text: // SPDX-License-Identifier: GPL-2.0-or-later
  /* -*- mode: c; c-basic-offset: 8; -*-
   * vim: noexpandtab sw=8 ts=8 sts=0:
   *
   * dir.c - Operations for configfs directories.
   *
   * Based on sysfs:
   * 	sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
   *
   * configfs Copyright (C) 2005 Oracle.  All rights reserved.
   */
  
  #undef DEBUG
  
  #include <linux/fs.h>
  #include <linux/fsnotify.h>
  #include <linux/mount.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/err.h>
  
  #include <linux/configfs.h>
  #include "configfs_internal.h"
  
  /*
   * Protects mutations of configfs_dirent linkage together with proper i_mutex
   * Also protects mutations of symlinks linkage to target configfs_dirent
   * Mutators of configfs_dirent linkage must *both* have the proper inode locked
   * and configfs_dirent_lock locked, in that order.
   * This allows one to safely traverse configfs_dirent trees and symlinks without
   * having to lock inodes.
   *
   * Protects setting of CONFIGFS_USET_DROPPING: checking the flag
   * unlocked is not reliable unless in detach_groups() called from
   * rmdir()/unregister() and from configfs_attach_group()
   */
  DEFINE_SPINLOCK(configfs_dirent_lock);
  
  static void configfs_d_iput(struct dentry * dentry,
  			    struct inode * inode)
  {
  	struct configfs_dirent *sd = dentry->d_fsdata;
  
  	if (sd) {
  		/* Coordinate with configfs_readdir */
  		spin_lock(&configfs_dirent_lock);
  		/*
  		 * Set sd->s_dentry to null only when this dentry is the one
  		 * that is going to be killed.  Otherwise configfs_d_iput may
  		 * run just after configfs_attach_attr and set sd->s_dentry to
  		 * NULL even it's still in use.
  		 */
  		if (sd->s_dentry == dentry)
  			sd->s_dentry = NULL;
  
  		spin_unlock(&configfs_dirent_lock);
  		configfs_put(sd);
  	}
  	iput(inode);
  }
  
  const struct dentry_operations configfs_dentry_ops = {
  	.d_iput		= configfs_d_iput,
  	.d_delete	= always_delete_dentry,
  };
  
  #ifdef CONFIG_LOCKDEP
  
  /*
   * Helpers to make lockdep happy with our recursive locking of default groups'
   * inodes (see configfs_attach_group() and configfs_detach_group()).
   * We put default groups i_mutexes in separate classes according to their depth
   * from the youngest non-default group ancestor.
   *
   * For a non-default group A having default groups A/B, A/C, and A/C/D, default
   * groups A/B and A/C will have their inode's mutex in class
   * default_group_class[0], and default group A/C/D will be in
   * default_group_class[1].
   *
   * The lock classes are declared and assigned in inode.c, according to the
   * s_depth value.
   * The s_depth value is initialized to -1, adjusted to >= 0 when attaching
   * default groups, and reset to -1 when all default groups are attached. During
   * attachment, if configfs_create() sees s_depth > 0, the lock class of the new
   * inode's mutex is set to default_group_class[s_depth - 1].
   */
  
  static void configfs_init_dirent_depth(struct configfs_dirent *sd)
  {
  	sd->s_depth = -1;
  }
  
  static void configfs_set_dir_dirent_depth(struct configfs_dirent *parent_sd,
  					  struct configfs_dirent *sd)
  {
  	int parent_depth = parent_sd->s_depth;
  
  	if (parent_depth >= 0)
  		sd->s_depth = parent_depth + 1;
  }
  
  static void
  configfs_adjust_dir_dirent_depth_before_populate(struct configfs_dirent *sd)
  {
  	/*
  	 * item's i_mutex class is already setup, so s_depth is now only
  	 * used to set new sub-directories s_depth, which is always done
  	 * with item's i_mutex locked.
  	 */
  	/*
  	 *  sd->s_depth == -1 iff we are a non default group.
  	 *  else (we are a default group) sd->s_depth > 0 (see
  	 *  create_dir()).
  	 */
  	if (sd->s_depth == -1)
  		/*
  		 * We are a non default group and we are going to create
  		 * default groups.
  		 */
  		sd->s_depth = 0;
  }
  
  static void
  configfs_adjust_dir_dirent_depth_after_populate(struct configfs_dirent *sd)
  {
  	/* We will not create default groups anymore. */
  	sd->s_depth = -1;
  }
  
  #else /* CONFIG_LOCKDEP */
  
  static void configfs_init_dirent_depth(struct configfs_dirent *sd)
  {
  }
  
  static void configfs_set_dir_dirent_depth(struct configfs_dirent *parent_sd,
  					  struct configfs_dirent *sd)
  {
  }
  
  static void
  configfs_adjust_dir_dirent_depth_before_populate(struct configfs_dirent *sd)
  {
  }
  
  static void
  configfs_adjust_dir_dirent_depth_after_populate(struct configfs_dirent *sd)
  {
  }
  
  #endif /* CONFIG_LOCKDEP */
  
  static struct configfs_fragment *new_fragment(void)
  {
  	struct configfs_fragment *p;
  
  	p = kmalloc(sizeof(struct configfs_fragment), GFP_KERNEL);
  	if (p) {
  		atomic_set(&p->frag_count, 1);
  		init_rwsem(&p->frag_sem);
  		p->frag_dead = false;
  	}
  	return p;
  }
  
  void put_fragment(struct configfs_fragment *frag)
  {
  	if (frag && atomic_dec_and_test(&frag->frag_count))
  		kfree(frag);
  }
  
  struct configfs_fragment *get_fragment(struct configfs_fragment *frag)
  {
  	if (likely(frag))
  		atomic_inc(&frag->frag_count);
  	return frag;
  }
  
  /*
   * Allocates a new configfs_dirent and links it to the parent configfs_dirent
   */
  static struct configfs_dirent *configfs_new_dirent(struct configfs_dirent *parent_sd,
  						   void *element, int type,
  						   struct configfs_fragment *frag)
  {
  	struct configfs_dirent * sd;
  
  	sd = kmem_cache_zalloc(configfs_dir_cachep, GFP_KERNEL);
  	if (!sd)
  		return ERR_PTR(-ENOMEM);
  
  	atomic_set(&sd->s_count, 1);
  	INIT_LIST_HEAD(&sd->s_children);
  	sd->s_element = element;
  	sd->s_type = type;
  	configfs_init_dirent_depth(sd);
  	spin_lock(&configfs_dirent_lock);
  	if (parent_sd->s_type & CONFIGFS_USET_DROPPING) {
  		spin_unlock(&configfs_dirent_lock);
  		kmem_cache_free(configfs_dir_cachep, sd);
  		return ERR_PTR(-ENOENT);
  	}
  	sd->s_frag = get_fragment(frag);
  	list_add(&sd->s_sibling, &parent_sd->s_children);
  	spin_unlock(&configfs_dirent_lock);
  
  	return sd;
  }
  
  /*
   *
   * Return -EEXIST if there is already a configfs element with the same
   * name for the same parent.
   *
   * called with parent inode's i_mutex held
   */
  static int configfs_dirent_exists(struct configfs_dirent *parent_sd,
  				  const unsigned char *new)
  {
  	struct configfs_dirent * sd;
  
  	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
  		if (sd->s_element) {
  			const unsigned char *existing = configfs_get_name(sd);
  			if (strcmp(existing, new))
  				continue;
  			else
  				return -EEXIST;
  		}
  	}
  
  	return 0;
  }
  
  
  int configfs_make_dirent(struct configfs_dirent * parent_sd,
  			 struct dentry * dentry, void * element,
  			 umode_t mode, int type, struct configfs_fragment *frag)
  {
  	struct configfs_dirent * sd;
  
  	sd = configfs_new_dirent(parent_sd, element, type, frag);
  	if (IS_ERR(sd))
  		return PTR_ERR(sd);
  
  	sd->s_mode = mode;
  	sd->s_dentry = dentry;
  	if (dentry)
  		dentry->d_fsdata = configfs_get(sd);
  
  	return 0;
  }
  
  static void configfs_remove_dirent(struct dentry *dentry)
  {
  	struct configfs_dirent *sd = dentry->d_fsdata;
  
  	if (!sd)
  		return;
  	spin_lock(&configfs_dirent_lock);
  	list_del_init(&sd->s_sibling);
  	spin_unlock(&configfs_dirent_lock);
  	configfs_put(sd);
  }
  
  /**
   *	configfs_create_dir - create a directory for an config_item.
   *	@item:		config_itemwe're creating directory for.
   *	@dentry:	config_item's dentry.
   *
   *	Note: user-created entries won't be allowed under this new directory
   *	until it is validated by configfs_dir_set_ready()
   */
  
  static int configfs_create_dir(struct config_item *item, struct dentry *dentry,
  				struct configfs_fragment *frag)
  {
  	int error;
  	umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;
  	struct dentry *p = dentry->d_parent;
  	struct inode *inode;
  
  	BUG_ON(!item);
  
  	error = configfs_dirent_exists(p->d_fsdata, dentry->d_name.name);
  	if (unlikely(error))
  		return error;
  
  	error = configfs_make_dirent(p->d_fsdata, dentry, item, mode,
  				     CONFIGFS_DIR | CONFIGFS_USET_CREATING,
  				     frag);
  	if (unlikely(error))
  		return error;
  
  	configfs_set_dir_dirent_depth(p->d_fsdata, dentry->d_fsdata);
  	inode = configfs_create(dentry, mode);
  	if (IS_ERR(inode))
  		goto out_remove;
  
  	inode->i_op = &configfs_dir_inode_operations;
  	inode->i_fop = &configfs_dir_operations;
  	/* directory inodes start off with i_nlink == 2 (for "." entry) */
  	inc_nlink(inode);
  	d_instantiate(dentry, inode);
  	/* already hashed */
  	dget(dentry);  /* pin directory dentries in core */
  	inc_nlink(d_inode(p));
  	item->ci_dentry = dentry;
  	return 0;
  
  out_remove:
  	configfs_remove_dirent(dentry);
  	return PTR_ERR(inode);
  }
  
  /*
   * Allow userspace to create new entries under a new directory created with
   * configfs_create_dir(), and under all of its chidlren directories recursively.
   * @sd		configfs_dirent of the new directory to validate
   *
   * Caller must hold configfs_dirent_lock.
   */
  static void configfs_dir_set_ready(struct configfs_dirent *sd)
  {
  	struct configfs_dirent *child_sd;
  
  	sd->s_type &= ~CONFIGFS_USET_CREATING;
  	list_for_each_entry(child_sd, &sd->s_children, s_sibling)
  		if (child_sd->s_type & CONFIGFS_USET_CREATING)
  			configfs_dir_set_ready(child_sd);
  }
  
  /*
   * Check that a directory does not belong to a directory hierarchy being
   * attached and not validated yet.
   * @sd		configfs_dirent of the directory to check
   *
   * @return	non-zero iff the directory was validated
   *
   * Note: takes configfs_dirent_lock, so the result may change from false to true
   * in two consecutive calls, but never from true to false.
   */
  int configfs_dirent_is_ready(struct configfs_dirent *sd)
  {
  	int ret;
  
  	spin_lock(&configfs_dirent_lock);
  	ret = !(sd->s_type & CONFIGFS_USET_CREATING);
  	spin_unlock(&configfs_dirent_lock);
  
  	return ret;
  }
  
  int configfs_create_link(struct configfs_dirent *target, struct dentry *parent,
  		struct dentry *dentry, char *body)
  {
  	int err = 0;
  	umode_t mode = S_IFLNK | S_IRWXUGO;
  	struct configfs_dirent *p = parent->d_fsdata;
  	struct inode *inode;
  
  	err = configfs_make_dirent(p, dentry, target, mode, CONFIGFS_ITEM_LINK,
  			p->s_frag);
  	if (err)
  		return err;
  
  	inode = configfs_create(dentry, mode);
  	if (IS_ERR(inode))
  		goto out_remove;
  
  	inode->i_link = body;
  	inode->i_op = &configfs_symlink_inode_operations;
  	d_instantiate(dentry, inode);
  	dget(dentry);  /* pin link dentries in core */
  	return 0;
  
  out_remove:
  	configfs_remove_dirent(dentry);
  	return PTR_ERR(inode);
  }
  
  static void remove_dir(struct dentry * d)
  {
  	struct dentry * parent = dget(d->d_parent);
  
  	configfs_remove_dirent(d);
  
  	if (d_really_is_positive(d))
  		simple_rmdir(d_inode(parent),d);
  
  	pr_debug(" o %pd removing done (%d)\n", d, d_count(d));
  
  	dput(parent);
  }
  
  /**
   * configfs_remove_dir - remove an config_item's directory.
   * @item:	config_item we're removing.
   *
   * The only thing special about this is that we remove any files in
   * the directory before we remove the directory, and we've inlined
   * what used to be configfs_rmdir() below, instead of calling separately.
   *
   * Caller holds the mutex of the item's inode
   */
  
  static void configfs_remove_dir(struct config_item * item)
  {
  	struct dentry * dentry = dget(item->ci_dentry);
  
  	if (!dentry)
  		return;
  
  	remove_dir(dentry);
  	/**
  	 * Drop reference from dget() on entrance.
  	 */
  	dput(dentry);
  }
  
  
  /* attaches attribute's configfs_dirent to the dentry corresponding to the
   * attribute file
   */
  static int configfs_attach_attr(struct configfs_dirent * sd, struct dentry * dentry)
  {
  	struct configfs_attribute * attr = sd->s_element;
  	struct inode *inode;
  
  	spin_lock(&configfs_dirent_lock);
  	dentry->d_fsdata = configfs_get(sd);
  	sd->s_dentry = dentry;
  	spin_unlock(&configfs_dirent_lock);
  
  	inode = configfs_create(dentry, (attr->ca_mode & S_IALLUGO) | S_IFREG);
  	if (IS_ERR(inode)) {
  		configfs_put(sd);
  		return PTR_ERR(inode);
  	}
  	if (sd->s_type & CONFIGFS_ITEM_BIN_ATTR) {
  		inode->i_size = 0;
  		inode->i_fop = &configfs_bin_file_operations;
  	} else {
  		inode->i_size = PAGE_SIZE;
  		inode->i_fop = &configfs_file_operations;
  	}
  	d_add(dentry, inode);
  	return 0;
  }
  
  static struct dentry * configfs_lookup(struct inode *dir,
  				       struct dentry *dentry,
  				       unsigned int flags)
  {
  	struct configfs_dirent * parent_sd = dentry->d_parent->d_fsdata;
  	struct configfs_dirent * sd;
  	int found = 0;
  	int err;
  
  	/*
  	 * Fake invisibility if dir belongs to a group/default groups hierarchy
  	 * being attached
  	 *
  	 * This forbids userspace to read/write attributes of items which may
  	 * not complete their initialization, since the dentries of the
  	 * attributes won't be instantiated.
  	 */
  	err = -ENOENT;
  	if (!configfs_dirent_is_ready(parent_sd))
  		goto out;
  
  	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
  		if (sd->s_type & CONFIGFS_NOT_PINNED) {
  			const unsigned char * name = configfs_get_name(sd);
  
  			if (strcmp(name, dentry->d_name.name))
  				continue;
  
  			found = 1;
  			err = configfs_attach_attr(sd, dentry);
  			break;
  		}
  	}
  
  	if (!found) {
  		/*
  		 * If it doesn't exist and it isn't a NOT_PINNED item,
  		 * it must be negative.
  		 */
  		if (dentry->d_name.len > NAME_MAX)
  			return ERR_PTR(-ENAMETOOLONG);
  		d_add(dentry, NULL);
  		return NULL;
  	}
  
  out:
  	return ERR_PTR(err);
  }
  
  /*
   * Only subdirectories count here.  Files (CONFIGFS_NOT_PINNED) are
   * attributes and are removed by rmdir().  We recurse, setting
   * CONFIGFS_USET_DROPPING on all children that are candidates for
   * default detach.
   * If there is an error, the caller will reset the flags via
   * configfs_detach_rollback().
   */
  static int configfs_detach_prep(struct dentry *dentry, struct dentry **wait)
  {
  	struct configfs_dirent *parent_sd = dentry->d_fsdata;
  	struct configfs_dirent *sd;
  	int ret;
  
  	/* Mark that we're trying to drop the group */
  	parent_sd->s_type |= CONFIGFS_USET_DROPPING;
  
  	ret = -EBUSY;
  	if (parent_sd->s_links)
  		goto out;
  
  	ret = 0;
  	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
  		if (!sd->s_element ||
  		    (sd->s_type & CONFIGFS_NOT_PINNED))
  			continue;
  		if (sd->s_type & CONFIGFS_USET_DEFAULT) {
  			/* Abort if racing with mkdir() */
  			if (sd->s_type & CONFIGFS_USET_IN_MKDIR) {
  				if (wait)
  					*wait= dget(sd->s_dentry);
  				return -EAGAIN;
  			}
  
  			/*
  			 * Yup, recursive.  If there's a problem, blame
  			 * deep nesting of default_groups
  			 */
  			ret = configfs_detach_prep(sd->s_dentry, wait);
  			if (!ret)
  				continue;
  		} else
  			ret = -ENOTEMPTY;
  
  		break;
  	}
  
  out:
  	return ret;
  }
  
  /*
   * Walk the tree, resetting CONFIGFS_USET_DROPPING wherever it was
   * set.
   */
  static void configfs_detach_rollback(struct dentry *dentry)
  {
  	struct configfs_dirent *parent_sd = dentry->d_fsdata;
  	struct configfs_dirent *sd;
  
  	parent_sd->s_type &= ~CONFIGFS_USET_DROPPING;
  
  	list_for_each_entry(sd, &parent_sd->s_children, s_sibling)
  		if (sd->s_type & CONFIGFS_USET_DEFAULT)
  			configfs_detach_rollback(sd->s_dentry);
  }
  
  static void detach_attrs(struct config_item * item)
  {
  	struct dentry * dentry = dget(item->ci_dentry);
  	struct configfs_dirent * parent_sd;
  	struct configfs_dirent * sd, * tmp;
  
  	if (!dentry)
  		return;
  
  	pr_debug("configfs %s: dropping attrs for  dir\n",
  		 dentry->d_name.name);
  
  	parent_sd = dentry->d_fsdata;
  	list_for_each_entry_safe(sd, tmp, &parent_sd->s_children, s_sibling) {
  		if (!sd->s_element || !(sd->s_type & CONFIGFS_NOT_PINNED))
  			continue;
  		spin_lock(&configfs_dirent_lock);
  		list_del_init(&sd->s_sibling);
  		spin_unlock(&configfs_dirent_lock);
  		configfs_drop_dentry(sd, dentry);
  		configfs_put(sd);
  	}
  
  	/**
  	 * Drop reference from dget() on entrance.
  	 */
  	dput(dentry);
  }
  
  static int populate_attrs(struct config_item *item)
  {
  	const struct config_item_type *t = item->ci_type;
  	struct configfs_attribute *attr;
  	struct configfs_bin_attribute *bin_attr;
  	int error = 0;
  	int i;
  
  	if (!t)
  		return -EINVAL;
  	if (t->ct_attrs) {
  		for (i = 0; (attr = t->ct_attrs[i]) != NULL; i++) {
  			if ((error = configfs_create_file(item, attr)))
  				break;
  		}
  	}
  	if (t->ct_bin_attrs) {
  		for (i = 0; (bin_attr = t->ct_bin_attrs[i]) != NULL; i++) {
  			error = configfs_create_bin_file(item, bin_attr);
  			if (error)
  				break;
  		}
  	}
  
  	if (error)
  		detach_attrs(item);
  
  	return error;
  }
  
  static int configfs_attach_group(struct config_item *parent_item,
  				 struct config_item *item,
  				 struct dentry *dentry,
  				 struct configfs_fragment *frag);
  static void configfs_detach_group(struct config_item *item);
  
  static void detach_groups(struct config_group *group)
  {
  	struct dentry * dentry = dget(group->cg_item.ci_dentry);
  	struct dentry *child;
  	struct configfs_dirent *parent_sd;
  	struct configfs_dirent *sd, *tmp;
  
  	if (!dentry)
  		return;
  
  	parent_sd = dentry->d_fsdata;
  	list_for_each_entry_safe(sd, tmp, &parent_sd->s_children, s_sibling) {
  		if (!sd->s_element ||
  		    !(sd->s_type & CONFIGFS_USET_DEFAULT))
  			continue;
  
  		child = sd->s_dentry;
  
  		inode_lock(d_inode(child));
  
  		configfs_detach_group(sd->s_element);
  		d_inode(child)->i_flags |= S_DEAD;
  		dont_mount(child);
  
  		inode_unlock(d_inode(child));
  
  		d_delete(child);
  		dput(child);
  	}
  
  	/**
  	 * Drop reference from dget() on entrance.
  	 */
  	dput(dentry);
  }
  
  /*
   * This fakes mkdir(2) on a default_groups[] entry.  It
   * creates a dentry, attachs it, and then does fixup
   * on the sd->s_type.
   *
   * We could, perhaps, tweak our parent's ->mkdir for a minute and
   * try using vfs_mkdir.  Just a thought.
   */
  static int create_default_group(struct config_group *parent_group,
  				struct config_group *group,
  				struct configfs_fragment *frag)
  {
  	int ret;
  	struct configfs_dirent *sd;
  	/* We trust the caller holds a reference to parent */
  	struct dentry *child, *parent = parent_group->cg_item.ci_dentry;
  
  	if (!group->cg_item.ci_name)
  		group->cg_item.ci_name = group->cg_item.ci_namebuf;
  
  	ret = -ENOMEM;
  	child = d_alloc_name(parent, group->cg_item.ci_name);
  	if (child) {
  		d_add(child, NULL);
  
  		ret = configfs_attach_group(&parent_group->cg_item,
  					    &group->cg_item, child, frag);
  		if (!ret) {
  			sd = child->d_fsdata;
  			sd->s_type |= CONFIGFS_USET_DEFAULT;
  		} else {
  			BUG_ON(d_inode(child));
  			d_drop(child);
  			dput(child);
  		}
  	}
  
  	return ret;
  }
  
  static int populate_groups(struct config_group *group,
  			   struct configfs_fragment *frag)
  {
  	struct config_group *new_group;
  	int ret = 0;
  
  	list_for_each_entry(new_group, &group->default_groups, group_entry) {
  		ret = create_default_group(group, new_group, frag);
  		if (ret) {
  			detach_groups(group);
  			break;
  		}
  	}
  
  	return ret;
  }
  
  void configfs_remove_default_groups(struct config_group *group)
  {
  	struct config_group *g, *n;
  
  	list_for_each_entry_safe(g, n, &group->default_groups, group_entry) {
  		list_del(&g->group_entry);
  		config_item_put(&g->cg_item);
  	}
  }
  EXPORT_SYMBOL(configfs_remove_default_groups);
  
  /*
   * All of link_obj/unlink_obj/link_group/unlink_group require that
   * subsys->su_mutex is held.
   */
  
  static void unlink_obj(struct config_item *item)
  {
  	struct config_group *group;
  
  	group = item->ci_group;
  	if (group) {
  		list_del_init(&item->ci_entry);
  
  		item->ci_group = NULL;
  		item->ci_parent = NULL;
  
  		/* Drop the reference for ci_entry */
  		config_item_put(item);
  
  		/* Drop the reference for ci_parent */
  		config_group_put(group);
  	}
  }
  
  static void link_obj(struct config_item *parent_item, struct config_item *item)
  {
  	/*
  	 * Parent seems redundant with group, but it makes certain
  	 * traversals much nicer.
  	 */
  	item->ci_parent = parent_item;
  
  	/*
  	 * We hold a reference on the parent for the child's ci_parent
  	 * link.
  	 */
  	item->ci_group = config_group_get(to_config_group(parent_item));
  	list_add_tail(&item->ci_entry, &item->ci_group->cg_children);
  
  	/*
  	 * We hold a reference on the child for ci_entry on the parent's
  	 * cg_children
  	 */
  	config_item_get(item);
  }
  
  static void unlink_group(struct config_group *group)
  {
  	struct config_group *new_group;
  
  	list_for_each_entry(new_group, &group->default_groups, group_entry)
  		unlink_group(new_group);
  
  	group->cg_subsys = NULL;
  	unlink_obj(&group->cg_item);
  }
  
  static void link_group(struct config_group *parent_group, struct config_group *group)
  {
  	struct config_group *new_group;
  	struct configfs_subsystem *subsys = NULL; /* gcc is a turd */
  
  	link_obj(&parent_group->cg_item, &group->cg_item);
  
  	if (parent_group->cg_subsys)
  		subsys = parent_group->cg_subsys;
  	else if (configfs_is_root(&parent_group->cg_item))
  		subsys = to_configfs_subsystem(group);
  	else
  		BUG();
  	group->cg_subsys = subsys;
  
  	list_for_each_entry(new_group, &group->default_groups, group_entry)
  		link_group(group, new_group);
  }
  
  /*
   * The goal is that configfs_attach_item() (and
   * configfs_attach_group()) can be called from either the VFS or this
   * module.  That is, they assume that the items have been created,
   * the dentry allocated, and the dcache is all ready to go.
   *
   * If they fail, they must clean up after themselves as if they
   * had never been called.  The caller (VFS or local function) will
   * handle cleaning up the dcache bits.
   *
   * configfs_detach_group() and configfs_detach_item() behave similarly on
   * the way out.  They assume that the proper semaphores are held, they
   * clean up the configfs items, and they expect their callers will
   * handle the dcache bits.
   */
  static int configfs_attach_item(struct config_item *parent_item,
  				struct config_item *item,
  				struct dentry *dentry,
  				struct configfs_fragment *frag)
  {
  	int ret;
  
  	ret = configfs_create_dir(item, dentry, frag);
  	if (!ret) {
  		ret = populate_attrs(item);
  		if (ret) {
  			/*
  			 * We are going to remove an inode and its dentry but
  			 * the VFS may already have hit and used them. Thus,
  			 * we must lock them as rmdir() would.
  			 */
  			inode_lock(d_inode(dentry));
  			configfs_remove_dir(item);
  			d_inode(dentry)->i_flags |= S_DEAD;
  			dont_mount(dentry);
  			inode_unlock(d_inode(dentry));
  			d_delete(dentry);
  		}
  	}
  
  	return ret;
  }
  
  /* Caller holds the mutex of the item's inode */
  static void configfs_detach_item(struct config_item *item)
  {
  	detach_attrs(item);
  	configfs_remove_dir(item);
  }
  
  static int configfs_attach_group(struct config_item *parent_item,
  				 struct config_item *item,
  				 struct dentry *dentry,
  				 struct configfs_fragment *frag)
  {
  	int ret;
  	struct configfs_dirent *sd;
  
  	ret = configfs_attach_item(parent_item, item, dentry, frag);
  	if (!ret) {
  		sd = dentry->d_fsdata;
  		sd->s_type |= CONFIGFS_USET_DIR;
  
  		/*
  		 * FYI, we're faking mkdir in populate_groups()
  		 * We must lock the group's inode to avoid races with the VFS
  		 * which can already hit the inode and try to add/remove entries
  		 * under it.
  		 *
  		 * We must also lock the inode to remove it safely in case of
  		 * error, as rmdir() would.
  		 */
  		inode_lock_nested(d_inode(dentry), I_MUTEX_CHILD);
  		configfs_adjust_dir_dirent_depth_before_populate(sd);
  		ret = populate_groups(to_config_group(item), frag);
  		if (ret) {
  			configfs_detach_item(item);
  			d_inode(dentry)->i_flags |= S_DEAD;
  			dont_mount(dentry);
  		}
  		configfs_adjust_dir_dirent_depth_after_populate(sd);
  		inode_unlock(d_inode(dentry));
  		if (ret)
  			d_delete(dentry);
  	}
  
  	return ret;
  }
  
  /* Caller holds the mutex of the group's inode */
  static void configfs_detach_group(struct config_item *item)
  {
  	detach_groups(to_config_group(item));
  	configfs_detach_item(item);
  }
  
  /*
   * After the item has been detached from the filesystem view, we are
   * ready to tear it out of the hierarchy.  Notify the client before
   * we do that so they can perform any cleanup that requires
   * navigating the hierarchy.  A client does not need to provide this
   * callback.  The subsystem semaphore MUST be held by the caller, and
   * references must be valid for both items.  It also assumes the
   * caller has validated ci_type.
   */
  static void client_disconnect_notify(struct config_item *parent_item,
  				     struct config_item *item)
  {
  	const struct config_item_type *type;
  
  	type = parent_item->ci_type;
  	BUG_ON(!type);
  
  	if (type->ct_group_ops && type->ct_group_ops->disconnect_notify)
  		type->ct_group_ops->disconnect_notify(to_config_group(parent_item),
  						      item);
  }
  
  /*
   * Drop the initial reference from make_item()/make_group()
   * This function assumes that reference is held on item
   * and that item holds a valid reference to the parent.  Also, it
   * assumes the caller has validated ci_type.
   */
  static void client_drop_item(struct config_item *parent_item,
  			     struct config_item *item)
  {
  	const struct config_item_type *type;
  
  	type = parent_item->ci_type;
  	BUG_ON(!type);
  
  	/*
  	 * If ->drop_item() exists, it is responsible for the
  	 * config_item_put().
  	 */
  	if (type->ct_group_ops && type->ct_group_ops->drop_item)
  		type->ct_group_ops->drop_item(to_config_group(parent_item),
  					      item);
  	else
  		config_item_put(item);
  }
  
  #ifdef DEBUG
  static void configfs_dump_one(struct configfs_dirent *sd, int level)
  {
  	pr_info("%*s\"%s\":\n", level, " ", configfs_get_name(sd));
  
  #define type_print(_type) if (sd->s_type & _type) pr_info("%*s %s\n", level, " ", #_type);
  	type_print(CONFIGFS_ROOT);
  	type_print(CONFIGFS_DIR);
  	type_print(CONFIGFS_ITEM_ATTR);
  	type_print(CONFIGFS_ITEM_LINK);
  	type_print(CONFIGFS_USET_DIR);
  	type_print(CONFIGFS_USET_DEFAULT);
  	type_print(CONFIGFS_USET_DROPPING);
  #undef type_print
  }
  
  static int configfs_dump(struct configfs_dirent *sd, int level)
  {
  	struct configfs_dirent *child_sd;
  	int ret = 0;
  
  	configfs_dump_one(sd, level);
  
  	if (!(sd->s_type & (CONFIGFS_DIR|CONFIGFS_ROOT)))
  		return 0;
  
  	list_for_each_entry(child_sd, &sd->s_children, s_sibling) {
  		ret = configfs_dump(child_sd, level + 2);
  		if (ret)
  			break;
  	}
  
  	return ret;
  }
  #endif
  
  
  /*
   * configfs_depend_item() and configfs_undepend_item()
   *
   * WARNING: Do not call these from a configfs callback!
   *
   * This describes these functions and their helpers.
   *
   * Allow another kernel system to depend on a config_item.  If this
   * happens, the item cannot go away until the dependent can live without
   * it.  The idea is to give client modules as simple an interface as
   * possible.  When a system asks them to depend on an item, they just
   * call configfs_depend_item().  If the item is live and the client
   * driver is in good shape, we'll happily do the work for them.
   *
   * Why is the locking complex?  Because configfs uses the VFS to handle
   * all locking, but this function is called outside the normal
   * VFS->configfs path.  So it must take VFS locks to prevent the
   * VFS->configfs stuff (configfs_mkdir(), configfs_rmdir(), etc).  This is
   * why you can't call these functions underneath configfs callbacks.
   *
   * Note, btw, that this can be called at *any* time, even when a configfs
   * subsystem isn't registered, or when configfs is loading or unloading.
   * Just like configfs_register_subsystem().  So we take the same
   * precautions.  We pin the filesystem.  We lock configfs_dirent_lock.
   * If we can find the target item in the
   * configfs tree, it must be part of the subsystem tree as well, so we
   * do not need the subsystem semaphore.  Holding configfs_dirent_lock helps
   * locking out mkdir() and rmdir(), who might be racing us.
   */
  
  /*
   * configfs_depend_prep()
   *
   * Only subdirectories count here.  Files (CONFIGFS_NOT_PINNED) are
   * attributes.  This is similar but not the same to configfs_detach_prep().
   * Note that configfs_detach_prep() expects the parent to be locked when it
   * is called, but we lock the parent *inside* configfs_depend_prep().  We
   * do that so we can unlock it if we find nothing.
   *
   * Here we do a depth-first search of the dentry hierarchy looking for
   * our object.
   * We deliberately ignore items tagged as dropping since they are virtually
   * dead, as well as items in the middle of attachment since they virtually
   * do not exist yet. This completes the locking out of racing mkdir() and
   * rmdir().
   * Note: subdirectories in the middle of attachment start with s_type =
   * CONFIGFS_DIR|CONFIGFS_USET_CREATING set by create_dir().  When
   * CONFIGFS_USET_CREATING is set, we ignore the item.  The actual set of
   * s_type is in configfs_new_dirent(), which has configfs_dirent_lock.
   *
   * If the target is not found, -ENOENT is bubbled up.
   *
   * This adds a requirement that all config_items be unique!
   *
   * This is recursive.  There isn't
   * much on the stack, though, so folks that need this function - be careful
   * about your stack!  Patches will be accepted to make it iterative.
   */
  static int configfs_depend_prep(struct dentry *origin,
  				struct config_item *target)
  {
  	struct configfs_dirent *child_sd, *sd;
  	int ret = 0;
  
  	BUG_ON(!origin || !origin->d_fsdata);
  	sd = origin->d_fsdata;
  
  	if (sd->s_element == target)  /* Boo-yah */
  		goto out;
  
  	list_for_each_entry(child_sd, &sd->s_children, s_sibling) {
  		if ((child_sd->s_type & CONFIGFS_DIR) &&
  		    !(child_sd->s_type & CONFIGFS_USET_DROPPING) &&
  		    !(child_sd->s_type & CONFIGFS_USET_CREATING)) {
  			ret = configfs_depend_prep(child_sd->s_dentry,
  						   target);
  			if (!ret)
  				goto out;  /* Child path boo-yah */
  		}
  	}
  
  	/* We looped all our children and didn't find target */
  	ret = -ENOENT;
  
  out:
  	return ret;
  }
  
  static int configfs_do_depend_item(struct dentry *subsys_dentry,
  				   struct config_item *target)
  {
  	struct configfs_dirent *p;
  	int ret;
  
  	spin_lock(&configfs_dirent_lock);
  	/* Scan the tree, return 0 if found */
  	ret = configfs_depend_prep(subsys_dentry, target);
  	if (ret)
  		goto out_unlock_dirent_lock;
  
  	/*
  	 * We are sure that the item is not about to be removed by rmdir(), and
  	 * not in the middle of attachment by mkdir().
  	 */
  	p = target->ci_dentry->d_fsdata;
  	p->s_dependent_count += 1;
  
  out_unlock_dirent_lock:
  	spin_unlock(&configfs_dirent_lock);
  
  	return ret;
  }
  
  static inline struct configfs_dirent *
  configfs_find_subsys_dentry(struct configfs_dirent *root_sd,
  			    struct config_item *subsys_item)
  {
  	struct configfs_dirent *p;
  	struct configfs_dirent *ret = NULL;
  
  	list_for_each_entry(p, &root_sd->s_children, s_sibling) {
  		if (p->s_type & CONFIGFS_DIR &&
  		    p->s_element == subsys_item) {
  			ret = p;
  			break;
  		}
  	}
  
  	return ret;
  }
  
  
  int configfs_depend_item(struct configfs_subsystem *subsys,
  			 struct config_item *target)
  {
  	int ret;
  	struct configfs_dirent *subsys_sd;
  	struct config_item *s_item = &subsys->su_group.cg_item;
  	struct dentry *root;
  
  	/*
  	 * Pin the configfs filesystem.  This means we can safely access
  	 * the root of the configfs filesystem.
  	 */
  	root = configfs_pin_fs();
  	if (IS_ERR(root))
  		return PTR_ERR(root);
  
  	/*
  	 * Next, lock the root directory.  We're going to check that the
  	 * subsystem is really registered, and so we need to lock out
  	 * configfs_[un]register_subsystem().
  	 */
  	inode_lock(d_inode(root));
  
  	subsys_sd = configfs_find_subsys_dentry(root->d_fsdata, s_item);
  	if (!subsys_sd) {
  		ret = -ENOENT;
  		goto out_unlock_fs;
  	}
  
  	/* Ok, now we can trust subsys/s_item */
  	ret = configfs_do_depend_item(subsys_sd->s_dentry, target);
  
  out_unlock_fs:
  	inode_unlock(d_inode(root));
  
  	/*
  	 * If we succeeded, the fs is pinned via other methods.  If not,
  	 * we're done with it anyway.  So release_fs() is always right.
  	 */
  	configfs_release_fs();
  
  	return ret;
  }
  EXPORT_SYMBOL(configfs_depend_item);
  
  /*
   * Release the dependent linkage.  This is much simpler than
   * configfs_depend_item() because we know that that the client driver is
   * pinned, thus the subsystem is pinned, and therefore configfs is pinned.
   */
  void configfs_undepend_item(struct config_item *target)
  {
  	struct configfs_dirent *sd;
  
  	/*
  	 * Since we can trust everything is pinned, we just need
  	 * configfs_dirent_lock.
  	 */
  	spin_lock(&configfs_dirent_lock);
  
  	sd = target->ci_dentry->d_fsdata;
  	BUG_ON(sd->s_dependent_count < 1);
  
  	sd->s_dependent_count -= 1;
  
  	/*
  	 * After this unlock, we cannot trust the item to stay alive!
  	 * DO NOT REFERENCE item after this unlock.
  	 */
  	spin_unlock(&configfs_dirent_lock);
  }
  EXPORT_SYMBOL(configfs_undepend_item);
  
  /*
   * caller_subsys is a caller's subsystem not target's. This is used to
   * determine if we should lock root and check subsys or not. When we are
   * in the same subsystem as our target there is no need to do locking as
   * we know that subsys is valid and is not unregistered during this function
   * as we are called from callback of one of his children and VFS holds a lock
   * on some inode. Otherwise we have to lock our root to  ensure that target's
   * subsystem it is not unregistered during this function.
   */
  int configfs_depend_item_unlocked(struct configfs_subsystem *caller_subsys,
  				  struct config_item *target)
  {
  	struct configfs_subsystem *target_subsys;
  	struct config_group *root, *parent;
  	struct configfs_dirent *subsys_sd;
  	int ret = -ENOENT;
  
  	/* Disallow this function for configfs root */
  	if (configfs_is_root(target))
  		return -EINVAL;
  
  	parent = target->ci_group;
  	/*
  	 * This may happen when someone is trying to depend root
  	 * directory of some subsystem
  	 */
  	if (configfs_is_root(&parent->cg_item)) {
  		target_subsys = to_configfs_subsystem(to_config_group(target));
  		root = parent;
  	} else {
  		target_subsys = parent->cg_subsys;
  		/* Find a cofnigfs root as we may need it for locking */
  		for (root = parent; !configfs_is_root(&root->cg_item);
  		     root = root->cg_item.ci_group)
  			;
  	}
  
  	if (target_subsys != caller_subsys) {
  		/*
  		 * We are in other configfs subsystem, so we have to do
  		 * additional locking to prevent other subsystem from being
  		 * unregistered
  		 */
  		inode_lock(d_inode(root->cg_item.ci_dentry));
  
  		/*
  		 * As we are trying to depend item from other subsystem
  		 * we have to check if this subsystem is still registered
  		 */
  		subsys_sd = configfs_find_subsys_dentry(
  				root->cg_item.ci_dentry->d_fsdata,
  				&target_subsys->su_group.cg_item);
  		if (!subsys_sd)
  			goto out_root_unlock;
  	} else {
  		subsys_sd = target_subsys->su_group.cg_item.ci_dentry->d_fsdata;
  	}
  
  	/* Now we can execute core of depend item */
  	ret = configfs_do_depend_item(subsys_sd->s_dentry, target);
  
  	if (target_subsys != caller_subsys)
  out_root_unlock:
  		/*
  		 * We were called from subsystem other than our target so we
  		 * took some locks so now it's time to release them
  		 */
  		inode_unlock(d_inode(root->cg_item.ci_dentry));
  
  	return ret;
  }
  EXPORT_SYMBOL(configfs_depend_item_unlocked);
  
  static int configfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
  {
  	int ret = 0;
  	int module_got = 0;
  	struct config_group *group = NULL;
  	struct config_item *item = NULL;
  	struct config_item *parent_item;
  	struct configfs_subsystem *subsys;
  	struct configfs_dirent *sd;
  	const struct config_item_type *type;
  	struct module *subsys_owner = NULL, *new_item_owner = NULL;
  	struct configfs_fragment *frag;
  	char *name;
  
  	sd = dentry->d_parent->d_fsdata;
  
  	/*
  	 * Fake invisibility if dir belongs to a group/default groups hierarchy
  	 * being attached
  	 */
  	if (!configfs_dirent_is_ready(sd)) {
  		ret = -ENOENT;
  		goto out;
  	}
  
  	if (!(sd->s_type & CONFIGFS_USET_DIR)) {
  		ret = -EPERM;
  		goto out;
  	}
  
  	frag = new_fragment();
  	if (!frag) {
  		ret = -ENOMEM;
  		goto out;
  	}
  
  	/* Get a working ref for the duration of this function */
  	parent_item = configfs_get_config_item(dentry->d_parent);
  	type = parent_item->ci_type;
  	subsys = to_config_group(parent_item)->cg_subsys;
  	BUG_ON(!subsys);
  
  	if (!type || !type->ct_group_ops ||
  	    (!type->ct_group_ops->make_group &&
  	     !type->ct_group_ops->make_item)) {
  		ret = -EPERM;  /* Lack-of-mkdir returns -EPERM */
  		goto out_put;
  	}
  
  	/*
  	 * The subsystem may belong to a different module than the item
  	 * being created.  We don't want to safely pin the new item but
  	 * fail to pin the subsystem it sits under.
  	 */
  	if (!subsys->su_group.cg_item.ci_type) {
  		ret = -EINVAL;
  		goto out_put;
  	}
  	subsys_owner = subsys->su_group.cg_item.ci_type->ct_owner;
  	if (!try_module_get(subsys_owner)) {
  		ret = -EINVAL;
  		goto out_put;
  	}
  
  	name = kmalloc(dentry->d_name.len + 1, GFP_KERNEL);
  	if (!name) {
  		ret = -ENOMEM;
  		goto out_subsys_put;
  	}
  
  	snprintf(name, dentry->d_name.len + 1, "%s", dentry->d_name.name);
  
  	mutex_lock(&subsys->su_mutex);
  	if (type->ct_group_ops->make_group) {
  		group = type->ct_group_ops->make_group(to_config_group(parent_item), name);
  		if (!group)
  			group = ERR_PTR(-ENOMEM);
  		if (!IS_ERR(group)) {
  			link_group(to_config_group(parent_item), group);
  			item = &group->cg_item;
  		} else
  			ret = PTR_ERR(group);
  	} else {
  		item = type->ct_group_ops->make_item(to_config_group(parent_item), name);
  		if (!item)
  			item = ERR_PTR(-ENOMEM);
  		if (!IS_ERR(item))
  			link_obj(parent_item, item);
  		else
  			ret = PTR_ERR(item);
  	}
  	mutex_unlock(&subsys->su_mutex);
  
  	kfree(name);
  	if (ret) {
  		/*
  		 * If ret != 0, then link_obj() was never called.
  		 * There are no extra references to clean up.
  		 */
  		goto out_subsys_put;
  	}
  
  	/*
  	 * link_obj() has been called (via link_group() for groups).
  	 * From here on out, errors must clean that up.
  	 */
  
  	type = item->ci_type;
  	if (!type) {
  		ret = -EINVAL;
  		goto out_unlink;
  	}
  
  	new_item_owner = type->ct_owner;
  	if (!try_module_get(new_item_owner)) {
  		ret = -EINVAL;
  		goto out_unlink;
  	}
  
  	/*
  	 * I hate doing it this way, but if there is
  	 * an error,  module_put() probably should
  	 * happen after any cleanup.
  	 */
  	module_got = 1;
  
  	/*
  	 * Make racing rmdir() fail if it did not tag parent with
  	 * CONFIGFS_USET_DROPPING
  	 * Note: if CONFIGFS_USET_DROPPING is already set, attach_group() will
  	 * fail and let rmdir() terminate correctly
  	 */
  	spin_lock(&configfs_dirent_lock);
  	/* This will make configfs_detach_prep() fail */
  	sd->s_type |= CONFIGFS_USET_IN_MKDIR;
  	spin_unlock(&configfs_dirent_lock);
  
  	if (group)
  		ret = configfs_attach_group(parent_item, item, dentry, frag);
  	else
  		ret = configfs_attach_item(parent_item, item, dentry, frag);
  
  	spin_lock(&configfs_dirent_lock);
  	sd->s_type &= ~CONFIGFS_USET_IN_MKDIR;
  	if (!ret)
  		configfs_dir_set_ready(dentry->d_fsdata);
  	spin_unlock(&configfs_dirent_lock);
  
  out_unlink:
  	if (ret) {
  		/* Tear down everything we built up */
  		mutex_lock(&subsys->su_mutex);
  
  		client_disconnect_notify(parent_item, item);
  		if (group)
  			unlink_group(group);
  		else
  			unlink_obj(item);
  		client_drop_item(parent_item, item);
  
  		mutex_unlock(&subsys->su_mutex);
  
  		if (module_got)
  			module_put(new_item_owner);
  	}
  
  out_subsys_put:
  	if (ret)
  		module_put(subsys_owner);
  
  out_put:
  	/*
  	 * link_obj()/link_group() took a reference from child->parent,
  	 * so the parent is safely pinned.  We can drop our working
  	 * reference.
  	 */
  	config_item_put(parent_item);
  	put_fragment(frag);
  
  out:
  	return ret;
  }
  
  static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
  {
  	struct config_item *parent_item;
  	struct config_item *item;
  	struct configfs_subsystem *subsys;
  	struct configfs_dirent *sd;
  	struct configfs_fragment *frag;
  	struct module *subsys_owner = NULL, *dead_item_owner = NULL;
  	int ret;
  
  	sd = dentry->d_fsdata;
  	if (sd->s_type & CONFIGFS_USET_DEFAULT)
  		return -EPERM;
  
  	/* Get a working ref until we have the child */
  	parent_item = configfs_get_config_item(dentry->d_parent);
  	subsys = to_config_group(parent_item)->cg_subsys;
  	BUG_ON(!subsys);
  
  	if (!parent_item->ci_type) {
  		config_item_put(parent_item);
  		return -EINVAL;
  	}
  
  	/* configfs_mkdir() shouldn't have allowed this */
  	BUG_ON(!subsys->su_group.cg_item.ci_type);
  	subsys_owner = subsys->su_group.cg_item.ci_type->ct_owner;
  
  	/*
  	 * Ensure that no racing symlink() will make detach_prep() fail while
  	 * the new link is temporarily attached
  	 */
  	do {
  		struct dentry *wait;
  
  		mutex_lock(&configfs_symlink_mutex);
  		spin_lock(&configfs_dirent_lock);
  		/*
  		 * Here's where we check for dependents.  We're protected by
  		 * configfs_dirent_lock.
  		 * If no dependent, atomically tag the item as dropping.
  		 */
  		ret = sd->s_dependent_count ? -EBUSY : 0;
  		if (!ret) {
  			ret = configfs_detach_prep(dentry, &wait);
  			if (ret)
  				configfs_detach_rollback(dentry);
  		}
  		spin_unlock(&configfs_dirent_lock);
  		mutex_unlock(&configfs_symlink_mutex);
  
  		if (ret) {
  			if (ret != -EAGAIN) {
  				config_item_put(parent_item);
  				return ret;
  			}
  
  			/* Wait until the racing operation terminates */
  			inode_lock(d_inode(wait));
  			inode_unlock(d_inode(wait));
  			dput(wait);
  		}
  	} while (ret == -EAGAIN);
  
  	frag = sd->s_frag;
  	if (down_write_killable(&frag->frag_sem)) {
  		spin_lock(&configfs_dirent_lock);
  		configfs_detach_rollback(dentry);
  		spin_unlock(&configfs_dirent_lock);
  		config_item_put(parent_item);
  		return -EINTR;
  	}
  	frag->frag_dead = true;
  	up_write(&frag->frag_sem);
  
  	/* Get a working ref for the duration of this function */
  	item = configfs_get_config_item(dentry);
  
  	/* Drop reference from above, item already holds one. */
  	config_item_put(parent_item);
  
  	if (item->ci_type)
  		dead_item_owner = item->ci_type->ct_owner;
  
  	if (sd->s_type & CONFIGFS_USET_DIR) {
  		configfs_detach_group(item);
  
  		mutex_lock(&subsys->su_mutex);
  		client_disconnect_notify(parent_item, item);
  		unlink_group(to_config_group(item));
  	} else {
  		configfs_detach_item(item);
  
  		mutex_lock(&subsys->su_mutex);
  		client_disconnect_notify(parent_item, item);
  		unlink_obj(item);
  	}
  
  	client_drop_item(parent_item, item);
  	mutex_unlock(&subsys->su_mutex);
  
  	/* Drop our reference from above */
  	config_item_put(item);
  
  	module_put(dead_item_owner);
  	module_put(subsys_owner);
  
  	return 0;
  }
  
  const struct inode_operations configfs_dir_inode_operations = {
  	.mkdir		= configfs_mkdir,
  	.rmdir		= configfs_rmdir,
  	.symlink	= configfs_symlink,
  	.unlink		= configfs_unlink,
  	.lookup		= configfs_lookup,
  	.setattr	= configfs_setattr,
  };
  
  const struct inode_operations configfs_root_inode_operations = {
  	.lookup		= configfs_lookup,
  	.setattr	= configfs_setattr,
  };
  
  static int configfs_dir_open(struct inode *inode, struct file *file)
  {
  	struct dentry * dentry = file->f_path.dentry;
  	struct configfs_dirent * parent_sd = dentry->d_fsdata;
  	int err;
  
  	inode_lock(d_inode(dentry));
  	/*
  	 * Fake invisibility if dir belongs to a group/default groups hierarchy
  	 * being attached
  	 */
  	err = -ENOENT;
  	if (configfs_dirent_is_ready(parent_sd)) {
  		file->private_data = configfs_new_dirent(parent_sd, NULL, 0, NULL);
  		if (IS_ERR(file->private_data))
  			err = PTR_ERR(file->private_data);
  		else
  			err = 0;
  	}
  	inode_unlock(d_inode(dentry));
  
  	return err;
  }
  
  static int configfs_dir_close(struct inode *inode, struct file *file)
  {
  	struct dentry * dentry = file->f_path.dentry;
  	struct configfs_dirent * cursor = file->private_data;
  
  	inode_lock(d_inode(dentry));
  	spin_lock(&configfs_dirent_lock);
  	list_del_init(&cursor->s_sibling);
  	spin_unlock(&configfs_dirent_lock);
  	inode_unlock(d_inode(dentry));
  
  	release_configfs_dirent(cursor);
  
  	return 0;
  }
  
  /* Relationship between s_mode and the DT_xxx types */
  static inline unsigned char dt_type(struct configfs_dirent *sd)
  {
  	return (sd->s_mode >> 12) & 15;
  }
  
  static int configfs_readdir(struct file *file, struct dir_context *ctx)
  {
  	struct dentry *dentry = file->f_path.dentry;
  	struct super_block *sb = dentry->d_sb;
  	struct configfs_dirent * parent_sd = dentry->d_fsdata;
  	struct configfs_dirent *cursor = file->private_data;
  	struct list_head *p, *q = &cursor->s_sibling;
  	ino_t ino = 0;
  
  	if (!dir_emit_dots(file, ctx))
  		return 0;
  	spin_lock(&configfs_dirent_lock);
  	if (ctx->pos == 2)
  		list_move(q, &parent_sd->s_children);
  	for (p = q->next; p != &parent_sd->s_children; p = p->next) {
  		struct configfs_dirent *next;
  		const char *name;
  		int len;
  		struct inode *inode = NULL;
  
  		next = list_entry(p, struct configfs_dirent, s_sibling);
  		if (!next->s_element)
  			continue;
  
  		/*
  		 * We'll have a dentry and an inode for
  		 * PINNED items and for open attribute
  		 * files.  We lock here to prevent a race
  		 * with configfs_d_iput() clearing
  		 * s_dentry before calling iput().
  		 *
  		 * Why do we go to the trouble?  If
  		 * someone has an attribute file open,
  		 * the inode number should match until
  		 * they close it.  Beyond that, we don't
  		 * care.
  		 */
  		dentry = next->s_dentry;
  		if (dentry)
  			inode = d_inode(dentry);
  		if (inode)
  			ino = inode->i_ino;
  		spin_unlock(&configfs_dirent_lock);
  		if (!inode)
  			ino = iunique(sb, 2);
  
  		name = configfs_get_name(next);
  		len = strlen(name);
  
  		if (!dir_emit(ctx, name, len, ino, dt_type(next)))
  			return 0;
  
  		spin_lock(&configfs_dirent_lock);
  		list_move(q, p);
  		p = q;
  		ctx->pos++;
  	}
  	spin_unlock(&configfs_dirent_lock);
  	return 0;
  }
  
  static loff_t configfs_dir_lseek(struct file *file, loff_t offset, int whence)
  {
  	struct dentry * dentry = file->f_path.dentry;
  
  	switch (whence) {
  		case 1:
  			offset += file->f_pos;
  			fallthrough;
  		case 0:
  			if (offset >= 0)
  				break;
  			fallthrough;
  		default:
  			return -EINVAL;
  	}
  	if (offset != file->f_pos) {
  		file->f_pos = offset;
  		if (file->f_pos >= 2) {
  			struct configfs_dirent *sd = dentry->d_fsdata;
  			struct configfs_dirent *cursor = file->private_data;
  			struct list_head *p;
  			loff_t n = file->f_pos - 2;
  
  			spin_lock(&configfs_dirent_lock);
  			list_del(&cursor->s_sibling);
  			p = sd->s_children.next;
  			while (n && p != &sd->s_children) {
  				struct configfs_dirent *next;
  				next = list_entry(p, struct configfs_dirent,
  						   s_sibling);
  				if (next->s_element)
  					n--;
  				p = p->next;
  			}
  			list_add_tail(&cursor->s_sibling, p);
  			spin_unlock(&configfs_dirent_lock);
  		}
  	}
  	return offset;
  }
  
  const struct file_operations configfs_dir_operations = {
  	.open		= configfs_dir_open,
  	.release	= configfs_dir_close,
  	.llseek		= configfs_dir_lseek,
  	.read		= generic_read_dir,
  	.iterate_shared	= configfs_readdir,
  };
  
  /**
   * configfs_register_group - creates a parent-child relation between two groups
   * @parent_group:	parent group
   * @group:		child group
   *
   * link groups, creates dentry for the child and attaches it to the
   * parent dentry.
   *
   * Return: 0 on success, negative errno code on error
   */
  int configfs_register_group(struct config_group *parent_group,
  			    struct config_group *group)
  {
  	struct configfs_subsystem *subsys = parent_group->cg_subsys;
  	struct dentry *parent;
  	struct configfs_fragment *frag;
  	int ret;
  
  	frag = new_fragment();
  	if (!frag)
  		return -ENOMEM;
  
  	mutex_lock(&subsys->su_mutex);
  	link_group(parent_group, group);
  	mutex_unlock(&subsys->su_mutex);
  
  	parent = parent_group->cg_item.ci_dentry;
  
  	inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);
  	ret = create_default_group(parent_group, group, frag);
  	if (ret)
  		goto err_out;
  
  	spin_lock(&configfs_dirent_lock);
  	configfs_dir_set_ready(group->cg_item.ci_dentry->d_fsdata);
  	spin_unlock(&configfs_dirent_lock);
  	inode_unlock(d_inode(parent));
  	put_fragment(frag);
  	return 0;
  err_out:
  	inode_unlock(d_inode(parent));
  	mutex_lock(&subsys->su_mutex);
  	unlink_group(group);
  	mutex_unlock(&subsys->su_mutex);
  	put_fragment(frag);
  	return ret;
  }
  EXPORT_SYMBOL(configfs_register_group);
  
  /**
   * configfs_unregister_group() - unregisters a child group from its parent
   * @group: parent group to be unregistered
   *
   * Undoes configfs_register_group()
   */
  void configfs_unregister_group(struct config_group *group)
  {
  	struct configfs_subsystem *subsys = group->cg_subsys;
  	struct dentry *dentry = group->cg_item.ci_dentry;
  	struct dentry *parent = group->cg_item.ci_parent->ci_dentry;
  	struct configfs_dirent *sd = dentry->d_fsdata;
  	struct configfs_fragment *frag = sd->s_frag;
  
  	down_write(&frag->frag_sem);
  	frag->frag_dead = true;
  	up_write(&frag->frag_sem);
  
  	inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);
  	spin_lock(&configfs_dirent_lock);
  	configfs_detach_prep(dentry, NULL);
  	spin_unlock(&configfs_dirent_lock);
  
  	configfs_detach_group(&group->cg_item);
  	d_inode(dentry)->i_flags |= S_DEAD;
  	dont_mount(dentry);
  	fsnotify_rmdir(d_inode(parent), dentry);
  	d_delete(dentry);
  	inode_unlock(d_inode(parent));
  
  	dput(dentry);
  
  	mutex_lock(&subsys->su_mutex);
  	unlink_group(group);
  	mutex_unlock(&subsys->su_mutex);
  }
  EXPORT_SYMBOL(configfs_unregister_group);
  
  /**
   * configfs_register_default_group() - allocates and registers a child group
   * @parent_group:	parent group
   * @name:		child group name
   * @item_type:		child item type description
   *
   * boilerplate to allocate and register a child group with its parent. We need
   * kzalloc'ed memory because child's default_group is initially empty.
   *
   * Return: allocated config group or ERR_PTR() on error
   */
  struct config_group *
  configfs_register_default_group(struct config_group *parent_group,
  				const char *name,
  				const struct config_item_type *item_type)
  {
  	int ret;
  	struct config_group *group;
  
  	group = kzalloc(sizeof(*group), GFP_KERNEL);
  	if (!group)
  		return ERR_PTR(-ENOMEM);
  	config_group_init_type_name(group, name, item_type);
  
  	ret = configfs_register_group(parent_group, group);
  	if (ret) {
  		kfree(group);
  		return ERR_PTR(ret);
  	}
  	return group;
  }
  EXPORT_SYMBOL(configfs_register_default_group);
  
  /**
   * configfs_unregister_default_group() - unregisters and frees a child group
   * @group:	the group to act on
   */
  void configfs_unregister_default_group(struct config_group *group)
  {
  	configfs_unregister_group(group);
  	kfree(group);
  }
  EXPORT_SYMBOL(configfs_unregister_default_group);
  
  int configfs_register_subsystem(struct configfs_subsystem *subsys)
  {
  	int err;
  	struct config_group *group = &subsys->su_group;
  	struct dentry *dentry;
  	struct dentry *root;
  	struct configfs_dirent *sd;
  	struct configfs_fragment *frag;
  
  	frag = new_fragment();
  	if (!frag)
  		return -ENOMEM;
  
  	root = configfs_pin_fs();
  	if (IS_ERR(root)) {
  		put_fragment(frag);
  		return PTR_ERR(root);
  	}
  
  	if (!group->cg_item.ci_name)
  		group->cg_item.ci_name = group->cg_item.ci_namebuf;
  
  	sd = root->d_fsdata;
  	link_group(to_config_group(sd->s_element), group);
  
  	inode_lock_nested(d_inode(root), I_MUTEX_PARENT);
  
  	err = -ENOMEM;
  	dentry = d_alloc_name(root, group->cg_item.ci_name);
  	if (dentry) {
  		d_add(dentry, NULL);
  
  		err = configfs_attach_group(sd->s_element, &group->cg_item,
  					    dentry, frag);
  		if (err) {
  			BUG_ON(d_inode(dentry));
  			d_drop(dentry);
  			dput(dentry);
  		} else {
  			spin_lock(&configfs_dirent_lock);
  			configfs_dir_set_ready(dentry->d_fsdata);
  			spin_unlock(&configfs_dirent_lock);
  		}
  	}
  
  	inode_unlock(d_inode(root));
  
  	if (err) {
  		unlink_group(group);
  		configfs_release_fs();
  	}
  	put_fragment(frag);
  
  	return err;
  }
  
  void configfs_unregister_subsystem(struct configfs_subsystem *subsys)
  {
  	struct config_group *group = &subsys->su_group;
  	struct dentry *dentry = group->cg_item.ci_dentry;
  	struct dentry *root = dentry->d_sb->s_root;
  	struct configfs_dirent *sd = dentry->d_fsdata;
  	struct configfs_fragment *frag = sd->s_frag;
  
  	if (dentry->d_parent != root) {
  		pr_err("Tried to unregister non-subsystem!\n");
  		return;
  	}
  
  	down_write(&frag->frag_sem);
  	frag->frag_dead = true;
  	up_write(&frag->frag_sem);
  
  	inode_lock_nested(d_inode(root),
  			  I_MUTEX_PARENT);
  	inode_lock_nested(d_inode(dentry), I_MUTEX_CHILD);
  	mutex_lock(&configfs_symlink_mutex);
  	spin_lock(&configfs_dirent_lock);
  	if (configfs_detach_prep(dentry, NULL)) {
  		pr_err("Tried to unregister non-empty subsystem!\n");
  	}
  	spin_unlock(&configfs_dirent_lock);
  	mutex_unlock(&configfs_symlink_mutex);
  	configfs_detach_group(&group->cg_item);
  	d_inode(dentry)->i_flags |= S_DEAD;
  	dont_mount(dentry);
  	fsnotify_rmdir(d_inode(root), dentry);
  	inode_unlock(d_inode(dentry));
  
  	d_delete(dentry);
  
  	inode_unlock(d_inode(root));
  
  	dput(dentry);
  
  	unlink_group(group);
  	configfs_release_fs();
  }
  
  EXPORT_SYMBOL(configfs_register_subsystem);
  EXPORT_SYMBOL(configfs_unregister_subsystem);
  