Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

9 files changed, 3498 insertions, 0 deletions

diff --git a/fs/configfs/Kconfig b/fs/configfs/Kconfig
new file mode 100644
index 000000000..272b64456
--- /dev/null
+++ b/fs/configfs/Kconfig
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config CONFIGFS_FS
+	tristate "Userspace-driven configuration filesystem"
+	select SYSFS
+	help
+	  configfs is a RAM-based filesystem that provides the converse
+	  of sysfs's functionality. Where sysfs is a filesystem-based
+	  view of kernel objects, configfs is a filesystem-based manager
+	  of kernel objects, or config_items.
+
+	  Both sysfs and configfs can and should exist together on the
+	  same system. One is not a replacement for the other.
diff --git a/fs/configfs/Makefile b/fs/configfs/Makefile
new file mode 100644
index 000000000..0200498ed
--- /dev/null
+++ b/fs/configfs/Makefile
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Makefile for the configfs virtual filesystem
+#
+
+obj-$(CONFIG_CONFIGFS_FS)	+= configfs.o
+
+configfs-objs	:= inode.o file.o dir.o symlink.o mount.o item.o
diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
new file mode 100644
index 000000000..c0395363e
--- /dev/null
+++ b/fs/configfs/configfs_internal.h
@@ -0,0 +1,159 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * configfs_internal.h - Internal stuff for configfs
+ *
+ * Based on sysfs:
+ * 	sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
+ *
+ * configfs Copyright (C) 2005 Oracle.  All rights reserved.
+ */
+
+#ifdef pr_fmt
+#undef pr_fmt
+#endif
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/slab.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+
+struct configfs_fragment {
+	atomic_t frag_count;
+	struct rw_semaphore frag_sem;
+	bool frag_dead;
+};
+
+void put_fragment(struct configfs_fragment *);
+struct configfs_fragment *get_fragment(struct configfs_fragment *);
+
+struct configfs_dirent {
+	atomic_t		s_count;
+	int			s_dependent_count;
+	struct list_head	s_sibling;
+	struct list_head	s_children;
+	int			s_links;
+	void			* s_element;
+	int			s_type;
+	umode_t			s_mode;
+	struct dentry		* s_dentry;
+	struct iattr		* s_iattr;
+#ifdef CONFIG_LOCKDEP
+	int			s_depth;
+#endif
+	struct configfs_fragment *s_frag;
+};
+
+#define CONFIGFS_ROOT		0x0001
+#define CONFIGFS_DIR		0x0002
+#define CONFIGFS_ITEM_ATTR	0x0004
+#define CONFIGFS_ITEM_BIN_ATTR	0x0008
+#define CONFIGFS_ITEM_LINK	0x0020
+#define CONFIGFS_USET_DIR	0x0040
+#define CONFIGFS_USET_DEFAULT	0x0080
+#define CONFIGFS_USET_DROPPING	0x0100
+#define CONFIGFS_USET_IN_MKDIR	0x0200
+#define CONFIGFS_USET_CREATING	0x0400
+#define CONFIGFS_NOT_PINNED	(CONFIGFS_ITEM_ATTR | CONFIGFS_ITEM_BIN_ATTR)
+
+extern struct mutex configfs_symlink_mutex;
+extern spinlock_t configfs_dirent_lock;
+
+extern struct kmem_cache *configfs_dir_cachep;
+
+extern int configfs_is_root(struct config_item *item);
+
+extern struct inode * configfs_new_inode(umode_t mode, struct configfs_dirent *, struct super_block *);
+extern struct inode *configfs_create(struct dentry *, umode_t mode);
+
+extern int configfs_create_file(struct config_item *, const struct configfs_attribute *);
+extern int configfs_create_bin_file(struct config_item *,
+				    const struct configfs_bin_attribute *);
+extern int configfs_make_dirent(struct configfs_dirent *, struct dentry *,
+				void *, umode_t, int, struct configfs_fragment *);
+extern int configfs_dirent_is_ready(struct configfs_dirent *);
+
+extern void configfs_hash_and_remove(struct dentry * dir, const char * name);
+
+extern const unsigned char * configfs_get_name(struct configfs_dirent *sd);
+extern void configfs_drop_dentry(struct configfs_dirent *sd, struct dentry *parent);
+extern int configfs_setattr(struct user_namespace *mnt_userns,
+			    struct dentry *dentry, struct iattr *iattr);
+
+extern struct dentry *configfs_pin_fs(void);
+extern void configfs_release_fs(void);
+
+extern const struct file_operations configfs_dir_operations;
+extern const struct file_operations configfs_file_operations;
+extern const struct file_operations configfs_bin_file_operations;
+extern const struct inode_operations configfs_dir_inode_operations;
+extern const struct inode_operations configfs_root_inode_operations;
+extern const struct inode_operations configfs_symlink_inode_operations;
+extern const struct dentry_operations configfs_dentry_ops;
+
+extern int configfs_symlink(struct user_namespace *mnt_userns,
+			    struct inode *dir, struct dentry *dentry,
+			    const char *symname);
+extern int configfs_unlink(struct inode *dir, struct dentry *dentry);
+
+int configfs_create_link(struct configfs_dirent *target, struct dentry *parent,
+		struct dentry *dentry, char *body);
+
+static inline struct config_item * to_item(struct dentry * dentry)
+{
+	struct configfs_dirent * sd = dentry->d_fsdata;
+	return ((struct config_item *) sd->s_element);
+}
+
+static inline struct configfs_attribute * to_attr(struct dentry * dentry)
+{
+	struct configfs_dirent * sd = dentry->d_fsdata;
+	return ((struct configfs_attribute *) sd->s_element);
+}
+
+static inline struct configfs_bin_attribute *to_bin_attr(struct dentry *dentry)
+{
+	struct configfs_attribute *attr = to_attr(dentry);
+
+	return container_of(attr, struct configfs_bin_attribute, cb_attr);
+}
+
+static inline struct config_item *configfs_get_config_item(struct dentry *dentry)
+{
+	struct config_item * item = NULL;
+
+	spin_lock(&dentry->d_lock);
+	if (!d_unhashed(dentry)) {
+		struct configfs_dirent * sd = dentry->d_fsdata;
+		item = config_item_get(sd->s_element);
+	}
+	spin_unlock(&dentry->d_lock);
+
+	return item;
+}
+
+static inline void release_configfs_dirent(struct configfs_dirent * sd)
+{
+	if (!(sd->s_type & CONFIGFS_ROOT)) {
+		kfree(sd->s_iattr);
+		put_fragment(sd->s_frag);
+		kmem_cache_free(configfs_dir_cachep, sd);
+	}
+}
+
+static inline struct configfs_dirent * configfs_get(struct configfs_dirent * sd)
+{
+	if (sd) {
+		WARN_ON(!atomic_read(&sd->s_count));
+		atomic_inc(&sd->s_count);
+	}
+	return sd;
+}
+
+static inline void configfs_put(struct configfs_dirent * sd)
+{
+	WARN_ON(!atomic_read(&sd->s_count));
+	if (atomic_dec_and_test(&sd->s_count))
+		release_configfs_dirent(sd);
+}
+
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
new file mode 100644
index 000000000..ec6519e1c
--- /dev/null
+++ b/fs/configfs/dir.c
@@ -0,0 +1,1955 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * 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);
+
+/*
+ * All of link_obj/unlink_obj/link_group/unlink_group require that
+ * subsys->su_mutex is held.
+ * But parent configfs_subsystem is NULL when config_item is root.
+ * Use this mutex when config_item is root.
+ */
+static DEFINE_MUTEX(configfs_subsystem_mutex);
+
+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_lookup 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.
+ *	@frag:		config_item's fragment.
+ *
+ *	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_put(dentry->d_fsdata);
+	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_put(dentry->d_fsdata);
+	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);
+}
+
+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;
+	struct inode *inode = NULL;
+
+	if (dentry->d_name.len > NAME_MAX)
+		return ERR_PTR(-ENAMETOOLONG);
+
+	/*
+	 * 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.
+	 */
+	if (!configfs_dirent_is_ready(parent_sd))
+		return ERR_PTR(-ENOENT);
+
+	spin_lock(&configfs_dirent_lock);
+	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+		if ((sd->s_type & CONFIGFS_NOT_PINNED) &&
+		    !strcmp(configfs_get_name(sd), dentry->d_name.name)) {
+			struct configfs_attribute *attr = sd->s_element;
+			umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
+
+			dentry->d_fsdata = configfs_get(sd);
+			sd->s_dentry = dentry;
+			spin_unlock(&configfs_dirent_lock);
+
+			inode = configfs_create(dentry, mode);
+			if (IS_ERR(inode)) {
+				configfs_put(sd);
+				return ERR_CAST(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;
+			}
+			goto done;
+		}
+	}
+	spin_unlock(&configfs_dirent_lock);
+done:
+	d_add(dentry, inode);
+	return NULL;
+}
+
+/*
+ * 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 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 user_namespace *mnt_userns, 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);
+	d_drop(dentry);
+	fsnotify_rmdir(d_inode(parent), 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;
+	mutex_lock(&configfs_subsystem_mutex);
+	link_group(to_config_group(sd->s_element), group);
+	mutex_unlock(&configfs_subsystem_mutex);
+
+	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) {
+		mutex_lock(&configfs_subsystem_mutex);
+		unlink_group(group);
+		mutex_unlock(&configfs_subsystem_mutex);
+		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);
+	inode_unlock(d_inode(dentry));
+
+	d_drop(dentry);
+	fsnotify_rmdir(d_inode(root), dentry);
+
+	inode_unlock(d_inode(root));
+
+	dput(dentry);
+
+	mutex_lock(&configfs_subsystem_mutex);
+	unlink_group(group);
+	mutex_unlock(&configfs_subsystem_mutex);
+	configfs_release_fs();
+}
+
+EXPORT_SYMBOL(configfs_register_subsystem);
+EXPORT_SYMBOL(configfs_unregister_subsystem);
diff --git a/fs/configfs/file.c b/fs/configfs/file.c
new file mode 100644
index 000000000..0ad321506
--- /dev/null
+++ b/fs/configfs/file.c
@@ -0,0 +1,482 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * file.c - operations for regular (text) files.
+ *
+ * Based on sysfs:
+ * 	sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
+ *
+ * configfs Copyright (C) 2005 Oracle.  All rights reserved.
+ */
+
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/mutex.h>
+#include <linux/vmalloc.h>
+#include <linux/uaccess.h>
+#include <linux/uio.h>
+#include <linux/configfs.h>
+#include "configfs_internal.h"
+
+/*
+ * A simple attribute can only be 4096 characters.  Why 4k?  Because the
+ * original code limited it to PAGE_SIZE.  That's a bad idea, though,
+ * because an attribute of 16k on ia64 won't work on x86.  So we limit to
+ * 4k, our minimum common page size.
+ */
+#define SIMPLE_ATTR_SIZE 4096
+
+struct configfs_buffer {
+	size_t			count;
+	loff_t			pos;
+	char			* page;
+	struct configfs_item_operations	* ops;
+	struct mutex		mutex;
+	int			needs_read_fill;
+	bool			read_in_progress;
+	bool			write_in_progress;
+	char			*bin_buffer;
+	int			bin_buffer_size;
+	int			cb_max_size;
+	struct config_item	*item;
+	struct module		*owner;
+	union {
+		struct configfs_attribute	*attr;
+		struct configfs_bin_attribute	*bin_attr;
+	};
+};
+
+static inline struct configfs_fragment *to_frag(struct file *file)
+{
+	struct configfs_dirent *sd = file->f_path.dentry->d_fsdata;
+
+	return sd->s_frag;
+}
+
+static int fill_read_buffer(struct file *file, struct configfs_buffer *buffer)
+{
+	struct configfs_fragment *frag = to_frag(file);
+	ssize_t count = -ENOENT;
+
+	if (!buffer->page)
+		buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
+	if (!buffer->page)
+		return -ENOMEM;
+
+	down_read(&frag->frag_sem);
+	if (!frag->frag_dead)
+		count = buffer->attr->show(buffer->item, buffer->page);
+	up_read(&frag->frag_sem);
+
+	if (count < 0)
+		return count;
+	if (WARN_ON_ONCE(count > (ssize_t)SIMPLE_ATTR_SIZE))
+		return -EIO;
+	buffer->needs_read_fill = 0;
+	buffer->count = count;
+	return 0;
+}
+
+static ssize_t configfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct file *file = iocb->ki_filp;
+	struct configfs_buffer *buffer = file->private_data;
+	ssize_t retval = 0;
+
+	mutex_lock(&buffer->mutex);
+	if (buffer->needs_read_fill) {
+		retval = fill_read_buffer(file, buffer);
+		if (retval)
+			goto out;
+	}
+	pr_debug("%s: count = %zd, pos = %lld, buf = %s\n",
+		 __func__, iov_iter_count(to), iocb->ki_pos, buffer->page);
+	if (iocb->ki_pos >= buffer->count)
+		goto out;
+	retval = copy_to_iter(buffer->page + iocb->ki_pos,
+			      buffer->count - iocb->ki_pos, to);
+	iocb->ki_pos += retval;
+	if (retval == 0)
+		retval = -EFAULT;
+out:
+	mutex_unlock(&buffer->mutex);
+	return retval;
+}
+
+static ssize_t configfs_bin_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct file *file = iocb->ki_filp;
+	struct configfs_fragment *frag = to_frag(file);
+	struct configfs_buffer *buffer = file->private_data;
+	ssize_t retval = 0;
+	ssize_t len;
+
+	mutex_lock(&buffer->mutex);
+
+	/* we don't support switching read/write modes */
+	if (buffer->write_in_progress) {
+		retval = -ETXTBSY;
+		goto out;
+	}
+	buffer->read_in_progress = true;
+
+	if (buffer->needs_read_fill) {
+		/* perform first read with buf == NULL to get extent */
+		down_read(&frag->frag_sem);
+		if (!frag->frag_dead)
+			len = buffer->bin_attr->read(buffer->item, NULL, 0);
+		else
+			len = -ENOENT;
+		up_read(&frag->frag_sem);
+		if (len <= 0) {
+			retval = len;
+			goto out;
+		}
+
+		/* do not exceed the maximum value */
+		if (buffer->cb_max_size && len > buffer->cb_max_size) {
+			retval = -EFBIG;
+			goto out;
+		}
+
+		buffer->bin_buffer = vmalloc(len);
+		if (buffer->bin_buffer == NULL) {
+			retval = -ENOMEM;
+			goto out;
+		}
+		buffer->bin_buffer_size = len;
+
+		/* perform second read to fill buffer */
+		down_read(&frag->frag_sem);
+		if (!frag->frag_dead)
+			len = buffer->bin_attr->read(buffer->item,
+						     buffer->bin_buffer, len);
+		else
+			len = -ENOENT;
+		up_read(&frag->frag_sem);
+		if (len < 0) {
+			retval = len;
+			vfree(buffer->bin_buffer);
+			buffer->bin_buffer_size = 0;
+			buffer->bin_buffer = NULL;
+			goto out;
+		}
+
+		buffer->needs_read_fill = 0;
+	}
+
+	if (iocb->ki_pos >= buffer->bin_buffer_size)
+		goto out;
+	retval = copy_to_iter(buffer->bin_buffer + iocb->ki_pos,
+			      buffer->bin_buffer_size - iocb->ki_pos, to);
+	iocb->ki_pos += retval;
+	if (retval == 0)
+		retval = -EFAULT;
+out:
+	mutex_unlock(&buffer->mutex);
+	return retval;
+}
+
+/* Fill @buffer with data coming from @from. */
+static int fill_write_buffer(struct configfs_buffer *buffer,
+			     struct iov_iter *from)
+{
+	int copied;
+
+	if (!buffer->page)
+		buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
+	if (!buffer->page)
+		return -ENOMEM;
+
+	copied = copy_from_iter(buffer->page, SIMPLE_ATTR_SIZE - 1, from);
+	buffer->needs_read_fill = 1;
+	/* if buf is assumed to contain a string, terminate it by \0,
+	 * so e.g. sscanf() can scan the string easily */
+	buffer->page[copied] = 0;
+	return copied ? : -EFAULT;
+}
+
+static int
+flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
+{
+	struct configfs_fragment *frag = to_frag(file);
+	int res = -ENOENT;
+
+	down_read(&frag->frag_sem);
+	if (!frag->frag_dead)
+		res = buffer->attr->store(buffer->item, buffer->page, count);
+	up_read(&frag->frag_sem);
+	return res;
+}
+
+
+/*
+ * There is no easy way for us to know if userspace is only doing a partial
+ * write, so we don't support them. We expect the entire buffer to come on the
+ * first write.
+ * Hint: if you're writing a value, first read the file, modify only the value
+ * you're changing, then write entire buffer back.
+ */
+static ssize_t configfs_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct configfs_buffer *buffer = file->private_data;
+	int len;
+
+	mutex_lock(&buffer->mutex);
+	len = fill_write_buffer(buffer, from);
+	if (len > 0)
+		len = flush_write_buffer(file, buffer, len);
+	if (len > 0)
+		iocb->ki_pos += len;
+	mutex_unlock(&buffer->mutex);
+	return len;
+}
+
+static ssize_t configfs_bin_write_iter(struct kiocb *iocb,
+				       struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct configfs_buffer *buffer = file->private_data;
+	void *tbuf = NULL;
+	size_t end_offset;
+	ssize_t len;
+
+	mutex_lock(&buffer->mutex);
+
+	/* we don't support switching read/write modes */
+	if (buffer->read_in_progress) {
+		len = -ETXTBSY;
+		goto out;
+	}
+	buffer->write_in_progress = true;
+
+	/* buffer grows? */
+	end_offset = iocb->ki_pos + iov_iter_count(from);
+	if (end_offset > buffer->bin_buffer_size) {
+		if (buffer->cb_max_size && end_offset > buffer->cb_max_size) {
+			len = -EFBIG;
+			goto out;
+		}
+
+		tbuf = vmalloc(end_offset);
+		if (tbuf == NULL) {
+			len = -ENOMEM;
+			goto out;
+		}
+
+		/* copy old contents */
+		if (buffer->bin_buffer) {
+			memcpy(tbuf, buffer->bin_buffer,
+				buffer->bin_buffer_size);
+			vfree(buffer->bin_buffer);
+		}
+
+		/* clear the new area */
+		memset(tbuf + buffer->bin_buffer_size, 0,
+			end_offset - buffer->bin_buffer_size);
+		buffer->bin_buffer = tbuf;
+		buffer->bin_buffer_size = end_offset;
+	}
+
+	len = copy_from_iter(buffer->bin_buffer + iocb->ki_pos,
+			     buffer->bin_buffer_size - iocb->ki_pos, from);
+	iocb->ki_pos += len;
+out:
+	mutex_unlock(&buffer->mutex);
+	return len ? : -EFAULT;
+}
+
+static int __configfs_open_file(struct inode *inode, struct file *file, int type)
+{
+	struct dentry *dentry = file->f_path.dentry;
+	struct configfs_fragment *frag = to_frag(file);
+	struct configfs_attribute *attr;
+	struct configfs_buffer *buffer;
+	int error;
+
+	error = -ENOMEM;
+	buffer = kzalloc(sizeof(struct configfs_buffer), GFP_KERNEL);
+	if (!buffer)
+		goto out;
+
+	error = -ENOENT;
+	down_read(&frag->frag_sem);
+	if (unlikely(frag->frag_dead))
+		goto out_free_buffer;
+
+	error = -EINVAL;
+	buffer->item = to_item(dentry->d_parent);
+	if (!buffer->item)
+		goto out_free_buffer;
+
+	attr = to_attr(dentry);
+	if (!attr)
+		goto out_free_buffer;
+
+	if (type & CONFIGFS_ITEM_BIN_ATTR) {
+		buffer->bin_attr = to_bin_attr(dentry);
+		buffer->cb_max_size = buffer->bin_attr->cb_max_size;
+	} else {
+		buffer->attr = attr;
+	}
+
+	buffer->owner = attr->ca_owner;
+	/* Grab the module reference for this attribute if we have one */
+	error = -ENODEV;
+	if (!try_module_get(buffer->owner))
+		goto out_free_buffer;
+
+	error = -EACCES;
+	if (!buffer->item->ci_type)
+		goto out_put_module;
+
+	buffer->ops = buffer->item->ci_type->ct_item_ops;
+
+	/* File needs write support.
+	 * The inode's perms must say it's ok,
+	 * and we must have a store method.
+	 */
+	if (file->f_mode & FMODE_WRITE) {
+		if (!(inode->i_mode & S_IWUGO))
+			goto out_put_module;
+		if ((type & CONFIGFS_ITEM_ATTR) && !attr->store)
+			goto out_put_module;
+		if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->write)
+			goto out_put_module;
+	}
+
+	/* File needs read support.
+	 * The inode's perms must say it's ok, and we there
+	 * must be a show method for it.
+	 */
+	if (file->f_mode & FMODE_READ) {
+		if (!(inode->i_mode & S_IRUGO))
+			goto out_put_module;
+		if ((type & CONFIGFS_ITEM_ATTR) && !attr->show)
+			goto out_put_module;
+		if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->read)
+			goto out_put_module;
+	}
+
+	mutex_init(&buffer->mutex);
+	buffer->needs_read_fill = 1;
+	buffer->read_in_progress = false;
+	buffer->write_in_progress = false;
+	file->private_data = buffer;
+	up_read(&frag->frag_sem);
+	return 0;
+
+out_put_module:
+	module_put(buffer->owner);
+out_free_buffer:
+	up_read(&frag->frag_sem);
+	kfree(buffer);
+out:
+	return error;
+}
+
+static int configfs_release(struct inode *inode, struct file *filp)
+{
+	struct configfs_buffer *buffer = filp->private_data;
+
+	module_put(buffer->owner);
+	if (buffer->page)
+		free_page((unsigned long)buffer->page);
+	mutex_destroy(&buffer->mutex);
+	kfree(buffer);
+	return 0;
+}
+
+static int configfs_open_file(struct inode *inode, struct file *filp)
+{
+	return __configfs_open_file(inode, filp, CONFIGFS_ITEM_ATTR);
+}
+
+static int configfs_open_bin_file(struct inode *inode, struct file *filp)
+{
+	return __configfs_open_file(inode, filp, CONFIGFS_ITEM_BIN_ATTR);
+}
+
+static int configfs_release_bin_file(struct inode *inode, struct file *file)
+{
+	struct configfs_buffer *buffer = file->private_data;
+
+	if (buffer->write_in_progress) {
+		struct configfs_fragment *frag = to_frag(file);
+
+		down_read(&frag->frag_sem);
+		if (!frag->frag_dead) {
+			/* result of ->release() is ignored */
+			buffer->bin_attr->write(buffer->item,
+					buffer->bin_buffer,
+					buffer->bin_buffer_size);
+		}
+		up_read(&frag->frag_sem);
+	}
+
+	vfree(buffer->bin_buffer);
+
+	configfs_release(inode, file);
+	return 0;
+}
+
+
+const struct file_operations configfs_file_operations = {
+	.read_iter	= configfs_read_iter,
+	.write_iter	= configfs_write_iter,
+	.llseek		= generic_file_llseek,
+	.open		= configfs_open_file,
+	.release	= configfs_release,
+};
+
+const struct file_operations configfs_bin_file_operations = {
+	.read_iter	= configfs_bin_read_iter,
+	.write_iter	= configfs_bin_write_iter,
+	.llseek		= NULL,		/* bin file is not seekable */
+	.open		= configfs_open_bin_file,
+	.release	= configfs_release_bin_file,
+};
+
+/**
+ *	configfs_create_file - create an attribute file for an item.
+ *	@item:	item we're creating for.
+ *	@attr:	atrribute descriptor.
+ */
+
+int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
+{
+	struct dentry *dir = item->ci_dentry;
+	struct configfs_dirent *parent_sd = dir->d_fsdata;
+	umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
+	int error = 0;
+
+	inode_lock_nested(d_inode(dir), I_MUTEX_NORMAL);
+	error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
+				     CONFIGFS_ITEM_ATTR, parent_sd->s_frag);
+	inode_unlock(d_inode(dir));
+
+	return error;
+}
+
+/**
+ *	configfs_create_bin_file - create a binary attribute file for an item.
+ *	@item:	item we're creating for.
+ *	@bin_attr: atrribute descriptor.
+ */
+
+int configfs_create_bin_file(struct config_item *item,
+		const struct configfs_bin_attribute *bin_attr)
+{
+	struct dentry *dir = item->ci_dentry;
+	struct configfs_dirent *parent_sd = dir->d_fsdata;
+	umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG;
+	int error = 0;
+
+	inode_lock_nested(dir->d_inode, I_MUTEX_NORMAL);
+	error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode,
+				     CONFIGFS_ITEM_BIN_ATTR, parent_sd->s_frag);
+	inode_unlock(dir->d_inode);
+
+	return error;
+}
diff --git a/fs/configfs/inode.c b/fs/configfs/inode.c
new file mode 100644
index 000000000..b601610e9
--- /dev/null
+++ b/fs/configfs/inode.c
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * inode.c - basic inode and dentry operations.
+ *
+ * Based on sysfs:
+ * 	sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
+ *
+ * configfs Copyright (C) 2005 Oracle.  All rights reserved.
+ *
+ * Please see Documentation/filesystems/configfs.rst for more
+ * information.
+ */
+
+#undef DEBUG
+
+#include <linux/pagemap.h>
+#include <linux/namei.h>
+#include <linux/backing-dev.h>
+#include <linux/capability.h>
+#include <linux/sched.h>
+#include <linux/lockdep.h>
+#include <linux/slab.h>
+
+#include <linux/configfs.h>
+#include "configfs_internal.h"
+
+#ifdef CONFIG_LOCKDEP
+static struct lock_class_key default_group_class[MAX_LOCK_DEPTH];
+#endif
+
+static const struct inode_operations configfs_inode_operations ={
+	.setattr	= configfs_setattr,
+};
+
+int configfs_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
+		     struct iattr *iattr)
+{
+	struct inode * inode = d_inode(dentry);
+	struct configfs_dirent * sd = dentry->d_fsdata;
+	struct iattr * sd_iattr;
+	unsigned int ia_valid = iattr->ia_valid;
+	int error;
+
+	if (!sd)
+		return -EINVAL;
+
+	sd_iattr = sd->s_iattr;
+	if (!sd_iattr) {
+		/* setting attributes for the first time, allocate now */
+		sd_iattr = kzalloc(sizeof(struct iattr), GFP_KERNEL);
+		if (!sd_iattr)
+			return -ENOMEM;
+		/* assign default attributes */
+		sd_iattr->ia_mode = sd->s_mode;
+		sd_iattr->ia_uid = GLOBAL_ROOT_UID;
+		sd_iattr->ia_gid = GLOBAL_ROOT_GID;
+		sd_iattr->ia_atime = sd_iattr->ia_mtime =
+			sd_iattr->ia_ctime = current_time(inode);
+		sd->s_iattr = sd_iattr;
+	}
+	/* attributes were changed atleast once in past */
+
+	error = simple_setattr(mnt_userns, dentry, iattr);
+	if (error)
+		return error;
+
+	if (ia_valid & ATTR_UID)
+		sd_iattr->ia_uid = iattr->ia_uid;
+	if (ia_valid & ATTR_GID)
+		sd_iattr->ia_gid = iattr->ia_gid;
+	if (ia_valid & ATTR_ATIME)
+		sd_iattr->ia_atime = iattr->ia_atime;
+	if (ia_valid & ATTR_MTIME)
+		sd_iattr->ia_mtime = iattr->ia_mtime;
+	if (ia_valid & ATTR_CTIME)
+		sd_iattr->ia_ctime = iattr->ia_ctime;
+	if (ia_valid & ATTR_MODE) {
+		umode_t mode = iattr->ia_mode;
+
+		if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
+			mode &= ~S_ISGID;
+		sd_iattr->ia_mode = sd->s_mode = mode;
+	}
+
+	return error;
+}
+
+static inline void set_default_inode_attr(struct inode * inode, umode_t mode)
+{
+	inode->i_mode = mode;
+	inode->i_atime = inode->i_mtime =
+		inode->i_ctime = current_time(inode);
+}
+
+static inline void set_inode_attr(struct inode * inode, struct iattr * iattr)
+{
+	inode->i_mode = iattr->ia_mode;
+	inode->i_uid = iattr->ia_uid;
+	inode->i_gid = iattr->ia_gid;
+	inode->i_atime = iattr->ia_atime;
+	inode->i_mtime = iattr->ia_mtime;
+	inode->i_ctime = iattr->ia_ctime;
+}
+
+struct inode *configfs_new_inode(umode_t mode, struct configfs_dirent *sd,
+				 struct super_block *s)
+{
+	struct inode * inode = new_inode(s);
+	if (inode) {
+		inode->i_ino = get_next_ino();
+		inode->i_mapping->a_ops = &ram_aops;
+		inode->i_op = &configfs_inode_operations;
+
+		if (sd->s_iattr) {
+			/* sysfs_dirent has non-default attributes
+			 * get them for the new inode from persistent copy
+			 * in sysfs_dirent
+			 */
+			set_inode_attr(inode, sd->s_iattr);
+		} else
+			set_default_inode_attr(inode, mode);
+	}
+	return inode;
+}
+
+#ifdef CONFIG_LOCKDEP
+
+static void configfs_set_inode_lock_class(struct configfs_dirent *sd,
+					  struct inode *inode)
+{
+	int depth = sd->s_depth;
+
+	if (depth > 0) {
+		if (depth <= ARRAY_SIZE(default_group_class)) {
+			lockdep_set_class(&inode->i_rwsem,
+					  &default_group_class[depth - 1]);
+		} else {
+			/*
+			 * In practice the maximum level of locking depth is
+			 * already reached. Just inform about possible reasons.
+			 */
+			pr_info("Too many levels of inodes for the locking correctness validator.\n");
+			pr_info("Spurious warnings may appear.\n");
+		}
+	}
+}
+
+#else /* CONFIG_LOCKDEP */
+
+static void configfs_set_inode_lock_class(struct configfs_dirent *sd,
+					  struct inode *inode)
+{
+}
+
+#endif /* CONFIG_LOCKDEP */
+
+struct inode *configfs_create(struct dentry *dentry, umode_t mode)
+{
+	struct inode *inode = NULL;
+	struct configfs_dirent *sd;
+	struct inode *p_inode;
+
+	if (!dentry)
+		return ERR_PTR(-ENOENT);
+
+	if (d_really_is_positive(dentry))
+		return ERR_PTR(-EEXIST);
+
+	sd = dentry->d_fsdata;
+	inode = configfs_new_inode(mode, sd, dentry->d_sb);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	p_inode = d_inode(dentry->d_parent);
+	p_inode->i_mtime = p_inode->i_ctime = current_time(p_inode);
+	configfs_set_inode_lock_class(sd, inode);
+	return inode;
+}
+
+/*
+ * Get the name for corresponding element represented by the given configfs_dirent
+ */
+const unsigned char * configfs_get_name(struct configfs_dirent *sd)
+{
+	struct configfs_attribute *attr;
+
+	BUG_ON(!sd || !sd->s_element);
+
+	/* These always have a dentry, so use that */
+	if (sd->s_type & (CONFIGFS_DIR | CONFIGFS_ITEM_LINK))
+		return sd->s_dentry->d_name.name;
+
+	if (sd->s_type & (CONFIGFS_ITEM_ATTR | CONFIGFS_ITEM_BIN_ATTR)) {
+		attr = sd->s_element;
+		return attr->ca_name;
+	}
+	return NULL;
+}
+
+
+/*
+ * Unhashes the dentry corresponding to given configfs_dirent
+ * Called with parent inode's i_mutex held.
+ */
+void configfs_drop_dentry(struct configfs_dirent * sd, struct dentry * parent)
+{
+	struct dentry * dentry = sd->s_dentry;
+
+	if (dentry) {
+		spin_lock(&dentry->d_lock);
+		if (simple_positive(dentry)) {
+			dget_dlock(dentry);
+			__d_drop(dentry);
+			spin_unlock(&dentry->d_lock);
+			simple_unlink(d_inode(parent), dentry);
+		} else
+			spin_unlock(&dentry->d_lock);
+	}
+}
+
+void configfs_hash_and_remove(struct dentry * dir, const char * name)
+{
+	struct configfs_dirent * sd;
+	struct configfs_dirent * parent_sd = dir->d_fsdata;
+
+	if (d_really_is_negative(dir))
+		/* no inode means this hasn't been made visible yet */
+		return;
+
+	inode_lock(d_inode(dir));
+	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+		if (!sd->s_element)
+			continue;
+		if (!strcmp(configfs_get_name(sd), name)) {
+			spin_lock(&configfs_dirent_lock);
+			list_del_init(&sd->s_sibling);
+			spin_unlock(&configfs_dirent_lock);
+			configfs_drop_dentry(sd, dir);
+			configfs_put(sd);
+			break;
+		}
+	}
+	inode_unlock(d_inode(dir));
+}
diff --git a/fs/configfs/item.c b/fs/configfs/item.c
new file mode 100644
index 000000000..254170a82
--- /dev/null
+++ b/fs/configfs/item.c
@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * item.c - library routines for handling generic config items
+ *
+ * Based on kobject:
+ *	kobject is Copyright (c) 2002-2003 Patrick Mochel
+ *
+ * configfs Copyright (C) 2005 Oracle.  All rights reserved.
+ *
+ * Please see the file Documentation/filesystems/configfs.rst for
+ * critical information about using the config_item interface.
+ */
+
+#include <linux/string.h>
+#include <linux/module.h>
+#include <linux/stat.h>
+#include <linux/slab.h>
+
+#include <linux/configfs.h>
+
+
+static inline struct config_item *to_item(struct list_head *entry)
+{
+	return container_of(entry, struct config_item, ci_entry);
+}
+
+/* Evil kernel */
+static void config_item_release(struct kref *kref);
+
+/**
+ *	config_item_init - initialize item.
+ *	@item:	item in question.
+ */
+static void config_item_init(struct config_item *item)
+{
+	kref_init(&item->ci_kref);
+	INIT_LIST_HEAD(&item->ci_entry);
+}
+
+/**
+ *	config_item_set_name - Set the name of an item
+ *	@item:	item.
+ *	@fmt:  The vsnprintf()'s format string.
+ *
+ *	If strlen(name) >= CONFIGFS_ITEM_NAME_LEN, then use a
+ *	dynamically allocated string that @item->ci_name points to.
+ *	Otherwise, use the static @item->ci_namebuf array.
+ */
+int config_item_set_name(struct config_item *item, const char *fmt, ...)
+{
+	int limit = CONFIGFS_ITEM_NAME_LEN;
+	int need;
+	va_list args;
+	char *name;
+
+	/*
+	 * First, try the static array
+	 */
+	va_start(args, fmt);
+	need = vsnprintf(item->ci_namebuf, limit, fmt, args);
+	va_end(args);
+	if (need < limit)
+		name = item->ci_namebuf;
+	else {
+		va_start(args, fmt);
+		name = kvasprintf(GFP_KERNEL, fmt, args);
+		va_end(args);
+		if (!name)
+			return -EFAULT;
+	}
+
+	/* Free the old name, if necessary. */
+	if (item->ci_name && item->ci_name != item->ci_namebuf)
+		kfree(item->ci_name);
+
+	/* Now, set the new name */
+	item->ci_name = name;
+	return 0;
+}
+EXPORT_SYMBOL(config_item_set_name);
+
+void config_item_init_type_name(struct config_item *item,
+				const char *name,
+				const struct config_item_type *type)
+{
+	config_item_set_name(item, "%s", name);
+	item->ci_type = type;
+	config_item_init(item);
+}
+EXPORT_SYMBOL(config_item_init_type_name);
+
+void config_group_init_type_name(struct config_group *group, const char *name,
+			 const struct config_item_type *type)
+{
+	config_item_set_name(&group->cg_item, "%s", name);
+	group->cg_item.ci_type = type;
+	config_group_init(group);
+}
+EXPORT_SYMBOL(config_group_init_type_name);
+
+struct config_item *config_item_get(struct config_item *item)
+{
+	if (item)
+		kref_get(&item->ci_kref);
+	return item;
+}
+EXPORT_SYMBOL(config_item_get);
+
+struct config_item *config_item_get_unless_zero(struct config_item *item)
+{
+	if (item && kref_get_unless_zero(&item->ci_kref))
+		return item;
+	return NULL;
+}
+EXPORT_SYMBOL(config_item_get_unless_zero);
+
+static void config_item_cleanup(struct config_item *item)
+{
+	const struct config_item_type *t = item->ci_type;
+	struct config_group *s = item->ci_group;
+	struct config_item *parent = item->ci_parent;
+
+	pr_debug("config_item %s: cleaning up\n", config_item_name(item));
+	if (item->ci_name != item->ci_namebuf)
+		kfree(item->ci_name);
+	item->ci_name = NULL;
+	if (t && t->ct_item_ops && t->ct_item_ops->release)
+		t->ct_item_ops->release(item);
+	if (s)
+		config_group_put(s);
+	if (parent)
+		config_item_put(parent);
+}
+
+static void config_item_release(struct kref *kref)
+{
+	config_item_cleanup(container_of(kref, struct config_item, ci_kref));
+}
+
+/**
+ *	config_item_put - decrement refcount for item.
+ *	@item:	item.
+ *
+ *	Decrement the refcount, and if 0, call config_item_cleanup().
+ */
+void config_item_put(struct config_item *item)
+{
+	if (item)
+		kref_put(&item->ci_kref, config_item_release);
+}
+EXPORT_SYMBOL(config_item_put);
+
+/**
+ *	config_group_init - initialize a group for use
+ *	@group:	config_group
+ */
+void config_group_init(struct config_group *group)
+{
+	config_item_init(&group->cg_item);
+	INIT_LIST_HEAD(&group->cg_children);
+	INIT_LIST_HEAD(&group->default_groups);
+}
+EXPORT_SYMBOL(config_group_init);
+
+/**
+ *	config_group_find_item - search for item in group.
+ *	@group:	group we're looking in.
+ *	@name:	item's name.
+ *
+ *	Iterate over @group->cg_list, looking for a matching config_item.
+ *	If matching item is found take a reference and return the item.
+ *	Caller must have locked group via @group->cg_subsys->su_mtx.
+ */
+struct config_item *config_group_find_item(struct config_group *group,
+					   const char *name)
+{
+	struct list_head *entry;
+	struct config_item *ret = NULL;
+
+	list_for_each(entry, &group->cg_children) {
+		struct config_item *item = to_item(entry);
+		if (config_item_name(item) &&
+		    !strcmp(config_item_name(item), name)) {
+			ret = config_item_get(item);
+			break;
+		}
+	}
+	return ret;
+}
+EXPORT_SYMBOL(config_group_find_item);
diff --git a/fs/configfs/mount.c b/fs/configfs/mount.c
new file mode 100644
index 000000000..c2d820063
--- /dev/null
+++ b/fs/configfs/mount.c
@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * mount.c - operations for initializing and mounting configfs.
+ *
+ * Based on sysfs:
+ * 	sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
+ *
+ * configfs Copyright (C) 2005 Oracle.  All rights reserved.
+ */
+
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/mount.h>
+#include <linux/fs_context.h>
+#include <linux/pagemap.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+
+#include <linux/configfs.h>
+#include "configfs_internal.h"
+
+/* Random magic number */
+#define CONFIGFS_MAGIC 0x62656570
+
+static struct vfsmount *configfs_mount = NULL;
+struct kmem_cache *configfs_dir_cachep;
+static int configfs_mnt_count = 0;
+
+
+static void configfs_free_inode(struct inode *inode)
+{
+	if (S_ISLNK(inode->i_mode))
+		kfree(inode->i_link);
+	free_inode_nonrcu(inode);
+}
+
+static const struct super_operations configfs_ops = {
+	.statfs		= simple_statfs,
+	.drop_inode	= generic_delete_inode,
+	.free_inode	= configfs_free_inode,
+};
+
+static struct config_group configfs_root_group = {
+	.cg_item = {
+		.ci_namebuf	= "root",
+		.ci_name	= configfs_root_group.cg_item.ci_namebuf,
+	},
+};
+
+int configfs_is_root(struct config_item *item)
+{
+	return item == &configfs_root_group.cg_item;
+}
+
+static struct configfs_dirent configfs_root = {
+	.s_sibling	= LIST_HEAD_INIT(configfs_root.s_sibling),
+	.s_children	= LIST_HEAD_INIT(configfs_root.s_children),
+	.s_element	= &configfs_root_group.cg_item,
+	.s_type		= CONFIGFS_ROOT,
+	.s_iattr	= NULL,
+};
+
+static int configfs_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+	struct inode *inode;
+	struct dentry *root;
+
+	sb->s_blocksize = PAGE_SIZE;
+	sb->s_blocksize_bits = PAGE_SHIFT;
+	sb->s_magic = CONFIGFS_MAGIC;
+	sb->s_op = &configfs_ops;
+	sb->s_time_gran = 1;
+
+	inode = configfs_new_inode(S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO,
+				   &configfs_root, sb);
+	if (inode) {
+		inode->i_op = &configfs_root_inode_operations;
+		inode->i_fop = &configfs_dir_operations;
+		/* directory inodes start off with i_nlink == 2 (for "." entry) */
+		inc_nlink(inode);
+	} else {
+		pr_debug("could not get root inode\n");
+		return -ENOMEM;
+	}
+
+	root = d_make_root(inode);
+	if (!root) {
+		pr_debug("%s: could not get root dentry!\n",__func__);
+		return -ENOMEM;
+	}
+	config_group_init(&configfs_root_group);
+	configfs_root_group.cg_item.ci_dentry = root;
+	root->d_fsdata = &configfs_root;
+	sb->s_root = root;
+	sb->s_d_op = &configfs_dentry_ops; /* the rest get that */
+	return 0;
+}
+
+static int configfs_get_tree(struct fs_context *fc)
+{
+	return get_tree_single(fc, configfs_fill_super);
+}
+
+static const struct fs_context_operations configfs_context_ops = {
+	.get_tree	= configfs_get_tree,
+};
+
+static int configfs_init_fs_context(struct fs_context *fc)
+{
+	fc->ops = &configfs_context_ops;
+	return 0;
+}
+
+static struct file_system_type configfs_fs_type = {
+	.owner		= THIS_MODULE,
+	.name		= "configfs",
+	.init_fs_context = configfs_init_fs_context,
+	.kill_sb	= kill_litter_super,
+};
+MODULE_ALIAS_FS("configfs");
+
+struct dentry *configfs_pin_fs(void)
+{
+	int err = simple_pin_fs(&configfs_fs_type, &configfs_mount,
+			     &configfs_mnt_count);
+	return err ? ERR_PTR(err) : configfs_mount->mnt_root;
+}
+
+void configfs_release_fs(void)
+{
+	simple_release_fs(&configfs_mount, &configfs_mnt_count);
+}
+
+
+static int __init configfs_init(void)
+{
+	int err = -ENOMEM;
+
+	configfs_dir_cachep = kmem_cache_create("configfs_dir_cache",
+						sizeof(struct configfs_dirent),
+						0, 0, NULL);
+	if (!configfs_dir_cachep)
+		goto out;
+
+	err = sysfs_create_mount_point(kernel_kobj, "config");
+	if (err)
+		goto out2;
+
+	err = register_filesystem(&configfs_fs_type);
+	if (err)
+		goto out3;
+
+	return 0;
+out3:
+	pr_err("Unable to register filesystem!\n");
+	sysfs_remove_mount_point(kernel_kobj, "config");
+out2:
+	kmem_cache_destroy(configfs_dir_cachep);
+	configfs_dir_cachep = NULL;
+out:
+	return err;
+}
+
+static void __exit configfs_exit(void)
+{
+	unregister_filesystem(&configfs_fs_type);
+	sysfs_remove_mount_point(kernel_kobj, "config");
+	kmem_cache_destroy(configfs_dir_cachep);
+	configfs_dir_cachep = NULL;
+}
+
+MODULE_AUTHOR("Oracle");
+MODULE_LICENSE("GPL");
+MODULE_VERSION("0.0.2");
+MODULE_DESCRIPTION("Simple RAM filesystem for user driven kernel subsystem configuration.");
+
+core_initcall(configfs_init);
+module_exit(configfs_exit);
diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
new file mode 100644
index 000000000..0623c3edc
--- /dev/null
+++ b/fs/configfs/symlink.c
@@ -0,0 +1,270 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * symlink.c - operations for configfs symlinks.
+ *
+ * Based on sysfs:
+ * 	sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
+ *
+ * configfs Copyright (C) 2005 Oracle.  All rights reserved.
+ */
+
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/namei.h>
+#include <linux/slab.h>
+
+#include <linux/configfs.h>
+#include "configfs_internal.h"
+
+/* Protects attachments of new symlinks */
+DEFINE_MUTEX(configfs_symlink_mutex);
+
+static int item_depth(struct config_item * item)
+{
+	struct config_item * p = item;
+	int depth = 0;
+	do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
+	return depth;
+}
+
+static int item_path_length(struct config_item * item)
+{
+	struct config_item * p = item;
+	int length = 1;
+	do {
+		length += strlen(config_item_name(p)) + 1;
+		p = p->ci_parent;
+	} while (p && !configfs_is_root(p));
+	return length;
+}
+
+static void fill_item_path(struct config_item * item, char * buffer, int length)
+{
+	struct config_item * p;
+
+	--length;
+	for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
+		int cur = strlen(config_item_name(p));
+
+		/* back up enough to print this bus id with '/' */
+		length -= cur;
+		memcpy(buffer + length, config_item_name(p), cur);
+		*(buffer + --length) = '/';
+	}
+}
+
+static int configfs_get_target_path(struct config_item *item,
+		struct config_item *target, char *path)
+{
+	int depth, size;
+	char *s;
+
+	depth = item_depth(item);
+	size = item_path_length(target) + depth * 3 - 1;
+	if (size > PATH_MAX)
+		return -ENAMETOOLONG;
+
+	pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
+
+	for (s = path; depth--; s += 3)
+		strcpy(s,"../");
+
+	fill_item_path(target, path, size);
+	pr_debug("%s: path = '%s'\n", __func__, path);
+	return 0;
+}
+
+static int create_link(struct config_item *parent_item,
+		       struct config_item *item,
+		       struct dentry *dentry)
+{
+	struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
+	char *body;
+	int ret;
+
+	if (!configfs_dirent_is_ready(target_sd))
+		return -ENOENT;
+
+	body = kzalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!body)
+		return -ENOMEM;
+
+	configfs_get(target_sd);
+	spin_lock(&configfs_dirent_lock);
+	if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
+		spin_unlock(&configfs_dirent_lock);
+		configfs_put(target_sd);
+		kfree(body);
+		return -ENOENT;
+	}
+	target_sd->s_links++;
+	spin_unlock(&configfs_dirent_lock);
+	ret = configfs_get_target_path(parent_item, item, body);
+	if (!ret)
+		ret = configfs_create_link(target_sd, parent_item->ci_dentry,
+					   dentry, body);
+	if (ret) {
+		spin_lock(&configfs_dirent_lock);
+		target_sd->s_links--;
+		spin_unlock(&configfs_dirent_lock);
+		configfs_put(target_sd);
+		kfree(body);
+	}
+	return ret;
+}
+
+
+static int get_target(const char *symname, struct path *path,
+		      struct config_item **target, struct super_block *sb)
+{
+	int ret;
+
+	ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
+	if (!ret) {
+		if (path->dentry->d_sb == sb) {
+			*target = configfs_get_config_item(path->dentry);
+			if (!*target) {
+				ret = -ENOENT;
+				path_put(path);
+			}
+		} else {
+			ret = -EPERM;
+			path_put(path);
+		}
+	}
+
+	return ret;
+}
+
+
+int configfs_symlink(struct user_namespace *mnt_userns, struct inode *dir,
+		     struct dentry *dentry, const char *symname)
+{
+	int ret;
+	struct path path;
+	struct configfs_dirent *sd;
+	struct config_item *parent_item;
+	struct config_item *target_item = NULL;
+	const struct config_item_type *type;
+
+	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))
+		return -ENOENT;
+
+	parent_item = configfs_get_config_item(dentry->d_parent);
+	type = parent_item->ci_type;
+
+	ret = -EPERM;
+	if (!type || !type->ct_item_ops ||
+	    !type->ct_item_ops->allow_link)
+		goto out_put;
+
+	/*
+	 * This is really sick.  What they wanted was a hybrid of
+	 * link(2) and symlink(2) - they wanted the target resolved
+	 * at syscall time (as link(2) would've done), be a directory
+	 * (which link(2) would've refused to do) *AND* be a deep
+	 * fucking magic, making the target busy from rmdir POV.
+	 * symlink(2) is nothing of that sort, and the locking it
+	 * gets matches the normal symlink(2) semantics.  Without
+	 * attempts to resolve the target (which might very well
+	 * not even exist yet) done prior to locking the parent
+	 * directory.  This perversion, OTOH, needs to resolve
+	 * the target, which would lead to obvious deadlocks if
+	 * attempted with any directories locked.
+	 *
+	 * Unfortunately, that garbage is userland ABI and we should've
+	 * said "no" back in 2005.  Too late now, so we get to
+	 * play very ugly games with locking.
+	 *
+	 * Try *ANYTHING* of that sort in new code, and you will
+	 * really regret it.  Just ask yourself - what could a BOFH
+	 * do to me and do I want to find it out first-hand?
+	 *
+	 *  AV, a thoroughly annoyed bastard.
+	 */
+	inode_unlock(dir);
+	ret = get_target(symname, &path, &target_item, dentry->d_sb);
+	inode_lock(dir);
+	if (ret)
+		goto out_put;
+
+	if (dentry->d_inode || d_unhashed(dentry))
+		ret = -EEXIST;
+	else
+		ret = inode_permission(&init_user_ns, dir,
+				       MAY_WRITE | MAY_EXEC);
+	if (!ret)
+		ret = type->ct_item_ops->allow_link(parent_item, target_item);
+	if (!ret) {
+		mutex_lock(&configfs_symlink_mutex);
+		ret = create_link(parent_item, target_item, dentry);
+		mutex_unlock(&configfs_symlink_mutex);
+		if (ret && type->ct_item_ops->drop_link)
+			type->ct_item_ops->drop_link(parent_item,
+						     target_item);
+	}
+
+	config_item_put(target_item);
+	path_put(&path);
+
+out_put:
+	config_item_put(parent_item);
+	return ret;
+}
+
+int configfs_unlink(struct inode *dir, struct dentry *dentry)
+{
+	struct configfs_dirent *sd = dentry->d_fsdata, *target_sd;
+	struct config_item *parent_item;
+	const struct config_item_type *type;
+	int ret;
+
+	ret = -EPERM;  /* What lack-of-symlink returns */
+	if (!(sd->s_type & CONFIGFS_ITEM_LINK))
+		goto out;
+
+	target_sd = sd->s_element;
+
+	parent_item = configfs_get_config_item(dentry->d_parent);
+	type = parent_item->ci_type;
+
+	spin_lock(&configfs_dirent_lock);
+	list_del_init(&sd->s_sibling);
+	spin_unlock(&configfs_dirent_lock);
+	configfs_drop_dentry(sd, dentry->d_parent);
+	dput(dentry);
+	configfs_put(sd);
+
+	/*
+	 * drop_link() must be called before
+	 * decrementing target's ->s_links, so that the order of
+	 * drop_link(this, target) and drop_item(target) is preserved.
+	 */
+	if (type && type->ct_item_ops &&
+	    type->ct_item_ops->drop_link)
+		type->ct_item_ops->drop_link(parent_item,
+					       target_sd->s_element);
+
+	spin_lock(&configfs_dirent_lock);
+	target_sd->s_links--;
+	spin_unlock(&configfs_dirent_lock);
+	configfs_put(target_sd);
+
+	config_item_put(parent_item);
+
+	ret = 0;
+
+out:
+	return ret;
+}
+
+const struct inode_operations configfs_symlink_inode_operations = {
+	.get_link = simple_get_link,
+	.setattr = configfs_setattr,
+};
+