Merge tag 'timers_urgent_for_v6.13_rc1' of git://git.kernel.org/pub/scm/linux/kernel...

[drm/drm-misc.git] / fs / tracefs / inode.c

// 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 int 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 -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 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 dentry *dentry, unsigned int flags)
{
        struct eventfs_inode *ei = dentry->d_fsdata;

        return !(ei && ei->is_freed);
}

static const struct dentry_operations tracefs_dentry_operations = {
        .d_revalidate = tracefs_d_revalidate,
        .d_release = tracefs_d_release,
};

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;
        sb->s_d_op = &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_litter_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;

        inode_lock(d_inode(parent));
        if (unlikely(IS_DEADDIR(d_inode(parent))))
                dentry = ERR_PTR(-ENOENT);
        else
                dentry = lookup_one_len(name, parent, strlen(name));
        if (!IS_ERR(dentry) && d_inode(dentry)) {
                dput(dentry);
                dentry = ERR_PTR(-EEXIST);
        }

        if (IS_ERR(dentry)) {
                inode_unlock(d_inode(parent));
                simple_release_fs(&tracefs_mount, &tracefs_mount_count);
        }

        return dentry;
}

struct dentry *tracefs_failed_creating(struct dentry *dentry)
{
        inode_unlock(d_inode(dentry->d_parent));
        dput(dentry);
        simple_release_fs(&tracefs_mount, &tracefs_mount_count);
        return NULL;
}

struct dentry *tracefs_end_creating(struct dentry *dentry)
{
        inode_unlock(d_inode(dentry->d_parent));
        return dentry;
}

/* 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_instantiate(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_instantiate(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);