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   1 /*
   2  *  linux/fs/ext2/balloc.c
   3  *
   4  * Copyright (C) 1992, 1993, 1994, 1995
   5  * Remy Card (card@masi.ibp.fr)
   6  * Laboratoire MASI - Institut Blaise Pascal
   7  * Universite Pierre et Marie Curie (Paris VI)
   8  *
   9  *  Enhanced block allocation by Stephen Tweedie (sct@redhat.com), 1993
  10  *  Big-endian to little-endian byte-swapping/bitmaps by
  11  *        David S. Miller (davem@caip.rutgers.edu), 1995
  12  */
  13
  14 #include "ext2.h"
  15 #include <linux/quotaops.h>
  16 #include <linux/sched.h>
  17 #include <linux/buffer_head.h>
  18 #include <linux/capability.h>
  19
  20 /*
  21  * balloc.c contains the blocks allocation and deallocation routines
  22  */
  23
  24 /*
  25  * The free blocks are managed by bitmaps.  A file system contains several
  26  * blocks groups.  Each group contains 1 bitmap block for blocks, 1 bitmap
  27  * block for inodes, N blocks for the inode table and data blocks.
  28  *
  29  * The file system contains group descriptors which are located after the
  30  * super block.  Each descriptor contains the number of the bitmap block and
  31  * the free blocks count in the block.  The descriptors are loaded in memory
  32  * when a file system is mounted (see ext2_read_super).
  33  */
  34
  35
  36 #define in_range(b, first, len) ((b) >= (first) && (b) <= (first) + (len) - 1)
  37
  38 struct ext2_group_desc * ext2_get_group_desc(struct super_block * sb,
  39                                              unsigned int block_group,
  40                                              struct buffer_head ** bh)
  41 {
  42         unsigned long group_desc;
  43         unsigned long offset;
  44         struct ext2_group_desc * desc;
  45         struct ext2_sb_info *sbi = EXT2_SB(sb);
  46
  47         if (block_group >= sbi->s_groups_count) {
  48                 ext2_error (sb, "ext2_get_group_desc",
  49                             "block_group >= groups_count - "
  50                             "block_group = %d, groups_count = %lu",
  51                             block_group, sbi->s_groups_count);
  52
  53                 return NULL;
  54         }
  55
  56         group_desc = block_group >> EXT2_DESC_PER_BLOCK_BITS(sb);
  57         offset = block_group & (EXT2_DESC_PER_BLOCK(sb) - 1);
  58         if (!sbi->s_group_desc[group_desc]) {
  59                 ext2_error (sb, "ext2_get_group_desc",
  60                             "Group descriptor not loaded - "
  61                             "block_group = %d, group_desc = %lu, desc = %lu",
  62                              block_group, group_desc, offset);
  63                 return NULL;
  64         }
  65
  66         desc = (struct ext2_group_desc *) sbi->s_group_desc[group_desc]->b_data;
  67         if (bh)
  68                 *bh = sbi->s_group_desc[group_desc];
  69         return desc + offset;
  70 }
  71
  72 /*
  73  * Read the bitmap for a given block_group, reading into the specified
  74  * slot in the superblock's bitmap cache.
  75  *
  76  * Return buffer_head on success or NULL in case of failure.
  77  */
  78 static struct buffer_head *
  79 read_block_bitmap(struct super_block *sb, unsigned int block_group)
  80 {
  81         struct ext2_group_desc * desc;
  82         struct buffer_head * bh = NULL;
  83
  84         desc = ext2_get_group_desc (sb, block_group, NULL);
  85         if (!desc)
  86                 goto error_out;
  87         bh = sb_bread(sb, le32_to_cpu(desc->bg_block_bitmap));
  88         if (!bh)
  89                 ext2_error (sb, "read_block_bitmap",
  90                             "Cannot read block bitmap - "
  91                             "block_group = %d, block_bitmap = %u",
  92                             block_group, le32_to_cpu(desc->bg_block_bitmap));
  93 error_out:
  94         return bh;
  95 }
  96
  97 /*
  98  * Set sb->s_dirt here because the superblock was "logically" altered.  We
  99  * need to recalculate its free blocks count and flush it out.
 100  */
 101 static int reserve_blocks(struct super_block *sb, int count)
 102 {
 103         struct ext2_sb_info *sbi = EXT2_SB(sb);
 104         struct ext2_super_block *es = sbi->s_es;
 105         unsigned free_blocks;
 106         unsigned root_blocks;
 107
 108         free_blocks = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
 109         root_blocks = le32_to_cpu(es->s_r_blocks_count);
 110
 111         if (free_blocks < count)
 112                 count = free_blocks;
 113
 114         if (free_blocks < root_blocks + count && !capable(CAP_SYS_RESOURCE) &&
 115             sbi->s_resuid != current->fsuid &&
 116             (sbi->s_resgid == 0 || !in_group_p (sbi->s_resgid))) {
 117                 /*
 118                  * We are too close to reserve and we are not privileged.
 119                  * Can we allocate anything at all?
 120                  */
 121                 if (free_blocks > root_blocks)
 122                         count = free_blocks - root_blocks;
 123                 else
 124                         return 0;
 125         }
 126
 127         percpu_counter_mod(&sbi->s_freeblocks_counter, -count);
 128         sb->s_dirt = 1;
 129         return count;
 130 }
 131
 132 static void release_blocks(struct super_block *sb, int count)
 133 {
 134         if (count) {
 135                 struct ext2_sb_info *sbi = EXT2_SB(sb);
 136
 137                 percpu_counter_mod(&sbi->s_freeblocks_counter, count);
 138                 sb->s_dirt = 1;
 139         }
 140 }
 141
 142 static int group_reserve_blocks(struct ext2_sb_info *sbi, int group_no,
 143         struct ext2_group_desc *desc, struct buffer_head *bh, int count)
 144 {
 145         unsigned free_blocks;
 146
 147         if (!desc->bg_free_blocks_count)
 148                 return 0;
 149
 150         spin_lock(sb_bgl_lock(sbi, group_no));
 151         free_blocks = le16_to_cpu(desc->bg_free_blocks_count);
 152         if (free_blocks < count)
 153                 count = free_blocks;
 154         desc->bg_free_blocks_count = cpu_to_le16(free_blocks - count);
 155         spin_unlock(sb_bgl_lock(sbi, group_no));
 156         mark_buffer_dirty(bh);
 157         return count;
 158 }
 159
 160 static void group_release_blocks(struct super_block *sb, int group_no,
 161         struct ext2_group_desc *desc, struct buffer_head *bh, int count)
 162 {
 163         if (count) {
 164                 struct ext2_sb_info *sbi = EXT2_SB(sb);
 165                 unsigned free_blocks;
 166
 167                 spin_lock(sb_bgl_lock(sbi, group_no));
 168                 free_blocks = le16_to_cpu(desc->bg_free_blocks_count);
 169                 desc->bg_free_blocks_count = cpu_to_le16(free_blocks + count);
 170                 spin_unlock(sb_bgl_lock(sbi, group_no));
 171                 sb->s_dirt = 1;
 172                 mark_buffer_dirty(bh);
 173         }
 174 }
 175
 176 /* Free given blocks, update quota and i_blocks field */
 177 void ext2_free_blocks (struct inode * inode, unsigned long block,
 178                        unsigned long count)
 179 {
 180         struct buffer_head *bitmap_bh = NULL;
 181         struct buffer_head * bh2;
 182         unsigned long block_group;
 183         unsigned long bit;
 184         unsigned long i;
 185         unsigned long overflow;
 186         struct super_block * sb = inode->i_sb;
 187         struct ext2_sb_info * sbi = EXT2_SB(sb);
 188         struct ext2_group_desc * desc;
 189         struct ext2_super_block * es = sbi->s_es;
 190         unsigned freed = 0, group_freed;
 191
 192         if (block < le32_to_cpu(es->s_first_data_block) ||
 193             block + count < block ||
 194             block + count > le32_to_cpu(es->s_blocks_count)) {
 195                 ext2_error (sb, "ext2_free_blocks",
 196                             "Freeing blocks not in datazone - "
 197                             "block = %lu, count = %lu", block, count);
 198                 goto error_return;
 199         }
 200
 201         ext2_debug ("freeing block(s) %lu-%lu\n", block, block + count - 1);
 202
 203 do_more:
 204         overflow = 0;
 205         block_group = (block - le32_to_cpu(es->s_first_data_block)) /
 206                       EXT2_BLOCKS_PER_GROUP(sb);
 207         bit = (block - le32_to_cpu(es->s_first_data_block)) %
 208                       EXT2_BLOCKS_PER_GROUP(sb);
 209         /*
 210          * Check to see if we are freeing blocks across a group
 211          * boundary.
 212          */
 213         if (bit + count > EXT2_BLOCKS_PER_GROUP(sb)) {
 214                 overflow = bit + count - EXT2_BLOCKS_PER_GROUP(sb);
 215                 count -= overflow;
 216         }
 217         brelse(bitmap_bh);
 218         bitmap_bh = read_block_bitmap(sb, block_group);
 219         if (!bitmap_bh)
 220                 goto error_return;
 221
 222         desc = ext2_get_group_desc (sb, block_group, &bh2);
 223         if (!desc)
 224                 goto error_return;
 225
 226         if (in_range (le32_to_cpu(desc->bg_block_bitmap), block, count) ||
 227             in_range (le32_to_cpu(desc->bg_inode_bitmap), block, count) ||
 228             in_range (block, le32_to_cpu(desc->bg_inode_table),
 229                       sbi->s_itb_per_group) ||
 230             in_range (block + count - 1, le32_to_cpu(desc->bg_inode_table),
 231                       sbi->s_itb_per_group))
 232                 ext2_error (sb, "ext2_free_blocks",
 233                             "Freeing blocks in system zones - "
 234                             "Block = %lu, count = %lu",
 235                             block, count);
 236
 237         for (i = 0, group_freed = 0; i < count; i++) {
 238                 if (!ext2_clear_bit_atomic(sb_bgl_lock(sbi, block_group),
 239                                                 bit + i, bitmap_bh->b_data)) {
 240                         ext2_error(sb, __FUNCTION__,
 241                                 "bit already cleared for block %lu", block + i);
 242                 } else {
 243                         group_freed++;
 244                 }
 245         }
 246
 247         mark_buffer_dirty(bitmap_bh);
 248         if (sb->s_flags & MS_SYNCHRONOUS)
 249                 sync_dirty_buffer(bitmap_bh);
 250
 251         group_release_blocks(sb, block_group, desc, bh2, group_freed);
 252         freed += group_freed;
 253
 254         if (overflow) {
 255                 block += count;
 256                 count = overflow;
 257                 goto do_more;
 258         }
 259 error_return:
 260         brelse(bitmap_bh);
 261         release_blocks(sb, freed);
 262         DQUOT_FREE_BLOCK(inode, freed);
 263 }
 264
 265 static int grab_block(spinlock_t *lock, char *map, unsigned size, int goal)
 266 {
 267         int k;
 268         char *p, *r;
 269
 270         if (!ext2_test_bit(goal, map))
 271                 goto got_it;
 272
 273 repeat:
 274         if (goal) {
 275                 /*
 276                  * The goal was occupied; search forward for a free
 277                  * block within the next XX blocks.
 278                  *
 279                  * end_goal is more or less random, but it has to be
 280                  * less than EXT2_BLOCKS_PER_GROUP. Aligning up to the
 281                  * next 64-bit boundary is simple..
 282                  */
 283                 k = (goal + 63) & ~63;
 284                 goal = ext2_find_next_zero_bit(map, k, goal);
 285                 if (goal < k)
 286                         goto got_it;
 287                 /*
 288                  * Search in the remainder of the current group.
 289                  */
 290         }
 291
 292         p = map + (goal >> 3);
 293         r = memscan(p, 0, (size - goal + 7) >> 3);
 294         k = (r - map) << 3;
 295         if (k < size) {
 296                 /*
 297                  * We have succeeded in finding a free byte in the block
 298                  * bitmap.  Now search backwards to find the start of this
 299                  * group of free blocks - won't take more than 7 iterations.
 300                  */
 301                 for (goal = k; goal && !ext2_test_bit (goal - 1, map); goal--)
 302                         ;
 303                 goto got_it;
 304         }
 305
 306         k = ext2_find_next_zero_bit ((u32 *)map, size, goal);
 307         if (k < size) {
 308                 goal = k;
 309                 goto got_it;
 310         }
 311         return -1;
 312 got_it:
 313         if (ext2_set_bit_atomic(lock, goal, (void *) map))
 314                 goto repeat;
 315         return goal;
 316 }
 317
 318 /*
 319  * ext2_new_block uses a goal block to assist allocation.  If the goal is
 320  * free, or there is a free block within 32 blocks of the goal, that block
 321  * is allocated.  Otherwise a forward search is made for a free block; within
 322  * each block group the search first looks for an entire free byte in the block
 323  * bitmap, and then for any free bit if that fails.
 324  * This function also updates quota and i_blocks field.
 325  */
 326 int ext2_new_block(struct inode *inode, unsigned long goal,
 327                         u32 *prealloc_count, u32 *prealloc_block, int *err)
 328 {
 329         struct buffer_head *bitmap_bh = NULL;
 330         struct buffer_head *gdp_bh;     /* bh2 */
 331         struct ext2_group_desc *desc;
 332         int group_no;                   /* i */
 333         int ret_block;                  /* j */
 334         int group_idx;                  /* k */
 335         int target_block;               /* tmp */
 336         int block = 0;
 337         struct super_block *sb = inode->i_sb;
 338         struct ext2_sb_info *sbi = EXT2_SB(sb);
 339         struct ext2_super_block *es = sbi->s_es;
 340         unsigned group_size = EXT2_BLOCKS_PER_GROUP(sb);
 341         unsigned prealloc_goal = es->s_prealloc_blocks;
 342         unsigned group_alloc = 0, es_alloc, dq_alloc;
 343         int nr_scanned_groups;
 344
 345         if (!prealloc_goal--)
 346                 prealloc_goal = EXT2_DEFAULT_PREALLOC_BLOCKS - 1;
 347         if (!prealloc_count || *prealloc_count)
 348                 prealloc_goal = 0;
 349
 350         if (DQUOT_ALLOC_BLOCK(inode, 1)) {
 351                 *err = -EDQUOT;
 352                 goto out;
 353         }
 354
 355         while (prealloc_goal && DQUOT_PREALLOC_BLOCK(inode, prealloc_goal))
 356                 prealloc_goal--;
 357
 358         dq_alloc = prealloc_goal + 1;
 359         es_alloc = reserve_blocks(sb, dq_alloc);
 360         if (!es_alloc) {
 361                 *err = -ENOSPC;
 362                 goto out_dquot;
 363         }
 364
 365         ext2_debug ("goal=%lu.\n", goal);
 366
 367         if (goal < le32_to_cpu(es->s_first_data_block) ||
 368             goal >= le32_to_cpu(es->s_blocks_count))
 369                 goal = le32_to_cpu(es->s_first_data_block);
 370         group_no = (goal - le32_to_cpu(es->s_first_data_block)) / group_size;
 371         desc = ext2_get_group_desc (sb, group_no, &gdp_bh);
 372         if (!desc) {
 373                 /*
 374                  * gdp_bh may still be uninitialised.  But group_release_blocks
 375                  * will not touch it because group_alloc is zero.
 376                  */
 377                 goto io_error;
 378         }
 379
 380         group_alloc = group_reserve_blocks(sbi, group_no, desc,
 381                                         gdp_bh, es_alloc);
 382         if (group_alloc) {
 383                 ret_block = ((goal - le32_to_cpu(es->s_first_data_block)) %
 384                                         group_size);
 385                 brelse(bitmap_bh);
 386                 bitmap_bh = read_block_bitmap(sb, group_no);
 387                 if (!bitmap_bh)
 388                         goto io_error;
 389
 390                 ext2_debug("goal is at %d:%d.\n", group_no, ret_block);
 391
 392                 ret_block = grab_block(sb_bgl_lock(sbi, group_no),
 393                                 bitmap_bh->b_data, group_size, ret_block);
 394                 if (ret_block >= 0)
 395                         goto got_block;
 396                 group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 397                 group_alloc = 0;
 398         }
 399
 400         ext2_debug ("Bit not found in block group %d.\n", group_no);
 401
 402         /*
 403          * Now search the rest of the groups.  We assume that
 404          * i and desc correctly point to the last group visited.
 405          */
 406         nr_scanned_groups = 0;
 407 retry:
 408         for (group_idx = 0; !group_alloc &&
 409                         group_idx < sbi->s_groups_count; group_idx++) {
 410                 group_no++;
 411                 if (group_no >= sbi->s_groups_count)
 412                         group_no = 0;
 413                 desc = ext2_get_group_desc(sb, group_no, &gdp_bh);
 414                 if (!desc)
 415                         goto io_error;
 416                 group_alloc = group_reserve_blocks(sbi, group_no, desc,
 417                                                 gdp_bh, es_alloc);
 418         }
 419         if (!group_alloc) {
 420                 *err = -ENOSPC;
 421                 goto out_release;
 422         }
 423         brelse(bitmap_bh);
 424         bitmap_bh = read_block_bitmap(sb, group_no);
 425         if (!bitmap_bh)
 426                 goto io_error;
 427
 428         ret_block = grab_block(sb_bgl_lock(sbi, group_no), bitmap_bh->b_data,
 429                                 group_size, 0);
 430         if (ret_block < 0) {
 431                 /*
 432                  * If a free block counter is corrupted we can loop inifintely.
 433                  * Detect that here.
 434                  */
 435                 nr_scanned_groups++;
 436                 if (nr_scanned_groups > 2 * sbi->s_groups_count) {
 437                         ext2_error(sb, "ext2_new_block",
 438                                 "corrupted free blocks counters");
 439                         goto io_error;
 440                 }
 441                 /*
 442                  * Someone else grabbed the last free block in this blockgroup
 443                  * before us.  Retry the scan.
 444                  */
 445                 group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 446                 group_alloc = 0;
 447                 goto retry;
 448         }
 449
 450 got_block:
 451         ext2_debug("using block group %d(%d)\n",
 452                 group_no, desc->bg_free_blocks_count);
 453
 454         target_block = ret_block + group_no * group_size +
 455                         le32_to_cpu(es->s_first_data_block);
 456
 457         if (target_block == le32_to_cpu(desc->bg_block_bitmap) ||
 458             target_block == le32_to_cpu(desc->bg_inode_bitmap) ||
 459             in_range(target_block, le32_to_cpu(desc->bg_inode_table),
 460                       sbi->s_itb_per_group))
 461                 ext2_error (sb, "ext2_new_block",
 462                             "Allocating block in system zone - "
 463                             "block = %u", target_block);
 464
 465         if (target_block >= le32_to_cpu(es->s_blocks_count)) {
 466                 ext2_error (sb, "ext2_new_block",
 467                             "block(%d) >= blocks count(%d) - "
 468                             "block_group = %d, es == %p ", ret_block,
 469                         le32_to_cpu(es->s_blocks_count), group_no, es);
 470                 goto io_error;
 471         }
 472         block = target_block;
 473
 474         /* OK, we _had_ allocated something */
 475         ext2_debug("found bit %d\n", ret_block);
 476
 477         dq_alloc--;
 478         es_alloc--;
 479         group_alloc--;
 480
 481         /*
 482          * Do block preallocation now if required.
 483          */
 484         write_lock(&EXT2_I(inode)->i_meta_lock);
 485         if (group_alloc && !*prealloc_count) {
 486                 unsigned n;
 487
 488                 for (n = 0; n < group_alloc && ++ret_block < group_size; n++) {
 489                         if (ext2_set_bit_atomic(sb_bgl_lock(sbi, group_no),
 490                                                 ret_block,
 491                                                 (void*) bitmap_bh->b_data))
 492                                 break;
 493                 }
 494                 *prealloc_block = block + 1;
 495                 *prealloc_count = n;
 496                 es_alloc -= n;
 497                 dq_alloc -= n;
 498                 group_alloc -= n;
 499         }
 500         write_unlock(&EXT2_I(inode)->i_meta_lock);
 501
 502         mark_buffer_dirty(bitmap_bh);
 503         if (sb->s_flags & MS_SYNCHRONOUS)
 504                 sync_dirty_buffer(bitmap_bh);
 505
 506         ext2_debug ("allocating block %d. ", block);
 507
 508         *err = 0;
 509 out_release:
 510         group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 511         release_blocks(sb, es_alloc);
 512 out_dquot:
 513         DQUOT_FREE_BLOCK(inode, dq_alloc);
 514 out:
 515         brelse(bitmap_bh);
 516         return block;
 517
 518 io_error:
 519         *err = -EIO;
 520         goto out_release;
 521 }
 522
 523 #ifdef EXT2FS_DEBUG
 524
 525 static int nibblemap[] = {4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};
 526
 527 unsigned long ext2_count_free (struct buffer_head * map, unsigned int numchars)
 528 {
 529         unsigned int i;
 530         unsigned long sum = 0;
 531
 532         if (!map)
 533                 return (0);
 534         for (i = 0; i < numchars; i++)
 535                 sum += nibblemap[map->b_data[i] & 0xf] +
 536                         nibblemap[(map->b_data[i] >> 4) & 0xf];
 537         return (sum);
 538 }
 539
 540 #endif  /*  EXT2FS_DEBUG  */
 541
 542 unsigned long ext2_count_free_blocks (struct super_block * sb)
 543 {
 544         struct ext2_group_desc * desc;
 545         unsigned long desc_count = 0;
 546         int i;
 547 #ifdef EXT2FS_DEBUG
 548         unsigned long bitmap_count, x;
 549         struct ext2_super_block *es;
 550
 551         es = EXT2_SB(sb)->s_es;
 552         desc_count = 0;
 553         bitmap_count = 0;
 554         desc = NULL;
 555         for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
 556                 struct buffer_head *bitmap_bh;
 557                 desc = ext2_get_group_desc (sb, i, NULL);
 558                 if (!desc)
 559                         continue;
 560                 desc_count += le16_to_cpu(desc->bg_free_blocks_count);
 561                 bitmap_bh = read_block_bitmap(sb, i);
 562                 if (!bitmap_bh)
 563                         continue;
 564
 565                 x = ext2_count_free(bitmap_bh, sb->s_blocksize);
 566                 printk ("group %d: stored = %d, counted = %lu\n",
 567                         i, le16_to_cpu(desc->bg_free_blocks_count), x);
 568                 bitmap_count += x;
 569                 brelse(bitmap_bh);
 570         }
 571         printk("ext2_count_free_blocks: stored = %lu, computed = %lu, %lu\n",
 572                 (long)le32_to_cpu(es->s_free_blocks_count),
 573                 desc_count, bitmap_count);
 574         return bitmap_count;
 575 #else
 576         for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
 577                 desc = ext2_get_group_desc (sb, i, NULL);
 578                 if (!desc)
 579                         continue;
 580                 desc_count += le16_to_cpu(desc->bg_free_blocks_count);
 581         }
 582         return desc_count;
 583 #endif
 584 }
 585
 586 static inline int
 587 block_in_use(unsigned long block, struct super_block *sb, unsigned char *map)
 588 {
 589         return ext2_test_bit ((block -
 590                 le32_to_cpu(EXT2_SB(sb)->s_es->s_first_data_block)) %
 591                          EXT2_BLOCKS_PER_GROUP(sb), map);
 592 }
 593
 594 static inline int test_root(int a, int b)
 595 {
 596         int num = b;
 597
 598         while (a > num)
 599                 num *= b;
 600         return num == a;
 601 }
 602
 603 static int ext2_group_sparse(int group)
 604 {
 605         if (group <= 1)
 606                 return 1;
 607         return (test_root(group, 3) || test_root(group, 5) ||
 608                 test_root(group, 7));
 609 }
 610
 611 /**
 612  *      ext2_bg_has_super - number of blocks used by the superblock in group
 613  *      @sb: superblock for filesystem
 614  *      @group: group number to check
 615  *
 616  *      Return the number of blocks used by the superblock (primary or backup)
 617  *      in this group.  Currently this will be only 0 or 1.
 618  */
 619 int ext2_bg_has_super(struct super_block *sb, int group)
 620 {
 621         if (EXT2_HAS_RO_COMPAT_FEATURE(sb,EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)&&
 622             !ext2_group_sparse(group))
 623                 return 0;
 624         return 1;
 625 }
 626
 627 /**
 628  *      ext2_bg_num_gdb - number of blocks used by the group table in group
 629  *      @sb: superblock for filesystem
 630  *      @group: group number to check
 631  *
 632  *      Return the number of blocks used by the group descriptor table
 633  *      (primary or backup) in this group.  In the future there may be a
 634  *      different number of descriptor blocks in each group.
 635  */
 636 unsigned long ext2_bg_num_gdb(struct super_block *sb, int group)
 637 {
 638         if (EXT2_HAS_RO_COMPAT_FEATURE(sb,EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)&&
 639             !ext2_group_sparse(group))
 640                 return 0;
 641         return EXT2_SB(sb)->s_gdb_count;
 642 }
 643