xref: /linux/block/partitions/core.c (revision dec1c62e91ba268ab2a6e339d4d7a59287d5eba1) 
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 	return sprintf(buf, "%u\n", bdev_alignment_offset(dev_to_bdev(dev)));
204 }
205 
206 static ssize_t part_discard_alignment_show(struct device *dev,
207 					   struct device_attribute *attr, char *buf)
208 {
209 	return sprintf(buf, "%u\n", bdev_discard_alignment(dev_to_bdev(dev)));
210 }
211 
212 static DEVICE_ATTR(partition, 0444, part_partition_show, NULL);
213 static DEVICE_ATTR(start, 0444, part_start_show, NULL);
214 static DEVICE_ATTR(size, 0444, part_size_show, NULL);
215 static DEVICE_ATTR(ro, 0444, part_ro_show, NULL);
216 static DEVICE_ATTR(alignment_offset, 0444, part_alignment_offset_show, NULL);
217 static DEVICE_ATTR(discard_alignment, 0444, part_discard_alignment_show, NULL);
218 static DEVICE_ATTR(stat, 0444, part_stat_show, NULL);
219 static DEVICE_ATTR(inflight, 0444, part_inflight_show, NULL);
220 #ifdef CONFIG_FAIL_MAKE_REQUEST
221 static struct device_attribute dev_attr_fail =
222 	__ATTR(make-it-fail, 0644, part_fail_show, part_fail_store);
223 #endif
224 
225 static struct attribute *part_attrs[] = {
226 	&dev_attr_partition.attr,
227 	&dev_attr_start.attr,
228 	&dev_attr_size.attr,
229 	&dev_attr_ro.attr,
230 	&dev_attr_alignment_offset.attr,
231 	&dev_attr_discard_alignment.attr,
232 	&dev_attr_stat.attr,
233 	&dev_attr_inflight.attr,
234 #ifdef CONFIG_FAIL_MAKE_REQUEST
235 	&dev_attr_fail.attr,
236 #endif
237 	NULL
238 };
239 
240 static struct attribute_group part_attr_group = {
241 	.attrs = part_attrs,
242 };
243 
244 static const struct attribute_group *part_attr_groups[] = {
245 	&part_attr_group,
246 #ifdef CONFIG_BLK_DEV_IO_TRACE
247 	&blk_trace_attr_group,
248 #endif
249 	NULL
250 };
251 
252 static void part_release(struct device *dev)
253 {
254 	put_disk(dev_to_bdev(dev)->bd_disk);
255 	iput(dev_to_bdev(dev)->bd_inode);
256 }
257 
258 static int part_uevent(struct device *dev, struct kobj_uevent_env *env)
259 {
260 	struct block_device *part = dev_to_bdev(dev);
261 
262 	add_uevent_var(env, "PARTN=%u", part->bd_partno);
263 	if (part->bd_meta_info && part->bd_meta_info->volname[0])
264 		add_uevent_var(env, "PARTNAME=%s", part->bd_meta_info->volname);
265 	return 0;
266 }
267 
268 struct device_type part_type = {
269 	.name		= "partition",
270 	.groups		= part_attr_groups,
271 	.release	= part_release,
272 	.uevent		= part_uevent,
273 };
274 
275 static void delete_partition(struct block_device *part)
276 {
277 	lockdep_assert_held(&part->bd_disk->open_mutex);
278 
279 	fsync_bdev(part);
280 	__invalidate_device(part, true);
281 
282 	xa_erase(&part->bd_disk->part_tbl, part->bd_partno);
283 	kobject_put(part->bd_holder_dir);
284 	device_del(&part->bd_device);
285 
286 	/*
287 	 * Remove the block device from the inode hash, so that it cannot be
288 	 * looked up any more even when openers still hold references.
289 	 */
290 	remove_inode_hash(part->bd_inode);
291 
292 	put_device(&part->bd_device);
293 }
294 
295 static ssize_t whole_disk_show(struct device *dev,
296 			       struct device_attribute *attr, char *buf)
297 {
298 	return 0;
299 }
300 static DEVICE_ATTR(whole_disk, 0444, whole_disk_show, NULL);
301 
302 /*
303  * Must be called either with open_mutex held, before a disk can be opened or
304  * after all disk users are gone.
305  */
306 static struct block_device *add_partition(struct gendisk *disk, int partno,
307 				sector_t start, sector_t len, int flags,
308 				struct partition_meta_info *info)
309 {
310 	dev_t devt = MKDEV(0, 0);
311 	struct device *ddev = disk_to_dev(disk);
312 	struct device *pdev;
313 	struct block_device *bdev;
314 	const char *dname;
315 	int err;
316 
317 	lockdep_assert_held(&disk->open_mutex);
318 
319 	if (partno >= DISK_MAX_PARTS)
320 		return ERR_PTR(-EINVAL);
321 
322 	/*
323 	 * Partitions are not supported on zoned block devices that are used as
324 	 * such.
325 	 */
326 	switch (disk->queue->limits.zoned) {
327 	case BLK_ZONED_HM:
328 		pr_warn("%s: partitions not supported on host managed zoned block device\n",
329 			disk->disk_name);
330 		return ERR_PTR(-ENXIO);
331 	case BLK_ZONED_HA:
332 		pr_info("%s: disabling host aware zoned block device support due to partitions\n",
333 			disk->disk_name);
334 		blk_queue_set_zoned(disk, BLK_ZONED_NONE);
335 		break;
336 	case BLK_ZONED_NONE:
337 		break;
338 	}
339 
340 	if (xa_load(&disk->part_tbl, partno))
341 		return ERR_PTR(-EBUSY);
342 
343 	/* ensure we always have a reference to the whole disk */
344 	get_device(disk_to_dev(disk));
345 
346 	err = -ENOMEM;
347 	bdev = bdev_alloc(disk, partno);
348 	if (!bdev)
349 		goto out_put_disk;
350 
351 	bdev->bd_start_sect = start;
352 	bdev_set_nr_sectors(bdev, len);
353 
354 	pdev = &bdev->bd_device;
355 	dname = dev_name(ddev);
356 	if (isdigit(dname[strlen(dname) - 1]))
357 		dev_set_name(pdev, "%sp%d", dname, partno);
358 	else
359 		dev_set_name(pdev, "%s%d", dname, partno);
360 
361 	device_initialize(pdev);
362 	pdev->class = &block_class;
363 	pdev->type = &part_type;
364 	pdev->parent = ddev;
365 
366 	/* in consecutive minor range? */
367 	if (bdev->bd_partno < disk->minors) {
368 		devt = MKDEV(disk->major, disk->first_minor + bdev->bd_partno);
369 	} else {
370 		err = blk_alloc_ext_minor();
371 		if (err < 0)
372 			goto out_put;
373 		devt = MKDEV(BLOCK_EXT_MAJOR, err);
374 	}
375 	pdev->devt = devt;
376 
377 	if (info) {
378 		err = -ENOMEM;
379 		bdev->bd_meta_info = kmemdup(info, sizeof(*info), GFP_KERNEL);
380 		if (!bdev->bd_meta_info)
381 			goto out_put;
382 	}
383 
384 	/* delay uevent until 'holders' subdir is created */
385 	dev_set_uevent_suppress(pdev, 1);
386 	err = device_add(pdev);
387 	if (err)
388 		goto out_put;
389 
390 	err = -ENOMEM;
391 	bdev->bd_holder_dir = kobject_create_and_add("holders", &pdev->kobj);
392 	if (!bdev->bd_holder_dir)
393 		goto out_del;
394 
395 	dev_set_uevent_suppress(pdev, 0);
396 	if (flags & ADDPART_FLAG_WHOLEDISK) {
397 		err = device_create_file(pdev, &dev_attr_whole_disk);
398 		if (err)
399 			goto out_del;
400 	}
401 
402 	/* everything is up and running, commence */
403 	err = xa_insert(&disk->part_tbl, partno, bdev, GFP_KERNEL);
404 	if (err)
405 		goto out_del;
406 	bdev_add(bdev, devt);
407 
408 	/* suppress uevent if the disk suppresses it */
409 	if (!dev_get_uevent_suppress(ddev))
410 		kobject_uevent(&pdev->kobj, KOBJ_ADD);
411 	return bdev;
412 
413 out_del:
414 	kobject_put(bdev->bd_holder_dir);
415 	device_del(pdev);
416 out_put:
417 	put_device(pdev);
418 	return ERR_PTR(err);
419 out_put_disk:
420 	put_disk(disk);
421 	return ERR_PTR(err);
422 }
423 
424 static bool partition_overlaps(struct gendisk *disk, sector_t start,
425 		sector_t length, int skip_partno)
426 {
427 	struct block_device *part;
428 	bool overlap = false;
429 	unsigned long idx;
430 
431 	rcu_read_lock();
432 	xa_for_each_start(&disk->part_tbl, idx, part, 1) {
433 		if (part->bd_partno != skip_partno &&
434 		    start < part->bd_start_sect + bdev_nr_sectors(part) &&
435 		    start + length > part->bd_start_sect) {
436 			overlap = true;
437 			break;
438 		}
439 	}
440 	rcu_read_unlock();
441 
442 	return overlap;
443 }
444 
445 int bdev_add_partition(struct gendisk *disk, int partno, sector_t start,
446 		sector_t length)
447 {
448 	struct block_device *part;
449 	int ret;
450 
451 	mutex_lock(&disk->open_mutex);
452 	if (!disk_live(disk)) {
453 		ret = -ENXIO;
454 		goto out;
455 	}
456 
457 	if (partition_overlaps(disk, start, length, -1)) {
458 		ret = -EBUSY;
459 		goto out;
460 	}
461 
462 	part = add_partition(disk, partno, start, length,
463 			ADDPART_FLAG_NONE, NULL);
464 	ret = PTR_ERR_OR_ZERO(part);
465 out:
466 	mutex_unlock(&disk->open_mutex);
467 	return ret;
468 }
469 
470 int bdev_del_partition(struct gendisk *disk, int partno)
471 {
472 	struct block_device *part = NULL;
473 	int ret = -ENXIO;
474 
475 	mutex_lock(&disk->open_mutex);
476 	part = xa_load(&disk->part_tbl, partno);
477 	if (!part)
478 		goto out_unlock;
479 
480 	ret = -EBUSY;
481 	if (atomic_read(&part->bd_openers))
482 		goto out_unlock;
483 
484 	delete_partition(part);
485 	ret = 0;
486 out_unlock:
487 	mutex_unlock(&disk->open_mutex);
488 	return ret;
489 }
490 
491 int bdev_resize_partition(struct gendisk *disk, int partno, sector_t start,
492 		sector_t length)
493 {
494 	struct block_device *part = NULL;
495 	int ret = -ENXIO;
496 
497 	mutex_lock(&disk->open_mutex);
498 	part = xa_load(&disk->part_tbl, partno);
499 	if (!part)
500 		goto out_unlock;
501 
502 	ret = -EINVAL;
503 	if (start != part->bd_start_sect)
504 		goto out_unlock;
505 
506 	ret = -EBUSY;
507 	if (partition_overlaps(disk, start, length, partno))
508 		goto out_unlock;
509 
510 	bdev_set_nr_sectors(part, length);
511 
512 	ret = 0;
513 out_unlock:
514 	mutex_unlock(&disk->open_mutex);
515 	return ret;
516 }
517 
518 static bool disk_unlock_native_capacity(struct gendisk *disk)
519 {
520 	if (!disk->fops->unlock_native_capacity ||
521 	    test_and_set_bit(GD_NATIVE_CAPACITY, &disk->state)) {
522 		printk(KERN_CONT "truncated\n");
523 		return false;
524 	}
525 
526 	printk(KERN_CONT "enabling native capacity\n");
527 	disk->fops->unlock_native_capacity(disk);
528 	return true;
529 }
530 
531 void blk_drop_partitions(struct gendisk *disk)
532 {
533 	struct block_device *part;
534 	unsigned long idx;
535 
536 	lockdep_assert_held(&disk->open_mutex);
537 
538 	xa_for_each_start(&disk->part_tbl, idx, part, 1)
539 		delete_partition(part);
540 }
541 
542 static bool blk_add_partition(struct gendisk *disk,
543 		struct parsed_partitions *state, int p)
544 {
545 	sector_t size = state->parts[p].size;
546 	sector_t from = state->parts[p].from;
547 	struct block_device *part;
548 
549 	if (!size)
550 		return true;
551 
552 	if (from >= get_capacity(disk)) {
553 		printk(KERN_WARNING
554 		       "%s: p%d start %llu is beyond EOD, ",
555 		       disk->disk_name, p, (unsigned long long) from);
556 		if (disk_unlock_native_capacity(disk))
557 			return false;
558 		return true;
559 	}
560 
561 	if (from + size > get_capacity(disk)) {
562 		printk(KERN_WARNING
563 		       "%s: p%d size %llu extends beyond EOD, ",
564 		       disk->disk_name, p, (unsigned long long) size);
565 
566 		if (disk_unlock_native_capacity(disk))
567 			return false;
568 
569 		/*
570 		 * We can not ignore partitions of broken tables created by for
571 		 * example camera firmware, but we limit them to the end of the
572 		 * disk to avoid creating invalid block devices.
573 		 */
574 		size = get_capacity(disk) - from;
575 	}
576 
577 	part = add_partition(disk, p, from, size, state->parts[p].flags,
578 			     &state->parts[p].info);
579 	if (IS_ERR(part) && PTR_ERR(part) != -ENXIO) {
580 		printk(KERN_ERR " %s: p%d could not be added: %ld\n",
581 		       disk->disk_name, p, -PTR_ERR(part));
582 		return true;
583 	}
584 
585 	if (IS_BUILTIN(CONFIG_BLK_DEV_MD) &&
586 	    (state->parts[p].flags & ADDPART_FLAG_RAID))
587 		md_autodetect_dev(part->bd_dev);
588 
589 	return true;
590 }
591 
592 static int blk_add_partitions(struct gendisk *disk)
593 {
594 	struct parsed_partitions *state;
595 	int ret = -EAGAIN, p;
596 
597 	if (disk->flags & GENHD_FL_NO_PART)
598 		return 0;
599 
600 	state = check_partition(disk);
601 	if (!state)
602 		return 0;
603 	if (IS_ERR(state)) {
604 		/*
605 		 * I/O error reading the partition table.  If we tried to read
606 		 * beyond EOD, retry after unlocking the native capacity.
607 		 */
608 		if (PTR_ERR(state) == -ENOSPC) {
609 			printk(KERN_WARNING "%s: partition table beyond EOD, ",
610 			       disk->disk_name);
611 			if (disk_unlock_native_capacity(disk))
612 				return -EAGAIN;
613 		}
614 		return -EIO;
615 	}
616 
617 	/*
618 	 * Partitions are not supported on host managed zoned block devices.
619 	 */
620 	if (disk->queue->limits.zoned == BLK_ZONED_HM) {
621 		pr_warn("%s: ignoring partition table on host managed zoned block device\n",
622 			disk->disk_name);
623 		ret = 0;
624 		goto out_free_state;
625 	}
626 
627 	/*
628 	 * If we read beyond EOD, try unlocking native capacity even if the
629 	 * partition table was successfully read as we could be missing some
630 	 * partitions.
631 	 */
632 	if (state->access_beyond_eod) {
633 		printk(KERN_WARNING
634 		       "%s: partition table partially beyond EOD, ",
635 		       disk->disk_name);
636 		if (disk_unlock_native_capacity(disk))
637 			goto out_free_state;
638 	}
639 
640 	/* tell userspace that the media / partition table may have changed */
641 	kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
642 
643 	for (p = 1; p < state->limit; p++)
644 		if (!blk_add_partition(disk, state, p))
645 			goto out_free_state;
646 
647 	ret = 0;
648 out_free_state:
649 	free_partitions(state);
650 	return ret;
651 }
652 
653 int bdev_disk_changed(struct gendisk *disk, bool invalidate)
654 {
655 	int ret = 0;
656 
657 	lockdep_assert_held(&disk->open_mutex);
658 
659 	if (!disk_live(disk))
660 		return -ENXIO;
661 
662 rescan:
663 	if (disk->open_partitions)
664 		return -EBUSY;
665 	sync_blockdev(disk->part0);
666 	invalidate_bdev(disk->part0);
667 	blk_drop_partitions(disk);
668 
669 	clear_bit(GD_NEED_PART_SCAN, &disk->state);
670 
671 	/*
672 	 * Historically we only set the capacity to zero for devices that
673 	 * support partitions (independ of actually having partitions created).
674 	 * Doing that is rather inconsistent, but changing it broke legacy
675 	 * udisks polling for legacy ide-cdrom devices.  Use the crude check
676 	 * below to get the sane behavior for most device while not breaking
677 	 * userspace for this particular setup.
678 	 */
679 	if (invalidate) {
680 		if (!(disk->flags & GENHD_FL_NO_PART) ||
681 		    !(disk->flags & GENHD_FL_REMOVABLE))
682 			set_capacity(disk, 0);
683 	}
684 
685 	if (get_capacity(disk)) {
686 		ret = blk_add_partitions(disk);
687 		if (ret == -EAGAIN)
688 			goto rescan;
689 	} else if (invalidate) {
690 		/*
691 		 * Tell userspace that the media / partition table may have
692 		 * changed.
693 		 */
694 		kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
695 	}
696 
697 	return ret;
698 }
699 /*
700  * Only exported for loop and dasd for historic reasons.  Don't use in new
701  * code!
702  */
703 EXPORT_SYMBOL_GPL(bdev_disk_changed);
704 
705 void *read_part_sector(struct parsed_partitions *state, sector_t n, Sector *p)
706 {
707 	struct address_space *mapping = state->disk->part0->bd_inode->i_mapping;
708 	struct page *page;
709 
710 	if (n >= get_capacity(state->disk)) {
711 		state->access_beyond_eod = true;
712 		return NULL;
713 	}
714 
715 	page = read_mapping_page(mapping,
716 			(pgoff_t)(n >> (PAGE_SHIFT - 9)), NULL);
717 	if (IS_ERR(page))
718 		goto out;
719 	if (PageError(page))
720 		goto out_put_page;
721 
722 	p->v = page;
723 	return (unsigned char *)page_address(page) +
724 			((n & ((1 << (PAGE_SHIFT - 9)) - 1)) << SECTOR_SHIFT);
725 out_put_page:
726 	put_page(page);
727 out:
728 	p->v = NULL;
729 	return NULL;
730 }
731