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
  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_fill_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 static inline int
  73 block_in_use(unsigned long block, struct super_block *sb, unsigned char *map)
  74 {
  75         return ext2_test_bit ((block -
  76                 le32_to_cpu(EXT2_SB(sb)->s_es->s_first_data_block)) %
  77                          EXT2_BLOCKS_PER_GROUP(sb), map);
  78 }
  79
  80 /*
  81  * Read the bitmap for a given block_group, reading into the specified
  82  * slot in the superblock's bitmap cache.
  83  *
  84  * Return buffer_head on success or NULL in case of failure.
  85  */
  86 static struct buffer_head *
  87 read_block_bitmap(struct super_block *sb, unsigned int block_group)
  88 {
  89         int i;
  90         struct ext2_group_desc * desc;
  91         struct buffer_head * bh = NULL;
  92         unsigned int bitmap_blk;
  93
  94         desc = ext2_get_group_desc (sb, block_group, NULL);
  95         if (!desc)
  96                 return NULL;
  97         bitmap_blk = le32_to_cpu(desc->bg_block_bitmap);
  98         bh = sb_bread(sb, bitmap_blk);
  99         if (!bh)
 100                 ext2_error (sb, __FUNCTION__,
 101                             "Cannot read block bitmap - "
 102                             "block_group = %d, block_bitmap = %u",
 103                             block_group, le32_to_cpu(desc->bg_block_bitmap));
 104
 105         /* check whether block bitmap block number is set */
 106         if (!block_in_use(bitmap_blk, sb, bh->b_data)) {
 107                 /* bad block bitmap */
 108                 goto error_out;
 109         }
 110         /* check whether the inode bitmap block number is set */
 111         bitmap_blk = le32_to_cpu(desc->bg_inode_bitmap);
 112         if (!block_in_use(bitmap_blk, sb, bh->b_data)) {
 113                 /* bad block bitmap */
 114                 goto error_out;
 115         }
 116         /* check whether the inode table block number is set */
 117         bitmap_blk = le32_to_cpu(desc->bg_inode_table);
 118         for (i = 0; i < EXT2_SB(sb)->s_itb_per_group; i++, bitmap_blk++) {
 119                 if (!block_in_use(bitmap_blk, sb, bh->b_data)) {
 120                         /* bad block bitmap */
 121                         goto error_out;
 122                 }
 123         }
 124
 125         return bh;
 126
 127 error_out:
 128         brelse(bh);
 129         ext2_error(sb, __FUNCTION__,
 130                         "Invalid block bitmap - "
 131                         "block_group = %d, block = %u",
 132                         block_group, bitmap_blk);
 133         return NULL;
 134 }
 135
 136 /*
 137  * Set sb->s_dirt here because the superblock was "logically" altered.  We
 138  * need to recalculate its free blocks count and flush it out.
 139  */
 140 static int reserve_blocks(struct super_block *sb, int count)
 141 {
 142         struct ext2_sb_info *sbi = EXT2_SB(sb);
 143         struct ext2_super_block *es = sbi->s_es;
 144         unsigned free_blocks;
 145         unsigned root_blocks;
 146
 147         free_blocks = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
 148         root_blocks = le32_to_cpu(es->s_r_blocks_count);
 149
 150         if (free_blocks < count)
 151                 count = free_blocks;
 152
 153         if (free_blocks < root_blocks + count && !capable(CAP_SYS_RESOURCE) &&
 154             sbi->s_resuid != current->fsuid &&
 155             (sbi->s_resgid == 0 || !in_group_p (sbi->s_resgid))) {
 156                 /*
 157                  * We are too close to reserve and we are not privileged.
 158                  * Can we allocate anything at all?
 159                  */
 160                 if (free_blocks > root_blocks)
 161                         count = free_blocks - root_blocks;
 162                 else
 163                         return 0;
 164         }
 165
 166         percpu_counter_sub(&sbi->s_freeblocks_counter, count);
 167         sb->s_dirt = 1;
 168         return count;
 169 }
 170
 171 static void release_blocks(struct super_block *sb, int count)
 172 {
 173         if (count) {
 174                 struct ext2_sb_info *sbi = EXT2_SB(sb);
 175
 176                 percpu_counter_add(&sbi->s_freeblocks_counter, count);
 177                 sb->s_dirt = 1;
 178         }
 179 }
 180
 181 static int group_reserve_blocks(struct ext2_sb_info *sbi, int group_no,
 182         struct ext2_group_desc *desc, struct buffer_head *bh, int count)
 183 {
 184         unsigned free_blocks;
 185
 186         if (!desc->bg_free_blocks_count)
 187                 return 0;
 188
 189         spin_lock(sb_bgl_lock(sbi, group_no));
 190         free_blocks = le16_to_cpu(desc->bg_free_blocks_count);
 191         if (free_blocks < count)
 192                 count = free_blocks;
 193         desc->bg_free_blocks_count = cpu_to_le16(free_blocks - count);
 194         spin_unlock(sb_bgl_lock(sbi, group_no));
 195         mark_buffer_dirty(bh);
 196         return count;
 197 }
 198
 199 static void group_release_blocks(struct super_block *sb, int group_no,
 200         struct ext2_group_desc *desc, struct buffer_head *bh, int count)
 201 {
 202         if (count) {
 203                 struct ext2_sb_info *sbi = EXT2_SB(sb);
 204                 unsigned free_blocks;
 205
 206                 spin_lock(sb_bgl_lock(sbi, group_no));
 207                 free_blocks = le16_to_cpu(desc->bg_free_blocks_count);
 208                 desc->bg_free_blocks_count = cpu_to_le16(free_blocks + count);
 209                 spin_unlock(sb_bgl_lock(sbi, group_no));
 210                 sb->s_dirt = 1;
 211                 mark_buffer_dirty(bh);
 212         }
 213 }
 214
 215 /* Free given blocks, update quota and i_blocks field */
 216 void ext2_free_blocks (struct inode * inode, unsigned long block,
 217                        unsigned long count)
 218 {
 219         struct buffer_head *bitmap_bh = NULL;
 220         struct buffer_head * bh2;
 221         unsigned long block_group;
 222         unsigned long bit;
 223         unsigned long i;
 224         unsigned long overflow;
 225         struct super_block * sb = inode->i_sb;
 226         struct ext2_sb_info * sbi = EXT2_SB(sb);
 227         struct ext2_group_desc * desc;
 228         struct ext2_super_block * es = sbi->s_es;
 229         unsigned freed = 0, group_freed;
 230
 231         if (block < le32_to_cpu(es->s_first_data_block) ||
 232             block + count < block ||
 233             block + count > le32_to_cpu(es->s_blocks_count)) {
 234                 ext2_error (sb, "ext2_free_blocks",
 235                             "Freeing blocks not in datazone - "
 236                             "block = %lu, count = %lu", block, count);
 237                 goto error_return;
 238         }
 239
 240         ext2_debug ("freeing block(s) %lu-%lu\n", block, block + count - 1);
 241
 242 do_more:
 243         overflow = 0;
 244         block_group = (block - le32_to_cpu(es->s_first_data_block)) /
 245                       EXT2_BLOCKS_PER_GROUP(sb);
 246         bit = (block - le32_to_cpu(es->s_first_data_block)) %
 247                       EXT2_BLOCKS_PER_GROUP(sb);
 248         /*
 249          * Check to see if we are freeing blocks across a group
 250          * boundary.
 251          */
 252         if (bit + count > EXT2_BLOCKS_PER_GROUP(sb)) {
 253                 overflow = bit + count - EXT2_BLOCKS_PER_GROUP(sb);
 254                 count -= overflow;
 255         }
 256         brelse(bitmap_bh);
 257         bitmap_bh = read_block_bitmap(sb, block_group);
 258         if (!bitmap_bh)
 259                 goto error_return;
 260
 261         desc = ext2_get_group_desc (sb, block_group, &bh2);
 262         if (!desc)
 263                 goto error_return;
 264
 265         if (in_range (le32_to_cpu(desc->bg_block_bitmap), block, count) ||
 266             in_range (le32_to_cpu(desc->bg_inode_bitmap), block, count) ||
 267             in_range (block, le32_to_cpu(desc->bg_inode_table),
 268                       sbi->s_itb_per_group) ||
 269             in_range (block + count - 1, le32_to_cpu(desc->bg_inode_table),
 270                       sbi->s_itb_per_group))
 271                 ext2_error (sb, "ext2_free_blocks",
 272                             "Freeing blocks in system zones - "
 273                             "Block = %lu, count = %lu",
 274                             block, count);
 275
 276         for (i = 0, group_freed = 0; i < count; i++) {
 277                 if (!ext2_clear_bit_atomic(sb_bgl_lock(sbi, block_group),
 278                                                 bit + i, bitmap_bh->b_data)) {
 279                         ext2_error(sb, __FUNCTION__,
 280                                 "bit already cleared for block %lu", block + i);
 281                 } else {
 282                         group_freed++;
 283                 }
 284         }
 285
 286         mark_buffer_dirty(bitmap_bh);
 287         if (sb->s_flags & MS_SYNCHRONOUS)
 288                 sync_dirty_buffer(bitmap_bh);
 289
 290         group_release_blocks(sb, block_group, desc, bh2, group_freed);
 291         freed += group_freed;
 292
 293         if (overflow) {
 294                 block += count;
 295                 count = overflow;
 296                 goto do_more;
 297         }
 298 error_return:
 299         brelse(bitmap_bh);
 300         release_blocks(sb, freed);
 301         DQUOT_FREE_BLOCK(inode, freed);
 302 }
 303
 304 static int grab_block(spinlock_t *lock, char *map, unsigned size, int goal)
 305 {
 306         int k;
 307         char *p, *r;
 308
 309         if (!ext2_test_bit(goal, map))
 310                 goto got_it;
 311
 312 repeat:
 313         if (goal) {
 314                 /*
 315                  * The goal was occupied; search forward for a free
 316                  * block within the next XX blocks.
 317                  *
 318                  * end_goal is more or less random, but it has to be
 319                  * less than EXT2_BLOCKS_PER_GROUP. Aligning up to the
 320                  * next 64-bit boundary is simple..
 321                  */
 322                 k = (goal + 63) & ~63;
 323                 goal = ext2_find_next_zero_bit(map, k, goal);
 324                 if (goal < k)
 325                         goto got_it;
 326                 /*
 327                  * Search in the remainder of the current group.
 328                  */
 329         }
 330
 331         p = map + (goal >> 3);
 332         r = memscan(p, 0, (size - goal + 7) >> 3);
 333         k = (r - map) << 3;
 334         if (k < size) {
 335                 /*
 336                  * We have succeeded in finding a free byte in the block
 337                  * bitmap.  Now search backwards to find the start of this
 338                  * group of free blocks - won't take more than 7 iterations.
 339                  */
 340                 for (goal = k; goal && !ext2_test_bit (goal - 1, map); goal--)
 341                         ;
 342                 goto got_it;
 343         }
 344
 345         k = ext2_find_next_zero_bit ((u32 *)map, size, goal);
 346         if (k < size) {
 347                 goal = k;
 348                 goto got_it;
 349         }
 350         return -1;
 351 got_it:
 352         if (ext2_set_bit_atomic(lock, goal, (void *) map))
 353                 goto repeat;
 354         return goal;
 355 }
 356
 357 /*
 358  * ext2_new_block uses a goal block to assist allocation.  If the goal is
 359  * free, or there is a free block within 32 blocks of the goal, that block
 360  * is allocated.  Otherwise a forward search is made for a free block; within
 361  * each block group the search first looks for an entire free byte in the block
 362  * bitmap, and then for any free bit if that fails.
 363  * This function also updates quota and i_blocks field.
 364  */
 365 int ext2_new_block(struct inode *inode, unsigned long goal,
 366                         u32 *prealloc_count, u32 *prealloc_block, int *err)
 367 {
 368         struct buffer_head *bitmap_bh = NULL;
 369         struct buffer_head *gdp_bh;     /* bh2 */
 370         struct ext2_group_desc *desc;
 371         int group_no;                   /* i */
 372         int ret_block;                  /* j */
 373         int group_idx;                  /* k */
 374         int target_block;               /* tmp */
 375         int block = 0;
 376         struct super_block *sb = inode->i_sb;
 377         struct ext2_sb_info *sbi = EXT2_SB(sb);
 378         struct ext2_super_block *es = sbi->s_es;
 379         unsigned group_size = EXT2_BLOCKS_PER_GROUP(sb);
 380         unsigned prealloc_goal = es->s_prealloc_blocks;
 381         unsigned group_alloc = 0, es_alloc, dq_alloc;
 382         int nr_scanned_groups;
 383
 384         if (!prealloc_goal--)
 385                 prealloc_goal = EXT2_DEFAULT_PREALLOC_BLOCKS - 1;
 386         if (!prealloc_count || *prealloc_count)
 387                 prealloc_goal = 0;
 388
 389         if (DQUOT_ALLOC_BLOCK(inode, 1)) {
 390                 *err = -EDQUOT;
 391                 goto out;
 392         }
 393
 394         while (prealloc_goal && DQUOT_PREALLOC_BLOCK(inode, prealloc_goal))
 395                 prealloc_goal--;
 396
 397         dq_alloc = prealloc_goal + 1;
 398         es_alloc = reserve_blocks(sb, dq_alloc);
 399         if (!es_alloc) {
 400                 *err = -ENOSPC;
 401                 goto out_dquot;
 402         }
 403
 404         ext2_debug ("goal=%lu.\n", goal);
 405
 406         if (goal < le32_to_cpu(es->s_first_data_block) ||
 407             goal >= le32_to_cpu(es->s_blocks_count))
 408                 goal = le32_to_cpu(es->s_first_data_block);
 409         group_no = (goal - le32_to_cpu(es->s_first_data_block)) / group_size;
 410         desc = ext2_get_group_desc (sb, group_no, &gdp_bh);
 411         if (!desc) {
 412                 /*
 413                  * gdp_bh may still be uninitialised.  But group_release_blocks
 414                  * will not touch it because group_alloc is zero.
 415                  */
 416                 goto io_error;
 417         }
 418
 419         group_alloc = group_reserve_blocks(sbi, group_no, desc,
 420                                         gdp_bh, es_alloc);
 421         if (group_alloc) {
 422                 ret_block = ((goal - le32_to_cpu(es->s_first_data_block)) %
 423                                         group_size);
 424                 brelse(bitmap_bh);
 425                 bitmap_bh = read_block_bitmap(sb, group_no);
 426                 if (!bitmap_bh)
 427                         goto io_error;
 428
 429                 ext2_debug("goal is at %d:%d.\n", group_no, ret_block);
 430
 431                 ret_block = grab_block(sb_bgl_lock(sbi, group_no),
 432                                 bitmap_bh->b_data, group_size, ret_block);
 433                 if (ret_block >= 0)
 434                         goto got_block;
 435                 group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 436                 group_alloc = 0;
 437         }
 438
 439         ext2_debug ("Bit not found in block group %d.\n", group_no);
 440
 441         /*
 442          * Now search the rest of the groups.  We assume that
 443          * i and desc correctly point to the last group visited.
 444          */
 445         nr_scanned_groups = 0;
 446 retry:
 447         for (group_idx = 0; !group_alloc &&
 448                         group_idx < sbi->s_groups_count; group_idx++) {
 449                 group_no++;
 450                 if (group_no >= sbi->s_groups_count)
 451                         group_no = 0;
 452                 desc = ext2_get_group_desc(sb, group_no, &gdp_bh);
 453                 if (!desc)
 454                         goto io_error;
 455                 group_alloc = group_reserve_blocks(sbi, group_no, desc,
 456                                                 gdp_bh, es_alloc);
 457         }
 458         if (!group_alloc) {
 459                 *err = -ENOSPC;
 460                 goto out_release;
 461         }
 462         brelse(bitmap_bh);
 463         bitmap_bh = read_block_bitmap(sb, group_no);
 464         if (!bitmap_bh)
 465                 goto io_error;
 466
 467         ret_block = grab_block(sb_bgl_lock(sbi, group_no), bitmap_bh->b_data,
 468                                 group_size, 0);
 469         if (ret_block < 0) {
 470                 /*
 471                  * If a free block counter is corrupted we can loop inifintely.
 472                  * Detect that here.
 473                  */
 474                 nr_scanned_groups++;
 475                 if (nr_scanned_groups > 2 * sbi->s_groups_count) {
 476                         ext2_error(sb, "ext2_new_block",
 477                                 "corrupted free blocks counters");
 478                         goto io_error;
 479                 }
 480                 /*
 481                  * Someone else grabbed the last free block in this blockgroup
 482                  * before us.  Retry the scan.
 483                  */
 484                 group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 485                 group_alloc = 0;
 486                 goto retry;
 487         }
 488
 489 got_block:
 490         ext2_debug("using block group %d(%d)\n",
 491                 group_no, desc->bg_free_blocks_count);
 492
 493         target_block = ret_block + group_no * group_size +
 494                         le32_to_cpu(es->s_first_data_block);
 495
 496         if (target_block == le32_to_cpu(desc->bg_block_bitmap) ||
 497             target_block == le32_to_cpu(desc->bg_inode_bitmap) ||
 498             in_range(target_block, le32_to_cpu(desc->bg_inode_table),
 499                       sbi->s_itb_per_group))
 500                 ext2_error (sb, "ext2_new_block",
 501                             "Allocating block in system zone - "
 502                             "block = %u", target_block);
 503
 504         if (target_block >= le32_to_cpu(es->s_blocks_count)) {
 505                 ext2_error (sb, "ext2_new_block",
 506                             "block(%d) >= blocks count(%d) - "
 507                             "block_group = %d, es == %p ", ret_block,
 508                         le32_to_cpu(es->s_blocks_count), group_no, es);
 509                 goto io_error;
 510         }
 511         block = target_block;
 512
 513         /* OK, we _had_ allocated something */
 514         ext2_debug("found bit %d\n", ret_block);
 515
 516         dq_alloc--;
 517         es_alloc--;
 518         group_alloc--;
 519
 520         /*
 521          * Do block preallocation now if required.
 522          */
 523         write_lock(&EXT2_I(inode)->i_meta_lock);
 524         if (group_alloc && !*prealloc_count) {
 525                 unsigned n;
 526
 527                 for (n = 0; n < group_alloc && ++ret_block < group_size; n++) {
 528                         if (ext2_set_bit_atomic(sb_bgl_lock(sbi, group_no),
 529                                                 ret_block,
 530                                                 (void*) bitmap_bh->b_data))
 531                                 break;
 532                 }
 533                 *prealloc_block = block + 1;
 534                 *prealloc_count = n;
 535                 es_alloc -= n;
 536                 dq_alloc -= n;
 537                 group_alloc -= n;
 538         }
 539         write_unlock(&EXT2_I(inode)->i_meta_lock);
 540
 541         mark_buffer_dirty(bitmap_bh);
 542         if (sb->s_flags & MS_SYNCHRONOUS)
 543                 sync_dirty_buffer(bitmap_bh);
 544
 545         ext2_debug ("allocating block %d. ", block);
 546
 547         *err = 0;
 548 out_release:
 549         group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 550         release_blocks(sb, es_alloc);
 551 out_dquot:
 552         DQUOT_FREE_BLOCK(inode, dq_alloc);
 553 out:
 554         brelse(bitmap_bh);
 555         return block;
 556
 557 io_error:
 558         *err = -EIO;
 559         goto out_release;
 560 }
 561
 562 #ifdef EXT2FS_DEBUG
 563
 564 static const int nibblemap[] = {4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};
 565
 566 unsigned long ext2_count_free (struct buffer_head * map, unsigned int numchars)
 567 {
 568         unsigned int i;
 569         unsigned long sum = 0;
 570
 571         if (!map)
 572                 return (0);
 573         for (i = 0; i < numchars; i++)
 574                 sum += nibblemap[map->b_data[i] & 0xf] +
 575                         nibblemap[(map->b_data[i] >> 4) & 0xf];
 576         return (sum);
 577 }
 578
 579 #endif  /*  EXT2FS_DEBUG  */
 580
 581 unsigned long ext2_count_free_blocks (struct super_block * sb)
 582 {
 583         struct ext2_group_desc * desc;
 584         unsigned long desc_count = 0;
 585         int i;
 586 #ifdef EXT2FS_DEBUG
 587         unsigned long bitmap_count, x;
 588         struct ext2_super_block *es;
 589
 590         es = EXT2_SB(sb)->s_es;
 591         desc_count = 0;
 592         bitmap_count = 0;
 593         desc = NULL;
 594         for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
 595                 struct buffer_head *bitmap_bh;
 596                 desc = ext2_get_group_desc (sb, i, NULL);
 597                 if (!desc)
 598                         continue;
 599                 desc_count += le16_to_cpu(desc->bg_free_blocks_count);
 600                 bitmap_bh = read_block_bitmap(sb, i);
 601                 if (!bitmap_bh)
 602                         continue;
 603
 604                 x = ext2_count_free(bitmap_bh, sb->s_blocksize);
 605                 printk ("group %d: stored = %d, counted = %lu\n",
 606                         i, le16_to_cpu(desc->bg_free_blocks_count), x);
 607                 bitmap_count += x;
 608                 brelse(bitmap_bh);
 609         }
 610         printk("ext2_count_free_blocks: stored = %lu, computed = %lu, %lu\n",
 611                 (long)le32_to_cpu(es->s_free_blocks_count),
 612                 desc_count, bitmap_count);
 613         return bitmap_count;
 614 #else
 615         for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
 616                 desc = ext2_get_group_desc (sb, i, NULL);
 617                 if (!desc)
 618                         continue;
 619                 desc_count += le16_to_cpu(desc->bg_free_blocks_count);
 620         }
 621         return desc_count;
 622 #endif
 623 }
 624
 625
 626 static inline int test_root(int a, int b)
 627 {
 628         int num = b;
 629
 630         while (a > num)
 631                 num *= b;
 632         return num == a;
 633 }
 634
 635 static int ext2_group_sparse(int group)
 636 {
 637         if (group <= 1)
 638                 return 1;
 639         return (test_root(group, 3) || test_root(group, 5) ||
 640                 test_root(group, 7));
 641 }
 642
 643 /**
 644  *      ext2_bg_has_super - number of blocks used by the superblock in group
 645  *      @sb: superblock for filesystem
 646  *      @group: group number to check
 647  *
 648  *      Return the number of blocks used by the superblock (primary or backup)
 649  *      in this group.  Currently this will be only 0 or 1.
 650  */
 651 int ext2_bg_has_super(struct super_block *sb, int group)
 652 {
 653         if (EXT2_HAS_RO_COMPAT_FEATURE(sb,EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)&&
 654             !ext2_group_sparse(group))
 655                 return 0;
 656         return 1;
 657 }
 658
 659 /**
 660  *      ext2_bg_num_gdb - number of blocks used by the group table in group
 661  *      @sb: superblock for filesystem
 662  *      @group: group number to check
 663  *
 664  *      Return the number of blocks used by the group descriptor table
 665  *      (primary or backup) in this group.  In the future there may be a
 666  *      different number of descriptor blocks in each group.
 667  */
 668 unsigned long ext2_bg_num_gdb(struct super_block *sb, int group)
 669 {
 670         if (EXT2_HAS_RO_COMPAT_FEATURE(sb,EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)&&
 671             !ext2_group_sparse(group))
 672                 return 0;
 673         return EXT2_SB(sb)->s_gdb_count;
 674 }
 675