summaryrefslogtreecommitdiff
path: root/fs/tracefs/inode.c
blob: 891653ba9cf35863f5cc83638b2a2a9a88a03444 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
// 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/mount.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/parser.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;

static struct inode *tracefs_alloc_inode(struct super_block *sb)
{
	struct tracefs_inode *ti;

	ti = kmem_cache_alloc(tracefs_inode_cachep, GFP_KERNEL);
	if (!ti)
		return NULL;

	ti->flags = 0;

	return &ti->vfs_inode;
}

static void tracefs_free_inode(struct inode *inode)
{
	kmem_cache_free(tracefs_inode_cachep, get_tracefs(inode));
}

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)
{
	char *name;
	int ret;

	name = get_dname(dentry);
	if (!name)
		return -ENOMEM;

	/*
	 * 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 const struct inode_operations tracefs_dir_inode_operations = {
	.lookup		= simple_lookup,
	.mkdir		= tracefs_syscall_mkdir,
	.rmdir		= tracefs_syscall_rmdir,
};

struct inode *tracefs_get_inode(struct super_block *sb)
{
	struct inode *inode = new_inode(sb);
	if (inode) {
		inode->i_ino = get_next_ino();
		inode->i_atime = inode->i_mtime = inode_set_ctime_current(inode);
	}
	return inode;
}

struct tracefs_mount_opts {
	kuid_t uid;
	kgid_t gid;
	umode_t mode;
	/* Opt_* bitfield. */
	unsigned int opts;
};

enum {
	Opt_uid,
	Opt_gid,
	Opt_mode,
	Opt_err
};

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

struct tracefs_fs_info {
	struct tracefs_mount_opts mount_opts;
};

static void change_gid(struct dentry *dentry, kgid_t gid)
{
	if (!dentry->d_inode)
		return;
	dentry->d_inode->i_gid = gid;
}

/*
 * Taken from d_walk, but without he need for handling renames.
 * Nothing can be renamed while walking the list, as tracefs
 * does not support renames. This is only called when mounting
 * or remounting the file system, to set all the files to
 * the given gid.
 */
static void set_gid(struct dentry *parent, kgid_t gid)
{
	struct dentry *this_parent;
	struct list_head *next;

	this_parent = parent;
	spin_lock(&this_parent->d_lock);

	change_gid(this_parent, gid);
repeat:
	next = this_parent->d_subdirs.next;
resume:
	while (next != &this_parent->d_subdirs) {
		struct list_head *tmp = next;
		struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
		next = tmp->next;

		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);

		change_gid(dentry, gid);

		if (!list_empty(&dentry->d_subdirs)) {
			spin_unlock(&this_parent->d_lock);
			spin_release(&dentry->d_lock.dep_map, _RET_IP_);
			this_parent = dentry;
			spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
			goto repeat;
		}
		spin_unlock(&dentry->d_lock);
	}
	/*
	 * All done at this level ... ascend and resume the search.
	 */
	rcu_read_lock();
ascend:
	if (this_parent != parent) {
		struct dentry *child = this_parent;
		this_parent = child->d_parent;

		spin_unlock(&child->d_lock);
		spin_lock(&this_parent->d_lock);

		/* go into the first sibling still alive */
		do {
			next = child->d_child.next;
			if (next == &this_parent->d_subdirs)
				goto ascend;
			child = list_entry(next, struct dentry, d_child);
		} while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
		rcu_read_unlock();
		goto resume;
	}
	rcu_read_unlock();
	spin_unlock(&this_parent->d_lock);
	return;
}

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

	opts->opts = 0;
	opts->mode = TRACEFS_DEFAULT_MODE;

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

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

		opts->opts |= BIT(token);
	}

	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_mount_opts *opts = &fsi->mount_opts;
	umode_t tmp_mode;

	/*
	 * On remount, only reset mode/uid/gid if they were provided as mount
	 * options.
	 */

	if (!remount || opts->opts & BIT(Opt_mode)) {
		tmp_mode = READ_ONCE(inode->i_mode) & ~S_IALLUGO;
		tmp_mode |= opts->mode;
		WRITE_ONCE(inode->i_mode, tmp_mode);
	}

	if (!remount || opts->opts & BIT(Opt_uid))
		inode->i_uid = opts->uid;

	if (!remount || opts->opts & BIT(Opt_gid)) {
		/* Set all the group ids to the mount option */
		set_gid(sb->s_root, opts->gid);
	}

	return 0;
}

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

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

	tracefs_apply_options(sb, true);

fail:
	return err;
}

static int tracefs_show_options(struct seq_file *m, struct dentry *root)
{
	struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
	struct tracefs_mount_opts *opts = &fsi->mount_opts;

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

	return 0;
}

static const struct super_operations tracefs_super_operations = {
	.alloc_inode    = tracefs_alloc_inode,
	.free_inode     = tracefs_free_inode,
	.drop_inode     = generic_delete_inode,
	.statfs		= simple_statfs,
	.remount_fs	= tracefs_remount,
	.show_options	= tracefs_show_options,
};

static void tracefs_dentry_iput(struct dentry *dentry, struct inode *inode)
{
	struct tracefs_inode *ti;

	if (!dentry || !inode)
		return;

	ti = get_tracefs(inode);
	if (ti && ti->flags & TRACEFS_EVENT_INODE)
		eventfs_set_ef_status_free(ti, dentry);
	iput(inode);
}

static const struct dentry_operations tracefs_dentry_operations = {
	.d_iput = tracefs_dentry_iput,
};

static int trace_fill_super(struct super_block *sb, void *data, int silent)
{
	static const struct tree_descr trace_files[] = {{""}};
	struct tracefs_fs_info *fsi;
	int err;

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

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

	err  =  simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
	if (err)
		goto fail;

	sb->s_op = &tracefs_super_operations;
	sb->s_d_op = &tracefs_dentry_operations;

	tracefs_apply_options(sb, false);

	return 0;

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

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

static struct file_system_type trace_fs_type = {
	.owner =	THIS_MODULE,
	.name =		"tracefs",
	.mount =	trace_mount,
	.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;
}

/**
 * eventfs_start_creating - start the process of creating a dentry
 * @name: Name of the file created for the dentry
 * @parent: The parent dentry where this dentry will be created
 *
 * This is a simple helper function for the dynamically created eventfs
 * files. When the directory of the eventfs files are accessed, their
 * dentries are created on the fly. This function is used to start that
 * process.
 */
struct dentry *eventfs_start_creating(const char *name, struct dentry *parent)
{
	struct dentry *dentry;
	int error;

	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;

	if (unlikely(IS_DEADDIR(parent->d_inode)))
		dentry = ERR_PTR(-ENOENT);
	else
		dentry = lookup_one_len(name, parent, strlen(name));

	if (!IS_ERR(dentry) && dentry->d_inode) {
		dput(dentry);
		dentry = ERR_PTR(-EEXIST);
	}

	if (IS_ERR(dentry))
		simple_release_fs(&tracefs_mount, &tracefs_mount_count);

	return dentry;
}

/**
 * eventfs_failed_creating - clean up a failed eventfs dentry creation
 * @dentry: The dentry to clean up
 *
 * If after calling eventfs_start_creating(), a failure is detected, the
 * resources created by eventfs_start_creating() needs to be cleaned up. In
 * that case, this function should be called to perform that clean up.
 */
struct dentry *eventfs_failed_creating(struct dentry *dentry)
{
	dput(dentry);
	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
	return NULL;
}

/**
 * eventfs_end_creating - Finish the process of creating a eventfs dentry
 * @dentry: The dentry that has successfully been created.
 *
 * This function is currently just a place holder to match
 * eventfs_start_creating(). In case any synchronization needs to be added,
 * this function will be used to implement that without having to modify
 * the callers of eventfs_start_creating().
 */
struct dentry *eventfs_end_creating(struct dentry *dentry)
{
	return dentry;
}

/**
 * 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 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);

	inode->i_mode = mode;
	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 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;

	/* 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, &simple_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_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(&ti->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_MEM_SPREAD|
						     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);