aboutsummaryrefslogtreecommitdiff
path: root/fs/sysfs/file.c
blob: a12ac0356c69cd409a856b5a551ce1768cf7ad16 (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
// SPDX-License-Identifier: GPL-2.0
/*
 * fs/sysfs/file.c - sysfs regular (text) file implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
 *
 * Please see Documentation/filesystems/sysfs.rst for more information.
 */

#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/seq_file.h>
#include <linux/mm.h>

#include "sysfs.h"

/*
 * Determine ktype->sysfs_ops for the given kernfs_node.  This function
 * must be called while holding an active reference.
 */
static const struct sysfs_ops *sysfs_file_ops(struct kernfs_node *kn)
{
	struct kobject *kobj = kn->parent->priv;

	if (kn->flags & KERNFS_LOCKDEP)
		lockdep_assert_held(kn);
	return kobj->ktype ? kobj->ktype->sysfs_ops : NULL;
}

/*
 * Reads on sysfs are handled through seq_file, which takes care of hairy
 * details like buffering and seeking.  The following function pipes
 * sysfs_ops->show() result through seq_file.
 */
static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
{
	struct kernfs_open_file *of = sf->private;
	struct kobject *kobj = of->kn->parent->priv;
	const struct sysfs_ops *ops = sysfs_file_ops(of->kn);
	ssize_t count;
	char *buf;

	if (WARN_ON_ONCE(!ops->show))
		return -EINVAL;

	/* acquire buffer and ensure that it's >= PAGE_SIZE and clear */
	count = seq_get_buf(sf, &buf);
	if (count < PAGE_SIZE) {
		seq_commit(sf, -1);
		return 0;
	}
	memset(buf, 0, PAGE_SIZE);

	count = ops->show(kobj, of->kn->priv, buf);
	if (count < 0)
		return count;

	/*
	 * The code works fine with PAGE_SIZE return but it's likely to
	 * indicate truncated result or overflow in normal use cases.
	 */
	if (count >= (ssize_t)PAGE_SIZE) {
		printk("fill_read_buffer: %pS returned bad count\n",
				ops->show);
		/* Try to struggle along */
		count = PAGE_SIZE - 1;
	}
	seq_commit(sf, count);
	return 0;
}

static ssize_t sysfs_kf_bin_read(struct kernfs_open_file *of, char *buf,
				 size_t count, loff_t pos)
{
	struct bin_attribute *battr = of->kn->priv;
	struct kobject *kobj = of->kn->parent->priv;
	loff_t size = file_inode(of->file)->i_size;

	if (!count)
		return 0;

	if (size) {
		if (pos >= size)
			return 0;
		if (pos + count > size)
			count = size - pos;
	}

	if (!battr->read)
		return -EIO;

	return battr->read(of->file, kobj, battr, buf, pos, count);
}

/* kernfs read callback for regular sysfs files with pre-alloc */
static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
			     size_t count, loff_t pos)
{
	const struct sysfs_ops *ops = sysfs_file_ops(of->kn);
	struct kobject *kobj = of->kn->parent->priv;
	ssize_t len;

	/*
	 * If buf != of->prealloc_buf, we don't know how
	 * large it is, so cannot safely pass it to ->show
	 */
	if (WARN_ON_ONCE(buf != of->prealloc_buf))
		return 0;
	len = ops->show(kobj, of->kn->priv, buf);
	if (len < 0)
		return len;
	if (pos) {
		if (len <= pos)
			return 0;
		len -= pos;
		memmove(buf, buf + pos, len);
	}
	return min_t(ssize_t, count, len);
}

/* kernfs write callback for regular sysfs files */
static ssize_t sysfs_kf_write(struct kernfs_open_file *of, char *buf,
			      size_t count, loff_t pos)
{
	const struct sysfs_ops *ops = sysfs_file_ops(of->kn);
	struct kobject *kobj = of->kn->parent->priv;

	if (!count)
		return 0;

	return ops->store(kobj, of->kn->priv, buf, count);
}

/* kernfs write callback for bin sysfs files */
static ssize_t sysfs_kf_bin_write(struct kernfs_open_file *of, char *buf,
				  size_t count, loff_t pos)
{
	struct bin_attribute *battr = of->kn->priv;
	struct kobject *kobj = of->kn->parent->priv;
	loff_t size = file_inode(of->file)->i_size;

	if (size) {
		if (size <= pos)
			return -EFBIG;
		count = min_t(ssize_t, count, size - pos);
	}
	if (!count)
		return 0;

	if (!battr->write)
		return -EIO;

	return battr->write(of->file, kobj, battr, buf, pos, count);
}

static int sysfs_kf_bin_mmap(struct kernfs_open_file *of,
			     struct vm_area_struct *vma)
{
	struct bin_attribute *battr = of->kn->priv;
	struct kobject *kobj = of->kn->parent->priv;

	return battr->mmap(of->file, kobj, battr, vma);
}

static int sysfs_kf_bin_open(struct kernfs_open_file *of)
{
	struct bin_attribute *battr = of->kn->priv;

	if (battr->f_mapping)
		of->file->f_mapping = battr->f_mapping();

	return 0;
}

void sysfs_notify(struct kobject *kobj, const char *dir, const char *attr)
{
	struct kernfs_node *kn = kobj->sd, *tmp;

	if (kn && dir)
		kn = kernfs_find_and_get(kn, dir);
	else
		kernfs_get(kn);

	if (kn && attr) {
		tmp = kernfs_find_and_get(kn, attr);
		kernfs_put(kn);
		kn = tmp;
	}

	if (kn) {
		kernfs_notify(kn);
		kernfs_put(kn);
	}
}
EXPORT_SYMBOL_GPL(sysfs_notify);

static const struct kernfs_ops sysfs_file_kfops_empty = {
};

static const struct kernfs_ops sysfs_file_kfops_ro = {
	.seq_show	= sysfs_kf_seq_show,
};

static const struct kernfs_ops sysfs_file_kfops_wo = {
	.write		= sysfs_kf_write,
};

static const struct kernfs_ops sysfs_file_kfops_rw = {
	.seq_show	= sysfs_kf_seq_show,
	.write		= sysfs_kf_write,
};

static const struct kernfs_ops sysfs_prealloc_kfops_ro = {
	.read		= sysfs_kf_read,
	.prealloc	= true,
};

static const struct kernfs_ops sysfs_prealloc_kfops_wo = {
	.write		= sysfs_kf_write,
	.prealloc	= true,
};

static const struct kernfs_ops sysfs_prealloc_kfops_rw = {
	.read		= sysfs_kf_read,
	.write		= sysfs_kf_write,
	.prealloc	= true,
};

static const struct kernfs_ops sysfs_bin_kfops_ro = {
	.read		= sysfs_kf_bin_read,
};

static const struct kernfs_ops sysfs_bin_kfops_wo = {
	.write		= sysfs_kf_bin_write,
};

static const struct kernfs_ops sysfs_bin_kfops_rw = {
	.read		= sysfs_kf_bin_read,
	.write		= sysfs_kf_bin_write,
};

static const struct kernfs_ops sysfs_bin_kfops_mmap = {
	.read		= sysfs_kf_bin_read,
	.write		= sysfs_kf_bin_write,
	.mmap		= sysfs_kf_bin_mmap,
	.open		= sysfs_kf_bin_open,
};

int sysfs_add_file_mode_ns(struct kernfs_node *parent,
		const struct attribute *attr, umode_t mode, kuid_t uid,
		kgid_t gid, const void *ns)
{
	struct kobject *kobj = parent->priv;
	const struct sysfs_ops *sysfs_ops = kobj->ktype->sysfs_ops;
	struct lock_class_key *key = NULL;
	const struct kernfs_ops *ops = NULL;
	struct kernfs_node *kn;

	/* every kobject with an attribute needs a ktype assigned */
	if (WARN(!sysfs_ops, KERN_ERR
			"missing sysfs attribute operations for kobject: %s\n",
			kobject_name(kobj)))
		return -EINVAL;

	if (mode & SYSFS_PREALLOC) {
		if (sysfs_ops->show && sysfs_ops->store)
			ops = &sysfs_prealloc_kfops_rw;
		else if (sysfs_ops->show)
			ops = &sysfs_prealloc_kfops_ro;
		else if (sysfs_ops->store)
			ops = &sysfs_prealloc_kfops_wo;
	} else {
		if (sysfs_ops->show && sysfs_ops->store)
			ops = &sysfs_file_kfops_rw;
		else if (sysfs_ops->show)
			ops = &sysfs_file_kfops_ro;
		else if (sysfs_ops->store)
			ops = &sysfs_file_kfops_wo;
	}

	if (!ops)
		ops = &sysfs_file_kfops_empty;

#ifdef CONFIG_DEBUG_LOCK_ALLOC
	if (!attr->ignore_lockdep)
		key = attr->key ?: (struct lock_class_key *)&attr->skey;
#endif

	kn = __kernfs_create_file(parent, attr->name, mode & 0777, uid, gid,
				  PAGE_SIZE, ops, (void *)attr, ns, key);
	if (IS_ERR(kn)) {
		if (PTR_ERR(kn) == -EEXIST)
			sysfs_warn_dup(parent, attr->name);
		return PTR_ERR(kn);
	}
	return 0;
}

int sysfs_add_bin_file_mode_ns(struct kernfs_node *parent,
		const struct bin_attribute *battr, umode_t mode,
		kuid_t uid, kgid_t gid, const void *ns)
{
	const struct attribute *attr = &battr->attr;
	struct lock_class_key *key = NULL;
	const struct kernfs_ops *ops;
	struct kernfs_node *kn;

	if (battr->mmap)
		ops = &sysfs_bin_kfops_mmap;
	else if (battr->read && battr->write)
		ops = &sysfs_bin_kfops_rw;
	else if (battr->read)
		ops = &sysfs_bin_kfops_ro;
	else if (battr->write)
		ops = &sysfs_bin_kfops_wo;
	else
		ops = &sysfs_file_kfops_empty;

#ifdef CONFIG_DEBUG_LOCK_ALLOC
	if (!attr->ignore_lockdep)
		key = attr->key ?: (struct lock_class_key *)&attr->skey;
#endif

	kn = __kernfs_create_file(parent, attr->name, mode & 0777, uid, gid,
				  battr->size, ops, (void *)attr, ns, key);
	if (IS_ERR(kn)) {
		if (PTR_ERR(kn) == -EEXIST)
			sysfs_warn_dup(parent, attr->name);
		return PTR_ERR(kn);
	}
	return 0;
}

/**
 * sysfs_create_file_ns - create an attribute file for an object with custom ns
 * @kobj: object we're creating for
 * @attr: attribute descriptor
 * @ns: namespace the new file should belong to
 */
int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr,
			 const void *ns)
{
	kuid_t uid;
	kgid_t gid;

	if (WARN_ON(!kobj || !kobj->sd || !attr))
		return -EINVAL;

	kobject_get_ownership(kobj, &uid, &gid);
	return sysfs_add_file_mode_ns(kobj->sd, attr, attr->mode, uid, gid, ns);
}
EXPORT_SYMBOL_GPL(sysfs_create_file_ns);

int sysfs_create_files(struct kobject *kobj, const struct attribute * const *ptr)
{
	int err = 0;
	int i;

	for (i = 0; ptr[i] && !err; i++)
		err = sysfs_create_file(kobj, ptr[i]);
	if (err)
		while (--i >= 0)
			sysfs_remove_file(kobj, ptr[i]);
	return err;
}
EXPORT_SYMBOL_GPL(sysfs_create_files);

/**
 * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @group: group name.
 */
int sysfs_add_file_to_group(struct kobject *kobj,
		const struct attribute *attr, const char *group)
{
	struct kernfs_node *parent;
	kuid_t uid;
	kgid_t gid;
	int error;

	if (group) {
		parent = kernfs_find_and_get(kobj->sd, group);
	} else {
		parent = kobj->sd;
		kernfs_get(parent);
	}

	if (!parent)
		return -ENOENT;

	kobject_get_ownership(kobj, &uid, &gid);
	error = sysfs_add_file_mode_ns(parent, attr, attr->mode, uid, gid,
				       NULL);
	kernfs_put(parent);

	return error;
}
EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);

/**
 * sysfs_chmod_file - update the modified mode value on an object attribute.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @mode: file permissions.
 *
 */
int sysfs_chmod_file(struct kobject *kobj, const struct attribute *attr,
		     umode_t mode)
{
	struct kernfs_node *kn;
	struct iattr newattrs;
	int rc;

	kn = kernfs_find_and_get(kobj->sd, attr->name);
	if (!kn)
		return -ENOENT;

	newattrs.ia_mode = (mode & S_IALLUGO) | (kn->mode & ~S_IALLUGO);
	newattrs.ia_valid = ATTR_MODE;

	rc = kernfs_setattr(kn, &newattrs);

	kernfs_put(kn);
	return rc;
}
EXPORT_SYMBOL_GPL(sysfs_chmod_file);

/**
 * sysfs_break_active_protection - break "active" protection
 * @kobj: The kernel object @attr is associated with.
 * @attr: The attribute to break the "active" protection for.
 *
 * With sysfs, just like kernfs, deletion of an attribute is postponed until
 * all active .show() and .store() callbacks have finished unless this function
 * is called. Hence this function is useful in methods that implement self
 * deletion.
 */
struct kernfs_node *sysfs_break_active_protection(struct kobject *kobj,
						  const struct attribute *attr)
{
	struct kernfs_node *kn;

	kobject_get(kobj);
	kn = kernfs_find_and_get(kobj->sd, attr->name);
	if (kn)
		kernfs_break_active_protection(kn);
	return kn;
}
EXPORT_SYMBOL_GPL(sysfs_break_active_protection);

/**
 * sysfs_unbreak_active_protection - restore "active" protection
 * @kn: Pointer returned by sysfs_break_active_protection().
 *
 * Undo the effects of sysfs_break_active_protection(). Since this function
 * calls kernfs_put() on the kernfs node that corresponds to the 'attr'
 * argument passed to sysfs_break_active_protection() that attribute may have
 * been removed between the sysfs_break_active_protection() and
 * sysfs_unbreak_active_protection() calls, it is not safe to access @kn after
 * this function has returned.
 */
void sysfs_unbreak_active_protection(struct kernfs_node *kn)
{
	struct kobject *kobj = kn->parent->priv;

	kernfs_unbreak_active_protection(kn);
	kernfs_put(kn);
	kobject_put(kobj);
}
EXPORT_SYMBOL_GPL(sysfs_unbreak_active_protection);

/**
 * sysfs_remove_file_ns - remove an object attribute with a custom ns tag
 * @kobj: object we're acting for
 * @attr: attribute descriptor
 * @ns: namespace tag of the file to remove
 *
 * Hash the attribute name and namespace tag and kill the victim.
 */
void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
			  const void *ns)
{
	struct kernfs_node *parent = kobj->sd;

	kernfs_remove_by_name_ns(parent, attr->name, ns);
}
EXPORT_SYMBOL_GPL(sysfs_remove_file_ns);

/**
 * sysfs_remove_file_self - remove an object attribute from its own method
 * @kobj: object we're acting for
 * @attr: attribute descriptor
 *
 * See kernfs_remove_self() for details.
 */
bool sysfs_remove_file_self(struct kobject *kobj, const struct attribute *attr)
{
	struct kernfs_node *parent = kobj->sd;
	struct kernfs_node *kn;
	bool ret;

	kn = kernfs_find_and_get(parent, attr->name);
	if (WARN_ON_ONCE(!kn))
		return false;

	ret = kernfs_remove_self(kn);

	kernfs_put(kn);
	return ret;
}
EXPORT_SYMBOL_GPL(sysfs_remove_file_self);

void sysfs_remove_files(struct kobject *kobj, const struct attribute * const *ptr)
{
	int i;

	for (i = 0; ptr[i]; i++)
		sysfs_remove_file(kobj, ptr[i]);
}
EXPORT_SYMBOL_GPL(sysfs_remove_files);

/**
 * sysfs_remove_file_from_group - remove an attribute file from a group.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @group: group name.
 */
void sysfs_remove_file_from_group(struct kobject *kobj,
		const struct attribute *attr, const char *group)
{
	struct kernfs_node *parent;

	if (group) {
		parent = kernfs_find_and_get(kobj->sd, group);
	} else {
		parent = kobj->sd;
		kernfs_get(parent);
	}

	if (parent) {
		kernfs_remove_by_name(parent, attr->name);
		kernfs_put(parent);
	}
}
EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);

/**
 *	sysfs_create_bin_file - create binary file for object.
 *	@kobj:	object.
 *	@attr:	attribute descriptor.
 */
int sysfs_create_bin_file(struct kobject *kobj,
			  const struct bin_attribute *attr)
{
	kuid_t uid;
	kgid_t gid;

	if (WARN_ON(!kobj || !kobj->sd || !attr))
		return -EINVAL;

	kobject_get_ownership(kobj, &uid, &gid);
	return sysfs_add_bin_file_mode_ns(kobj->sd, attr, attr->attr.mode, uid,
					   gid, NULL);
}
EXPORT_SYMBOL_GPL(sysfs_create_bin_file);

/**
 *	sysfs_remove_bin_file - remove binary file for object.
 *	@kobj:	object.
 *	@attr:	attribute descriptor.
 */
void sysfs_remove_bin_file(struct kobject *kobj,
			   const struct bin_attribute *attr)
{
	kernfs_remove_by_name(kobj->sd, attr->attr.name);
}
EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);

static int internal_change_owner(struct kernfs_node *kn, kuid_t kuid,
				 kgid_t kgid)
{
	struct iattr newattrs = {
		.ia_valid = ATTR_UID | ATTR_GID,
		.ia_uid = kuid,
		.ia_gid = kgid,
	};
	return kernfs_setattr(kn, &newattrs);
}

/**
 *	sysfs_link_change_owner - change owner of a sysfs file.
 *	@kobj:	object of the kernfs_node the symlink is located in.
 *	@targ:	object of the kernfs_node the symlink points to.
 *	@name:	name of the link.
 *	@kuid:	new owner's kuid
 *	@kgid:	new owner's kgid
 *
 * This function looks up the sysfs symlink entry @name under @kobj and changes
 * the ownership to @kuid/@kgid. The symlink is looked up in the namespace of
 * @targ.
 *
 * Returns 0 on success or error code on failure.
 */
int sysfs_link_change_owner(struct kobject *kobj, struct kobject *targ,
			    const char *name, kuid_t kuid, kgid_t kgid)
{
	struct kernfs_node *kn = NULL;
	int error;

	if (!name || !kobj->state_in_sysfs || !targ->state_in_sysfs)
		return -EINVAL;

	error = -ENOENT;
	kn = kernfs_find_and_get_ns(kobj->sd, name, targ->sd->ns);
	if (!kn)
		goto out;

	error = -EINVAL;
	if (kernfs_type(kn) != KERNFS_LINK)
		goto out;
	if (kn->symlink.target_kn->priv != targ)
		goto out;

	error = internal_change_owner(kn, kuid, kgid);

out:
	kernfs_put(kn);
	return error;
}

/**
 *	sysfs_file_change_owner - change owner of a sysfs file.
 *	@kobj:	object.
 *	@name:	name of the file to change.
 *	@kuid:	new owner's kuid
 *	@kgid:	new owner's kgid
 *
 * This function looks up the sysfs entry @name under @kobj and changes the
 * ownership to @kuid/@kgid.
 *
 * Returns 0 on success or error code on failure.
 */
int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
			    kgid_t kgid)
{
	struct kernfs_node *kn;
	int error;

	if (!name)
		return -EINVAL;

	if (!kobj->state_in_sysfs)
		return -EINVAL;

	kn = kernfs_find_and_get(kobj->sd, name);
	if (!kn)
		return -ENOENT;

	error = internal_change_owner(kn, kuid, kgid);

	kernfs_put(kn);

	return error;
}
EXPORT_SYMBOL_GPL(sysfs_file_change_owner);

/**
 *	sysfs_change_owner - change owner of the given object.
 *	@kobj:	object.
 *	@kuid:	new owner's kuid
 *	@kgid:	new owner's kgid
 *
 * Change the owner of the default directory, files, groups, and attributes of
 * @kobj to @kuid/@kgid. Note that sysfs_change_owner mirrors how the sysfs
 * entries for a kobject are added by driver core. In summary,
 * sysfs_change_owner() takes care of the default directory entry for @kobj,
 * the default attributes associated with the ktype of @kobj and the default
 * attributes associated with the ktype of @kobj.
 * Additional properties not added by driver core have to be changed by the
 * driver or subsystem which created them. This is similar to how
 * driver/subsystem specific entries are removed.
 *
 * Returns 0 on success or error code on failure.
 */
int sysfs_change_owner(struct kobject *kobj, kuid_t kuid, kgid_t kgid)
{
	int error;
	const struct kobj_type *ktype;

	if (!kobj->state_in_sysfs)
		return -EINVAL;

	/* Change the owner of the kobject itself. */
	error = internal_change_owner(kobj->sd, kuid, kgid);
	if (error)
		return error;

	ktype = get_ktype(kobj);
	if (ktype) {
		/*
		 * Change owner of the default groups associated with the
		 * ktype of @kobj.
		 */
		error = sysfs_groups_change_owner(kobj, ktype->default_groups,
						  kuid, kgid);
		if (error)
			return error;
	}

	return 0;
}
EXPORT_SYMBOL_GPL(sysfs_change_owner);

/**
 *	sysfs_emit - scnprintf equivalent, aware of PAGE_SIZE buffer.
 *	@buf:	start of PAGE_SIZE buffer.
 *	@fmt:	format
 *	@...:	optional arguments to @format
 *
 *
 * Returns number of characters written to @buf.
 */
int sysfs_emit(char *buf, const char *fmt, ...)
{
	va_list args;
	int len;

	if (WARN(!buf || offset_in_page(buf),
		 "invalid sysfs_emit: buf:%p\n", buf))
		return 0;

	va_start(args, fmt);
	len = vscnprintf(buf, PAGE_SIZE, fmt, args);
	va_end(args);

	return len;
}
EXPORT_SYMBOL_GPL(sysfs_emit);

/**
 *	sysfs_emit_at - scnprintf equivalent, aware of PAGE_SIZE buffer.
 *	@buf:	start of PAGE_SIZE buffer.
 *	@at:	offset in @buf to start write in bytes
 *		@at must be >= 0 && < PAGE_SIZE
 *	@fmt:	format
 *	@...:	optional arguments to @fmt
 *
 *
 * Returns number of characters written starting at &@buf[@at].
 */
int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
{
	va_list args;
	int len;

	if (WARN(!buf || offset_in_page(buf) || at < 0 || at >= PAGE_SIZE,
		 "invalid sysfs_emit_at: buf:%p at:%d\n", buf, at))
		return 0;

	va_start(args, fmt);
	len = vscnprintf(buf + at, PAGE_SIZE - at, fmt, args);
	va_end(args);

	return len;
}
EXPORT_SYMBOL_GPL(sysfs_emit_at);