1 files changed, 827 insertions, 0 deletions

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
new file mode 100644
index 000000000000..d9d8932a7b9c
--- /dev/null
+++ b/fs/tracefs/inode.c
@@ -0,0 +1,827 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  inode.c - part of tracefs, a pseudo file system for activating tracing
+ *
+ * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
+ *
+ *  Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
+ *
+ * tracefs is the file system that is used by the tracing infrastructure.
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
+#include <linux/kobject.h>
+#include <linux/namei.h>
+#include <linux/tracefs.h>
+#include <linux/fsnotify.h>
+#include <linux/security.h>
+#include <linux/seq_file.h>
+#include <linux/magic.h>
+#include <linux/slab.h>
+#include "internal.h"
+
+#define TRACEFS_DEFAULT_MODE	0700
+static struct kmem_cache *tracefs_inode_cachep __ro_after_init;
+
+static struct vfsmount *tracefs_mount;
+static int tracefs_mount_count;
+static bool tracefs_registered;
+
+/*
+ * Keep track of all tracefs_inodes in order to update their
+ * flags if necessary on a remount.
+ */
+static DEFINE_SPINLOCK(tracefs_inode_lock);
+static LIST_HEAD(tracefs_inodes);
+
+static struct inode *tracefs_alloc_inode(struct super_block *sb)
+{
+	struct tracefs_inode *ti;
+	unsigned long flags;
+
+	ti = alloc_inode_sb(sb, tracefs_inode_cachep, GFP_KERNEL);
+	if (!ti)
+		return NULL;
+
+	spin_lock_irqsave(&tracefs_inode_lock, flags);
+	list_add_rcu(&ti->list, &tracefs_inodes);
+	spin_unlock_irqrestore(&tracefs_inode_lock, flags);
+
+	return &ti->vfs_inode;
+}
+
+static void tracefs_free_inode(struct inode *inode)
+{
+	struct tracefs_inode *ti = get_tracefs(inode);
+
+	kmem_cache_free(tracefs_inode_cachep, ti);
+}
+
+static void tracefs_destroy_inode(struct inode *inode)
+{
+	struct tracefs_inode *ti = get_tracefs(inode);
+	unsigned long flags;
+
+	spin_lock_irqsave(&tracefs_inode_lock, flags);
+	list_del_rcu(&ti->list);
+	spin_unlock_irqrestore(&tracefs_inode_lock, flags);
+}
+
+static ssize_t default_read_file(struct file *file, char __user *buf,
+				 size_t count, loff_t *ppos)
+{
+	return 0;
+}
+
+static ssize_t default_write_file(struct file *file, const char __user *buf,
+				   size_t count, loff_t *ppos)
+{
+	return count;
+}
+
+static const struct file_operations tracefs_file_operations = {
+	.read =		default_read_file,
+	.write =	default_write_file,
+	.open =		simple_open,
+	.llseek =	noop_llseek,
+};
+
+static struct tracefs_dir_ops {
+	int (*mkdir)(const char *name);
+	int (*rmdir)(const char *name);
+} tracefs_ops __ro_after_init;
+
+static char *get_dname(struct dentry *dentry)
+{
+	const char *dname;
+	char *name;
+	int len = dentry->d_name.len;
+
+	dname = dentry->d_name.name;
+	name = kmalloc(len + 1, GFP_KERNEL);
+	if (!name)
+		return NULL;
+	memcpy(name, dname, len);
+	name[len] = 0;
+	return name;
+}
+
+static struct dentry *tracefs_syscall_mkdir(struct mnt_idmap *idmap,
+					    struct inode *inode, struct dentry *dentry,
+					    umode_t mode)
+{
+	struct tracefs_inode *ti;
+	char *name;
+	int ret;
+
+	name = get_dname(dentry);
+	if (!name)
+		return ERR_PTR(-ENOMEM);
+
+	/*
+	 * This is a new directory that does not take the default of
+	 * the rootfs. It becomes the default permissions for all the
+	 * files and directories underneath it.
+	 */
+	ti = get_tracefs(inode);
+	ti->flags |= TRACEFS_INSTANCE_INODE;
+	ti->private = inode;
+
+	/*
+	 * The mkdir call can call the generic functions that create
+	 * the files within the tracefs system. It is up to the individual
+	 * mkdir routine to handle races.
+	 */
+	inode_unlock(inode);
+	ret = tracefs_ops.mkdir(name);
+	inode_lock(inode);
+
+	kfree(name);
+
+	return ERR_PTR(ret);
+}
+
+static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
+{
+	char *name;
+	int ret;
+
+	name = get_dname(dentry);
+	if (!name)
+		return -ENOMEM;
+
+	/*
+	 * The rmdir call can call the generic functions that create
+	 * the files within the tracefs system. It is up to the individual
+	 * rmdir routine to handle races.
+	 * This time we need to unlock not only the parent (inode) but
+	 * also the directory that is being deleted.
+	 */
+	inode_unlock(inode);
+	inode_unlock(d_inode(dentry));
+
+	ret = tracefs_ops.rmdir(name);
+
+	inode_lock_nested(inode, I_MUTEX_PARENT);
+	inode_lock(d_inode(dentry));
+
+	kfree(name);
+
+	return ret;
+}
+
+static void set_tracefs_inode_owner(struct inode *inode)
+{
+	struct tracefs_inode *ti = get_tracefs(inode);
+	struct inode *root_inode = ti->private;
+	kuid_t uid;
+	kgid_t gid;
+
+	uid = root_inode->i_uid;
+	gid = root_inode->i_gid;
+
+	/*
+	 * If the root is not the mount point, then check the root's
+	 * permissions. If it was never set, then default to the
+	 * mount point.
+	 */
+	if (root_inode != d_inode(root_inode->i_sb->s_root)) {
+		struct tracefs_inode *rti;
+
+		rti = get_tracefs(root_inode);
+		root_inode = d_inode(root_inode->i_sb->s_root);
+
+		if (!(rti->flags & TRACEFS_UID_PERM_SET))
+			uid = root_inode->i_uid;
+
+		if (!(rti->flags & TRACEFS_GID_PERM_SET))
+			gid = root_inode->i_gid;
+	}
+
+	/*
+	 * If this inode has never been referenced, then update
+	 * the permissions to the superblock.
+	 */
+	if (!(ti->flags & TRACEFS_UID_PERM_SET))
+		inode->i_uid = uid;
+
+	if (!(ti->flags & TRACEFS_GID_PERM_SET))
+		inode->i_gid = gid;
+}
+
+static int tracefs_permission(struct mnt_idmap *idmap,
+			      struct inode *inode, int mask)
+{
+	set_tracefs_inode_owner(inode);
+	return generic_permission(idmap, inode, mask);
+}
+
+static int tracefs_getattr(struct mnt_idmap *idmap,
+			   const struct path *path, struct kstat *stat,
+			   u32 request_mask, unsigned int flags)
+{
+	struct inode *inode = d_backing_inode(path->dentry);
+
+	set_tracefs_inode_owner(inode);
+	generic_fillattr(idmap, request_mask, inode, stat);
+	return 0;
+}
+
+static int tracefs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+			   struct iattr *attr)
+{
+	unsigned int ia_valid = attr->ia_valid;
+	struct inode *inode = d_inode(dentry);
+	struct tracefs_inode *ti = get_tracefs(inode);
+
+	if (ia_valid & ATTR_UID)
+		ti->flags |= TRACEFS_UID_PERM_SET;
+
+	if (ia_valid & ATTR_GID)
+		ti->flags |= TRACEFS_GID_PERM_SET;
+
+	return simple_setattr(idmap, dentry, attr);
+}
+
+static const struct inode_operations tracefs_instance_dir_inode_operations = {
+	.lookup		= simple_lookup,
+	.mkdir		= tracefs_syscall_mkdir,
+	.rmdir		= tracefs_syscall_rmdir,
+	.permission	= tracefs_permission,
+	.getattr	= tracefs_getattr,
+	.setattr	= tracefs_setattr,
+};
+
+static const struct inode_operations tracefs_dir_inode_operations = {
+	.lookup		= simple_lookup,
+	.permission	= tracefs_permission,
+	.getattr	= tracefs_getattr,
+	.setattr	= tracefs_setattr,
+};
+
+static const struct inode_operations tracefs_file_inode_operations = {
+	.permission	= tracefs_permission,
+	.getattr	= tracefs_getattr,
+	.setattr	= tracefs_setattr,
+};
+
+struct inode *tracefs_get_inode(struct super_block *sb)
+{
+	struct inode *inode = new_inode(sb);
+	if (inode) {
+		inode->i_ino = get_next_ino();
+		simple_inode_init_ts(inode);
+	}
+	return inode;
+}
+
+struct tracefs_fs_info {
+	kuid_t uid;
+	kgid_t gid;
+	umode_t mode;
+	/* Opt_* bitfield. */
+	unsigned int opts;
+};
+
+enum {
+	Opt_uid,
+	Opt_gid,
+	Opt_mode,
+};
+
+static const struct fs_parameter_spec tracefs_param_specs[] = {
+	fsparam_gid	("gid",		Opt_gid),
+	fsparam_u32oct	("mode",	Opt_mode),
+	fsparam_uid	("uid",		Opt_uid),
+	{}
+};
+
+static int tracefs_parse_param(struct fs_context *fc, struct fs_parameter *param)
+{
+	struct tracefs_fs_info *opts = fc->s_fs_info;
+	struct fs_parse_result result;
+	int opt;
+
+	opt = fs_parse(fc, tracefs_param_specs, param, &result);
+	if (opt < 0)
+		return opt;
+
+	switch (opt) {
+	case Opt_uid:
+		opts->uid = result.uid;
+		break;
+	case Opt_gid:
+		opts->gid = result.gid;
+		break;
+	case Opt_mode:
+		opts->mode = result.uint_32 & S_IALLUGO;
+		break;
+	/*
+	 * We might like to report bad mount options here;
+	 * but traditionally tracefs has ignored all mount options
+	 */
+	}
+
+	opts->opts |= BIT(opt);
+
+	return 0;
+}
+
+static int tracefs_apply_options(struct super_block *sb, bool remount)
+{
+	struct tracefs_fs_info *fsi = sb->s_fs_info;
+	struct inode *inode = d_inode(sb->s_root);
+	struct tracefs_inode *ti;
+	bool update_uid, update_gid;
+	umode_t tmp_mode;
+
+	/*
+	 * On remount, only reset mode/uid/gid if they were provided as mount
+	 * options.
+	 */
+
+	if (!remount || fsi->opts & BIT(Opt_mode)) {
+		tmp_mode = READ_ONCE(inode->i_mode) & ~S_IALLUGO;
+		tmp_mode |= fsi->mode;
+		WRITE_ONCE(inode->i_mode, tmp_mode);
+	}
+
+	if (!remount || fsi->opts & BIT(Opt_uid))
+		inode->i_uid = fsi->uid;
+
+	if (!remount || fsi->opts & BIT(Opt_gid))
+		inode->i_gid = fsi->gid;
+
+	if (remount && (fsi->opts & BIT(Opt_uid) || fsi->opts & BIT(Opt_gid))) {
+
+		update_uid = fsi->opts & BIT(Opt_uid);
+		update_gid = fsi->opts & BIT(Opt_gid);
+
+		rcu_read_lock();
+		list_for_each_entry_rcu(ti, &tracefs_inodes, list) {
+			if (update_uid) {
+				ti->flags &= ~TRACEFS_UID_PERM_SET;
+				ti->vfs_inode.i_uid = fsi->uid;
+			}
+
+			if (update_gid) {
+				ti->flags &= ~TRACEFS_GID_PERM_SET;
+				ti->vfs_inode.i_gid = fsi->gid;
+			}
+
+			/*
+			 * Note, the above ti->vfs_inode updates are
+			 * used in eventfs_remount() so they must come
+			 * before calling it.
+			 */
+			if (ti->flags & TRACEFS_EVENT_INODE)
+				eventfs_remount(ti, update_uid, update_gid);
+		}
+		rcu_read_unlock();
+	}
+
+	return 0;
+}
+
+static int tracefs_reconfigure(struct fs_context *fc)
+{
+	struct super_block *sb = fc->root->d_sb;
+	struct tracefs_fs_info *sb_opts = sb->s_fs_info;
+	struct tracefs_fs_info *new_opts = fc->s_fs_info;
+
+	if (!new_opts)
+		return 0;
+
+	sync_filesystem(sb);
+	/* structure copy of new mount options to sb */
+	*sb_opts = *new_opts;
+
+	return tracefs_apply_options(sb, true);
+}
+
+static int tracefs_show_options(struct seq_file *m, struct dentry *root)
+{
+	struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
+
+	if (!uid_eq(fsi->uid, GLOBAL_ROOT_UID))
+		seq_printf(m, ",uid=%u",
+			   from_kuid_munged(&init_user_ns, fsi->uid));
+	if (!gid_eq(fsi->gid, GLOBAL_ROOT_GID))
+		seq_printf(m, ",gid=%u",
+			   from_kgid_munged(&init_user_ns, fsi->gid));
+	if (fsi->mode != TRACEFS_DEFAULT_MODE)
+		seq_printf(m, ",mode=%o", fsi->mode);
+
+	return 0;
+}
+
+static int tracefs_drop_inode(struct inode *inode)
+{
+	struct tracefs_inode *ti = get_tracefs(inode);
+
+	/*
+	 * This inode is being freed and cannot be used for
+	 * eventfs. Clear the flag so that it doesn't call into
+	 * eventfs during the remount flag updates. The eventfs_inode
+	 * gets freed after an RCU cycle, so the content will still
+	 * be safe if the iteration is going on now.
+	 */
+	ti->flags &= ~TRACEFS_EVENT_INODE;
+
+	return 1;
+}
+
+static const struct super_operations tracefs_super_operations = {
+	.alloc_inode    = tracefs_alloc_inode,
+	.free_inode     = tracefs_free_inode,
+	.destroy_inode  = tracefs_destroy_inode,
+	.drop_inode     = tracefs_drop_inode,
+	.statfs		= simple_statfs,
+	.show_options	= tracefs_show_options,
+};
+
+/*
+ * It would be cleaner if eventfs had its own dentry ops.
+ *
+ * Note that d_revalidate is called potentially under RCU,
+ * so it can't take the eventfs mutex etc. It's fine - if
+ * we open a file just as it's marked dead, things will
+ * still work just fine, and just see the old stale case.
+ */
+static void tracefs_d_release(struct dentry *dentry)
+{
+	if (dentry->d_fsdata)
+		eventfs_d_release(dentry);
+}
+
+static int tracefs_d_revalidate(struct inode *inode, const struct qstr *name,
+				struct dentry *dentry, unsigned int flags)
+{
+	struct eventfs_inode *ei = dentry->d_fsdata;
+
+	return !(ei && ei->is_freed);
+}
+
+static int tracefs_d_delete(const struct dentry *dentry)
+{
+	/*
+	 * We want to keep eventfs dentries around but not tracefs
+	 * ones. eventfs dentries have content in d_fsdata.
+	 * Use d_fsdata to determine if it's a eventfs dentry or not.
+	 */
+	return dentry->d_fsdata == NULL;
+}
+
+static const struct dentry_operations tracefs_dentry_operations = {
+	.d_revalidate = tracefs_d_revalidate,
+	.d_release = tracefs_d_release,
+	.d_delete = tracefs_d_delete,
+};
+
+static int tracefs_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+	static const struct tree_descr trace_files[] = {{""}};
+	int err;
+
+	err = simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
+	if (err)
+		return err;
+
+	sb->s_op = &tracefs_super_operations;
+	set_default_d_op(sb, &tracefs_dentry_operations);
+
+	return 0;
+}
+
+static int tracefs_get_tree(struct fs_context *fc)
+{
+	int err = get_tree_single(fc, tracefs_fill_super);
+
+	if (err)
+		return err;
+
+	return tracefs_reconfigure(fc);
+}
+
+static void tracefs_free_fc(struct fs_context *fc)
+{
+	kfree(fc->s_fs_info);
+}
+
+static const struct fs_context_operations tracefs_context_ops = {
+	.free		= tracefs_free_fc,
+	.parse_param	= tracefs_parse_param,
+	.get_tree	= tracefs_get_tree,
+	.reconfigure	= tracefs_reconfigure,
+};
+
+static int tracefs_init_fs_context(struct fs_context *fc)
+{
+	struct tracefs_fs_info *fsi;
+
+	fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
+	if (!fsi)
+		return -ENOMEM;
+
+	fsi->mode = TRACEFS_DEFAULT_MODE;
+
+	fc->s_fs_info = fsi;
+	fc->ops = &tracefs_context_ops;
+	return 0;
+}
+
+static struct file_system_type trace_fs_type = {
+	.owner =	THIS_MODULE,
+	.name =		"tracefs",
+	.init_fs_context = tracefs_init_fs_context,
+	.parameters	= tracefs_param_specs,
+	.kill_sb =	kill_anon_super,
+};
+MODULE_ALIAS_FS("tracefs");
+
+struct dentry *tracefs_start_creating(const char *name, struct dentry *parent)
+{
+	struct dentry *dentry;
+	int error;
+
+	pr_debug("tracefs: creating file '%s'\n",name);
+
+	error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
+			      &tracefs_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 = tracefs_mount->mnt_root;
+
+	dentry = simple_start_creating(parent, name);
+	if (IS_ERR(dentry))
+		simple_release_fs(&tracefs_mount, &tracefs_mount_count);
+
+	return dentry;
+}
+
+struct dentry *tracefs_failed_creating(struct dentry *dentry)
+{
+	simple_done_creating(dentry);
+	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
+	return NULL;
+}
+
+struct dentry *tracefs_end_creating(struct dentry *dentry)
+{
+	simple_done_creating(dentry);
+	return dentry;	// borrowed
+}
+
+/* Find the inode that this will use for default */
+static struct inode *instance_inode(struct dentry *parent, struct inode *inode)
+{
+	struct tracefs_inode *ti;
+
+	/* If parent is NULL then use root inode */
+	if (!parent)
+		return d_inode(inode->i_sb->s_root);
+
+	/* Find the inode that is flagged as an instance or the root inode */
+	while (!IS_ROOT(parent)) {
+		ti = get_tracefs(d_inode(parent));
+		if (ti->flags & TRACEFS_INSTANCE_INODE)
+			break;
+		parent = parent->d_parent;
+	}
+
+	return d_inode(parent);
+}
+
+/**
+ * tracefs_create_file - create a file in the tracefs 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 tracefs 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 tracefs.  It allows for a
+ * wide range of flexibility in creating a file, or a directory (if you want
+ * to create a directory, the tracefs_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 tracefs_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 tracefs is not enabled in the kernel, the value -%ENODEV will be
+ * returned.
+ */
+struct dentry *tracefs_create_file(const char *name, umode_t mode,
+				   struct dentry *parent, void *data,
+				   const struct file_operations *fops)
+{
+	struct tracefs_inode *ti;
+	struct dentry *dentry;
+	struct inode *inode;
+
+	if (security_locked_down(LOCKDOWN_TRACEFS))
+		return NULL;
+
+	if (!(mode & S_IFMT))
+		mode |= S_IFREG;
+	BUG_ON(!S_ISREG(mode));
+	dentry = tracefs_start_creating(name, parent);
+
+	if (IS_ERR(dentry))
+		return NULL;
+
+	inode = tracefs_get_inode(dentry->d_sb);
+	if (unlikely(!inode))
+		return tracefs_failed_creating(dentry);
+
+	ti = get_tracefs(inode);
+	ti->private = instance_inode(parent, inode);
+
+	inode->i_mode = mode;
+	inode->i_op = &tracefs_file_inode_operations;
+	inode->i_fop = fops ? fops : &tracefs_file_operations;
+	inode->i_private = data;
+	inode->i_uid = d_inode(dentry->d_parent)->i_uid;
+	inode->i_gid = d_inode(dentry->d_parent)->i_gid;
+	d_make_persistent(dentry, inode);
+	fsnotify_create(d_inode(dentry->d_parent), dentry);
+	return tracefs_end_creating(dentry);
+}
+
+static struct dentry *__create_dir(const char *name, struct dentry *parent,
+				   const struct inode_operations *ops)
+{
+	struct tracefs_inode *ti;
+	struct dentry *dentry = tracefs_start_creating(name, parent);
+	struct inode *inode;
+
+	if (IS_ERR(dentry))
+		return NULL;
+
+	inode = tracefs_get_inode(dentry->d_sb);
+	if (unlikely(!inode))
+		return tracefs_failed_creating(dentry);
+
+	/* Do not set bits for OTH */
+	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUSR| S_IRGRP | S_IXUSR | S_IXGRP;
+	inode->i_op = ops;
+	inode->i_fop = &simple_dir_operations;
+	inode->i_uid = d_inode(dentry->d_parent)->i_uid;
+	inode->i_gid = d_inode(dentry->d_parent)->i_gid;
+
+	ti = get_tracefs(inode);
+	ti->private = instance_inode(parent, inode);
+
+	/* directory inodes start off with i_nlink == 2 (for "." entry) */
+	inc_nlink(inode);
+	d_make_persistent(dentry, inode);
+	inc_nlink(d_inode(dentry->d_parent));
+	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
+	return tracefs_end_creating(dentry);
+}
+
+/**
+ * tracefs_create_dir - create a directory in the tracefs 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 tracefs filesystem.
+ *
+ * This function creates a directory in tracefs with the given name.
+ *
+ * This function will return a pointer to a dentry if it succeeds.  This
+ * pointer must be passed to the tracefs_remove() function when the file is
+ * to be removed. If an error occurs, %NULL will be returned.
+ *
+ * If tracing is not enabled in the kernel, the value -%ENODEV will be
+ * returned.
+ */
+struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
+{
+	if (security_locked_down(LOCKDOWN_TRACEFS))
+		return NULL;
+
+	return __create_dir(name, parent, &tracefs_dir_inode_operations);
+}
+
+/**
+ * tracefs_create_instance_dir - create the tracing instances directory
+ * @name: The name of the instances directory to create
+ * @parent: The parent directory that the instances directory will exist
+ * @mkdir: The function to call when a mkdir is performed.
+ * @rmdir: The function to call when a rmdir is performed.
+ *
+ * Only one instances directory is allowed.
+ *
+ * The instances directory is special as it allows for mkdir and rmdir
+ * to be done by userspace. When a mkdir or rmdir is performed, the inode
+ * locks are released and the methods passed in (@mkdir and @rmdir) are
+ * called without locks and with the name of the directory being created
+ * within the instances directory.
+ *
+ * Returns the dentry of the instances directory.
+ */
+__init struct dentry *tracefs_create_instance_dir(const char *name,
+					  struct dentry *parent,
+					  int (*mkdir)(const char *name),
+					  int (*rmdir)(const char *name))
+{
+	struct dentry *dentry;
+
+	/* Only allow one instance of the instances directory. */
+	if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
+		return NULL;
+
+	dentry = __create_dir(name, parent, &tracefs_instance_dir_inode_operations);
+	if (!dentry)
+		return NULL;
+
+	tracefs_ops.mkdir = mkdir;
+	tracefs_ops.rmdir = rmdir;
+
+	return dentry;
+}
+
+static void remove_one(struct dentry *victim)
+{
+	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
+}
+
+/**
+ * tracefs_remove - 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 tracefs that
+ * was previously created with a call to another tracefs function
+ * (like tracefs_create_file() or variants thereof.)
+ */
+void tracefs_remove(struct dentry *dentry)
+{
+	if (IS_ERR_OR_NULL(dentry))
+		return;
+
+	simple_pin_fs(&trace_fs_type, &tracefs_mount, &tracefs_mount_count);
+	simple_recursive_removal(dentry, remove_one);
+	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
+}
+
+/**
+ * tracefs_initialized - Tells whether tracefs has been registered
+ */
+bool tracefs_initialized(void)
+{
+	return tracefs_registered;
+}
+
+static void init_once(void *foo)
+{
+	struct tracefs_inode *ti = (struct tracefs_inode *) foo;
+
+	/* inode_init_once() calls memset() on the vfs_inode portion */
+	inode_init_once(&ti->vfs_inode);
+
+	/* Zero out the rest */
+	memset_after(ti, 0, vfs_inode);
+}
+
+static int __init tracefs_init(void)
+{
+	int retval;
+
+	tracefs_inode_cachep = kmem_cache_create("tracefs_inode_cache",
+						 sizeof(struct tracefs_inode),
+						 0, (SLAB_RECLAIM_ACCOUNT|
+						     SLAB_ACCOUNT),
+						 init_once);
+	if (!tracefs_inode_cachep)
+		return -ENOMEM;
+
+	retval = sysfs_create_mount_point(kernel_kobj, "tracing");
+	if (retval)
+		return -EINVAL;
+
+	retval = register_filesystem(&trace_fs_type);
+	if (!retval)
+		tracefs_registered = true;
+
+	return retval;
+}
+core_initcall(tracefs_init);