished.
  	 */
  	if (!(kn->flags & KERNFS_SUICIDAL)) {
  		kn->flags |= KERNFS_SUICIDAL;
  		__kernfs_remove(kn);
  		kn->flags |= KERNFS_SUICIDED;
  		ret = true;
  	} else {
  		wait_queue_head_t *waitq = &kernfs_root(kn)->deactivate_waitq;
  		DEFINE_WAIT(wait);
  
  		while (true) {
  			prepare_to_wait(waitq, &wait, TASK_UNINTERRUPTIBLE);
  
  			if ((kn->flags & KERNFS_SUICIDED) &&
  			    atomic_read(&kn->active) == KN_DEACTIVATED_BIAS)
  				break;
  
  			mutex_unlock(&kernfs_mutex);
  			schedule();
  			mutex_lock(&kernfs_mutex);
  		}
  		finish_wait(waitq, &wait);
  		WARN_ON_ONCE(!RB_EMPTY_NODE(&kn->rb));
  		ret = false;
  	}
  
  	/*
  	 * This must be done while holding kernfs_mutex; otherwise, waiting
  	 * for SUICIDED && deactivated could finish prematurely.
  	 */
  	kernfs_unbreak_active_protection(kn);
  
  	mutex_unlock(&kernfs_mutex);
  	return ret;
  }
  
  /**

   * kernfs_remove_by_name_ns - find a kernfs_node by name and remove it
   * @parent: parent of the target
   * @name: name of the kernfs_node to remove
   * @ns: namespace tag of the kernfs_node to remove

   *

   * Look for the kernfs_node with @name and @ns under @parent and remove it.
   * Returns 0 on success, -ENOENT if such entry doesn't exist.

   */

  int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,

  			     const void *ns)
  {

  	struct kernfs_node *kn;

  	if (!parent) {

  		WARN(1, KERN_WARNING "kernfs: can not remove '%s', no directory
  ",

  			name);
  		return -ENOENT;
  	}

  	mutex_lock(&kernfs_mutex);

  	kn = kernfs_find_ns(parent, name, ns);
  	if (kn)

  		__kernfs_remove(kn);

  	mutex_unlock(&kernfs_mutex);

  	if (kn)

  		return 0;
  	else
  		return -ENOENT;
  }
  
  /**
   * kernfs_rename_ns - move and rename a kernfs_node

   * @kn: target node

   * @new_parent: new parent to put @sd under
   * @new_name: new name
   * @new_ns: new namespace tag
   */

  int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,

  		     const char *new_name, const void *new_ns)
  {

  	struct kernfs_node *old_parent;
  	const char *old_name = NULL;

  	int error;

  	/* can't move or rename root */
  	if (!kn->parent)
  		return -EINVAL;

  	mutex_lock(&kernfs_mutex);

  	error = -ENOENT;

  	if (!kernfs_active(kn) || !kernfs_active(new_parent) ||
  	    (new_parent->flags & KERNFS_EMPTY_DIR))

  		goto out;

  	error = 0;

  	if ((kn->parent == new_parent) && (kn->ns == new_ns) &&
  	    (strcmp(kn->name, new_name) == 0))

  		goto out;	/* nothing to rename */

  
  	error = -EEXIST;
  	if (kernfs_find_ns(new_parent, new_name, new_ns))

  		goto out;

  	/* rename kernfs_node */

  	if (strcmp(kn->name, new_name) != 0) {

  		error = -ENOMEM;

  		new_name = kstrdup_const(new_name, GFP_KERNEL);

  		if (!new_name)

  			goto out;

  	} else {
  		new_name = NULL;

  	}
  
  	/*
  	 * Move to the appropriate place in the appropriate directories rbtree.
  	 */

  	kernfs_unlink_sibling(kn);

  	kernfs_get(new_parent);

  
  	/* rename_lock protects ->parent and ->name accessors */
  	spin_lock_irq(&kernfs_rename_lock);
  
  	old_parent = kn->parent;

  	kn->parent = new_parent;

  
  	kn->ns = new_ns;
  	if (new_name) {

  		old_name = kn->name;

  		kn->name = new_name;
  	}
  
  	spin_unlock_irq(&kernfs_rename_lock);

  	kn->hash = kernfs_name_hash(kn->name, kn->ns);

  	kernfs_link_sibling(kn);

  	kernfs_put(old_parent);

  	kfree_const(old_name);

  	error = 0;

   out:

  	mutex_unlock(&kernfs_mutex);

  	return error;
  }

  /* Relationship between s_mode and the DT_xxx types */

  static inline unsigned char dt_type(struct kernfs_node *kn)

  {

  	return (kn->mode >> 12) & 15;

  }

  static int kernfs_dir_fop_release(struct inode *inode, struct file *filp)

  {
  	kernfs_put(filp->private_data);
  	return 0;
  }

  static struct kernfs_node *kernfs_dir_pos(const void *ns,

  	struct kernfs_node *parent, loff_t hash, struct kernfs_node *pos)

  {
  	if (pos) {

  		int valid = kernfs_active(pos) &&

  			pos->parent == parent && hash == pos->hash;

  		kernfs_put(pos);
  		if (!valid)
  			pos = NULL;
  	}
  	if (!pos && (hash > 1) && (hash < INT_MAX)) {

  		struct rb_node *node = parent->dir.children.rb_node;

  		while (node) {

  			pos = rb_to_kn(node);

  			if (hash < pos->hash)

  				node = node->rb_left;

  			else if (hash > pos->hash)

  				node = node->rb_right;
  			else
  				break;
  		}
  	}

  	/* Skip over entries which are dying/dead or in the wrong namespace */
  	while (pos && (!kernfs_active(pos) || pos->ns != ns)) {

  		struct rb_node *node = rb_next(&pos->rb);

  		if (!node)
  			pos = NULL;
  		else

  			pos = rb_to_kn(node);

  	}
  	return pos;
  }

  static struct kernfs_node *kernfs_dir_next_pos(const void *ns,

  	struct kernfs_node *parent, ino_t ino, struct kernfs_node *pos)

  {

  	pos = kernfs_dir_pos(ns, parent, ino, pos);

  	if (pos) {

  		do {

  			struct rb_node *node = rb_next(&pos->rb);

  			if (!node)
  				pos = NULL;
  			else

  				pos = rb_to_kn(node);

  		} while (pos && (!kernfs_active(pos) || pos->ns != ns));
  	}

  	return pos;
  }

  static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)

  {
  	struct dentry *dentry = file->f_path.dentry;

  	struct kernfs_node *parent = dentry->d_fsdata;
  	struct kernfs_node *pos = file->private_data;

  	const void *ns = NULL;
  
  	if (!dir_emit_dots(file, ctx))
  		return 0;

  	mutex_lock(&kernfs_mutex);

  	if (kernfs_ns_enabled(parent))

  		ns = kernfs_info(dentry->d_sb)->ns;

  	for (pos = kernfs_dir_pos(ns, parent, ctx->pos, pos);

  	     pos;

  	     pos = kernfs_dir_next_pos(ns, parent, ctx->pos, pos)) {

  		const char *name = pos->name;

  		unsigned int type = dt_type(pos);
  		int len = strlen(name);

  		ino_t ino = pos->ino;

  		ctx->pos = pos->hash;

  		file->private_data = pos;
  		kernfs_get(pos);

  		mutex_unlock(&kernfs_mutex);

  		if (!dir_emit(ctx, name, len, ino, type))
  			return 0;

  		mutex_lock(&kernfs_mutex);

  	}

  	mutex_unlock(&kernfs_mutex);

  	file->private_data = NULL;
  	ctx->pos = INT_MAX;
  	return 0;
  }

  const struct file_operations kernfs_dir_fops = {

  	.read		= generic_read_dir,

  	.iterate_shared	= kernfs_fop_readdir,

  	.release	= kernfs_dir_fop_release,

  	.llseek		= generic_file_llseek,

  };