xref: /openbmc/linux/fs/tracefs/inode.c (revision f0931824)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *  inode.c - part of tracefs, a pseudo file system for activating tracing
4  *
5  * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
6  *
7  *  Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
8  *
9  * tracefs is the file system that is used by the tracing infrastructure.
10  */
11 
12 #include <linux/module.h>
13 #include <linux/fs.h>
14 #include <linux/mount.h>
15 #include <linux/kobject.h>
16 #include <linux/namei.h>
17 #include <linux/tracefs.h>
18 #include <linux/fsnotify.h>
19 #include <linux/security.h>
20 #include <linux/seq_file.h>
21 #include <linux/parser.h>
22 #include <linux/magic.h>
23 #include <linux/slab.h>
24 #include "internal.h"
25 
26 #define TRACEFS_DEFAULT_MODE	0700
27 static struct kmem_cache *tracefs_inode_cachep __ro_after_init;
28 
29 static struct vfsmount *tracefs_mount;
30 static int tracefs_mount_count;
31 static bool tracefs_registered;
32 
33 static struct inode *tracefs_alloc_inode(struct super_block *sb)
34 {
35 	struct tracefs_inode *ti;
36 
37 	ti = kmem_cache_alloc(tracefs_inode_cachep, GFP_KERNEL);
38 	if (!ti)
39 		return NULL;
40 
41 	return &ti->vfs_inode;
42 }
43 
44 static void tracefs_free_inode(struct inode *inode)
45 {
46 	kmem_cache_free(tracefs_inode_cachep, get_tracefs(inode));
47 }
48 
49 static ssize_t default_read_file(struct file *file, char __user *buf,
50 				 size_t count, loff_t *ppos)
51 {
52 	return 0;
53 }
54 
55 static ssize_t default_write_file(struct file *file, const char __user *buf,
56 				   size_t count, loff_t *ppos)
57 {
58 	return count;
59 }
60 
61 static const struct file_operations tracefs_file_operations = {
62 	.read =		default_read_file,
63 	.write =	default_write_file,
64 	.open =		simple_open,
65 	.llseek =	noop_llseek,
66 };
67 
68 static struct tracefs_dir_ops {
69 	int (*mkdir)(const char *name);
70 	int (*rmdir)(const char *name);
71 } tracefs_ops __ro_after_init;
72 
73 static char *get_dname(struct dentry *dentry)
74 {
75 	const char *dname;
76 	char *name;
77 	int len = dentry->d_name.len;
78 
79 	dname = dentry->d_name.name;
80 	name = kmalloc(len + 1, GFP_KERNEL);
81 	if (!name)
82 		return NULL;
83 	memcpy(name, dname, len);
84 	name[len] = 0;
85 	return name;
86 }
87 
88 static int tracefs_syscall_mkdir(struct mnt_idmap *idmap,
89 				 struct inode *inode, struct dentry *dentry,
90 				 umode_t mode)
91 {
92 	struct tracefs_inode *ti;
93 	char *name;
94 	int ret;
95 
96 	name = get_dname(dentry);
97 	if (!name)
98 		return -ENOMEM;
99 
100 	/*
101 	 * This is a new directory that does not take the default of
102 	 * the rootfs. It becomes the default permissions for all the
103 	 * files and directories underneath it.
104 	 */
105 	ti = get_tracefs(inode);
106 	ti->flags |= TRACEFS_INSTANCE_INODE;
107 	ti->private = inode;
108 
109 	/*
110 	 * The mkdir call can call the generic functions that create
111 	 * the files within the tracefs system. It is up to the individual
112 	 * mkdir routine to handle races.
113 	 */
114 	inode_unlock(inode);
115 	ret = tracefs_ops.mkdir(name);
116 	inode_lock(inode);
117 
118 	kfree(name);
119 
120 	return ret;
121 }
122 
123 static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
124 {
125 	char *name;
126 	int ret;
127 
128 	name = get_dname(dentry);
129 	if (!name)
130 		return -ENOMEM;
131 
132 	/*
133 	 * The rmdir call can call the generic functions that create
134 	 * the files within the tracefs system. It is up to the individual
135 	 * rmdir routine to handle races.
136 	 * This time we need to unlock not only the parent (inode) but
137 	 * also the directory that is being deleted.
138 	 */
139 	inode_unlock(inode);
140 	inode_unlock(d_inode(dentry));
141 
142 	ret = tracefs_ops.rmdir(name);
143 
144 	inode_lock_nested(inode, I_MUTEX_PARENT);
145 	inode_lock(d_inode(dentry));
146 
147 	kfree(name);
148 
149 	return ret;
150 }
151 
152 static void set_tracefs_inode_owner(struct inode *inode)
153 {
154 	struct tracefs_inode *ti = get_tracefs(inode);
155 	struct inode *root_inode = ti->private;
156 
157 	/*
158 	 * If this inode has never been referenced, then update
159 	 * the permissions to the superblock.
160 	 */
161 	if (!(ti->flags & TRACEFS_UID_PERM_SET))
162 		inode->i_uid = root_inode->i_uid;
163 
164 	if (!(ti->flags & TRACEFS_GID_PERM_SET))
165 		inode->i_gid = root_inode->i_gid;
166 }
167 
168 static int tracefs_permission(struct mnt_idmap *idmap,
169 			      struct inode *inode, int mask)
170 {
171 	set_tracefs_inode_owner(inode);
172 	return generic_permission(idmap, inode, mask);
173 }
174 
175 static int tracefs_getattr(struct mnt_idmap *idmap,
176 			   const struct path *path, struct kstat *stat,
177 			   u32 request_mask, unsigned int flags)
178 {
179 	struct inode *inode = d_backing_inode(path->dentry);
180 
181 	set_tracefs_inode_owner(inode);
182 	generic_fillattr(idmap, request_mask, inode, stat);
183 	return 0;
184 }
185 
186 static int tracefs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
187 			   struct iattr *attr)
188 {
189 	unsigned int ia_valid = attr->ia_valid;
190 	struct inode *inode = d_inode(dentry);
191 	struct tracefs_inode *ti = get_tracefs(inode);
192 
193 	if (ia_valid & ATTR_UID)
194 		ti->flags |= TRACEFS_UID_PERM_SET;
195 
196 	if (ia_valid & ATTR_GID)
197 		ti->flags |= TRACEFS_GID_PERM_SET;
198 
199 	return simple_setattr(idmap, dentry, attr);
200 }
201 
202 static const struct inode_operations tracefs_instance_dir_inode_operations = {
203 	.lookup		= simple_lookup,
204 	.mkdir		= tracefs_syscall_mkdir,
205 	.rmdir		= tracefs_syscall_rmdir,
206 	.permission	= tracefs_permission,
207 	.getattr	= tracefs_getattr,
208 	.setattr	= tracefs_setattr,
209 };
210 
211 static const struct inode_operations tracefs_dir_inode_operations = {
212 	.lookup		= simple_lookup,
213 	.permission	= tracefs_permission,
214 	.getattr	= tracefs_getattr,
215 	.setattr	= tracefs_setattr,
216 };
217 
218 static const struct inode_operations tracefs_file_inode_operations = {
219 	.permission	= tracefs_permission,
220 	.getattr	= tracefs_getattr,
221 	.setattr	= tracefs_setattr,
222 };
223 
224 struct inode *tracefs_get_inode(struct super_block *sb)
225 {
226 	struct inode *inode = new_inode(sb);
227 	if (inode) {
228 		inode->i_ino = get_next_ino();
229 		inode->i_atime = inode->i_mtime = inode_set_ctime_current(inode);
230 	}
231 	return inode;
232 }
233 
234 struct tracefs_mount_opts {
235 	kuid_t uid;
236 	kgid_t gid;
237 	umode_t mode;
238 	/* Opt_* bitfield. */
239 	unsigned int opts;
240 };
241 
242 enum {
243 	Opt_uid,
244 	Opt_gid,
245 	Opt_mode,
246 	Opt_err
247 };
248 
249 static const match_table_t tokens = {
250 	{Opt_uid, "uid=%u"},
251 	{Opt_gid, "gid=%u"},
252 	{Opt_mode, "mode=%o"},
253 	{Opt_err, NULL}
254 };
255 
256 struct tracefs_fs_info {
257 	struct tracefs_mount_opts mount_opts;
258 };
259 
260 static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
261 {
262 	substring_t args[MAX_OPT_ARGS];
263 	int option;
264 	int token;
265 	kuid_t uid;
266 	kgid_t gid;
267 	char *p;
268 
269 	opts->opts = 0;
270 	opts->mode = TRACEFS_DEFAULT_MODE;
271 
272 	while ((p = strsep(&data, ",")) != NULL) {
273 		if (!*p)
274 			continue;
275 
276 		token = match_token(p, tokens, args);
277 		switch (token) {
278 		case Opt_uid:
279 			if (match_int(&args[0], &option))
280 				return -EINVAL;
281 			uid = make_kuid(current_user_ns(), option);
282 			if (!uid_valid(uid))
283 				return -EINVAL;
284 			opts->uid = uid;
285 			break;
286 		case Opt_gid:
287 			if (match_int(&args[0], &option))
288 				return -EINVAL;
289 			gid = make_kgid(current_user_ns(), option);
290 			if (!gid_valid(gid))
291 				return -EINVAL;
292 			opts->gid = gid;
293 			break;
294 		case Opt_mode:
295 			if (match_octal(&args[0], &option))
296 				return -EINVAL;
297 			opts->mode = option & S_IALLUGO;
298 			break;
299 		/*
300 		 * We might like to report bad mount options here;
301 		 * but traditionally tracefs has ignored all mount options
302 		 */
303 		}
304 
305 		opts->opts |= BIT(token);
306 	}
307 
308 	return 0;
309 }
310 
311 static int tracefs_apply_options(struct super_block *sb, bool remount)
312 {
313 	struct tracefs_fs_info *fsi = sb->s_fs_info;
314 	struct inode *inode = d_inode(sb->s_root);
315 	struct tracefs_mount_opts *opts = &fsi->mount_opts;
316 	umode_t tmp_mode;
317 
318 	/*
319 	 * On remount, only reset mode/uid/gid if they were provided as mount
320 	 * options.
321 	 */
322 
323 	if (!remount || opts->opts & BIT(Opt_mode)) {
324 		tmp_mode = READ_ONCE(inode->i_mode) & ~S_IALLUGO;
325 		tmp_mode |= opts->mode;
326 		WRITE_ONCE(inode->i_mode, tmp_mode);
327 	}
328 
329 	if (!remount || opts->opts & BIT(Opt_uid))
330 		inode->i_uid = opts->uid;
331 
332 	if (!remount || opts->opts & BIT(Opt_gid))
333 		inode->i_gid = opts->gid;
334 
335 	return 0;
336 }
337 
338 static int tracefs_remount(struct super_block *sb, int *flags, char *data)
339 {
340 	int err;
341 	struct tracefs_fs_info *fsi = sb->s_fs_info;
342 
343 	sync_filesystem(sb);
344 	err = tracefs_parse_options(data, &fsi->mount_opts);
345 	if (err)
346 		goto fail;
347 
348 	tracefs_apply_options(sb, true);
349 
350 fail:
351 	return err;
352 }
353 
354 static int tracefs_show_options(struct seq_file *m, struct dentry *root)
355 {
356 	struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
357 	struct tracefs_mount_opts *opts = &fsi->mount_opts;
358 
359 	if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
360 		seq_printf(m, ",uid=%u",
361 			   from_kuid_munged(&init_user_ns, opts->uid));
362 	if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
363 		seq_printf(m, ",gid=%u",
364 			   from_kgid_munged(&init_user_ns, opts->gid));
365 	if (opts->mode != TRACEFS_DEFAULT_MODE)
366 		seq_printf(m, ",mode=%o", opts->mode);
367 
368 	return 0;
369 }
370 
371 static const struct super_operations tracefs_super_operations = {
372 	.alloc_inode    = tracefs_alloc_inode,
373 	.free_inode     = tracefs_free_inode,
374 	.drop_inode     = generic_delete_inode,
375 	.statfs		= simple_statfs,
376 	.remount_fs	= tracefs_remount,
377 	.show_options	= tracefs_show_options,
378 };
379 
380 /*
381  * It would be cleaner if eventfs had its own dentry ops.
382  *
383  * Note that d_revalidate is called potentially under RCU,
384  * so it can't take the eventfs mutex etc. It's fine - if
385  * we open a file just as it's marked dead, things will
386  * still work just fine, and just see the old stale case.
387  */
388 static void tracefs_d_release(struct dentry *dentry)
389 {
390 	if (dentry->d_fsdata)
391 		eventfs_d_release(dentry);
392 }
393 
394 static int tracefs_d_revalidate(struct dentry *dentry, unsigned int flags)
395 {
396 	struct eventfs_inode *ei = dentry->d_fsdata;
397 
398 	return !(ei && ei->is_freed);
399 }
400 
401 static const struct dentry_operations tracefs_dentry_operations = {
402 	.d_revalidate = tracefs_d_revalidate,
403 	.d_release = tracefs_d_release,
404 };
405 
406 static int trace_fill_super(struct super_block *sb, void *data, int silent)
407 {
408 	static const struct tree_descr trace_files[] = {{""}};
409 	struct tracefs_fs_info *fsi;
410 	int err;
411 
412 	fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
413 	sb->s_fs_info = fsi;
414 	if (!fsi) {
415 		err = -ENOMEM;
416 		goto fail;
417 	}
418 
419 	err = tracefs_parse_options(data, &fsi->mount_opts);
420 	if (err)
421 		goto fail;
422 
423 	err  =  simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
424 	if (err)
425 		goto fail;
426 
427 	sb->s_op = &tracefs_super_operations;
428 	sb->s_d_op = &tracefs_dentry_operations;
429 
430 	tracefs_apply_options(sb, false);
431 
432 	return 0;
433 
434 fail:
435 	kfree(fsi);
436 	sb->s_fs_info = NULL;
437 	return err;
438 }
439 
440 static struct dentry *trace_mount(struct file_system_type *fs_type,
441 			int flags, const char *dev_name,
442 			void *data)
443 {
444 	return mount_single(fs_type, flags, data, trace_fill_super);
445 }
446 
447 static struct file_system_type trace_fs_type = {
448 	.owner =	THIS_MODULE,
449 	.name =		"tracefs",
450 	.mount =	trace_mount,
451 	.kill_sb =	kill_litter_super,
452 };
453 MODULE_ALIAS_FS("tracefs");
454 
455 struct dentry *tracefs_start_creating(const char *name, struct dentry *parent)
456 {
457 	struct dentry *dentry;
458 	int error;
459 
460 	pr_debug("tracefs: creating file '%s'\n",name);
461 
462 	error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
463 			      &tracefs_mount_count);
464 	if (error)
465 		return ERR_PTR(error);
466 
467 	/* If the parent is not specified, we create it in the root.
468 	 * We need the root dentry to do this, which is in the super
469 	 * block. A pointer to that is in the struct vfsmount that we
470 	 * have around.
471 	 */
472 	if (!parent)
473 		parent = tracefs_mount->mnt_root;
474 
475 	inode_lock(d_inode(parent));
476 	if (unlikely(IS_DEADDIR(d_inode(parent))))
477 		dentry = ERR_PTR(-ENOENT);
478 	else
479 		dentry = lookup_one_len(name, parent, strlen(name));
480 	if (!IS_ERR(dentry) && d_inode(dentry)) {
481 		dput(dentry);
482 		dentry = ERR_PTR(-EEXIST);
483 	}
484 
485 	if (IS_ERR(dentry)) {
486 		inode_unlock(d_inode(parent));
487 		simple_release_fs(&tracefs_mount, &tracefs_mount_count);
488 	}
489 
490 	return dentry;
491 }
492 
493 struct dentry *tracefs_failed_creating(struct dentry *dentry)
494 {
495 	inode_unlock(d_inode(dentry->d_parent));
496 	dput(dentry);
497 	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
498 	return NULL;
499 }
500 
501 struct dentry *tracefs_end_creating(struct dentry *dentry)
502 {
503 	inode_unlock(d_inode(dentry->d_parent));
504 	return dentry;
505 }
506 
507 /* Find the inode that this will use for default */
508 static struct inode *instance_inode(struct dentry *parent, struct inode *inode)
509 {
510 	struct tracefs_inode *ti;
511 
512 	/* If parent is NULL then use root inode */
513 	if (!parent)
514 		return d_inode(inode->i_sb->s_root);
515 
516 	/* Find the inode that is flagged as an instance or the root inode */
517 	while (!IS_ROOT(parent)) {
518 		ti = get_tracefs(d_inode(parent));
519 		if (ti->flags & TRACEFS_INSTANCE_INODE)
520 			break;
521 		parent = parent->d_parent;
522 	}
523 
524 	return d_inode(parent);
525 }
526 
527 /**
528  * tracefs_create_file - create a file in the tracefs filesystem
529  * @name: a pointer to a string containing the name of the file to create.
530  * @mode: the permission that the file should have.
531  * @parent: a pointer to the parent dentry for this file.  This should be a
532  *          directory dentry if set.  If this parameter is NULL, then the
533  *          file will be created in the root of the tracefs filesystem.
534  * @data: a pointer to something that the caller will want to get to later
535  *        on.  The inode.i_private pointer will point to this value on
536  *        the open() call.
537  * @fops: a pointer to a struct file_operations that should be used for
538  *        this file.
539  *
540  * This is the basic "create a file" function for tracefs.  It allows for a
541  * wide range of flexibility in creating a file, or a directory (if you want
542  * to create a directory, the tracefs_create_dir() function is
543  * recommended to be used instead.)
544  *
545  * This function will return a pointer to a dentry if it succeeds.  This
546  * pointer must be passed to the tracefs_remove() function when the file is
547  * to be removed (no automatic cleanup happens if your module is unloaded,
548  * you are responsible here.)  If an error occurs, %NULL will be returned.
549  *
550  * If tracefs is not enabled in the kernel, the value -%ENODEV will be
551  * returned.
552  */
553 struct dentry *tracefs_create_file(const char *name, umode_t mode,
554 				   struct dentry *parent, void *data,
555 				   const struct file_operations *fops)
556 {
557 	struct tracefs_inode *ti;
558 	struct dentry *dentry;
559 	struct inode *inode;
560 
561 	if (security_locked_down(LOCKDOWN_TRACEFS))
562 		return NULL;
563 
564 	if (!(mode & S_IFMT))
565 		mode |= S_IFREG;
566 	BUG_ON(!S_ISREG(mode));
567 	dentry = tracefs_start_creating(name, parent);
568 
569 	if (IS_ERR(dentry))
570 		return NULL;
571 
572 	inode = tracefs_get_inode(dentry->d_sb);
573 	if (unlikely(!inode))
574 		return tracefs_failed_creating(dentry);
575 
576 	ti = get_tracefs(inode);
577 	ti->private = instance_inode(parent, inode);
578 
579 	inode->i_mode = mode;
580 	inode->i_op = &tracefs_file_inode_operations;
581 	inode->i_fop = fops ? fops : &tracefs_file_operations;
582 	inode->i_private = data;
583 	inode->i_uid = d_inode(dentry->d_parent)->i_uid;
584 	inode->i_gid = d_inode(dentry->d_parent)->i_gid;
585 	d_instantiate(dentry, inode);
586 	fsnotify_create(d_inode(dentry->d_parent), dentry);
587 	return tracefs_end_creating(dentry);
588 }
589 
590 static struct dentry *__create_dir(const char *name, struct dentry *parent,
591 				   const struct inode_operations *ops)
592 {
593 	struct tracefs_inode *ti;
594 	struct dentry *dentry = tracefs_start_creating(name, parent);
595 	struct inode *inode;
596 
597 	if (IS_ERR(dentry))
598 		return NULL;
599 
600 	inode = tracefs_get_inode(dentry->d_sb);
601 	if (unlikely(!inode))
602 		return tracefs_failed_creating(dentry);
603 
604 	/* Do not set bits for OTH */
605 	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUSR| S_IRGRP | S_IXUSR | S_IXGRP;
606 	inode->i_op = ops;
607 	inode->i_fop = &simple_dir_operations;
608 	inode->i_uid = d_inode(dentry->d_parent)->i_uid;
609 	inode->i_gid = d_inode(dentry->d_parent)->i_gid;
610 
611 	ti = get_tracefs(inode);
612 	ti->private = instance_inode(parent, inode);
613 
614 	/* directory inodes start off with i_nlink == 2 (for "." entry) */
615 	inc_nlink(inode);
616 	d_instantiate(dentry, inode);
617 	inc_nlink(d_inode(dentry->d_parent));
618 	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
619 	return tracefs_end_creating(dentry);
620 }
621 
622 /**
623  * tracefs_create_dir - create a directory in the tracefs filesystem
624  * @name: a pointer to a string containing the name of the directory to
625  *        create.
626  * @parent: a pointer to the parent dentry for this file.  This should be a
627  *          directory dentry if set.  If this parameter is NULL, then the
628  *          directory will be created in the root of the tracefs filesystem.
629  *
630  * This function creates a directory in tracefs with the given name.
631  *
632  * This function will return a pointer to a dentry if it succeeds.  This
633  * pointer must be passed to the tracefs_remove() function when the file is
634  * to be removed. If an error occurs, %NULL will be returned.
635  *
636  * If tracing is not enabled in the kernel, the value -%ENODEV will be
637  * returned.
638  */
639 struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
640 {
641 	if (security_locked_down(LOCKDOWN_TRACEFS))
642 		return NULL;
643 
644 	return __create_dir(name, parent, &tracefs_dir_inode_operations);
645 }
646 
647 /**
648  * tracefs_create_instance_dir - create the tracing instances directory
649  * @name: The name of the instances directory to create
650  * @parent: The parent directory that the instances directory will exist
651  * @mkdir: The function to call when a mkdir is performed.
652  * @rmdir: The function to call when a rmdir is performed.
653  *
654  * Only one instances directory is allowed.
655  *
656  * The instances directory is special as it allows for mkdir and rmdir
657  * to be done by userspace. When a mkdir or rmdir is performed, the inode
658  * locks are released and the methods passed in (@mkdir and @rmdir) are
659  * called without locks and with the name of the directory being created
660  * within the instances directory.
661  *
662  * Returns the dentry of the instances directory.
663  */
664 __init struct dentry *tracefs_create_instance_dir(const char *name,
665 					  struct dentry *parent,
666 					  int (*mkdir)(const char *name),
667 					  int (*rmdir)(const char *name))
668 {
669 	struct dentry *dentry;
670 
671 	/* Only allow one instance of the instances directory. */
672 	if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
673 		return NULL;
674 
675 	dentry = __create_dir(name, parent, &tracefs_instance_dir_inode_operations);
676 	if (!dentry)
677 		return NULL;
678 
679 	tracefs_ops.mkdir = mkdir;
680 	tracefs_ops.rmdir = rmdir;
681 
682 	return dentry;
683 }
684 
685 static void remove_one(struct dentry *victim)
686 {
687 	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
688 }
689 
690 /**
691  * tracefs_remove - recursively removes a directory
692  * @dentry: a pointer to a the dentry of the directory to be removed.
693  *
694  * This function recursively removes a directory tree in tracefs that
695  * was previously created with a call to another tracefs function
696  * (like tracefs_create_file() or variants thereof.)
697  */
698 void tracefs_remove(struct dentry *dentry)
699 {
700 	if (IS_ERR_OR_NULL(dentry))
701 		return;
702 
703 	simple_pin_fs(&trace_fs_type, &tracefs_mount, &tracefs_mount_count);
704 	simple_recursive_removal(dentry, remove_one);
705 	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
706 }
707 
708 /**
709  * tracefs_initialized - Tells whether tracefs has been registered
710  */
711 bool tracefs_initialized(void)
712 {
713 	return tracefs_registered;
714 }
715 
716 static void init_once(void *foo)
717 {
718 	struct tracefs_inode *ti = (struct tracefs_inode *) foo;
719 
720 	/* inode_init_once() calls memset() on the vfs_inode portion */
721 	inode_init_once(&ti->vfs_inode);
722 
723 	/* Zero out the rest */
724 	memset_after(ti, 0, vfs_inode);
725 }
726 
727 static int __init tracefs_init(void)
728 {
729 	int retval;
730 
731 	tracefs_inode_cachep = kmem_cache_create("tracefs_inode_cache",
732 						 sizeof(struct tracefs_inode),
733 						 0, (SLAB_RECLAIM_ACCOUNT|
734 						     SLAB_MEM_SPREAD|
735 						     SLAB_ACCOUNT),
736 						 init_once);
737 	if (!tracefs_inode_cachep)
738 		return -ENOMEM;
739 
740 	retval = sysfs_create_mount_point(kernel_kobj, "tracing");
741 	if (retval)
742 		return -EINVAL;
743 
744 	retval = register_filesystem(&trace_fs_type);
745 	if (!retval)
746 		tracefs_registered = true;
747 
748 	return retval;
749 }
750 core_initcall(tracefs_init);
751