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