fs/ext2/balloc.c

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