Adding upstream version 6.1.76.upstream/6.1.76

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

1 files changed, 1835 insertions, 0 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
new file mode 100644
index 000000000..44842e6cf
--- /dev/null
+++ b/fs/kernfs/dir.c
@@ -0,0 +1,1835 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * fs/kernfs/dir.c - kernfs directory implementation
+ *
+ * Copyright (c) 2001-3 Patrick Mochel
+ * Copyright (c) 2007 SUSE Linux Products GmbH
+ * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
+ */
+
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/idr.h>
+#include <linux/slab.h>
+#include <linux/security.h>
+#include <linux/hash.h>
+
+#include "kernfs-internal.h"
+
+static DEFINE_SPINLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
+/*
+ * Don't use rename_lock to piggy back on pr_cont_buf. We don't want to
+ * call pr_cont() while holding rename_lock. Because sometimes pr_cont()
+ * will perform wakeups when releasing console_sem. Holding rename_lock
+ * will introduce deadlock if the scheduler reads the kernfs_name in the
+ * wakeup path.
+ */
+static DEFINE_SPINLOCK(kernfs_pr_cont_lock);
+static char kernfs_pr_cont_buf[PATH_MAX];	/* protected by pr_cont_lock */
+static DEFINE_SPINLOCK(kernfs_idr_lock);	/* root->ino_idr */
+
+#define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
+
+static bool __kernfs_active(struct kernfs_node *kn)
+{
+	return atomic_read(&kn->active) >= 0;
+}
+
+static bool kernfs_active(struct kernfs_node *kn)
+{
+	lockdep_assert_held(&kernfs_root(kn)->kernfs_rwsem);
+	return __kernfs_active(kn);
+}
+
+static bool kernfs_lockdep(struct kernfs_node *kn)
+{
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	return kn->flags & KERNFS_LOCKDEP;
+#else
+	return false;
+#endif
+}
+
+static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
+{
+	if (!kn)
+		return strlcpy(buf, "(null)", buflen);
+
+	return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
+}
+
+/* kernfs_node_depth - compute depth from @from to @to */
+static size_t kernfs_depth(struct kernfs_node *from, struct kernfs_node *to)
+{
+	size_t depth = 0;
+
+	while (to->parent && to != from) {
+		depth++;
+		to = to->parent;
+	}
+	return depth;
+}
+
+static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a,
+						  struct kernfs_node *b)
+{
+	size_t da, db;
+	struct kernfs_root *ra = kernfs_root(a), *rb = kernfs_root(b);
+
+	if (ra != rb)
+		return NULL;
+
+	da = kernfs_depth(ra->kn, a);
+	db = kernfs_depth(rb->kn, b);
+
+	while (da > db) {
+		a = a->parent;
+		da--;
+	}
+	while (db > da) {
+		b = b->parent;
+		db--;
+	}
+
+	/* worst case b and a will be the same at root */
+	while (b != a) {
+		b = b->parent;
+		a = a->parent;
+	}
+
+	return a;
+}
+
+/**
+ * kernfs_path_from_node_locked - find a pseudo-absolute path to @kn_to,
+ * where kn_from is treated as root of the path.
+ * @kn_from: kernfs node which should be treated as root for the path
+ * @kn_to: kernfs node to which path is needed
+ * @buf: buffer to copy the path into
+ * @buflen: size of @buf
+ *
+ * We need to handle couple of scenarios here:
+ * [1] when @kn_from is an ancestor of @kn_to at some level
+ * kn_from: /n1/n2/n3
+ * kn_to:   /n1/n2/n3/n4/n5
+ * result:  /n4/n5
+ *
+ * [2] when @kn_from is on a different hierarchy and we need to find common
+ * ancestor between @kn_from and @kn_to.
+ * kn_from: /n1/n2/n3/n4
+ * kn_to:   /n1/n2/n5
+ * result:  /../../n5
+ * OR
+ * kn_from: /n1/n2/n3/n4/n5   [depth=5]
+ * kn_to:   /n1/n2/n3         [depth=3]
+ * result:  /../..
+ *
+ * [3] when @kn_to is NULL result will be "(null)"
+ *
+ * Returns the length of the full path.  If the full length is equal to or
+ * greater than @buflen, @buf contains the truncated path with the trailing
+ * '\0'.  On error, -errno is returned.
+ */
+static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
+					struct kernfs_node *kn_from,
+					char *buf, size_t buflen)
+{
+	struct kernfs_node *kn, *common;
+	const char parent_str[] = "/..";
+	size_t depth_from, depth_to, len = 0;
+	int i, j;
+
+	if (!kn_to)
+		return strlcpy(buf, "(null)", buflen);
+
+	if (!kn_from)
+		kn_from = kernfs_root(kn_to)->kn;
+
+	if (kn_from == kn_to)
+		return strlcpy(buf, "/", buflen);
+
+	if (!buf)
+		return -EINVAL;
+
+	common = kernfs_common_ancestor(kn_from, kn_to);
+	if (WARN_ON(!common))
+		return -EINVAL;
+
+	depth_to = kernfs_depth(common, kn_to);
+	depth_from = kernfs_depth(common, kn_from);
+
+	buf[0] = '\0';
+
+	for (i = 0; i < depth_from; i++)
+		len += strlcpy(buf + len, parent_str,
+			       len < buflen ? buflen - len : 0);
+
+	/* Calculate how many bytes we need for the rest */
+	for (i = depth_to - 1; i >= 0; i--) {
+		for (kn = kn_to, j = 0; j < i; j++)
+			kn = kn->parent;
+		len += strlcpy(buf + len, "/",
+			       len < buflen ? buflen - len : 0);
+		len += strlcpy(buf + len, kn->name,
+			       len < buflen ? buflen - len : 0);
+	}
+
+	return len;
+}
+
+/**
+ * kernfs_name - obtain the name of a given node
+ * @kn: kernfs_node of interest
+ * @buf: buffer to copy @kn's name into
+ * @buflen: size of @buf
+ *
+ * Copies the name of @kn into @buf of @buflen bytes.  The behavior is
+ * similar to strlcpy().  It returns the length of @kn's name and if @buf
+ * isn't long enough, it's filled upto @buflen-1 and nul terminated.
+ *
+ * Fills buffer with "(null)" if @kn is NULL.
+ *
+ * This function can be called from any context.
+ */
+int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
+{
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	ret = kernfs_name_locked(kn, buf, buflen);
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	return ret;
+}
+
+/**
+ * kernfs_path_from_node - build path of node @to relative to @from.
+ * @from: parent kernfs_node relative to which we need to build the path
+ * @to: kernfs_node of interest
+ * @buf: buffer to copy @to's path into
+ * @buflen: size of @buf
+ *
+ * Builds @to's path relative to @from in @buf. @from and @to must
+ * be on the same kernfs-root. If @from is not parent of @to, then a relative
+ * path (which includes '..'s) as needed to reach from @from to @to is
+ * returned.
+ *
+ * Returns the length of the full path.  If the full length is equal to or
+ * greater than @buflen, @buf contains the truncated path with the trailing
+ * '\0'.  On error, -errno is returned.
+ */
+int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
+			  char *buf, size_t buflen)
+{
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	ret = kernfs_path_from_node_locked(to, from, buf, buflen);
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kernfs_path_from_node);
+
+/**
+ * pr_cont_kernfs_name - pr_cont name of a kernfs_node
+ * @kn: kernfs_node of interest
+ *
+ * This function can be called from any context.
+ */
+void pr_cont_kernfs_name(struct kernfs_node *kn)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&kernfs_pr_cont_lock, flags);
+
+	kernfs_name(kn, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf));
+	pr_cont("%s", kernfs_pr_cont_buf);
+
+	spin_unlock_irqrestore(&kernfs_pr_cont_lock, flags);
+}
+
+/**
+ * pr_cont_kernfs_path - pr_cont path of a kernfs_node
+ * @kn: kernfs_node of interest
+ *
+ * This function can be called from any context.
+ */
+void pr_cont_kernfs_path(struct kernfs_node *kn)
+{
+	unsigned long flags;
+	int sz;
+
+	spin_lock_irqsave(&kernfs_pr_cont_lock, flags);
+
+	sz = kernfs_path_from_node(kn, NULL, kernfs_pr_cont_buf,
+				   sizeof(kernfs_pr_cont_buf));
+	if (sz < 0) {
+		pr_cont("(error)");
+		goto out;
+	}
+
+	if (sz >= sizeof(kernfs_pr_cont_buf)) {
+		pr_cont("(name too long)");
+		goto out;
+	}
+
+	pr_cont("%s", kernfs_pr_cont_buf);
+
+out:
+	spin_unlock_irqrestore(&kernfs_pr_cont_lock, flags);
+}
+
+/**
+ * kernfs_get_parent - determine the parent node and pin it
+ * @kn: kernfs_node of interest
+ *
+ * Determines @kn's parent, pins and returns it.  This function can be
+ * called from any context.
+ */
+struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
+{
+	struct kernfs_node *parent;
+	unsigned long flags;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	parent = kn->parent;
+	kernfs_get(parent);
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+
+	return parent;
+}
+
+/**
+ *	kernfs_name_hash
+ *	@name: Null terminated string to hash
+ *	@ns:   Namespace tag to hash
+ *
+ *	Returns 31 bit hash of ns + name (so it fits in an off_t )
+ */
+static unsigned int kernfs_name_hash(const char *name, const void *ns)
+{
+	unsigned long hash = init_name_hash(ns);
+	unsigned int len = strlen(name);
+	while (len--)
+		hash = partial_name_hash(*name++, hash);
+	hash = end_name_hash(hash);
+	hash &= 0x7fffffffU;
+	/* Reserve hash numbers 0, 1 and INT_MAX for magic directory entries */
+	if (hash < 2)
+		hash += 2;
+	if (hash >= INT_MAX)
+		hash = INT_MAX - 1;
+	return hash;
+}
+
+static int kernfs_name_compare(unsigned int hash, const char *name,
+			       const void *ns, const struct kernfs_node *kn)
+{
+	if (hash < kn->hash)
+		return -1;
+	if (hash > kn->hash)
+		return 1;
+	if (ns < kn->ns)
+		return -1;
+	if (ns > kn->ns)
+		return 1;
+	return strcmp(name, kn->name);
+}
+
+static int kernfs_sd_compare(const struct kernfs_node *left,
+			     const struct kernfs_node *right)
+{
+	return kernfs_name_compare(left->hash, left->name, left->ns, right);
+}
+
+/**
+ *	kernfs_link_sibling - link kernfs_node into sibling rbtree
+ *	@kn: kernfs_node of interest
+ *
+ *	Link @kn into its sibling rbtree which starts from
+ *	@kn->parent->dir.children.
+ *
+ *	Locking:
+ *	kernfs_rwsem held exclusive
+ *
+ *	RETURNS:
+ *	0 on susccess -EEXIST on failure.
+ */
+static int kernfs_link_sibling(struct kernfs_node *kn)
+{
+	struct rb_node **node = &kn->parent->dir.children.rb_node;
+	struct rb_node *parent = NULL;
+
+	while (*node) {
+		struct kernfs_node *pos;
+		int result;
+
+		pos = rb_to_kn(*node);
+		parent = *node;
+		result = kernfs_sd_compare(kn, pos);
+		if (result < 0)
+			node = &pos->rb.rb_left;
+		else if (result > 0)
+			node = &pos->rb.rb_right;
+		else
+			return -EEXIST;
+	}
+
+	/* add new node and rebalance the tree */
+	rb_link_node(&kn->rb, parent, node);
+	rb_insert_color(&kn->rb, &kn->parent->dir.children);
+
+	/* successfully added, account subdir number */
+	if (kernfs_type(kn) == KERNFS_DIR)
+		kn->parent->dir.subdirs++;
+	kernfs_inc_rev(kn->parent);
+
+	return 0;
+}
+
+/**
+ *	kernfs_unlink_sibling - unlink kernfs_node from sibling rbtree
+ *	@kn: kernfs_node of interest
+ *
+ *	Try to unlink @kn from its sibling rbtree which starts from
+ *	kn->parent->dir.children.  Returns %true if @kn was actually
+ *	removed, %false if @kn wasn't on the rbtree.
+ *
+ *	Locking:
+ *	kernfs_rwsem held exclusive
+ */
+static bool kernfs_unlink_sibling(struct kernfs_node *kn)
+{
+	if (RB_EMPTY_NODE(&kn->rb))
+		return false;
+
+	if (kernfs_type(kn) == KERNFS_DIR)
+		kn->parent->dir.subdirs--;
+	kernfs_inc_rev(kn->parent);
+
+	rb_erase(&kn->rb, &kn->parent->dir.children);
+	RB_CLEAR_NODE(&kn->rb);
+	return true;
+}
+
+/**
+ *	kernfs_get_active - get an active reference to kernfs_node
+ *	@kn: kernfs_node to get an active reference to
+ *
+ *	Get an active reference of @kn.  This function is noop if @kn
+ *	is NULL.
+ *
+ *	RETURNS:
+ *	Pointer to @kn on success, NULL on failure.
+ */
+struct kernfs_node *kernfs_get_active(struct kernfs_node *kn)
+{
+	if (unlikely(!kn))
+		return NULL;
+
+	if (!atomic_inc_unless_negative(&kn->active))
+		return NULL;
+
+	if (kernfs_lockdep(kn))
+		rwsem_acquire_read(&kn->dep_map, 0, 1, _RET_IP_);
+	return kn;
+}
+
+/**
+ *	kernfs_put_active - put an active reference to kernfs_node
+ *	@kn: kernfs_node to put an active reference to
+ *
+ *	Put an active reference to @kn.  This function is noop if @kn
+ *	is NULL.
+ */
+void kernfs_put_active(struct kernfs_node *kn)
+{
+	int v;
+
+	if (unlikely(!kn))
+		return;
+
+	if (kernfs_lockdep(kn))
+		rwsem_release(&kn->dep_map, _RET_IP_);
+	v = atomic_dec_return(&kn->active);
+	if (likely(v != KN_DEACTIVATED_BIAS))
+		return;
+
+	wake_up_all(&kernfs_root(kn)->deactivate_waitq);
+}
+
+/**
+ * kernfs_drain - drain kernfs_node
+ * @kn: kernfs_node to drain
+ *
+ * Drain existing usages and nuke all existing mmaps of @kn.  Mutiple
+ * removers may invoke this function concurrently on @kn and all will
+ * return after draining is complete.
+ */
+static void kernfs_drain(struct kernfs_node *kn)
+	__releases(&kernfs_root(kn)->kernfs_rwsem)
+	__acquires(&kernfs_root(kn)->kernfs_rwsem)
+{
+	struct kernfs_root *root = kernfs_root(kn);
+
+	lockdep_assert_held_write(&root->kernfs_rwsem);
+	WARN_ON_ONCE(kernfs_active(kn));
+
+	/*
+	 * Skip draining if already fully drained. This avoids draining and its
+	 * lockdep annotations for nodes which have never been activated
+	 * allowing embedding kernfs_remove() in create error paths without
+	 * worrying about draining.
+	 */
+	if (atomic_read(&kn->active) == KN_DEACTIVATED_BIAS &&
+	    !kernfs_should_drain_open_files(kn))
+		return;
+
+	up_write(&root->kernfs_rwsem);
+
+	if (kernfs_lockdep(kn)) {
+		rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
+		if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
+			lock_contended(&kn->dep_map, _RET_IP_);
+	}
+
+	wait_event(root->deactivate_waitq,
+		   atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);
+
+	if (kernfs_lockdep(kn)) {
+		lock_acquired(&kn->dep_map, _RET_IP_);
+		rwsem_release(&kn->dep_map, _RET_IP_);
+	}
+
+	if (kernfs_should_drain_open_files(kn))
+		kernfs_drain_open_files(kn);
+
+	down_write(&root->kernfs_rwsem);
+}
+
+/**
+ * kernfs_get - get a reference count on a kernfs_node
+ * @kn: the target kernfs_node
+ */
+void kernfs_get(struct kernfs_node *kn)
+{
+	if (kn) {
+		WARN_ON(!atomic_read(&kn->count));
+		atomic_inc(&kn->count);
+	}
+}
+EXPORT_SYMBOL_GPL(kernfs_get);
+
+/**
+ * kernfs_put - put a reference count on a kernfs_node
+ * @kn: the target kernfs_node
+ *
+ * Put a reference count of @kn and destroy it if it reached zero.
+ */
+void kernfs_put(struct kernfs_node *kn)
+{
+	struct kernfs_node *parent;
+	struct kernfs_root *root;
+
+	if (!kn || !atomic_dec_and_test(&kn->count))
+		return;
+	root = kernfs_root(kn);
+ repeat:
+	/*
+	 * Moving/renaming is always done while holding reference.
+	 * kn->parent won't change beneath us.
+	 */
+	parent = kn->parent;
+
+	WARN_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS,
+		  "kernfs_put: %s/%s: released with incorrect active_ref %d\n",
+		  parent ? parent->name : "", kn->name, atomic_read(&kn->active));
+
+	if (kernfs_type(kn) == KERNFS_LINK)
+		kernfs_put(kn->symlink.target_kn);
+
+	kfree_const(kn->name);
+
+	if (kn->iattr) {
+		simple_xattrs_free(&kn->iattr->xattrs);
+		kmem_cache_free(kernfs_iattrs_cache, kn->iattr);
+	}
+	spin_lock(&kernfs_idr_lock);
+	idr_remove(&root->ino_idr, (u32)kernfs_ino(kn));
+	spin_unlock(&kernfs_idr_lock);
+	kmem_cache_free(kernfs_node_cache, kn);
+
+	kn = parent;
+	if (kn) {
+		if (atomic_dec_and_test(&kn->count))
+			goto repeat;
+	} else {
+		/* just released the root kn, free @root too */
+		idr_destroy(&root->ino_idr);
+		kfree(root);
+	}
+}
+EXPORT_SYMBOL_GPL(kernfs_put);
+
+/**
+ * kernfs_node_from_dentry - determine kernfs_node associated with a dentry
+ * @dentry: the dentry in question
+ *
+ * Return the kernfs_node associated with @dentry.  If @dentry is not a
+ * kernfs one, %NULL is returned.
+ *
+ * While the returned kernfs_node will stay accessible as long as @dentry
+ * is accessible, the returned node can be in any state and the caller is
+ * fully responsible for determining what's accessible.
+ */
+struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
+{
+	if (dentry->d_sb->s_op == &kernfs_sops)
+		return kernfs_dentry_node(dentry);
+	return NULL;
+}
+
+static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
+					     struct kernfs_node *parent,
+					     const char *name, umode_t mode,
+					     kuid_t uid, kgid_t gid,
+					     unsigned flags)
+{
+	struct kernfs_node *kn;
+	u32 id_highbits;
+	int ret;
+
+	name = kstrdup_const(name, GFP_KERNEL);
+	if (!name)
+		return NULL;
+
+	kn = kmem_cache_zalloc(kernfs_node_cache, GFP_KERNEL);
+	if (!kn)
+		goto err_out1;
+
+	idr_preload(GFP_KERNEL);
+	spin_lock(&kernfs_idr_lock);
+	ret = idr_alloc_cyclic(&root->ino_idr, kn, 1, 0, GFP_ATOMIC);
+	if (ret >= 0 && ret < root->last_id_lowbits)
+		root->id_highbits++;
+	id_highbits = root->id_highbits;
+	root->last_id_lowbits = ret;
+	spin_unlock(&kernfs_idr_lock);
+	idr_preload_end();
+	if (ret < 0)
+		goto err_out2;
+
+	kn->id = (u64)id_highbits << 32 | ret;
+
+	atomic_set(&kn->count, 1);
+	atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
+	RB_CLEAR_NODE(&kn->rb);
+
+	kn->name = name;
+	kn->mode = mode;
+	kn->flags = flags;
+
+	if (!uid_eq(uid, GLOBAL_ROOT_UID) || !gid_eq(gid, GLOBAL_ROOT_GID)) {
+		struct iattr iattr = {
+			.ia_valid = ATTR_UID | ATTR_GID,
+			.ia_uid = uid,
+			.ia_gid = gid,
+		};
+
+		ret = __kernfs_setattr(kn, &iattr);
+		if (ret < 0)
+			goto err_out3;
+	}
+
+	if (parent) {
+		ret = security_kernfs_init_security(parent, kn);
+		if (ret)
+			goto err_out3;
+	}
+
+	return kn;
+
+ err_out3:
+	spin_lock(&kernfs_idr_lock);
+	idr_remove(&root->ino_idr, (u32)kernfs_ino(kn));
+	spin_unlock(&kernfs_idr_lock);
+ err_out2:
+	kmem_cache_free(kernfs_node_cache, kn);
+ err_out1:
+	kfree_const(name);
+	return NULL;
+}
+
+struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
+				    const char *name, umode_t mode,
+				    kuid_t uid, kgid_t gid,
+				    unsigned flags)
+{
+	struct kernfs_node *kn;
+
+	kn = __kernfs_new_node(kernfs_root(parent), parent,
+			       name, mode, uid, gid, flags);
+	if (kn) {
+		kernfs_get(parent);
+		kn->parent = parent;
+	}
+	return kn;
+}
+
+/*
+ * kernfs_find_and_get_node_by_id - get kernfs_node from node id
+ * @root: the kernfs root
+ * @id: the target node id
+ *
+ * @id's lower 32bits encode ino and upper gen.  If the gen portion is
+ * zero, all generations are matched.
+ *
+ * RETURNS:
+ * NULL on failure. Return a kernfs node with reference counter incremented
+ */
+struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
+						   u64 id)
+{
+	struct kernfs_node *kn;
+	ino_t ino = kernfs_id_ino(id);
+	u32 gen = kernfs_id_gen(id);
+
+	spin_lock(&kernfs_idr_lock);
+
+	kn = idr_find(&root->ino_idr, (u32)ino);
+	if (!kn)
+		goto err_unlock;
+
+	if (sizeof(ino_t) >= sizeof(u64)) {
+		/* we looked up with the low 32bits, compare the whole */
+		if (kernfs_ino(kn) != ino)
+			goto err_unlock;
+	} else {
+		/* 0 matches all generations */
+		if (unlikely(gen && kernfs_gen(kn) != gen))
+			goto err_unlock;
+	}
+
+	/*
+	 * We should fail if @kn has never been activated and guarantee success
+	 * if the caller knows that @kn is active. Both can be achieved by
+	 * __kernfs_active() which tests @kn->active without kernfs_rwsem.
+	 */
+	if (unlikely(!__kernfs_active(kn) || !atomic_inc_not_zero(&kn->count)))
+		goto err_unlock;
+
+	spin_unlock(&kernfs_idr_lock);
+	return kn;
+err_unlock:
+	spin_unlock(&kernfs_idr_lock);
+	return NULL;
+}
+
+/**
+ *	kernfs_add_one - add kernfs_node to parent without warning
+ *	@kn: kernfs_node to be added
+ *
+ *	The caller must already have initialized @kn->parent.  This
+ *	function increments nlink of the parent's inode if @kn is a
+ *	directory and link into the children list of the parent.
+ *
+ *	RETURNS:
+ *	0 on success, -EEXIST if entry with the given name already
+ *	exists.
+ */
+int kernfs_add_one(struct kernfs_node *kn)
+{
+	struct kernfs_node *parent = kn->parent;
+	struct kernfs_root *root = kernfs_root(parent);
+	struct kernfs_iattrs *ps_iattr;
+	bool has_ns;
+	int ret;
+
+	down_write(&root->kernfs_rwsem);
+
+	ret = -EINVAL;
+	has_ns = kernfs_ns_enabled(parent);
+	if (WARN(has_ns != (bool)kn->ns, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
+		 has_ns ? "required" : "invalid", parent->name, kn->name))
+		goto out_unlock;
+
+	if (kernfs_type(parent) != KERNFS_DIR)
+		goto out_unlock;
+
+	ret = -ENOENT;
+	if (parent->flags & (KERNFS_REMOVING | KERNFS_EMPTY_DIR))
+		goto out_unlock;
+
+	kn->hash = kernfs_name_hash(kn->name, kn->ns);
+
+	ret = kernfs_link_sibling(kn);
+	if (ret)
+		goto out_unlock;
+
+	/* Update timestamps on the parent */
+	ps_iattr = parent->iattr;
+	if (ps_iattr) {
+		ktime_get_real_ts64(&ps_iattr->ia_ctime);
+		ps_iattr->ia_mtime = ps_iattr->ia_ctime;
+	}
+
+	up_write(&root->kernfs_rwsem);
+
+	/*
+	 * Activate the new node unless CREATE_DEACTIVATED is requested.
+	 * If not activated here, the kernfs user is responsible for
+	 * activating the node with kernfs_activate().  A node which hasn't
+	 * been activated is not visible to userland and its removal won't
+	 * trigger deactivation.
+	 */
+	if (!(kernfs_root(kn)->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
+		kernfs_activate(kn);
+	return 0;
+
+out_unlock:
+	up_write(&root->kernfs_rwsem);
+	return ret;
+}
+
+/**
+ * kernfs_find_ns - find kernfs_node with the given name
+ * @parent: kernfs_node to search under
+ * @name: name to look for
+ * @ns: the namespace tag to use
+ *
+ * Look for kernfs_node with name @name under @parent.  Returns pointer to
+ * the found kernfs_node on success, %NULL on failure.
+ */
+static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
+					  const unsigned char *name,
+					  const void *ns)
+{
+	struct rb_node *node = parent->dir.children.rb_node;
+	bool has_ns = kernfs_ns_enabled(parent);
+	unsigned int hash;
+
+	lockdep_assert_held(&kernfs_root(parent)->kernfs_rwsem);
+
+	if (has_ns != (bool)ns) {
+		WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
+		     has_ns ? "required" : "invalid", parent->name, name);
+		return NULL;
+	}
+
+	hash = kernfs_name_hash(name, ns);
+	while (node) {
+		struct kernfs_node *kn;
+		int result;
+
+		kn = rb_to_kn(node);
+		result = kernfs_name_compare(hash, name, ns, kn);
+		if (result < 0)
+			node = node->rb_left;
+		else if (result > 0)
+			node = node->rb_right;
+		else
+			return kn;
+	}
+	return NULL;
+}
+
+static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
+					  const unsigned char *path,
+					  const void *ns)
+{
+	size_t len;
+	char *p, *name;
+
+	lockdep_assert_held_read(&kernfs_root(parent)->kernfs_rwsem);
+
+	spin_lock_irq(&kernfs_pr_cont_lock);
+
+	len = strlcpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf));
+
+	if (len >= sizeof(kernfs_pr_cont_buf)) {
+		spin_unlock_irq(&kernfs_pr_cont_lock);
+		return NULL;
+	}
+
+	p = kernfs_pr_cont_buf;
+
+	while ((name = strsep(&p, "/")) && parent) {
+		if (*name == '\0')
+			continue;
+		parent = kernfs_find_ns(parent, name, ns);
+	}
+
+	spin_unlock_irq(&kernfs_pr_cont_lock);
+
+	return parent;
+}
+
+/**
+ * kernfs_find_and_get_ns - find and get kernfs_node with the given name
+ * @parent: kernfs_node to search under
+ * @name: name to look for
+ * @ns: the namespace tag to use
+ *
+ * Look for kernfs_node with name @name under @parent and get a reference
+ * if found.  This function may sleep and returns pointer to the found
+ * kernfs_node on success, %NULL on failure.
+ */
+struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
+					   const char *name, const void *ns)
+{
+	struct kernfs_node *kn;
+	struct kernfs_root *root = kernfs_root(parent);
+
+	down_read(&root->kernfs_rwsem);
+	kn = kernfs_find_ns(parent, name, ns);
+	kernfs_get(kn);
+	up_read(&root->kernfs_rwsem);
+
+	return kn;
+}
+EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
+
+/**
+ * kernfs_walk_and_get_ns - find and get kernfs_node with the given path
+ * @parent: kernfs_node to search under
+ * @path: path to look for
+ * @ns: the namespace tag to use
+ *
+ * Look for kernfs_node with path @path under @parent and get a reference
+ * if found.  This function may sleep and returns pointer to the found
+ * kernfs_node on success, %NULL on failure.
+ */
+struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
+					   const char *path, const void *ns)
+{
+	struct kernfs_node *kn;
+	struct kernfs_root *root = kernfs_root(parent);
+
+	down_read(&root->kernfs_rwsem);
+	kn = kernfs_walk_ns(parent, path, ns);
+	kernfs_get(kn);
+	up_read(&root->kernfs_rwsem);
+
+	return kn;
+}
+
+/**
+ * kernfs_create_root - create a new kernfs hierarchy
+ * @scops: optional syscall operations for the hierarchy
+ * @flags: KERNFS_ROOT_* flags
+ * @priv: opaque data associated with the new directory
+ *
+ * Returns the root of the new hierarchy on success, ERR_PTR() value on
+ * failure.
+ */
+struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
+				       unsigned int flags, void *priv)
+{
+	struct kernfs_root *root;
+	struct kernfs_node *kn;
+
+	root = kzalloc(sizeof(*root), GFP_KERNEL);
+	if (!root)
+		return ERR_PTR(-ENOMEM);
+
+	idr_init(&root->ino_idr);
+	init_rwsem(&root->kernfs_rwsem);
+	INIT_LIST_HEAD(&root->supers);
+
+	/*
+	 * On 64bit ino setups, id is ino.  On 32bit, low 32bits are ino.
+	 * High bits generation.  The starting value for both ino and
+	 * genenration is 1.  Initialize upper 32bit allocation
+	 * accordingly.
+	 */
+	if (sizeof(ino_t) >= sizeof(u64))
+		root->id_highbits = 0;
+	else
+		root->id_highbits = 1;
+
+	kn = __kernfs_new_node(root, NULL, "", S_IFDIR | S_IRUGO | S_IXUGO,
+			       GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
+			       KERNFS_DIR);
+	if (!kn) {
+		idr_destroy(&root->ino_idr);
+		kfree(root);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	kn->priv = priv;
+	kn->dir.root = root;
+
+	root->syscall_ops = scops;
+	root->flags = flags;
+	root->kn = kn;
+	init_waitqueue_head(&root->deactivate_waitq);
+
+	if (!(root->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
+		kernfs_activate(kn);
+
+	return root;
+}
+
+/**
+ * kernfs_destroy_root - destroy a kernfs hierarchy
+ * @root: root of the hierarchy to destroy
+ *
+ * Destroy the hierarchy anchored at @root by removing all existing
+ * directories and destroying @root.
+ */
+void kernfs_destroy_root(struct kernfs_root *root)
+{
+	/*
+	 *  kernfs_remove holds kernfs_rwsem from the root so the root
+	 *  shouldn't be freed during the operation.
+	 */
+	kernfs_get(root->kn);
+	kernfs_remove(root->kn);
+	kernfs_put(root->kn); /* will also free @root */
+}
+
+/**
+ * kernfs_root_to_node - return the kernfs_node associated with a kernfs_root
+ * @root: root to use to lookup
+ */
+struct kernfs_node *kernfs_root_to_node(struct kernfs_root *root)
+{
+	return root->kn;
+}
+
+/**
+ * kernfs_create_dir_ns - create a directory
+ * @parent: parent in which to create a new directory
+ * @name: name of the new directory
+ * @mode: mode of the new directory
+ * @uid: uid of the new directory
+ * @gid: gid of the new directory
+ * @priv: opaque data associated with the new directory
+ * @ns: optional namespace tag of the directory
+ *
+ * Returns the created node on success, ERR_PTR() value on failure.
+ */
+struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
+					 const char *name, umode_t mode,
+					 kuid_t uid, kgid_t gid,
+					 void *priv, const void *ns)
+{
+	struct kernfs_node *kn;
+	int rc;
+
+	/* allocate */
+	kn = kernfs_new_node(parent, name, mode | S_IFDIR,
+			     uid, gid, KERNFS_DIR);
+	if (!kn)
+		return ERR_PTR(-ENOMEM);
+
+	kn->dir.root = parent->dir.root;
+	kn->ns = ns;
+	kn->priv = priv;
+
+	/* link in */
+	rc = kernfs_add_one(kn);
+	if (!rc)
+		return kn;
+
+	kernfs_put(kn);
+	return ERR_PTR(rc);
+}
+
+/**
+ * kernfs_create_empty_dir - create an always empty directory
+ * @parent: parent in which to create a new directory
+ * @name: name of the new directory
+ *
+ * Returns the created node on success, ERR_PTR() value on failure.
+ */
+struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
+					    const char *name)
+{
+	struct kernfs_node *kn;
+	int rc;
+
+	/* allocate */
+	kn = kernfs_new_node(parent, name, S_IRUGO|S_IXUGO|S_IFDIR,
+			     GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, KERNFS_DIR);
+	if (!kn)
+		return ERR_PTR(-ENOMEM);
+
+	kn->flags |= KERNFS_EMPTY_DIR;
+	kn->dir.root = parent->dir.root;
+	kn->ns = NULL;
+	kn->priv = NULL;
+
+	/* link in */
+	rc = kernfs_add_one(kn);
+	if (!rc)
+		return kn;
+
+	kernfs_put(kn);
+	return ERR_PTR(rc);
+}
+
+static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
+{
+	struct kernfs_node *kn;
+	struct kernfs_root *root;
+
+	if (flags & LOOKUP_RCU)
+		return -ECHILD;
+
+	/* Negative hashed dentry? */
+	if (d_really_is_negative(dentry)) {
+		struct kernfs_node *parent;
+
+		/* If the kernfs parent node has changed discard and
+		 * proceed to ->lookup.
+		 */
+		spin_lock(&dentry->d_lock);
+		parent = kernfs_dentry_node(dentry->d_parent);
+		if (parent) {
+			spin_unlock(&dentry->d_lock);
+			root = kernfs_root(parent);
+			down_read(&root->kernfs_rwsem);
+			if (kernfs_dir_changed(parent, dentry)) {
+				up_read(&root->kernfs_rwsem);
+				return 0;
+			}
+			up_read(&root->kernfs_rwsem);
+		} else
+			spin_unlock(&dentry->d_lock);
+
+		/* The kernfs parent node hasn't changed, leave the
+		 * dentry negative and return success.
+		 */
+		return 1;
+	}
+
+	kn = kernfs_dentry_node(dentry);
+	root = kernfs_root(kn);
+	down_read(&root->kernfs_rwsem);
+
+	/* The kernfs node has been deactivated */
+	if (!kernfs_active(kn))
+		goto out_bad;
+
+	/* The kernfs node has been moved? */
+	if (kernfs_dentry_node(dentry->d_parent) != kn->parent)
+		goto out_bad;
+
+	/* The kernfs node has been renamed */
+	if (strcmp(dentry->d_name.name, kn->name) != 0)
+		goto out_bad;
+
+	/* The kernfs node has been moved to a different namespace */
+	if (kn->parent && kernfs_ns_enabled(kn->parent) &&
+	    kernfs_info(dentry->d_sb)->ns != kn->ns)
+		goto out_bad;
+
+	up_read(&root->kernfs_rwsem);
+	return 1;
+out_bad:
+	up_read(&root->kernfs_rwsem);
+	return 0;
+}
+
+const struct dentry_operations kernfs_dops = {
+	.d_revalidate	= kernfs_dop_revalidate,
+};
+
+static struct dentry *kernfs_iop_lookup(struct inode *dir,
+					struct dentry *dentry,
+					unsigned int flags)
+{
+	struct kernfs_node *parent = dir->i_private;
+	struct kernfs_node *kn;
+	struct kernfs_root *root;
+	struct inode *inode = NULL;
+	const void *ns = NULL;
+
+	root = kernfs_root(parent);
+	down_read(&root->kernfs_rwsem);
+	if (kernfs_ns_enabled(parent))
+		ns = kernfs_info(dir->i_sb)->ns;
+
+	kn = kernfs_find_ns(parent, dentry->d_name.name, ns);
+	/* attach dentry and inode */
+	if (kn) {
+		/* Inactive nodes are invisible to the VFS so don't
+		 * create a negative.
+		 */
+		if (!kernfs_active(kn)) {
+			up_read(&root->kernfs_rwsem);
+			return NULL;
+		}
+		inode = kernfs_get_inode(dir->i_sb, kn);
+		if (!inode)
+			inode = ERR_PTR(-ENOMEM);
+	}
+	/*
+	 * Needed for negative dentry validation.
+	 * The negative dentry can be created in kernfs_iop_lookup()
+	 * or transforms from positive dentry in dentry_unlink_inode()
+	 * called from vfs_rmdir().
+	 */
+	if (!IS_ERR(inode))
+		kernfs_set_rev(parent, dentry);
+	up_read(&root->kernfs_rwsem);
+
+	/* instantiate and hash (possibly negative) dentry */
+	return d_splice_alias(inode, dentry);
+}
+
+static int kernfs_iop_mkdir(struct user_namespace *mnt_userns,
+			    struct inode *dir, struct dentry *dentry,
+			    umode_t mode)
+{
+	struct kernfs_node *parent = dir->i_private;
+	struct kernfs_syscall_ops *scops = kernfs_root(parent)->syscall_ops;
+	int ret;
+
+	if (!scops || !scops->mkdir)
+		return -EPERM;
+
+	if (!kernfs_get_active(parent))
+		return -ENODEV;
+
+	ret = scops->mkdir(parent, dentry->d_name.name, mode);
+
+	kernfs_put_active(parent);
+	return ret;
+}
+
+static int kernfs_iop_rmdir(struct inode *dir, struct dentry *dentry)
+{
+	struct kernfs_node *kn  = kernfs_dentry_node(dentry);
+	struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;
+	int ret;
+
+	if (!scops || !scops->rmdir)
+		return -EPERM;
+
+	if (!kernfs_get_active(kn))
+		return -ENODEV;
+
+	ret = scops->rmdir(kn);
+
+	kernfs_put_active(kn);
+	return ret;
+}
+
+static int kernfs_iop_rename(struct user_namespace *mnt_userns,
+			     struct inode *old_dir, struct dentry *old_dentry,
+			     struct inode *new_dir, struct dentry *new_dentry,
+			     unsigned int flags)
+{
+	struct kernfs_node *kn = kernfs_dentry_node(old_dentry);
+	struct kernfs_node *new_parent = new_dir->i_private;
+	struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;
+	int ret;
+
+	if (flags)
+		return -EINVAL;
+
+	if (!scops || !scops->rename)
+		return -EPERM;
+
+	if (!kernfs_get_active(kn))
+		return -ENODEV;
+
+	if (!kernfs_get_active(new_parent)) {
+		kernfs_put_active(kn);
+		return -ENODEV;
+	}
+
+	ret = scops->rename(kn, new_parent, new_dentry->d_name.name);
+
+	kernfs_put_active(new_parent);
+	kernfs_put_active(kn);
+	return ret;
+}
+
+const struct inode_operations kernfs_dir_iops = {
+	.lookup		= kernfs_iop_lookup,
+	.permission	= kernfs_iop_permission,
+	.setattr	= kernfs_iop_setattr,
+	.getattr	= kernfs_iop_getattr,
+	.listxattr	= kernfs_iop_listxattr,
+
+	.mkdir		= kernfs_iop_mkdir,
+	.rmdir		= kernfs_iop_rmdir,
+	.rename		= kernfs_iop_rename,
+};
+
+static struct kernfs_node *kernfs_leftmost_descendant(struct kernfs_node *pos)
+{
+	struct kernfs_node *last;
+
+	while (true) {
+		struct rb_node *rbn;
+
+		last = pos;
+
+		if (kernfs_type(pos) != KERNFS_DIR)
+			break;
+
+		rbn = rb_first(&pos->dir.children);
+		if (!rbn)
+			break;
+
+		pos = rb_to_kn(rbn);
+	}
+
+	return last;
+}
+
+/**
+ * kernfs_next_descendant_post - find the next descendant for post-order walk
+ * @pos: the current position (%NULL to initiate traversal)
+ * @root: kernfs_node whose descendants to walk
+ *
+ * Find the next descendant to visit for post-order traversal of @root's
+ * descendants.  @root is included in the iteration and the last node to be
+ * visited.
+ */
+static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
+						       struct kernfs_node *root)
+{
+	struct rb_node *rbn;
+
+	lockdep_assert_held_write(&kernfs_root(root)->kernfs_rwsem);
+
+	/* if first iteration, visit leftmost descendant which may be root */
+	if (!pos)
+		return kernfs_leftmost_descendant(root);
+
+	/* if we visited @root, we're done */
+	if (pos == root)
+		return NULL;
+
+	/* if there's an unvisited sibling, visit its leftmost descendant */
+	rbn = rb_next(&pos->rb);
+	if (rbn)
+		return kernfs_leftmost_descendant(rb_to_kn(rbn));
+
+	/* no sibling left, visit parent */
+	return pos->parent;
+}
+
+static void kernfs_activate_one(struct kernfs_node *kn)
+{
+	lockdep_assert_held_write(&kernfs_root(kn)->kernfs_rwsem);
+
+	kn->flags |= KERNFS_ACTIVATED;
+
+	if (kernfs_active(kn) || (kn->flags & (KERNFS_HIDDEN | KERNFS_REMOVING)))
+		return;
+
+	WARN_ON_ONCE(kn->parent && RB_EMPTY_NODE(&kn->rb));
+	WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS);
+
+	atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
+}
+
+/**
+ * kernfs_activate - activate a node which started deactivated
+ * @kn: kernfs_node whose subtree is to be activated
+ *
+ * If the root has KERNFS_ROOT_CREATE_DEACTIVATED set, a newly created node
+ * needs to be explicitly activated.  A node which hasn't been activated
+ * isn't visible to userland and deactivation is skipped during its
+ * removal.  This is useful to construct atomic init sequences where
+ * creation of multiple nodes should either succeed or fail atomically.
+ *
+ * The caller is responsible for ensuring that this function is not called
+ * after kernfs_remove*() is invoked on @kn.
+ */
+void kernfs_activate(struct kernfs_node *kn)
+{
+	struct kernfs_node *pos;
+	struct kernfs_root *root = kernfs_root(kn);
+
+	down_write(&root->kernfs_rwsem);
+
+	pos = NULL;
+	while ((pos = kernfs_next_descendant_post(pos, kn)))
+		kernfs_activate_one(pos);
+
+	up_write(&root->kernfs_rwsem);
+}
+
+/**
+ * kernfs_show - show or hide a node
+ * @kn: kernfs_node to show or hide
+ * @show: whether to show or hide
+ *
+ * If @show is %false, @kn is marked hidden and deactivated. A hidden node is
+ * ignored in future activaitons. If %true, the mark is removed and activation
+ * state is restored. This function won't implicitly activate a new node in a
+ * %KERNFS_ROOT_CREATE_DEACTIVATED root which hasn't been activated yet.
+ *
+ * To avoid recursion complexities, directories aren't supported for now.
+ */
+void kernfs_show(struct kernfs_node *kn, bool show)
+{
+	struct kernfs_root *root = kernfs_root(kn);
+
+	if (WARN_ON_ONCE(kernfs_type(kn) == KERNFS_DIR))
+		return;
+
+	down_write(&root->kernfs_rwsem);
+
+	if (show) {
+		kn->flags &= ~KERNFS_HIDDEN;
+		if (kn->flags & KERNFS_ACTIVATED)
+			kernfs_activate_one(kn);
+	} else {
+		kn->flags |= KERNFS_HIDDEN;
+		if (kernfs_active(kn))
+			atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
+		kernfs_drain(kn);
+	}
+
+	up_write(&root->kernfs_rwsem);
+}
+
+static void __kernfs_remove(struct kernfs_node *kn)
+{
+	struct kernfs_node *pos;
+
+	/* Short-circuit if non-root @kn has already finished removal. */
+	if (!kn)
+		return;
+
+	lockdep_assert_held_write(&kernfs_root(kn)->kernfs_rwsem);
+
+	/*
+	 * This is for kernfs_remove_self() which plays with active ref
+	 * after removal.
+	 */
+	if (kn->parent && RB_EMPTY_NODE(&kn->rb))
+		return;
+
+	pr_debug("kernfs %s: removing\n", kn->name);
+
+	/* prevent new usage by marking all nodes removing and deactivating */
+	pos = NULL;
+	while ((pos = kernfs_next_descendant_post(pos, kn))) {
+		pos->flags |= KERNFS_REMOVING;
+		if (kernfs_active(pos))
+			atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
+	}
+
+	/* deactivate and unlink the subtree node-by-node */
+	do {
+		pos = kernfs_leftmost_descendant(kn);
+
+		/*
+		 * kernfs_drain() may drop kernfs_rwsem temporarily and @pos's
+		 * base ref could have been put by someone else by the time
+		 * the function returns.  Make sure it doesn't go away
+		 * underneath us.
+		 */
+		kernfs_get(pos);
+
+		kernfs_drain(pos);
+
+		/*
+		 * kernfs_unlink_sibling() succeeds once per node.  Use it
+		 * to decide who's responsible for cleanups.
+		 */
+		if (!pos->parent || kernfs_unlink_sibling(pos)) {
+			struct kernfs_iattrs *ps_iattr =
+				pos->parent ? pos->parent->iattr : NULL;
+
+			/* update timestamps on the parent */
+			if (ps_iattr) {
+				ktime_get_real_ts64(&ps_iattr->ia_ctime);
+				ps_iattr->ia_mtime = ps_iattr->ia_ctime;
+			}
+
+			kernfs_put(pos);
+		}
+
+		kernfs_put(pos);
+	} while (pos != kn);
+}
+
+/**
+ * kernfs_remove - remove a kernfs_node recursively
+ * @kn: the kernfs_node to remove
+ *
+ * Remove @kn along with all its subdirectories and files.
+ */
+void kernfs_remove(struct kernfs_node *kn)
+{
+	struct kernfs_root *root;
+
+	if (!kn)
+		return;
+
+	root = kernfs_root(kn);
+
+	down_write(&root->kernfs_rwsem);
+	__kernfs_remove(kn);
+	up_write(&root->kernfs_rwsem);
+}
+
+/**
+ * kernfs_break_active_protection - break out of active protection
+ * @kn: the self kernfs_node
+ *
+ * The caller must be running off of a kernfs operation which is invoked
+ * with an active reference - e.g. one of kernfs_ops.  Each invocation of
+ * this function must also be matched with an invocation of
+ * kernfs_unbreak_active_protection().
+ *
+ * This function releases the active reference of @kn the caller is
+ * holding.  Once this function is called, @kn may be removed at any point
+ * and the caller is solely responsible for ensuring that the objects it
+ * dereferences are accessible.
+ */
+void kernfs_break_active_protection(struct kernfs_node *kn)
+{
+	/*
+	 * Take out ourself out of the active ref dependency chain.  If
+	 * we're called without an active ref, lockdep will complain.
+	 */
+	kernfs_put_active(kn);
+}
+
+/**
+ * kernfs_unbreak_active_protection - undo kernfs_break_active_protection()
+ * @kn: the self kernfs_node
+ *
+ * If kernfs_break_active_protection() was called, this function must be
+ * invoked before finishing the kernfs operation.  Note that while this
+ * function restores the active reference, it doesn't and can't actually
+ * restore the active protection - @kn may already or be in the process of
+ * being removed.  Once kernfs_break_active_protection() is invoked, that
+ * protection is irreversibly gone for the kernfs operation instance.
+ *
+ * While this function may be called at any point after
+ * kernfs_break_active_protection() is invoked, its most useful location
+ * would be right before the enclosing kernfs operation returns.
+ */
+void kernfs_unbreak_active_protection(struct kernfs_node *kn)
+{
+	/*
+	 * @kn->active could be in any state; however, the increment we do
+	 * here will be undone as soon as the enclosing kernfs operation
+	 * finishes and this temporary bump can't break anything.  If @kn
+	 * is alive, nothing changes.  If @kn is being deactivated, the
+	 * soon-to-follow put will either finish deactivation or restore
+	 * deactivated state.  If @kn is already removed, the temporary
+	 * bump is guaranteed to be gone before @kn is released.
+	 */
+	atomic_inc(&kn->active);
+	if (kernfs_lockdep(kn))
+		rwsem_acquire(&kn->dep_map, 0, 1, _RET_IP_);
+}
+
+/**
+ * kernfs_remove_self - remove a kernfs_node from its own method
+ * @kn: the self kernfs_node to remove
+ *
+ * The caller must be running off of a kernfs operation which is invoked
+ * with an active reference - e.g. one of kernfs_ops.  This can be used to
+ * implement a file operation which deletes itself.
+ *
+ * For example, the "delete" file for a sysfs device directory can be
+ * implemented by invoking kernfs_remove_self() on the "delete" file
+ * itself.  This function breaks the circular dependency of trying to
+ * deactivate self while holding an active ref itself.  It isn't necessary
+ * to modify the usual removal path to use kernfs_remove_self().  The
+ * "delete" implementation can simply invoke kernfs_remove_self() on self
+ * before proceeding with the usual removal path.  kernfs will ignore later
+ * kernfs_remove() on self.
+ *
+ * kernfs_remove_self() can be called multiple times concurrently on the
+ * same kernfs_node.  Only the first one actually performs removal and
+ * returns %true.  All others will wait until the kernfs operation which
+ * won self-removal finishes and return %false.  Note that the losers wait
+ * for the completion of not only the winning kernfs_remove_self() but also
+ * the whole kernfs_ops which won the arbitration.  This can be used to
+ * guarantee, for example, all concurrent writes to a "delete" file to
+ * finish only after the whole operation is complete.
+ */
+bool kernfs_remove_self(struct kernfs_node *kn)
+{
+	bool ret;
+	struct kernfs_root *root = kernfs_root(kn);
+
+	down_write(&root->kernfs_rwsem);
+	kernfs_break_active_protection(kn);
+
+	/*
+	 * SUICIDAL is used to arbitrate among competing invocations.  Only
+	 * the first one will actually perform removal.  When the removal
+	 * is complete, SUICIDED is set and the active ref is restored
+	 * while kernfs_rwsem for held exclusive.  The ones which lost
+	 * arbitration waits for SUICIDED && drained which can happen only
+	 * after the enclosing kernfs operation which executed the winning
+	 * instance of kernfs_remove_self() finished.
+	 */
+	if (!(kn->flags & KERNFS_SUICIDAL)) {
+		kn->flags |= KERNFS_SUICIDAL;
+		__kernfs_remove(kn);
+		kn->flags |= KERNFS_SUICIDED;
+		ret = true;
+	} else {
+		wait_queue_head_t *waitq = &kernfs_root(kn)->deactivate_waitq;
+		DEFINE_WAIT(wait);
+
+		while (true) {
+			prepare_to_wait(waitq, &wait, TASK_UNINTERRUPTIBLE);
+
+			if ((kn->flags & KERNFS_SUICIDED) &&
+			    atomic_read(&kn->active) == KN_DEACTIVATED_BIAS)
+				break;
+
+			up_write(&root->kernfs_rwsem);
+			schedule();
+			down_write(&root->kernfs_rwsem);
+		}
+		finish_wait(waitq, &wait);
+		WARN_ON_ONCE(!RB_EMPTY_NODE(&kn->rb));
+		ret = false;
+	}
+
+	/*
+	 * This must be done while kernfs_rwsem held exclusive; otherwise,
+	 * waiting for SUICIDED && deactivated could finish prematurely.
+	 */
+	kernfs_unbreak_active_protection(kn);
+
+	up_write(&root->kernfs_rwsem);
+	return ret;
+}
+
+/**
+ * kernfs_remove_by_name_ns - find a kernfs_node by name and remove it
+ * @parent: parent of the target
+ * @name: name of the kernfs_node to remove
+ * @ns: namespace tag of the kernfs_node to remove
+ *
+ * Look for the kernfs_node with @name and @ns under @parent and remove it.
+ * Returns 0 on success, -ENOENT if such entry doesn't exist.
+ */
+int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
+			     const void *ns)
+{
+	struct kernfs_node *kn;
+	struct kernfs_root *root;
+
+	if (!parent) {
+		WARN(1, KERN_WARNING "kernfs: can not remove '%s', no directory\n",
+			name);
+		return -ENOENT;
+	}
+
+	root = kernfs_root(parent);
+	down_write(&root->kernfs_rwsem);
+
+	kn = kernfs_find_ns(parent, name, ns);
+	if (kn) {
+		kernfs_get(kn);
+		__kernfs_remove(kn);
+		kernfs_put(kn);
+	}
+
+	up_write(&root->kernfs_rwsem);
+
+	if (kn)
+		return 0;
+	else
+		return -ENOENT;
+}
+
+/**
+ * kernfs_rename_ns - move and rename a kernfs_node
+ * @kn: target node
+ * @new_parent: new parent to put @sd under
+ * @new_name: new name
+ * @new_ns: new namespace tag
+ */
+int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
+		     const char *new_name, const void *new_ns)
+{
+	struct kernfs_node *old_parent;
+	struct kernfs_root *root;
+	const char *old_name = NULL;
+	int error;
+
+	/* can't move or rename root */
+	if (!kn->parent)
+		return -EINVAL;
+
+	root = kernfs_root(kn);
+	down_write(&root->kernfs_rwsem);
+
+	error = -ENOENT;
+	if (!kernfs_active(kn) || !kernfs_active(new_parent) ||
+	    (new_parent->flags & KERNFS_EMPTY_DIR))
+		goto out;
+
+	error = 0;
+	if ((kn->parent == new_parent) && (kn->ns == new_ns) &&
+	    (strcmp(kn->name, new_name) == 0))
+		goto out;	/* nothing to rename */
+
+	error = -EEXIST;
+	if (kernfs_find_ns(new_parent, new_name, new_ns))
+		goto out;
+
+	/* rename kernfs_node */
+	if (strcmp(kn->name, new_name) != 0) {
+		error = -ENOMEM;
+		new_name = kstrdup_const(new_name, GFP_KERNEL);
+		if (!new_name)
+			goto out;
+	} else {
+		new_name = NULL;
+	}
+
+	/*
+	 * Move to the appropriate place in the appropriate directories rbtree.
+	 */
+	kernfs_unlink_sibling(kn);
+	kernfs_get(new_parent);
+
+	/* rename_lock protects ->parent and ->name accessors */
+	spin_lock_irq(&kernfs_rename_lock);
+
+	old_parent = kn->parent;
+	kn->parent = new_parent;
+
+	kn->ns = new_ns;
+	if (new_name) {
+		old_name = kn->name;
+		kn->name = new_name;
+	}
+
+	spin_unlock_irq(&kernfs_rename_lock);
+
+	kn->hash = kernfs_name_hash(kn->name, kn->ns);
+	kernfs_link_sibling(kn);
+
+	kernfs_put(old_parent);
+	kfree_const(old_name);
+
+	error = 0;
+ out:
+	up_write(&root->kernfs_rwsem);
+	return error;
+}
+
+/* Relationship between mode and the DT_xxx types */
+static inline unsigned char dt_type(struct kernfs_node *kn)
+{
+	return (kn->mode >> 12) & 15;
+}
+
+static int kernfs_dir_fop_release(struct inode *inode, struct file *filp)
+{
+	kernfs_put(filp->private_data);
+	return 0;
+}
+
+static struct kernfs_node *kernfs_dir_pos(const void *ns,
+	struct kernfs_node *parent, loff_t hash, struct kernfs_node *pos)
+{
+	if (pos) {
+		int valid = kernfs_active(pos) &&
+			pos->parent == parent && hash == pos->hash;
+		kernfs_put(pos);
+		if (!valid)
+			pos = NULL;
+	}
+	if (!pos && (hash > 1) && (hash < INT_MAX)) {
+		struct rb_node *node = parent->dir.children.rb_node;
+		while (node) {
+			pos = rb_to_kn(node);
+
+			if (hash < pos->hash)
+				node = node->rb_left;
+			else if (hash > pos->hash)
+				node = node->rb_right;
+			else
+				break;
+		}
+	}
+	/* Skip over entries which are dying/dead or in the wrong namespace */
+	while (pos && (!kernfs_active(pos) || pos->ns != ns)) {
+		struct rb_node *node = rb_next(&pos->rb);
+		if (!node)
+			pos = NULL;
+		else
+			pos = rb_to_kn(node);
+	}
+	return pos;
+}
+
+static struct kernfs_node *kernfs_dir_next_pos(const void *ns,
+	struct kernfs_node *parent, ino_t ino, struct kernfs_node *pos)
+{
+	pos = kernfs_dir_pos(ns, parent, ino, pos);
+	if (pos) {
+		do {
+			struct rb_node *node = rb_next(&pos->rb);
+			if (!node)
+				pos = NULL;
+			else
+				pos = rb_to_kn(node);
+		} while (pos && (!kernfs_active(pos) || pos->ns != ns));
+	}
+	return pos;
+}
+
+static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
+{
+	struct dentry *dentry = file->f_path.dentry;
+	struct kernfs_node *parent = kernfs_dentry_node(dentry);
+	struct kernfs_node *pos = file->private_data;
+	struct kernfs_root *root;
+	const void *ns = NULL;
+
+	if (!dir_emit_dots(file, ctx))
+		return 0;
+
+	root = kernfs_root(parent);
+	down_read(&root->kernfs_rwsem);
+
+	if (kernfs_ns_enabled(parent))
+		ns = kernfs_info(dentry->d_sb)->ns;
+
+	for (pos = kernfs_dir_pos(ns, parent, ctx->pos, pos);
+	     pos;
+	     pos = kernfs_dir_next_pos(ns, parent, ctx->pos, pos)) {
+		const char *name = pos->name;
+		unsigned int type = dt_type(pos);
+		int len = strlen(name);
+		ino_t ino = kernfs_ino(pos);
+
+		ctx->pos = pos->hash;
+		file->private_data = pos;
+		kernfs_get(pos);
+
+		up_read(&root->kernfs_rwsem);
+		if (!dir_emit(ctx, name, len, ino, type))
+			return 0;
+		down_read(&root->kernfs_rwsem);
+	}
+	up_read(&root->kernfs_rwsem);
+	file->private_data = NULL;
+	ctx->pos = INT_MAX;
+	return 0;
+}
+
+const struct file_operations kernfs_dir_fops = {
+	.read		= generic_read_dir,
+	.iterate_shared	= kernfs_fop_readdir,
+	.release	= kernfs_dir_fop_release,
+	.llseek		= generic_file_llseek,
+};