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 "ext2.h"
  15 #include <linux/quotaops.h>
  16 #include <linux/sched.h>
  17 #include <linux/buffer_head.h>
  18 #include <linux/capability.h>
  19 #include <linux/vs_dlimit.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 long free_blocks;
 107         unsigned long 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         DLIMIT_ADJUST_BLOCK(sb, vx_current_xid(), &free_blocks, &root_blocks);
 113
 114         if (free_blocks < count)
 115                 count = free_blocks;
 116
 117         if (free_blocks < root_blocks + count && !capable(CAP_SYS_RESOURCE) &&
 118             sbi->s_resuid != current->fsuid &&
 119             (sbi->s_resgid == 0 || !in_group_p (sbi->s_resgid))) {
 120                 /*
 121                  * We are too close to reserve and we are not privileged.
 122                  * Can we allocate anything at all?
 123                  */
 124                 if (free_blocks > root_blocks)
 125                         count = free_blocks - root_blocks;
 126                 else
 127                         return 0;
 128         }
 129
 130         percpu_counter_mod(&sbi->s_freeblocks_counter, -count);
 131         sb->s_dirt = 1;
 132         return count;
 133 }
 134
 135 static void release_blocks(struct super_block *sb, int count)
 136 {
 137         if (count) {
 138                 struct ext2_sb_info *sbi = EXT2_SB(sb);
 139
 140                 percpu_counter_mod(&sbi->s_freeblocks_counter, count);
 141                 sb->s_dirt = 1;
 142         }
 143 }
 144
 145 static int group_reserve_blocks(struct ext2_sb_info *sbi, int group_no,
 146         struct ext2_group_desc *desc, struct buffer_head *bh, int count)
 147 {
 148         unsigned free_blocks;
 149
 150         if (!desc->bg_free_blocks_count)
 151                 return 0;
 152
 153         spin_lock(sb_bgl_lock(sbi, group_no));
 154         free_blocks = le16_to_cpu(desc->bg_free_blocks_count);
 155         if (free_blocks < count)
 156                 count = free_blocks;
 157         desc->bg_free_blocks_count = cpu_to_le16(free_blocks - count);
 158         spin_unlock(sb_bgl_lock(sbi, group_no));
 159         mark_buffer_dirty(bh);
 160         return count;
 161 }
 162
 163 static void group_release_blocks(struct super_block *sb, int group_no,
 164         struct ext2_group_desc *desc, struct buffer_head *bh, int count)
 165 {
 166         if (count) {
 167                 struct ext2_sb_info *sbi = EXT2_SB(sb);
 168                 unsigned free_blocks;
 169
 170                 spin_lock(sb_bgl_lock(sbi, group_no));
 171                 free_blocks = le16_to_cpu(desc->bg_free_blocks_count);
 172                 desc->bg_free_blocks_count = cpu_to_le16(free_blocks + count);
 173                 spin_unlock(sb_bgl_lock(sbi, group_no));
 174                 sb->s_dirt = 1;
 175                 mark_buffer_dirty(bh);
 176         }
 177 }
 178
 179 /* Free given blocks, update quota and i_blocks field */
 180 void ext2_free_blocks (struct inode * inode, unsigned long block,
 181                        unsigned long count)
 182 {
 183         struct buffer_head *bitmap_bh = NULL;
 184         struct buffer_head * bh2;
 185         unsigned long block_group;
 186         unsigned long bit;
 187         unsigned long i;
 188         unsigned long overflow;
 189         struct super_block * sb = inode->i_sb;
 190         struct ext2_sb_info * sbi = EXT2_SB(sb);
 191         struct ext2_group_desc * desc;
 192         struct ext2_super_block * es = sbi->s_es;
 193         unsigned freed = 0, group_freed;
 194
 195         if (block < le32_to_cpu(es->s_first_data_block) ||
 196             block + count < block ||
 197             block + count > le32_to_cpu(es->s_blocks_count)) {
 198                 ext2_error (sb, "ext2_free_blocks",
 199                             "Freeing blocks not in datazone - "
 200                             "block = %lu, count = %lu", block, count);
 201                 goto error_return;
 202         }
 203
 204         ext2_debug ("freeing block(s) %lu-%lu\n", block, block + count - 1);
 205
 206 do_more:
 207         overflow = 0;
 208         block_group = (block - le32_to_cpu(es->s_first_data_block)) /
 209                       EXT2_BLOCKS_PER_GROUP(sb);
 210         bit = (block - le32_to_cpu(es->s_first_data_block)) %
 211                       EXT2_BLOCKS_PER_GROUP(sb);
 212         /*
 213          * Check to see if we are freeing blocks across a group
 214          * boundary.
 215          */
 216         if (bit + count > EXT2_BLOCKS_PER_GROUP(sb)) {
 217                 overflow = bit + count - EXT2_BLOCKS_PER_GROUP(sb);
 218                 count -= overflow;
 219         }
 220         brelse(bitmap_bh);
 221         bitmap_bh = read_block_bitmap(sb, block_group);
 222         if (!bitmap_bh)
 223                 goto error_return;
 224
 225         desc = ext2_get_group_desc (sb, block_group, &bh2);
 226         if (!desc)
 227                 goto error_return;
 228
 229         if (in_range (le32_to_cpu(desc->bg_block_bitmap), block, count) ||
 230             in_range (le32_to_cpu(desc->bg_inode_bitmap), block, count) ||
 231             in_range (block, le32_to_cpu(desc->bg_inode_table),
 232                       sbi->s_itb_per_group) ||
 233             in_range (block + count - 1, le32_to_cpu(desc->bg_inode_table),
 234                       sbi->s_itb_per_group))
 235                 ext2_error (sb, "ext2_free_blocks",
 236                             "Freeing blocks in system zones - "
 237                             "Block = %lu, count = %lu",
 238                             block, count);
 239
 240         for (i = 0, group_freed = 0; i < count; i++) {
 241                 if (!ext2_clear_bit_atomic(sb_bgl_lock(sbi, block_group),
 242                                                 bit + i, bitmap_bh->b_data)) {
 243                         ext2_error(sb, __FUNCTION__,
 244                                 "bit already cleared for block %lu", block + i);
 245                 } else {
 246                         group_freed++;
 247                 }
 248         }
 249
 250         mark_buffer_dirty(bitmap_bh);
 251         if (sb->s_flags & MS_SYNCHRONOUS)
 252                 sync_dirty_buffer(bitmap_bh);
 253
 254         group_release_blocks(sb, block_group, desc, bh2, group_freed);
 255         freed += group_freed;
 256
 257         if (overflow) {
 258                 block += count;
 259                 count = overflow;
 260                 goto do_more;
 261         }
 262 error_return:
 263         brelse(bitmap_bh);
 264         DLIMIT_FREE_BLOCK(inode, freed);
 265         release_blocks(sb, freed);
 266         DQUOT_FREE_BLOCK(inode, freed);
 267 }
 268
 269 static int grab_block(spinlock_t *lock, char *map, unsigned size, int goal)
 270 {
 271         int k;
 272         char *p, *r;
 273
 274         if (!ext2_test_bit(goal, map))
 275                 goto got_it;
 276
 277 repeat:
 278         if (goal) {
 279                 /*
 280                  * The goal was occupied; search forward for a free
 281                  * block within the next XX blocks.
 282                  *
 283                  * end_goal is more or less random, but it has to be
 284                  * less than EXT2_BLOCKS_PER_GROUP. Aligning up to the
 285                  * next 64-bit boundary is simple..
 286                  */
 287                 k = (goal + 63) & ~63;
 288                 goal = ext2_find_next_zero_bit(map, k, goal);
 289                 if (goal < k)
 290                         goto got_it;
 291                 /*
 292                  * Search in the remainder of the current group.
 293                  */
 294         }
 295
 296         p = map + (goal >> 3);
 297         r = memscan(p, 0, (size - goal + 7) >> 3);
 298         k = (r - map) << 3;
 299         if (k < size) {
 300                 /*
 301                  * We have succeeded in finding a free byte in the block
 302                  * bitmap.  Now search backwards to find the start of this
 303                  * group of free blocks - won't take more than 7 iterations.
 304                  */
 305                 for (goal = k; goal && !ext2_test_bit (goal - 1, map); goal--)
 306                         ;
 307                 goto got_it;
 308         }
 309
 310         k = ext2_find_next_zero_bit ((u32 *)map, size, goal);
 311         if (k < size) {
 312                 goal = k;
 313                 goto got_it;
 314         }
 315         return -1;
 316 got_it:
 317         if (ext2_set_bit_atomic(lock, goal, (void *) map))
 318                 goto repeat;
 319         return goal;
 320 }
 321
 322 /*
 323  * ext2_new_block uses a goal block to assist allocation.  If the goal is
 324  * free, or there is a free block within 32 blocks of the goal, that block
 325  * is allocated.  Otherwise a forward search is made for a free block; within
 326  * each block group the search first looks for an entire free byte in the block
 327  * bitmap, and then for any free bit if that fails.
 328  * This function also updates quota and i_blocks field.
 329  */
 330 int ext2_new_block(struct inode *inode, unsigned long goal,
 331                         u32 *prealloc_count, u32 *prealloc_block, int *err)
 332 {
 333         struct buffer_head *bitmap_bh = NULL;
 334         struct buffer_head *gdp_bh;     /* bh2 */
 335         struct ext2_group_desc *desc;
 336         int group_no;                   /* i */
 337         int ret_block;                  /* j */
 338         int group_idx;                  /* k */
 339         int target_block;               /* tmp */
 340         int block = 0;
 341         struct super_block *sb = inode->i_sb;
 342         struct ext2_sb_info *sbi = EXT2_SB(sb);
 343         struct ext2_super_block *es = sbi->s_es;
 344         unsigned group_size = EXT2_BLOCKS_PER_GROUP(sb);
 345         unsigned prealloc_goal = es->s_prealloc_blocks;
 346         unsigned group_alloc = 0, es_alloc, dq_alloc;
 347         int nr_scanned_groups;
 348
 349         if (!prealloc_goal--)
 350                 prealloc_goal = EXT2_DEFAULT_PREALLOC_BLOCKS - 1;
 351         if (!prealloc_count || *prealloc_count)
 352                 prealloc_goal = 0;
 353
 354         if (DQUOT_ALLOC_BLOCK(inode, 1)) {
 355                 *err = -EDQUOT;
 356                 goto out;
 357         }
 358
 359         while (prealloc_goal && DQUOT_PREALLOC_BLOCK(inode, prealloc_goal))
 360                 prealloc_goal--;
 361
 362         dq_alloc = prealloc_goal + 1;
 363         es_alloc = reserve_blocks(sb, dq_alloc);
 364         if (!es_alloc) {
 365                 *err = -ENOSPC;
 366                 goto out_dquot;
 367         }
 368         if (DLIMIT_ALLOC_BLOCK(inode, es_alloc)) {
 369                 *err = -ENOSPC;
 370                 goto out_dlimit;
 371         }
 372
 373         ext2_debug ("goal=%lu.\n", goal);
 374
 375         if (goal < le32_to_cpu(es->s_first_data_block) ||
 376             goal >= le32_to_cpu(es->s_blocks_count))
 377                 goal = le32_to_cpu(es->s_first_data_block);
 378         group_no = (goal - le32_to_cpu(es->s_first_data_block)) / group_size;
 379         desc = ext2_get_group_desc (sb, group_no, &gdp_bh);
 380         if (!desc) {
 381                 /*
 382                  * gdp_bh may still be uninitialised.  But group_release_blocks
 383                  * will not touch it because group_alloc is zero.
 384                  */
 385                 goto io_error;
 386         }
 387
 388         group_alloc = group_reserve_blocks(sbi, group_no, desc,
 389                                         gdp_bh, es_alloc);
 390         if (group_alloc) {
 391                 ret_block = ((goal - le32_to_cpu(es->s_first_data_block)) %
 392                                         group_size);
 393                 brelse(bitmap_bh);
 394                 bitmap_bh = read_block_bitmap(sb, group_no);
 395                 if (!bitmap_bh)
 396                         goto io_error;
 397
 398                 ext2_debug("goal is at %d:%d.\n", group_no, ret_block);
 399
 400                 ret_block = grab_block(sb_bgl_lock(sbi, group_no),
 401                                 bitmap_bh->b_data, group_size, ret_block);
 402                 if (ret_block >= 0)
 403                         goto got_block;
 404                 group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 405                 group_alloc = 0;
 406         }
 407
 408         ext2_debug ("Bit not found in block group %d.\n", group_no);
 409
 410         /*
 411          * Now search the rest of the groups.  We assume that
 412          * i and desc correctly point to the last group visited.
 413          */
 414         nr_scanned_groups = 0;
 415 retry:
 416         for (group_idx = 0; !group_alloc &&
 417                         group_idx < sbi->s_groups_count; group_idx++) {
 418                 group_no++;
 419                 if (group_no >= sbi->s_groups_count)
 420                         group_no = 0;
 421                 desc = ext2_get_group_desc(sb, group_no, &gdp_bh);
 422                 if (!desc)
 423                         goto io_error;
 424                 group_alloc = group_reserve_blocks(sbi, group_no, desc,
 425                                                 gdp_bh, es_alloc);
 426         }
 427         if (!group_alloc) {
 428                 *err = -ENOSPC;
 429                 goto out_release;
 430         }
 431         brelse(bitmap_bh);
 432         bitmap_bh = read_block_bitmap(sb, group_no);
 433         if (!bitmap_bh)
 434                 goto io_error;
 435
 436         ret_block = grab_block(sb_bgl_lock(sbi, group_no), bitmap_bh->b_data,
 437                                 group_size, 0);
 438         if (ret_block < 0) {
 439                 /*
 440                  * If a free block counter is corrupted we can loop inifintely.
 441                  * Detect that here.
 442                  */
 443                 nr_scanned_groups++;
 444                 if (nr_scanned_groups > 2 * sbi->s_groups_count) {
 445                         ext2_error(sb, "ext2_new_block",
 446                                 "corrupted free blocks counters");
 447                         goto io_error;
 448                 }
 449                 /*
 450                  * Someone else grabbed the last free block in this blockgroup
 451                  * before us.  Retry the scan.
 452                  */
 453                 group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 454                 group_alloc = 0;
 455                 goto retry;
 456         }
 457
 458 got_block:
 459         ext2_debug("using block group %d(%d)\n",
 460                 group_no, desc->bg_free_blocks_count);
 461
 462         target_block = ret_block + group_no * group_size +
 463                         le32_to_cpu(es->s_first_data_block);
 464
 465         if (target_block == le32_to_cpu(desc->bg_block_bitmap) ||
 466             target_block == le32_to_cpu(desc->bg_inode_bitmap) ||
 467             in_range(target_block, le32_to_cpu(desc->bg_inode_table),
 468                       sbi->s_itb_per_group))
 469                 ext2_error (sb, "ext2_new_block",
 470                             "Allocating block in system zone - "
 471                             "block = %u", target_block);
 472
 473         if (target_block >= le32_to_cpu(es->s_blocks_count)) {
 474                 ext2_error (sb, "ext2_new_block",
 475                             "block(%d) >= blocks count(%d) - "
 476                             "block_group = %d, es == %p ", ret_block,
 477                         le32_to_cpu(es->s_blocks_count), group_no, es);
 478                 goto io_error;
 479         }
 480         block = target_block;
 481
 482         /* OK, we _had_ allocated something */
 483         ext2_debug("found bit %d\n", ret_block);
 484
 485         dq_alloc--;
 486         es_alloc--;
 487         group_alloc--;
 488
 489         /*
 490          * Do block preallocation now if required.
 491          */
 492         write_lock(&EXT2_I(inode)->i_meta_lock);
 493         if (group_alloc && !*prealloc_count) {
 494                 unsigned n;
 495
 496                 for (n = 0; n < group_alloc && ++ret_block < group_size; n++) {
 497                         if (ext2_set_bit_atomic(sb_bgl_lock(sbi, group_no),
 498                                                 ret_block,
 499                                                 (void*) bitmap_bh->b_data))
 500                                 break;
 501                 }
 502                 *prealloc_block = block + 1;
 503                 *prealloc_count = n;
 504                 es_alloc -= n;
 505                 dq_alloc -= n;
 506                 group_alloc -= n;
 507         }
 508         write_unlock(&EXT2_I(inode)->i_meta_lock);
 509
 510         mark_buffer_dirty(bitmap_bh);
 511         if (sb->s_flags & MS_SYNCHRONOUS)
 512                 sync_dirty_buffer(bitmap_bh);
 513
 514         ext2_debug ("allocating block %d. ", block);
 515
 516         *err = 0;
 517 out_release:
 518         group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 519         DLIMIT_FREE_BLOCK(inode, es_alloc);
 520 out_dlimit:
 521         release_blocks(sb, es_alloc);
 522 out_dquot:
 523         DQUOT_FREE_BLOCK(inode, dq_alloc);
 524 out:
 525         brelse(bitmap_bh);
 526         return block;
 527
 528 io_error:
 529         *err = -EIO;
 530         goto out_release;
 531 }
 532
 533 #ifdef EXT2FS_DEBUG
 534
 535 static int nibblemap[] = {4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};
 536
 537 unsigned long ext2_count_free (struct buffer_head * map, unsigned int numchars)
 538 {
 539         unsigned int i;
 540         unsigned long sum = 0;
 541
 542         if (!map)
 543                 return (0);
 544         for (i = 0; i < numchars; i++)
 545                 sum += nibblemap[map->b_data[i] & 0xf] +
 546                         nibblemap[(map->b_data[i] >> 4) & 0xf];
 547         return (sum);
 548 }
 549
 550 #endif  /*  EXT2FS_DEBUG  */
 551
 552 unsigned long ext2_count_free_blocks (struct super_block * sb)
 553 {
 554         struct ext2_group_desc * desc;
 555         unsigned long desc_count = 0;
 556         int i;
 557 #ifdef EXT2FS_DEBUG
 558         unsigned long bitmap_count, x;
 559         struct ext2_super_block *es;
 560
 561         es = EXT2_SB(sb)->s_es;
 562         desc_count = 0;
 563         bitmap_count = 0;
 564         desc = NULL;
 565         for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
 566                 struct buffer_head *bitmap_bh;
 567                 desc = ext2_get_group_desc (sb, i, NULL);
 568                 if (!desc)
 569                         continue;
 570                 desc_count += le16_to_cpu(desc->bg_free_blocks_count);
 571                 bitmap_bh = read_block_bitmap(sb, i);
 572                 if (!bitmap_bh)
 573                         continue;
 574
 575                 x = ext2_count_free(bitmap_bh, sb->s_blocksize);
 576                 printk ("group %d: stored = %d, counted = %lu\n",
 577                         i, le16_to_cpu(desc->bg_free_blocks_count), x);
 578                 bitmap_count += x;
 579                 brelse(bitmap_bh);
 580         }
 581         printk("ext2_count_free_blocks: stored = %lu, computed = %lu, %lu\n",
 582                 (long)le32_to_cpu(es->s_free_blocks_count),
 583                 desc_count, bitmap_count);
 584         return bitmap_count;
 585 #else
 586         for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
 587                 desc = ext2_get_group_desc (sb, i, NULL);
 588                 if (!desc)
 589                         continue;
 590                 desc_count += le16_to_cpu(desc->bg_free_blocks_count);
 591         }
 592         return desc_count;
 593 #endif
 594 }
 595
 596 static inline int
 597 block_in_use(unsigned long block, struct super_block *sb, unsigned char *map)
 598 {
 599         return ext2_test_bit ((block -
 600                 le32_to_cpu(EXT2_SB(sb)->s_es->s_first_data_block)) %
 601                          EXT2_BLOCKS_PER_GROUP(sb), map);
 602 }
 603
 604 static inline int test_root(int a, int b)
 605 {
 606         int num = b;
 607
 608         while (a > num)
 609                 num *= b;
 610         return num == a;
 611 }
 612
 613 static int ext2_group_sparse(int group)
 614 {
 615         if (group <= 1)
 616                 return 1;
 617         return (test_root(group, 3) || test_root(group, 5) ||
 618                 test_root(group, 7));
 619 }
 620
 621 /**
 622  *      ext2_bg_has_super - number of blocks used by the superblock in group
 623  *      @sb: superblock for filesystem
 624  *      @group: group number to check
 625  *
 626  *      Return the number of blocks used by the superblock (primary or backup)
 627  *      in this group.  Currently this will be only 0 or 1.
 628  */
 629 int ext2_bg_has_super(struct super_block *sb, int group)
 630 {
 631         if (EXT2_HAS_RO_COMPAT_FEATURE(sb,EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)&&
 632             !ext2_group_sparse(group))
 633                 return 0;
 634         return 1;
 635 }
 636
 637 /**
 638  *      ext2_bg_num_gdb - number of blocks used by the group table in group
 639  *      @sb: superblock for filesystem
 640  *      @group: group number to check
 641  *
 642  *      Return the number of blocks used by the group descriptor table
 643  *      (primary or backup) in this group.  In the future there may be a
 644  *      different number of descriptor blocks in each group.
 645  */
 646 unsigned long ext2_bg_num_gdb(struct super_block *sb, int group)
 647 {
 648         if (EXT2_HAS_RO_COMPAT_FEATURE(sb,EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)&&
 649             !ext2_group_sparse(group))
 650                 return 0;
 651         return EXT2_SB(sb)->s_gdb_count;
 652 }
 653