litmus-rt.git - The LITMUS^RT kernel.

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The LITMUS^RT kernel.

Bjoern Brandenburg

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gkh@linuxfoundation.org> 2013-11-29 21:08:39 -0500 sysfs, kernfs: move dir core code to fs/kernfs/dir.c' href='/cgit/cgit.cgi/litmus-rt-ext-res.git/commit/fs/kernfs/dir.c?id=fd7b9f7b9776b11df629e9dd3865320bf57ce588'>fd7b9f7b9776

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/*
 * fs/kernfs/dir.c - kernfs directory implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
 *
 * This file is released under the GPLv2.
 */

#include <linux/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"

DEFINE_MUTEX(kernfs_mutex);
static DEFINE_SPINLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
static char kernfs_pr_cont_buf[PATH_MAX];	/* protected by rename_lock */

#define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)

static bool kernfs_active(struct kernfs_node *kn)
{
	lockdep_assert_held(&kernfs_mutex);
	return atomic_read(&kn->active) >= 0;
}

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)
{
	return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
}

static char * __must_check kernfs_path_locked(struct kernfs_node *kn, char *buf,
					      size_t buflen)
{
	char *p = buf + buflen;
	int len;

	*--p = '\0';

	do {
		len = strlen(kn->name);
		if (p - buf < len + 1) {
			buf[0] = '\0';
			p = NULL;
			break;
		}
		p -= len;
		memcpy(p, kn->name, len);
		*--p = '/';
		kn = kn->parent;
	} while (kn && kn->parent);

	return p;
}

/**
 * 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.
 *
 * 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 - build full path of a given node
 * @kn: kernfs_node of interest
 * @buf: buffer to copy @kn's name into
 * @buflen: size of @buf
 *
 * Builds and returns the full path of @kn in @buf of @buflen bytes.  The
 * path is built from the end of @buf so the returned pointer usually
 * doesn't match @buf.  If @buf isn't long enough, @buf is nul terminated
 * and %NULL is returned.
 */
char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
{
	unsigned long flags;
	char *p;

	spin_lock_irqsave(&kernfs_rename_lock, flags);
	p = kernfs_path_locked(kn, buf, buflen);
	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
	return p;
}
EXPORT_SYMBOL_GPL(kernfs_path);

/**
 * 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_rename_lock, flags);

	kernfs_name_locked(kn, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf));
	pr_cont("%s", kernfs_pr_cont_buf);

	spin_unlock_irqrestore(&kernfs_rename_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;
	char *p;

	spin_lock_irqsave(&kernfs_rename_lock, flags);

	p = kernfs_path_locked(kn, kernfs_pr_cont_buf,
			       sizeof(kernfs_pr_cont_buf));
	if (p)
		pr_cont("%s", p);
	else
		pr_cont("<name too long>");

	spin_unlock_irqrestore(&kernfs_rename_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();
	unsigned int len = strlen(name);
	while (len--)
		hash = partial_name_hash(*name++, hash);
	hash = (end_name_hash(hash) ^ hash_ptr((void *)ns, 31));
	hash &= 0x7fffffffU;
	/* Reserve hash numbers 0, 1 and INT_MAX for magic directory entries */
	if (hash < 2)
		hash += 2;
	if (hash >= INT_MAX)
		hash = INT_MAX - 1;
	return hash;
}

static int kernfs_name_compare(unsigned int hash, const char *name,
			       const void *ns, const struct kernfs_node *kn)
{
	if (hash != kn->hash)
		return hash - kn->hash;
	if (ns != kn->ns)
		return ns - kn->ns;
	return strcmp(name, kn->name);
}

static int kernfs_sd_compare(const struct kernfs_node *left,
			     const struct kernfs_node *right)
{
	return kernfs_name_compare(left->hash, left->name, left->ns, right);
}

/**
 *	kernfs_link_sibling - link kernfs_node into sibling rbtree
 *	@kn: kernfs_node of interest
 *
 *	Link @kn into its sibling rbtree which starts from
 *	@kn->parent->dir.children.
 *
 *	Locking:
 *	mutex_lock(kernfs_mutex)
 *
 *	RETURNS:
 *	0 on susccess -EEXIST on failure.
 */
static int kernfs_link_sibling(struct kernfs_node *kn)
{
	struct rb_node **node = &kn->parent->dir.children.rb_node;
	struct rb_node *parent = NULL;

	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++;

	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:
 *	mutex_lock(kernfs_mutex)
 */
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--;

	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)
{
	struct kernfs_root *root = kernfs_root(kn);
	int v;

	if (unlikely(!kn))
		return;

	if (kernfs_lockdep(kn))
		rwsem_release(&kn->dep_map, 1, _RET_IP_);
	v = atomic_dec_return(&kn->active);
	if (likely(v != KN_DEACTIVATED_BIAS))
		return;

	wake_up_all(&root->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_mutex) __acquires(&kernfs_mutex)
{
	struct kernfs_root *root = kernfs_root(kn);

	lockdep_assert_held(&kernfs_mutex);
	WARN_ON_ONCE(kernfs_active(kn));

	mutex_unlock(&kernfs_mutex);

	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_);
	}

	/* but everyone should wait for draining */
	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, 1, _RET_IP_);
	}

	kernfs_unmap_bin_file(kn);

	mutex_lock(&kernfs_mutex);
}

/**
 * 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);
	if (!(kn->flags & KERNFS_STATIC_NAME))
		kfree(kn->name);
	if (kn->iattr) {
		if (kn->iattr->ia_secdata)
			security_release_secctx(kn->iattr->ia_secdata,
						kn->iattr->ia_secdata_len);
		simple_xattrs_free(&kn->iattr->xattrs);
	}
	kfree(kn->iattr);
	ida_simple_remove(&root->ino_ida, kn->ino);
	kmem_cache_free(kernfs_node_cache, kn);

	kn = parent;
	if (kn) {
		if (atomic_dec_and_test(&kn->count))
			goto repeat;
	} else {
		/* just released the root kn, free @root too */
		ida_destroy(&root->ino_ida);
		kfree(root);
	}
}
EXPORT_SYMBOL_GPL(kernfs_put);

static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
{
	struct kernfs_node *kn;

	if (flags & LOOKUP_RCU)
		return -ECHILD;

	/* Always perform fresh lookup for negatives */
	if (!dentry->d_inode)
		goto out_bad_unlocked;

	kn = dentry->d_fsdata;
	mutex_lock(&kernfs_mutex);

	/* The kernfs node has been deactivated */
	if (!kernfs_active(kn))
		goto out_bad;

	/* The kernfs node has been moved? */
	if (dentry->d_parent->d_fsdata != kn->parent)
		goto out_bad;

	/* The kernfs node has been renamed */
	if (strcmp(dentry->d_name.name, kn->name) != 0)
		goto out_bad;

	/* The kernfs node has been moved to a different namespace */
	if (kn->parent && kernfs_ns_enabled(kn->parent) &&
	    kernfs_info(dentry->d_sb)->ns != kn->ns)
		goto out_bad;

	mutex_unlock(&kernfs_mutex);
out_valid:
	return 1;
out_bad:
	mutex_unlock(&kernfs_mutex);
out_bad_unlocked:
	/*
	 * @dentry doesn't match the underlying kernfs node, drop the
	 * dentry and force lookup.  If we have submounts we must allow the
	 * vfs caches to lie about the state of the filesystem to prevent
	 * leaks and other nasty things, so use check_submounts_and_drop()
	 * instead of d_drop().
	 */
	if (check_submounts_and_drop(dentry) != 0)
		goto out_valid;

	return 0;
}

static void kernfs_dop_release(struct dentry *dentry)
{
	kernfs_put(dentry->d_fsdata);
}

const struct dentry_operations kernfs_dops = {
	.d_revalidate	= kernfs_dop_revalidate,
	.d_release	= kernfs_dop_release,
};

/**
 * 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 dentry->d_fsdata;
	return NULL;
}

static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
					     const char *name, umode_t mode,
					     unsigned flags)
{
	char *dup_name = NULL;
	struct kernfs_node *kn;
	int ret;

	if (!(flags & KERNFS_STATIC_NAME)) {
		name = dup_name = kstrdup(name, GFP_KERNEL);
		if (!name)
			return NULL;
	}

	kn = kmem_cache_zalloc(kernfs_node_cache, GFP_KERNEL);
	if (!kn)
		goto err_out1;

	ret = ida_simple_get(&root->ino_ida, 1, 0, GFP_KERNEL);
	if (ret < 0)
		goto err_out2;
	kn->ino = ret;

	atomic_set(&kn->count, 1);
	atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
	RB_CLEAR_NODE(&kn->rb);

	kn->name = name;
	kn->mode = mode;
	kn->flags = flags;

	return kn;

 err_out2:
	kmem_cache_free(kernfs_node_cache, kn);
 err_out1:
	kfree(dup_name);
	return NULL;
}

struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
				    const char *name, umode_t mode,
				    unsigned flags)
{
	struct kernfs_node *kn;

	kn = __kernfs_new_node(kernfs_root(parent), name, mode, flags);
	if (kn) {
		kernfs_get(parent);
		kn->parent = parent;
	}
	return kn;
}

/**
 *	kernfs_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_iattrs *ps_iattr;
	bool has_ns;
	int ret;

	mutex_lock(&kernfs_mutex);

	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_ACTIVATED) && !kernfs_active(parent))
		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) {
		struct iattr *ps_iattrs = &ps_iattr->ia_iattr;
		ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
	}

	mutex_unlock(&kernfs_mutex);

	/*
	 * 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:
	mutex_unlock(&kernfs_mutex);
	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_mutex);

	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;
}

/**
 * kernfs_find_and_get_ns - find and get kernfs_node with the given name
 * @parent: kernfs_node to search under
 * @name: name to look for
 * @ns: the namespace tag to use
 *
 * Look for kernfs_node with name @name under @parent and get a reference
 * if found.  This function may sleep and returns pointer to the found
 * kernfs_node on success, %NULL on failure.
 */
struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
					   const char *name, const void *ns)
{
	struct kernfs_node *kn;

	mutex_lock(&kernfs_mutex);
	kn = kernfs_find_ns(parent, name, ns);
	kernfs_get(kn);
	mutex_unlock(&kernfs_mutex);

	return kn;
}
EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);

/**
 * kernfs_create_root - create a new kernfs hierarchy
 * @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);

	ida_init(&root->ino_ida);
	INIT_LIST_HEAD(&root->supers);

	kn = __kernfs_new_node(root, "", S_IFDIR | S_IRUGO | S_IXUGO,
			       KERNFS_DIR);
	if (!kn) {
		ida_destroy(&root->ino_ida);
		kfree(root);
		return ERR_PTR(-ENOMEM);
	}

	kn->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(root->kn);	/* will also free @root */
}

/**
 * kernfs_create_dir_ns - create a directory
 * @parent: parent in which to create a new directory
 * @name: name of the new directory
 * @mode: mode of the new directory
 * @priv: opaque data associated with the new directory
 * @ns: optional namespace tag of the directory
 *
 * Returns the created node on success, ERR_PTR() value on failure.
 */
struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
					 const char *name, umode_t mode,
					 void *priv, const void *ns)
{
	struct kernfs_node *kn;
	int rc;

	/* allocate */
	kn = kernfs_new_node(parent, name, mode | S_IFDIR, KERNFS_DIR);
	if (!kn)
		return ERR_PTR(-ENOMEM);

	kn->dir.root = parent->dir.root;
	kn->ns = ns;
	kn->priv = priv;

	/* link in */
	rc = kernfs_add_one(kn);
	if (!rc)
		return kn;

	kernfs_put(kn);
	return ERR_PTR(rc);
}

static struct dentry *kernfs_iop_lookup(struct inode *dir,
					struct dentry *dentry,
					unsigned int flags)
{
	struct dentry *ret;
	struct kernfs_node *parent = dentry->d_parent->d_fsdata;
	struct kernfs_node *kn;
	struct inode *inode;
	const void *ns = NULL;

	mutex_lock(&kernfs_mutex);

	if (kernfs_ns_enabled(parent))
		ns = kernfs_info(dir->i_sb)->ns;

	kn = kernfs_find_ns(parent, dentry->d_name.name, ns);

	/* no such entry */
	if (!kn || !kernfs_active(kn)) {
		ret = NULL;
		goto out_unlock;
	}
	kernfs_get(kn);
	dentry->d_fsdata = kn;

	/* attach dentry and inode */
	inode = kernfs_get_inode(dir->i_sb, kn);
	if (!inode) {
		ret = ERR_PTR(-ENOMEM);
		goto out_unlock;
	}

	/* instantiate and hash dentry */
	ret = d_materialise_unique(dentry, inode);
 out_unlock:
	mutex_unlock(&kernfs_mutex);
	return ret;
}

static int kernfs_iop_mkdir(struct inode *dir, struct dentry *dentry,
			    umode_t mode)
{
	struct kernfs_node *parent = dir->i_private;
	struct kernfs_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  = dentry->d_fsdata;
	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;
}


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