fs/debugfs/inode.c - linux - Git at Google

 /*
  *  inode.c - part of debugfs, a tiny little debug file system
  *
  *  Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
  *  Copyright (C) 2004 IBM Inc.
  *
  *	This program is free software; you can redistribute it and/or
  *	modify it under the terms of the GNU General Public License version
  *	2 as published by the Free Software Foundation.
  *
  *  debugfs is for people to use instead of /proc or /sys.
  *  See Documentation/DocBook/kernel-api for more details.
  *
  */

 #include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/mount.h>
 #include <linux/pagemap.h>
 #include <linux/init.h>
 #include <linux/kobject.h>
 #include <linux/namei.h>
 #include <linux/debugfs.h>
 #include <linux/fsnotify.h>
 #include <linux/string.h>
 #include <linux/seq_file.h>
 #include <linux/parser.h>
 #include <linux/magic.h>
 #include <linux/slab.h>

 #define DEBUGFS_DEFAULT_MODE	0700

 static struct vfsmount *debugfs_mount;
 static int debugfs_mount_count;
 static bool debugfs_registered;

 static struct inode *debugfs_get_inode(struct super_block *sb)
 {
 	struct inode *inode = new_inode(sb);
 	if (inode) {
 		inode->i_ino = get_next_ino();
 		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 	}
 	return inode;
 }

 static inline int debugfs_positive(struct dentry *dentry)
 {
 	return dentry->d_inode && !d_unhashed(dentry);
 }

 struct debugfs_mount_opts {
 	kuid_t uid;
 	kgid_t gid;
 	umode_t mode;
 };

 enum {
 	Opt_uid,
 	Opt_gid,
 	Opt_mode,
 	Opt_err
 };

 static const match_table_t tokens = {
 	{Opt_uid, "uid=%u"},
 	{Opt_gid, "gid=%u"},
 	{Opt_mode, "mode=%o"},
 	{Opt_err, NULL}
 };

 struct debugfs_fs_info {
 	struct debugfs_mount_opts mount_opts;
 };

 static int debugfs_parse_options(char *data, struct debugfs_mount_opts *opts)
 {
 	substring_t args[MAX_OPT_ARGS];
 	int option;
 	int token;
 	kuid_t uid;
 	kgid_t gid;
 	char *p;

 	opts->mode = DEBUGFS_DEFAULT_MODE;

 	while ((p = strsep(&data, ",")) != NULL) {
 		if (!*p)
 			continue;

 		token = match_token(p, tokens, args);
 		switch (token) {
 		case Opt_uid:
 			if (match_int(&args[0], &option))
 				return -EINVAL;
 			uid = make_kuid(current_user_ns(), option);
 			if (!uid_valid(uid))
 				return -EINVAL;
 			opts->uid = uid;
 			break;
 		case Opt_gid:
 			if (match_int(&args[0], &option))
 				return -EINVAL;
 			gid = make_kgid(current_user_ns(), option);
 			if (!gid_valid(gid))
 				return -EINVAL;
 			opts->gid = gid;
 			break;
 		case Opt_mode:
 			if (match_octal(&args[0], &option))
 				return -EINVAL;
 			opts->mode = option & S_IALLUGO;
 			break;
 		/*
 		 * We might like to report bad mount options here;
 		 * but traditionally debugfs has ignored all mount options
 		 */
 		}
 	}

 	return 0;
 }

 static int debugfs_apply_options(struct super_block *sb)
 {
 	struct debugfs_fs_info *fsi = sb->s_fs_info;
 	struct inode *inode = sb->s_root->d_inode;
 	struct debugfs_mount_opts *opts = &fsi->mount_opts;

 	inode->i_mode &= ~S_IALLUGO;
 	inode->i_mode |= opts->mode;

 	inode->i_uid = opts->uid;
 	inode->i_gid = opts->gid;

 	return 0;
 }

 static int debugfs_remount(struct super_block *sb, int *flags, char *data)
 {
 	int err;
 	struct debugfs_fs_info *fsi = sb->s_fs_info;

 	sync_filesystem(sb);
 	err = debugfs_parse_options(data, &fsi->mount_opts);
 	if (err)
 		goto fail;

 	debugfs_apply_options(sb);

 fail:
 	return err;
 }

 static int debugfs_show_options(struct seq_file *m, struct dentry *root)
 {
 	struct debugfs_fs_info *fsi = root->d_sb->s_fs_info;
 	struct debugfs_mount_opts *opts = &fsi->mount_opts;

 	if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
 		seq_printf(m, ",uid=%u",
 			   from_kuid_munged(&init_user_ns, opts->uid));
 	if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
 		seq_printf(m, ",gid=%u",
 			   from_kgid_munged(&init_user_ns, opts->gid));
 	if (opts->mode != DEBUGFS_DEFAULT_MODE)
 		seq_printf(m, ",mode=%o", opts->mode);

 	return 0;
 }

 static const struct super_operations debugfs_super_operations = {
 	.statfs		= simple_statfs,
 	.remount_fs	= debugfs_remount,
 	.show_options	= debugfs_show_options,
 };

 static struct vfsmount *debugfs_automount(struct path *path)
 {
 	struct vfsmount *(*f)(void *);
 	f = (struct vfsmount *(*)(void *))path->dentry->d_fsdata;
 	return f(path->dentry->d_inode->i_private);
 }

 static const struct dentry_operations debugfs_dops = {
 	.d_delete = always_delete_dentry,
 	.d_automount = debugfs_automount,
 };

 static int debug_fill_super(struct super_block *sb, void *data, int silent)
 {
 	static struct tree_descr debug_files[] = {{""}};
 	struct debugfs_fs_info *fsi;
 	int err;

 	save_mount_options(sb, data);

 	fsi = kzalloc(sizeof(struct debugfs_fs_info), GFP_KERNEL);
 	sb->s_fs_info = fsi;
 	if (!fsi) {
 		err = -ENOMEM;
 		goto fail;
 	}

 	err = debugfs_parse_options(data, &fsi->mount_opts);
 	if (err)
 		goto fail;

 	err  =  simple_fill_super(sb, DEBUGFS_MAGIC, debug_files);
 	if (err)
 		goto fail;

 	sb->s_op = &debugfs_super_operations;
 	sb->s_d_op = &debugfs_dops;

 	debugfs_apply_options(sb);

 	return 0;

 fail:
 	kfree(fsi);
 	sb->s_fs_info = NULL;
 	return err;
 }

 static struct dentry *debug_mount(struct file_system_type *fs_type,
 			int flags, const char *dev_name,
 			void *data)
 {
 	return mount_single(fs_type, flags, data, debug_fill_super);
 }

 static struct file_system_type debug_fs_type = {
 	.owner =	THIS_MODULE,
 	.name =		"debugfs",
 	.mount =	debug_mount,
 	.kill_sb =	kill_litter_super,
 };
 MODULE_ALIAS_FS("debugfs");

 static struct dentry *start_creating(const char *name, struct dentry *parent)
 {
 	struct dentry *dentry;
 	int error;

 	pr_debug("debugfs: creating file '%s'\n",name);

 	error = simple_pin_fs(&debug_fs_type, &debugfs_mount,
 			      &debugfs_mount_count);
 	if (error)
 		return ERR_PTR(error);

 	/* If the parent is not specified, we create it in the root.
 	 * We need the root dentry to do this, which is in the super
 	 * block. A pointer to that is in the struct vfsmount that we
 	 * have around.
 	 */
 	if (!parent)
 		parent = debugfs_mount->mnt_root;

 	mutex_lock(&parent->d_inode->i_mutex);
 	dentry = lookup_one_len(name, parent, strlen(name));
 	if (!IS_ERR(dentry) && dentry->d_inode) {
 		dput(dentry);
 		dentry = ERR_PTR(-EEXIST);
 	}
 	if (IS_ERR(dentry))
 		mutex_unlock(&parent->d_inode->i_mutex);
 	return dentry;
 }

 static struct dentry *failed_creating(struct dentry *dentry)
 {
 	mutex_unlock(&dentry->d_parent->d_inode->i_mutex);
 	dput(dentry);
 	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 	return NULL;
 }

 static struct dentry *end_creating(struct dentry *dentry)
 {
 	mutex_unlock(&dentry->d_parent->d_inode->i_mutex);
 	return dentry;
 }

 /**
  * debugfs_create_file - create a file in the debugfs filesystem
  * @name: a pointer to a string containing the name of the file to create.
  * @mode: the permission that the file should have.
  * @parent: a pointer to the parent dentry for this file.  This should be a
  *          directory dentry if set.  If this parameter is NULL, then the
  *          file will be created in the root of the debugfs filesystem.
  * @data: a pointer to something that the caller will want to get to later
  *        on.  The inode.i_private pointer will point to this value on
  *        the open() call.
  * @fops: a pointer to a struct file_operations that should be used for
  *        this file.
  *
  * This is the basic "create a file" function for debugfs.  It allows for a
  * wide range of flexibility in creating a file, or a directory (if you want
  * to create a directory, the debugfs_create_dir() function is
  * recommended to be used instead.)
  *
  * This function will return a pointer to a dentry if it succeeds.  This
  * pointer must be passed to the debugfs_remove() function when the file is
  * to be removed (no automatic cleanup happens if your module is unloaded,
  * you are responsible here.)  If an error occurs, %NULL will be returned.
  *
  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
  * returned.
  */
 struct dentry *debugfs_create_file(const char *name, umode_t mode,
 				   struct dentry *parent, void *data,
 				   const struct file_operations *fops)
 {
 	struct dentry *dentry;
 	struct inode *inode;

 	if (!(mode & S_IFMT))
 		mode |= S_IFREG;
 	BUG_ON(!S_ISREG(mode));
 	dentry = start_creating(name, parent);

 	if (IS_ERR(dentry))
 		return NULL;

 	inode = debugfs_get_inode(dentry->d_sb);
 	if (unlikely(!inode))
 		return failed_creating(dentry);

 	inode->i_mode = mode;
 	inode->i_fop = fops ? fops : &debugfs_file_operations;
 	inode->i_private = data;
 	d_instantiate(dentry, inode);
 	fsnotify_create(dentry->d_parent->d_inode, dentry);
 	return end_creating(dentry);
 }
 EXPORT_SYMBOL_GPL(debugfs_create_file);

 /**
  * debugfs_create_file_size - create a file in the debugfs filesystem
  * @name: a pointer to a string containing the name of the file to create.
  * @mode: the permission that the file should have.
  * @parent: a pointer to the parent dentry for this file.  This should be a
  *          directory dentry if set.  If this parameter is NULL, then the
  *          file will be created in the root of the debugfs filesystem.
  * @data: a pointer to something that the caller will want to get to later
  *        on.  The inode.i_private pointer will point to this value on
  *        the open() call.
  * @fops: a pointer to a struct file_operations that should be used for
  *        this file.
  * @file_size: initial file size
  *
  * This is the basic "create a file" function for debugfs.  It allows for a
  * wide range of flexibility in creating a file, or a directory (if you want
  * to create a directory, the debugfs_create_dir() function is
  * recommended to be used instead.)
  *
  * This function will return a pointer to a dentry if it succeeds.  This
  * pointer must be passed to the debugfs_remove() function when the file is
  * to be removed (no automatic cleanup happens if your module is unloaded,
  * you are responsible here.)  If an error occurs, %NULL will be returned.
  *
  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
  * returned.
  */
 struct dentry *debugfs_create_file_size(const char *name, umode_t mode,
 					struct dentry *parent, void *data,
 					const struct file_operations *fops,
 					loff_t file_size)
 {
 	struct dentry *de = debugfs_create_file(name, mode, parent, data, fops);

 	if (de)
 		de->d_inode->i_size = file_size;
 	return de;
 }
 EXPORT_SYMBOL_GPL(debugfs_create_file_size);

 /**
  * debugfs_create_dir - create a directory in the debugfs filesystem
  * @name: a pointer to a string containing the name of the directory to
  *        create.
  * @parent: a pointer to the parent dentry for this file.  This should be a
  *          directory dentry if set.  If this parameter is NULL, then the
  *          directory will be created in the root of the debugfs filesystem.
  *
  * This function creates a directory in debugfs with the given name.
  *
  * This function will return a pointer to a dentry if it succeeds.  This
  * pointer must be passed to the debugfs_remove() function when the file is
  * to be removed (no automatic cleanup happens if your module is unloaded,
  * you are responsible here.)  If an error occurs, %NULL will be returned.
  *
  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
  * returned.
  */
 struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
 {
 	struct dentry *dentry = start_creating(name, parent);
 	struct inode *inode;

 	if (IS_ERR(dentry))
 		return NULL;

 	inode = debugfs_get_inode(dentry->d_sb);
 	if (unlikely(!inode))
 		return failed_creating(dentry);

 	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
 	inode->i_op = &simple_dir_inode_operations;
 	inode->i_fop = &simple_dir_operations;

 	/* directory inodes start off with i_nlink == 2 (for "." entry) */
 	inc_nlink(inode);
 	d_instantiate(dentry, inode);
 	inc_nlink(dentry->d_parent->d_inode);
 	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
 	return end_creating(dentry);
 }
 EXPORT_SYMBOL_GPL(debugfs_create_dir);

 /**
  * debugfs_create_automount - create automount point in the debugfs filesystem
  * @name: a pointer to a string containing the name of the file to create.
  * @parent: a pointer to the parent dentry for this file.  This should be a
  *          directory dentry if set.  If this parameter is NULL, then the
  *          file will be created in the root of the debugfs filesystem.
  * @f: function to be called when pathname resolution steps on that one.
  * @data: opaque argument to pass to f().
  *
  * @f should return what ->d_automount() would.
  */
 struct dentry *debugfs_create_automount(const char *name,
 					struct dentry *parent,
 					struct vfsmount *(*f)(void *),
 					void *data)
 {
 	struct dentry *dentry = start_creating(name, parent);
 	struct inode *inode;

 	if (IS_ERR(dentry))
 		return NULL;

 	inode = debugfs_get_inode(dentry->d_sb);
 	if (unlikely(!inode))
 		return failed_creating(dentry);

 	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
 	inode->i_flags |= S_AUTOMOUNT;
 	inode->i_private = data;
 	dentry->d_fsdata = (void *)f;
 	d_instantiate(dentry, inode);
 	return end_creating(dentry);
 }
 EXPORT_SYMBOL(debugfs_create_automount);

 /**
  * debugfs_create_symlink- create a symbolic link in the debugfs filesystem
  * @name: a pointer to a string containing the name of the symbolic link to
  *        create.
  * @parent: a pointer to the parent dentry for this symbolic link.  This
  *          should be a directory dentry if set.  If this parameter is NULL,
  *          then the symbolic link will be created in the root of the debugfs
  *          filesystem.
  * @target: a pointer to a string containing the path to the target of the
  *          symbolic link.
  *
  * This function creates a symbolic link with the given name in debugfs that
  * links to the given target path.
  *
  * This function will return a pointer to a dentry if it succeeds.  This
  * pointer must be passed to the debugfs_remove() function when the symbolic
  * link is to be removed (no automatic cleanup happens if your module is
  * unloaded, you are responsible here.)  If an error occurs, %NULL will be
  * returned.
  *
  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
  * returned.
  */
 struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
 				      const char *target)
 {
 	struct dentry *dentry;
 	struct inode *inode;
 	char *link = kstrdup(target, GFP_KERNEL);
 	if (!link)
 		return NULL;

 	dentry = start_creating(name, parent);
 	if (IS_ERR(dentry)) {
 		kfree(link);
 		return NULL;
 	}

 	inode = debugfs_get_inode(dentry->d_sb);
 	if (unlikely(!inode)) {
 		kfree(link);
 		return failed_creating(dentry);
 	}
 	inode->i_mode = S_IFLNK | S_IRWXUGO;
 	inode->i_op = &debugfs_link_operations;
 	inode->i_private = link;
 	d_instantiate(dentry, inode);
 	return end_creating(dentry);
 }
 EXPORT_SYMBOL_GPL(debugfs_create_symlink);

 static int __debugfs_remove(struct dentry *dentry, struct dentry *parent)
 {
 	int ret = 0;

 	if (debugfs_positive(dentry)) {
 		if (dentry->d_inode) {
 			dget(dentry);
 			switch (dentry->d_inode->i_mode & S_IFMT) {
 			case S_IFDIR:
 				ret = simple_rmdir(parent->d_inode, dentry);
 				break;
 			case S_IFLNK:
 				kfree(dentry->d_inode->i_private);
 				/* fall through */
 			default:
 				simple_unlink(parent->d_inode, dentry);
 				break;
 			}
 			if (!ret)
 				d_delete(dentry);
 			dput(dentry);
 		}
 	}
 	return ret;
 }

 /**
  * debugfs_remove - removes a file or directory from the debugfs filesystem
  * @dentry: a pointer to a the dentry of the file or directory to be
  *          removed.
  *
  * This function removes a file or directory in debugfs that was previously
  * created with a call to another debugfs function (like
  * debugfs_create_file() or variants thereof.)
  *
  * This function is required to be called in order for the file to be
  * removed, no automatic cleanup of files will happen when a module is
  * removed, you are responsible here.
  */
 void debugfs_remove(struct dentry *dentry)
 {
 	struct dentry *parent;
 	int ret;

 	if (IS_ERR_OR_NULL(dentry))
 		return;

 	parent = dentry->d_parent;
 	if (!parent || !parent->d_inode)
 		return;

 	mutex_lock(&parent->d_inode->i_mutex);
 	ret = __debugfs_remove(dentry, parent);
 	mutex_unlock(&parent->d_inode->i_mutex);
 	if (!ret)
 		simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 }
 EXPORT_SYMBOL_GPL(debugfs_remove);

 /**
  * debugfs_remove_recursive - recursively removes a directory
  * @dentry: a pointer to a the dentry of the directory to be removed.
  *
  * This function recursively removes a directory tree in debugfs that
  * was previously created with a call to another debugfs function
  * (like debugfs_create_file() or variants thereof.)
  *
  * This function is required to be called in order for the file to be
  * removed, no automatic cleanup of files will happen when a module is
  * removed, you are responsible here.
  */
 void debugfs_remove_recursive(struct dentry *dentry)
 {
 	struct dentry *child, *parent;

 	if (IS_ERR_OR_NULL(dentry))
 		return;

 	parent = dentry->d_parent;
 	if (!parent || !parent->d_inode)
 		return;

 	parent = dentry;
  down:
 	mutex_lock(&parent->d_inode->i_mutex);
  loop:
 	/*
 	 * The parent->d_subdirs is protected by the d_lock. Outside that
 	 * lock, the child can be unlinked and set to be freed which can
 	 * use the d_u.d_child as the rcu head and corrupt this list.
 	 */
 	spin_lock(&parent->d_lock);
 	list_for_each_entry(child, &parent->d_subdirs, d_child) {
 		if (!debugfs_positive(child))
 			continue;

 		/* perhaps simple_empty(child) makes more sense */
 		if (!list_empty(&child->d_subdirs)) {
 			spin_unlock(&parent->d_lock);
 			mutex_unlock(&parent->d_inode->i_mutex);
 			parent = child;
 			goto down;
 		}

 		spin_unlock(&parent->d_lock);

 		if (!__debugfs_remove(child, parent))
 			simple_release_fs(&debugfs_mount, &debugfs_mount_count);

 		/*
 		 * The parent->d_lock protects agaist child from unlinking
 		 * from d_subdirs. When releasing the parent->d_lock we can
 		 * no longer trust that the next pointer is valid.
 		 * Restart the loop. We'll skip this one with the
 		 * debugfs_positive() check.
 		 */
 		goto loop;
 	}
 	spin_unlock(&parent->d_lock);

 	mutex_unlock(&parent->d_inode->i_mutex);
 	child = parent;
 	parent = parent->d_parent;
 	mutex_lock(&parent->d_inode->i_mutex);

 	if (child != dentry)
 		/* go up */
 		goto loop;

 	if (!__debugfs_remove(child, parent))
 		simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 	mutex_unlock(&parent->d_inode->i_mutex);
 }
 EXPORT_SYMBOL_GPL(debugfs_remove_recursive);

 /**
  * debugfs_rename - rename a file/directory in the debugfs filesystem
  * @old_dir: a pointer to the parent dentry for the renamed object. This
  *          should be a directory dentry.
  * @old_dentry: dentry of an object to be renamed.
  * @new_dir: a pointer to the parent dentry where the object should be
  *          moved. This should be a directory dentry.
  * @new_name: a pointer to a string containing the target name.
  *
  * This function renames a file/directory in debugfs.  The target must not
  * exist for rename to succeed.
  *
  * This function will return a pointer to old_dentry (which is updated to
  * reflect renaming) if it succeeds. If an error occurs, %NULL will be
  * returned.
  *
  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
  * returned.
  */
 struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
 		struct dentry *new_dir, const char *new_name)
 {
 	int error;
 	struct dentry *dentry = NULL, *trap;
 	const char *old_name;

 	trap = lock_rename(new_dir, old_dir);
 	/* Source or destination directories don't exist? */
 	if (!old_dir->d_inode || !new_dir->d_inode)
 		goto exit;
 	/* Source does not exist, cyclic rename, or mountpoint? */
 	if (!old_dentry->d_inode || old_dentry == trap ||
 	    d_mountpoint(old_dentry))
 		goto exit;
 	dentry = lookup_one_len(new_name, new_dir, strlen(new_name));
 	/* Lookup failed, cyclic rename or target exists? */
 	if (IS_ERR(dentry) || dentry == trap || dentry->d_inode)
 		goto exit;

 	old_name = fsnotify_oldname_init(old_dentry->d_name.name);

 	error = simple_rename(old_dir->d_inode, old_dentry, new_dir->d_inode,
 		dentry);
 	if (error) {
 		fsnotify_oldname_free(old_name);
 		goto exit;
 	}
 	d_move(old_dentry, dentry);
 	fsnotify_move(old_dir->d_inode, new_dir->d_inode, old_name,
 		S_ISDIR(old_dentry->d_inode->i_mode),
 		NULL, old_dentry);
 	fsnotify_oldname_free(old_name);
 	unlock_rename(new_dir, old_dir);
 	dput(dentry);
 	return old_dentry;
 exit:
 	if (dentry && !IS_ERR(dentry))
 		dput(dentry);
 	unlock_rename(new_dir, old_dir);
 	return NULL;
 }
 EXPORT_SYMBOL_GPL(debugfs_rename);

 /**
  * debugfs_initialized - Tells whether debugfs has been registered
  */
 bool debugfs_initialized(void)
 {
 	return debugfs_registered;
 }
 EXPORT_SYMBOL_GPL(debugfs_initialized);


 static struct kobject *debug_kobj;

 static int __init debugfs_init(void)
 {
 	int retval;

 	debug_kobj = kobject_create_and_add("debug", kernel_kobj);
 	if (!debug_kobj)
 		return -EINVAL;

 	retval = register_filesystem(&debug_fs_type);
 	if (retval)
 		kobject_put(debug_kobj);
 	else
 		debugfs_registered = true;

 	return retval;
 }
 core_initcall(debugfs_init);
	/*
	* inode.c - part of debugfs, a tiny little debug file system
	*
	* Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
	* Copyright (C) 2004 IBM Inc.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License version
	* 2 as published by the Free Software Foundation.
	*
	* debugfs is for people to use instead of /proc or /sys.
	* See Documentation/DocBook/kernel-api for more details.
	*
	*/

	#include <linux/module.h>
	#include <linux/fs.h>
	#include <linux/mount.h>
	#include <linux/pagemap.h>
	#include <linux/init.h>
	#include <linux/kobject.h>
	#include <linux/namei.h>
	#include <linux/debugfs.h>
	#include <linux/fsnotify.h>
	#include <linux/string.h>
	#include <linux/seq_file.h>
	#include <linux/parser.h>
	#include <linux/magic.h>
	#include <linux/slab.h>

	#define DEBUGFS_DEFAULT_MODE 0700

	static struct vfsmount *debugfs_mount;
	static int debugfs_mount_count;
	static bool debugfs_registered;

	static struct inode debugfs_get_inode(struct super_block sb)
	{
	struct inode *inode = new_inode(sb);
	if (inode) {
	inode->i_ino = get_next_ino();
	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
	}
	return inode;
	}

	static inline int debugfs_positive(struct dentry *dentry)
	{
	return dentry->d_inode && !d_unhashed(dentry);
	}

	struct debugfs_mount_opts {
	kuid_t uid;
	kgid_t gid;
	umode_t mode;
	};

	enum {
	Opt_uid,
	Opt_gid,
	Opt_mode,
	Opt_err
	};

	static const match_table_t tokens = {
	{Opt_uid, "uid=%u"},
	{Opt_gid, "gid=%u"},
	{Opt_mode, "mode=%o"},
	{Opt_err, NULL}
	};

	struct debugfs_fs_info {
	struct debugfs_mount_opts mount_opts;
	};

	static int debugfs_parse_options(char data, struct debugfs_mount_opts opts)
	{
	substring_t args[MAX_OPT_ARGS];
	int option;
	int token;
	kuid_t uid;
	kgid_t gid;
	char *p;

	opts->mode = DEBUGFS_DEFAULT_MODE;

	while ((p = strsep(&data, ",")) != NULL) {
	if (!*p)
	continue;

	token = match_token(p, tokens, args);
	switch (token) {
	case Opt_uid:
	if (match_int(&args[0], &option))
	return -EINVAL;
	uid = make_kuid(current_user_ns(), option);
	if (!uid_valid(uid))
	return -EINVAL;
	opts->uid = uid;
	break;
	case Opt_gid:
	if (match_int(&args[0], &option))
	return -EINVAL;
	gid = make_kgid(current_user_ns(), option);
	if (!gid_valid(gid))
	return -EINVAL;
	opts->gid = gid;
	break;
	case Opt_mode:
	if (match_octal(&args[0], &option))
	return -EINVAL;
	opts->mode = option & S_IALLUGO;
	break;
	/*
	* We might like to report bad mount options here;
	* but traditionally debugfs has ignored all mount options
	*/
	}
	}

	return 0;
	}

	static int debugfs_apply_options(struct super_block *sb)
	{
	struct debugfs_fs_info *fsi = sb->s_fs_info;
	struct inode *inode = sb->s_root->d_inode;
	struct debugfs_mount_opts *opts = &fsi->mount_opts;

	inode->i_mode &= ~S_IALLUGO;
	inode->i_mode \|= opts->mode;

	inode->i_uid = opts->uid;
	inode->i_gid = opts->gid;

	return 0;
	}

	static int debugfs_remount(struct super_block sb, int flags, char *data)
	{
	int err;
	struct debugfs_fs_info *fsi = sb->s_fs_info;

	sync_filesystem(sb);
	err = debugfs_parse_options(data, &fsi->mount_opts);
	if (err)
	goto fail;

	debugfs_apply_options(sb);

	fail:
	return err;
	}

	static int debugfs_show_options(struct seq_file m, struct dentry root)
	{
	struct debugfs_fs_info *fsi = root->d_sb->s_fs_info;
	struct debugfs_mount_opts *opts = &fsi->mount_opts;

	if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
	seq_printf(m, ",uid=%u",
	from_kuid_munged(&init_user_ns, opts->uid));
	if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
	seq_printf(m, ",gid=%u",
	from_kgid_munged(&init_user_ns, opts->gid));
	if (opts->mode != DEBUGFS_DEFAULT_MODE)
	seq_printf(m, ",mode=%o", opts->mode);

	return 0;
	}

	static const struct super_operations debugfs_super_operations = {
	.statfs = simple_statfs,
	.remount_fs = debugfs_remount,
	.show_options = debugfs_show_options,
	};

	static struct vfsmount debugfs_automount(struct path path)
	{
	struct vfsmount (f)(void *);
	f = (struct vfsmount ()(void *))path->dentry->d_fsdata;
	return f(path->dentry->d_inode->i_private);
	}

	static const struct dentry_operations debugfs_dops = {
	.d_delete = always_delete_dentry,
	.d_automount = debugfs_automount,
	};

	static int debug_fill_super(struct super_block sb, void data, int silent)
	{
	static struct tree_descr debug_files[] = {{""}};
	struct debugfs_fs_info *fsi;
	int err;

	save_mount_options(sb, data);

	fsi = kzalloc(sizeof(struct debugfs_fs_info), GFP_KERNEL);
	sb->s_fs_info = fsi;
	if (!fsi) {
	err = -ENOMEM;
	goto fail;
	}

	err = debugfs_parse_options(data, &fsi->mount_opts);
	if (err)
	goto fail;

	err = simple_fill_super(sb, DEBUGFS_MAGIC, debug_files);
	if (err)
	goto fail;

	sb->s_op = &debugfs_super_operations;
	sb->s_d_op = &debugfs_dops;

	debugfs_apply_options(sb);

	return 0;

	fail:
	kfree(fsi);
	sb->s_fs_info = NULL;
	return err;
	}

	static struct dentry debug_mount(struct file_system_type fs_type,
	int flags, const char *dev_name,
	void *data)
	{
	return mount_single(fs_type, flags, data, debug_fill_super);
	}

	static struct file_system_type debug_fs_type = {
	.owner = THIS_MODULE,
	.name = "debugfs",
	.mount = debug_mount,
	.kill_sb = kill_litter_super,
	};
	MODULE_ALIAS_FS("debugfs");

	static struct dentry start_creating(const char name, struct dentry *parent)
	{
	struct dentry *dentry;
	int error;

	pr_debug("debugfs: creating file '%s'\n",name);

	error = simple_pin_fs(&debug_fs_type, &debugfs_mount,
	&debugfs_mount_count);
	if (error)
	return ERR_PTR(error);

	/* If the parent is not specified, we create it in the root.
	* We need the root dentry to do this, which is in the super
	* block. A pointer to that is in the struct vfsmount that we
	* have around.
	*/
	if (!parent)
	parent = debugfs_mount->mnt_root;

	mutex_lock(&parent->d_inode->i_mutex);
	dentry = lookup_one_len(name, parent, strlen(name));
	if (!IS_ERR(dentry) && dentry->d_inode) {
	dput(dentry);
	dentry = ERR_PTR(-EEXIST);
	}
	if (IS_ERR(dentry))
	mutex_unlock(&parent->d_inode->i_mutex);
	return dentry;
	}

	static struct dentry failed_creating(struct dentry dentry)
	{
	mutex_unlock(&dentry->d_parent->d_inode->i_mutex);
	dput(dentry);
	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
	return NULL;
	}

	static struct dentry end_creating(struct dentry dentry)
	{
	mutex_unlock(&dentry->d_parent->d_inode->i_mutex);
	return dentry;
	}

	/**
	* debugfs_create_file - create a file in the debugfs filesystem
	* @name: a pointer to a string containing the name of the file to create.
	* @mode: the permission that the file should have.
	* @parent: a pointer to the parent dentry for this file. This should be a
	* directory dentry if set. If this parameter is NULL, then the
	* file will be created in the root of the debugfs filesystem.
	* @data: a pointer to something that the caller will want to get to later
	* on. The inode.i_private pointer will point to this value on
	* the open() call.
	* @fops: a pointer to a struct file_operations that should be used for
	* this file.
	*
	* This is the basic "create a file" function for debugfs. It allows for a
	* wide range of flexibility in creating a file, or a directory (if you want
	* to create a directory, the debugfs_create_dir() function is
	* recommended to be used instead.)
	*
	* This function will return a pointer to a dentry if it succeeds. This
	* pointer must be passed to the debugfs_remove() function when the file is
	* to be removed (no automatic cleanup happens if your module is unloaded,
	* you are responsible here.) If an error occurs, %NULL will be returned.
	*
	* If debugfs is not enabled in the kernel, the value -%ENODEV will be
	* returned.
	*/
	struct dentry debugfs_create_file(const char name, umode_t mode,
	struct dentry parent, void data,
	const struct file_operations *fops)
	{
	struct dentry *dentry;
	struct inode *inode;

	if (!(mode & S_IFMT))
	mode \|= S_IFREG;
	BUG_ON(!S_ISREG(mode));
	dentry = start_creating(name, parent);

	if (IS_ERR(dentry))
	return NULL;

	inode = debugfs_get_inode(dentry->d_sb);
	if (unlikely(!inode))
	return failed_creating(dentry);

	inode->i_mode = mode;
	inode->i_fop = fops ? fops : &debugfs_file_operations;
	inode->i_private = data;
	d_instantiate(dentry, inode);
	fsnotify_create(dentry->d_parent->d_inode, dentry);
	return end_creating(dentry);
	}
	EXPORT_SYMBOL_GPL(debugfs_create_file);

	/**
	* debugfs_create_file_size - create a file in the debugfs filesystem
	* @name: a pointer to a string containing the name of the file to create.
	* @mode: the permission that the file should have.
	* @parent: a pointer to the parent dentry for this file. This should be a
	* directory dentry if set. If this parameter is NULL, then the
	* file will be created in the root of the debugfs filesystem.
	* @data: a pointer to something that the caller will want to get to later
	* on. The inode.i_private pointer will point to this value on
	* the open() call.
	* @fops: a pointer to a struct file_operations that should be used for
	* this file.
	* @file_size: initial file size
	*
	* This is the basic "create a file" function for debugfs. It allows for a
	* wide range of flexibility in creating a file, or a directory (if you want
	* to create a directory, the debugfs_create_dir() function is
	* recommended to be used instead.)
	*
	* This function will return a pointer to a dentry if it succeeds. This
	* pointer must be passed to the debugfs_remove() function when the file is
	* to be removed (no automatic cleanup happens if your module is unloaded,
	* you are responsible here.) If an error occurs, %NULL will be returned.
	*
	* If debugfs is not enabled in the kernel, the value -%ENODEV will be
	* returned.
	*/
	struct dentry debugfs_create_file_size(const char name, umode_t mode,
	struct dentry parent, void data,
	const struct file_operations *fops,
	loff_t file_size)
	{
	struct dentry *de = debugfs_create_file(name, mode, parent, data, fops);

	if (de)
	de->d_inode->i_size = file_size;
	return de;
	}
	EXPORT_SYMBOL_GPL(debugfs_create_file_size);

	/**
	* debugfs_create_dir - create a directory in the debugfs filesystem
	* @name: a pointer to a string containing the name of the directory to
	* create.
	* @parent: a pointer to the parent dentry for this file. This should be a
	* directory dentry if set. If this parameter is NULL, then the
	* directory will be created in the root of the debugfs filesystem.
	*
	* This function creates a directory in debugfs with the given name.
	*
	* This function will return a pointer to a dentry if it succeeds. This
	* pointer must be passed to the debugfs_remove() function when the file is
	* to be removed (no automatic cleanup happens if your module is unloaded,
	* you are responsible here.) If an error occurs, %NULL will be returned.
	*
	* If debugfs is not enabled in the kernel, the value -%ENODEV will be
	* returned.
	*/
	struct dentry debugfs_create_dir(const char name, struct dentry *parent)
	{
	struct dentry *dentry = start_creating(name, parent);
	struct inode *inode;

	if (IS_ERR(dentry))
	return NULL;

	inode = debugfs_get_inode(dentry->d_sb);
	if (unlikely(!inode))
	return failed_creating(dentry);

	inode->i_mode = S_IFDIR \| S_IRWXU \| S_IRUGO \| S_IXUGO;
	inode->i_op = &simple_dir_inode_operations;
	inode->i_fop = &simple_dir_operations;

	/* directory inodes start off with i_nlink == 2 (for "." entry) */
	inc_nlink(inode);
	d_instantiate(dentry, inode);
	inc_nlink(dentry->d_parent->d_inode);
	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
	return end_creating(dentry);
	}
	EXPORT_SYMBOL_GPL(debugfs_create_dir);

	/**
	* debugfs_create_automount - create automount point in the debugfs filesystem
	* @name: a pointer to a string containing the name of the file to create.
	* @parent: a pointer to the parent dentry for this file. This should be a
	* directory dentry if set. If this parameter is NULL, then the
	* file will be created in the root of the debugfs filesystem.
	* @f: function to be called when pathname resolution steps on that one.
	* @data: opaque argument to pass to f().
	*
	* @f should return what ->d_automount() would.
	*/
	struct dentry debugfs_create_automount(const char name,
	struct dentry *parent,
	struct vfsmount (f)(void *),
	void *data)
	{
	struct dentry *dentry = start_creating(name, parent);
	struct inode *inode;

	if (IS_ERR(dentry))
	return NULL;

	inode = debugfs_get_inode(dentry->d_sb);
	if (unlikely(!inode))
	return failed_creating(dentry);

	inode->i_mode = S_IFDIR \| S_IRWXU \| S_IRUGO \| S_IXUGO;
	inode->i_flags \|= S_AUTOMOUNT;
	inode->i_private = data;
	dentry->d_fsdata = (void *)f;
	d_instantiate(dentry, inode);
	return end_creating(dentry);
	}
	EXPORT_SYMBOL(debugfs_create_automount);

	/**
	* debugfs_create_symlink- create a symbolic link in the debugfs filesystem
	* @name: a pointer to a string containing the name of the symbolic link to
	* create.
	* @parent: a pointer to the parent dentry for this symbolic link. This
	* should be a directory dentry if set. If this parameter is NULL,
	* then the symbolic link will be created in the root of the debugfs
	* filesystem.
	* @target: a pointer to a string containing the path to the target of the
	* symbolic link.
	*
	* This function creates a symbolic link with the given name in debugfs that
	* links to the given target path.
	*
	* This function will return a pointer to a dentry if it succeeds. This
	* pointer must be passed to the debugfs_remove() function when the symbolic
	* link is to be removed (no automatic cleanup happens if your module is
	* unloaded, you are responsible here.) If an error occurs, %NULL will be
	* returned.
	*
	* If debugfs is not enabled in the kernel, the value -%ENODEV will be
	* returned.
	*/
	struct dentry debugfs_create_symlink(const char name, struct dentry *parent,
	const char *target)
	{
	struct dentry *dentry;
	struct inode *inode;
	char *link = kstrdup(target, GFP_KERNEL);
	if (!link)
	return NULL;

	dentry = start_creating(name, parent);
	if (IS_ERR(dentry)) {
	kfree(link);
	return NULL;
	}

	inode = debugfs_get_inode(dentry->d_sb);
	if (unlikely(!inode)) {
	kfree(link);
	return failed_creating(dentry);
	}
	inode->i_mode = S_IFLNK \| S_IRWXUGO;
	inode->i_op = &debugfs_link_operations;
	inode->i_private = link;
	d_instantiate(dentry, inode);
	return end_creating(dentry);
	}
	EXPORT_SYMBOL_GPL(debugfs_create_symlink);

	static int __debugfs_remove(struct dentry dentry, struct dentry parent)
	{
	int ret = 0;

	if (debugfs_positive(dentry)) {
	if (dentry->d_inode) {
	dget(dentry);
	switch (dentry->d_inode->i_mode & S_IFMT) {
	case S_IFDIR:
	ret = simple_rmdir(parent->d_inode, dentry);
	break;
	case S_IFLNK:
	kfree(dentry->d_inode->i_private);
	/* fall through */
	default:
	simple_unlink(parent->d_inode, dentry);
	break;
	}
	if (!ret)
	d_delete(dentry);
	dput(dentry);
	}
	}
	return ret;
	}

	/**
	* debugfs_remove - removes a file or directory from the debugfs filesystem
	* @dentry: a pointer to a the dentry of the file or directory to be
	* removed.
	*
	* This function removes a file or directory in debugfs that was previously
	* created with a call to another debugfs function (like
	* debugfs_create_file() or variants thereof.)
	*
	* This function is required to be called in order for the file to be
	* removed, no automatic cleanup of files will happen when a module is
	* removed, you are responsible here.
	*/
	void debugfs_remove(struct dentry *dentry)
	{
	struct dentry *parent;
	int ret;

	if (IS_ERR_OR_NULL(dentry))
	return;

	parent = dentry->d_parent;
	if (!parent \|\| !parent->d_inode)
	return;

	mutex_lock(&parent->d_inode->i_mutex);
	ret = __debugfs_remove(dentry, parent);
	mutex_unlock(&parent->d_inode->i_mutex);
	if (!ret)
	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
	}
	EXPORT_SYMBOL_GPL(debugfs_remove);

	/**
	* debugfs_remove_recursive - recursively removes a directory
	* @dentry: a pointer to a the dentry of the directory to be removed.
	*
	* This function recursively removes a directory tree in debugfs that
	* was previously created with a call to another debugfs function
	* (like debugfs_create_file() or variants thereof.)
	*
	* This function is required to be called in order for the file to be
	* removed, no automatic cleanup of files will happen when a module is
	* removed, you are responsible here.
	*/
	void debugfs_remove_recursive(struct dentry *dentry)
	{
	struct dentry child, parent;

	if (IS_ERR_OR_NULL(dentry))
	return;

	parent = dentry->d_parent;
	if (!parent \|\| !parent->d_inode)
	return;

	parent = dentry;
	down:
	mutex_lock(&parent->d_inode->i_mutex);
	loop:
	/*
	* The parent->d_subdirs is protected by the d_lock. Outside that
	* lock, the child can be unlinked and set to be freed which can
	* use the d_u.d_child as the rcu head and corrupt this list.
	*/
	spin_lock(&parent->d_lock);
	list_for_each_entry(child, &parent->d_subdirs, d_child) {
	if (!debugfs_positive(child))
	continue;

	/* perhaps simple_empty(child) makes more sense */
	if (!list_empty(&child->d_subdirs)) {
	spin_unlock(&parent->d_lock);
	mutex_unlock(&parent->d_inode->i_mutex);
	parent = child;
	goto down;
	}

	spin_unlock(&parent->d_lock);

	if (!__debugfs_remove(child, parent))
	simple_release_fs(&debugfs_mount, &debugfs_mount_count);

	/*
	* The parent->d_lock protects agaist child from unlinking
	* from d_subdirs. When releasing the parent->d_lock we can
	* no longer trust that the next pointer is valid.
	* Restart the loop. We'll skip this one with the
	* debugfs_positive() check.
	*/
	goto loop;
	}
	spin_unlock(&parent->d_lock);

	mutex_unlock(&parent->d_inode->i_mutex);
	child = parent;
	parent = parent->d_parent;
	mutex_lock(&parent->d_inode->i_mutex);

	if (child != dentry)
	/* go up */
	goto loop;

	if (!__debugfs_remove(child, parent))
	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
	mutex_unlock(&parent->d_inode->i_mutex);
	}
	EXPORT_SYMBOL_GPL(debugfs_remove_recursive);

	/**
	* debugfs_rename - rename a file/directory in the debugfs filesystem
	* @old_dir: a pointer to the parent dentry for the renamed object. This
	* should be a directory dentry.
	* @old_dentry: dentry of an object to be renamed.
	* @new_dir: a pointer to the parent dentry where the object should be
	* moved. This should be a directory dentry.
	* @new_name: a pointer to a string containing the target name.
	*
	* This function renames a file/directory in debugfs. The target must not
	* exist for rename to succeed.
	*
	* This function will return a pointer to old_dentry (which is updated to
	* reflect renaming) if it succeeds. If an error occurs, %NULL will be
	* returned.
	*
	* If debugfs is not enabled in the kernel, the value -%ENODEV will be
	* returned.
	*/
	struct dentry debugfs_rename(struct dentry old_dir, struct dentry *old_dentry,
	struct dentry new_dir, const char new_name)
	{
	int error;
	struct dentry dentry = NULL, trap;
	const char *old_name;

	trap = lock_rename(new_dir, old_dir);
	/* Source or destination directories don't exist? */
	if (!old_dir->d_inode \|\| !new_dir->d_inode)
	goto exit;
	/* Source does not exist, cyclic rename, or mountpoint? */
	if (!old_dentry->d_inode \|\| old_dentry == trap \|\|
	d_mountpoint(old_dentry))
	goto exit;
	dentry = lookup_one_len(new_name, new_dir, strlen(new_name));
	/* Lookup failed, cyclic rename or target exists? */
	if (IS_ERR(dentry) \|\| dentry == trap \|\| dentry->d_inode)
	goto exit;

	old_name = fsnotify_oldname_init(old_dentry->d_name.name);

	error = simple_rename(old_dir->d_inode, old_dentry, new_dir->d_inode,
	dentry);
	if (error) {
	fsnotify_oldname_free(old_name);
	goto exit;
	}
	d_move(old_dentry, dentry);
	fsnotify_move(old_dir->d_inode, new_dir->d_inode, old_name,
	S_ISDIR(old_dentry->d_inode->i_mode),
	NULL, old_dentry);
	fsnotify_oldname_free(old_name);
	unlock_rename(new_dir, old_dir);
	dput(dentry);
	return old_dentry;
	exit:
	if (dentry && !IS_ERR(dentry))
	dput(dentry);
	unlock_rename(new_dir, old_dir);
	return NULL;
	}
	EXPORT_SYMBOL_GPL(debugfs_rename);

	/**
	* debugfs_initialized - Tells whether debugfs has been registered
	*/
	bool debugfs_initialized(void)
	{
	return debugfs_registered;
	}
	EXPORT_SYMBOL_GPL(debugfs_initialized);


	static struct kobject *debug_kobj;

	static int __init debugfs_init(void)
	{
	int retval;

	debug_kobj = kobject_create_and_add("debug", kernel_kobj);
	if (!debug_kobj)
	return -EINVAL;

	retval = register_filesystem(&debug_fs_type);
	if (retval)
	kobject_put(debug_kobj);
	else
	debugfs_registered = true;

	return retval;
	}
	core_initcall(debugfs_init);