/*
   * /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/namei.h>
  #include <linux/mm.h>
  #include <linux/module.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;
  
  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, struct nsproxy *namespaces);
  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;
  	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;
  
  	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:
  	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);
  }
  
  /* 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);
  		spin_lock(&sysctl_lock);
  	} else {
  		/* anything non-NULL; we'll never dereference it */
  		p->unregistering = ERR_PTR(-EINVAL);
  	}
  	/*
  	 * do not remove from the list until nobody holds it; walking the
  	 * list in do_sysctl() relies on that.
  	 */
  	erase_header(p);
  }
  
  static void sysctl_head_get(struct ctl_table_header *head)
  {
  	spin_lock(&sysctl_lock);
  	head->count++;
  	spin_unlock(&sysctl_lock);
  }
  
  void sysctl_head_put(struct ctl_table_header *head)
  {
  	spin_lock(&sysctl_lock);
  	if (!--head->count)
  		kfree_rcu(head, rcu);
  	spin_unlock(&sysctl_lock);
  }
  
  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 nsproxy *namespaces)
  {
  	struct ctl_table_set *set = &root->default_set;
  	if (root->lookup)
  		set = root->lookup(root, namespaces);
  	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;
  }
  
  void register_sysctl_root(struct ctl_table_root *root)
  {
  }
  
  /*
   * 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 inode *inode;
  	struct proc_inode *ei;
  
  	inode = new_inode(sb);
  	if (!inode)
  		goto out;
  
  	inode->i_ino = get_next_ino();
  
  	sysctl_head_get(head);
  	ei = PROC_I(inode);
  	ei->sysctl = head;
  	ei->sysctl_entry = table;
  
  	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
  	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;
  	}
  out:
  	return inode;
  }
  
  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;
  	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, current->nsproxy);
  		err = ERR_PTR(ret);
  		if (ret)
  			goto out;
  	}
  
  	err = ERR_PTR(-ENOMEM);
  	inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
  	if (!inode)
  		goto out;
  
  	err = NULL;
  	d_set_d_op(dentry, &proc_sys_dentry_operations);
  	d_add(dentry, inode);
  
  out:
  	if (h)
  		sysctl_head_finish(h);
  	sysctl_head_finish(head);
  	return err;
  }
  
  static ssize_t proc_sys_call_handler(struct file *filp, void __user *buf,
  		size_t count, loff_t *ppos, int write)
  {
  	struct inode *inode = file_inode(filp);
  	struct ctl_table_header *head = grab_header(inode);
  	struct ctl_table *table = PROC_I(inode)->sysctl_entry;
  	ssize_t error;
  	size_t res;
  
  	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;
  
  	/* careful: calling conventions are nasty here */
  	res = count;
  	error = table->proc_handler(table, write, buf, &res, ppos);
  	if (!error)
  		error = res;
  out:
  	sysctl_head_finish(head);
  
  	return error;
  }
  
  static ssize_t proc_sys_read(struct file *filp, char __user *buf,
  				size_t count, loff_t *ppos)
  {
  	return proc_sys_call_handler(filp, (void __user *)buf, count, ppos, 0);
  }
  
  static ssize_t proc_sys_write(struct file *filp, const char __user *buf,
  				size_t count, loff_t *ppos)
  {
  	return proc_sys_call_handler(filp, (void __user *)buf, count, ppos, 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 unsigned int 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;
  	unsigned int ret = DEFAULT_POLLMASK;
  	unsigned long event;
  
  	/* sysctl was unregistered */
  	if (IS_ERR(head))
  		return POLLERR | POLLHUP;
  
  	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 = POLLIN | POLLRDNORM | POLLERR | POLLPRI;
  	}
  
  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(qname.name, qname.len);
  
  	child = d_lookup(dir, &qname);
  	if (!child) {
  		child = d_alloc(dir, &qname);
  		if (child) {
  			inode = proc_sys_make_inode(dir->d_sb, head, table);
  			if (!inode) {
  				dput(child);
  				return false;
  			} else {
  				d_set_d_op(child, &proc_sys_dentry_operations);
  				d_add(child, inode);
  			}
  		} else {
  			return false;
  		}
  	}
  	inode = child->d_inode;
  	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 (S_ISLNK(table->mode)) {
  		/* It is not an error if we can not follow the link ignore it */
  		int err = sysctl_follow_link(&head, &table, current->nsproxy);
  		if (err)
  			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, 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))
  		return 0;
  
  	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;
  		}
  	}
  	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 = dentry->d_inode;
  	int error;
  
  	if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
  		return -EPERM;
  
  	error = inode_change_ok(inode, attr);
  	if (error)
  		return error;
  
  	setattr_copy(inode, attr);
  	mark_inode_dirty(inode);
  	return 0;
  }
  
  static int proc_sys_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
  {
  	struct inode *inode = dentry->d_inode;
  	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		= proc_sys_read,
  	.write		= proc_sys_write,
  	.llseek		= default_llseek,
  };
  
  static const struct file_operations proc_sys_dir_file_operations = {
  	.read		= generic_read_dir,
  	.iterate	= 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(dentry->d_inode)->sysctl->unregistering;
  }
  
  static int proc_sys_delete(const struct dentry *dentry)
  {
  	return !!PROC_I(dentry->d_inode)->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 *parent, 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 = ACCESS_ONCE(dentry->d_inode);
  	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 (unlikely(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 nsproxy *namespaces)
  {
  	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, namespaces);
  	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(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_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");
  		}
  		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 = kzalloc(sizeof(struct ctl_table) * (nr_files + 1),
  				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;
  
  	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_fops = &proc_sys_dir_file_operations;
  	proc_sys_root->nlink = 0;
  
  	return sysctl_init();
  }