xref: /linux/fs/tracefs/inode.c (revision daa121128a2d2ac6006159e2c47676e4fcd21eab)
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/fs_context.h>
15 #include <linux/fs_parser.h>
16 #include <linux/kobject.h>
17 #include <linux/namei.h>
18 #include <linux/tracefs.h>
19 #include <linux/fsnotify.h>
20 #include <linux/security.h>
21 #include <linux/seq_file.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 /*
34  * Keep track of all tracefs_inodes in order to update their
35  * flags if necessary on a remount.
36  */
37 static DEFINE_SPINLOCK(tracefs_inode_lock);
38 static LIST_HEAD(tracefs_inodes);
39 
40 static struct inode *tracefs_alloc_inode(struct super_block *sb)
41 {
42 	struct tracefs_inode *ti;
43 	unsigned long flags;
44 
45 	ti = kmem_cache_alloc(tracefs_inode_cachep, GFP_KERNEL);
46 	if (!ti)
47 		return NULL;
48 
49 	spin_lock_irqsave(&tracefs_inode_lock, flags);
50 	list_add_rcu(&ti->list, &tracefs_inodes);
51 	spin_unlock_irqrestore(&tracefs_inode_lock, flags);
52 
53 	return &ti->vfs_inode;
54 }
55 
56 static void tracefs_free_inode_rcu(struct rcu_head *rcu)
57 {
58 	struct tracefs_inode *ti;
59 
60 	ti = container_of(rcu, struct tracefs_inode, rcu);
61 	kmem_cache_free(tracefs_inode_cachep, ti);
62 }
63 
64 static void tracefs_free_inode(struct inode *inode)
65 {
66 	struct tracefs_inode *ti = get_tracefs(inode);
67 	unsigned long flags;
68 
69 	spin_lock_irqsave(&tracefs_inode_lock, flags);
70 	list_del_rcu(&ti->list);
71 	spin_unlock_irqrestore(&tracefs_inode_lock, flags);
72 
73 	call_rcu(&ti->rcu, tracefs_free_inode_rcu);
74 }
75 
76 static ssize_t default_read_file(struct file *file, char __user *buf,
77 				 size_t count, loff_t *ppos)
78 {
79 	return 0;
80 }
81 
82 static ssize_t default_write_file(struct file *file, const char __user *buf,
83 				   size_t count, loff_t *ppos)
84 {
85 	return count;
86 }
87 
88 static const struct file_operations tracefs_file_operations = {
89 	.read =		default_read_file,
90 	.write =	default_write_file,
91 	.open =		simple_open,
92 	.llseek =	noop_llseek,
93 };
94 
95 static struct tracefs_dir_ops {
96 	int (*mkdir)(const char *name);
97 	int (*rmdir)(const char *name);
98 } tracefs_ops __ro_after_init;
99 
100 static char *get_dname(struct dentry *dentry)
101 {
102 	const char *dname;
103 	char *name;
104 	int len = dentry->d_name.len;
105 
106 	dname = dentry->d_name.name;
107 	name = kmalloc(len + 1, GFP_KERNEL);
108 	if (!name)
109 		return NULL;
110 	memcpy(name, dname, len);
111 	name[len] = 0;
112 	return name;
113 }
114 
115 static int tracefs_syscall_mkdir(struct mnt_idmap *idmap,
116 				 struct inode *inode, struct dentry *dentry,
117 				 umode_t mode)
118 {
119 	struct tracefs_inode *ti;
120 	char *name;
121 	int ret;
122 
123 	name = get_dname(dentry);
124 	if (!name)
125 		return -ENOMEM;
126 
127 	/*
128 	 * This is a new directory that does not take the default of
129 	 * the rootfs. It becomes the default permissions for all the
130 	 * files and directories underneath it.
131 	 */
132 	ti = get_tracefs(inode);
133 	ti->flags |= TRACEFS_INSTANCE_INODE;
134 	ti->private = inode;
135 
136 	/*
137 	 * The mkdir call can call the generic functions that create
138 	 * the files within the tracefs system. It is up to the individual
139 	 * mkdir routine to handle races.
140 	 */
141 	inode_unlock(inode);
142 	ret = tracefs_ops.mkdir(name);
143 	inode_lock(inode);
144 
145 	kfree(name);
146 
147 	return ret;
148 }
149 
150 static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
151 {
152 	char *name;
153 	int ret;
154 
155 	name = get_dname(dentry);
156 	if (!name)
157 		return -ENOMEM;
158 
159 	/*
160 	 * The rmdir call can call the generic functions that create
161 	 * the files within the tracefs system. It is up to the individual
162 	 * rmdir routine to handle races.
163 	 * This time we need to unlock not only the parent (inode) but
164 	 * also the directory that is being deleted.
165 	 */
166 	inode_unlock(inode);
167 	inode_unlock(d_inode(dentry));
168 
169 	ret = tracefs_ops.rmdir(name);
170 
171 	inode_lock_nested(inode, I_MUTEX_PARENT);
172 	inode_lock(d_inode(dentry));
173 
174 	kfree(name);
175 
176 	return ret;
177 }
178 
179 static void set_tracefs_inode_owner(struct inode *inode)
180 {
181 	struct tracefs_inode *ti = get_tracefs(inode);
182 	struct inode *root_inode = ti->private;
183 	kuid_t uid;
184 	kgid_t gid;
185 
186 	uid = root_inode->i_uid;
187 	gid = root_inode->i_gid;
188 
189 	/*
190 	 * If the root is not the mount point, then check the root's
191 	 * permissions. If it was never set, then default to the
192 	 * mount point.
193 	 */
194 	if (root_inode != d_inode(root_inode->i_sb->s_root)) {
195 		struct tracefs_inode *rti;
196 
197 		rti = get_tracefs(root_inode);
198 		root_inode = d_inode(root_inode->i_sb->s_root);
199 
200 		if (!(rti->flags & TRACEFS_UID_PERM_SET))
201 			uid = root_inode->i_uid;
202 
203 		if (!(rti->flags & TRACEFS_GID_PERM_SET))
204 			gid = root_inode->i_gid;
205 	}
206 
207 	/*
208 	 * If this inode has never been referenced, then update
209 	 * the permissions to the superblock.
210 	 */
211 	if (!(ti->flags & TRACEFS_UID_PERM_SET))
212 		inode->i_uid = uid;
213 
214 	if (!(ti->flags & TRACEFS_GID_PERM_SET))
215 		inode->i_gid = gid;
216 }
217 
218 static int tracefs_permission(struct mnt_idmap *idmap,
219 			      struct inode *inode, int mask)
220 {
221 	set_tracefs_inode_owner(inode);
222 	return generic_permission(idmap, inode, mask);
223 }
224 
225 static int tracefs_getattr(struct mnt_idmap *idmap,
226 			   const struct path *path, struct kstat *stat,
227 			   u32 request_mask, unsigned int flags)
228 {
229 	struct inode *inode = d_backing_inode(path->dentry);
230 
231 	set_tracefs_inode_owner(inode);
232 	generic_fillattr(idmap, request_mask, inode, stat);
233 	return 0;
234 }
235 
236 static int tracefs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
237 			   struct iattr *attr)
238 {
239 	unsigned int ia_valid = attr->ia_valid;
240 	struct inode *inode = d_inode(dentry);
241 	struct tracefs_inode *ti = get_tracefs(inode);
242 
243 	if (ia_valid & ATTR_UID)
244 		ti->flags |= TRACEFS_UID_PERM_SET;
245 
246 	if (ia_valid & ATTR_GID)
247 		ti->flags |= TRACEFS_GID_PERM_SET;
248 
249 	return simple_setattr(idmap, dentry, attr);
250 }
251 
252 static const struct inode_operations tracefs_instance_dir_inode_operations = {
253 	.lookup		= simple_lookup,
254 	.mkdir		= tracefs_syscall_mkdir,
255 	.rmdir		= tracefs_syscall_rmdir,
256 	.permission	= tracefs_permission,
257 	.getattr	= tracefs_getattr,
258 	.setattr	= tracefs_setattr,
259 };
260 
261 static const struct inode_operations tracefs_dir_inode_operations = {
262 	.lookup		= simple_lookup,
263 	.permission	= tracefs_permission,
264 	.getattr	= tracefs_getattr,
265 	.setattr	= tracefs_setattr,
266 };
267 
268 static const struct inode_operations tracefs_file_inode_operations = {
269 	.permission	= tracefs_permission,
270 	.getattr	= tracefs_getattr,
271 	.setattr	= tracefs_setattr,
272 };
273 
274 struct inode *tracefs_get_inode(struct super_block *sb)
275 {
276 	struct inode *inode = new_inode(sb);
277 	if (inode) {
278 		inode->i_ino = get_next_ino();
279 		simple_inode_init_ts(inode);
280 	}
281 	return inode;
282 }
283 
284 struct tracefs_fs_info {
285 	kuid_t uid;
286 	kgid_t gid;
287 	umode_t mode;
288 	/* Opt_* bitfield. */
289 	unsigned int opts;
290 };
291 
292 enum {
293 	Opt_uid,
294 	Opt_gid,
295 	Opt_mode,
296 };
297 
298 static const struct fs_parameter_spec tracefs_param_specs[] = {
299 	fsparam_u32	("gid",		Opt_gid),
300 	fsparam_u32oct	("mode",	Opt_mode),
301 	fsparam_u32	("uid",		Opt_uid),
302 	{}
303 };
304 
305 static int tracefs_parse_param(struct fs_context *fc, struct fs_parameter *param)
306 {
307 	struct tracefs_fs_info *opts = fc->s_fs_info;
308 	struct fs_parse_result result;
309 	kuid_t uid;
310 	kgid_t gid;
311 	int opt;
312 
313 	opt = fs_parse(fc, tracefs_param_specs, param, &result);
314 	if (opt < 0)
315 		return opt;
316 
317 	switch (opt) {
318 	case Opt_uid:
319 		uid = make_kuid(current_user_ns(), result.uint_32);
320 		if (!uid_valid(uid))
321 			return invalf(fc, "Unknown uid");
322 		opts->uid = uid;
323 		break;
324 	case Opt_gid:
325 		gid = make_kgid(current_user_ns(), result.uint_32);
326 		if (!gid_valid(gid))
327 			return invalf(fc, "Unknown gid");
328 		opts->gid = gid;
329 		break;
330 	case Opt_mode:
331 		opts->mode = result.uint_32 & S_IALLUGO;
332 		break;
333 	/*
334 	 * We might like to report bad mount options here;
335 	 * but traditionally tracefs has ignored all mount options
336 	 */
337 	}
338 
339 	opts->opts |= BIT(opt);
340 
341 	return 0;
342 }
343 
344 static int tracefs_apply_options(struct super_block *sb, bool remount)
345 {
346 	struct tracefs_fs_info *fsi = sb->s_fs_info;
347 	struct inode *inode = d_inode(sb->s_root);
348 	struct tracefs_inode *ti;
349 	bool update_uid, update_gid;
350 	umode_t tmp_mode;
351 
352 	/*
353 	 * On remount, only reset mode/uid/gid if they were provided as mount
354 	 * options.
355 	 */
356 
357 	if (!remount || fsi->opts & BIT(Opt_mode)) {
358 		tmp_mode = READ_ONCE(inode->i_mode) & ~S_IALLUGO;
359 		tmp_mode |= fsi->mode;
360 		WRITE_ONCE(inode->i_mode, tmp_mode);
361 	}
362 
363 	if (!remount || fsi->opts & BIT(Opt_uid))
364 		inode->i_uid = fsi->uid;
365 
366 	if (!remount || fsi->opts & BIT(Opt_gid))
367 		inode->i_gid = fsi->gid;
368 
369 	if (remount && (fsi->opts & BIT(Opt_uid) || fsi->opts & BIT(Opt_gid))) {
370 
371 		update_uid = fsi->opts & BIT(Opt_uid);
372 		update_gid = fsi->opts & BIT(Opt_gid);
373 
374 		rcu_read_lock();
375 		list_for_each_entry_rcu(ti, &tracefs_inodes, list) {
376 			if (update_uid)
377 				ti->flags &= ~TRACEFS_UID_PERM_SET;
378 
379 			if (update_gid)
380 				ti->flags &= ~TRACEFS_GID_PERM_SET;
381 
382 			if (ti->flags & TRACEFS_EVENT_INODE)
383 				eventfs_remount(ti, update_uid, update_gid);
384 		}
385 		rcu_read_unlock();
386 	}
387 
388 	return 0;
389 }
390 
391 static int tracefs_reconfigure(struct fs_context *fc)
392 {
393 	struct super_block *sb = fc->root->d_sb;
394 	struct tracefs_fs_info *sb_opts = sb->s_fs_info;
395 	struct tracefs_fs_info *new_opts = fc->s_fs_info;
396 
397 	sync_filesystem(sb);
398 	/* structure copy of new mount options to sb */
399 	*sb_opts = *new_opts;
400 
401 	return tracefs_apply_options(sb, true);
402 }
403 
404 static int tracefs_show_options(struct seq_file *m, struct dentry *root)
405 {
406 	struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
407 
408 	if (!uid_eq(fsi->uid, GLOBAL_ROOT_UID))
409 		seq_printf(m, ",uid=%u",
410 			   from_kuid_munged(&init_user_ns, fsi->uid));
411 	if (!gid_eq(fsi->gid, GLOBAL_ROOT_GID))
412 		seq_printf(m, ",gid=%u",
413 			   from_kgid_munged(&init_user_ns, fsi->gid));
414 	if (fsi->mode != TRACEFS_DEFAULT_MODE)
415 		seq_printf(m, ",mode=%o", fsi->mode);
416 
417 	return 0;
418 }
419 
420 static const struct super_operations tracefs_super_operations = {
421 	.alloc_inode    = tracefs_alloc_inode,
422 	.free_inode     = tracefs_free_inode,
423 	.drop_inode     = generic_delete_inode,
424 	.statfs		= simple_statfs,
425 	.show_options	= tracefs_show_options,
426 };
427 
428 /*
429  * It would be cleaner if eventfs had its own dentry ops.
430  *
431  * Note that d_revalidate is called potentially under RCU,
432  * so it can't take the eventfs mutex etc. It's fine - if
433  * we open a file just as it's marked dead, things will
434  * still work just fine, and just see the old stale case.
435  */
436 static void tracefs_d_release(struct dentry *dentry)
437 {
438 	if (dentry->d_fsdata)
439 		eventfs_d_release(dentry);
440 }
441 
442 static int tracefs_d_revalidate(struct dentry *dentry, unsigned int flags)
443 {
444 	struct eventfs_inode *ei = dentry->d_fsdata;
445 
446 	return !(ei && ei->is_freed);
447 }
448 
449 static void tracefs_d_iput(struct dentry *dentry, struct inode *inode)
450 {
451 	struct tracefs_inode *ti = get_tracefs(inode);
452 
453 	/*
454 	 * This inode is being freed and cannot be used for
455 	 * eventfs. Clear the flag so that it doesn't call into
456 	 * eventfs during the remount flag updates. The eventfs_inode
457 	 * gets freed after an RCU cycle, so the content will still
458 	 * be safe if the iteration is going on now.
459 	 */
460 	ti->flags &= ~TRACEFS_EVENT_INODE;
461 }
462 
463 static const struct dentry_operations tracefs_dentry_operations = {
464 	.d_iput = tracefs_d_iput,
465 	.d_revalidate = tracefs_d_revalidate,
466 	.d_release = tracefs_d_release,
467 };
468 
469 static int tracefs_fill_super(struct super_block *sb, struct fs_context *fc)
470 {
471 	static const struct tree_descr trace_files[] = {{""}};
472 	int err;
473 
474 	err = simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
475 	if (err)
476 		return err;
477 
478 	sb->s_op = &tracefs_super_operations;
479 	sb->s_d_op = &tracefs_dentry_operations;
480 
481 	tracefs_apply_options(sb, false);
482 
483 	return 0;
484 }
485 
486 static int tracefs_get_tree(struct fs_context *fc)
487 {
488 	return get_tree_single(fc, tracefs_fill_super);
489 }
490 
491 static void tracefs_free_fc(struct fs_context *fc)
492 {
493 	kfree(fc->s_fs_info);
494 }
495 
496 static const struct fs_context_operations tracefs_context_ops = {
497 	.free		= tracefs_free_fc,
498 	.parse_param	= tracefs_parse_param,
499 	.get_tree	= tracefs_get_tree,
500 	.reconfigure	= tracefs_reconfigure,
501 };
502 
503 static int tracefs_init_fs_context(struct fs_context *fc)
504 {
505 	struct tracefs_fs_info *fsi;
506 
507 	fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
508 	if (!fsi)
509 		return -ENOMEM;
510 
511 	fsi->mode = TRACEFS_DEFAULT_MODE;
512 
513 	fc->s_fs_info = fsi;
514 	fc->ops = &tracefs_context_ops;
515 	return 0;
516 }
517 
518 static struct file_system_type trace_fs_type = {
519 	.owner =	THIS_MODULE,
520 	.name =		"tracefs",
521 	.init_fs_context = tracefs_init_fs_context,
522 	.parameters	= tracefs_param_specs,
523 	.kill_sb =	kill_litter_super,
524 };
525 MODULE_ALIAS_FS("tracefs");
526 
527 struct dentry *tracefs_start_creating(const char *name, struct dentry *parent)
528 {
529 	struct dentry *dentry;
530 	int error;
531 
532 	pr_debug("tracefs: creating file '%s'\n",name);
533 
534 	error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
535 			      &tracefs_mount_count);
536 	if (error)
537 		return ERR_PTR(error);
538 
539 	/* If the parent is not specified, we create it in the root.
540 	 * We need the root dentry to do this, which is in the super
541 	 * block. A pointer to that is in the struct vfsmount that we
542 	 * have around.
543 	 */
544 	if (!parent)
545 		parent = tracefs_mount->mnt_root;
546 
547 	inode_lock(d_inode(parent));
548 	if (unlikely(IS_DEADDIR(d_inode(parent))))
549 		dentry = ERR_PTR(-ENOENT);
550 	else
551 		dentry = lookup_one_len(name, parent, strlen(name));
552 	if (!IS_ERR(dentry) && d_inode(dentry)) {
553 		dput(dentry);
554 		dentry = ERR_PTR(-EEXIST);
555 	}
556 
557 	if (IS_ERR(dentry)) {
558 		inode_unlock(d_inode(parent));
559 		simple_release_fs(&tracefs_mount, &tracefs_mount_count);
560 	}
561 
562 	return dentry;
563 }
564 
565 struct dentry *tracefs_failed_creating(struct dentry *dentry)
566 {
567 	inode_unlock(d_inode(dentry->d_parent));
568 	dput(dentry);
569 	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
570 	return NULL;
571 }
572 
573 struct dentry *tracefs_end_creating(struct dentry *dentry)
574 {
575 	inode_unlock(d_inode(dentry->d_parent));
576 	return dentry;
577 }
578 
579 /* Find the inode that this will use for default */
580 static struct inode *instance_inode(struct dentry *parent, struct inode *inode)
581 {
582 	struct tracefs_inode *ti;
583 
584 	/* If parent is NULL then use root inode */
585 	if (!parent)
586 		return d_inode(inode->i_sb->s_root);
587 
588 	/* Find the inode that is flagged as an instance or the root inode */
589 	while (!IS_ROOT(parent)) {
590 		ti = get_tracefs(d_inode(parent));
591 		if (ti->flags & TRACEFS_INSTANCE_INODE)
592 			break;
593 		parent = parent->d_parent;
594 	}
595 
596 	return d_inode(parent);
597 }
598 
599 /**
600  * tracefs_create_file - create a file in the tracefs filesystem
601  * @name: a pointer to a string containing the name of the file to create.
602  * @mode: the permission that the file should have.
603  * @parent: a pointer to the parent dentry for this file.  This should be a
604  *          directory dentry if set.  If this parameter is NULL, then the
605  *          file will be created in the root of the tracefs filesystem.
606  * @data: a pointer to something that the caller will want to get to later
607  *        on.  The inode.i_private pointer will point to this value on
608  *        the open() call.
609  * @fops: a pointer to a struct file_operations that should be used for
610  *        this file.
611  *
612  * This is the basic "create a file" function for tracefs.  It allows for a
613  * wide range of flexibility in creating a file, or a directory (if you want
614  * to create a directory, the tracefs_create_dir() function is
615  * recommended to be used instead.)
616  *
617  * This function will return a pointer to a dentry if it succeeds.  This
618  * pointer must be passed to the tracefs_remove() function when the file is
619  * to be removed (no automatic cleanup happens if your module is unloaded,
620  * you are responsible here.)  If an error occurs, %NULL will be returned.
621  *
622  * If tracefs is not enabled in the kernel, the value -%ENODEV will be
623  * returned.
624  */
625 struct dentry *tracefs_create_file(const char *name, umode_t mode,
626 				   struct dentry *parent, void *data,
627 				   const struct file_operations *fops)
628 {
629 	struct tracefs_inode *ti;
630 	struct dentry *dentry;
631 	struct inode *inode;
632 
633 	if (security_locked_down(LOCKDOWN_TRACEFS))
634 		return NULL;
635 
636 	if (!(mode & S_IFMT))
637 		mode |= S_IFREG;
638 	BUG_ON(!S_ISREG(mode));
639 	dentry = tracefs_start_creating(name, parent);
640 
641 	if (IS_ERR(dentry))
642 		return NULL;
643 
644 	inode = tracefs_get_inode(dentry->d_sb);
645 	if (unlikely(!inode))
646 		return tracefs_failed_creating(dentry);
647 
648 	ti = get_tracefs(inode);
649 	ti->private = instance_inode(parent, inode);
650 
651 	inode->i_mode = mode;
652 	inode->i_op = &tracefs_file_inode_operations;
653 	inode->i_fop = fops ? fops : &tracefs_file_operations;
654 	inode->i_private = data;
655 	inode->i_uid = d_inode(dentry->d_parent)->i_uid;
656 	inode->i_gid = d_inode(dentry->d_parent)->i_gid;
657 	d_instantiate(dentry, inode);
658 	fsnotify_create(d_inode(dentry->d_parent), dentry);
659 	return tracefs_end_creating(dentry);
660 }
661 
662 static struct dentry *__create_dir(const char *name, struct dentry *parent,
663 				   const struct inode_operations *ops)
664 {
665 	struct tracefs_inode *ti;
666 	struct dentry *dentry = tracefs_start_creating(name, parent);
667 	struct inode *inode;
668 
669 	if (IS_ERR(dentry))
670 		return NULL;
671 
672 	inode = tracefs_get_inode(dentry->d_sb);
673 	if (unlikely(!inode))
674 		return tracefs_failed_creating(dentry);
675 
676 	/* Do not set bits for OTH */
677 	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUSR| S_IRGRP | S_IXUSR | S_IXGRP;
678 	inode->i_op = ops;
679 	inode->i_fop = &simple_dir_operations;
680 	inode->i_uid = d_inode(dentry->d_parent)->i_uid;
681 	inode->i_gid = d_inode(dentry->d_parent)->i_gid;
682 
683 	ti = get_tracefs(inode);
684 	ti->private = instance_inode(parent, inode);
685 
686 	/* directory inodes start off with i_nlink == 2 (for "." entry) */
687 	inc_nlink(inode);
688 	d_instantiate(dentry, inode);
689 	inc_nlink(d_inode(dentry->d_parent));
690 	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
691 	return tracefs_end_creating(dentry);
692 }
693 
694 /**
695  * tracefs_create_dir - create a directory in the tracefs filesystem
696  * @name: a pointer to a string containing the name of the directory to
697  *        create.
698  * @parent: a pointer to the parent dentry for this file.  This should be a
699  *          directory dentry if set.  If this parameter is NULL, then the
700  *          directory will be created in the root of the tracefs filesystem.
701  *
702  * This function creates a directory in tracefs with the given name.
703  *
704  * This function will return a pointer to a dentry if it succeeds.  This
705  * pointer must be passed to the tracefs_remove() function when the file is
706  * to be removed. If an error occurs, %NULL will be returned.
707  *
708  * If tracing is not enabled in the kernel, the value -%ENODEV will be
709  * returned.
710  */
711 struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
712 {
713 	if (security_locked_down(LOCKDOWN_TRACEFS))
714 		return NULL;
715 
716 	return __create_dir(name, parent, &tracefs_dir_inode_operations);
717 }
718 
719 /**
720  * tracefs_create_instance_dir - create the tracing instances directory
721  * @name: The name of the instances directory to create
722  * @parent: The parent directory that the instances directory will exist
723  * @mkdir: The function to call when a mkdir is performed.
724  * @rmdir: The function to call when a rmdir is performed.
725  *
726  * Only one instances directory is allowed.
727  *
728  * The instances directory is special as it allows for mkdir and rmdir
729  * to be done by userspace. When a mkdir or rmdir is performed, the inode
730  * locks are released and the methods passed in (@mkdir and @rmdir) are
731  * called without locks and with the name of the directory being created
732  * within the instances directory.
733  *
734  * Returns the dentry of the instances directory.
735  */
736 __init struct dentry *tracefs_create_instance_dir(const char *name,
737 					  struct dentry *parent,
738 					  int (*mkdir)(const char *name),
739 					  int (*rmdir)(const char *name))
740 {
741 	struct dentry *dentry;
742 
743 	/* Only allow one instance of the instances directory. */
744 	if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
745 		return NULL;
746 
747 	dentry = __create_dir(name, parent, &tracefs_instance_dir_inode_operations);
748 	if (!dentry)
749 		return NULL;
750 
751 	tracefs_ops.mkdir = mkdir;
752 	tracefs_ops.rmdir = rmdir;
753 
754 	return dentry;
755 }
756 
757 static void remove_one(struct dentry *victim)
758 {
759 	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
760 }
761 
762 /**
763  * tracefs_remove - recursively removes a directory
764  * @dentry: a pointer to a the dentry of the directory to be removed.
765  *
766  * This function recursively removes a directory tree in tracefs that
767  * was previously created with a call to another tracefs function
768  * (like tracefs_create_file() or variants thereof.)
769  */
770 void tracefs_remove(struct dentry *dentry)
771 {
772 	if (IS_ERR_OR_NULL(dentry))
773 		return;
774 
775 	simple_pin_fs(&trace_fs_type, &tracefs_mount, &tracefs_mount_count);
776 	simple_recursive_removal(dentry, remove_one);
777 	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
778 }
779 
780 /**
781  * tracefs_initialized - Tells whether tracefs has been registered
782  */
783 bool tracefs_initialized(void)
784 {
785 	return tracefs_registered;
786 }
787 
788 static void init_once(void *foo)
789 {
790 	struct tracefs_inode *ti = (struct tracefs_inode *) foo;
791 
792 	/* inode_init_once() calls memset() on the vfs_inode portion */
793 	inode_init_once(&ti->vfs_inode);
794 
795 	/* Zero out the rest */
796 	memset_after(ti, 0, vfs_inode);
797 }
798 
799 static int __init tracefs_init(void)
800 {
801 	int retval;
802 
803 	tracefs_inode_cachep = kmem_cache_create("tracefs_inode_cache",
804 						 sizeof(struct tracefs_inode),
805 						 0, (SLAB_RECLAIM_ACCOUNT|
806 						     SLAB_ACCOUNT),
807 						 init_once);
808 	if (!tracefs_inode_cachep)
809 		return -ENOMEM;
810 
811 	retval = sysfs_create_mount_point(kernel_kobj, "tracing");
812 	if (retval)
813 		return -EINVAL;
814 
815 	retval = register_filesystem(&trace_fs_type);
816 	if (!retval)
817 		tracefs_registered = true;
818 
819 	return retval;
820 }
821 core_initcall(tracefs_init);
822