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
22static struct kobject *sysfs_file_kobj(struct kernfs_node *kn)
23{
24 guard(rcu)();
25 return rcu_dereference(kn->__parent)->priv;
26}
27
28/*
29 * Determine ktype->sysfs_ops for the given kernfs_node. This function
30 * must be called while holding an active reference.
31 */
32static const struct sysfs_ops *sysfs_file_ops(struct kernfs_node *kn)
33{
34 struct kobject *kobj = sysfs_file_kobj(kn);
35
36 if (kn->flags & KERNFS_LOCKDEP)
37 lockdep_assert_held(kn);
38 return kobj->ktype ? kobj->ktype->sysfs_ops : NULL;
39}
40
41/*
42 * Reads on sysfs are handled through seq_file, which takes care of hairy
43 * details like buffering and seeking. The following function pipes
44 * sysfs_ops->show() result through seq_file.
45 */
46static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
47{
48 struct kernfs_open_file *of = sf->private;
49 struct kobject *kobj = sysfs_file_kobj(kn: of->kn);
50 const struct sysfs_ops *ops = sysfs_file_ops(kn: of->kn);
51 ssize_t count;
52 char *buf;
53
54 if (WARN_ON_ONCE(!ops->show))
55 return -EINVAL;
56
57 /* acquire buffer and ensure that it's >= PAGE_SIZE and clear */
58 count = seq_get_buf(m: sf, bufp: &buf);
59 if (count < PAGE_SIZE) {
60 seq_commit(m: sf, num: -1);
61 return 0;
62 }
63 memset(buf, 0, PAGE_SIZE);
64
65 count = ops->show(kobj, of->kn->priv, buf);
66 if (count < 0)
67 return count;
68
69 /*
70 * The code works fine with PAGE_SIZE return but it's likely to
71 * indicate truncated result or overflow in normal use cases.
72 */
73 if (count >= (ssize_t)PAGE_SIZE) {
74 printk("fill_read_buffer: %pS returned bad count\n",
75 ops->show);
76 /* Try to struggle along */
77 count = PAGE_SIZE - 1;
78 }
79 seq_commit(m: sf, num: count);
80 return 0;
81}
82
83static ssize_t sysfs_kf_bin_read(struct kernfs_open_file *of, char *buf,
84 size_t count, loff_t pos)
85{
86 const struct bin_attribute *battr = of->kn->priv;
87 struct kobject *kobj = sysfs_file_kobj(kn: of->kn);
88 loff_t size = file_inode(f: of->file)->i_size;
89
90 if (!count)
91 return 0;
92
93 if (size) {
94 if (pos >= size)
95 return 0;
96 if (pos + count > size)
97 count = size - pos;
98 }
99
100 if (!battr->read)
101 return -EIO;
102
103 return battr->read(of->file, kobj, battr, buf, pos, count);
104}
105
106/* kernfs read callback for regular sysfs files with pre-alloc */
107static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
108 size_t count, loff_t pos)
109{
110 const struct sysfs_ops *ops = sysfs_file_ops(kn: of->kn);
111 struct kobject *kobj = sysfs_file_kobj(kn: of->kn);
112 ssize_t len;
113
114 /*
115 * If buf != of->prealloc_buf, we don't know how
116 * large it is, so cannot safely pass it to ->show
117 */
118 if (WARN_ON_ONCE(buf != of->prealloc_buf))
119 return 0;
120 len = ops->show(kobj, of->kn->priv, buf);
121 if (len < 0)
122 return len;
123 if (pos) {
124 if (len <= pos)
125 return 0;
126 len -= pos;
127 memmove(buf, buf + pos, len);
128 }
129 return min_t(ssize_t, count, len);
130}
131
132/* kernfs write callback for regular sysfs files */
133static ssize_t sysfs_kf_write(struct kernfs_open_file *of, char *buf,
134 size_t count, loff_t pos)
135{
136 const struct sysfs_ops *ops = sysfs_file_ops(kn: of->kn);
137 struct kobject *kobj = sysfs_file_kobj(kn: of->kn);
138
139 if (!count)
140 return 0;
141
142 return ops->store(kobj, of->kn->priv, buf, count);
143}
144
145/* kernfs write callback for bin sysfs files */
146static ssize_t sysfs_kf_bin_write(struct kernfs_open_file *of, char *buf,
147 size_t count, loff_t pos)
148{
149 const struct bin_attribute *battr = of->kn->priv;
150 struct kobject *kobj = sysfs_file_kobj(kn: of->kn);
151 loff_t size = file_inode(f: of->file)->i_size;
152
153 if (size) {
154 if (size <= pos)
155 return -EFBIG;
156 count = min_t(ssize_t, count, size - pos);
157 }
158 if (!count)
159 return 0;
160
161 if (!battr->write)
162 return -EIO;
163
164 return battr->write(of->file, kobj, battr, buf, pos, count);
165}
166
167static int sysfs_kf_bin_mmap(struct kernfs_open_file *of,
168 struct vm_area_struct *vma)
169{
170 const struct bin_attribute *battr = of->kn->priv;
171 struct kobject *kobj = sysfs_file_kobj(kn: of->kn);
172
173 return battr->mmap(of->file, kobj, battr, vma);
174}
175
176static loff_t sysfs_kf_bin_llseek(struct kernfs_open_file *of, loff_t offset,
177 int whence)
178{
179 const struct bin_attribute *battr = of->kn->priv;
180 struct kobject *kobj = sysfs_file_kobj(kn: of->kn);
181
182 if (battr->llseek)
183 return battr->llseek(of->file, kobj, battr, offset, whence);
184 else
185 return generic_file_llseek(file: of->file, offset, whence);
186}
187
188static int sysfs_kf_bin_open(struct kernfs_open_file *of)
189{
190 const struct bin_attribute *battr = of->kn->priv;
191
192 if (battr->f_mapping)
193 of->file->f_mapping = battr->f_mapping();
194
195 return 0;
196}
197
198void sysfs_notify(struct kobject *kobj, const char *dir, const char *attr)
199{
200 struct kernfs_node *kn = kobj->sd, *tmp;
201
202 if (kn && dir)
203 kn = kernfs_find_and_get(kn, name: dir);
204 else
205 kernfs_get(kn);
206
207 if (kn && attr) {
208 tmp = kernfs_find_and_get(kn, name: attr);
209 kernfs_put(kn);
210 kn = tmp;
211 }
212
213 if (kn) {
214 kernfs_notify(kn);
215 kernfs_put(kn);
216 }
217}
218EXPORT_SYMBOL_GPL(sysfs_notify);
219
220static const struct kernfs_ops sysfs_file_kfops_empty = {
221};
222
223static const struct kernfs_ops sysfs_file_kfops_ro = {
224 .seq_show = sysfs_kf_seq_show,
225};
226
227static const struct kernfs_ops sysfs_file_kfops_wo = {
228 .write = sysfs_kf_write,
229};
230
231static const struct kernfs_ops sysfs_file_kfops_rw = {
232 .seq_show = sysfs_kf_seq_show,
233 .write = sysfs_kf_write,
234};
235
236static const struct kernfs_ops sysfs_prealloc_kfops_ro = {
237 .read = sysfs_kf_read,
238 .prealloc = true,
239};
240
241static const struct kernfs_ops sysfs_prealloc_kfops_wo = {
242 .write = sysfs_kf_write,
243 .prealloc = true,
244};
245
246static const struct kernfs_ops sysfs_prealloc_kfops_rw = {
247 .read = sysfs_kf_read,
248 .write = sysfs_kf_write,
249 .prealloc = true,
250};
251
252static const struct kernfs_ops sysfs_bin_kfops_ro = {
253 .read = sysfs_kf_bin_read,
254};
255
256static const struct kernfs_ops sysfs_bin_kfops_wo = {
257 .write = sysfs_kf_bin_write,
258};
259
260static const struct kernfs_ops sysfs_bin_kfops_rw = {
261 .read = sysfs_kf_bin_read,
262 .write = sysfs_kf_bin_write,
263};
264
265static const struct kernfs_ops sysfs_bin_kfops_mmap = {
266 .read = sysfs_kf_bin_read,
267 .write = sysfs_kf_bin_write,
268 .mmap = sysfs_kf_bin_mmap,
269 .open = sysfs_kf_bin_open,
270 .llseek = sysfs_kf_bin_llseek,
271};
272
273int sysfs_add_file_mode_ns(struct kernfs_node *parent,
274 const struct attribute *attr, umode_t mode, kuid_t uid,
275 kgid_t gid, const void *ns)
276{
277 struct kobject *kobj = parent->priv;
278 const struct sysfs_ops *sysfs_ops = kobj->ktype->sysfs_ops;
279 struct lock_class_key *key = NULL;
280 const struct kernfs_ops *ops = NULL;
281 struct kernfs_node *kn;
282
283 /* every kobject with an attribute needs a ktype assigned */
284 if (WARN(!sysfs_ops, KERN_ERR
285 "missing sysfs attribute operations for kobject: %s\n",
286 kobject_name(kobj)))
287 return -EINVAL;
288
289 if (mode & SYSFS_PREALLOC) {
290 if (sysfs_ops->show && sysfs_ops->store)
291 ops = &sysfs_prealloc_kfops_rw;
292 else if (sysfs_ops->show)
293 ops = &sysfs_prealloc_kfops_ro;
294 else if (sysfs_ops->store)
295 ops = &sysfs_prealloc_kfops_wo;
296 } else {
297 if (sysfs_ops->show && sysfs_ops->store)
298 ops = &sysfs_file_kfops_rw;
299 else if (sysfs_ops->show)
300 ops = &sysfs_file_kfops_ro;
301 else if (sysfs_ops->store)
302 ops = &sysfs_file_kfops_wo;
303 }
304
305 if (!ops)
306 ops = &sysfs_file_kfops_empty;
307
308#ifdef CONFIG_DEBUG_LOCK_ALLOC
309 if (!attr->ignore_lockdep)
310 key = attr->key ?: (struct lock_class_key *)&attr->skey;
311#endif
312
313 kn = __kernfs_create_file(parent, name: attr->name, mode: mode & 0777, uid, gid,
314 PAGE_SIZE, ops, priv: (void *)attr, ns, key);
315 if (IS_ERR(ptr: kn)) {
316 if (PTR_ERR(ptr: kn) == -EEXIST)
317 sysfs_warn_dup(parent, name: attr->name);
318 return PTR_ERR(ptr: kn);
319 }
320 return 0;
321}
322
323int sysfs_add_bin_file_mode_ns(struct kernfs_node *parent,
324 const struct bin_attribute *battr, umode_t mode, size_t size,
325 kuid_t uid, kgid_t gid, const void *ns)
326{
327 const struct attribute *attr = &battr->attr;
328 struct lock_class_key *key = NULL;
329 const struct kernfs_ops *ops;
330 struct kernfs_node *kn;
331
332 if (battr->mmap)
333 ops = &sysfs_bin_kfops_mmap;
334 else if (battr->read && battr->write)
335 ops = &sysfs_bin_kfops_rw;
336 else if (battr->read)
337 ops = &sysfs_bin_kfops_ro;
338 else if (battr->write)
339 ops = &sysfs_bin_kfops_wo;
340 else
341 ops = &sysfs_file_kfops_empty;
342
343#ifdef CONFIG_DEBUG_LOCK_ALLOC
344 if (!attr->ignore_lockdep)
345 key = attr->key ?: (struct lock_class_key *)&attr->skey;
346#endif
347
348 kn = __kernfs_create_file(parent, name: attr->name, mode: mode & 0777, uid, gid,
349 size, ops, priv: (void *)attr, ns, key);
350 if (IS_ERR(ptr: kn)) {
351 if (PTR_ERR(ptr: kn) == -EEXIST)
352 sysfs_warn_dup(parent, name: attr->name);
353 return PTR_ERR(ptr: kn);
354 }
355 return 0;
356}
357
358/**
359 * sysfs_create_file_ns - create an attribute file for an object with custom ns
360 * @kobj: object we're creating for
361 * @attr: attribute descriptor
362 * @ns: namespace the new file should belong to
363 */
364int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr,
365 const void *ns)
366{
367 kuid_t uid;
368 kgid_t gid;
369
370 if (WARN_ON(!kobj || !kobj->sd || !attr))
371 return -EINVAL;
372
373 kobject_get_ownership(kobj, uid: &uid, gid: &gid);
374 return sysfs_add_file_mode_ns(parent: kobj->sd, attr, mode: attr->mode, uid, gid, ns);
375}
376EXPORT_SYMBOL_GPL(sysfs_create_file_ns);
377
378int sysfs_create_files(struct kobject *kobj, const struct attribute * const *ptr)
379{
380 int err = 0;
381 int i;
382
383 for (i = 0; ptr[i] && !err; i++)
384 err = sysfs_create_file(kobj, attr: ptr[i]);
385 if (err)
386 while (--i >= 0)
387 sysfs_remove_file(kobj, attr: ptr[i]);
388 return err;
389}
390EXPORT_SYMBOL_GPL(sysfs_create_files);
391
392/**
393 * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
394 * @kobj: object we're acting for.
395 * @attr: attribute descriptor.
396 * @group: group name.
397 */
398int sysfs_add_file_to_group(struct kobject *kobj,
399 const struct attribute *attr, const char *group)
400{
401 struct kernfs_node *parent;
402 kuid_t uid;
403 kgid_t gid;
404 int error;
405
406 if (group) {
407 parent = kernfs_find_and_get(kn: kobj->sd, name: group);
408 } else {
409 parent = kobj->sd;
410 kernfs_get(kn: parent);
411 }
412
413 if (!parent)
414 return -ENOENT;
415
416 kobject_get_ownership(kobj, uid: &uid, gid: &gid);
417 error = sysfs_add_file_mode_ns(parent, attr, mode: attr->mode, uid, gid,
418 NULL);
419 kernfs_put(kn: parent);
420
421 return error;
422}
423EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);
424
425/**
426 * sysfs_chmod_file - update the modified mode value on an object attribute.
427 * @kobj: object we're acting for.
428 * @attr: attribute descriptor.
429 * @mode: file permissions.
430 *
431 */
432int sysfs_chmod_file(struct kobject *kobj, const struct attribute *attr,
433 umode_t mode)
434{
435 struct kernfs_node *kn;
436 struct iattr newattrs;
437 int rc;
438
439 kn = kernfs_find_and_get(kn: kobj->sd, name: attr->name);
440 if (!kn)
441 return -ENOENT;
442
443 newattrs.ia_mode = (mode & S_IALLUGO) | (kn->mode & ~S_IALLUGO);
444 newattrs.ia_valid = ATTR_MODE;
445
446 rc = kernfs_setattr(kn, iattr: &newattrs);
447
448 kernfs_put(kn);
449 return rc;
450}
451EXPORT_SYMBOL_GPL(sysfs_chmod_file);
452
453/**
454 * sysfs_break_active_protection - break "active" protection
455 * @kobj: The kernel object @attr is associated with.
456 * @attr: The attribute to break the "active" protection for.
457 *
458 * With sysfs, just like kernfs, deletion of an attribute is postponed until
459 * all active .show() and .store() callbacks have finished unless this function
460 * is called. Hence this function is useful in methods that implement self
461 * deletion.
462 */
463struct kernfs_node *sysfs_break_active_protection(struct kobject *kobj,
464 const struct attribute *attr)
465{
466 struct kernfs_node *kn;
467
468 kobject_get(kobj);
469 kn = kernfs_find_and_get(kn: kobj->sd, name: attr->name);
470 if (kn)
471 kernfs_break_active_protection(kn);
472 else
473 kobject_put(kobj);
474 return kn;
475}
476EXPORT_SYMBOL_GPL(sysfs_break_active_protection);
477
478/**
479 * sysfs_unbreak_active_protection - restore "active" protection
480 * @kn: Pointer returned by sysfs_break_active_protection().
481 *
482 * Undo the effects of sysfs_break_active_protection(). Since this function
483 * calls kernfs_put() on the kernfs node that corresponds to the 'attr'
484 * argument passed to sysfs_break_active_protection() that attribute may have
485 * been removed between the sysfs_break_active_protection() and
486 * sysfs_unbreak_active_protection() calls, it is not safe to access @kn after
487 * this function has returned.
488 */
489void sysfs_unbreak_active_protection(struct kernfs_node *kn)
490{
491 struct kobject *kobj = sysfs_file_kobj(kn);
492
493 kernfs_unbreak_active_protection(kn);
494 kernfs_put(kn);
495 kobject_put(kobj);
496}
497EXPORT_SYMBOL_GPL(sysfs_unbreak_active_protection);
498
499/**
500 * sysfs_remove_file_ns - remove an object attribute with a custom ns tag
501 * @kobj: object we're acting for
502 * @attr: attribute descriptor
503 * @ns: namespace tag of the file to remove
504 *
505 * Hash the attribute name and namespace tag and kill the victim.
506 */
507void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
508 const void *ns)
509{
510 struct kernfs_node *parent = kobj->sd;
511
512 kernfs_remove_by_name_ns(parent, name: attr->name, ns);
513}
514EXPORT_SYMBOL_GPL(sysfs_remove_file_ns);
515
516/**
517 * sysfs_remove_file_self - remove an object attribute from its own method
518 * @kobj: object we're acting for
519 * @attr: attribute descriptor
520 *
521 * See kernfs_remove_self() for details.
522 */
523bool sysfs_remove_file_self(struct kobject *kobj, const struct attribute *attr)
524{
525 struct kernfs_node *parent = kobj->sd;
526 struct kernfs_node *kn;
527 bool ret;
528
529 kn = kernfs_find_and_get(kn: parent, name: attr->name);
530 if (WARN_ON_ONCE(!kn))
531 return false;
532
533 ret = kernfs_remove_self(kn);
534
535 kernfs_put(kn);
536 return ret;
537}
538EXPORT_SYMBOL_GPL(sysfs_remove_file_self);
539
540void sysfs_remove_files(struct kobject *kobj, const struct attribute * const *ptr)
541{
542 int i;
543
544 for (i = 0; ptr[i]; i++)
545 sysfs_remove_file(kobj, attr: ptr[i]);
546}
547EXPORT_SYMBOL_GPL(sysfs_remove_files);
548
549/**
550 * sysfs_remove_file_from_group - remove an attribute file from a group.
551 * @kobj: object we're acting for.
552 * @attr: attribute descriptor.
553 * @group: group name.
554 */
555void sysfs_remove_file_from_group(struct kobject *kobj,
556 const struct attribute *attr, const char *group)
557{
558 struct kernfs_node *parent;
559
560 if (group) {
561 parent = kernfs_find_and_get(kn: kobj->sd, name: group);
562 } else {
563 parent = kobj->sd;
564 kernfs_get(kn: parent);
565 }
566
567 if (parent) {
568 kernfs_remove_by_name(parent, name: attr->name);
569 kernfs_put(kn: parent);
570 }
571}
572EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);
573
574/**
575 * sysfs_create_bin_file - create binary file for object.
576 * @kobj: object.
577 * @attr: attribute descriptor.
578 */
579int sysfs_create_bin_file(struct kobject *kobj,
580 const struct bin_attribute *attr)
581{
582 kuid_t uid;
583 kgid_t gid;
584
585 if (WARN_ON(!kobj || !kobj->sd || !attr))
586 return -EINVAL;
587
588 kobject_get_ownership(kobj, uid: &uid, gid: &gid);
589 return sysfs_add_bin_file_mode_ns(parent: kobj->sd, battr: attr, mode: attr->attr.mode,
590 size: attr->size, uid, gid, NULL);
591}
592EXPORT_SYMBOL_GPL(sysfs_create_bin_file);
593
594/**
595 * sysfs_remove_bin_file - remove binary file for object.
596 * @kobj: object.
597 * @attr: attribute descriptor.
598 */
599void sysfs_remove_bin_file(struct kobject *kobj,
600 const struct bin_attribute *attr)
601{
602 kernfs_remove_by_name(parent: kobj->sd, name: attr->attr.name);
603}
604EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);
605
606static int internal_change_owner(struct kernfs_node *kn, kuid_t kuid,
607 kgid_t kgid)
608{
609 struct iattr newattrs = {
610 .ia_valid = ATTR_UID | ATTR_GID,
611 .ia_uid = kuid,
612 .ia_gid = kgid,
613 };
614 return kernfs_setattr(kn, iattr: &newattrs);
615}
616
617/**
618 * sysfs_link_change_owner - change owner of a sysfs file.
619 * @kobj: object of the kernfs_node the symlink is located in.
620 * @targ: object of the kernfs_node the symlink points to.
621 * @name: name of the link.
622 * @kuid: new owner's kuid
623 * @kgid: new owner's kgid
624 *
625 * This function looks up the sysfs symlink entry @name under @kobj and changes
626 * the ownership to @kuid/@kgid. The symlink is looked up in the namespace of
627 * @targ.
628 *
629 * Returns 0 on success or error code on failure.
630 */
631int sysfs_link_change_owner(struct kobject *kobj, struct kobject *targ,
632 const char *name, kuid_t kuid, kgid_t kgid)
633{
634 struct kernfs_node *kn = NULL;
635 int error;
636
637 if (!name || !kobj->state_in_sysfs || !targ->state_in_sysfs)
638 return -EINVAL;
639
640 error = -ENOENT;
641 kn = kernfs_find_and_get_ns(parent: kobj->sd, name, ns: targ->sd->ns);
642 if (!kn)
643 goto out;
644
645 error = -EINVAL;
646 if (kernfs_type(kn) != KERNFS_LINK)
647 goto out;
648 if (kn->symlink.target_kn->priv != targ)
649 goto out;
650
651 error = internal_change_owner(kn, kuid, kgid);
652
653out:
654 kernfs_put(kn);
655 return error;
656}
657
658/**
659 * sysfs_file_change_owner - change owner of a sysfs file.
660 * @kobj: object.
661 * @name: name of the file to change.
662 * @kuid: new owner's kuid
663 * @kgid: new owner's kgid
664 *
665 * This function looks up the sysfs entry @name under @kobj and changes the
666 * ownership to @kuid/@kgid.
667 *
668 * Returns 0 on success or error code on failure.
669 */
670int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
671 kgid_t kgid)
672{
673 struct kernfs_node *kn;
674 int error;
675
676 if (!name)
677 return -EINVAL;
678
679 if (!kobj->state_in_sysfs)
680 return -EINVAL;
681
682 kn = kernfs_find_and_get(kn: kobj->sd, name);
683 if (!kn)
684 return -ENOENT;
685
686 error = internal_change_owner(kn, kuid, kgid);
687
688 kernfs_put(kn);
689
690 return error;
691}
692EXPORT_SYMBOL_GPL(sysfs_file_change_owner);
693
694/**
695 * sysfs_change_owner - change owner of the given object.
696 * @kobj: object.
697 * @kuid: new owner's kuid
698 * @kgid: new owner's kgid
699 *
700 * Change the owner of the default directory, files, groups, and attributes of
701 * @kobj to @kuid/@kgid. Note that sysfs_change_owner mirrors how the sysfs
702 * entries for a kobject are added by driver core. In summary,
703 * sysfs_change_owner() takes care of the default directory entry for @kobj,
704 * the default attributes associated with the ktype of @kobj and the default
705 * attributes associated with the ktype of @kobj.
706 * Additional properties not added by driver core have to be changed by the
707 * driver or subsystem which created them. This is similar to how
708 * driver/subsystem specific entries are removed.
709 *
710 * Returns 0 on success or error code on failure.
711 */
712int sysfs_change_owner(struct kobject *kobj, kuid_t kuid, kgid_t kgid)
713{
714 int error;
715 const struct kobj_type *ktype;
716
717 if (!kobj->state_in_sysfs)
718 return -EINVAL;
719
720 /* Change the owner of the kobject itself. */
721 error = internal_change_owner(kn: kobj->sd, kuid, kgid);
722 if (error)
723 return error;
724
725 ktype = get_ktype(kobj);
726 if (ktype) {
727 /*
728 * Change owner of the default groups associated with the
729 * ktype of @kobj.
730 */
731 error = sysfs_groups_change_owner(kobj, groups: ktype->default_groups,
732 kuid, kgid);
733 if (error)
734 return error;
735 }
736
737 return 0;
738}
739EXPORT_SYMBOL_GPL(sysfs_change_owner);
740
741/**
742 * sysfs_emit - scnprintf equivalent, aware of PAGE_SIZE buffer.
743 * @buf: start of PAGE_SIZE buffer.
744 * @fmt: format
745 * @...: optional arguments to @format
746 *
747 *
748 * Returns number of characters written to @buf.
749 */
750int sysfs_emit(char *buf, const char *fmt, ...)
751{
752 va_list args;
753 int len;
754
755 if (WARN(!buf || offset_in_page(buf),
756 "invalid sysfs_emit: buf:%p\n", buf))
757 return 0;
758
759 va_start(args, fmt);
760 len = vscnprintf(buf, PAGE_SIZE, fmt, args);
761 va_end(args);
762
763 return len;
764}
765EXPORT_SYMBOL_GPL(sysfs_emit);
766
767/**
768 * sysfs_emit_at - scnprintf equivalent, aware of PAGE_SIZE buffer.
769 * @buf: start of PAGE_SIZE buffer.
770 * @at: offset in @buf to start write in bytes
771 * @at must be >= 0 && < PAGE_SIZE
772 * @fmt: format
773 * @...: optional arguments to @fmt
774 *
775 *
776 * Returns number of characters written starting at &@buf[@at].
777 */
778int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
779{
780 va_list args;
781 int len;
782
783 if (WARN(!buf || offset_in_page(buf) || at < 0 || at >= PAGE_SIZE,
784 "invalid sysfs_emit_at: buf:%p at:%d\n", buf, at))
785 return 0;
786
787 va_start(args, fmt);
788 len = vscnprintf(buf: buf + at, PAGE_SIZE - at, fmt, args);
789 va_end(args);
790
791 return len;
792}
793EXPORT_SYMBOL_GPL(sysfs_emit_at);
794
795/**
796 * sysfs_bin_attr_simple_read - read callback to simply copy from memory.
797 * @file: attribute file which is being read.
798 * @kobj: object to which the attribute belongs.
799 * @attr: attribute descriptor.
800 * @buf: destination buffer.
801 * @off: offset in bytes from which to read.
802 * @count: maximum number of bytes to read.
803 *
804 * Simple ->read() callback for bin_attributes backed by a buffer in memory.
805 * The @private and @size members in struct bin_attribute must be set to the
806 * buffer's location and size before the bin_attribute is created in sysfs.
807 *
808 * Bounds check for @off and @count is done in sysfs_kf_bin_read().
809 * Negative value check for @off is done in vfs_setpos() and default_llseek().
810 *
811 * Returns number of bytes written to @buf.
812 */
813ssize_t sysfs_bin_attr_simple_read(struct file *file, struct kobject *kobj,
814 const struct bin_attribute *attr, char *buf,
815 loff_t off, size_t count)
816{
817 memcpy(buf, attr->private + off, count);
818 return count;
819}
820EXPORT_SYMBOL_GPL(sysfs_bin_attr_simple_read);
821

source code of linux/fs/sysfs/file.c