xref: /openbmc/linux/block/partitions/core.c (revision 8dd3cdea)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (C) 1991-1998  Linus Torvalds
4  * Re-organised Feb 1998 Russell King
5  * Copyright (C) 2020 Christoph Hellwig
6  */
7 #include <linux/fs.h>
8 #include <linux/major.h>
9 #include <linux/slab.h>
10 #include <linux/ctype.h>
11 #include <linux/vmalloc.h>
12 #include <linux/blktrace_api.h>
13 #include <linux/raid/detect.h>
14 #include "check.h"
15 
16 static int (*check_part[])(struct parsed_partitions *) = {
17 	/*
18 	 * Probe partition formats with tables at disk address 0
19 	 * that also have an ADFS boot block at 0xdc0.
20 	 */
21 #ifdef CONFIG_ACORN_PARTITION_ICS
22 	adfspart_check_ICS,
23 #endif
24 #ifdef CONFIG_ACORN_PARTITION_POWERTEC
25 	adfspart_check_POWERTEC,
26 #endif
27 #ifdef CONFIG_ACORN_PARTITION_EESOX
28 	adfspart_check_EESOX,
29 #endif
30 
31 	/*
32 	 * Now move on to formats that only have partition info at
33 	 * disk address 0xdc0.  Since these may also have stale
34 	 * PC/BIOS partition tables, they need to come before
35 	 * the msdos entry.
36 	 */
37 #ifdef CONFIG_ACORN_PARTITION_CUMANA
38 	adfspart_check_CUMANA,
39 #endif
40 #ifdef CONFIG_ACORN_PARTITION_ADFS
41 	adfspart_check_ADFS,
42 #endif
43 
44 #ifdef CONFIG_CMDLINE_PARTITION
45 	cmdline_partition,
46 #endif
47 #ifdef CONFIG_EFI_PARTITION
48 	efi_partition,		/* this must come before msdos */
49 #endif
50 #ifdef CONFIG_SGI_PARTITION
51 	sgi_partition,
52 #endif
53 #ifdef CONFIG_LDM_PARTITION
54 	ldm_partition,		/* this must come before msdos */
55 #endif
56 #ifdef CONFIG_MSDOS_PARTITION
57 	msdos_partition,
58 #endif
59 #ifdef CONFIG_OSF_PARTITION
60 	osf_partition,
61 #endif
62 #ifdef CONFIG_SUN_PARTITION
63 	sun_partition,
64 #endif
65 #ifdef CONFIG_AMIGA_PARTITION
66 	amiga_partition,
67 #endif
68 #ifdef CONFIG_ATARI_PARTITION
69 	atari_partition,
70 #endif
71 #ifdef CONFIG_MAC_PARTITION
72 	mac_partition,
73 #endif
74 #ifdef CONFIG_ULTRIX_PARTITION
75 	ultrix_partition,
76 #endif
77 #ifdef CONFIG_IBM_PARTITION
78 	ibm_partition,
79 #endif
80 #ifdef CONFIG_KARMA_PARTITION
81 	karma_partition,
82 #endif
83 #ifdef CONFIG_SYSV68_PARTITION
84 	sysv68_partition,
85 #endif
86 	NULL
87 };
88 
89 static void bdev_set_nr_sectors(struct block_device *bdev, sector_t sectors)
90 {
91 	spin_lock(&bdev->bd_size_lock);
92 	i_size_write(bdev->bd_inode, (loff_t)sectors << SECTOR_SHIFT);
93 	bdev->bd_nr_sectors = sectors;
94 	spin_unlock(&bdev->bd_size_lock);
95 }
96 
97 static struct parsed_partitions *allocate_partitions(struct gendisk *hd)
98 {
99 	struct parsed_partitions *state;
100 	int nr = DISK_MAX_PARTS;
101 
102 	state = kzalloc(sizeof(*state), GFP_KERNEL);
103 	if (!state)
104 		return NULL;
105 
106 	state->parts = vzalloc(array_size(nr, sizeof(state->parts[0])));
107 	if (!state->parts) {
108 		kfree(state);
109 		return NULL;
110 	}
111 
112 	state->limit = nr;
113 
114 	return state;
115 }
116 
117 static void free_partitions(struct parsed_partitions *state)
118 {
119 	vfree(state->parts);
120 	kfree(state);
121 }
122 
123 static struct parsed_partitions *check_partition(struct gendisk *hd)
124 {
125 	struct parsed_partitions *state;
126 	int i, res, err;
127 
128 	state = allocate_partitions(hd);
129 	if (!state)
130 		return NULL;
131 	state->pp_buf = (char *)__get_free_page(GFP_KERNEL);
132 	if (!state->pp_buf) {
133 		free_partitions(state);
134 		return NULL;
135 	}
136 	state->pp_buf[0] = '\0';
137 
138 	state->disk = hd;
139 	snprintf(state->name, BDEVNAME_SIZE, "%s", hd->disk_name);
140 	snprintf(state->pp_buf, PAGE_SIZE, " %s:", state->name);
141 	if (isdigit(state->name[strlen(state->name)-1]))
142 		sprintf(state->name, "p");
143 
144 	i = res = err = 0;
145 	while (!res && check_part[i]) {
146 		memset(state->parts, 0, state->limit * sizeof(state->parts[0]));
147 		res = check_part[i++](state);
148 		if (res < 0) {
149 			/*
150 			 * We have hit an I/O error which we don't report now.
151 			 * But record it, and let the others do their job.
152 			 */
153 			err = res;
154 			res = 0;
155 		}
156 
157 	}
158 	if (res > 0) {
159 		printk(KERN_INFO "%s", state->pp_buf);
160 
161 		free_page((unsigned long)state->pp_buf);
162 		return state;
163 	}
164 	if (state->access_beyond_eod)
165 		err = -ENOSPC;
166 	/*
167 	 * The partition is unrecognized. So report I/O errors if there were any
168 	 */
169 	if (err)
170 		res = err;
171 	if (res) {
172 		strlcat(state->pp_buf,
173 			" unable to read partition table\n", PAGE_SIZE);
174 		printk(KERN_INFO "%s", state->pp_buf);
175 	}
176 
177 	free_page((unsigned long)state->pp_buf);
178 	free_partitions(state);
179 	return ERR_PTR(res);
180 }
181 
182 static ssize_t part_partition_show(struct device *dev,
183 				   struct device_attribute *attr, char *buf)
184 {
185 	return sprintf(buf, "%d\n", dev_to_bdev(dev)->bd_partno);
186 }
187 
188 static ssize_t part_start_show(struct device *dev,
189 			       struct device_attribute *attr, char *buf)
190 {
191 	return sprintf(buf, "%llu\n", dev_to_bdev(dev)->bd_start_sect);
192 }
193 
194 static ssize_t part_ro_show(struct device *dev,
195 			    struct device_attribute *attr, char *buf)
196 {
197 	return sprintf(buf, "%d\n", bdev_read_only(dev_to_bdev(dev)));
198 }
199 
200 static ssize_t part_alignment_offset_show(struct device *dev,
201 					  struct device_attribute *attr, char *buf)
202 {
203 	struct block_device *bdev = dev_to_bdev(dev);
204 
205 	return sprintf(buf, "%u\n",
206 		queue_limit_alignment_offset(&bdev_get_queue(bdev)->limits,
207 				bdev->bd_start_sect));
208 }
209 
210 static ssize_t part_discard_alignment_show(struct device *dev,
211 					   struct device_attribute *attr, char *buf)
212 {
213 	struct block_device *bdev = dev_to_bdev(dev);
214 
215 	return sprintf(buf, "%u\n",
216 		queue_limit_discard_alignment(&bdev_get_queue(bdev)->limits,
217 				bdev->bd_start_sect));
218 }
219 
220 static DEVICE_ATTR(partition, 0444, part_partition_show, NULL);
221 static DEVICE_ATTR(start, 0444, part_start_show, NULL);
222 static DEVICE_ATTR(size, 0444, part_size_show, NULL);
223 static DEVICE_ATTR(ro, 0444, part_ro_show, NULL);
224 static DEVICE_ATTR(alignment_offset, 0444, part_alignment_offset_show, NULL);
225 static DEVICE_ATTR(discard_alignment, 0444, part_discard_alignment_show, NULL);
226 static DEVICE_ATTR(stat, 0444, part_stat_show, NULL);
227 static DEVICE_ATTR(inflight, 0444, part_inflight_show, NULL);
228 #ifdef CONFIG_FAIL_MAKE_REQUEST
229 static struct device_attribute dev_attr_fail =
230 	__ATTR(make-it-fail, 0644, part_fail_show, part_fail_store);
231 #endif
232 
233 static struct attribute *part_attrs[] = {
234 	&dev_attr_partition.attr,
235 	&dev_attr_start.attr,
236 	&dev_attr_size.attr,
237 	&dev_attr_ro.attr,
238 	&dev_attr_alignment_offset.attr,
239 	&dev_attr_discard_alignment.attr,
240 	&dev_attr_stat.attr,
241 	&dev_attr_inflight.attr,
242 #ifdef CONFIG_FAIL_MAKE_REQUEST
243 	&dev_attr_fail.attr,
244 #endif
245 	NULL
246 };
247 
248 static struct attribute_group part_attr_group = {
249 	.attrs = part_attrs,
250 };
251 
252 static const struct attribute_group *part_attr_groups[] = {
253 	&part_attr_group,
254 #ifdef CONFIG_BLK_DEV_IO_TRACE
255 	&blk_trace_attr_group,
256 #endif
257 	NULL
258 };
259 
260 static void part_release(struct device *dev)
261 {
262 	put_disk(dev_to_bdev(dev)->bd_disk);
263 	iput(dev_to_bdev(dev)->bd_inode);
264 }
265 
266 static int part_uevent(struct device *dev, struct kobj_uevent_env *env)
267 {
268 	struct block_device *part = dev_to_bdev(dev);
269 
270 	add_uevent_var(env, "PARTN=%u", part->bd_partno);
271 	if (part->bd_meta_info && part->bd_meta_info->volname[0])
272 		add_uevent_var(env, "PARTNAME=%s", part->bd_meta_info->volname);
273 	return 0;
274 }
275 
276 struct device_type part_type = {
277 	.name		= "partition",
278 	.groups		= part_attr_groups,
279 	.release	= part_release,
280 	.uevent		= part_uevent,
281 };
282 
283 static void delete_partition(struct block_device *part)
284 {
285 	lockdep_assert_held(&part->bd_disk->open_mutex);
286 
287 	fsync_bdev(part);
288 	__invalidate_device(part, true);
289 
290 	xa_erase(&part->bd_disk->part_tbl, part->bd_partno);
291 	kobject_put(part->bd_holder_dir);
292 	device_del(&part->bd_device);
293 
294 	/*
295 	 * Remove the block device from the inode hash, so that it cannot be
296 	 * looked up any more even when openers still hold references.
297 	 */
298 	remove_inode_hash(part->bd_inode);
299 
300 	put_device(&part->bd_device);
301 }
302 
303 static ssize_t whole_disk_show(struct device *dev,
304 			       struct device_attribute *attr, char *buf)
305 {
306 	return 0;
307 }
308 static DEVICE_ATTR(whole_disk, 0444, whole_disk_show, NULL);
309 
310 /*
311  * Must be called either with open_mutex held, before a disk can be opened or
312  * after all disk users are gone.
313  */
314 static struct block_device *add_partition(struct gendisk *disk, int partno,
315 				sector_t start, sector_t len, int flags,
316 				struct partition_meta_info *info)
317 {
318 	dev_t devt = MKDEV(0, 0);
319 	struct device *ddev = disk_to_dev(disk);
320 	struct device *pdev;
321 	struct block_device *bdev;
322 	const char *dname;
323 	int err;
324 
325 	lockdep_assert_held(&disk->open_mutex);
326 
327 	if (partno >= DISK_MAX_PARTS)
328 		return ERR_PTR(-EINVAL);
329 
330 	/*
331 	 * Partitions are not supported on zoned block devices that are used as
332 	 * such.
333 	 */
334 	switch (disk->queue->limits.zoned) {
335 	case BLK_ZONED_HM:
336 		pr_warn("%s: partitions not supported on host managed zoned block device\n",
337 			disk->disk_name);
338 		return ERR_PTR(-ENXIO);
339 	case BLK_ZONED_HA:
340 		pr_info("%s: disabling host aware zoned block device support due to partitions\n",
341 			disk->disk_name);
342 		blk_queue_set_zoned(disk, BLK_ZONED_NONE);
343 		break;
344 	case BLK_ZONED_NONE:
345 		break;
346 	}
347 
348 	if (xa_load(&disk->part_tbl, partno))
349 		return ERR_PTR(-EBUSY);
350 
351 	/* ensure we always have a reference to the whole disk */
352 	get_device(disk_to_dev(disk));
353 
354 	err = -ENOMEM;
355 	bdev = bdev_alloc(disk, partno);
356 	if (!bdev)
357 		goto out_put_disk;
358 
359 	bdev->bd_start_sect = start;
360 	bdev_set_nr_sectors(bdev, len);
361 
362 	pdev = &bdev->bd_device;
363 	dname = dev_name(ddev);
364 	if (isdigit(dname[strlen(dname) - 1]))
365 		dev_set_name(pdev, "%sp%d", dname, partno);
366 	else
367 		dev_set_name(pdev, "%s%d", dname, partno);
368 
369 	device_initialize(pdev);
370 	pdev->class = &block_class;
371 	pdev->type = &part_type;
372 	pdev->parent = ddev;
373 
374 	/* in consecutive minor range? */
375 	if (bdev->bd_partno < disk->minors) {
376 		devt = MKDEV(disk->major, disk->first_minor + bdev->bd_partno);
377 	} else {
378 		err = blk_alloc_ext_minor();
379 		if (err < 0)
380 			goto out_put;
381 		devt = MKDEV(BLOCK_EXT_MAJOR, err);
382 	}
383 	pdev->devt = devt;
384 
385 	if (info) {
386 		err = -ENOMEM;
387 		bdev->bd_meta_info = kmemdup(info, sizeof(*info), GFP_KERNEL);
388 		if (!bdev->bd_meta_info)
389 			goto out_put;
390 	}
391 
392 	/* delay uevent until 'holders' subdir is created */
393 	dev_set_uevent_suppress(pdev, 1);
394 	err = device_add(pdev);
395 	if (err)
396 		goto out_put;
397 
398 	err = -ENOMEM;
399 	bdev->bd_holder_dir = kobject_create_and_add("holders", &pdev->kobj);
400 	if (!bdev->bd_holder_dir)
401 		goto out_del;
402 
403 	dev_set_uevent_suppress(pdev, 0);
404 	if (flags & ADDPART_FLAG_WHOLEDISK) {
405 		err = device_create_file(pdev, &dev_attr_whole_disk);
406 		if (err)
407 			goto out_del;
408 	}
409 
410 	/* everything is up and running, commence */
411 	err = xa_insert(&disk->part_tbl, partno, bdev, GFP_KERNEL);
412 	if (err)
413 		goto out_del;
414 	bdev_add(bdev, devt);
415 
416 	/* suppress uevent if the disk suppresses it */
417 	if (!dev_get_uevent_suppress(ddev))
418 		kobject_uevent(&pdev->kobj, KOBJ_ADD);
419 	return bdev;
420 
421 out_del:
422 	kobject_put(bdev->bd_holder_dir);
423 	device_del(pdev);
424 out_put:
425 	put_device(pdev);
426 	return ERR_PTR(err);
427 out_put_disk:
428 	put_disk(disk);
429 	return ERR_PTR(err);
430 }
431 
432 static bool partition_overlaps(struct gendisk *disk, sector_t start,
433 		sector_t length, int skip_partno)
434 {
435 	struct block_device *part;
436 	bool overlap = false;
437 	unsigned long idx;
438 
439 	rcu_read_lock();
440 	xa_for_each_start(&disk->part_tbl, idx, part, 1) {
441 		if (part->bd_partno != skip_partno &&
442 		    start < part->bd_start_sect + bdev_nr_sectors(part) &&
443 		    start + length > part->bd_start_sect) {
444 			overlap = true;
445 			break;
446 		}
447 	}
448 	rcu_read_unlock();
449 
450 	return overlap;
451 }
452 
453 int bdev_add_partition(struct gendisk *disk, int partno, sector_t start,
454 		sector_t length)
455 {
456 	struct block_device *part;
457 	int ret;
458 
459 	mutex_lock(&disk->open_mutex);
460 	if (!disk_live(disk)) {
461 		ret = -ENXIO;
462 		goto out;
463 	}
464 
465 	if (partition_overlaps(disk, start, length, -1)) {
466 		ret = -EBUSY;
467 		goto out;
468 	}
469 
470 	part = add_partition(disk, partno, start, length,
471 			ADDPART_FLAG_NONE, NULL);
472 	ret = PTR_ERR_OR_ZERO(part);
473 out:
474 	mutex_unlock(&disk->open_mutex);
475 	return ret;
476 }
477 
478 int bdev_del_partition(struct gendisk *disk, int partno)
479 {
480 	struct block_device *part = NULL;
481 	int ret = -ENXIO;
482 
483 	mutex_lock(&disk->open_mutex);
484 	part = xa_load(&disk->part_tbl, partno);
485 	if (!part)
486 		goto out_unlock;
487 
488 	ret = -EBUSY;
489 	if (part->bd_openers)
490 		goto out_unlock;
491 
492 	delete_partition(part);
493 	ret = 0;
494 out_unlock:
495 	mutex_unlock(&disk->open_mutex);
496 	return ret;
497 }
498 
499 int bdev_resize_partition(struct gendisk *disk, int partno, sector_t start,
500 		sector_t length)
501 {
502 	struct block_device *part = NULL;
503 	int ret = -ENXIO;
504 
505 	mutex_lock(&disk->open_mutex);
506 	part = xa_load(&disk->part_tbl, partno);
507 	if (!part)
508 		goto out_unlock;
509 
510 	ret = -EINVAL;
511 	if (start != part->bd_start_sect)
512 		goto out_unlock;
513 
514 	ret = -EBUSY;
515 	if (partition_overlaps(disk, start, length, partno))
516 		goto out_unlock;
517 
518 	bdev_set_nr_sectors(part, length);
519 
520 	ret = 0;
521 out_unlock:
522 	mutex_unlock(&disk->open_mutex);
523 	return ret;
524 }
525 
526 static bool disk_unlock_native_capacity(struct gendisk *disk)
527 {
528 	if (!disk->fops->unlock_native_capacity ||
529 	    test_and_set_bit(GD_NATIVE_CAPACITY, &disk->state)) {
530 		printk(KERN_CONT "truncated\n");
531 		return false;
532 	}
533 
534 	printk(KERN_CONT "enabling native capacity\n");
535 	disk->fops->unlock_native_capacity(disk);
536 	return true;
537 }
538 
539 void blk_drop_partitions(struct gendisk *disk)
540 {
541 	struct block_device *part;
542 	unsigned long idx;
543 
544 	lockdep_assert_held(&disk->open_mutex);
545 
546 	xa_for_each_start(&disk->part_tbl, idx, part, 1)
547 		delete_partition(part);
548 }
549 
550 static bool blk_add_partition(struct gendisk *disk,
551 		struct parsed_partitions *state, int p)
552 {
553 	sector_t size = state->parts[p].size;
554 	sector_t from = state->parts[p].from;
555 	struct block_device *part;
556 
557 	if (!size)
558 		return true;
559 
560 	if (from >= get_capacity(disk)) {
561 		printk(KERN_WARNING
562 		       "%s: p%d start %llu is beyond EOD, ",
563 		       disk->disk_name, p, (unsigned long long) from);
564 		if (disk_unlock_native_capacity(disk))
565 			return false;
566 		return true;
567 	}
568 
569 	if (from + size > get_capacity(disk)) {
570 		printk(KERN_WARNING
571 		       "%s: p%d size %llu extends beyond EOD, ",
572 		       disk->disk_name, p, (unsigned long long) size);
573 
574 		if (disk_unlock_native_capacity(disk))
575 			return false;
576 
577 		/*
578 		 * We can not ignore partitions of broken tables created by for
579 		 * example camera firmware, but we limit them to the end of the
580 		 * disk to avoid creating invalid block devices.
581 		 */
582 		size = get_capacity(disk) - from;
583 	}
584 
585 	part = add_partition(disk, p, from, size, state->parts[p].flags,
586 			     &state->parts[p].info);
587 	if (IS_ERR(part) && PTR_ERR(part) != -ENXIO) {
588 		printk(KERN_ERR " %s: p%d could not be added: %ld\n",
589 		       disk->disk_name, p, -PTR_ERR(part));
590 		return true;
591 	}
592 
593 	if (IS_BUILTIN(CONFIG_BLK_DEV_MD) &&
594 	    (state->parts[p].flags & ADDPART_FLAG_RAID))
595 		md_autodetect_dev(part->bd_dev);
596 
597 	return true;
598 }
599 
600 static int blk_add_partitions(struct gendisk *disk)
601 {
602 	struct parsed_partitions *state;
603 	int ret = -EAGAIN, p;
604 
605 	if (disk->flags & GENHD_FL_NO_PART)
606 		return 0;
607 
608 	state = check_partition(disk);
609 	if (!state)
610 		return 0;
611 	if (IS_ERR(state)) {
612 		/*
613 		 * I/O error reading the partition table.  If we tried to read
614 		 * beyond EOD, retry after unlocking the native capacity.
615 		 */
616 		if (PTR_ERR(state) == -ENOSPC) {
617 			printk(KERN_WARNING "%s: partition table beyond EOD, ",
618 			       disk->disk_name);
619 			if (disk_unlock_native_capacity(disk))
620 				return -EAGAIN;
621 		}
622 		return -EIO;
623 	}
624 
625 	/*
626 	 * Partitions are not supported on host managed zoned block devices.
627 	 */
628 	if (disk->queue->limits.zoned == BLK_ZONED_HM) {
629 		pr_warn("%s: ignoring partition table on host managed zoned block device\n",
630 			disk->disk_name);
631 		ret = 0;
632 		goto out_free_state;
633 	}
634 
635 	/*
636 	 * If we read beyond EOD, try unlocking native capacity even if the
637 	 * partition table was successfully read as we could be missing some
638 	 * partitions.
639 	 */
640 	if (state->access_beyond_eod) {
641 		printk(KERN_WARNING
642 		       "%s: partition table partially beyond EOD, ",
643 		       disk->disk_name);
644 		if (disk_unlock_native_capacity(disk))
645 			goto out_free_state;
646 	}
647 
648 	/* tell userspace that the media / partition table may have changed */
649 	kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
650 
651 	for (p = 1; p < state->limit; p++)
652 		if (!blk_add_partition(disk, state, p))
653 			goto out_free_state;
654 
655 	ret = 0;
656 out_free_state:
657 	free_partitions(state);
658 	return ret;
659 }
660 
661 int bdev_disk_changed(struct gendisk *disk, bool invalidate)
662 {
663 	int ret = 0;
664 
665 	lockdep_assert_held(&disk->open_mutex);
666 
667 	if (!disk_live(disk))
668 		return -ENXIO;
669 
670 rescan:
671 	if (disk->open_partitions)
672 		return -EBUSY;
673 	sync_blockdev(disk->part0);
674 	invalidate_bdev(disk->part0);
675 	blk_drop_partitions(disk);
676 
677 	clear_bit(GD_NEED_PART_SCAN, &disk->state);
678 
679 	/*
680 	 * Historically we only set the capacity to zero for devices that
681 	 * support partitions (independ of actually having partitions created).
682 	 * Doing that is rather inconsistent, but changing it broke legacy
683 	 * udisks polling for legacy ide-cdrom devices.  Use the crude check
684 	 * below to get the sane behavior for most device while not breaking
685 	 * userspace for this particular setup.
686 	 */
687 	if (invalidate) {
688 		if (!(disk->flags & GENHD_FL_NO_PART) ||
689 		    !(disk->flags & GENHD_FL_REMOVABLE))
690 			set_capacity(disk, 0);
691 	}
692 
693 	if (get_capacity(disk)) {
694 		ret = blk_add_partitions(disk);
695 		if (ret == -EAGAIN)
696 			goto rescan;
697 	} else if (invalidate) {
698 		/*
699 		 * Tell userspace that the media / partition table may have
700 		 * changed.
701 		 */
702 		kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
703 	}
704 
705 	return ret;
706 }
707 /*
708  * Only exported for loop and dasd for historic reasons.  Don't use in new
709  * code!
710  */
711 EXPORT_SYMBOL_GPL(bdev_disk_changed);
712 
713 void *read_part_sector(struct parsed_partitions *state, sector_t n, Sector *p)
714 {
715 	struct address_space *mapping = state->disk->part0->bd_inode->i_mapping;
716 	struct page *page;
717 
718 	if (n >= get_capacity(state->disk)) {
719 		state->access_beyond_eod = true;
720 		return NULL;
721 	}
722 
723 	page = read_mapping_page(mapping,
724 			(pgoff_t)(n >> (PAGE_SHIFT - 9)), NULL);
725 	if (IS_ERR(page))
726 		goto out;
727 	if (PageError(page))
728 		goto out_put_page;
729 
730 	p->v = page;
731 	return (unsigned char *)page_address(page) +
732 			((n & ((1 << (PAGE_SHIFT - 9)) - 1)) << SECTOR_SHIFT);
733 out_put_page:
734 	put_page(page);
735 out:
736 	p->v = NULL;
737 	return NULL;
738 }
739