/*
   * 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/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);
  
  #define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
  
  /**
   *	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();
  	unsigned int len = strlen(name);
  	while (len--)
  		hash = partial_name_hash(*name++, hash);
  	hash = (end_name_hash(hash) ^ hash_ptr((void *)ns, 31));
  	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 hash - kn->hash;
  	if (ns != kn->ns)
  		return ns - kn->ns;
  	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;
  
  	if (kernfs_type(kn) == KERNFS_DIR)
  		kn->parent->dir.subdirs++;
  
  	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);
  	return 0;
  }
  
  /**
   *	kernfs_unlink_sibling - unlink kernfs_node from sibling rbtree
   *	@kn: kernfs_node of interest
   *
   *	Unlink @kn from its sibling rbtree which starts from
   *	kn->parent->dir.children.
   *
   *	Locking:
   *	mutex_lock(kernfs_mutex)
   */
  static void kernfs_unlink_sibling(struct kernfs_node *kn)
  {
  	if (kernfs_type(kn) == KERNFS_DIR)
  		kn->parent->dir.subdirs--;
  
  	rb_erase(&kn->rb, &kn->parent->dir.children);
  }
  
  /**
   *	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 (kn->flags & KERNFS_LOCKDEP)
  		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)
  {
  	int v;
  
  	if (unlikely(!kn))
  		return;
  
  	if (kn->flags & KERNFS_LOCKDEP)
  		rwsem_release(&kn->dep_map, 1, _RET_IP_);
  	v = atomic_dec_return(&kn->active);
  	if (likely(v != KN_DEACTIVATED_BIAS))
  		return;
  
  	/*
  	 * atomic_dec_return() is a mb(), we'll always see the updated
  	 * kn->u.completion.
  	 */
  	complete(kn->u.completion);
  }
  
  /**
   *	kernfs_deactivate - deactivate kernfs_node
   *	@kn: kernfs_node to deactivate
   *
   *	Deny new active references and drain existing ones.
   */
  static void kernfs_deactivate(struct kernfs_node *kn)
  {
  	DECLARE_COMPLETION_ONSTACK(wait);
  	int v;
  
  	BUG_ON(!(kn->flags & KERNFS_REMOVED));
  
  	if (!(kernfs_type(kn) & KERNFS_ACTIVE_REF))
  		return;
  
  	kn->u.completion = (void *)&wait;
  
  	if (kn->flags & KERNFS_LOCKDEP)
  		rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
  	/* atomic_add_return() is a mb(), put_active() will always see
  	 * the updated kn->u.completion.
  	 */
  	v = atomic_add_return(KN_DEACTIVATED_BIAS, &kn->active);
  
  	if (v != KN_DEACTIVATED_BIAS) {
  		if (kn->flags & KERNFS_LOCKDEP)
  			lock_contended(&kn->dep_map, _RET_IP_);
  		wait_for_completion(&wait);
  	}
  
  	if (kn->flags & KERNFS_LOCKDEP) {
  		lock_acquired(&kn->dep_map, _RET_IP_);
  		rwsem_release(&kn->dep_map, 1, _RET_IP_);
  	}
  }
  
  /**
   * 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(!(kn->flags & KERNFS_REMOVED), "kernfs: free using entry: %s/%s
  ",
  	     parent ? parent->name : "", kn->name);
  
  	if (kernfs_type(kn) == KERNFS_LINK)
  		kernfs_put(kn->symlink.target_kn);
  	if (!(kn->flags & KERNFS_STATIC_NAME))
  		kfree(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 (!dentry->d_inode)
  		goto out_bad_unlocked;
  
  	kn = dentry->d_fsdata;
  	mutex_lock(&kernfs_mutex);
  
  	/* The kernfs node has been deleted */
  	if (kn->flags & KERNFS_REMOVED)
  		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);
  out_valid:
  	return 1;
  out_bad:
  	mutex_unlock(&kernfs_mutex);
  out_bad_unlocked:
  	/*
  	 * @dentry doesn't match the underlying kernfs node, drop the
  	 * dentry and force lookup.  If we have submounts we must allow the
  	 * vfs caches to lie about the state of the filesystem to prevent
  	 * leaks and other nasty things, so use check_submounts_and_drop()
  	 * instead of d_drop().
  	 */
  	if (check_submounts_and_drop(dentry) != 0)
  		goto out_valid;
  
  	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,
  };
  
  static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
  					     const char *name, umode_t mode,
  					     unsigned flags)
  {
  	char *dup_name = NULL;
  	struct kernfs_node *kn;
  	int ret;
  
  	if (!(flags & KERNFS_STATIC_NAME)) {
  		name = dup_name = kstrdup(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, 0);
  
  	kn->name = name;
  	kn->mode = mode;
  	kn->flags = flags | KERNFS_REMOVED;
  
  	return kn;
  
   err_out2:
  	kmem_cache_free(kernfs_node_cache, kn);
   err_out1:
  	kfree(dup_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_addrm_start - prepare for kernfs_node add/remove
   *	@acxt: pointer to kernfs_addrm_cxt to be used
   *
   *	This function is called when the caller is about to add or remove
   *	kernfs_node.  This function acquires kernfs_mutex.  @acxt is used
   *	to keep and pass context to other addrm functions.
   *
   *	LOCKING:
   *	Kernel thread context (may sleep).  kernfs_mutex is locked on
   *	return.
   */
  void kernfs_addrm_start(struct kernfs_addrm_cxt *acxt)
  	__acquires(kernfs_mutex)
  {
  	memset(acxt, 0, sizeof(*acxt));
  
  	mutex_lock(&kernfs_mutex);
  }
  
  /**
   *	kernfs_add_one - add kernfs_node to parent without warning
   *	@acxt: addrm context to use
   *	@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.
   *
   *	This function should be called between calls to
   *	kernfs_addrm_start() and kernfs_addrm_finish() and should be passed
   *	the same @acxt as passed to kernfs_addrm_start().
   *
   *	LOCKING:
   *	Determined by kernfs_addrm_start().
   *
   *	RETURNS:
   *	0 on success, -EEXIST if entry with the given name already
   *	exists.
   */
  int kernfs_add_one(struct kernfs_addrm_cxt *acxt, struct kernfs_node *kn)
  {
  	struct kernfs_node *parent = kn->parent;
  	bool has_ns = kernfs_ns_enabled(parent);
  	struct kernfs_iattrs *ps_iattr;
  	int ret;
  
  	if (has_ns != (bool)kn->ns) {
  		WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'
  ",
  		     has_ns ? "required" : "invalid", parent->name, kn->name);
  		return -EINVAL;
  	}
  
  	if (kernfs_type(parent) != KERNFS_DIR)
  		return -EINVAL;
  
  	if (parent->flags & KERNFS_REMOVED)
  		return -ENOENT;
  
  	kn->hash = kernfs_name_hash(kn->name, kn->ns);
  
  	ret = kernfs_link_sibling(kn);
  	if (ret)
  		return ret;
  
  	/* Update timestamps on the parent */
  	ps_iattr = parent->iattr;
  	if (ps_iattr) {
  		struct iattr *ps_iattrs = &ps_iattr->ia_iattr;
  		ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
  	}
  
  	/* Mark the entry added into directory tree */
  	kn->flags &= ~KERNFS_REMOVED;
  
  	return 0;
  }
  
  /**
   *	kernfs_remove_one - remove kernfs_node from parent
   *	@acxt: addrm context to use
   *	@kn: kernfs_node to be removed
   *
   *	Mark @kn removed and drop nlink of parent inode if @kn is a
   *	directory.  @kn is unlinked from the children list.
   *
   *	This function should be called between calls to
   *	kernfs_addrm_start() and kernfs_addrm_finish() and should be
   *	passed the same @acxt as passed to kernfs_addrm_start().
   *
   *	LOCKING:
   *	Determined by kernfs_addrm_start().
   */
  static void kernfs_remove_one(struct kernfs_addrm_cxt *acxt,
  			      struct kernfs_node *kn)
  {
  	struct kernfs_iattrs *ps_iattr;
  
  	/*
  	 * Removal can be called multiple times on the same node.  Only the
  	 * first invocation is effective and puts the base ref.
  	 */
  	if (kn->flags & KERNFS_REMOVED)
  		return;
  
  	if (kn->parent) {
  		kernfs_unlink_sibling(kn);
  
  		/* Update timestamps on the parent */
  		ps_iattr = kn->parent->iattr;
  		if (ps_iattr) {
  			ps_iattr->ia_iattr.ia_ctime = CURRENT_TIME;
  			ps_iattr->ia_iattr.ia_mtime = CURRENT_TIME;
  		}
  	}
  
  	kn->flags |= KERNFS_REMOVED;
  	kn->u.removed_list = acxt->removed;
  	acxt->removed = kn;
  }
  
  /**
   *	kernfs_addrm_finish - finish up kernfs_node add/remove
   *	@acxt: addrm context to finish up
   *
   *	Finish up kernfs_node add/remove.  Resources acquired by
   *	kernfs_addrm_start() are released and removed kernfs_nodes are
   *	cleaned up.
   *
   *	LOCKING:
   *	kernfs_mutex is released.
   */
  void kernfs_addrm_finish(struct kernfs_addrm_cxt *acxt)
  	__releases(kernfs_mutex)
  {
  	/* release resources acquired by kernfs_addrm_start() */
  	mutex_unlock(&kernfs_mutex);
  
  	/* kill removed kernfs_nodes */
  	while (acxt->removed) {
  		struct kernfs_node *kn = acxt->removed;
  
  		acxt->removed = kn->u.removed_list;
  
  		kernfs_deactivate(kn);
  		kernfs_unmap_bin_file(kn);
  		kernfs_put(kn);
  	}
  }
  
  /**
   * 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;
  }
  
  /**
   * 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_create_root - create a new kernfs hierarchy
   * @kdops: optional directory syscall operations for the hierarchy
   * @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_dir_ops *kdops, 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);
  
  	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->flags &= ~KERNFS_REMOVED;
  	kn->priv = priv;
  	kn->dir.root = root;
  
  	root->dir_ops = kdops;
  	root->kn = 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_addrm_cxt acxt;
  	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 */
  	kernfs_addrm_start(&acxt);
  	rc = kernfs_add_one(&acxt, kn);
  	kernfs_addrm_finish(&acxt);
  
  	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) {
  		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_materialise_unique(dentry, inode);
   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_dir_ops *kdops = kernfs_root(parent)->dir_ops;
  
  	if (!kdops || !kdops->mkdir)
  		return -EPERM;
  
  	return kdops->mkdir(parent, dentry->d_name.name, mode);
  }
  
  static int kernfs_iop_rmdir(struct inode *dir, struct dentry *dentry)
  {
  	struct kernfs_node *kn  = dentry->d_fsdata;
  	struct kernfs_dir_ops *kdops = kernfs_root(kn)->dir_ops;
  
  	if (!kdops || !kdops->rmdir)
  		return -EPERM;
  
  	return kdops->rmdir(kn);
  }
  
  static int kernfs_iop_rename(struct inode *old_dir, struct dentry *old_dentry,
  			     struct inode *new_dir, struct dentry *new_dentry)
  {
  	struct kernfs_node *kn  = old_dentry->d_fsdata;
  	struct kernfs_node *new_parent = new_dir->i_private;
  	struct kernfs_dir_ops *kdops = kernfs_root(kn)->dir_ops;
  
  	if (!kdops || !kdops->rename)
  		return -EPERM;
  
  	return kdops->rename(kn, new_parent, new_dentry->d_name.name);
  }
  
  const struct inode_operations kernfs_dir_iops = {
  	.lookup		= kernfs_iop_lookup,
  	.permission	= kernfs_iop_permission,
  	.setattr	= kernfs_iop_setattr,
  	.getattr	= kernfs_iop_getattr,
  	.setxattr	= kernfs_iop_setxattr,
  	.removexattr	= kernfs_iop_removexattr,
  	.getxattr	= kernfs_iop_getxattr,
  	.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;
  }
  
  static void __kernfs_remove(struct kernfs_addrm_cxt *acxt,
  			    struct kernfs_node *kn)
  {
  	struct kernfs_node *pos, *next;
  
  	if (!kn)
  		return;
  
  	pr_debug("kernfs %s: removing
  ", kn->name);
  
  	next = NULL;
  	do {
  		pos = next;
  		next = kernfs_next_descendant_post(pos, kn);
  		if (pos)
  			kernfs_remove_one(acxt, pos);
  	} while (next);
  }
  
  /**
   * 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)
  {
  	struct kernfs_addrm_cxt acxt;
  
  	kernfs_addrm_start(&acxt);
  	__kernfs_remove(&acxt, kn);
  	kernfs_addrm_finish(&acxt);
  }
  
  /**
   * 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_addrm_cxt acxt;
  	struct kernfs_node *kn;
  
  	if (!parent) {
  		WARN(1, KERN_WARNING "kernfs: can not remove '%s', no directory
  ",
  			name);
  		return -ENOENT;
  	}
  
  	kernfs_addrm_start(&acxt);
  
  	kn = kernfs_find_ns(parent, name, ns);
  	if (kn)
  		__kernfs_remove(&acxt, kn);
  
  	kernfs_addrm_finish(&acxt);
  
  	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)
  {
  	int error;
  
  	mutex_lock(&kernfs_mutex);
  
  	error = -ENOENT;
  	if ((kn->flags | new_parent->flags) & KERNFS_REMOVED)
  		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(new_name, GFP_KERNEL);
  		if (!new_name)
  			goto out;
  
  		if (kn->flags & KERNFS_STATIC_NAME)
  			kn->flags &= ~KERNFS_STATIC_NAME;
  		else
  			kfree(kn->name);
  
  		kn->name = new_name;
  	}
  
  	/*
  	 * Move to the appropriate place in the appropriate directories rbtree.
  	 */
  	kernfs_unlink_sibling(kn);
  	kernfs_get(new_parent);
  	kernfs_put(kn->parent);
  	kn->ns = new_ns;
  	kn->hash = kernfs_name_hash(kn->name, kn->ns);
  	kn->parent = new_parent;
  	kernfs_link_sibling(kn);
  
  	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 = !(pos->flags & KERNFS_REMOVED) &&
  			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 in the wrong namespace */
  	while (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 && 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;
  }
  
  static loff_t kernfs_dir_fop_llseek(struct file *file, loff_t offset,
  				    int whence)
  {
  	struct inode *inode = file_inode(file);
  	loff_t ret;
  
  	mutex_lock(&inode->i_mutex);
  	ret = generic_file_llseek(file, offset, whence);
  	mutex_unlock(&inode->i_mutex);
  
  	return ret;
  }
  
  const struct file_operations kernfs_dir_fops = {
  	.read		= generic_read_dir,
  	.iterate	= kernfs_fop_readdir,
  	.release	= kernfs_dir_fop_release,
  	.llseek		= kernfs_dir_fop_llseek,
  };