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 */
26 static 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 */
40 static 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
77 static 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 */
101 static 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 */
127 static 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 */
140 static 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
161 static 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
170 static 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
182 static 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
192 void 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 }
212 EXPORT_SYMBOL_GPL(sysfs_notify);
213
214 static const struct kernfs_ops sysfs_file_kfops_empty = {
215 };
216
217 static const struct kernfs_ops sysfs_file_kfops_ro = {
218 .seq_show = sysfs_kf_seq_show,
219 };
220
221 static const struct kernfs_ops sysfs_file_kfops_wo = {
222 .write = sysfs_kf_write,
223 };
224
225 static const struct kernfs_ops sysfs_file_kfops_rw = {
226 .seq_show = sysfs_kf_seq_show,
227 .write = sysfs_kf_write,
228 };
229
230 static const struct kernfs_ops sysfs_prealloc_kfops_ro = {
231 .read = sysfs_kf_read,
232 .prealloc = true,
233 };
234
235 static const struct kernfs_ops sysfs_prealloc_kfops_wo = {
236 .write = sysfs_kf_write,
237 .prealloc = true,
238 };
239
240 static const struct kernfs_ops sysfs_prealloc_kfops_rw = {
241 .read = sysfs_kf_read,
242 .write = sysfs_kf_write,
243 .prealloc = true,
244 };
245
246 static const struct kernfs_ops sysfs_bin_kfops_ro = {
247 .read = sysfs_kf_bin_read,
248 };
249
250 static const struct kernfs_ops sysfs_bin_kfops_wo = {
251 .write = sysfs_kf_bin_write,
252 };
253
254 static const struct kernfs_ops sysfs_bin_kfops_rw = {
255 .read = sysfs_kf_bin_read,
256 .write = sysfs_kf_bin_write,
257 };
258
259 static 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
267 int 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
317 int 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 */
358 int 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 }
370 EXPORT_SYMBOL_GPL(sysfs_create_file_ns);
371
372 int 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 }
384 EXPORT_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 */
392 int 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 }
417 EXPORT_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 */
426 int 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 }
445 EXPORT_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 */
457 struct 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 else
467 kobject_put(kobj);
468 return kn;
469 }
470 EXPORT_SYMBOL_GPL(sysfs_break_active_protection);
471
472 /**
473 * sysfs_unbreak_active_protection - restore "active" protection
474 * @kn: Pointer returned by sysfs_break_active_protection().
475 *
476 * Undo the effects of sysfs_break_active_protection(). Since this function
477 * calls kernfs_put() on the kernfs node that corresponds to the 'attr'
478 * argument passed to sysfs_break_active_protection() that attribute may have
479 * been removed between the sysfs_break_active_protection() and
480 * sysfs_unbreak_active_protection() calls, it is not safe to access @kn after
481 * this function has returned.
482 */
483 void sysfs_unbreak_active_protection(struct kernfs_node *kn)
484 {
485 struct kobject *kobj = kn->parent->priv;
486
487 kernfs_unbreak_active_protection(kn);
488 kernfs_put(kn);
489 kobject_put(kobj);
490 }
491 EXPORT_SYMBOL_GPL(sysfs_unbreak_active_protection);
492
493 /**
494 * sysfs_remove_file_ns - remove an object attribute with a custom ns tag
495 * @kobj: object we're acting for
496 * @attr: attribute descriptor
497 * @ns: namespace tag of the file to remove
498 *
499 * Hash the attribute name and namespace tag and kill the victim.
500 */
501 void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
502 const void *ns)
503 {
504 struct kernfs_node *parent = kobj->sd;
505
506 kernfs_remove_by_name_ns(parent, attr->name, ns);
507 }
508 EXPORT_SYMBOL_GPL(sysfs_remove_file_ns);
509
510 /**
511 * sysfs_remove_file_self - remove an object attribute from its own method
512 * @kobj: object we're acting for
513 * @attr: attribute descriptor
514 *
515 * See kernfs_remove_self() for details.
516 */
517 bool sysfs_remove_file_self(struct kobject *kobj, const struct attribute *attr)
518 {
519 struct kernfs_node *parent = kobj->sd;
520 struct kernfs_node *kn;
521 bool ret;
522
523 kn = kernfs_find_and_get(parent, attr->name);
524 if (WARN_ON_ONCE(!kn))
525 return false;
526
527 ret = kernfs_remove_self(kn);
528
529 kernfs_put(kn);
530 return ret;
531 }
532 EXPORT_SYMBOL_GPL(sysfs_remove_file_self);
533
534 void sysfs_remove_files(struct kobject *kobj, const struct attribute * const *ptr)
535 {
536 int i;
537
538 for (i = 0; ptr[i]; i++)
539 sysfs_remove_file(kobj, ptr[i]);
540 }
541 EXPORT_SYMBOL_GPL(sysfs_remove_files);
542
543 /**
544 * sysfs_remove_file_from_group - remove an attribute file from a group.
545 * @kobj: object we're acting for.
546 * @attr: attribute descriptor.
547 * @group: group name.
548 */
549 void sysfs_remove_file_from_group(struct kobject *kobj,
550 const struct attribute *attr, const char *group)
551 {
552 struct kernfs_node *parent;
553
554 if (group) {
555 parent = kernfs_find_and_get(kobj->sd, group);
556 } else {
557 parent = kobj->sd;
558 kernfs_get(parent);
559 }
560
561 if (parent) {
562 kernfs_remove_by_name(parent, attr->name);
563 kernfs_put(parent);
564 }
565 }
566 EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);
567
568 /**
569 * sysfs_create_bin_file - create binary file for object.
570 * @kobj: object.
571 * @attr: attribute descriptor.
572 */
573 int sysfs_create_bin_file(struct kobject *kobj,
574 const struct bin_attribute *attr)
575 {
576 kuid_t uid;
577 kgid_t gid;
578
579 if (WARN_ON(!kobj || !kobj->sd || !attr))
580 return -EINVAL;
581
582 kobject_get_ownership(kobj, &uid, &gid);
583 return sysfs_add_bin_file_mode_ns(kobj->sd, attr, attr->attr.mode, uid,
584 gid, NULL);
585 }
586 EXPORT_SYMBOL_GPL(sysfs_create_bin_file);
587
588 /**
589 * sysfs_remove_bin_file - remove binary file for object.
590 * @kobj: object.
591 * @attr: attribute descriptor.
592 */
593 void sysfs_remove_bin_file(struct kobject *kobj,
594 const struct bin_attribute *attr)
595 {
596 kernfs_remove_by_name(kobj->sd, attr->attr.name);
597 }
598 EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);
599
600 static int internal_change_owner(struct kernfs_node *kn, kuid_t kuid,
601 kgid_t kgid)
602 {
603 struct iattr newattrs = {
604 .ia_valid = ATTR_UID | ATTR_GID,
605 .ia_uid = kuid,
606 .ia_gid = kgid,
607 };
608 return kernfs_setattr(kn, &newattrs);
609 }
610
611 /**
612 * sysfs_link_change_owner - change owner of a sysfs file.
613 * @kobj: object of the kernfs_node the symlink is located in.
614 * @targ: object of the kernfs_node the symlink points to.
615 * @name: name of the link.
616 * @kuid: new owner's kuid
617 * @kgid: new owner's kgid
618 *
619 * This function looks up the sysfs symlink entry @name under @kobj and changes
620 * the ownership to @kuid/@kgid. The symlink is looked up in the namespace of
621 * @targ.
622 *
623 * Returns 0 on success or error code on failure.
624 */
625 int sysfs_link_change_owner(struct kobject *kobj, struct kobject *targ,
626 const char *name, kuid_t kuid, kgid_t kgid)
627 {
628 struct kernfs_node *kn = NULL;
629 int error;
630
631 if (!name || !kobj->state_in_sysfs || !targ->state_in_sysfs)
632 return -EINVAL;
633
634 error = -ENOENT;
635 kn = kernfs_find_and_get_ns(kobj->sd, name, targ->sd->ns);
636 if (!kn)
637 goto out;
638
639 error = -EINVAL;
640 if (kernfs_type(kn) != KERNFS_LINK)
641 goto out;
642 if (kn->symlink.target_kn->priv != targ)
643 goto out;
644
645 error = internal_change_owner(kn, kuid, kgid);
646
647 out:
648 kernfs_put(kn);
649 return error;
650 }
651
652 /**
653 * sysfs_file_change_owner - change owner of a sysfs file.
654 * @kobj: object.
655 * @name: name of the file to change.
656 * @kuid: new owner's kuid
657 * @kgid: new owner's kgid
658 *
659 * This function looks up the sysfs entry @name under @kobj and changes the
660 * ownership to @kuid/@kgid.
661 *
662 * Returns 0 on success or error code on failure.
663 */
664 int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
665 kgid_t kgid)
666 {
667 struct kernfs_node *kn;
668 int error;
669
670 if (!name)
671 return -EINVAL;
672
673 if (!kobj->state_in_sysfs)
674 return -EINVAL;
675
676 kn = kernfs_find_and_get(kobj->sd, name);
677 if (!kn)
678 return -ENOENT;
679
680 error = internal_change_owner(kn, kuid, kgid);
681
682 kernfs_put(kn);
683
684 return error;
685 }
686 EXPORT_SYMBOL_GPL(sysfs_file_change_owner);
687
688 /**
689 * sysfs_change_owner - change owner of the given object.
690 * @kobj: object.
691 * @kuid: new owner's kuid
692 * @kgid: new owner's kgid
693 *
694 * Change the owner of the default directory, files, groups, and attributes of
695 * @kobj to @kuid/@kgid. Note that sysfs_change_owner mirrors how the sysfs
696 * entries for a kobject are added by driver core. In summary,
697 * sysfs_change_owner() takes care of the default directory entry for @kobj,
698 * the default attributes associated with the ktype of @kobj and the default
699 * attributes associated with the ktype of @kobj.
700 * Additional properties not added by driver core have to be changed by the
701 * driver or subsystem which created them. This is similar to how
702 * driver/subsystem specific entries are removed.
703 *
704 * Returns 0 on success or error code on failure.
705 */
706 int sysfs_change_owner(struct kobject *kobj, kuid_t kuid, kgid_t kgid)
707 {
708 int error;
709 const struct kobj_type *ktype;
710
711 if (!kobj->state_in_sysfs)
712 return -EINVAL;
713
714 /* Change the owner of the kobject itself. */
715 error = internal_change_owner(kobj->sd, kuid, kgid);
716 if (error)
717 return error;
718
719 ktype = get_ktype(kobj);
720 if (ktype) {
721 /*
722 * Change owner of the default groups associated with the
723 * ktype of @kobj.
724 */
725 error = sysfs_groups_change_owner(kobj, ktype->default_groups,
726 kuid, kgid);
727 if (error)
728 return error;
729 }
730
731 return 0;
732 }
733 EXPORT_SYMBOL_GPL(sysfs_change_owner);
734
735 /**
736 * sysfs_emit - scnprintf equivalent, aware of PAGE_SIZE buffer.
737 * @buf: start of PAGE_SIZE buffer.
738 * @fmt: format
739 * @...: optional arguments to @format
740 *
741 *
742 * Returns number of characters written to @buf.
743 */
744 int sysfs_emit(char *buf, const char *fmt, ...)
745 {
746 va_list args;
747 int len;
748
749 if (WARN(!buf || offset_in_page(buf),
750 "invalid sysfs_emit: buf:%p\n", buf))
751 return 0;
752
753 va_start(args, fmt);
754 len = vscnprintf(buf, PAGE_SIZE, fmt, args);
755 va_end(args);
756
757 return len;
758 }
759 EXPORT_SYMBOL_GPL(sysfs_emit);
760
761 /**
762 * sysfs_emit_at - scnprintf equivalent, aware of PAGE_SIZE buffer.
763 * @buf: start of PAGE_SIZE buffer.
764 * @at: offset in @buf to start write in bytes
765 * @at must be >= 0 && < PAGE_SIZE
766 * @fmt: format
767 * @...: optional arguments to @fmt
768 *
769 *
770 * Returns number of characters written starting at &@buf[@at].
771 */
772 int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
773 {
774 va_list args;
775 int len;
776
777 if (WARN(!buf || offset_in_page(buf) || at < 0 || at >= PAGE_SIZE,
778 "invalid sysfs_emit_at: buf:%p at:%d\n", buf, at))
779 return 0;
780
781 va_start(args, fmt);
782 len = vscnprintf(buf + at, PAGE_SIZE - at, fmt, args);
783 va_end(args);
784
785 return len;
786 }
787 EXPORT_SYMBOL_GPL(sysfs_emit_at);
788
789 /**
790 * sysfs_bin_attr_simple_read - read callback to simply copy from memory.
791 * @file: attribute file which is being read.
792 * @kobj: object to which the attribute belongs.
793 * @attr: attribute descriptor.
794 * @buf: destination buffer.
795 * @off: offset in bytes from which to read.
796 * @count: maximum number of bytes to read.
797 *
798 * Simple ->read() callback for bin_attributes backed by a buffer in memory.
799 * The @private and @size members in struct bin_attribute must be set to the
800 * buffer's location and size before the bin_attribute is created in sysfs.
801 *
802 * Bounds check for @off and @count is done in sysfs_kf_bin_read().
803 * Negative value check for @off is done in vfs_setpos() and default_llseek().
804 *
805 * Returns number of bytes written to @buf.
806 */
807 ssize_t sysfs_bin_attr_simple_read(struct file *file, struct kobject *kobj,
808 struct bin_attribute *attr, char *buf,
809 loff_t off, size_t count)
810 {
811 memcpy(buf, attr->private + off, count);
812 return count;
813 }
814 EXPORT_SYMBOL_GPL(sysfs_bin_attr_simple_read);
815
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