// SPDX-License-Identifier: GPL-2.0

  /*
   * /proc/sys support
   */

  #include <linux/init.h>

  #include <linux/sysctl.h>

  #include <linux/poll.h>

  #include <linux/proc_fs.h>

  #include <linux/printk.h>

  #include <linux/security.h>

  #include <linux/sched.h>

  #include <linux/cred.h>

  #include <linux/namei.h>

  #include <linux/mm.h>

  #include <linux/uio.h>

  #include <linux/module.h>

  #include <linux/bpf-cgroup.h>

  #include <linux/mount.h>

  #include "internal.h"

  static const struct dentry_operations proc_sys_dentry_operations;

  static const struct file_operations proc_sys_file_operations;

  static const struct inode_operations proc_sys_inode_operations;

  static const struct file_operations proc_sys_dir_file_operations;
  static const struct inode_operations proc_sys_dir_operations;

  /* shared constants to be used in various sysctls */
  const int sysctl_vals[] = { 0, 1, INT_MAX };
  EXPORT_SYMBOL(sysctl_vals);

  /* Support for permanently empty directories */
  
  struct ctl_table sysctl_mount_point[] = {
  	{ }
  };
  
  static bool is_empty_dir(struct ctl_table_header *head)
  {
  	return head->ctl_table[0].child == sysctl_mount_point;
  }
  
  static void set_empty_dir(struct ctl_dir *dir)
  {
  	dir->header.ctl_table[0].child = sysctl_mount_point;
  }
  
  static void clear_empty_dir(struct ctl_dir *dir)
  
  {
  	dir->header.ctl_table[0].child = NULL;
  }

  void proc_sys_poll_notify(struct ctl_table_poll *poll)
  {
  	if (!poll)
  		return;
  
  	atomic_inc(&poll->event);
  	wake_up_interruptible(&poll->wait);
  }

  static struct ctl_table root_table[] = {
  	{
  		.procname = "",

  		.mode = S_IFDIR|S_IRUGO|S_IXUGO,

  	},
  	{ }
  };

  static struct ctl_table_root sysctl_table_root = {

  	.default_set.dir.header = {

  		{{.count = 1,
  		  .nreg = 1,

  		  .ctl_table = root_table }},

  		.ctl_table_arg = root_table,

  		.root = &sysctl_table_root,
  		.set = &sysctl_table_root.default_set,
  	},

  };

  
  static DEFINE_SPINLOCK(sysctl_lock);

  static void drop_sysctl_table(struct ctl_table_header *header);

  static int sysctl_follow_link(struct ctl_table_header **phead,

  	struct ctl_table **pentry);

  static int insert_links(struct ctl_table_header *head);
  static void put_links(struct ctl_table_header *header);

  static void sysctl_print_dir(struct ctl_dir *dir)
  {
  	if (dir->header.parent)
  		sysctl_print_dir(dir->header.parent);

  	pr_cont("%s/", dir->header.ctl_table[0].procname);

  }

  static int namecmp(const char *name1, int len1, const char *name2, int len2)
  {
  	int minlen;
  	int cmp;
  
  	minlen = len1;
  	if (minlen > len2)
  		minlen = len2;
  
  	cmp = memcmp(name1, name2, minlen);
  	if (cmp == 0)
  		cmp = len1 - len2;
  	return cmp;
  }

  /* Called under sysctl_lock */

  static struct ctl_table *find_entry(struct ctl_table_header **phead,

  	struct ctl_dir *dir, const char *name, int namelen)

  {
  	struct ctl_table_header *head;
  	struct ctl_table *entry;

  	struct rb_node *node = dir->root.rb_node;

  	while (node)
  	{
  		struct ctl_node *ctl_node;
  		const char *procname;
  		int cmp;
  
  		ctl_node = rb_entry(node, struct ctl_node, node);
  		head = ctl_node->header;
  		entry = &head->ctl_table[ctl_node - head->node];
  		procname = entry->procname;
  
  		cmp = namecmp(name, namelen, procname, strlen(procname));
  		if (cmp < 0)
  			node = node->rb_left;
  		else if (cmp > 0)
  			node = node->rb_right;
  		else {
  			*phead = head;
  			return entry;

  		}
  	}
  	return NULL;
  }

  static int insert_entry(struct ctl_table_header *head, struct ctl_table *entry)
  {
  	struct rb_node *node = &head->node[entry - head->ctl_table].node;
  	struct rb_node **p = &head->parent->root.rb_node;
  	struct rb_node *parent = NULL;
  	const char *name = entry->procname;
  	int namelen = strlen(name);
  
  	while (*p) {
  		struct ctl_table_header *parent_head;
  		struct ctl_table *parent_entry;
  		struct ctl_node *parent_node;
  		const char *parent_name;
  		int cmp;
  
  		parent = *p;
  		parent_node = rb_entry(parent, struct ctl_node, node);
  		parent_head = parent_node->header;
  		parent_entry = &parent_head->ctl_table[parent_node - parent_head->node];
  		parent_name = parent_entry->procname;
  
  		cmp = namecmp(name, namelen, parent_name, strlen(parent_name));
  		if (cmp < 0)
  			p = &(*p)->rb_left;
  		else if (cmp > 0)
  			p = &(*p)->rb_right;
  		else {

  			pr_err("sysctl duplicate entry: ");

  			sysctl_print_dir(head->parent);

  			pr_cont("/%s
  ", entry->procname);

  			return -EEXIST;
  		}
  	}
  
  	rb_link_node(node, parent, p);

  	rb_insert_color(node, &head->parent->root);

  	return 0;
  }
  
  static void erase_entry(struct ctl_table_header *head, struct ctl_table *entry)
  {
  	struct rb_node *node = &head->node[entry - head->ctl_table].node;
  
  	rb_erase(node, &head->parent->root);
  }

  static void init_header(struct ctl_table_header *head,
  	struct ctl_table_root *root, struct ctl_table_set *set,

  	struct ctl_node *node, struct ctl_table *table)

  {

  	head->ctl_table = table;

  	head->ctl_table_arg = table;

  	head->used = 0;
  	head->count = 1;
  	head->nreg = 1;
  	head->unregistering = NULL;
  	head->root = root;
  	head->set = set;
  	head->parent = NULL;

  	head->node = node;

  	INIT_HLIST_HEAD(&head->inodes);

  	if (node) {
  		struct ctl_table *entry;

  		for (entry = table; entry->procname; entry++, node++)

  			node->header = head;

  	}

  }

  static void erase_header(struct ctl_table_header *head)
  {

  	struct ctl_table *entry;
  	for (entry = head->ctl_table; entry->procname; entry++)
  		erase_entry(head, entry);

  }

  static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)

  {

  	struct ctl_table *entry;

  	int err;

  	/* Is this a permanently empty directory? */
  	if (is_empty_dir(&dir->header))
  		return -EROFS;
  
  	/* Am I creating a permanently empty directory? */
  	if (header->ctl_table == sysctl_mount_point) {
  		if (!RB_EMPTY_ROOT(&dir->root))
  			return -EINVAL;
  		set_empty_dir(dir);
  	}

  	dir->header.nreg++;

  	header->parent = dir;

  	err = insert_links(header);
  	if (err)
  		goto fail_links;

  	for (entry = header->ctl_table; entry->procname; entry++) {
  		err = insert_entry(header, entry);
  		if (err)
  			goto fail;
  	}

  	return 0;

  fail:
  	erase_header(header);
  	put_links(header);

  fail_links:

  	if (header->ctl_table == sysctl_mount_point)
  		clear_empty_dir(dir);

  	header->parent = NULL;
  	drop_sysctl_table(&dir->header);
  	return err;

  }

  /* called under sysctl_lock */
  static int use_table(struct ctl_table_header *p)
  {
  	if (unlikely(p->unregistering))
  		return 0;
  	p->used++;
  	return 1;
  }
  
  /* called under sysctl_lock */
  static void unuse_table(struct ctl_table_header *p)
  {
  	if (!--p->used)
  		if (unlikely(p->unregistering))
  			complete(p->unregistering);
  }

  static void proc_sys_invalidate_dcache(struct ctl_table_header *head)

  {

  	proc_invalidate_siblings_dcache(&head->inodes, &sysctl_lock);

  }

  /* called under sysctl_lock, will reacquire if has to wait */
  static void start_unregistering(struct ctl_table_header *p)
  {
  	/*
  	 * if p->used is 0, nobody will ever touch that entry again;
  	 * we'll eliminate all paths to it before dropping sysctl_lock
  	 */
  	if (unlikely(p->used)) {
  		struct completion wait;
  		init_completion(&wait);
  		p->unregistering = &wait;
  		spin_unlock(&sysctl_lock);
  		wait_for_completion(&wait);

  	} else {
  		/* anything non-NULL; we'll never dereference it */
  		p->unregistering = ERR_PTR(-EINVAL);

  		spin_unlock(&sysctl_lock);

  	}
  	/*

  	 * Invalidate dentries for unregistered sysctls: namespaced sysctls

  	 * can have duplicate names and contaminate dcache very badly.
  	 */

  	proc_sys_invalidate_dcache(p);

  	/*

  	 * do not remove from the list until nobody holds it; walking the
  	 * list in do_sysctl() relies on that.
  	 */

  	spin_lock(&sysctl_lock);

  	erase_header(p);

  }

  static struct ctl_table_header *sysctl_head_grab(struct ctl_table_header *head)
  {

  	BUG_ON(!head);

  	spin_lock(&sysctl_lock);
  	if (!use_table(head))
  		head = ERR_PTR(-ENOENT);
  	spin_unlock(&sysctl_lock);
  	return head;
  }
  
  static void sysctl_head_finish(struct ctl_table_header *head)
  {
  	if (!head)
  		return;
  	spin_lock(&sysctl_lock);
  	unuse_table(head);
  	spin_unlock(&sysctl_lock);
  }
  
  static struct ctl_table_set *

  lookup_header_set(struct ctl_table_root *root)

  {
  	struct ctl_table_set *set = &root->default_set;
  	if (root->lookup)

  		set = root->lookup(root);

  	return set;
  }

  static struct ctl_table *lookup_entry(struct ctl_table_header **phead,

  				      struct ctl_dir *dir,

  				      const char *name, int namelen)
  {
  	struct ctl_table_header *head;
  	struct ctl_table *entry;

  
  	spin_lock(&sysctl_lock);

  	entry = find_entry(&head, dir, name, namelen);
  	if (entry && use_table(head))
  		*phead = head;
  	else
  		entry = NULL;

  	spin_unlock(&sysctl_lock);
  	return entry;
  }

  static struct ctl_node *first_usable_entry(struct rb_node *node)

  {

  	struct ctl_node *ctl_node;

  	for (;node; node = rb_next(node)) {
  		ctl_node = rb_entry(node, struct ctl_node, node);
  		if (use_table(ctl_node->header))
  			return ctl_node;

  	}

  	return NULL;
  }

  static void first_entry(struct ctl_dir *dir,

  	struct ctl_table_header **phead, struct ctl_table **pentry)
  {

  	struct ctl_table_header *head = NULL;

  	struct ctl_table *entry = NULL;

  	struct ctl_node *ctl_node;

  
  	spin_lock(&sysctl_lock);

  	ctl_node = first_usable_entry(rb_first(&dir->root));

  	spin_unlock(&sysctl_lock);

  	if (ctl_node) {
  		head = ctl_node->header;
  		entry = &head->ctl_table[ctl_node - head->node];
  	}

  	*phead = head;
  	*pentry = entry;
  }

  static void next_entry(struct ctl_table_header **phead, struct ctl_table **pentry)

  {

  	struct ctl_table_header *head = *phead;
  	struct ctl_table *entry = *pentry;

  	struct ctl_node *ctl_node = &head->node[entry - head->ctl_table];

  	spin_lock(&sysctl_lock);
  	unuse_table(head);
  
  	ctl_node = first_usable_entry(rb_next(&ctl_node->node));
  	spin_unlock(&sysctl_lock);
  	head = NULL;
  	if (ctl_node) {
  		head = ctl_node->header;
  		entry = &head->ctl_table[ctl_node - head->node];

  	}
  	*phead = head;
  	*pentry = entry;

  }

  /*
   * sysctl_perm does NOT grant the superuser all rights automatically, because
   * some sysctl variables are readonly even to root.
   */
  
  static int test_perm(int mode, int op)
  {

  	if (uid_eq(current_euid(), GLOBAL_ROOT_UID))

  		mode >>= 6;

  	else if (in_egroup_p(GLOBAL_ROOT_GID))

  		mode >>= 3;
  	if ((op & ~mode & (MAY_READ|MAY_WRITE|MAY_EXEC)) == 0)
  		return 0;
  	return -EACCES;
  }

  static int sysctl_perm(struct ctl_table_header *head, struct ctl_table *table, int op)

  {

  	struct ctl_table_root *root = head->root;

  	int mode;
  
  	if (root->permissions)

  		mode = root->permissions(head, table);

  	else
  		mode = table->mode;
  
  	return test_perm(mode, op);
  }

  static struct inode *proc_sys_make_inode(struct super_block *sb,
  		struct ctl_table_header *head, struct ctl_table *table)

  {

  	struct ctl_table_root *root = head->root;

  	struct inode *inode;

  	struct proc_inode *ei;

  	inode = new_inode(sb);

  	if (!inode)

  		return ERR_PTR(-ENOMEM);

  	inode->i_ino = get_next_ino();

  	ei = PROC_I(inode);

  	spin_lock(&sysctl_lock);

  	if (unlikely(head->unregistering)) {
  		spin_unlock(&sysctl_lock);
  		iput(inode);

  		return ERR_PTR(-ENOENT);

  	}
  	ei->sysctl = head;
  	ei->sysctl_entry = table;

  	hlist_add_head_rcu(&ei->sibling_inodes, &head->inodes);

  	head->count++;
  	spin_unlock(&sysctl_lock);

  	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);

  	inode->i_mode = table->mode;

  	if (!S_ISDIR(table->mode)) {

  		inode->i_mode |= S_IFREG;
  		inode->i_op = &proc_sys_inode_operations;
  		inode->i_fop = &proc_sys_file_operations;
  	} else {
  		inode->i_mode |= S_IFDIR;

  		inode->i_op = &proc_sys_dir_operations;
  		inode->i_fop = &proc_sys_dir_file_operations;

  		if (is_empty_dir(head))
  			make_empty_dir_inode(inode);

  	}

  
  	if (root->set_ownership)
  		root->set_ownership(head, table, &inode->i_uid, &inode->i_gid);

  	else {
  		inode->i_uid = GLOBAL_ROOT_UID;
  		inode->i_gid = GLOBAL_ROOT_GID;
  	}

  	return inode;
  }

  void proc_sys_evict_inode(struct inode *inode, struct ctl_table_header *head)
  {
  	spin_lock(&sysctl_lock);

  	hlist_del_init_rcu(&PROC_I(inode)->sibling_inodes);

  	if (!--head->count)
  		kfree_rcu(head, rcu);
  	spin_unlock(&sysctl_lock);
  }

  static struct ctl_table_header *grab_header(struct inode *inode)

  {

  	struct ctl_table_header *head = PROC_I(inode)->sysctl;
  	if (!head)

  		head = &sysctl_table_root.default_set.dir.header;

  	return sysctl_head_grab(head);

  }

  static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,

  					unsigned int flags)

  {
  	struct ctl_table_header *head = grab_header(dir);

  	struct ctl_table_header *h = NULL;

  	const struct qstr *name = &dentry->d_name;

  	struct ctl_table *p;
  	struct inode *inode;
  	struct dentry *err = ERR_PTR(-ENOENT);

  	struct ctl_dir *ctl_dir;

  	int ret;

  	if (IS_ERR(head))
  		return ERR_CAST(head);

  	ctl_dir = container_of(head, struct ctl_dir, header);

  	p = lookup_entry(&h, ctl_dir, name->name, name->len);

  	if (!p)

  		goto out;

  	if (S_ISLNK(p->mode)) {

  		ret = sysctl_follow_link(&h, &p);

  		err = ERR_PTR(ret);
  		if (ret)
  			goto out;
  	}

  	inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);

  	if (IS_ERR(inode)) {
  		err = ERR_CAST(inode);

  		goto out;

  	}

  	d_set_d_op(dentry, &proc_sys_dentry_operations);

  	err = d_splice_alias(inode, dentry);

  
  out:

  	if (h)
  		sysctl_head_finish(h);

  	sysctl_head_finish(head);
  	return err;
  }

  static ssize_t proc_sys_call_handler(struct kiocb *iocb, struct iov_iter *iter,
  		int write)

  {

  	struct inode *inode = file_inode(iocb->ki_filp);

  	struct ctl_table_header *head = grab_header(inode);
  	struct ctl_table *table = PROC_I(inode)->sysctl_entry;

  	size_t count = iov_iter_count(iter);
  	char *kbuf;

  	ssize_t error;

  	if (IS_ERR(head))
  		return PTR_ERR(head);

  
  	/*
  	 * At this point we know that the sysctl was not unregistered
  	 * and won't be until we finish.
  	 */
  	error = -EPERM;

  	if (sysctl_perm(head, table, write ? MAY_WRITE : MAY_READ))

  		goto out;

  	/* if that can happen at all, it should be -EINVAL, not -EISDIR */
  	error = -EINVAL;
  	if (!table->proc_handler)
  		goto out;

  	/* don't even try if the size is too large */

  	error = -ENOMEM;
  	if (count >= KMALLOC_MAX_SIZE)
  		goto out;

  	kbuf = kzalloc(count + 1, GFP_KERNEL);
  	if (!kbuf)
  		goto out;

  	if (write) {

  		error = -EFAULT;
  		if (!copy_from_iter_full(kbuf, count, iter))
  			goto out_free_buf;
  		kbuf[count] = '\0';

  	}
  
  	error = BPF_CGROUP_RUN_PROG_SYSCTL(head, table, write, &kbuf, &count,

  					   &iocb->ki_pos);

  	if (error)

  		goto out_free_buf;

  	/* careful: calling conventions are nasty here */

  	error = table->proc_handler(table, write, kbuf, &count, &iocb->ki_pos);

  	if (error)
  		goto out_free_buf;
  
  	if (!write) {
  		error = -EFAULT;

  		if (copy_to_iter(kbuf, count, iter) < count)

  			goto out_free_buf;

  	}

  	error = count;
  out_free_buf:
  	kfree(kbuf);

  out:
  	sysctl_head_finish(head);
  
  	return error;
  }

  static ssize_t proc_sys_read(struct kiocb *iocb, struct iov_iter *iter)

  {

  	return proc_sys_call_handler(iocb, iter, 0);

  }

  static ssize_t proc_sys_write(struct kiocb *iocb, struct iov_iter *iter)

  {

  	return proc_sys_call_handler(iocb, iter, 1);

  }

  static int proc_sys_open(struct inode *inode, struct file *filp)
  {

  	struct ctl_table_header *head = grab_header(inode);

  	struct ctl_table *table = PROC_I(inode)->sysctl_entry;

  	/* sysctl was unregistered */
  	if (IS_ERR(head))
  		return PTR_ERR(head);

  	if (table->poll)
  		filp->private_data = proc_sys_poll_event(table->poll);

  	sysctl_head_finish(head);

  	return 0;
  }

  static __poll_t proc_sys_poll(struct file *filp, poll_table *wait)

  {

  	struct inode *inode = file_inode(filp);

  	struct ctl_table_header *head = grab_header(inode);

  	struct ctl_table *table = PROC_I(inode)->sysctl_entry;

  	__poll_t ret = DEFAULT_POLLMASK;

  	unsigned long event;
  
  	/* sysctl was unregistered */
  	if (IS_ERR(head))

  		return EPOLLERR | EPOLLHUP;

  
  	if (!table->proc_handler)
  		goto out;
  
  	if (!table->poll)
  		goto out;

  	event = (unsigned long)filp->private_data;

  	poll_wait(filp, &table->poll->wait, wait);
  
  	if (event != atomic_read(&table->poll->event)) {
  		filp->private_data = proc_sys_poll_event(table->poll);

  		ret = EPOLLIN | EPOLLRDNORM | EPOLLERR | EPOLLPRI;

  	}
  
  out:

  	sysctl_head_finish(head);

  	return ret;
  }

  static bool proc_sys_fill_cache(struct file *file,
  				struct dir_context *ctx,

  				struct ctl_table_header *head,
  				struct ctl_table *table)

  {

  	struct dentry *child, *dir = file->f_path.dentry;

  	struct inode *inode;
  	struct qstr qname;
  	ino_t ino = 0;
  	unsigned type = DT_UNKNOWN;

  
  	qname.name = table->procname;
  	qname.len  = strlen(table->procname);

  	qname.hash = full_name_hash(dir, qname.name, qname.len);

  	child = d_lookup(dir, &qname);
  	if (!child) {

  		DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
  		child = d_alloc_parallel(dir, &qname, &wq);
  		if (IS_ERR(child))
  			return false;
  		if (d_in_lookup(child)) {

  			struct dentry *res;

  			inode = proc_sys_make_inode(dir->d_sb, head, table);

  			if (IS_ERR(inode)) {

  				d_lookup_done(child);

  				dput(child);

  				return false;

  			}

  			d_set_d_op(child, &proc_sys_dentry_operations);

  			res = d_splice_alias(inode, child);
  			d_lookup_done(child);
  			if (unlikely(res)) {
  				if (IS_ERR(res)) {
  					dput(child);
  					return false;
  				}
  				dput(child);
  				child = res;
  			}

  		}
  	}

  	inode = d_inode(child);

  	ino  = inode->i_ino;
  	type = inode->i_mode >> 12;

  	dput(child);

  	return dir_emit(ctx, qname.name, qname.len, ino, type);

  }

  static bool proc_sys_link_fill_cache(struct file *file,
  				    struct dir_context *ctx,

  				    struct ctl_table_header *head,
  				    struct ctl_table *table)
  {

  	bool ret = true;

  	head = sysctl_head_grab(head);

  	if (IS_ERR(head))
  		return false;

  	/* It is not an error if we can not follow the link ignore it */
  	if (sysctl_follow_link(&head, &table))
  		goto out;

  	ret = proc_sys_fill_cache(file, ctx, head, table);

  out:
  	sysctl_head_finish(head);
  	return ret;
  }

  static int scan(struct ctl_table_header *head, struct ctl_table *table,

  		unsigned long *pos, struct file *file,

  		struct dir_context *ctx)

  {

  	bool res;

  	if ((*pos)++ < ctx->pos)
  		return true;

  	if (unlikely(S_ISLNK(table->mode)))

  		res = proc_sys_link_fill_cache(file, ctx, head, table);

  	else

  		res = proc_sys_fill_cache(file, ctx, head, table);

  	if (res)
  		ctx->pos = *pos;

  	return res;

  }

  static int proc_sys_readdir(struct file *file, struct dir_context *ctx)

  {

  	struct ctl_table_header *head = grab_header(file_inode(file));

  	struct ctl_table_header *h = NULL;

  	struct ctl_table *entry;

  	struct ctl_dir *ctl_dir;

  	unsigned long pos;

  
  	if (IS_ERR(head))
  		return PTR_ERR(head);

  	ctl_dir = container_of(head, struct ctl_dir, header);

  	if (!dir_emit_dots(file, ctx))

  		goto out;

  	pos = 2;

  	for (first_entry(ctl_dir, &h, &entry); h; next_entry(&h, &entry)) {

  		if (!scan(h, entry, &pos, file, ctx)) {

  			sysctl_head_finish(h);
  			break;

  		}
  	}

  out:

  	sysctl_head_finish(head);

  	return 0;

  }

  static int proc_sys_permission(struct inode *inode, int mask)

  {
  	/*
  	 * sysctl entries that are not writeable,
  	 * are _NOT_ writeable, capabilities or not.
  	 */

  	struct ctl_table_header *head;
  	struct ctl_table *table;

  	int error;

  	/* Executable files are not allowed under /proc/sys/ */
  	if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode))
  		return -EACCES;
  
  	head = grab_header(inode);

  	if (IS_ERR(head))
  		return PTR_ERR(head);

  	table = PROC_I(inode)->sysctl_entry;

  	if (!table) /* global root - r-xr-xr-x */
  		error = mask & MAY_WRITE ? -EACCES : 0;
  	else /* Use the permissions on the sysctl table entry */

  		error = sysctl_perm(head, table, mask & ~MAY_NOT_BLOCK);

  	sysctl_head_finish(head);
  	return error;
  }
  
  static int proc_sys_setattr(struct dentry *dentry, struct iattr *attr)
  {

  	struct inode *inode = d_inode(dentry);

  	int error;
  
  	if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
  		return -EPERM;

  	error = setattr_prepare(dentry, attr);

  	if (error)
  		return error;

  	setattr_copy(inode, attr);
  	mark_inode_dirty(inode);
  	return 0;

  }

  static int proc_sys_getattr(const struct path *path, struct kstat *stat,
  			    u32 request_mask, unsigned int query_flags)

  {

  	struct inode *inode = d_inode(path->dentry);

  	struct ctl_table_header *head = grab_header(inode);
  	struct ctl_table *table = PROC_I(inode)->sysctl_entry;
  
  	if (IS_ERR(head))
  		return PTR_ERR(head);
  
  	generic_fillattr(inode, stat);
  	if (table)
  		stat->mode = (stat->mode & S_IFMT) | table->mode;
  
  	sysctl_head_finish(head);
  	return 0;
  }

  static const struct file_operations proc_sys_file_operations = {

  	.open		= proc_sys_open,
  	.poll		= proc_sys_poll,

  	.read_iter	= proc_sys_read,
  	.write_iter	= proc_sys_write,
  	.splice_read	= generic_file_splice_read,
  	.splice_write	= iter_file_splice_write,

  	.llseek		= default_llseek,

  };
  
  static const struct file_operations proc_sys_dir_file_operations = {

  	.read		= generic_read_dir,

  	.iterate_shared	= proc_sys_readdir,

  	.llseek		= generic_file_llseek,

  };

  static const struct inode_operations proc_sys_inode_operations = {

  	.permission	= proc_sys_permission,
  	.setattr	= proc_sys_setattr,
  	.getattr	= proc_sys_getattr,
  };
  
  static const struct inode_operations proc_sys_dir_operations = {

  	.lookup		= proc_sys_lookup,
  	.permission	= proc_sys_permission,
  	.setattr	= proc_sys_setattr,

  	.getattr	= proc_sys_getattr,

  };

  static int proc_sys_revalidate(struct dentry *dentry, unsigned int flags)

  {

  	if (flags & LOOKUP_RCU)

  		return -ECHILD;

  	return !PROC_I(d_inode(dentry))->sysctl->unregistering;

  }

  static int proc_sys_delete(const struct dentry *dentry)

  {

  	return !!PROC_I(d_inode(dentry))->sysctl->unregistering;

  }

  static int sysctl_is_seen(struct ctl_table_header *p)
  {
  	struct ctl_table_set *set = p->set;
  	int res;
  	spin_lock(&sysctl_lock);
  	if (p->unregistering)
  		res = 0;
  	else if (!set->is_seen)
  		res = 1;
  	else
  		res = set->is_seen(set);
  	spin_unlock(&sysctl_lock);
  	return res;
  }

  static int proc_sys_compare(const struct dentry *dentry,

  		unsigned int len, const char *str, const struct qstr *name)

  {

  	struct ctl_table_header *head;

  	struct inode *inode;

  	/* Although proc doesn't have negative dentries, rcu-walk means
  	 * that inode here can be NULL */

  	/* AV: can it, indeed? */

  	inode = d_inode_rcu(dentry);

  	if (!inode)

  		return 1;

  	if (name->len != len)

  		return 1;

  	if (memcmp(name->name, str, len))

  		return 1;

  	head = rcu_dereference(PROC_I(inode)->sysctl);
  	return !head || !sysctl_is_seen(head);

  }

  static const struct dentry_operations proc_sys_dentry_operations = {

  	.d_revalidate	= proc_sys_revalidate,

  	.d_delete	= proc_sys_delete,
  	.d_compare	= proc_sys_compare,

  };

  static struct ctl_dir *find_subdir(struct ctl_dir *dir,
  				   const char *name, int namelen)

  {

  	struct ctl_table_header *head;
  	struct ctl_table *entry;

  	entry = find_entry(&head, dir, name, namelen);

  	if (!entry)
  		return ERR_PTR(-ENOENT);

  	if (!S_ISDIR(entry->mode))
  		return ERR_PTR(-ENOTDIR);
  	return container_of(head, struct ctl_dir, header);

  }
  
  static struct ctl_dir *new_dir(struct ctl_table_set *set,

  			       const char *name, int namelen)

  {
  	struct ctl_table *table;
  	struct ctl_dir *new;

  	struct ctl_node *node;

  	char *new_name;

  	new = kzalloc(sizeof(*new) + sizeof(struct ctl_node) +
  		      sizeof(struct ctl_table)*2 +  namelen + 1,
  		      GFP_KERNEL);

  	if (!new)

  		return NULL;

  	node = (struct ctl_node *)(new + 1);
  	table = (struct ctl_table *)(node + 1);

  	new_name = (char *)(table + 2);
  	memcpy(new_name, name, namelen);
  	new_name[namelen] = '\0';
  	table[0].procname = new_name;
  	table[0].mode = S_IFDIR|S_IRUGO|S_IXUGO;

  	init_header(&new->header, set->dir.header.root, set, node, table);

  
  	return new;

  }

  /**
   * get_subdir - find or create a subdir with the specified name.
   * @dir:  Directory to create the subdirectory in
   * @name: The name of the subdirectory to find or create
   * @namelen: The length of name
   *
   * Takes a directory with an elevated reference count so we know that
   * if we drop the lock the directory will not go away.  Upon success
   * the reference is moved from @dir to the returned subdirectory.
   * Upon error an error code is returned and the reference on @dir is
   * simply dropped.
   */

  static struct ctl_dir *get_subdir(struct ctl_dir *dir,
  				  const char *name, int namelen)

  {

  	struct ctl_table_set *set = dir->header.set;

  	struct ctl_dir *subdir, *new = NULL;

  	int err;

  	spin_lock(&sysctl_lock);

  	subdir = find_subdir(dir, name, namelen);

  	if (!IS_ERR(subdir))
  		goto found;
  	if (PTR_ERR(subdir) != -ENOENT)
  		goto failed;
  
  	spin_unlock(&sysctl_lock);
  	new = new_dir(set, name, namelen);
  	spin_lock(&sysctl_lock);
  	subdir = ERR_PTR(-ENOMEM);
  	if (!new)
  		goto failed;

  	/* Was the subdir added while we dropped the lock? */

  	subdir = find_subdir(dir, name, namelen);

  	if (!IS_ERR(subdir))
  		goto found;
  	if (PTR_ERR(subdir) != -ENOENT)
  		goto failed;

  	/* Nope.  Use the our freshly made directory entry. */

  	err = insert_header(dir, &new->header);
  	subdir = ERR_PTR(err);
  	if (err)

  		goto failed;

  	subdir = new;
  found:
  	subdir->header.nreg++;
  failed:

  	if (IS_ERR(subdir)) {

  		pr_err("sysctl could not get directory: ");

  		sysctl_print_dir(dir);

  		pr_cont("/%*.*s %ld
  ",

  			namelen, namelen, name, PTR_ERR(subdir));

  	}

  	drop_sysctl_table(&dir->header);
  	if (new)
  		drop_sysctl_table(&new->header);
  	spin_unlock(&sysctl_lock);
  	return subdir;

  }

  static struct ctl_dir *xlate_dir(struct ctl_table_set *set, struct ctl_dir *dir)
  {
  	struct ctl_dir *parent;
  	const char *procname;
  	if (!dir->header.parent)
  		return &set->dir;
  	parent = xlate_dir(set, dir->header.parent);
  	if (IS_ERR(parent))
  		return parent;
  	procname = dir->header.ctl_table[0].procname;
  	return find_subdir(parent, procname, strlen(procname));
  }
  
  static int sysctl_follow_link(struct ctl_table_header **phead,

  	struct ctl_table **pentry)

  {
  	struct ctl_table_header *head;
  	struct ctl_table_root *root;
  	struct ctl_table_set *set;
  	struct ctl_table *entry;
  	struct ctl_dir *dir;
  	int ret;

  	ret = 0;
  	spin_lock(&sysctl_lock);
  	root = (*pentry)->data;

  	set = lookup_header_set(root);

  	dir = xlate_dir(set, (*phead)->parent);
  	if (IS_ERR(dir))
  		ret = PTR_ERR(dir);
  	else {
  		const char *procname = (*pentry)->procname;
  		head = NULL;
  		entry = find_entry(&head, dir, procname, strlen(procname));
  		ret = -ENOENT;
  		if (entry && use_table(head)) {
  			unuse_table(*phead);
  			*phead = head;
  			*pentry = entry;
  			ret = 0;
  		}
  	}
  
  	spin_unlock(&sysctl_lock);
  	return ret;
  }

  static int sysctl_err(const char *path, struct ctl_table *table, char *fmt, ...)

  {

  	struct va_format vaf;
  	va_list args;

  	va_start(args, fmt);
  	vaf.fmt = fmt;
  	vaf.va = &args;

  	pr_err("sysctl table check failed: %s/%s %pV
  ",
  	       path, table->procname, &vaf);

  	va_end(args);
  	return -EINVAL;

  }

  static int sysctl_check_table_array(const char *path, struct ctl_table *table)
  {
  	int err = 0;

  	if ((table->proc_handler == proc_douintvec) ||
  	    (table->proc_handler == proc_douintvec_minmax)) {

  		if (table->maxlen != sizeof(unsigned int))

  			err |= sysctl_err(path, table, "array not allowed");

  	}
  
  	return err;
  }

  static int sysctl_check_table(const char *path, struct ctl_table *table)

  {

  	int err = 0;

  	for (; table->procname; table++) {

  		if (table->child)

  			err |= sysctl_err(path, table, "Not a file");

  
  		if ((table->proc_handler == proc_dostring) ||
  		    (table->proc_handler == proc_dointvec) ||

  		    (table->proc_handler == proc_douintvec) ||

  		    (table->proc_handler == proc_douintvec_minmax) ||

  		    (table->proc_handler == proc_dointvec_minmax) ||
  		    (table->proc_handler == proc_dointvec_jiffies) ||
  		    (table->proc_handler == proc_dointvec_userhz_jiffies) ||
  		    (table->proc_handler == proc_dointvec_ms_jiffies) ||
  		    (table->proc_handler == proc_doulongvec_minmax) ||
  		    (table->proc_handler == proc_doulongvec_ms_jiffies_minmax)) {
  			if (!table->data)

  				err |= sysctl_err(path, table, "No data");

  			if (!table->maxlen)

  				err |= sysctl_err(path, table, "No maxlen");

  			else
  				err |= sysctl_check_table_array(path, table);

  		}
  		if (!table->proc_handler)

  			err |= sysctl_err(path, table, "No proc_handler");

  
  		if ((table->mode & (S_IRUGO|S_IWUGO)) != table->mode)

  			err |= sysctl_err(path, table, "bogus .mode 0%o",

  				table->mode);

  	}

  	return err;

  }

  static struct ctl_table_header *new_links(struct ctl_dir *dir, struct ctl_table *table,
  	struct ctl_table_root *link_root)
  {
  	struct ctl_table *link_table, *entry, *link;
  	struct ctl_table_header *links;

  	struct ctl_node *node;

  	char *link_name;
  	int nr_entries, name_bytes;
  
  	name_bytes = 0;
  	nr_entries = 0;
  	for (entry = table; entry->procname; entry++) {
  		nr_entries++;
  		name_bytes += strlen(entry->procname) + 1;
  	}
  
  	links = kzalloc(sizeof(struct ctl_table_header) +

  			sizeof(struct ctl_node)*nr_entries +

  			sizeof(struct ctl_table)*(nr_entries + 1) +
  			name_bytes,
  			GFP_KERNEL);
  
  	if (!links)
  		return NULL;

  	node = (struct ctl_node *)(links + 1);
  	link_table = (struct ctl_table *)(node + nr_entries);

  	link_name = (char *)&link_table[nr_entries + 1];
  
  	for (link = link_table, entry = table; entry->procname; link++, entry++) {
  		int len = strlen(entry->procname) + 1;
  		memcpy(link_name, entry->procname, len);
  		link->procname = link_name;
  		link->mode = S_IFLNK|S_IRWXUGO;
  		link->data = link_root;
  		link_name += len;
  	}

  	init_header(links, dir->header.root, dir->header.set, node, link_table);

  	links->nreg = nr_entries;
  
  	return links;
  }
  
  static bool get_links(struct ctl_dir *dir,
  	struct ctl_table *table, struct ctl_table_root *link_root)
  {
  	struct ctl_table_header *head;
  	struct ctl_table *entry, *link;
  
  	/* Are there links available for every entry in table? */
  	for (entry = table; entry->procname; entry++) {
  		const char *procname = entry->procname;
  		link = find_entry(&head, dir, procname, strlen(procname));
  		if (!link)
  			return false;
  		if (S_ISDIR(link->mode) && S_ISDIR(entry->mode))
  			continue;
  		if (S_ISLNK(link->mode) && (link->data == link_root))
  			continue;
  		return false;
  	}
  
  	/* The checks passed.  Increase the registration count on the links */
  	for (entry = table; entry->procname; entry++) {
  		const char *procname = entry->procname;
  		link = find_entry(&head, dir, procname, strlen(procname));
  		head->nreg++;
  	}
  	return true;
  }
  
  static int insert_links(struct ctl_table_header *head)
  {
  	struct ctl_table_set *root_set = &sysctl_table_root.default_set;
  	struct ctl_dir *core_parent = NULL;
  	struct ctl_table_header *links;
  	int err;
  
  	if (head->set == root_set)
  		return 0;
  
  	core_parent = xlate_dir(root_set, head->parent);
  	if (IS_ERR(core_parent))
  		return 0;
  
  	if (get_links(core_parent, head->ctl_table, head->root))
  		return 0;
  
  	core_parent->header.nreg++;
  	spin_unlock(&sysctl_lock);
  
  	links = new_links(core_parent, head->ctl_table, head->root);
  
  	spin_lock(&sysctl_lock);
  	err = -ENOMEM;
  	if (!links)
  		goto out;
  
  	err = 0;
  	if (get_links(core_parent, head->ctl_table, head->root)) {
  		kfree(links);
  		goto out;
  	}
  
  	err = insert_header(core_parent, links);
  	if (err)
  		kfree(links);
  out:
  	drop_sysctl_table(&core_parent->header);
  	return err;
  }

  /**

   * __register_sysctl_table - register a leaf sysctl table

   * @set: Sysctl tree to register on

   * @path: The path to the directory the sysctl table is in.
   * @table: the top-level table structure
   *
   * Register a sysctl table hierarchy. @table should be a filled in ctl_table
   * array. A completely 0 filled entry terminates the table.
   *
   * The members of the &struct ctl_table structure are used as follows:
   *
   * procname - the name of the sysctl file under /proc/sys. Set to %NULL to not
   *            enter a sysctl file
   *
   * data - a pointer to data for use by proc_handler
   *
   * maxlen - the maximum size in bytes of the data
   *

   * mode - the file permissions for the /proc/sys file

   *

   * child - must be %NULL.

   *
   * proc_handler - the text handler routine (described below)
   *

   * extra1, extra2 - extra pointers usable by the proc handler routines
   *
   * Leaf nodes in the sysctl tree will be represented by a single file
   * under /proc; non-leaf nodes will be represented by directories.
   *

   * There must be a proc_handler routine for any terminal nodes.
   * Several default handlers are available to cover common cases -

   *
   * proc_dostring(), proc_dointvec(), proc_dointvec_jiffies(),
   * proc_dointvec_userhz_jiffies(), proc_dointvec_minmax(),
   * proc_doulongvec_ms_jiffies_minmax(), proc_doulongvec_minmax()
   *
   * It is the handler's job to read the input buffer from user memory
   * and process it. The handler should return 0 on success.
   *
   * This routine returns %NULL on a failure to register, and a pointer
   * to the table header on success.
   */

  struct ctl_table_header *__register_sysctl_table(

  	struct ctl_table_set *set,

  	const char *path, struct ctl_table *table)

  {

  	struct ctl_table_root *root = set->dir.header.root;

  	struct ctl_table_header *header;

  	const char *name, *nextname;

  	struct ctl_dir *dir;

  	struct ctl_table *entry;
  	struct ctl_node *node;
  	int nr_entries = 0;
  
  	for (entry = table; entry->procname; entry++)
  		nr_entries++;

  	header = kzalloc(sizeof(struct ctl_table_header) +
  			 sizeof(struct ctl_node)*nr_entries, GFP_KERNEL);

  	if (!header)
  		return NULL;

  	node = (struct ctl_node *)(header + 1);
  	init_header(header, root, set, node, table);

  	if (sysctl_check_table(path, table))
  		goto fail;
  
  	spin_lock(&sysctl_lock);

  	dir = &set->dir;

  	/* Reference moved down the diretory tree get_subdir */

  	dir->header.nreg++;
  	spin_unlock(&sysctl_lock);

  	/* Find the directory for the ctl_table */

  	for (name = path; name; name = nextname) {
  		int namelen;
  		nextname = strchr(name, '/');
  		if (nextname) {
  			namelen = nextname - name;
  			nextname++;
  		} else {
  			namelen = strlen(name);
  		}
  		if (namelen == 0)
  			continue;

  		dir = get_subdir(dir, name, namelen);

  		if (IS_ERR(dir))
  			goto fail;

  	}

  	spin_lock(&sysctl_lock);

  	if (insert_header(dir, header))

  		goto fail_put_dir_locked;

  	drop_sysctl_table(&dir->header);

  	spin_unlock(&sysctl_lock);
  
  	return header;

  fail_put_dir_locked:
  	drop_sysctl_table(&dir->header);

  	spin_unlock(&sysctl_lock);
  fail:
  	kfree(header);
  	dump_stack();
  	return NULL;

  }

  /**
   * register_sysctl - register a sysctl table
   * @path: The path to the directory the sysctl table is in.
   * @table: the table structure
   *
   * Register a sysctl table. @table should be a filled in ctl_table
   * array. A completely 0 filled entry terminates the table.
   *
   * See __register_sysctl_table for more details.
   */
  struct ctl_table_header *register_sysctl(const char *path, struct ctl_table *table)
  {
  	return __register_sysctl_table(&sysctl_table_root.default_set,
  					path, table);
  }
  EXPORT_SYMBOL(register_sysctl);

  static char *append_path(const char *path, char *pos, const char *name)
  {
  	int namelen;
  	namelen = strlen(name);
  	if (((pos - path) + namelen + 2) >= PATH_MAX)
  		return NULL;
  	memcpy(pos, name, namelen);
  	pos[namelen] = '/';
  	pos[namelen + 1] = '\0';
  	pos += namelen + 1;
  	return pos;
  }

  static int count_subheaders(struct ctl_table *table)
  {
  	int has_files = 0;
  	int nr_subheaders = 0;
  	struct ctl_table *entry;
  
  	/* special case: no directory and empty directory */
  	if (!table || !table->procname)
  		return 1;
  
  	for (entry = table; entry->procname; entry++) {
  		if (entry->child)
  			nr_subheaders += count_subheaders(entry->child);
  		else
  			has_files = 1;
  	}
  	return nr_subheaders + has_files;
  }
  
  static int register_leaf_sysctl_tables(const char *path, char *pos,

  	struct ctl_table_header ***subheader, struct ctl_table_set *set,

  	struct ctl_table *table)
  {
  	struct ctl_table *ctl_table_arg = NULL;
  	struct ctl_table *entry, *files;
  	int nr_files = 0;
  	int nr_dirs = 0;
  	int err = -ENOMEM;
  
  	for (entry = table; entry->procname; entry++) {
  		if (entry->child)
  			nr_dirs++;
  		else
  			nr_files++;
  	}
  
  	files = table;
  	/* If there are mixed files and directories we need a new table */
  	if (nr_dirs && nr_files) {
  		struct ctl_table *new;

  		files = kcalloc(nr_files + 1, sizeof(struct ctl_table),

  				GFP_KERNEL);
  		if (!files)
  			goto out;
  
  		ctl_table_arg = files;
  		for (new = files, entry = table; entry->procname; entry++) {
  			if (entry->child)
  				continue;
  			*new = *entry;
  			new++;
  		}
  	}
  
  	/* Register everything except a directory full of subdirectories */
  	if (nr_files || !nr_dirs) {
  		struct ctl_table_header *header;

  		header = __register_sysctl_table(set, path, files);

  		if (!header) {
  			kfree(ctl_table_arg);
  			goto out;
  		}
  
  		/* Remember if we need to free the file table */
  		header->ctl_table_arg = ctl_table_arg;
  		**subheader = header;
  		(*subheader)++;
  	}
  
  	/* Recurse into the subdirectories. */
  	for (entry = table; entry->procname; entry++) {
  		char *child_pos;
  
  		if (!entry->child)
  			continue;
  
  		err = -ENAMETOOLONG;
  		child_pos = append_path(path, pos, entry->procname);
  		if (!child_pos)
  			goto out;
  
  		err = register_leaf_sysctl_tables(path, child_pos, subheader,

  						  set, entry->child);

  		pos[0] = '\0';
  		if (err)
  			goto out;
  	}
  	err = 0;
  out:
  	/* On failure our caller will unregister all registered subheaders */
  	return err;
  }

  /**
   * __register_sysctl_paths - register a sysctl table hierarchy

   * @set: Sysctl tree to register on

   * @path: The path to the directory the sysctl table is in.
   * @table: the top-level table structure
   *
   * Register a sysctl table hierarchy. @table should be a filled in ctl_table
   * array. A completely 0 filled entry terminates the table.
   *
   * See __register_sysctl_table for more details.
   */
  struct ctl_table_header *__register_sysctl_paths(

  	struct ctl_table_set *set,

  	const struct ctl_path *path, struct ctl_table *table)
  {

  	struct ctl_table *ctl_table_arg = table;

  	int nr_subheaders = count_subheaders(table);
  	struct ctl_table_header *header = NULL, **subheaders, **subheader;

  	const struct ctl_path *component;
  	char *new_path, *pos;
  
  	pos = new_path = kmalloc(PATH_MAX, GFP_KERNEL);
  	if (!new_path)
  		return NULL;
  
  	pos[0] = '\0';
  	for (component = path; component->procname; component++) {
  		pos = append_path(new_path, pos, component->procname);
  		if (!pos)
  			goto out;
  	}

  	while (table->procname && table->child && !table[1].procname) {
  		pos = append_path(new_path, pos, table->procname);
  		if (!pos)
  			goto out;
  		table = table->child;
  	}

  	if (nr_subheaders == 1) {

  		header = __register_sysctl_table(set, new_path, table);

  		if (header)
  			header->ctl_table_arg = ctl_table_arg;
  	} else {
  		header = kzalloc(sizeof(*header) +
  				 sizeof(*subheaders)*nr_subheaders, GFP_KERNEL);
  		if (!header)
  			goto out;
  
  		subheaders = (struct ctl_table_header **) (header + 1);
  		subheader = subheaders;

  		header->ctl_table_arg = ctl_table_arg;

  
  		if (register_leaf_sysctl_tables(new_path, pos, &subheader,

  						set, table))

  			goto err_register_leaves;
  	}

  out:
  	kfree(new_path);
  	return header;

  
  err_register_leaves:
  	while (subheader > subheaders) {
  		struct ctl_table_header *subh = *(--subheader);
  		struct ctl_table *table = subh->ctl_table_arg;
  		unregister_sysctl_table(subh);
  		kfree(table);
  	}
  	kfree(header);
  	header = NULL;
  	goto out;

  }

  /**
   * register_sysctl_table_path - register a sysctl table hierarchy
   * @path: The path to the directory the sysctl table is in.
   * @table: the top-level table structure
   *
   * Register a sysctl table hierarchy. @table should be a filled in ctl_table
   * array. A completely 0 filled entry terminates the table.
   *
   * See __register_sysctl_paths for more details.
   */
  struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
  						struct ctl_table *table)
  {

  	return __register_sysctl_paths(&sysctl_table_root.default_set,

  					path, table);
  }
  EXPORT_SYMBOL(register_sysctl_paths);
  
  /**
   * register_sysctl_table - register a sysctl table hierarchy
   * @table: the top-level table structure
   *
   * Register a sysctl table hierarchy. @table should be a filled in ctl_table
   * array. A completely 0 filled entry terminates the table.
   *
   * See register_sysctl_paths for more details.
   */
  struct ctl_table_header *register_sysctl_table(struct ctl_table *table)
  {
  	static const struct ctl_path null_path[] = { {} };
  
  	return register_sysctl_paths(null_path, table);
  }
  EXPORT_SYMBOL(register_sysctl_table);

  static void put_links(struct ctl_table_header *header)
  {
  	struct ctl_table_set *root_set = &sysctl_table_root.default_set;
  	struct ctl_table_root *root = header->root;
  	struct ctl_dir *parent = header->parent;
  	struct ctl_dir *core_parent;
  	struct ctl_table *entry;
  
  	if (header->set == root_set)
  		return;
  
  	core_parent = xlate_dir(root_set, parent);
  	if (IS_ERR(core_parent))
  		return;
  
  	for (entry = header->ctl_table; entry->procname; entry++) {
  		struct ctl_table_header *link_head;
  		struct ctl_table *link;
  		const char *name = entry->procname;
  
  		link = find_entry(&link_head, core_parent, name, strlen(name));
  		if (link &&
  		    ((S_ISDIR(link->mode) && S_ISDIR(entry->mode)) ||
  		     (S_ISLNK(link->mode) && (link->data == root)))) {
  			drop_sysctl_table(link_head);
  		}
  		else {

  			pr_err("sysctl link missing during unregister: ");

  			sysctl_print_dir(parent);

  			pr_cont("/%s
  ", name);

  		}
  	}
  }

  static void drop_sysctl_table(struct ctl_table_header *header)
  {

  	struct ctl_dir *parent = header->parent;

  	if (--header->nreg)
  		return;

  	if (parent) {

  		put_links(header);

  		start_unregistering(header);
  	}

  	if (!--header->count)
  		kfree_rcu(header, rcu);

  
  	if (parent)
  		drop_sysctl_table(&parent->header);

  }

  /**
   * unregister_sysctl_table - unregister a sysctl table hierarchy
   * @header: the header returned from register_sysctl_table
   *
   * Unregisters the sysctl table and all children. proc entries may not
   * actually be removed until they are no longer used by anyone.
   */
  void unregister_sysctl_table(struct ctl_table_header * header)
  {

  	int nr_subheaders;

  	might_sleep();
  
  	if (header == NULL)
  		return;

  	nr_subheaders = count_subheaders(header->ctl_table_arg);
  	if (unlikely(nr_subheaders > 1)) {
  		struct ctl_table_header **subheaders;
  		int i;
  
  		subheaders = (struct ctl_table_header **)(header + 1);
  		for (i = nr_subheaders -1; i >= 0; i--) {
  			struct ctl_table_header *subh = subheaders[i];
  			struct ctl_table *table = subh->ctl_table_arg;
  			unregister_sysctl_table(subh);
  			kfree(table);
  		}
  		kfree(header);
  		return;
  	}

  	spin_lock(&sysctl_lock);

  	drop_sysctl_table(header);

  	spin_unlock(&sysctl_lock);
  }
  EXPORT_SYMBOL(unregister_sysctl_table);

  void setup_sysctl_set(struct ctl_table_set *set,

  	struct ctl_table_root *root,

  	int (*is_seen)(struct ctl_table_set *))
  {

  	memset(set, 0, sizeof(*set));

  	set->is_seen = is_seen;

  	init_header(&set->dir.header, root, set, NULL, root_table);

  }

  void retire_sysctl_set(struct ctl_table_set *set)
  {

  	WARN_ON(!RB_EMPTY_ROOT(&set->dir.root));

  }

  int __init proc_sys_init(void)

  {

  	struct proc_dir_entry *proc_sys_root;

  	proc_sys_root = proc_mkdir("sys", NULL);

  	proc_sys_root->proc_iops = &proc_sys_dir_operations;

  	proc_sys_root->proc_dir_ops = &proc_sys_dir_file_operations;

  	proc_sys_root->nlink = 0;

  
  	return sysctl_init();

  }

  struct sysctl_alias {
  	const char *kernel_param;
  	const char *sysctl_param;
  };
  
  /*
   * Historically some settings had both sysctl and a command line parameter.
   * With the generic sysctl. parameter support, we can handle them at a single
   * place and only keep the historical name for compatibility. This is not meant
   * to add brand new aliases. When adding existing aliases, consider whether
   * the possibly different moment of changing the value (e.g. from early_param
   * to the moment do_sysctl_args() is called) is an issue for the specific
   * parameter.
   */
  static const struct sysctl_alias sysctl_aliases[] = {

  	{"hardlockup_all_cpu_backtrace",	"kernel.hardlockup_all_cpu_backtrace" },
  	{"hung_task_panic",			"kernel.hung_task_panic" },
  	{"numa_zonelist_order",			"vm.numa_zonelist_order" },
  	{"softlockup_all_cpu_backtrace",	"kernel.softlockup_all_cpu_backtrace" },
  	{"softlockup_panic",			"kernel.softlockup_panic" },

  	{ }
  };
  
  static const char *sysctl_find_alias(char *param)
  {
  	const struct sysctl_alias *alias;
  
  	for (alias = &sysctl_aliases[0]; alias->kernel_param != NULL; alias++) {
  		if (strcmp(alias->kernel_param, param) == 0)
  			return alias->sysctl_param;
  	}
  
  	return NULL;
  }

  /* Set sysctl value passed on kernel command line. */
  static int process_sysctl_arg(char *param, char *val,
  			       const char *unused, void *arg)
  {
  	char *path;
  	struct vfsmount **proc_mnt = arg;
  	struct file_system_type *proc_fs_type;
  	struct file *file;
  	int len;
  	int err;
  	loff_t pos = 0;
  	ssize_t wret;

  	if (strncmp(param, "sysctl", sizeof("sysctl") - 1) == 0) {
  		param += sizeof("sysctl") - 1;

  		if (param[0] != '/' && param[0] != '.')
  			return 0;

  		param++;
  	} else {
  		param = (char *) sysctl_find_alias(param);
  		if (!param)
  			return 0;
  	}

  
  	/*
  	 * To set sysctl options, we use a temporary mount of proc, look up the
  	 * respective sys/ file and write to it. To avoid mounting it when no
  	 * options were given, we mount it only when the first sysctl option is
  	 * found. Why not a persistent mount? There are problems with a
  	 * persistent mount of proc in that it forces userspace not to use any
  	 * proc mount options.
  	 */
  	if (!*proc_mnt) {
  		proc_fs_type = get_fs_type("proc");
  		if (!proc_fs_type) {
  			pr_err("Failed to find procfs to set sysctl from command line
  ");
  			return 0;
  		}
  		*proc_mnt = kern_mount(proc_fs_type);
  		put_filesystem(proc_fs_type);
  		if (IS_ERR(*proc_mnt)) {
  			pr_err("Failed to mount procfs to set sysctl from command line
  ");
  			return 0;
  		}
  	}
  
  	path = kasprintf(GFP_KERNEL, "sys/%s", param);
  	if (!path)
  		panic("%s: Failed to allocate path for %s
  ", __func__, param);
  	strreplace(path, '.', '/');
  
  	file = file_open_root((*proc_mnt)->mnt_root, *proc_mnt, path, O_WRONLY, 0);
  	if (IS_ERR(file)) {
  		err = PTR_ERR(file);
  		if (err == -ENOENT)
  			pr_err("Failed to set sysctl parameter '%s=%s': parameter not found
  ",
  				param, val);
  		else if (err == -EACCES)
  			pr_err("Failed to set sysctl parameter '%s=%s': permission denied (read-only?)
  ",
  				param, val);
  		else
  			pr_err("Error %pe opening proc file to set sysctl parameter '%s=%s'
  ",
  				file, param, val);
  		goto out;
  	}
  	len = strlen(val);
  	wret = kernel_write(file, val, len, &pos);
  	if (wret < 0) {
  		err = wret;
  		if (err == -EINVAL)
  			pr_err("Failed to set sysctl parameter '%s=%s': invalid value
  ",
  				param, val);
  		else
  			pr_err("Error %pe writing to proc file to set sysctl parameter '%s=%s'
  ",
  				ERR_PTR(err), param, val);
  	} else if (wret != len) {
  		pr_err("Wrote only %zd bytes of %d writing to proc file %s to set sysctl parameter '%s=%s
  ",
  			wret, len, path, param, val);
  	}
  
  	err = filp_close(file, NULL);
  	if (err)
  		pr_err("Error %pe closing proc file to set sysctl parameter '%s=%s
  ",
  			ERR_PTR(err), param, val);
  out:
  	kfree(path);
  	return 0;
  }
  
  void do_sysctl_args(void)
  {
  	char *command_line;
  	struct vfsmount *proc_mnt = NULL;
  
  	command_line = kstrdup(saved_command_line, GFP_KERNEL);
  	if (!command_line)
  		panic("%s: Failed to allocate copy of command line
  ", __func__);
  
  	parse_args("Setting sysctl args", command_line,
  		   NULL, 0, -1, -1, &proc_mnt, process_sysctl_arg);
  
  	if (proc_mnt)
  		kern_unmount(proc_mnt);
  
  	kfree(command_line);
  }