sysfs, kernfs: move dir core code to fs/kernfs/dir.c

Move core dir code to fs/kernfs/dir.c.  fs/sysfs/dir.c now only
contains sysfs_warn_dup() and sysfs wrappers around kernfs interfaces.
The respective declarations in fs/sysfs/sysfs.h are moved to
fs/kernfs/kernfs-internal.h.

This is pure relocation.

v2: sysfs_symlink_target_lock was mistakenly relocated to kernfs.  It
    should remain with sysfs.  Fixed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 988 insertions, 0 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 1061602ce81a..a4ca4de3cb21 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -7,3 +7,991 @@
  *
  * This file is released under the GPLv2.
  */
+
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/idr.h>
+#include <linux/slab.h>
+#include <linux/security.h>
+#include <linux/hash.h>
+
+#include "kernfs-internal.h"
+
+DEFINE_MUTEX(sysfs_mutex);
+
+#define to_sysfs_dirent(X) rb_entry((X), struct sysfs_dirent, s_rb)
+
+static DEFINE_SPINLOCK(sysfs_ino_lock);
+static DEFINE_IDA(sysfs_ino_ida);
+
+/**
+ *	sysfs_name_hash
+ *	@name: Null terminated string to hash
+ *	@ns:   Namespace tag to hash
+ *
+ *	Returns 31 bit hash of ns + name (so it fits in an off_t )
+ */
+static unsigned int sysfs_name_hash(const char *name, const void *ns)
+{
+	unsigned long hash = init_name_hash();
+	unsigned int len = strlen(name);
+	while (len--)
+		hash = partial_name_hash(*name++, hash);
+	hash = (end_name_hash(hash) ^ hash_ptr((void *)ns, 31));
+	hash &= 0x7fffffffU;
+	/* Reserve hash numbers 0, 1 and INT_MAX for magic directory entries */
+	if (hash < 1)
+		hash += 2;
+	if (hash >= INT_MAX)
+		hash = INT_MAX - 1;
+	return hash;
+}
+
+static int sysfs_name_compare(unsigned int hash, const char *name,
+			      const void *ns, const struct sysfs_dirent *sd)
+{
+	if (hash != sd->s_hash)
+		return hash - sd->s_hash;
+	if (ns != sd->s_ns)
+		return ns - sd->s_ns;
+	return strcmp(name, sd->s_name);
+}
+
+static int sysfs_sd_compare(const struct sysfs_dirent *left,
+			    const struct sysfs_dirent *right)
+{
+	return sysfs_name_compare(left->s_hash, left->s_name, left->s_ns,
+				  right);
+}
+
+/**
+ *	sysfs_link_sibling - link sysfs_dirent into sibling rbtree
+ *	@sd: sysfs_dirent of interest
+ *
+ *	Link @sd into its sibling rbtree which starts from
+ *	sd->s_parent->s_dir.children.
+ *
+ *	Locking:
+ *	mutex_lock(sysfs_mutex)
+ *
+ *	RETURNS:
+ *	0 on susccess -EEXIST on failure.
+ */
+static int sysfs_link_sibling(struct sysfs_dirent *sd)
+{
+	struct rb_node **node = &sd->s_parent->s_dir.children.rb_node;
+	struct rb_node *parent = NULL;
+
+	if (sysfs_type(sd) == SYSFS_DIR)
+		sd->s_parent->s_dir.subdirs++;
+
+	while (*node) {
+		struct sysfs_dirent *pos;
+		int result;
+
+		pos = to_sysfs_dirent(*node);
+		parent = *node;
+		result = sysfs_sd_compare(sd, pos);
+		if (result < 0)
+			node = &pos->s_rb.rb_left;
+		else if (result > 0)
+			node = &pos->s_rb.rb_right;
+		else
+			return -EEXIST;
+	}
+	/* add new node and rebalance the tree */
+	rb_link_node(&sd->s_rb, parent, node);
+	rb_insert_color(&sd->s_rb, &sd->s_parent->s_dir.children);
+	return 0;
+}
+
+/**
+ *	sysfs_unlink_sibling - unlink sysfs_dirent from sibling rbtree
+ *	@sd: sysfs_dirent of interest
+ *
+ *	Unlink @sd from its sibling rbtree which starts from
+ *	sd->s_parent->s_dir.children.
+ *
+ *	Locking:
+ *	mutex_lock(sysfs_mutex)
+ */
+static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
+{
+	if (sysfs_type(sd) == SYSFS_DIR)
+		sd->s_parent->s_dir.subdirs--;
+
+	rb_erase(&sd->s_rb, &sd->s_parent->s_dir.children);
+}
+
+/**
+ *	sysfs_get_active - get an active reference to sysfs_dirent
+ *	@sd: sysfs_dirent to get an active reference to
+ *
+ *	Get an active reference of @sd.  This function is noop if @sd
+ *	is NULL.
+ *
+ *	RETURNS:
+ *	Pointer to @sd on success, NULL on failure.
+ */
+struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd)
+{
+	if (unlikely(!sd))
+		return NULL;
+
+	if (!atomic_inc_unless_negative(&sd->s_active))
+		return NULL;
+
+	if (sd->s_flags & SYSFS_FLAG_LOCKDEP)
+		rwsem_acquire_read(&sd->dep_map, 0, 1, _RET_IP_);
+	return sd;
+}
+
+/**
+ *	sysfs_put_active - put an active reference to sysfs_dirent
+ *	@sd: sysfs_dirent to put an active reference to
+ *
+ *	Put an active reference to @sd.  This function is noop if @sd
+ *	is NULL.
+ */
+void sysfs_put_active(struct sysfs_dirent *sd)
+{
+	int v;
+
+	if (unlikely(!sd))
+		return;
+
+	if (sd->s_flags & SYSFS_FLAG_LOCKDEP)
+		rwsem_release(&sd->dep_map, 1, _RET_IP_);
+	v = atomic_dec_return(&sd->s_active);
+	if (likely(v != SD_DEACTIVATED_BIAS))
+		return;
+
+	/* atomic_dec_return() is a mb(), we'll always see the updated
+	 * sd->u.completion.
+	 */
+	complete(sd->u.completion);
+}
+
+/**
+ *	sysfs_deactivate - deactivate sysfs_dirent
+ *	@sd: sysfs_dirent to deactivate
+ *
+ *	Deny new active references and drain existing ones.
+ */
+static void sysfs_deactivate(struct sysfs_dirent *sd)
+{
+	DECLARE_COMPLETION_ONSTACK(wait);
+	int v;
+
+	BUG_ON(!(sd->s_flags & SYSFS_FLAG_REMOVED));
+
+	if (!(sysfs_type(sd) & SYSFS_ACTIVE_REF))
+		return;
+
+	sd->u.completion = (void *)&wait;
+
+	rwsem_acquire(&sd->dep_map, 0, 0, _RET_IP_);
+	/* atomic_add_return() is a mb(), put_active() will always see
+	 * the updated sd->u.completion.
+	 */
+	v = atomic_add_return(SD_DEACTIVATED_BIAS, &sd->s_active);
+
+	if (v != SD_DEACTIVATED_BIAS) {
+		lock_contended(&sd->dep_map, _RET_IP_);
+		wait_for_completion(&wait);
+	}
+
+	lock_acquired(&sd->dep_map, _RET_IP_);
+	rwsem_release(&sd->dep_map, 1, _RET_IP_);
+}
+
+static int sysfs_alloc_ino(unsigned int *pino)
+{
+	int ino, rc;
+
+ retry:
+	spin_lock(&sysfs_ino_lock);
+	rc = ida_get_new_above(&sysfs_ino_ida, 2, &ino);
+	spin_unlock(&sysfs_ino_lock);
+
+	if (rc == -EAGAIN) {
+		if (ida_pre_get(&sysfs_ino_ida, GFP_KERNEL))
+			goto retry;
+		rc = -ENOMEM;
+	}
+
+	*pino = ino;
+	return rc;
+}
+
+static void sysfs_free_ino(unsigned int ino)
+{
+	spin_lock(&sysfs_ino_lock);
+	ida_remove(&sysfs_ino_ida, ino);
+	spin_unlock(&sysfs_ino_lock);
+}
+
+/**
+ * kernfs_get - get a reference count on a sysfs_dirent
+ * @sd: the target sysfs_dirent
+ */
+void kernfs_get(struct sysfs_dirent *sd)
+{
+	if (sd) {
+		WARN_ON(!atomic_read(&sd->s_count));
+		atomic_inc(&sd->s_count);
+	}
+}
+EXPORT_SYMBOL_GPL(kernfs_get);
+
+/**
+ * kernfs_put - put a reference count on a sysfs_dirent
+ * @sd: the target sysfs_dirent
+ *
+ * Put a reference count of @sd and destroy it if it reached zero.
+ */
+void kernfs_put(struct sysfs_dirent *sd)
+{
+	struct sysfs_dirent *parent_sd;
+
+	if (!sd || !atomic_dec_and_test(&sd->s_count))
+		return;
+ repeat:
+	/* Moving/renaming is always done while holding reference.
+	 * sd->s_parent won't change beneath us.
+	 */
+	parent_sd = sd->s_parent;
+
+	WARN(!(sd->s_flags & SYSFS_FLAG_REMOVED),
+		"sysfs: free using entry: %s/%s\n",
+		parent_sd ? parent_sd->s_name : "", sd->s_name);
+
+	if (sysfs_type(sd) == SYSFS_KOBJ_LINK)
+		kernfs_put(sd->s_symlink.target_sd);
+	if (sysfs_type(sd) & SYSFS_COPY_NAME)
+		kfree(sd->s_name);
+	if (sd->s_iattr && sd->s_iattr->ia_secdata)
+		security_release_secctx(sd->s_iattr->ia_secdata,
+					sd->s_iattr->ia_secdata_len);
+	kfree(sd->s_iattr);
+	sysfs_free_ino(sd->s_ino);
+	kmem_cache_free(sysfs_dir_cachep, sd);
+
+	sd = parent_sd;
+	if (sd && atomic_dec_and_test(&sd->s_count))
+		goto repeat;
+}
+EXPORT_SYMBOL_GPL(kernfs_put);
+
+static int sysfs_dentry_delete(const struct dentry *dentry)
+{
+	struct sysfs_dirent *sd = dentry->d_fsdata;
+	return !(sd && !(sd->s_flags & SYSFS_FLAG_REMOVED));
+}
+
+static int sysfs_dentry_revalidate(struct dentry *dentry, unsigned int flags)
+{
+	struct sysfs_dirent *sd;
+
+	if (flags & LOOKUP_RCU)
+		return -ECHILD;
+
+	sd = dentry->d_fsdata;
+	mutex_lock(&sysfs_mutex);
+
+	/* The sysfs dirent has been deleted */
+	if (sd->s_flags & SYSFS_FLAG_REMOVED)
+		goto out_bad;
+
+	/* The sysfs dirent has been moved? */
+	if (dentry->d_parent->d_fsdata != sd->s_parent)
+		goto out_bad;
+
+	/* The sysfs dirent has been renamed */
+	if (strcmp(dentry->d_name.name, sd->s_name) != 0)
+		goto out_bad;
+
+	/* The sysfs dirent has been moved to a different namespace */
+	if (sd->s_parent && (sd->s_parent->s_flags & SYSFS_FLAG_NS) &&
+	    sysfs_info(dentry->d_sb)->ns != sd->s_ns)
+		goto out_bad;
+
+	mutex_unlock(&sysfs_mutex);
+out_valid:
+	return 1;
+out_bad:
+	/* Remove the dentry from the dcache hashes.
+	 * If this is a deleted dentry we use d_drop instead of d_delete
+	 * so sysfs doesn't need to cope with negative dentries.
+	 *
+	 * If this is a dentry that has simply been renamed we
+	 * use d_drop to remove it from the dcache lookup on its
+	 * old parent.  If this dentry persists later when a lookup
+	 * is performed at its new name the dentry will be readded
+	 * to the dcache hashes.
+	 */
+	mutex_unlock(&sysfs_mutex);
+
+	/* If we have submounts we must allow the vfs caches
+	 * to lie about the state of the filesystem to prevent
+	 * leaks and other nasty things.
+	 */
+	if (check_submounts_and_drop(dentry) != 0)
+		goto out_valid;
+
+	return 0;
+}
+
+static void sysfs_dentry_release(struct dentry *dentry)
+{
+	kernfs_put(dentry->d_fsdata);
+}
+
+const struct dentry_operations sysfs_dentry_ops = {
+	.d_revalidate	= sysfs_dentry_revalidate,
+	.d_delete	= sysfs_dentry_delete,
+	.d_release	= sysfs_dentry_release,
+};
+
+struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
+{
+	char *dup_name = NULL;
+	struct sysfs_dirent *sd;
+
+	if (type & SYSFS_COPY_NAME) {
+		name = dup_name = kstrdup(name, GFP_KERNEL);
+		if (!name)
+			return NULL;
+	}
+
+	sd = kmem_cache_zalloc(sysfs_dir_cachep, GFP_KERNEL);
+	if (!sd)
+		goto err_out1;
+
+	if (sysfs_alloc_ino(&sd->s_ino))
+		goto err_out2;
+
+	atomic_set(&sd->s_count, 1);
+	atomic_set(&sd->s_active, 0);
+
+	sd->s_name = name;
+	sd->s_mode = mode;
+	sd->s_flags = type | SYSFS_FLAG_REMOVED;
+
+	return sd;
+
+ err_out2:
+	kmem_cache_free(sysfs_dir_cachep, sd);
+ err_out1:
+	kfree(dup_name);
+	return NULL;
+}
+
+/**
+ *	sysfs_addrm_start - prepare for sysfs_dirent add/remove
+ *	@acxt: pointer to sysfs_addrm_cxt to be used
+ *
+ *	This function is called when the caller is about to add or remove
+ *	sysfs_dirent.  This function acquires sysfs_mutex.  @acxt is used
+ *	to keep and pass context to other addrm functions.
+ *
+ *	LOCKING:
+ *	Kernel thread context (may sleep).  sysfs_mutex is locked on
+ *	return.
+ */
+void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt)
+	__acquires(sysfs_mutex)
+{
+	memset(acxt, 0, sizeof(*acxt));
+
+	mutex_lock(&sysfs_mutex);
+}
+
+/**
+ *	sysfs_add_one - add sysfs_dirent to parent without warning
+ *	@acxt: addrm context to use
+ *	@sd: sysfs_dirent to be added
+ *	@parent_sd: the parent sysfs_dirent to add @sd to
+ *
+ *	Get @parent_sd and set @sd->s_parent to it and increment nlink of
+ *	the parent inode if @sd is a directory and link into the children
+ *	list of the parent.
+ *
+ *	This function should be called between calls to
+ *	sysfs_addrm_start() and sysfs_addrm_finish() and should be
+ *	passed the same @acxt as passed to sysfs_addrm_start().
+ *
+ *	LOCKING:
+ *	Determined by sysfs_addrm_start().
+ *
+ *	RETURNS:
+ *	0 on success, -EEXIST if entry with the given name already
+ *	exists.
+ */
+int sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd,
+		  struct sysfs_dirent *parent_sd)
+{
+	bool has_ns = parent_sd->s_flags & SYSFS_FLAG_NS;
+	struct sysfs_inode_attrs *ps_iattr;
+	int ret;
+
+	if (has_ns != (bool)sd->s_ns) {
+		WARN(1, KERN_WARNING "sysfs: ns %s in '%s' for '%s'\n",
+		     has_ns ? "required" : "invalid",
+		     parent_sd->s_name, sd->s_name);
+		return -EINVAL;
+	}
+
+	if (sysfs_type(parent_sd) != SYSFS_DIR)
+		return -EINVAL;
+
+	sd->s_hash = sysfs_name_hash(sd->s_name, sd->s_ns);
+	sd->s_parent = parent_sd;
+	kernfs_get(parent_sd);
+
+	ret = sysfs_link_sibling(sd);
+	if (ret)
+		return ret;
+
+	/* Update timestamps on the parent */
+	ps_iattr = parent_sd->s_iattr;
+	if (ps_iattr) {
+		struct iattr *ps_iattrs = &ps_iattr->ia_iattr;
+		ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
+	}
+
+	/* Mark the entry added into directory tree */
+	sd->s_flags &= ~SYSFS_FLAG_REMOVED;
+
+	return 0;
+}
+
+/**
+ *	sysfs_remove_one - remove sysfs_dirent from parent
+ *	@acxt: addrm context to use
+ *	@sd: sysfs_dirent to be removed
+ *
+ *	Mark @sd removed and drop nlink of parent inode if @sd is a
+ *	directory.  @sd is unlinked from the children list.
+ *
+ *	This function should be called between calls to
+ *	sysfs_addrm_start() and sysfs_addrm_finish() and should be
+ *	passed the same @acxt as passed to sysfs_addrm_start().
+ *
+ *	LOCKING:
+ *	Determined by sysfs_addrm_start().
+ */
+static void sysfs_remove_one(struct sysfs_addrm_cxt *acxt,
+			     struct sysfs_dirent *sd)
+{
+	struct sysfs_inode_attrs *ps_iattr;
+
+	/*
+	 * Removal can be called multiple times on the same node.  Only the
+	 * first invocation is effective and puts the base ref.
+	 */
+	if (sd->s_flags & SYSFS_FLAG_REMOVED)
+		return;
+
+	sysfs_unlink_sibling(sd);
+
+	/* Update timestamps on the parent */
+	ps_iattr = sd->s_parent->s_iattr;
+	if (ps_iattr) {
+		struct iattr *ps_iattrs = &ps_iattr->ia_iattr;
+		ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
+	}
+
+	sd->s_flags |= SYSFS_FLAG_REMOVED;
+	sd->u.removed_list = acxt->removed;
+	acxt->removed = sd;
+}
+
+/**
+ *	sysfs_addrm_finish - finish up sysfs_dirent add/remove
+ *	@acxt: addrm context to finish up
+ *
+ *	Finish up sysfs_dirent add/remove.  Resources acquired by
+ *	sysfs_addrm_start() are released and removed sysfs_dirents are
+ *	cleaned up.
+ *
+ *	LOCKING:
+ *	sysfs_mutex is released.
+ */
+void sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt)
+	__releases(sysfs_mutex)
+{
+	/* release resources acquired by sysfs_addrm_start() */
+	mutex_unlock(&sysfs_mutex);
+
+	/* kill removed sysfs_dirents */
+	while (acxt->removed) {
+		struct sysfs_dirent *sd = acxt->removed;
+
+		acxt->removed = sd->u.removed_list;
+
+		sysfs_deactivate(sd);
+		sysfs_unmap_bin_file(sd);
+		kernfs_put(sd);
+	}
+}
+
+/**
+ * kernfs_find_ns - find sysfs_dirent with the given name
+ * @parent: sysfs_dirent to search under
+ * @name: name to look for
+ * @ns: the namespace tag to use
+ *
+ * Look for sysfs_dirent with name @name under @parent.  Returns pointer to
+ * the found sysfs_dirent on success, %NULL on failure.
+ */
+static struct sysfs_dirent *kernfs_find_ns(struct sysfs_dirent *parent,
+					   const unsigned char *name,
+					   const void *ns)
+{
+	struct rb_node *node = parent->s_dir.children.rb_node;
+	bool has_ns = parent->s_flags & SYSFS_FLAG_NS;
+	unsigned int hash;
+
+	lockdep_assert_held(&sysfs_mutex);
+
+	if (has_ns != (bool)ns) {
+		WARN(1, KERN_WARNING "sysfs: ns %s in '%s' for '%s'\n",
+		     has_ns ? "required" : "invalid",
+		     parent->s_name, name);
+		return NULL;
+	}
+
+	hash = sysfs_name_hash(name, ns);
+	while (node) {
+		struct sysfs_dirent *sd;
+		int result;
+
+		sd = to_sysfs_dirent(node);
+		result = sysfs_name_compare(hash, name, ns, sd);
+		if (result < 0)
+			node = node->rb_left;
+		else if (result > 0)
+			node = node->rb_right;
+		else
+			return sd;
+	}
+	return NULL;
+}
+
+/**
+ * kernfs_find_and_get_ns - find and get sysfs_dirent with the given name
+ * @parent: sysfs_dirent to search under
+ * @name: name to look for
+ * @ns: the namespace tag to use
+ *
+ * Look for sysfs_dirent with name @name under @parent and get a reference
+ * if found.  This function may sleep and returns pointer to the found
+ * sysfs_dirent on success, %NULL on failure.
+ */
+struct sysfs_dirent *kernfs_find_and_get_ns(struct sysfs_dirent *parent,
+					    const char *name, const void *ns)
+{
+	struct sysfs_dirent *sd;
+
+	mutex_lock(&sysfs_mutex);
+	sd = kernfs_find_ns(parent, name, ns);
+	kernfs_get(sd);
+	mutex_unlock(&sysfs_mutex);
+
+	return sd;
+}
+EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
+
+/**
+ * kernfs_create_dir_ns - create a directory
+ * @parent: parent in which to create a new directory
+ * @name: name of the new directory
+ * @priv: opaque data associated with the new directory
+ * @ns: optional namespace tag of the directory
+ *
+ * Returns the created node on success, ERR_PTR() value on failure.
+ */
+struct sysfs_dirent *kernfs_create_dir_ns(struct sysfs_dirent *parent,
+					  const char *name, void *priv,
+					  const void *ns)
+{
+	umode_t mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
+	struct sysfs_addrm_cxt acxt;
+	struct sysfs_dirent *sd;
+	int rc;
+
+	/* allocate */
+	sd = sysfs_new_dirent(name, mode, SYSFS_DIR);
+	if (!sd)
+		return ERR_PTR(-ENOMEM);
+
+	sd->s_ns = ns;
+	sd->priv = priv;
+
+	/* link in */
+	sysfs_addrm_start(&acxt);
+	rc = sysfs_add_one(&acxt, sd, parent);
+	sysfs_addrm_finish(&acxt);
+
+	if (!rc)
+		return sd;
+
+	kernfs_put(sd);
+	return ERR_PTR(rc);
+}
+
+static struct dentry *sysfs_lookup(struct inode *dir, struct dentry *dentry,
+				   unsigned int flags)
+{
+	struct dentry *ret = NULL;
+	struct dentry *parent = dentry->d_parent;
+	struct sysfs_dirent *parent_sd = parent->d_fsdata;
+	struct sysfs_dirent *sd;
+	struct inode *inode;
+	const void *ns = NULL;
+
+	mutex_lock(&sysfs_mutex);
+
+	if (parent_sd->s_flags & SYSFS_FLAG_NS)
+		ns = sysfs_info(dir->i_sb)->ns;
+
+	sd = kernfs_find_ns(parent_sd, dentry->d_name.name, ns);
+
+	/* no such entry */
+	if (!sd) {
+		ret = ERR_PTR(-ENOENT);
+		goto out_unlock;
+	}
+	kernfs_get(sd);
+	dentry->d_fsdata = sd;
+
+	/* attach dentry and inode */
+	inode = sysfs_get_inode(dir->i_sb, sd);
+	if (!inode) {
+		ret = ERR_PTR(-ENOMEM);
+		goto out_unlock;
+	}
+
+	/* instantiate and hash dentry */
+	ret = d_materialise_unique(dentry, inode);
+ out_unlock:
+	mutex_unlock(&sysfs_mutex);
+	return ret;
+}
+
+const struct inode_operations sysfs_dir_inode_operations = {
+	.lookup		= sysfs_lookup,
+	.permission	= sysfs_permission,
+	.setattr	= sysfs_setattr,
+	.getattr	= sysfs_getattr,
+	.setxattr	= sysfs_setxattr,
+};
+
+static struct sysfs_dirent *sysfs_leftmost_descendant(struct sysfs_dirent *pos)
+{
+	struct sysfs_dirent *last;
+
+	while (true) {
+		struct rb_node *rbn;
+
+		last = pos;
+
+		if (sysfs_type(pos) != SYSFS_DIR)
+			break;
+
+		rbn = rb_first(&pos->s_dir.children);
+		if (!rbn)
+			break;
+
+		pos = to_sysfs_dirent(rbn);
+	}
+
+	return last;
+}
+
+/**
+ * sysfs_next_descendant_post - find the next descendant for post-order walk
+ * @pos: the current position (%NULL to initiate traversal)
+ * @root: sysfs_dirent whose descendants to walk
+ *
+ * Find the next descendant to visit for post-order traversal of @root's
+ * descendants.  @root is included in the iteration and the last node to be
+ * visited.
+ */
+static struct sysfs_dirent *sysfs_next_descendant_post(struct sysfs_dirent *pos,
+						       struct sysfs_dirent *root)
+{
+	struct rb_node *rbn;
+
+	lockdep_assert_held(&sysfs_mutex);
+
+	/* if first iteration, visit leftmost descendant which may be root */
+	if (!pos)
+		return sysfs_leftmost_descendant(root);
+
+	/* if we visited @root, we're done */
+	if (pos == root)
+		return NULL;
+
+	/* if there's an unvisited sibling, visit its leftmost descendant */
+	rbn = rb_next(&pos->s_rb);
+	if (rbn)
+		return sysfs_leftmost_descendant(to_sysfs_dirent(rbn));
+
+	/* no sibling left, visit parent */
+	return pos->s_parent;
+}
+
+static void __kernfs_remove(struct sysfs_addrm_cxt *acxt,
+			    struct sysfs_dirent *sd)
+{
+	struct sysfs_dirent *pos, *next;
+
+	if (!sd)
+		return;
+
+	pr_debug("sysfs %s: removing\n", sd->s_name);
+
+	next = NULL;
+	do {
+		pos = next;
+		next = sysfs_next_descendant_post(pos, sd);
+		if (pos)
+			sysfs_remove_one(acxt, pos);
+	} while (next);
+}
+
+/**
+ * kernfs_remove - remove a sysfs_dirent recursively
+ * @sd: the sysfs_dirent to remove
+ *
+ * Remove @sd along with all its subdirectories and files.
+ */
+void kernfs_remove(struct sysfs_dirent *sd)
+{
+	struct sysfs_addrm_cxt acxt;
+
+	sysfs_addrm_start(&acxt);
+	__kernfs_remove(&acxt, sd);
+	sysfs_addrm_finish(&acxt);
+}
+
+/**
+ * kernfs_remove_by_name_ns - find a sysfs_dirent by name and remove it
+ * @dir_sd: parent of the target
+ * @name: name of the sysfs_dirent to remove
+ * @ns: namespace tag of the sysfs_dirent to remove
+ *
+ * Look for the sysfs_dirent with @name and @ns under @dir_sd and remove
+ * it.  Returns 0 on success, -ENOENT if such entry doesn't exist.
+ */
+int kernfs_remove_by_name_ns(struct sysfs_dirent *dir_sd, const char *name,
+			     const void *ns)
+{
+	struct sysfs_addrm_cxt acxt;
+	struct sysfs_dirent *sd;
+
+	if (!dir_sd) {
+		WARN(1, KERN_WARNING "sysfs: can not remove '%s', no directory\n",
+			name);
+		return -ENOENT;
+	}
+
+	sysfs_addrm_start(&acxt);
+
+	sd = kernfs_find_ns(dir_sd, name, ns);
+	if (sd)
+		__kernfs_remove(&acxt, sd);
+
+	sysfs_addrm_finish(&acxt);
+
+	if (sd)
+		return 0;
+	else
+		return -ENOENT;
+}
+
+/**
+ * kernfs_rename_ns - move and rename a kernfs_node
+ * @sd: target node
+ * @new_parent: new parent to put @sd under
+ * @new_name: new name
+ * @new_ns: new namespace tag
+ */
+int kernfs_rename_ns(struct sysfs_dirent *sd, struct sysfs_dirent *new_parent,
+		     const char *new_name, const void *new_ns)
+{
+	int error;
+
+	mutex_lock(&sysfs_mutex);
+
+	error = 0;
+	if ((sd->s_parent == new_parent) && (sd->s_ns == new_ns) &&
+	    (strcmp(sd->s_name, new_name) == 0))
+		goto out;	/* nothing to rename */
+
+	error = -EEXIST;
+	if (kernfs_find_ns(new_parent, new_name, new_ns))
+		goto out;
+
+	/* rename sysfs_dirent */
+	if (strcmp(sd->s_name, new_name) != 0) {
+		error = -ENOMEM;
+		new_name = kstrdup(new_name, GFP_KERNEL);
+		if (!new_name)
+			goto out;
+
+		kfree(sd->s_name);
+		sd->s_name = new_name;
+	}
+
+	/*
+	 * Move to the appropriate place in the appropriate directories rbtree.
+	 */
+	sysfs_unlink_sibling(sd);
+	kernfs_get(new_parent);
+	kernfs_put(sd->s_parent);
+	sd->s_ns = new_ns;
+	sd->s_hash = sysfs_name_hash(sd->s_name, sd->s_ns);
+	sd->s_parent = new_parent;
+	sysfs_link_sibling(sd);
+
+	error = 0;
+ out:
+	mutex_unlock(&sysfs_mutex);
+	return error;
+}
+
+/**
+ * kernfs_enable_ns - enable namespace under a directory
+ * @sd: directory of interest, should be empty
+ *
+ * This is to be called right after @sd is created to enable namespace
+ * under it.  All children of @sd must have non-NULL namespace tags and
+ * only the ones which match the super_block's tag will be visible.
+ */
+void kernfs_enable_ns(struct sysfs_dirent *sd)
+{
+	WARN_ON_ONCE(sysfs_type(sd) != SYSFS_DIR);
+	WARN_ON_ONCE(!RB_EMPTY_ROOT(&sd->s_dir.children));
+	sd->s_flags |= SYSFS_FLAG_NS;
+}
+
+/* Relationship between s_mode and the DT_xxx types */
+static inline unsigned char dt_type(struct sysfs_dirent *sd)
+{
+	return (sd->s_mode >> 12) & 15;
+}
+
+static int sysfs_dir_release(struct inode *inode, struct file *filp)
+{
+	kernfs_put(filp->private_data);
+	return 0;
+}
+
+static struct sysfs_dirent *sysfs_dir_pos(const void *ns,
+	struct sysfs_dirent *parent_sd,	loff_t hash, struct sysfs_dirent *pos)
+{
+	if (pos) {
+		int valid = !(pos->s_flags & SYSFS_FLAG_REMOVED) &&
+			pos->s_parent == parent_sd &&
+			hash == pos->s_hash;
+		kernfs_put(pos);
+		if (!valid)
+			pos = NULL;
+	}
+	if (!pos && (hash > 1) && (hash < INT_MAX)) {
+		struct rb_node *node = parent_sd->s_dir.children.rb_node;
+		while (node) {
+			pos = to_sysfs_dirent(node);
+
+			if (hash < pos->s_hash)
+				node = node->rb_left;
+			else if (hash > pos->s_hash)
+				node = node->rb_right;
+			else
+				break;
+		}
+	}
+	/* Skip over entries in the wrong namespace */
+	while (pos && pos->s_ns != ns) {
+		struct rb_node *node = rb_next(&pos->s_rb);
+		if (!node)
+			pos = NULL;
+		else
+			pos = to_sysfs_dirent(node);
+	}
+	return pos;
+}
+
+static struct sysfs_dirent *sysfs_dir_next_pos(const void *ns,
+	struct sysfs_dirent *parent_sd,	ino_t ino, struct sysfs_dirent *pos)
+{
+	pos = sysfs_dir_pos(ns, parent_sd, ino, pos);
+	if (pos)
+		do {
+			struct rb_node *node = rb_next(&pos->s_rb);
+			if (!node)
+				pos = NULL;
+			else
+				pos = to_sysfs_dirent(node);
+		} while (pos && pos->s_ns != ns);
+	return pos;
+}
+
+static int sysfs_readdir(struct file *file, struct dir_context *ctx)
+{
+	struct dentry *dentry = file->f_path.dentry;
+	struct sysfs_dirent *parent_sd = dentry->d_fsdata;
+	struct sysfs_dirent *pos = file->private_data;
+	const void *ns = NULL;
+
+	if (!dir_emit_dots(file, ctx))
+		return 0;
+	mutex_lock(&sysfs_mutex);
+
+	if (parent_sd->s_flags & SYSFS_FLAG_NS)
+		ns = sysfs_info(dentry->d_sb)->ns;
+
+	for (pos = sysfs_dir_pos(ns, parent_sd, ctx->pos, pos);
+	     pos;
+	     pos = sysfs_dir_next_pos(ns, parent_sd, ctx->pos, pos)) {
+		const char *name = pos->s_name;
+		unsigned int type = dt_type(pos);
+		int len = strlen(name);
+		ino_t ino = pos->s_ino;
+
+		ctx->pos = pos->s_hash;
+		file->private_data = pos;
+		kernfs_get(pos);
+
+		mutex_unlock(&sysfs_mutex);
+		if (!dir_emit(ctx, name, len, ino, type))
+			return 0;
+		mutex_lock(&sysfs_mutex);
+	}
+	mutex_unlock(&sysfs_mutex);
+	file->private_data = NULL;
+	ctx->pos = INT_MAX;
+	return 0;
+}
+
+static loff_t sysfs_dir_llseek(struct file *file, loff_t offset, int whence)
+{
+	struct inode *inode = file_inode(file);
+	loff_t ret;
+
+	mutex_lock(&inode->i_mutex);
+	ret = generic_file_llseek(file, offset, whence);
+	mutex_unlock(&inode->i_mutex);
+
+	return ret;
+}
+
+const struct file_operations sysfs_dir_operations = {
+	.read		= generic_read_dir,
+	.iterate	= sysfs_readdir,
+	.release	= sysfs_dir_release,
+	.llseek		= sysfs_dir_llseek,
+};