fs/kernfs/mount.c - kernel/msm-5.4 - Gitiles

 /*
  * fs/kernfs/mount.c - kernfs mount 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/fs.h>
 #include <linux/mount.h>
 #include <linux/init.h>
 #include <linux/magic.h>
 #include <linux/slab.h>
 #include <linux/pagemap.h>
 #include <linux/namei.h>
 #include <linux/seq_file.h>
 #include <linux/exportfs.h>

 #include "kernfs-internal.h"

 struct kmem_cache *kernfs_node_cache;

 static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
 {
 	struct kernfs_root *root = kernfs_info(sb)->root;
 	struct kernfs_syscall_ops *scops = root->syscall_ops;

 	if (scops && scops->remount_fs)
 		return scops->remount_fs(root, flags, data);
 	return 0;
 }

 static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
 {
 	struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
 	struct kernfs_syscall_ops *scops = root->syscall_ops;

 	if (scops && scops->show_options)
 		return scops->show_options(sf, root);
 	return 0;
 }

 static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
 {
 	struct kernfs_node *node = kernfs_dentry_node(dentry);
 	struct kernfs_root *root = kernfs_root(node);
 	struct kernfs_syscall_ops *scops = root->syscall_ops;

 	if (scops && scops->show_path)
 		return scops->show_path(sf, node, root);

 	seq_dentry(sf, dentry, " \t\n\\");
 	return 0;
 }

 const struct super_operations kernfs_sops = {
 	.statfs		= simple_statfs,
 	.drop_inode	= generic_delete_inode,
 	.evict_inode	= kernfs_evict_inode,

 	.remount_fs	= kernfs_sop_remount_fs,
 	.show_options	= kernfs_sop_show_options,
 	.show_path	= kernfs_sop_show_path,
 };

 /*
  * Similar to kernfs_fh_get_inode, this one gets kernfs node from inode
  * number and generation
  */
 struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root,
 	const union kernfs_node_id *id)
 {
 	struct kernfs_node *kn;

 	kn = kernfs_find_and_get_node_by_ino(root, id->ino);
 	if (!kn)
 		return NULL;
 	if (kn->id.generation != id->generation) {
 		kernfs_put(kn);
 		return NULL;
 	}
 	return kn;
 }

 static struct inode *kernfs_fh_get_inode(struct super_block *sb,
 		u64 ino, u32 generation)
 {
 	struct kernfs_super_info *info = kernfs_info(sb);
 	struct inode *inode;
 	struct kernfs_node *kn;

 	if (ino == 0)
 		return ERR_PTR(-ESTALE);

 	kn = kernfs_find_and_get_node_by_ino(info->root, ino);
 	if (!kn)
 		return ERR_PTR(-ESTALE);
 	inode = kernfs_get_inode(sb, kn);
 	kernfs_put(kn);
 	if (!inode)
 		return ERR_PTR(-ESTALE);

 	if (generation && inode->i_generation != generation) {
 		/* we didn't find the right inode.. */
 		iput(inode);
 		return ERR_PTR(-ESTALE);
 	}
 	return inode;
 }

 static struct dentry *kernfs_fh_to_dentry(struct super_block *sb, struct fid *fid,
 		int fh_len, int fh_type)
 {
 	return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
 				    kernfs_fh_get_inode);
 }

 static struct dentry *kernfs_fh_to_parent(struct super_block *sb, struct fid *fid,
 		int fh_len, int fh_type)
 {
 	return generic_fh_to_parent(sb, fid, fh_len, fh_type,
 				    kernfs_fh_get_inode);
 }

 static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
 {
 	struct kernfs_node *kn = kernfs_dentry_node(child);

 	return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
 }

 static const struct export_operations kernfs_export_ops = {
 	.fh_to_dentry	= kernfs_fh_to_dentry,
 	.fh_to_parent	= kernfs_fh_to_parent,
 	.get_parent	= kernfs_get_parent_dentry,
 };

 /**
  * kernfs_root_from_sb - determine kernfs_root associated with a super_block
  * @sb: the super_block in question
  *
  * Return the kernfs_root associated with @sb.  If @sb is not a kernfs one,
  * %NULL is returned.
  */
 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
 {
 	if (sb->s_op == &kernfs_sops)
 		return kernfs_info(sb)->root;
 	return NULL;
 }

 /*
  * find the next ancestor in the path down to @child, where @parent was the
  * ancestor whose descendant we want to find.
  *
  * Say the path is /a/b/c/d.  @child is d, @parent is NULL.  We return the root
  * node.  If @parent is b, then we return the node for c.
  * Passing in d as @parent is not ok.
  */
 static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
 					      struct kernfs_node *parent)
 {
 	if (child == parent) {
 		pr_crit_once("BUG in find_next_ancestor: called with parent == child");
 		return NULL;
 	}

 	while (child->parent != parent) {
 		if (!child->parent)
 			return NULL;
 		child = child->parent;
 	}

 	return child;
 }

 /**
  * kernfs_node_dentry - get a dentry for the given kernfs_node
  * @kn: kernfs_node for which a dentry is needed
  * @sb: the kernfs super_block
  */
 struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 				  struct super_block *sb)
 {
 	struct dentry *dentry;
 	struct kernfs_node *knparent = NULL;

 	BUG_ON(sb->s_op != &kernfs_sops);

 	dentry = dget(sb->s_root);

 	/* Check if this is the root kernfs_node */
 	if (!kn->parent)
 		return dentry;

 	knparent = find_next_ancestor(kn, NULL);
 	if (WARN_ON(!knparent))
 		return ERR_PTR(-EINVAL);

 	do {
 		struct dentry *dtmp;
 		struct kernfs_node *kntmp;

 		if (kn == knparent)
 			return dentry;
 		kntmp = find_next_ancestor(kn, knparent);
 		if (WARN_ON(!kntmp))
 			return ERR_PTR(-EINVAL);
 		dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
 					       strlen(kntmp->name));
 		dput(dentry);
 		if (IS_ERR(dtmp))
 			return dtmp;
 		knparent = kntmp;
 		dentry = dtmp;
 	} while (true);
 }

 static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
 {
 	struct kernfs_super_info *info = kernfs_info(sb);
 	struct inode *inode;
 	struct dentry *root;

 	info->sb = sb;
 	/* Userspace would break if executables or devices appear on sysfs */
 	sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
 	sb->s_blocksize = PAGE_SIZE;
 	sb->s_blocksize_bits = PAGE_SHIFT;
 	sb->s_magic = magic;
 	sb->s_op = &kernfs_sops;
 	sb->s_xattr = kernfs_xattr_handlers;
 	if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
 		sb->s_export_op = &kernfs_export_ops;
 	sb->s_time_gran = 1;

 	/* sysfs dentries and inodes don't require IO to create */
 	sb->s_shrink.seeks = 0;

 	/* get root inode, initialize and unlock it */
 	mutex_lock(&kernfs_mutex);
 	inode = kernfs_get_inode(sb, info->root->kn);
 	mutex_unlock(&kernfs_mutex);
 	if (!inode) {
 		pr_debug("kernfs: could not get root inode\n");
 		return -ENOMEM;
 	}

 	/* instantiate and link root dentry */
 	root = d_make_root(inode);
 	if (!root) {
 		pr_debug("%s: could not get root dentry!\n", __func__);
 		return -ENOMEM;
 	}
 	sb->s_root = root;
 	sb->s_d_op = &kernfs_dops;
 	return 0;
 }

 static int kernfs_test_super(struct super_block *sb, void *data)
 {
 	struct kernfs_super_info *sb_info = kernfs_info(sb);
 	struct kernfs_super_info *info = data;

 	return sb_info->root == info->root && sb_info->ns == info->ns;
 }

 static int kernfs_set_super(struct super_block *sb, void *data)
 {
 	int error;
 	error = set_anon_super(sb, data);
 	if (!error)
 		sb->s_fs_info = data;
 	return error;
 }

 /**
  * kernfs_super_ns - determine the namespace tag of a kernfs super_block
  * @sb: super_block of interest
  *
  * Return the namespace tag associated with kernfs super_block @sb.
  */
 const void *kernfs_super_ns(struct super_block *sb)
 {
 	struct kernfs_super_info *info = kernfs_info(sb);

 	return info->ns;
 }

 /**
  * kernfs_mount_ns - kernfs mount helper
  * @fs_type: file_system_type of the fs being mounted
  * @flags: mount flags specified for the mount
  * @root: kernfs_root of the hierarchy being mounted
  * @magic: file system specific magic number
  * @new_sb_created: tell the caller if we allocated a new superblock
  * @ns: optional namespace tag of the mount
  *
  * This is to be called from each kernfs user's file_system_type->mount()
  * implementation, which should pass through the specified @fs_type and
  * @flags, and specify the hierarchy and namespace tag to mount via @root
  * and @ns, respectively.
  *
  * The return value can be passed to the vfs layer verbatim.
  */
 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
 				struct kernfs_root *root, unsigned long magic,
 				bool *new_sb_created, const void *ns)
 {
 	struct super_block *sb;
 	struct kernfs_super_info *info;
 	int error;

 	info = kzalloc(sizeof(*info), GFP_KERNEL);
 	if (!info)
 		return ERR_PTR(-ENOMEM);

 	info->root = root;
 	info->ns = ns;
 	INIT_LIST_HEAD(&info->node);

 	sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
 			 &init_user_ns, info);
 	if (IS_ERR(sb) || sb->s_fs_info != info)
 		kfree(info);
 	if (IS_ERR(sb))
 		return ERR_CAST(sb);

 	if (new_sb_created)
 		*new_sb_created = !sb->s_root;

 	if (!sb->s_root) {
 		struct kernfs_super_info *info = kernfs_info(sb);

 		error = kernfs_fill_super(sb, magic);
 		if (error) {
 			deactivate_locked_super(sb);
 			return ERR_PTR(error);
 		}
 		sb->s_flags |= SB_ACTIVE;

 		mutex_lock(&kernfs_mutex);
 		list_add(&info->node, &root->supers);
 		mutex_unlock(&kernfs_mutex);
 	}

 	return dget(sb->s_root);
 }

 /**
  * kernfs_kill_sb - kill_sb for kernfs
  * @sb: super_block being killed
  *
  * This can be used directly for file_system_type->kill_sb().  If a kernfs
  * user needs extra cleanup, it can implement its own kill_sb() and call
  * this function at the end.
  */
 void kernfs_kill_sb(struct super_block *sb)
 {
 	struct kernfs_super_info *info = kernfs_info(sb);

 	mutex_lock(&kernfs_mutex);
 	list_del(&info->node);
 	mutex_unlock(&kernfs_mutex);

 	/*
 	 * Remove the superblock from fs_supers/s_instances
 	 * so we can't find it, before freeing kernfs_super_info.
 	 */
 	kill_anon_super(sb);
 	kfree(info);
 }

 /**
  * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
  * @kernfs_root: the kernfs_root in question
  * @ns: the namespace tag
  *
  * Pin the superblock so the superblock won't be destroyed in subsequent
  * operations.  This can be used to block ->kill_sb() which may be useful
  * for kernfs users which dynamically manage superblocks.
  *
  * Returns NULL if there's no superblock associated to this kernfs_root, or
  * -EINVAL if the superblock is being freed.
  */
 struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
 {
 	struct kernfs_super_info *info;
 	struct super_block *sb = NULL;

 	mutex_lock(&kernfs_mutex);
 	list_for_each_entry(info, &root->supers, node) {
 		if (info->ns == ns) {
 			sb = info->sb;
 			if (!atomic_inc_not_zero(&info->sb->s_active))
 				sb = ERR_PTR(-EINVAL);
 			break;
 		}
 	}
 	mutex_unlock(&kernfs_mutex);
 	return sb;
 }

 void __init kernfs_init(void)
 {

 	/*
 	 * the slab is freed in RCU context, so kernfs_find_and_get_node_by_ino
 	 * can access the slab lock free. This could introduce stale nodes,
 	 * please see how kernfs_find_and_get_node_by_ino filters out stale
 	 * nodes.
 	 */
 	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
 					      sizeof(struct kernfs_node),
 					      0,
 					      SLAB_PANIC | SLAB_TYPESAFE_BY_RCU,
 					      NULL);
 }
	/*
	* fs/kernfs/mount.c - kernfs mount 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/fs.h>
	#include <linux/mount.h>
	#include <linux/init.h>
	#include <linux/magic.h>
	#include <linux/slab.h>
	#include <linux/pagemap.h>
	#include <linux/namei.h>
	#include <linux/seq_file.h>
	#include <linux/exportfs.h>

	#include "kernfs-internal.h"

	struct kmem_cache *kernfs_node_cache;

	static int kernfs_sop_remount_fs(struct super_block sb, int flags, char *data)
	{
	struct kernfs_root *root = kernfs_info(sb)->root;
	struct kernfs_syscall_ops *scops = root->syscall_ops;

	if (scops && scops->remount_fs)
	return scops->remount_fs(root, flags, data);
	return 0;
	}

	static int kernfs_sop_show_options(struct seq_file sf, struct dentry dentry)
	{
	struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
	struct kernfs_syscall_ops *scops = root->syscall_ops;

	if (scops && scops->show_options)
	return scops->show_options(sf, root);
	return 0;
	}

	static int kernfs_sop_show_path(struct seq_file sf, struct dentry dentry)
	{
	struct kernfs_node *node = kernfs_dentry_node(dentry);
	struct kernfs_root *root = kernfs_root(node);
	struct kernfs_syscall_ops *scops = root->syscall_ops;

	if (scops && scops->show_path)
	return scops->show_path(sf, node, root);

	seq_dentry(sf, dentry, " \t\n\\");
	return 0;
	}

	const struct super_operations kernfs_sops = {
	.statfs = simple_statfs,
	.drop_inode = generic_delete_inode,
	.evict_inode = kernfs_evict_inode,

	.remount_fs = kernfs_sop_remount_fs,
	.show_options = kernfs_sop_show_options,
	.show_path = kernfs_sop_show_path,
	};

	/*
	* Similar to kernfs_fh_get_inode, this one gets kernfs node from inode
	* number and generation
	*/
	struct kernfs_node kernfs_get_node_by_id(struct kernfs_root root,
	const union kernfs_node_id *id)
	{
	struct kernfs_node *kn;

	kn = kernfs_find_and_get_node_by_ino(root, id->ino);
	if (!kn)
	return NULL;
	if (kn->id.generation != id->generation) {
	kernfs_put(kn);
	return NULL;
	}
	return kn;
	}

	static struct inode kernfs_fh_get_inode(struct super_block sb,
	u64 ino, u32 generation)
	{
	struct kernfs_super_info *info = kernfs_info(sb);
	struct inode *inode;
	struct kernfs_node *kn;

	if (ino == 0)
	return ERR_PTR(-ESTALE);

	kn = kernfs_find_and_get_node_by_ino(info->root, ino);
	if (!kn)
	return ERR_PTR(-ESTALE);
	inode = kernfs_get_inode(sb, kn);
	kernfs_put(kn);
	if (!inode)
	return ERR_PTR(-ESTALE);

	if (generation && inode->i_generation != generation) {
	/* we didn't find the right inode.. */
	iput(inode);
	return ERR_PTR(-ESTALE);
	}
	return inode;
	}

	static struct dentry kernfs_fh_to_dentry(struct super_block sb, struct fid *fid,
	int fh_len, int fh_type)
	{
	return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
	kernfs_fh_get_inode);
	}

	static struct dentry kernfs_fh_to_parent(struct super_block sb, struct fid *fid,
	int fh_len, int fh_type)
	{
	return generic_fh_to_parent(sb, fid, fh_len, fh_type,
	kernfs_fh_get_inode);
	}

	static struct dentry kernfs_get_parent_dentry(struct dentry child)
	{
	struct kernfs_node *kn = kernfs_dentry_node(child);

	return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
	}

	static const struct export_operations kernfs_export_ops = {
	.fh_to_dentry = kernfs_fh_to_dentry,
	.fh_to_parent = kernfs_fh_to_parent,
	.get_parent = kernfs_get_parent_dentry,
	};

	/**
	* kernfs_root_from_sb - determine kernfs_root associated with a super_block
	* @sb: the super_block in question
	*
	* Return the kernfs_root associated with @sb. If @sb is not a kernfs one,
	* %NULL is returned.
	*/
	struct kernfs_root kernfs_root_from_sb(struct super_block sb)
	{
	if (sb->s_op == &kernfs_sops)
	return kernfs_info(sb)->root;
	return NULL;
	}

	/*
	* find the next ancestor in the path down to @child, where @parent was the
	* ancestor whose descendant we want to find.
	*
	* Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root
	* node. If @parent is b, then we return the node for c.
	* Passing in d as @parent is not ok.
	*/
	static struct kernfs_node find_next_ancestor(struct kernfs_node child,
	struct kernfs_node *parent)
	{
	if (child == parent) {
	pr_crit_once("BUG in find_next_ancestor: called with parent == child");
	return NULL;
	}

	while (child->parent != parent) {
	if (!child->parent)
	return NULL;
	child = child->parent;
	}

	return child;
	}

	/**
	* kernfs_node_dentry - get a dentry for the given kernfs_node
	* @kn: kernfs_node for which a dentry is needed
	* @sb: the kernfs super_block
	*/
	struct dentry kernfs_node_dentry(struct kernfs_node kn,
	struct super_block *sb)
	{
	struct dentry *dentry;
	struct kernfs_node *knparent = NULL;

	BUG_ON(sb->s_op != &kernfs_sops);

	dentry = dget(sb->s_root);

	/* Check if this is the root kernfs_node */
	if (!kn->parent)
	return dentry;

	knparent = find_next_ancestor(kn, NULL);
	if (WARN_ON(!knparent))
	return ERR_PTR(-EINVAL);

	do {
	struct dentry *dtmp;
	struct kernfs_node *kntmp;

	if (kn == knparent)
	return dentry;
	kntmp = find_next_ancestor(kn, knparent);
	if (WARN_ON(!kntmp))
	return ERR_PTR(-EINVAL);
	dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
	strlen(kntmp->name));
	dput(dentry);
	if (IS_ERR(dtmp))
	return dtmp;
	knparent = kntmp;
	dentry = dtmp;
	} while (true);
	}

	static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
	{
	struct kernfs_super_info *info = kernfs_info(sb);
	struct inode *inode;
	struct dentry *root;

	info->sb = sb;
	/* Userspace would break if executables or devices appear on sysfs */
	sb->s_iflags \|= SB_I_NOEXEC \| SB_I_NODEV;
	sb->s_blocksize = PAGE_SIZE;
	sb->s_blocksize_bits = PAGE_SHIFT;
	sb->s_magic = magic;
	sb->s_op = &kernfs_sops;
	sb->s_xattr = kernfs_xattr_handlers;
	if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
	sb->s_export_op = &kernfs_export_ops;
	sb->s_time_gran = 1;

	/* sysfs dentries and inodes don't require IO to create */
	sb->s_shrink.seeks = 0;

	/* get root inode, initialize and unlock it */
	mutex_lock(&kernfs_mutex);
	inode = kernfs_get_inode(sb, info->root->kn);
	mutex_unlock(&kernfs_mutex);
	if (!inode) {
	pr_debug("kernfs: could not get root inode\n");
	return -ENOMEM;
	}

	/* instantiate and link root dentry */
	root = d_make_root(inode);
	if (!root) {
	pr_debug("%s: could not get root dentry!\n", __func__);
	return -ENOMEM;
	}
	sb->s_root = root;
	sb->s_d_op = &kernfs_dops;
	return 0;
	}

	static int kernfs_test_super(struct super_block sb, void data)
	{
	struct kernfs_super_info *sb_info = kernfs_info(sb);
	struct kernfs_super_info *info = data;

	return sb_info->root == info->root && sb_info->ns == info->ns;
	}

	static int kernfs_set_super(struct super_block sb, void data)
	{
	int error;
	error = set_anon_super(sb, data);
	if (!error)
	sb->s_fs_info = data;
	return error;
	}

	/**
	* kernfs_super_ns - determine the namespace tag of a kernfs super_block
	* @sb: super_block of interest
	*
	* Return the namespace tag associated with kernfs super_block @sb.
	*/
	const void kernfs_super_ns(struct super_block sb)
	{
	struct kernfs_super_info *info = kernfs_info(sb);

	return info->ns;
	}

	/**
	* kernfs_mount_ns - kernfs mount helper
	* @fs_type: file_system_type of the fs being mounted
	* @flags: mount flags specified for the mount
	* @root: kernfs_root of the hierarchy being mounted
	* @magic: file system specific magic number
	* @new_sb_created: tell the caller if we allocated a new superblock
	* @ns: optional namespace tag of the mount
	*
	* This is to be called from each kernfs user's file_system_type->mount()
	* implementation, which should pass through the specified @fs_type and
	* @flags, and specify the hierarchy and namespace tag to mount via @root
	* and @ns, respectively.
	*
	* The return value can be passed to the vfs layer verbatim.
	*/
	struct dentry kernfs_mount_ns(struct file_system_type fs_type, int flags,
	struct kernfs_root *root, unsigned long magic,
	bool new_sb_created, const void ns)
	{
	struct super_block *sb;
	struct kernfs_super_info *info;
	int error;

	info = kzalloc(sizeof(*info), GFP_KERNEL);
	if (!info)
	return ERR_PTR(-ENOMEM);

	info->root = root;
	info->ns = ns;
	INIT_LIST_HEAD(&info->node);

	sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
	&init_user_ns, info);
	if (IS_ERR(sb) \|\| sb->s_fs_info != info)
	kfree(info);
	if (IS_ERR(sb))
	return ERR_CAST(sb);

	if (new_sb_created)
	*new_sb_created = !sb->s_root;

	if (!sb->s_root) {
	struct kernfs_super_info *info = kernfs_info(sb);

	error = kernfs_fill_super(sb, magic);
	if (error) {
	deactivate_locked_super(sb);
	return ERR_PTR(error);
	}
	sb->s_flags \|= SB_ACTIVE;

	mutex_lock(&kernfs_mutex);
	list_add(&info->node, &root->supers);
	mutex_unlock(&kernfs_mutex);
	}

	return dget(sb->s_root);
	}

	/**
	* kernfs_kill_sb - kill_sb for kernfs
	* @sb: super_block being killed
	*
	* This can be used directly for file_system_type->kill_sb(). If a kernfs
	* user needs extra cleanup, it can implement its own kill_sb() and call
	* this function at the end.
	*/
	void kernfs_kill_sb(struct super_block *sb)
	{
	struct kernfs_super_info *info = kernfs_info(sb);

	mutex_lock(&kernfs_mutex);
	list_del(&info->node);
	mutex_unlock(&kernfs_mutex);

	/*
	* Remove the superblock from fs_supers/s_instances
	* so we can't find it, before freeing kernfs_super_info.
	*/
	kill_anon_super(sb);
	kfree(info);
	}

	/**
	* kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
	* @kernfs_root: the kernfs_root in question
	* @ns: the namespace tag
	*
	* Pin the superblock so the superblock won't be destroyed in subsequent
	* operations. This can be used to block ->kill_sb() which may be useful
	* for kernfs users which dynamically manage superblocks.
	*
	* Returns NULL if there's no superblock associated to this kernfs_root, or
	* -EINVAL if the superblock is being freed.
	*/
	struct super_block kernfs_pin_sb(struct kernfs_root root, const void *ns)
	{
	struct kernfs_super_info *info;
	struct super_block *sb = NULL;

	mutex_lock(&kernfs_mutex);
	list_for_each_entry(info, &root->supers, node) {
	if (info->ns == ns) {
	sb = info->sb;
	if (!atomic_inc_not_zero(&info->sb->s_active))
	sb = ERR_PTR(-EINVAL);
	break;
	}
	}
	mutex_unlock(&kernfs_mutex);
	return sb;
	}

	void __init kernfs_init(void)
	{

	/*
	* the slab is freed in RCU context, so kernfs_find_and_get_node_by_ino
	* can access the slab lock free. This could introduce stale nodes,
	* please see how kernfs_find_and_get_node_by_ino filters out stale
	* nodes.
	*/
	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
	sizeof(struct kernfs_node),
	0,
	SLAB_PANIC \| SLAB_TYPESAFE_BY_RCU,
	NULL);
	}