1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * fs/sysfs/file.c - sysfs regular (text) file implementation
  4 *
  5 * Copyright (c) 2001-3 Patrick Mochel
  6 * Copyright (c) 2007 SUSE Linux Products GmbH
  7 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
  8 *
  9 * Please see Documentation/filesystems/sysfs.rst for more information.
 10 */
 11
 12#include <linux/module.h>
 13#include <linux/kobject.h>
 14#include <linux/slab.h>
 15#include <linux/list.h>
 16#include <linux/mutex.h>
 17#include <linux/seq_file.h>
 18#include <linux/mm.h>
 19
 20#include "sysfs.h"
 
 21
 22/*
 23 * Determine ktype->sysfs_ops for the given kernfs_node.  This function
 24 * must be called while holding an active reference.
 25 */
 26static const struct sysfs_ops *sysfs_file_ops(struct kernfs_node *kn)
 27{
 28	struct kobject *kobj = kn->parent->priv;
 29
 30	if (kn->flags & KERNFS_LOCKDEP)
 31		lockdep_assert_held(kn);
 32	return kobj->ktype ? kobj->ktype->sysfs_ops : NULL;
 33}
 34
 35/*
 36 * Reads on sysfs are handled through seq_file, which takes care of hairy
 37 * details like buffering and seeking.  The following function pipes
 38 * sysfs_ops->show() result through seq_file.
 39 */
 40static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
 41{
 42	struct kernfs_open_file *of = sf->private;
 43	struct kobject *kobj = of->kn->parent->priv;
 44	const struct sysfs_ops *ops = sysfs_file_ops(of->kn);
 45	ssize_t count;
 46	char *buf;
 47
 48	if (WARN_ON_ONCE(!ops->show))
 49		return -EINVAL;
 50
 51	/* acquire buffer and ensure that it's >= PAGE_SIZE and clear */
 52	count = seq_get_buf(sf, &buf);
 53	if (count < PAGE_SIZE) {
 54		seq_commit(sf, -1);
 55		return 0;
 56	}
 57	memset(buf, 0, PAGE_SIZE);
 58
 59	count = ops->show(kobj, of->kn->priv, buf);
 60	if (count < 0)
 61		return count;
 
 
 
 
 
 
 62
 63	/*
 64	 * The code works fine with PAGE_SIZE return but it's likely to
 65	 * indicate truncated result or overflow in normal use cases.
 66	 */
 67	if (count >= (ssize_t)PAGE_SIZE) {
 68		printk("fill_read_buffer: %pS returned bad count\n",
 69				ops->show);
 70		/* Try to struggle along */
 71		count = PAGE_SIZE - 1;
 72	}
 73	seq_commit(sf, count);
 74	return 0;
 75}
 76
 77static ssize_t sysfs_kf_bin_read(struct kernfs_open_file *of, char *buf,
 78				 size_t count, loff_t pos)
 79{
 80	struct bin_attribute *battr = of->kn->priv;
 81	struct kobject *kobj = of->kn->parent->priv;
 82	loff_t size = file_inode(of->file)->i_size;
 83
 84	if (!count)
 85		return 0;
 86
 87	if (size) {
 88		if (pos >= size)
 89			return 0;
 90		if (pos + count > size)
 91			count = size - pos;
 92	}
 93
 94	if (!battr->read)
 95		return -EIO;
 96
 97	return battr->read(of->file, kobj, battr, buf, pos, count);
 98}
 99
100/* kernfs read callback for regular sysfs files with pre-alloc */
101static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
102			     size_t count, loff_t pos)
103{
104	const struct sysfs_ops *ops = sysfs_file_ops(of->kn);
105	struct kobject *kobj = of->kn->parent->priv;
106	ssize_t len;
107
108	/*
109	 * If buf != of->prealloc_buf, we don't know how
110	 * large it is, so cannot safely pass it to ->show
111	 */
112	if (WARN_ON_ONCE(buf != of->prealloc_buf))
113		return 0;
114	len = ops->show(kobj, of->kn->priv, buf);
115	if (len < 0)
116		return len;
117	if (pos) {
118		if (len <= pos)
119			return 0;
120		len -= pos;
121		memmove(buf, buf + pos, len);
122	}
123	return min_t(ssize_t, count, len);
124}
125
126/* kernfs write callback for regular sysfs files */
127static ssize_t sysfs_kf_write(struct kernfs_open_file *of, char *buf,
128			      size_t count, loff_t pos)
129{
130	const struct sysfs_ops *ops = sysfs_file_ops(of->kn);
131	struct kobject *kobj = of->kn->parent->priv;
132
133	if (!count)
134		return 0;
135
136	return ops->store(kobj, of->kn->priv, buf, count);
137}
138
139/* kernfs write callback for bin sysfs files */
140static ssize_t sysfs_kf_bin_write(struct kernfs_open_file *of, char *buf,
141				  size_t count, loff_t pos)
142{
143	struct bin_attribute *battr = of->kn->priv;
144	struct kobject *kobj = of->kn->parent->priv;
145	loff_t size = file_inode(of->file)->i_size;
146
147	if (size) {
148		if (size <= pos)
149			return -EFBIG;
150		count = min_t(ssize_t, count, size - pos);
151	}
152	if (!count)
153		return 0;
154
155	if (!battr->write)
156		return -EIO;
157
158	return battr->write(of->file, kobj, battr, buf, pos, count);
159}
160
161static int sysfs_kf_bin_mmap(struct kernfs_open_file *of,
162			     struct vm_area_struct *vma)
163{
164	struct bin_attribute *battr = of->kn->priv;
165	struct kobject *kobj = of->kn->parent->priv;
166
167	return battr->mmap(of->file, kobj, battr, vma);
168}
169
170static loff_t sysfs_kf_bin_llseek(struct kernfs_open_file *of, loff_t offset,
171				  int whence)
172{
173	struct bin_attribute *battr = of->kn->priv;
174	struct kobject *kobj = of->kn->parent->priv;
175
176	if (battr->llseek)
177		return battr->llseek(of->file, kobj, battr, offset, whence);
178	else
179		return generic_file_llseek(of->file, offset, whence);
180}
181
182static int sysfs_kf_bin_open(struct kernfs_open_file *of)
183{
184	struct bin_attribute *battr = of->kn->priv;
185
186	if (battr->f_mapping)
187		of->file->f_mapping = battr->f_mapping();
188
189	return 0;
190}
191
192void sysfs_notify(struct kobject *kobj, const char *dir, const char *attr)
193{
194	struct kernfs_node *kn = kobj->sd, *tmp;
195
196	if (kn && dir)
197		kn = kernfs_find_and_get(kn, dir);
198	else
199		kernfs_get(kn);
200
201	if (kn && attr) {
202		tmp = kernfs_find_and_get(kn, attr);
203		kernfs_put(kn);
204		kn = tmp;
205	}
206
207	if (kn) {
208		kernfs_notify(kn);
209		kernfs_put(kn);
210	}
211}
212EXPORT_SYMBOL_GPL(sysfs_notify);
213
214static const struct kernfs_ops sysfs_file_kfops_empty = {
215};
216
217static const struct kernfs_ops sysfs_file_kfops_ro = {
218	.seq_show	= sysfs_kf_seq_show,
219};
220
221static const struct kernfs_ops sysfs_file_kfops_wo = {
222	.write		= sysfs_kf_write,
223};
224
225static const struct kernfs_ops sysfs_file_kfops_rw = {
226	.seq_show	= sysfs_kf_seq_show,
227	.write		= sysfs_kf_write,
228};
229
230static const struct kernfs_ops sysfs_prealloc_kfops_ro = {
231	.read		= sysfs_kf_read,
232	.prealloc	= true,
233};
234
235static const struct kernfs_ops sysfs_prealloc_kfops_wo = {
236	.write		= sysfs_kf_write,
237	.prealloc	= true,
238};
239
240static const struct kernfs_ops sysfs_prealloc_kfops_rw = {
241	.read		= sysfs_kf_read,
242	.write		= sysfs_kf_write,
243	.prealloc	= true,
244};
245
246static const struct kernfs_ops sysfs_bin_kfops_ro = {
247	.read		= sysfs_kf_bin_read,
248};
249
250static const struct kernfs_ops sysfs_bin_kfops_wo = {
251	.write		= sysfs_kf_bin_write,
252};
253
254static const struct kernfs_ops sysfs_bin_kfops_rw = {
255	.read		= sysfs_kf_bin_read,
256	.write		= sysfs_kf_bin_write,
257};
258
259static const struct kernfs_ops sysfs_bin_kfops_mmap = {
260	.read		= sysfs_kf_bin_read,
261	.write		= sysfs_kf_bin_write,
262	.mmap		= sysfs_kf_bin_mmap,
263	.open		= sysfs_kf_bin_open,
264	.llseek		= sysfs_kf_bin_llseek,
265};
266
267int sysfs_add_file_mode_ns(struct kernfs_node *parent,
268		const struct attribute *attr, umode_t mode, kuid_t uid,
269		kgid_t gid, const void *ns)
270{
271	struct kobject *kobj = parent->priv;
272	const struct sysfs_ops *sysfs_ops = kobj->ktype->sysfs_ops;
273	struct lock_class_key *key = NULL;
274	const struct kernfs_ops *ops = NULL;
275	struct kernfs_node *kn;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
276
277	/* every kobject with an attribute needs a ktype assigned */
278	if (WARN(!sysfs_ops, KERN_ERR
279			"missing sysfs attribute operations for kobject: %s\n",
280			kobject_name(kobj)))
281		return -EINVAL;
282
283	if (mode & SYSFS_PREALLOC) {
284		if (sysfs_ops->show && sysfs_ops->store)
285			ops = &sysfs_prealloc_kfops_rw;
286		else if (sysfs_ops->show)
287			ops = &sysfs_prealloc_kfops_ro;
288		else if (sysfs_ops->store)
289			ops = &sysfs_prealloc_kfops_wo;
290	} else {
291		if (sysfs_ops->show && sysfs_ops->store)
292			ops = &sysfs_file_kfops_rw;
293		else if (sysfs_ops->show)
294			ops = &sysfs_file_kfops_ro;
295		else if (sysfs_ops->store)
296			ops = &sysfs_file_kfops_wo;
297	}
298
299	if (!ops)
300		ops = &sysfs_file_kfops_empty;
 
 
 
 
 
 
 
 
 
 
 
301
302#ifdef CONFIG_DEBUG_LOCK_ALLOC
303	if (!attr->ignore_lockdep)
304		key = attr->key ?: (struct lock_class_key *)&attr->skey;
305#endif
306
307	kn = __kernfs_create_file(parent, attr->name, mode & 0777, uid, gid,
308				  PAGE_SIZE, ops, (void *)attr, ns, key);
309	if (IS_ERR(kn)) {
310		if (PTR_ERR(kn) == -EEXIST)
311			sysfs_warn_dup(parent, attr->name);
312		return PTR_ERR(kn);
313	}
314	return 0;
315}
316
317int sysfs_add_bin_file_mode_ns(struct kernfs_node *parent,
318		const struct bin_attribute *battr, umode_t mode,
319		kuid_t uid, kgid_t gid, const void *ns)
320{
321	const struct attribute *attr = &battr->attr;
322	struct lock_class_key *key = NULL;
323	const struct kernfs_ops *ops;
324	struct kernfs_node *kn;
325
326	if (battr->mmap)
327		ops = &sysfs_bin_kfops_mmap;
328	else if (battr->read && battr->write)
329		ops = &sysfs_bin_kfops_rw;
330	else if (battr->read)
331		ops = &sysfs_bin_kfops_ro;
332	else if (battr->write)
333		ops = &sysfs_bin_kfops_wo;
334	else
335		ops = &sysfs_file_kfops_empty;
336
337#ifdef CONFIG_DEBUG_LOCK_ALLOC
338	if (!attr->ignore_lockdep)
339		key = attr->key ?: (struct lock_class_key *)&attr->skey;
340#endif
341
342	kn = __kernfs_create_file(parent, attr->name, mode & 0777, uid, gid,
343				  battr->size, ops, (void *)attr, ns, key);
344	if (IS_ERR(kn)) {
345		if (PTR_ERR(kn) == -EEXIST)
346			sysfs_warn_dup(parent, attr->name);
347		return PTR_ERR(kn);
348	}
349	return 0;
350}
351
352/**
353 * sysfs_create_file_ns - create an attribute file for an object with custom ns
354 * @kobj: object we're creating for
355 * @attr: attribute descriptor
356 * @ns: namespace the new file should belong to
357 */
358int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr,
359			 const void *ns)
360{
361	kuid_t uid;
362	kgid_t gid;
363
364	if (WARN_ON(!kobj || !kobj->sd || !attr))
365		return -EINVAL;
366
367	kobject_get_ownership(kobj, &uid, &gid);
368	return sysfs_add_file_mode_ns(kobj->sd, attr, attr->mode, uid, gid, ns);
369}
370EXPORT_SYMBOL_GPL(sysfs_create_file_ns);
371
372int sysfs_create_files(struct kobject *kobj, const struct attribute * const *ptr)
373{
374	int err = 0;
375	int i;
376
377	for (i = 0; ptr[i] && !err; i++)
378		err = sysfs_create_file(kobj, ptr[i]);
379	if (err)
380		while (--i >= 0)
381			sysfs_remove_file(kobj, ptr[i]);
382	return err;
383}
384EXPORT_SYMBOL_GPL(sysfs_create_files);
385
386/**
387 * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
388 * @kobj: object we're acting for.
389 * @attr: attribute descriptor.
390 * @group: group name.
391 */
392int sysfs_add_file_to_group(struct kobject *kobj,
393		const struct attribute *attr, const char *group)
394{
395	struct kernfs_node *parent;
396	kuid_t uid;
397	kgid_t gid;
398	int error;
399
400	if (group) {
401		parent = kernfs_find_and_get(kobj->sd, group);
402	} else {
403		parent = kobj->sd;
404		kernfs_get(parent);
405	}
406
407	if (!parent)
408		return -ENOENT;
409
410	kobject_get_ownership(kobj, &uid, &gid);
411	error = sysfs_add_file_mode_ns(parent, attr, attr->mode, uid, gid,
412				       NULL);
413	kernfs_put(parent);
414
415	return error;
416}
417EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);
418
419/**
420 * sysfs_chmod_file - update the modified mode value on an object attribute.
421 * @kobj: object we're acting for.
422 * @attr: attribute descriptor.
423 * @mode: file permissions.
424 *
425 */
426int sysfs_chmod_file(struct kobject *kobj, const struct attribute *attr,
427		     umode_t mode)
428{
429	struct kernfs_node *kn;
430	struct iattr newattrs;
431	int rc;
432
433	kn = kernfs_find_and_get(kobj->sd, attr->name);
434	if (!kn)
435		return -ENOENT;
436
437	newattrs.ia_mode = (mode & S_IALLUGO) | (kn->mode & ~S_IALLUGO);
438	newattrs.ia_valid = ATTR_MODE;
439
440	rc = kernfs_setattr(kn, &newattrs);
441
442	kernfs_put(kn);
443	return rc;
444}
445EXPORT_SYMBOL_GPL(sysfs_chmod_file);
446
447/**
448 * sysfs_break_active_protection - break "active" protection
449 * @kobj: The kernel object @attr is associated with.
450 * @attr: The attribute to break the "active" protection for.
451 *
452 * With sysfs, just like kernfs, deletion of an attribute is postponed until
453 * all active .show() and .store() callbacks have finished unless this function
454 * is called. Hence this function is useful in methods that implement self
455 * deletion.
456 */
457struct kernfs_node *sysfs_break_active_protection(struct kobject *kobj,
458						  const struct attribute *attr)
459{
460	struct kernfs_node *kn;
461
462	kobject_get(kobj);
463	kn = kernfs_find_and_get(kobj->sd, attr->name);
464	if (kn)
465		kernfs_break_active_protection(kn);
466	return kn;
467}
468EXPORT_SYMBOL_GPL(sysfs_break_active_protection);
469
470/**
471 * sysfs_unbreak_active_protection - restore "active" protection
472 * @kn: Pointer returned by sysfs_break_active_protection().
473 *
474 * Undo the effects of sysfs_break_active_protection(). Since this function
475 * calls kernfs_put() on the kernfs node that corresponds to the 'attr'
476 * argument passed to sysfs_break_active_protection() that attribute may have
477 * been removed between the sysfs_break_active_protection() and
478 * sysfs_unbreak_active_protection() calls, it is not safe to access @kn after
479 * this function has returned.
480 */
481void sysfs_unbreak_active_protection(struct kernfs_node *kn)
482{
483	struct kobject *kobj = kn->parent->priv;
484
485	kernfs_unbreak_active_protection(kn);
486	kernfs_put(kn);
487	kobject_put(kobj);
488}
489EXPORT_SYMBOL_GPL(sysfs_unbreak_active_protection);
490
491/**
492 * sysfs_remove_file_ns - remove an object attribute with a custom ns tag
493 * @kobj: object we're acting for
494 * @attr: attribute descriptor
495 * @ns: namespace tag of the file to remove
496 *
497 * Hash the attribute name and namespace tag and kill the victim.
498 */
499void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
500			  const void *ns)
501{
502	struct kernfs_node *parent = kobj->sd;
503
504	kernfs_remove_by_name_ns(parent, attr->name, ns);
505}
506EXPORT_SYMBOL_GPL(sysfs_remove_file_ns);
507
508/**
509 * sysfs_remove_file_self - remove an object attribute from its own method
510 * @kobj: object we're acting for
511 * @attr: attribute descriptor
512 *
513 * See kernfs_remove_self() for details.
514 */
515bool sysfs_remove_file_self(struct kobject *kobj, const struct attribute *attr)
516{
517	struct kernfs_node *parent = kobj->sd;
518	struct kernfs_node *kn;
519	bool ret;
520
521	kn = kernfs_find_and_get(parent, attr->name);
522	if (WARN_ON_ONCE(!kn))
523		return false;
524
525	ret = kernfs_remove_self(kn);
526
527	kernfs_put(kn);
528	return ret;
529}
530EXPORT_SYMBOL_GPL(sysfs_remove_file_self);
531
532void sysfs_remove_files(struct kobject *kobj, const struct attribute * const *ptr)
533{
534	int i;
535
536	for (i = 0; ptr[i]; i++)
537		sysfs_remove_file(kobj, ptr[i]);
538}
539EXPORT_SYMBOL_GPL(sysfs_remove_files);
540
541/**
542 * sysfs_remove_file_from_group - remove an attribute file from a group.
543 * @kobj: object we're acting for.
544 * @attr: attribute descriptor.
545 * @group: group name.
546 */
547void sysfs_remove_file_from_group(struct kobject *kobj,
548		const struct attribute *attr, const char *group)
549{
550	struct kernfs_node *parent;
551
552	if (group) {
553		parent = kernfs_find_and_get(kobj->sd, group);
554	} else {
555		parent = kobj->sd;
556		kernfs_get(parent);
557	}
558
559	if (parent) {
560		kernfs_remove_by_name(parent, attr->name);
561		kernfs_put(parent);
562	}
563}
564EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);
565
566/**
567 *	sysfs_create_bin_file - create binary file for object.
568 *	@kobj:	object.
569 *	@attr:	attribute descriptor.
570 */
571int sysfs_create_bin_file(struct kobject *kobj,
572			  const struct bin_attribute *attr)
573{
574	kuid_t uid;
575	kgid_t gid;
576
577	if (WARN_ON(!kobj || !kobj->sd || !attr))
578		return -EINVAL;
579
580	kobject_get_ownership(kobj, &uid, &gid);
581	return sysfs_add_bin_file_mode_ns(kobj->sd, attr, attr->attr.mode, uid,
582					   gid, NULL);
583}
584EXPORT_SYMBOL_GPL(sysfs_create_bin_file);
585
586/**
587 *	sysfs_remove_bin_file - remove binary file for object.
588 *	@kobj:	object.
589 *	@attr:	attribute descriptor.
590 */
591void sysfs_remove_bin_file(struct kobject *kobj,
592			   const struct bin_attribute *attr)
593{
594	kernfs_remove_by_name(kobj->sd, attr->attr.name);
595}
596EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);
597
598static int internal_change_owner(struct kernfs_node *kn, kuid_t kuid,
599				 kgid_t kgid)
600{
601	struct iattr newattrs = {
602		.ia_valid = ATTR_UID | ATTR_GID,
603		.ia_uid = kuid,
604		.ia_gid = kgid,
605	};
606	return kernfs_setattr(kn, &newattrs);
607}
608
609/**
610 *	sysfs_link_change_owner - change owner of a sysfs file.
611 *	@kobj:	object of the kernfs_node the symlink is located in.
612 *	@targ:	object of the kernfs_node the symlink points to.
613 *	@name:	name of the link.
614 *	@kuid:	new owner's kuid
615 *	@kgid:	new owner's kgid
616 *
617 * This function looks up the sysfs symlink entry @name under @kobj and changes
618 * the ownership to @kuid/@kgid. The symlink is looked up in the namespace of
619 * @targ.
620 *
621 * Returns 0 on success or error code on failure.
622 */
623int sysfs_link_change_owner(struct kobject *kobj, struct kobject *targ,
624			    const char *name, kuid_t kuid, kgid_t kgid)
625{
626	struct kernfs_node *kn = NULL;
627	int error;
628
629	if (!name || !kobj->state_in_sysfs || !targ->state_in_sysfs)
630		return -EINVAL;
631
632	error = -ENOENT;
633	kn = kernfs_find_and_get_ns(kobj->sd, name, targ->sd->ns);
634	if (!kn)
635		goto out;
636
637	error = -EINVAL;
638	if (kernfs_type(kn) != KERNFS_LINK)
639		goto out;
640	if (kn->symlink.target_kn->priv != targ)
641		goto out;
642
643	error = internal_change_owner(kn, kuid, kgid);
644
645out:
646	kernfs_put(kn);
647	return error;
648}
649
650/**
651 *	sysfs_file_change_owner - change owner of a sysfs file.
652 *	@kobj:	object.
653 *	@name:	name of the file to change.
654 *	@kuid:	new owner's kuid
655 *	@kgid:	new owner's kgid
656 *
657 * This function looks up the sysfs entry @name under @kobj and changes the
658 * ownership to @kuid/@kgid.
659 *
660 * Returns 0 on success or error code on failure.
661 */
662int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
663			    kgid_t kgid)
664{
665	struct kernfs_node *kn;
666	int error;
667
668	if (!name)
669		return -EINVAL;
670
671	if (!kobj->state_in_sysfs)
672		return -EINVAL;
673
674	kn = kernfs_find_and_get(kobj->sd, name);
675	if (!kn)
676		return -ENOENT;
677
678	error = internal_change_owner(kn, kuid, kgid);
679
680	kernfs_put(kn);
681
682	return error;
683}
684EXPORT_SYMBOL_GPL(sysfs_file_change_owner);
685
686/**
687 *	sysfs_change_owner - change owner of the given object.
688 *	@kobj:	object.
689 *	@kuid:	new owner's kuid
690 *	@kgid:	new owner's kgid
691 *
692 * Change the owner of the default directory, files, groups, and attributes of
693 * @kobj to @kuid/@kgid. Note that sysfs_change_owner mirrors how the sysfs
694 * entries for a kobject are added by driver core. In summary,
695 * sysfs_change_owner() takes care of the default directory entry for @kobj,
696 * the default attributes associated with the ktype of @kobj and the default
697 * attributes associated with the ktype of @kobj.
698 * Additional properties not added by driver core have to be changed by the
699 * driver or subsystem which created them. This is similar to how
700 * driver/subsystem specific entries are removed.
701 *
702 * Returns 0 on success or error code on failure.
703 */
704int sysfs_change_owner(struct kobject *kobj, kuid_t kuid, kgid_t kgid)
705{
706	int error;
707	const struct kobj_type *ktype;
708
709	if (!kobj->state_in_sysfs)
710		return -EINVAL;
711
712	/* Change the owner of the kobject itself. */
713	error = internal_change_owner(kobj->sd, kuid, kgid);
714	if (error)
715		return error;
716
717	ktype = get_ktype(kobj);
718	if (ktype) {
719		/*
720		 * Change owner of the default groups associated with the
721		 * ktype of @kobj.
722		 */
723		error = sysfs_groups_change_owner(kobj, ktype->default_groups,
724						  kuid, kgid);
725		if (error)
726			return error;
727	}
728
729	return 0;
730}
731EXPORT_SYMBOL_GPL(sysfs_change_owner);
732
733/**
734 *	sysfs_emit - scnprintf equivalent, aware of PAGE_SIZE buffer.
735 *	@buf:	start of PAGE_SIZE buffer.
736 *	@fmt:	format
737 *	@...:	optional arguments to @format
738 *
739 *
740 * Returns number of characters written to @buf.
741 */
742int sysfs_emit(char *buf, const char *fmt, ...)
743{
744	va_list args;
745	int len;
746
747	if (WARN(!buf || offset_in_page(buf),
748		 "invalid sysfs_emit: buf:%p\n", buf))
749		return 0;
750
751	va_start(args, fmt);
752	len = vscnprintf(buf, PAGE_SIZE, fmt, args);
753	va_end(args);
754
755	return len;
756}
757EXPORT_SYMBOL_GPL(sysfs_emit);
758
759/**
760 *	sysfs_emit_at - scnprintf equivalent, aware of PAGE_SIZE buffer.
761 *	@buf:	start of PAGE_SIZE buffer.
762 *	@at:	offset in @buf to start write in bytes
763 *		@at must be >= 0 && < PAGE_SIZE
764 *	@fmt:	format
765 *	@...:	optional arguments to @fmt
766 *
767 *
768 * Returns number of characters written starting at &@buf[@at].
769 */
770int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
771{
772	va_list args;
773	int len;
774
775	if (WARN(!buf || offset_in_page(buf) || at < 0 || at >= PAGE_SIZE,
776		 "invalid sysfs_emit_at: buf:%p at:%d\n", buf, at))
777		return 0;
778
779	va_start(args, fmt);
780	len = vscnprintf(buf + at, PAGE_SIZE - at, fmt, args);
781	va_end(args);
782
783	return len;
784}
785EXPORT_SYMBOL_GPL(sysfs_emit_at);