block/partition-generic.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  Code extracted from drivers/block/genhd.c
   4  *  Copyright (C) 1991-1998  Linus Torvalds
   5  *  Re-organised Feb 1998 Russell King
   6  *
   7  *  We now have independent partition support from the
   8  *  block drivers, which allows all the partition code to
   9  *  be grouped in one location, and it to be mostly self
  10  *  contained.
  11  */
  12
  13 #include <linux/init.h>
  14 #include <linux/module.h>
  15 #include <linux/fs.h>
  16 #include <linux/slab.h>
  17 #include <linux/kmod.h>
  18 #include <linux/ctype.h>
  19 #include <linux/genhd.h>
  20 #include <linux/blktrace_api.h>
  21
  22 #include "partitions/check.h"
  23
  24 #ifdef CONFIG_BLK_DEV_MD
  25 extern void md_autodetect_dev(dev_t dev);
  26 #endif
  27
  28 /*
  29  * disk_name() is used by partition check code and the genhd driver.
  30  * It formats the devicename of the indicated disk into
  31  * the supplied buffer (of size at least 32), and returns
  32  * a pointer to that same buffer (for convenience).
  33  */
  34
  35 char *disk_name(struct gendisk *hd, int partno, char *buf)
  36 {
  37         if (!partno)
  38                 snprintf(buf, BDEVNAME_SIZE, "%s", hd->disk_name);
  39         else if (isdigit(hd->disk_name[strlen(hd->disk_name)-1]))
  40                 snprintf(buf, BDEVNAME_SIZE, "%sp%d", hd->disk_name, partno);
  41         else
  42                 snprintf(buf, BDEVNAME_SIZE, "%s%d", hd->disk_name, partno);
  43
  44         return buf;
  45 }
  46
  47 const char *bdevname(struct block_device *bdev, char *buf)
  48 {
  49         return disk_name(bdev->bd_disk, bdev->bd_part->partno, buf);
  50 }
  51
  52 EXPORT_SYMBOL(bdevname);
  53
  54 const char *bio_devname(struct bio *bio, char *buf)
  55 {
  56         return disk_name(bio->bi_disk, bio->bi_partno, buf);
  57 }
  58 EXPORT_SYMBOL(bio_devname);
  59
  60 /*
  61  * There's very little reason to use this, you should really
  62  * have a struct block_device just about everywhere and use
  63  * bdevname() instead.
  64  */
  65 const char *__bdevname(dev_t dev, char *buffer)
  66 {
  67         scnprintf(buffer, BDEVNAME_SIZE, "unknown-block(%u,%u)",
  68                                 MAJOR(dev), MINOR(dev));
  69         return buffer;
  70 }
  71
  72 EXPORT_SYMBOL(__bdevname);
  73
  74 static ssize_t part_partition_show(struct device *dev,
  75                                    struct device_attribute *attr, char *buf)
  76 {
  77         struct hd_struct *p = dev_to_part(dev);
  78
  79         return sprintf(buf, "%d\n", p->partno);
  80 }
  81
  82 static ssize_t part_start_show(struct device *dev,
  83                                struct device_attribute *attr, char *buf)
  84 {
  85         struct hd_struct *p = dev_to_part(dev);
  86
  87         return sprintf(buf, "%llu\n",(unsigned long long)p->start_sect);
  88 }
  89
  90 ssize_t part_size_show(struct device *dev,
  91                        struct device_attribute *attr, char *buf)
  92 {
  93         struct hd_struct *p = dev_to_part(dev);
  94         return sprintf(buf, "%llu\n",(unsigned long long)part_nr_sects_read(p));
  95 }
  96
  97 static ssize_t part_ro_show(struct device *dev,
  98                             struct device_attribute *attr, char *buf)
  99 {
 100         struct hd_struct *p = dev_to_part(dev);
 101         return sprintf(buf, "%d\n", p->policy ? 1 : 0);
 102 }
 103
 104 static ssize_t part_alignment_offset_show(struct device *dev,
 105                                           struct device_attribute *attr, char *buf)
 106 {
 107         struct hd_struct *p = dev_to_part(dev);
 108         return sprintf(buf, "%llu\n", (unsigned long long)p->alignment_offset);
 109 }
 110
 111 static ssize_t part_discard_alignment_show(struct device *dev,
 112                                            struct device_attribute *attr, char *buf)
 113 {
 114         struct hd_struct *p = dev_to_part(dev);
 115         return sprintf(buf, "%u\n", p->discard_alignment);
 116 }
 117
 118 ssize_t part_stat_show(struct device *dev,
 119                        struct device_attribute *attr, char *buf)
 120 {
 121         struct hd_struct *p = dev_to_part(dev);
 122         struct request_queue *q = part_to_disk(p)->queue;
 123         unsigned int inflight[2];
 124         int cpu;
 125
 126         cpu = part_stat_lock();
 127         part_round_stats(q, cpu, p);
 128         part_stat_unlock();
 129         part_in_flight(q, p, inflight);
 130         return sprintf(buf,
 131                 "%8lu %8lu %8llu %8u "
 132                 "%8lu %8lu %8llu %8u "
 133                 "%8u %8u %8u "
 134                 "%8lu %8lu %8llu %8u"
 135                 "\n",
 136                 part_stat_read(p, ios[STAT_READ]),
 137                 part_stat_read(p, merges[STAT_READ]),
 138                 (unsigned long long)part_stat_read(p, sectors[STAT_READ]),
 139                 (unsigned int)part_stat_read_msecs(p, STAT_READ),
 140                 part_stat_read(p, ios[STAT_WRITE]),
 141                 part_stat_read(p, merges[STAT_WRITE]),
 142                 (unsigned long long)part_stat_read(p, sectors[STAT_WRITE]),
 143                 (unsigned int)part_stat_read_msecs(p, STAT_WRITE),
 144                 inflight[0],
 145                 jiffies_to_msecs(part_stat_read(p, io_ticks)),
 146                 jiffies_to_msecs(part_stat_read(p, time_in_queue)),
 147                 part_stat_read(p, ios[STAT_DISCARD]),
 148                 part_stat_read(p, merges[STAT_DISCARD]),
 149                 (unsigned long long)part_stat_read(p, sectors[STAT_DISCARD]),
 150                 (unsigned int)part_stat_read_msecs(p, STAT_DISCARD));
 151 }
 152
 153 ssize_t part_inflight_show(struct device *dev, struct device_attribute *attr,
 154                            char *buf)
 155 {
 156         struct hd_struct *p = dev_to_part(dev);
 157         struct request_queue *q = part_to_disk(p)->queue;
 158         unsigned int inflight[2];
 159
 160         part_in_flight_rw(q, p, inflight);
 161         return sprintf(buf, "%8u %8u\n", inflight[0], inflight[1]);
 162 }
 163
 164 #ifdef CONFIG_FAIL_MAKE_REQUEST
 165 ssize_t part_fail_show(struct device *dev,
 166                        struct device_attribute *attr, char *buf)
 167 {
 168         struct hd_struct *p = dev_to_part(dev);
 169
 170         return sprintf(buf, "%d\n", p->make_it_fail);
 171 }
 172
 173 ssize_t part_fail_store(struct device *dev,
 174                         struct device_attribute *attr,
 175                         const char *buf, size_t count)
 176 {
 177         struct hd_struct *p = dev_to_part(dev);
 178         int i;
 179
 180         if (count > 0 && sscanf(buf, "%d", &i) > 0)
 181                 p->make_it_fail = (i == 0) ? 0 : 1;
 182
 183         return count;
 184 }
 185 #endif
 186
 187 static DEVICE_ATTR(partition, 0444, part_partition_show, NULL);
 188 static DEVICE_ATTR(start, 0444, part_start_show, NULL);
 189 static DEVICE_ATTR(size, 0444, part_size_show, NULL);
 190 static DEVICE_ATTR(ro, 0444, part_ro_show, NULL);
 191 static DEVICE_ATTR(alignment_offset, 0444, part_alignment_offset_show, NULL);
 192 static DEVICE_ATTR(discard_alignment, 0444, part_discard_alignment_show, NULL);
 193 static DEVICE_ATTR(stat, 0444, part_stat_show, NULL);
 194 static DEVICE_ATTR(inflight, 0444, part_inflight_show, NULL);
 195 #ifdef CONFIG_FAIL_MAKE_REQUEST
 196 static struct device_attribute dev_attr_fail =
 197         __ATTR(make-it-fail, 0644, part_fail_show, part_fail_store);
 198 #endif
 199
 200 static struct attribute *part_attrs[] = {
 201         &dev_attr_partition.attr,
 202         &dev_attr_start.attr,
 203         &dev_attr_size.attr,
 204         &dev_attr_ro.attr,
 205         &dev_attr_alignment_offset.attr,
 206         &dev_attr_discard_alignment.attr,
 207         &dev_attr_stat.attr,
 208         &dev_attr_inflight.attr,
 209 #ifdef CONFIG_FAIL_MAKE_REQUEST
 210         &dev_attr_fail.attr,
 211 #endif
 212         NULL
 213 };
 214
 215 static struct attribute_group part_attr_group = {
 216         .attrs = part_attrs,
 217 };
 218
 219 static const struct attribute_group *part_attr_groups[] = {
 220         &part_attr_group,
 221 #ifdef CONFIG_BLK_DEV_IO_TRACE
 222         &blk_trace_attr_group,
 223 #endif
 224         NULL
 225 };
 226
 227 static void part_release(struct device *dev)
 228 {
 229         struct hd_struct *p = dev_to_part(dev);
 230         blk_free_devt(dev->devt);
 231         hd_free_part(p);
 232         kfree(p);
 233 }
 234
 235 static int part_uevent(struct device *dev, struct kobj_uevent_env *env)
 236 {
 237         struct hd_struct *part = dev_to_part(dev);
 238
 239         add_uevent_var(env, "PARTN=%u", part->partno);
 240         if (part->info && part->info->volname[0])
 241                 add_uevent_var(env, "PARTNAME=%s", part->info->volname);
 242         return 0;
 243 }
 244
 245 struct device_type part_type = {
 246         .name           = "partition",
 247         .groups         = part_attr_groups,
 248         .release        = part_release,
 249         .uevent         = part_uevent,
 250 };
 251
 252 static void delete_partition_rcu_cb(struct rcu_head *head)
 253 {
 254         struct hd_struct *part = container_of(head, struct hd_struct, rcu_head);
 255
 256         part->start_sect = 0;
 257         part->nr_sects = 0;
 258         part_stat_set_all(part, 0);
 259         put_device(part_to_dev(part));
 260 }
 261
 262 void __delete_partition(struct percpu_ref *ref)
 263 {
 264         struct hd_struct *part = container_of(ref, struct hd_struct, ref);
 265         call_rcu(&part->rcu_head, delete_partition_rcu_cb);
 266 }
 267
 268 /*
 269  * Must be called either with bd_mutex held, before a disk can be opened or
 270  * after all disk users are gone.
 271  */
 272 void delete_partition(struct gendisk *disk, int partno)
 273 {
 274         struct disk_part_tbl *ptbl =
 275                 rcu_dereference_protected(disk->part_tbl, 1);
 276         struct hd_struct *part;
 277
 278         if (partno >= ptbl->len)
 279                 return;
 280
 281         part = rcu_dereference_protected(ptbl->part[partno], 1);
 282         if (!part)
 283                 return;
 284
 285         rcu_assign_pointer(ptbl->part[partno], NULL);
 286         rcu_assign_pointer(ptbl->last_lookup, NULL);
 287         kobject_put(part->holder_dir);
 288         device_del(part_to_dev(part));
 289
 290         hd_struct_kill(part);
 291 }
 292
 293 static ssize_t whole_disk_show(struct device *dev,
 294                                struct device_attribute *attr, char *buf)
 295 {
 296         return 0;
 297 }
 298 static DEVICE_ATTR(whole_disk, 0444, whole_disk_show, NULL);
 299
 300 /*
 301  * Must be called either with bd_mutex held, before a disk can be opened or
 302  * after all disk users are gone.
 303  */
 304 struct hd_struct *add_partition(struct gendisk *disk, int partno,
 305                                 sector_t start, sector_t len, int flags,
 306                                 struct partition_meta_info *info)
 307 {
 308         struct hd_struct *p;
 309         dev_t devt = MKDEV(0, 0);
 310         struct device *ddev = disk_to_dev(disk);
 311         struct device *pdev;
 312         struct disk_part_tbl *ptbl;
 313         const char *dname;
 314         int err;
 315
 316         err = disk_expand_part_tbl(disk, partno);
 317         if (err)
 318                 return ERR_PTR(err);
 319         ptbl = rcu_dereference_protected(disk->part_tbl, 1);
 320
 321         if (ptbl->part[partno])
 322                 return ERR_PTR(-EBUSY);
 323
 324         p = kzalloc(sizeof(*p), GFP_KERNEL);
 325         if (!p)
 326                 return ERR_PTR(-EBUSY);
 327
 328         if (!init_part_stats(p)) {
 329                 err = -ENOMEM;
 330                 goto out_free;
 331         }
 332
 333         seqcount_init(&p->nr_sects_seq);
 334         pdev = part_to_dev(p);
 335
 336         p->start_sect = start;
 337         p->alignment_offset =
 338                 queue_limit_alignment_offset(&disk->queue->limits, start);
 339         p->discard_alignment =
 340                 queue_limit_discard_alignment(&disk->queue->limits, start);
 341         p->nr_sects = len;
 342         p->partno = partno;
 343         p->policy = get_disk_ro(disk);
 344
 345         if (info) {
 346                 struct partition_meta_info *pinfo = alloc_part_info(disk);
 347                 if (!pinfo) {
 348                         err = -ENOMEM;
 349                         goto out_free_stats;
 350                 }
 351                 memcpy(pinfo, info, sizeof(*info));
 352                 p->info = pinfo;
 353         }
 354
 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         err = blk_alloc_devt(p, &devt);
 367         if (err)
 368                 goto out_free_info;
 369         pdev->devt = devt;
 370
 371         /* delay uevent until 'holders' subdir is created */
 372         dev_set_uevent_suppress(pdev, 1);
 373         err = device_add(pdev);
 374         if (err)
 375                 goto out_put;
 376
 377         err = -ENOMEM;
 378         p->holder_dir = kobject_create_and_add("holders", &pdev->kobj);
 379         if (!p->holder_dir)
 380                 goto out_del;
 381
 382         dev_set_uevent_suppress(pdev, 0);
 383         if (flags & ADDPART_FLAG_WHOLEDISK) {
 384                 err = device_create_file(pdev, &dev_attr_whole_disk);
 385                 if (err)
 386                         goto out_del;
 387         }
 388
 389         err = hd_ref_init(p);
 390         if (err) {
 391                 if (flags & ADDPART_FLAG_WHOLEDISK)
 392                         goto out_remove_file;
 393                 goto out_del;
 394         }
 395
 396         /* everything is up and running, commence */
 397         rcu_assign_pointer(ptbl->part[partno], p);
 398
 399         /* suppress uevent if the disk suppresses it */
 400         if (!dev_get_uevent_suppress(ddev))
 401                 kobject_uevent(&pdev->kobj, KOBJ_ADD);
 402         return p;
 403
 404 out_free_info:
 405         free_part_info(p);
 406 out_free_stats:
 407         free_part_stats(p);
 408 out_free:
 409         kfree(p);
 410         return ERR_PTR(err);
 411 out_remove_file:
 412         device_remove_file(pdev, &dev_attr_whole_disk);
 413 out_del:
 414         kobject_put(p->holder_dir);
 415         device_del(pdev);
 416 out_put:
 417         put_device(pdev);
 418         return ERR_PTR(err);
 419 }
 420
 421 static bool disk_unlock_native_capacity(struct gendisk *disk)
 422 {
 423         const struct block_device_operations *bdops = disk->fops;
 424
 425         if (bdops->unlock_native_capacity &&
 426             !(disk->flags & GENHD_FL_NATIVE_CAPACITY)) {
 427                 printk(KERN_CONT "enabling native capacity\n");
 428                 bdops->unlock_native_capacity(disk);
 429                 disk->flags |= GENHD_FL_NATIVE_CAPACITY;
 430                 return true;
 431         } else {
 432                 printk(KERN_CONT "truncated\n");
 433                 return false;
 434         }
 435 }
 436
 437 static int drop_partitions(struct gendisk *disk, struct block_device *bdev)
 438 {
 439         struct disk_part_iter piter;
 440         struct hd_struct *part;
 441         int res;
 442
 443         if (bdev->bd_part_count || bdev->bd_super)
 444                 return -EBUSY;
 445         res = invalidate_partition(disk, 0);
 446         if (res)
 447                 return res;
 448
 449         disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY);
 450         while ((part = disk_part_iter_next(&piter)))
 451                 delete_partition(disk, part->partno);
 452         disk_part_iter_exit(&piter);
 453
 454         return 0;
 455 }
 456
 457 static bool part_zone_aligned(struct gendisk *disk,
 458                               struct block_device *bdev,
 459                               sector_t from, sector_t size)
 460 {
 461         unsigned int zone_sectors = bdev_zone_sectors(bdev);
 462
 463         /*
 464          * If this function is called, then the disk is a zoned block device
 465          * (host-aware or host-managed). This can be detected even if the
 466          * zoned block device support is disabled (CONFIG_BLK_DEV_ZONED not
 467          * set). In this case, however, only host-aware devices will be seen
 468          * as a block device is not created for host-managed devices. Without
 469          * zoned block device support, host-aware drives can still be used as
 470          * regular block devices (no zone operation) and their zone size will
 471          * be reported as 0. Allow this case.
 472          */
 473         if (!zone_sectors)
 474                 return true;
 475
 476         /*
 477          * Check partition start and size alignement. If the drive has a
 478          * smaller last runt zone, ignore it and allow the partition to
 479          * use it. Check the zone size too: it should be a power of 2 number
 480          * of sectors.
 481          */
 482         if (WARN_ON_ONCE(!is_power_of_2(zone_sectors))) {
 483                 u32 rem;
 484
 485                 div_u64_rem(from, zone_sectors, &rem);
 486                 if (rem)
 487                         return false;
 488                 if ((from + size) < get_capacity(disk)) {
 489                         div_u64_rem(size, zone_sectors, &rem);
 490                         if (rem)
 491                                 return false;
 492                 }
 493
 494         } else {
 495
 496                 if (from & (zone_sectors - 1))
 497                         return false;
 498                 if ((from + size) < get_capacity(disk) &&
 499                     (size & (zone_sectors - 1)))
 500                         return false;
 501
 502         }
 503
 504         return true;
 505 }
 506
 507 int rescan_partitions(struct gendisk *disk, struct block_device *bdev)
 508 {
 509         struct parsed_partitions *state = NULL;
 510         struct hd_struct *part;
 511         int p, highest, res;
 512 rescan:
 513         if (state && !IS_ERR(state)) {
 514                 free_partitions(state);
 515                 state = NULL;
 516         }
 517
 518         res = drop_partitions(disk, bdev);
 519         if (res)
 520                 return res;
 521
 522         if (disk->fops->revalidate_disk)
 523                 disk->fops->revalidate_disk(disk);
 524         check_disk_size_change(disk, bdev, true);
 525         bdev->bd_invalidated = 0;
 526         if (!get_capacity(disk) || !(state = check_partition(disk, bdev)))
 527                 return 0;
 528         if (IS_ERR(state)) {
 529                 /*
 530                  * I/O error reading the partition table.  If any
 531                  * partition code tried to read beyond EOD, retry
 532                  * after unlocking native capacity.
 533                  */
 534                 if (PTR_ERR(state) == -ENOSPC) {
 535                         printk(KERN_WARNING "%s: partition table beyond EOD, ",
 536                                disk->disk_name);
 537                         if (disk_unlock_native_capacity(disk))
 538                                 goto rescan;
 539                 }
 540                 return -EIO;
 541         }
 542         /*
 543          * If any partition code tried to read beyond EOD, try
 544          * unlocking native capacity even if partition table is
 545          * successfully read as we could be missing some partitions.
 546          */
 547         if (state->access_beyond_eod) {
 548                 printk(KERN_WARNING
 549                        "%s: partition table partially beyond EOD, ",
 550                        disk->disk_name);
 551                 if (disk_unlock_native_capacity(disk))
 552                         goto rescan;
 553         }
 554
 555         /* tell userspace that the media / partition table may have changed */
 556         kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
 557
 558         /* Detect the highest partition number and preallocate
 559          * disk->part_tbl.  This is an optimization and not strictly
 560          * necessary.
 561          */
 562         for (p = 1, highest = 0; p < state->limit; p++)
 563                 if (state->parts[p].size)
 564                         highest = p;
 565
 566         disk_expand_part_tbl(disk, highest);
 567
 568         /* add partitions */
 569         for (p = 1; p < state->limit; p++) {
 570                 sector_t size, from;
 571
 572                 size = state->parts[p].size;
 573                 if (!size)
 574                         continue;
 575
 576                 from = state->parts[p].from;
 577                 if (from >= get_capacity(disk)) {
 578                         printk(KERN_WARNING
 579                                "%s: p%d start %llu is beyond EOD, ",
 580                                disk->disk_name, p, (unsigned long long) from);
 581                         if (disk_unlock_native_capacity(disk))
 582                                 goto rescan;
 583                         continue;
 584                 }
 585
 586                 if (from + size > get_capacity(disk)) {
 587                         printk(KERN_WARNING
 588                                "%s: p%d size %llu extends beyond EOD, ",
 589                                disk->disk_name, p, (unsigned long long) size);
 590
 591                         if (disk_unlock_native_capacity(disk)) {
 592                                 /* free state and restart */
 593                                 goto rescan;
 594                         } else {
 595                                 /*
 596                                  * we can not ignore partitions of broken tables
 597                                  * created by for example camera firmware, but
 598                                  * we limit them to the end of the disk to avoid
 599                                  * creating invalid block devices
 600                                  */
 601                                 size = get_capacity(disk) - from;
 602                         }
 603                 }
 604
 605                 /*
 606                  * On a zoned block device, partitions should be aligned on the
 607                  * device zone size (i.e. zone boundary crossing not allowed).
 608                  * Otherwise, resetting the write pointer of the last zone of
 609                  * one partition may impact the following partition.
 610                  */
 611                 if (bdev_is_zoned(bdev) &&
 612                     !part_zone_aligned(disk, bdev, from, size)) {
 613                         printk(KERN_WARNING
 614                                "%s: p%d start %llu+%llu is not zone aligned\n",
 615                                disk->disk_name, p, (unsigned long long) from,
 616                                (unsigned long long) size);
 617                         continue;
 618                 }
 619
 620                 part = add_partition(disk, p, from, size,
 621                                      state->parts[p].flags,
 622                                      &state->parts[p].info);
 623                 if (IS_ERR(part)) {
 624                         printk(KERN_ERR " %s: p%d could not be added: %ld\n",
 625                                disk->disk_name, p, -PTR_ERR(part));
 626                         continue;
 627                 }
 628 #ifdef CONFIG_BLK_DEV_MD
 629                 if (state->parts[p].flags & ADDPART_FLAG_RAID)
 630                         md_autodetect_dev(part_to_dev(part)->devt);
 631 #endif
 632         }
 633         free_partitions(state);
 634         return 0;
 635 }
 636
 637 int invalidate_partitions(struct gendisk *disk, struct block_device *bdev)
 638 {
 639         int res;
 640
 641         if (!bdev->bd_invalidated)
 642                 return 0;
 643
 644         res = drop_partitions(disk, bdev);
 645         if (res)
 646                 return res;
 647
 648         set_capacity(disk, 0);
 649         check_disk_size_change(disk, bdev, false);
 650         bdev->bd_invalidated = 0;
 651         /* tell userspace that the media / partition table may have changed */
 652         kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
 653
 654         return 0;
 655 }
 656
 657 unsigned char *read_dev_sector(struct block_device *bdev, sector_t n, Sector *p)
 658 {
 659         struct address_space *mapping = bdev->bd_inode->i_mapping;
 660         struct page *page;
 661
 662         page = read_mapping_page(mapping, (pgoff_t)(n >> (PAGE_SHIFT-9)), NULL);
 663         if (!IS_ERR(page)) {
 664                 if (PageError(page))
 665                         goto fail;
 666                 p->v = page;
 667                 return (unsigned char *)page_address(page) +  ((n & ((1 << (PAGE_SHIFT - 9)) - 1)) << 9);
 668 fail:
 669                 put_page(page);
 670         }
 671         p->v = NULL;
 672         return NULL;
 673 }
 674
 675 EXPORT_SYMBOL(read_dev_sector);