xref: /openbmc/linux/block/partitions/core.c (revision 240e6d25) 
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/genhd.h>
12 #include <linux/vmalloc.h>
13 #include <linux/blktrace_api.h>
14 #include <linux/raid/detect.h>
15 #include "check.h"
16 
17 static int (*check_part[])(struct parsed_partitions *) = {
18 	/*
19 	 * Probe partition formats with tables at disk address 0
20 	 * that also have an ADFS boot block at 0xdc0.
21 	 */
22 #ifdef CONFIG_ACORN_PARTITION_ICS
23 	adfspart_check_ICS,
24 #endif
25 #ifdef CONFIG_ACORN_PARTITION_POWERTEC
26 	adfspart_check_POWERTEC,
27 #endif
28 #ifdef CONFIG_ACORN_PARTITION_EESOX
29 	adfspart_check_EESOX,
30 #endif
31 
32 	/*
33 	 * Now move on to formats that only have partition info at
34 	 * disk address 0xdc0.  Since these may also have stale
35 	 * PC/BIOS partition tables, they need to come before
36 	 * the msdos entry.
37 	 */
38 #ifdef CONFIG_ACORN_PARTITION_CUMANA
39 	adfspart_check_CUMANA,
40 #endif
41 #ifdef CONFIG_ACORN_PARTITION_ADFS
42 	adfspart_check_ADFS,
43 #endif
44 
45 #ifdef CONFIG_CMDLINE_PARTITION
46 	cmdline_partition,
47 #endif
48 #ifdef CONFIG_EFI_PARTITION
49 	efi_partition,		/* this must come before msdos */
50 #endif
51 #ifdef CONFIG_SGI_PARTITION
52 	sgi_partition,
53 #endif
54 #ifdef CONFIG_LDM_PARTITION
55 	ldm_partition,		/* this must come before msdos */
56 #endif
57 #ifdef CONFIG_MSDOS_PARTITION
58 	msdos_partition,
59 #endif
60 #ifdef CONFIG_OSF_PARTITION
61 	osf_partition,
62 #endif
63 #ifdef CONFIG_SUN_PARTITION
64 	sun_partition,
65 #endif
66 #ifdef CONFIG_AMIGA_PARTITION
67 	amiga_partition,
68 #endif
69 #ifdef CONFIG_ATARI_PARTITION
70 	atari_partition,
71 #endif
72 #ifdef CONFIG_MAC_PARTITION
73 	mac_partition,
74 #endif
75 #ifdef CONFIG_ULTRIX_PARTITION
76 	ultrix_partition,
77 #endif
78 #ifdef CONFIG_IBM_PARTITION
79 	ibm_partition,
80 #endif
81 #ifdef CONFIG_KARMA_PARTITION
82 	karma_partition,
83 #endif
84 #ifdef CONFIG_SYSV68_PARTITION
85 	sysv68_partition,
86 #endif
87 	NULL
88 };
89 
90 static void bdev_set_nr_sectors(struct block_device *bdev, sector_t sectors)
91 {
92 	spin_lock(&bdev->bd_size_lock);
93 	i_size_write(bdev->bd_inode, (loff_t)sectors << SECTOR_SHIFT);
94 	bdev->bd_nr_sectors = sectors;
95 	spin_unlock(&bdev->bd_size_lock);
96 }
97 
98 static struct parsed_partitions *allocate_partitions(struct gendisk *hd)
99 {
100 	struct parsed_partitions *state;
101 	int nr;
102 
103 	state = kzalloc(sizeof(*state), GFP_KERNEL);
104 	if (!state)
105 		return NULL;
106 
107 	nr = disk_max_parts(hd);
108 	state->parts = vzalloc(array_size(nr, sizeof(state->parts[0])));
109 	if (!state->parts) {
110 		kfree(state);
111 		return NULL;
112 	}
113 
114 	state->limit = nr;
115 
116 	return state;
117 }
118 
119 static void free_partitions(struct parsed_partitions *state)
120 {
121 	vfree(state->parts);
122 	kfree(state);
123 }
124 
125 static struct parsed_partitions *check_partition(struct gendisk *hd)
126 {
127 	struct parsed_partitions *state;
128 	int i, res, err;
129 
130 	state = allocate_partitions(hd);
131 	if (!state)
132 		return NULL;
133 	state->pp_buf = (char *)__get_free_page(GFP_KERNEL);
134 	if (!state->pp_buf) {
135 		free_partitions(state);
136 		return NULL;
137 	}
138 	state->pp_buf[0] = '\0';
139 
140 	state->disk = hd;
141 	snprintf(state->name, BDEVNAME_SIZE, "%s", hd->disk_name);
142 	snprintf(state->pp_buf, PAGE_SIZE, " %s:", state->name);
143 	if (isdigit(state->name[strlen(state->name)-1]))
144 		sprintf(state->name, "p");
145 
146 	i = res = err = 0;
147 	while (!res && check_part[i]) {
148 		memset(state->parts, 0, state->limit * sizeof(state->parts[0]));
149 		res = check_part[i++](state);
150 		if (res < 0) {
151 			/*
152 			 * We have hit an I/O error which we don't report now.
153 			 * But record it, and let the others do their job.
154 			 */
155 			err = res;
156 			res = 0;
157 		}
158 
159 	}
160 	if (res > 0) {
161 		printk(KERN_INFO "%s", state->pp_buf);
162 
163 		free_page((unsigned long)state->pp_buf);
164 		return state;
165 	}
166 	if (state->access_beyond_eod)
167 		err = -ENOSPC;
168 	/*
169 	 * The partition is unrecognized. So report I/O errors if there were any
170 	 */
171 	if (err)
172 		res = err;
173 	if (res) {
174 		strlcat(state->pp_buf,
175 			" unable to read partition table\n", PAGE_SIZE);
176 		printk(KERN_INFO "%s", state->pp_buf);
177 	}
178 
179 	free_page((unsigned long)state->pp_buf);
180 	free_partitions(state);
181 	return ERR_PTR(res);
182 }
183 
184 static ssize_t part_partition_show(struct device *dev,
185 				   struct device_attribute *attr, char *buf)
186 {
187 	return sprintf(buf, "%d\n", dev_to_bdev(dev)->bd_partno);
188 }
189 
190 static ssize_t part_start_show(struct device *dev,
191 			       struct device_attribute *attr, char *buf)
192 {
193 	return sprintf(buf, "%llu\n", dev_to_bdev(dev)->bd_start_sect);
194 }
195 
196 static ssize_t part_ro_show(struct device *dev,
197 			    struct device_attribute *attr, char *buf)
198 {
199 	return sprintf(buf, "%d\n", bdev_read_only(dev_to_bdev(dev)));
200 }
201 
202 static ssize_t part_alignment_offset_show(struct device *dev,
203 					  struct device_attribute *attr, char *buf)
204 {
205 	struct block_device *bdev = dev_to_bdev(dev);
206 
207 	return sprintf(buf, "%u\n",
208 		queue_limit_alignment_offset(&bdev_get_queue(bdev)->limits,
209 				bdev->bd_start_sect));
210 }
211 
212 static ssize_t part_discard_alignment_show(struct device *dev,
213 					   struct device_attribute *attr, char *buf)
214 {
215 	struct block_device *bdev = dev_to_bdev(dev);
216 
217 	return sprintf(buf, "%u\n",
218 		queue_limit_discard_alignment(&bdev_get_queue(bdev)->limits,
219 				bdev->bd_start_sect));
220 }
221 
222 static DEVICE_ATTR(partition, 0444, part_partition_show, NULL);
223 static DEVICE_ATTR(start, 0444, part_start_show, NULL);
224 static DEVICE_ATTR(size, 0444, part_size_show, NULL);
225 static DEVICE_ATTR(ro, 0444, part_ro_show, NULL);
226 static DEVICE_ATTR(alignment_offset, 0444, part_alignment_offset_show, NULL);
227 static DEVICE_ATTR(discard_alignment, 0444, part_discard_alignment_show, NULL);
228 static DEVICE_ATTR(stat, 0444, part_stat_show, NULL);
229 static DEVICE_ATTR(inflight, 0444, part_inflight_show, NULL);
230 #ifdef CONFIG_FAIL_MAKE_REQUEST
231 static struct device_attribute dev_attr_fail =
232 	__ATTR(make-it-fail, 0644, part_fail_show, part_fail_store);
233 #endif
234 
235 static struct attribute *part_attrs[] = {
236 	&dev_attr_partition.attr,
237 	&dev_attr_start.attr,
238 	&dev_attr_size.attr,
239 	&dev_attr_ro.attr,
240 	&dev_attr_alignment_offset.attr,
241 	&dev_attr_discard_alignment.attr,
242 	&dev_attr_stat.attr,
243 	&dev_attr_inflight.attr,
244 #ifdef CONFIG_FAIL_MAKE_REQUEST
245 	&dev_attr_fail.attr,
246 #endif
247 	NULL
248 };
249 
250 static struct attribute_group part_attr_group = {
251 	.attrs = part_attrs,
252 };
253 
254 static const struct attribute_group *part_attr_groups[] = {
255 	&part_attr_group,
256 #ifdef CONFIG_BLK_DEV_IO_TRACE
257 	&blk_trace_attr_group,
258 #endif
259 	NULL
260 };
261 
262 static void part_release(struct device *dev)
263 {
264 	put_disk(dev_to_bdev(dev)->bd_disk);
265 	iput(dev_to_bdev(dev)->bd_inode);
266 }
267 
268 static int part_uevent(struct device *dev, struct kobj_uevent_env *env)
269 {
270 	struct block_device *part = dev_to_bdev(dev);
271 
272 	add_uevent_var(env, "PARTN=%u", part->bd_partno);
273 	if (part->bd_meta_info && part->bd_meta_info->volname[0])
274 		add_uevent_var(env, "PARTNAME=%s", part->bd_meta_info->volname);
275 	return 0;
276 }
277 
278 struct device_type part_type = {
279 	.name		= "partition",
280 	.groups		= part_attr_groups,
281 	.release	= part_release,
282 	.uevent		= part_uevent,
283 };
284 
285 static void delete_partition(struct block_device *part)
286 {
287 	lockdep_assert_held(&part->bd_disk->open_mutex);
288 
289 	fsync_bdev(part);
290 	__invalidate_device(part, true);
291 
292 	xa_erase(&part->bd_disk->part_tbl, part->bd_partno);
293 	kobject_put(part->bd_holder_dir);
294 	device_del(&part->bd_device);
295 
296 	/*
297 	 * Remove the block device from the inode hash, so that it cannot be
298 	 * looked up any more even when openers still hold references.
299 	 */
300 	remove_inode_hash(part->bd_inode);
301 
302 	put_device(&part->bd_device);
303 }
304 
305 static ssize_t whole_disk_show(struct device *dev,
306 			       struct device_attribute *attr, char *buf)
307 {
308 	return 0;
309 }
310 static DEVICE_ATTR(whole_disk, 0444, whole_disk_show, NULL);
311 
312 /*
313  * Must be called either with open_mutex held, before a disk can be opened or
314  * after all disk users are gone.
315  */
316 static struct block_device *add_partition(struct gendisk *disk, int partno,
317 				sector_t start, sector_t len, int flags,
318 				struct partition_meta_info *info)
319 {
320 	dev_t devt = MKDEV(0, 0);
321 	struct device *ddev = disk_to_dev(disk);
322 	struct device *pdev;
323 	struct block_device *bdev;
324 	const char *dname;
325 	int err;
326 
327 	lockdep_assert_held(&disk->open_mutex);
328 
329 	if (partno >= disk_max_parts(disk))
330 		return ERR_PTR(-EINVAL);
331 
332 	/*
333 	 * Partitions are not supported on zoned block devices that are used as
334 	 * such.
335 	 */
336 	switch (disk->queue->limits.zoned) {
337 	case BLK_ZONED_HM:
338 		pr_warn("%s: partitions not supported on host managed zoned block device\n",
339 			disk->disk_name);
340 		return ERR_PTR(-ENXIO);
341 	case BLK_ZONED_HA:
342 		pr_info("%s: disabling host aware zoned block device support due to partitions\n",
343 			disk->disk_name);
344 		blk_queue_set_zoned(disk, BLK_ZONED_NONE);
345 		break;
346 	case BLK_ZONED_NONE:
347 		break;
348 	}
349 
350 	if (xa_load(&disk->part_tbl, partno))
351 		return ERR_PTR(-EBUSY);
352 
353 	/* ensure we always have a reference to the whole disk */
354 	get_device(disk_to_dev(disk));
355 
356 	err = -ENOMEM;
357 	bdev = bdev_alloc(disk, partno);
358 	if (!bdev)
359 		goto out_put_disk;
360 
361 	bdev->bd_start_sect = start;
362 	bdev_set_nr_sectors(bdev, len);
363 
364 	pdev = &bdev->bd_device;
365 	dname = dev_name(ddev);
366 	if (isdigit(dname[strlen(dname) - 1]))
367 		dev_set_name(pdev, "%sp%d", dname, partno);
368 	else
369 		dev_set_name(pdev, "%s%d", dname, partno);
370 
371 	device_initialize(pdev);
372 	pdev->class = &block_class;
373 	pdev->type = &part_type;
374 	pdev->parent = ddev;
375 
376 	/* in consecutive minor range? */
377 	if (bdev->bd_partno < disk->minors) {
378 		devt = MKDEV(disk->major, disk->first_minor + bdev->bd_partno);
379 	} else {
380 		err = blk_alloc_ext_minor();
381 		if (err < 0)
382 			goto out_put;
383 		devt = MKDEV(BLOCK_EXT_MAJOR, err);
384 	}
385 	pdev->devt = devt;
386 
387 	if (info) {
388 		err = -ENOMEM;
389 		bdev->bd_meta_info = kmemdup(info, sizeof(*info), GFP_KERNEL);
390 		if (!bdev->bd_meta_info)
391 			goto out_put;
392 	}
393 
394 	/* delay uevent until 'holders' subdir is created */
395 	dev_set_uevent_suppress(pdev, 1);
396 	err = device_add(pdev);
397 	if (err)
398 		goto out_put;
399 
400 	err = -ENOMEM;
401 	bdev->bd_holder_dir = kobject_create_and_add("holders", &pdev->kobj);
402 	if (!bdev->bd_holder_dir)
403 		goto out_del;
404 
405 	dev_set_uevent_suppress(pdev, 0);
406 	if (flags & ADDPART_FLAG_WHOLEDISK) {
407 		err = device_create_file(pdev, &dev_attr_whole_disk);
408 		if (err)
409 			goto out_del;
410 	}
411 
412 	/* everything is up and running, commence */
413 	err = xa_insert(&disk->part_tbl, partno, bdev, GFP_KERNEL);
414 	if (err)
415 		goto out_del;
416 	bdev_add(bdev, devt);
417 
418 	/* suppress uevent if the disk suppresses it */
419 	if (!dev_get_uevent_suppress(ddev))
420 		kobject_uevent(&pdev->kobj, KOBJ_ADD);
421 	return bdev;
422 
423 out_del:
424 	kobject_put(bdev->bd_holder_dir);
425 	device_del(pdev);
426 out_put:
427 	put_device(pdev);
428 	return ERR_PTR(err);
429 out_put_disk:
430 	put_disk(disk);
431 	return ERR_PTR(err);
432 }
433 
434 static bool partition_overlaps(struct gendisk *disk, sector_t start,
435 		sector_t length, int skip_partno)
436 {
437 	struct block_device *part;
438 	bool overlap = false;
439 	unsigned long idx;
440 
441 	rcu_read_lock();
442 	xa_for_each_start(&disk->part_tbl, idx, part, 1) {
443 		if (part->bd_partno != skip_partno &&
444 		    start < part->bd_start_sect + bdev_nr_sectors(part) &&
445 		    start + length > part->bd_start_sect) {
446 			overlap = true;
447 			break;
448 		}
449 	}
450 	rcu_read_unlock();
451 
452 	return overlap;
453 }
454 
455 int bdev_add_partition(struct gendisk *disk, int partno, sector_t start,
456 		sector_t length)
457 {
458 	struct block_device *part;
459 	int ret;
460 
461 	mutex_lock(&disk->open_mutex);
462 	if (!disk_live(disk)) {
463 		ret = -ENXIO;
464 		goto out;
465 	}
466 
467 	if (partition_overlaps(disk, start, length, -1)) {
468 		ret = -EBUSY;
469 		goto out;
470 	}
471 
472 	part = add_partition(disk, partno, start, length,
473 			ADDPART_FLAG_NONE, NULL);
474 	ret = PTR_ERR_OR_ZERO(part);
475 out:
476 	mutex_unlock(&disk->open_mutex);
477 	return ret;
478 }
479 
480 int bdev_del_partition(struct gendisk *disk, int partno)
481 {
482 	struct block_device *part = NULL;
483 	int ret = -ENXIO;
484 
485 	mutex_lock(&disk->open_mutex);
486 	part = xa_load(&disk->part_tbl, partno);
487 	if (!part)
488 		goto out_unlock;
489 
490 	ret = -EBUSY;
491 	if (part->bd_openers)
492 		goto out_unlock;
493 
494 	delete_partition(part);
495 	ret = 0;
496 out_unlock:
497 	mutex_unlock(&disk->open_mutex);
498 	return ret;
499 }
500 
501 int bdev_resize_partition(struct gendisk *disk, int partno, sector_t start,
502 		sector_t length)
503 {
504 	struct block_device *part = NULL;
505 	int ret = -ENXIO;
506 
507 	mutex_lock(&disk->open_mutex);
508 	part = xa_load(&disk->part_tbl, partno);
509 	if (!part)
510 		goto out_unlock;
511 
512 	ret = -EINVAL;
513 	if (start != part->bd_start_sect)
514 		goto out_unlock;
515 
516 	ret = -EBUSY;
517 	if (partition_overlaps(disk, start, length, partno))
518 		goto out_unlock;
519 
520 	bdev_set_nr_sectors(part, length);
521 
522 	ret = 0;
523 out_unlock:
524 	mutex_unlock(&disk->open_mutex);
525 	return ret;
526 }
527 
528 static bool disk_unlock_native_capacity(struct gendisk *disk)
529 {
530 	const struct block_device_operations *bdops = disk->fops;
531 
532 	if (bdops->unlock_native_capacity &&
533 	    !(disk->flags & GENHD_FL_NATIVE_CAPACITY)) {
534 		printk(KERN_CONT "enabling native capacity\n");
535 		bdops->unlock_native_capacity(disk);
536 		disk->flags |= GENHD_FL_NATIVE_CAPACITY;
537 		return true;
538 	} else {
539 		printk(KERN_CONT "truncated\n");
540 		return false;
541 	}
542 }
543 
544 void blk_drop_partitions(struct gendisk *disk)
545 {
546 	struct block_device *part;
547 	unsigned long idx;
548 
549 	lockdep_assert_held(&disk->open_mutex);
550 
551 	xa_for_each_start(&disk->part_tbl, idx, part, 1)
552 		delete_partition(part);
553 }
554 
555 static bool blk_add_partition(struct gendisk *disk,
556 		struct parsed_partitions *state, int p)
557 {
558 	sector_t size = state->parts[p].size;
559 	sector_t from = state->parts[p].from;
560 	struct block_device *part;
561 
562 	if (!size)
563 		return true;
564 
565 	if (from >= get_capacity(disk)) {
566 		printk(KERN_WARNING
567 		       "%s: p%d start %llu is beyond EOD, ",
568 		       disk->disk_name, p, (unsigned long long) from);
569 		if (disk_unlock_native_capacity(disk))
570 			return false;
571 		return true;
572 	}
573 
574 	if (from + size > get_capacity(disk)) {
575 		printk(KERN_WARNING
576 		       "%s: p%d size %llu extends beyond EOD, ",
577 		       disk->disk_name, p, (unsigned long long) size);
578 
579 		if (disk_unlock_native_capacity(disk))
580 			return false;
581 
582 		/*
583 		 * We can not ignore partitions of broken tables created by for
584 		 * example camera firmware, but we limit them to the end of the
585 		 * disk to avoid creating invalid block devices.
586 		 */
587 		size = get_capacity(disk) - from;
588 	}
589 
590 	part = add_partition(disk, p, from, size, state->parts[p].flags,
591 			     &state->parts[p].info);
592 	if (IS_ERR(part) && PTR_ERR(part) != -ENXIO) {
593 		printk(KERN_ERR " %s: p%d could not be added: %ld\n",
594 		       disk->disk_name, p, -PTR_ERR(part));
595 		return true;
596 	}
597 
598 	if (IS_BUILTIN(CONFIG_BLK_DEV_MD) &&
599 	    (state->parts[p].flags & ADDPART_FLAG_RAID))
600 		md_autodetect_dev(part->bd_dev);
601 
602 	return true;
603 }
604 
605 static int blk_add_partitions(struct gendisk *disk)
606 {
607 	struct parsed_partitions *state;
608 	int ret = -EAGAIN, p;
609 
610 	if (!disk_part_scan_enabled(disk))
611 		return 0;
612 
613 	state = check_partition(disk);
614 	if (!state)
615 		return 0;
616 	if (IS_ERR(state)) {
617 		/*
618 		 * I/O error reading the partition table.  If we tried to read
619 		 * beyond EOD, retry after unlocking the native capacity.
620 		 */
621 		if (PTR_ERR(state) == -ENOSPC) {
622 			printk(KERN_WARNING "%s: partition table beyond EOD, ",
623 			       disk->disk_name);
624 			if (disk_unlock_native_capacity(disk))
625 				return -EAGAIN;
626 		}
627 		return -EIO;
628 	}
629 
630 	/*
631 	 * Partitions are not supported on host managed zoned block devices.
632 	 */
633 	if (disk->queue->limits.zoned == BLK_ZONED_HM) {
634 		pr_warn("%s: ignoring partition table on host managed zoned block device\n",
635 			disk->disk_name);
636 		ret = 0;
637 		goto out_free_state;
638 	}
639 
640 	/*
641 	 * If we read beyond EOD, try unlocking native capacity even if the
642 	 * partition table was successfully read as we could be missing some
643 	 * partitions.
644 	 */
645 	if (state->access_beyond_eod) {
646 		printk(KERN_WARNING
647 		       "%s: partition table partially beyond EOD, ",
648 		       disk->disk_name);
649 		if (disk_unlock_native_capacity(disk))
650 			goto out_free_state;
651 	}
652 
653 	/* tell userspace that the media / partition table may have changed */
654 	kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
655 
656 	for (p = 1; p < state->limit; p++)
657 		if (!blk_add_partition(disk, state, p))
658 			goto out_free_state;
659 
660 	ret = 0;
661 out_free_state:
662 	free_partitions(state);
663 	return ret;
664 }
665 
666 int bdev_disk_changed(struct gendisk *disk, bool invalidate)
667 {
668 	int ret = 0;
669 
670 	lockdep_assert_held(&disk->open_mutex);
671 
672 	if (!disk_live(disk))
673 		return -ENXIO;
674 
675 rescan:
676 	if (disk->open_partitions)
677 		return -EBUSY;
678 	sync_blockdev(disk->part0);
679 	invalidate_bdev(disk->part0);
680 	blk_drop_partitions(disk);
681 
682 	clear_bit(GD_NEED_PART_SCAN, &disk->state);
683 
684 	/*
685 	 * Historically we only set the capacity to zero for devices that
686 	 * support partitions (independ of actually having partitions created).
687 	 * Doing that is rather inconsistent, but changing it broke legacy
688 	 * udisks polling for legacy ide-cdrom devices.  Use the crude check
689 	 * below to get the sane behavior for most device while not breaking
690 	 * userspace for this particular setup.
691 	 */
692 	if (invalidate) {
693 		if (disk_part_scan_enabled(disk) ||
694 		    !(disk->flags & GENHD_FL_REMOVABLE))
695 			set_capacity(disk, 0);
696 	}
697 
698 	if (get_capacity(disk)) {
699 		ret = blk_add_partitions(disk);
700 		if (ret == -EAGAIN)
701 			goto rescan;
702 	} else if (invalidate) {
703 		/*
704 		 * Tell userspace that the media / partition table may have
705 		 * changed.
706 		 */
707 		kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
708 	}
709 
710 	return ret;
711 }
712 /*
713  * Only exported for loop and dasd for historic reasons.  Don't use in new
714  * code!
715  */
716 EXPORT_SYMBOL_GPL(bdev_disk_changed);
717 
718 void *read_part_sector(struct parsed_partitions *state, sector_t n, Sector *p)
719 {
720 	struct address_space *mapping = state->disk->part0->bd_inode->i_mapping;
721 	struct page *page;
722 
723 	if (n >= get_capacity(state->disk)) {
724 		state->access_beyond_eod = true;
725 		return NULL;
726 	}
727 
728 	page = read_mapping_page(mapping,
729 			(pgoff_t)(n >> (PAGE_SHIFT - 9)), NULL);
730 	if (IS_ERR(page))
731 		goto out;
732 	if (PageError(page))
733 		goto out_put_page;
734 
735 	p->v = page;
736 	return (unsigned char *)page_address(page) +
737 			((n & ((1 << (PAGE_SHIFT - 9)) - 1)) << SECTOR_SHIFT);
738 out_put_page:
739 	put_page(page);
740 out:
741 	p->v = NULL;
742 	return NULL;
743 }
744