fs/ext4/balloc.c

   1 /*
   2  *  linux/fs/ext4/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/time.h>
  15 #include <linux/capability.h>
  16 #include <linux/fs.h>
  17 #include <linux/jbd2.h>
  18 #include <linux/quotaops.h>
  19 #include <linux/buffer_head.h>
  20 #include "ext4.h"
  21 #include "ext4_jbd2.h"
  22 #include "mballoc.h"
  23
  24 #include <trace/events/ext4.h>
  25
  26 static unsigned ext4_num_base_meta_clusters(struct super_block *sb,
  27                                             ext4_group_t block_group);
  28 /*
  29  * balloc.c contains the blocks allocation and deallocation routines
  30  */
  31
  32 /*
  33  * Calculate the block group number and offset into the block/cluster
  34  * allocation bitmap, given a block number
  35  */
  36 void ext4_get_group_no_and_offset(struct super_block *sb, ext4_fsblk_t blocknr,
  37                 ext4_group_t *blockgrpp, ext4_grpblk_t *offsetp)
  38 {
  39         struct ext4_super_block *es = EXT4_SB(sb)->s_es;
  40         ext4_grpblk_t offset;
  41
  42         blocknr = blocknr - le32_to_cpu(es->s_first_data_block);
  43         offset = do_div(blocknr, EXT4_BLOCKS_PER_GROUP(sb)) >>
  44                 EXT4_SB(sb)->s_cluster_bits;
  45         if (offsetp)
  46                 *offsetp = offset;
  47         if (blockgrpp)
  48                 *blockgrpp = blocknr;
  49
  50 }
  51
  52 static int ext4_block_in_group(struct super_block *sb, ext4_fsblk_t block,
  53                         ext4_group_t block_group)
  54 {
  55         ext4_group_t actual_group;
  56         ext4_get_group_no_and_offset(sb, block, &actual_group, NULL);
  57         if (actual_group == block_group)
  58                 return 1;
  59         return 0;
  60 }
  61
  62 /* Return the number of clusters used for file system metadata; this
  63  * represents the overhead needed by the file system.
  64  */
  65 unsigned ext4_num_overhead_clusters(struct super_block *sb,
  66                                     ext4_group_t block_group,
  67                                     struct ext4_group_desc *gdp)
  68 {
  69         unsigned num_clusters;
  70         int block_cluster = -1, inode_cluster = -1, itbl_cluster = -1, i, c;
  71         ext4_fsblk_t start = ext4_group_first_block_no(sb, block_group);
  72         ext4_fsblk_t itbl_blk;
  73         struct ext4_sb_info *sbi = EXT4_SB(sb);
  74
  75         /* This is the number of clusters used by the superblock,
  76          * block group descriptors, and reserved block group
  77          * descriptor blocks */
  78         num_clusters = ext4_num_base_meta_clusters(sb, block_group);
  79
  80         /*
  81          * For the allocation bitmaps and inode table, we first need
  82          * to check to see if the block is in the block group.  If it
  83          * is, then check to see if the cluster is already accounted
  84          * for in the clusters used for the base metadata cluster, or
  85          * if we can increment the base metadata cluster to include
  86          * that block.  Otherwise, we will have to track the cluster
  87          * used for the allocation bitmap or inode table explicitly.
  88          * Normally all of these blocks are contiguous, so the special
  89          * case handling shouldn't be necessary except for *very*
  90          * unusual file system layouts.
  91          */
  92         if (ext4_block_in_group(sb, ext4_block_bitmap(sb, gdp), block_group)) {
  93                 block_cluster = EXT4_B2C(sbi, (start -
  94                                                ext4_block_bitmap(sb, gdp)));
  95                 if (block_cluster < num_clusters)
  96                         block_cluster = -1;
  97                 else if (block_cluster == num_clusters) {
  98                         num_clusters++;
  99                         block_cluster = -1;
 100                 }
 101         }
 102
 103         if (ext4_block_in_group(sb, ext4_inode_bitmap(sb, gdp), block_group)) {
 104                 inode_cluster = EXT4_B2C(sbi,
 105                                          start - ext4_inode_bitmap(sb, gdp));
 106                 if (inode_cluster < num_clusters)
 107                         inode_cluster = -1;
 108                 else if (inode_cluster == num_clusters) {
 109                         num_clusters++;
 110                         inode_cluster = -1;
 111                 }
 112         }
 113
 114         itbl_blk = ext4_inode_table(sb, gdp);
 115         for (i = 0; i < sbi->s_itb_per_group; i++) {
 116                 if (ext4_block_in_group(sb, itbl_blk + i, block_group)) {
 117                         c = EXT4_B2C(sbi, start - itbl_blk + i);
 118                         if ((c < num_clusters) || (c == inode_cluster) ||
 119                             (c == block_cluster) || (c == itbl_cluster))
 120                                 continue;
 121                         if (c == num_clusters) {
 122                                 num_clusters++;
 123                                 continue;
 124                         }
 125                         num_clusters++;
 126                         itbl_cluster = c;
 127                 }
 128         }
 129
 130         if (block_cluster != -1)
 131                 num_clusters++;
 132         if (inode_cluster != -1)
 133                 num_clusters++;
 134
 135         return num_clusters;
 136 }
 137
 138 static unsigned int num_clusters_in_group(struct super_block *sb,
 139                                           ext4_group_t block_group)
 140 {
 141         unsigned int blocks;
 142
 143         if (block_group == ext4_get_groups_count(sb) - 1) {
 144                 /*
 145                  * Even though mke2fs always initializes the first and
 146                  * last group, just in case some other tool was used,
 147                  * we need to make sure we calculate the right free
 148                  * blocks.
 149                  */
 150                 blocks = ext4_blocks_count(EXT4_SB(sb)->s_es) -
 151                         ext4_group_first_block_no(sb, block_group);
 152         } else
 153                 blocks = EXT4_BLOCKS_PER_GROUP(sb);
 154         return EXT4_NUM_B2C(EXT4_SB(sb), blocks);
 155 }
 156
 157 /* Initializes an uninitialized block bitmap */
 158 void ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
 159                             ext4_group_t block_group,
 160                             struct ext4_group_desc *gdp)
 161 {
 162         unsigned int bit, bit_max;
 163         struct ext4_sb_info *sbi = EXT4_SB(sb);
 164         ext4_fsblk_t start, tmp;
 165         int flex_bg = 0;
 166
 167         J_ASSERT_BH(bh, buffer_locked(bh));
 168
 169         /* If checksum is bad mark all blocks used to prevent allocation
 170          * essentially implementing a per-group read-only flag. */
 171         if (!ext4_group_desc_csum_verify(sbi, block_group, gdp)) {
 172                 ext4_error(sb, "Checksum bad for group %u", block_group);
 173                 ext4_free_group_clusters_set(sb, gdp, 0);
 174                 ext4_free_inodes_set(sb, gdp, 0);
 175                 ext4_itable_unused_set(sb, gdp, 0);
 176                 memset(bh->b_data, 0xff, sb->s_blocksize);
 177                 return;
 178         }
 179         memset(bh->b_data, 0, sb->s_blocksize);
 180
 181         bit_max = ext4_num_base_meta_clusters(sb, block_group);
 182         for (bit = 0; bit < bit_max; bit++)
 183                 ext4_set_bit(bit, bh->b_data);
 184
 185         start = ext4_group_first_block_no(sb, block_group);
 186
 187         if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG))
 188                 flex_bg = 1;
 189
 190         /* Set bits for block and inode bitmaps, and inode table */
 191         tmp = ext4_block_bitmap(sb, gdp);
 192         if (!flex_bg || ext4_block_in_group(sb, tmp, block_group))
 193                 ext4_set_bit(EXT4_B2C(sbi, tmp - start), bh->b_data);
 194
 195         tmp = ext4_inode_bitmap(sb, gdp);
 196         if (!flex_bg || ext4_block_in_group(sb, tmp, block_group))
 197                 ext4_set_bit(EXT4_B2C(sbi, tmp - start), bh->b_data);
 198
 199         tmp = ext4_inode_table(sb, gdp);
 200         for (; tmp < ext4_inode_table(sb, gdp) +
 201                      sbi->s_itb_per_group; tmp++) {
 202                 if (!flex_bg || ext4_block_in_group(sb, tmp, block_group))
 203                         ext4_set_bit(EXT4_B2C(sbi, tmp - start), bh->b_data);
 204         }
 205
 206         /*
 207          * Also if the number of blocks within the group is less than
 208          * the blocksize * 8 ( which is the size of bitmap ), set rest
 209          * of the block bitmap to 1
 210          */
 211         ext4_mark_bitmap_end(num_clusters_in_group(sb, block_group),
 212                              sb->s_blocksize * 8, bh->b_data);
 213 }
 214
 215 /* Return the number of free blocks in a block group.  It is used when
 216  * the block bitmap is uninitialized, so we can't just count the bits
 217  * in the bitmap. */
 218 unsigned ext4_free_clusters_after_init(struct super_block *sb,
 219                                        ext4_group_t block_group,
 220                                        struct ext4_group_desc *gdp)
 221 {
 222         return num_clusters_in_group(sb, block_group) -
 223                 ext4_num_overhead_clusters(sb, block_group, gdp);
 224 }
 225
 226 /*
 227  * The free blocks are managed by bitmaps.  A file system contains several
 228  * blocks groups.  Each group contains 1 bitmap block for blocks, 1 bitmap
 229  * block for inodes, N blocks for the inode table and data blocks.
 230  *
 231  * The file system contains group descriptors which are located after the
 232  * super block.  Each descriptor contains the number of the bitmap block and
 233  * the free blocks count in the block.  The descriptors are loaded in memory
 234  * when a file system is mounted (see ext4_fill_super).
 235  */
 236
 237 /**
 238  * ext4_get_group_desc() -- load group descriptor from disk
 239  * @sb:                 super block
 240  * @block_group:        given block group
 241  * @bh:                 pointer to the buffer head to store the block
 242  *                      group descriptor
 243  */
 244 struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
 245                                              ext4_group_t block_group,
 246                                              struct buffer_head **bh)
 247 {
 248         unsigned int group_desc;
 249         unsigned int offset;
 250         ext4_group_t ngroups = ext4_get_groups_count(sb);
 251         struct ext4_group_desc *desc;
 252         struct ext4_sb_info *sbi = EXT4_SB(sb);
 253
 254         if (block_group >= ngroups) {
 255                 ext4_error(sb, "block_group >= groups_count - block_group = %u,"
 256                            " groups_count = %u", block_group, ngroups);
 257
 258                 return NULL;
 259         }
 260
 261         group_desc = block_group >> EXT4_DESC_PER_BLOCK_BITS(sb);
 262         offset = block_group & (EXT4_DESC_PER_BLOCK(sb) - 1);
 263         if (!sbi->s_group_desc[group_desc]) {
 264                 ext4_error(sb, "Group descriptor not loaded - "
 265                            "block_group = %u, group_desc = %u, desc = %u",
 266                            block_group, group_desc, offset);
 267                 return NULL;
 268         }
 269
 270         desc = (struct ext4_group_desc *)(
 271                 (__u8 *)sbi->s_group_desc[group_desc]->b_data +
 272                 offset * EXT4_DESC_SIZE(sb));
 273         if (bh)
 274                 *bh = sbi->s_group_desc[group_desc];
 275         return desc;
 276 }
 277
 278 static int ext4_valid_block_bitmap(struct super_block *sb,
 279                                         struct ext4_group_desc *desc,
 280                                         unsigned int block_group,
 281                                         struct buffer_head *bh)
 282 {
 283         ext4_grpblk_t offset;
 284         ext4_grpblk_t next_zero_bit;
 285         ext4_fsblk_t bitmap_blk;
 286         ext4_fsblk_t group_first_block;
 287
 288         if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {
 289                 /* with FLEX_BG, the inode/block bitmaps and itable
 290                  * blocks may not be in the group at all
 291                  * so the bitmap validation will be skipped for those groups
 292                  * or it has to also read the block group where the bitmaps
 293                  * are located to verify they are set.
 294                  */
 295                 return 1;
 296         }
 297         group_first_block = ext4_group_first_block_no(sb, block_group);
 298
 299         /* check whether block bitmap block number is set */
 300         bitmap_blk = ext4_block_bitmap(sb, desc);
 301         offset = bitmap_blk - group_first_block;
 302         if (!ext4_test_bit(offset, bh->b_data))
 303                 /* bad block bitmap */
 304                 goto err_out;
 305
 306         /* check whether the inode bitmap block number is set */
 307         bitmap_blk = ext4_inode_bitmap(sb, desc);
 308         offset = bitmap_blk - group_first_block;
 309         if (!ext4_test_bit(offset, bh->b_data))
 310                 /* bad block bitmap */
 311                 goto err_out;
 312
 313         /* check whether the inode table block number is set */
 314         bitmap_blk = ext4_inode_table(sb, desc);
 315         offset = bitmap_blk - group_first_block;
 316         next_zero_bit = ext4_find_next_zero_bit(bh->b_data,
 317                                 offset + EXT4_SB(sb)->s_itb_per_group,
 318                                 offset);
 319         if (next_zero_bit >= offset + EXT4_SB(sb)->s_itb_per_group)
 320                 /* good bitmap for inode tables */
 321                 return 1;
 322
 323 err_out:
 324         ext4_error(sb, "Invalid block bitmap - block_group = %d, block = %llu",
 325                         block_group, bitmap_blk);
 326         return 0;
 327 }
 328 /**
 329  * ext4_read_block_bitmap()
 330  * @sb:                 super block
 331  * @block_group:        given block group
 332  *
 333  * Read the bitmap for a given block_group,and validate the
 334  * bits for block/inode/inode tables are set in the bitmaps
 335  *
 336  * Return buffer_head on success or NULL in case of failure.
 337  */
 338 struct buffer_head *
 339 ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
 340 {
 341         struct ext4_group_desc *desc;
 342         struct buffer_head *bh = NULL;
 343         ext4_fsblk_t bitmap_blk;
 344
 345         desc = ext4_get_group_desc(sb, block_group, NULL);
 346         if (!desc)
 347                 return NULL;
 348         bitmap_blk = ext4_block_bitmap(sb, desc);
 349         bh = sb_getblk(sb, bitmap_blk);
 350         if (unlikely(!bh)) {
 351                 ext4_error(sb, "Cannot read block bitmap - "
 352                             "block_group = %u, block_bitmap = %llu",
 353                             block_group, bitmap_blk);
 354                 return NULL;
 355         }
 356
 357         if (bitmap_uptodate(bh))
 358                 return bh;
 359
 360         lock_buffer(bh);
 361         if (bitmap_uptodate(bh)) {
 362                 unlock_buffer(bh);
 363                 return bh;
 364         }
 365         ext4_lock_group(sb, block_group);
 366         if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
 367                 ext4_init_block_bitmap(sb, bh, block_group, desc);
 368                 set_bitmap_uptodate(bh);
 369                 set_buffer_uptodate(bh);
 370                 ext4_unlock_group(sb, block_group);
 371                 unlock_buffer(bh);
 372                 return bh;
 373         }
 374         ext4_unlock_group(sb, block_group);
 375         if (buffer_uptodate(bh)) {
 376                 /*
 377                  * if not uninit if bh is uptodate,
 378                  * bitmap is also uptodate
 379                  */
 380                 set_bitmap_uptodate(bh);
 381                 unlock_buffer(bh);
 382                 return bh;
 383         }
 384         /*
 385          * submit the buffer_head for read. We can
 386          * safely mark the bitmap as uptodate now.
 387          * We do it here so the bitmap uptodate bit
 388          * get set with buffer lock held.
 389          */
 390         trace_ext4_read_block_bitmap_load(sb, block_group);
 391         set_bitmap_uptodate(bh);
 392         if (bh_submit_read(bh) < 0) {
 393                 put_bh(bh);
 394                 ext4_error(sb, "Cannot read block bitmap - "
 395                             "block_group = %u, block_bitmap = %llu",
 396                             block_group, bitmap_blk);
 397                 return NULL;
 398         }
 399         ext4_valid_block_bitmap(sb, desc, block_group, bh);
 400         /*
 401          * file system mounted not to panic on error,
 402          * continue with corrupt bitmap
 403          */
 404         return bh;
 405 }
 406
 407 /**
 408  * ext4_has_free_clusters()
 409  * @sbi:        in-core super block structure.
 410  * @nclusters:  number of needed blocks
 411  * @flags:      flags from ext4_mb_new_blocks()
 412  *
 413  * Check if filesystem has nclusters free & available for allocation.
 414  * On success return 1, return 0 on failure.
 415  */
 416 static int ext4_has_free_clusters(struct ext4_sb_info *sbi,
 417                                   s64 nclusters, unsigned int flags)
 418 {
 419         s64 free_clusters, dirty_clusters, root_clusters;
 420         struct percpu_counter *fcc = &sbi->s_freeclusters_counter;
 421         struct percpu_counter *dcc = &sbi->s_dirtyclusters_counter;
 422
 423         free_clusters  = percpu_counter_read_positive(fcc);
 424         dirty_clusters = percpu_counter_read_positive(dcc);
 425         root_clusters = EXT4_B2C(sbi, ext4_r_blocks_count(sbi->s_es));
 426
 427         if (free_clusters - (nclusters + root_clusters + dirty_clusters) <
 428                                         EXT4_FREECLUSTERS_WATERMARK) {
 429                 free_clusters  = EXT4_C2B(sbi, percpu_counter_sum_positive(fcc));
 430                 dirty_clusters = percpu_counter_sum_positive(dcc);
 431         }
 432         /* Check whether we have space after accounting for current
 433          * dirty clusters & root reserved clusters.
 434          */
 435         if (free_clusters >= ((root_clusters + nclusters) + dirty_clusters))
 436                 return 1;
 437
 438         /* Hm, nope.  Are (enough) root reserved clusters available? */
 439         if (sbi->s_resuid == current_fsuid() ||
 440             ((sbi->s_resgid != 0) && in_group_p(sbi->s_resgid)) ||
 441             capable(CAP_SYS_RESOURCE) ||
 442                 (flags & EXT4_MB_USE_ROOT_BLOCKS)) {
 443
 444                 if (free_clusters >= (nclusters + dirty_clusters))
 445                         return 1;
 446         }
 447
 448         return 0;
 449 }
 450
 451 int ext4_claim_free_clusters(struct ext4_sb_info *sbi,
 452                              s64 nclusters, unsigned int flags)
 453 {
 454         if (ext4_has_free_clusters(sbi, nclusters, flags)) {
 455                 percpu_counter_add(&sbi->s_dirtyclusters_counter, nclusters);
 456                 return 0;
 457         } else
 458                 return -ENOSPC;
 459 }
 460
 461 /**
 462  * ext4_should_retry_alloc()
 463  * @sb:                 super block
 464  * @retries             number of attemps has been made
 465  *
 466  * ext4_should_retry_alloc() is called when ENOSPC is returned, and if
 467  * it is profitable to retry the operation, this function will wait
 468  * for the current or committing transaction to complete, and then
 469  * return TRUE.
 470  *
 471  * if the total number of retries exceed three times, return FALSE.
 472  */
 473 int ext4_should_retry_alloc(struct super_block *sb, int *retries)
 474 {
 475         if (!ext4_has_free_clusters(EXT4_SB(sb), 1, 0) ||
 476             (*retries)++ > 3 ||
 477             !EXT4_SB(sb)->s_journal)
 478                 return 0;
 479
 480         jbd_debug(1, "%s: retrying operation after ENOSPC\n", sb->s_id);
 481
 482         return jbd2_journal_force_commit_nested(EXT4_SB(sb)->s_journal);
 483 }
 484
 485 /*
 486  * ext4_new_meta_blocks() -- allocate block for meta data (indexing) blocks
 487  *
 488  * @handle:             handle to this transaction
 489  * @inode:              file inode
 490  * @goal:               given target block(filesystem wide)
 491  * @count:              pointer to total number of clusters needed
 492  * @errp:               error code
 493  *
 494  * Return 1st allocated block number on success, *count stores total account
 495  * error stores in errp pointer
 496  */
 497 ext4_fsblk_t ext4_new_meta_blocks(handle_t *handle, struct inode *inode,
 498                                   ext4_fsblk_t goal, unsigned int flags,
 499                                   unsigned long *count, int *errp)
 500 {
 501         struct ext4_allocation_request ar;
 502         ext4_fsblk_t ret;
 503
 504         memset(&ar, 0, sizeof(ar));
 505         /* Fill with neighbour allocated blocks */
 506         ar.inode = inode;
 507         ar.goal = goal;
 508         ar.len = count ? *count : 1;
 509         ar.flags = flags;
 510
 511         ret = ext4_mb_new_blocks(handle, &ar, errp);
 512         if (count)
 513                 *count = ar.len;
 514         /*
 515          * Account for the allocated meta blocks.  We will never
 516          * fail EDQUOT for metdata, but we do account for it.
 517          */
 518         if (!(*errp) &&
 519             ext4_test_inode_state(inode, EXT4_STATE_DELALLOC_RESERVED)) {
 520                 spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
 521                 EXT4_I(inode)->i_allocated_meta_blocks += ar.len;
 522                 spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
 523                 dquot_alloc_block_nofail(inode,
 524                                 EXT4_C2B(EXT4_SB(inode->i_sb), ar.len));
 525         }
 526         return ret;
 527 }
 528
 529 /**
 530  * ext4_count_free_clusters() -- count filesystem free clusters
 531  * @sb:         superblock
 532  *
 533  * Adds up the number of free clusters from each block group.
 534  */
 535 ext4_fsblk_t ext4_count_free_clusters(struct super_block *sb)
 536 {
 537         ext4_fsblk_t desc_count;
 538         struct ext4_group_desc *gdp;
 539         ext4_group_t i;
 540         ext4_group_t ngroups = ext4_get_groups_count(sb);
 541 #ifdef EXT4FS_DEBUG
 542         struct ext4_super_block *es;
 543         ext4_fsblk_t bitmap_count;
 544         unsigned int x;
 545         struct buffer_head *bitmap_bh = NULL;
 546
 547         es = EXT4_SB(sb)->s_es;
 548         desc_count = 0;
 549         bitmap_count = 0;
 550         gdp = NULL;
 551
 552         for (i = 0; i < ngroups; i++) {
 553                 gdp = ext4_get_group_desc(sb, i, NULL);
 554                 if (!gdp)
 555                         continue;
 556                 desc_count += ext4_free_group_clusters(sb, gdp);
 557                 brelse(bitmap_bh);
 558                 bitmap_bh = ext4_read_block_bitmap(sb, i);
 559                 if (bitmap_bh == NULL)
 560                         continue;
 561
 562                 x = ext4_count_free(bitmap_bh, sb->s_blocksize);
 563                 printk(KERN_DEBUG "group %u: stored = %d, counted = %u\n",
 564                         i, ext4_free_group_clusters(sb, gdp), x);
 565                 bitmap_count += x;
 566         }
 567         brelse(bitmap_bh);
 568         printk(KERN_DEBUG "ext4_count_free_clusters: stored = %llu"
 569                ", computed = %llu, %llu\n",
 570                EXT4_B2C(EXT4_SB(sb), ext4_free_blocks_count(es)),
 571                desc_count, bitmap_count);
 572         return bitmap_count;
 573 #else
 574         desc_count = 0;
 575         for (i = 0; i < ngroups; i++) {
 576                 gdp = ext4_get_group_desc(sb, i, NULL);
 577                 if (!gdp)
 578                         continue;
 579                 desc_count += ext4_free_group_clusters(sb, gdp);
 580         }
 581
 582         return desc_count;
 583 #endif
 584 }
 585
 586 static inline int test_root(ext4_group_t a, int b)
 587 {
 588         int num = b;
 589
 590         while (a > num)
 591                 num *= b;
 592         return num == a;
 593 }
 594
 595 static int ext4_group_sparse(ext4_group_t group)
 596 {
 597         if (group <= 1)
 598                 return 1;
 599         if (!(group & 1))
 600                 return 0;
 601         return (test_root(group, 7) || test_root(group, 5) ||
 602                 test_root(group, 3));
 603 }
 604
 605 /**
 606  *      ext4_bg_has_super - number of blocks used by the superblock in group
 607  *      @sb: superblock for filesystem
 608  *      @group: group number to check
 609  *
 610  *      Return the number of blocks used by the superblock (primary or backup)
 611  *      in this group.  Currently this will be only 0 or 1.
 612  */
 613 int ext4_bg_has_super(struct super_block *sb, ext4_group_t group)
 614 {
 615         if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
 616                                 EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER) &&
 617                         !ext4_group_sparse(group))
 618                 return 0;
 619         return 1;
 620 }
 621
 622 static unsigned long ext4_bg_num_gdb_meta(struct super_block *sb,
 623                                         ext4_group_t group)
 624 {
 625         unsigned long metagroup = group / EXT4_DESC_PER_BLOCK(sb);
 626         ext4_group_t first = metagroup * EXT4_DESC_PER_BLOCK(sb);
 627         ext4_group_t last = first + EXT4_DESC_PER_BLOCK(sb) - 1;
 628
 629         if (group == first || group == first + 1 || group == last)
 630                 return 1;
 631         return 0;
 632 }
 633
 634 static unsigned long ext4_bg_num_gdb_nometa(struct super_block *sb,
 635                                         ext4_group_t group)
 636 {
 637         if (!ext4_bg_has_super(sb, group))
 638                 return 0;
 639
 640         if (EXT4_HAS_INCOMPAT_FEATURE(sb,EXT4_FEATURE_INCOMPAT_META_BG))
 641                 return le32_to_cpu(EXT4_SB(sb)->s_es->s_first_meta_bg);
 642         else
 643                 return EXT4_SB(sb)->s_gdb_count;
 644 }
 645
 646 /**
 647  *      ext4_bg_num_gdb - number of blocks used by the group table in group
 648  *      @sb: superblock for filesystem
 649  *      @group: group number to check
 650  *
 651  *      Return the number of blocks used by the group descriptor table
 652  *      (primary or backup) in this group.  In the future there may be a
 653  *      different number of descriptor blocks in each group.
 654  */
 655 unsigned long ext4_bg_num_gdb(struct super_block *sb, ext4_group_t group)
 656 {
 657         unsigned long first_meta_bg =
 658                         le32_to_cpu(EXT4_SB(sb)->s_es->s_first_meta_bg);
 659         unsigned long metagroup = group / EXT4_DESC_PER_BLOCK(sb);
 660
 661         if (!EXT4_HAS_INCOMPAT_FEATURE(sb,EXT4_FEATURE_INCOMPAT_META_BG) ||
 662                         metagroup < first_meta_bg)
 663                 return ext4_bg_num_gdb_nometa(sb, group);
 664
 665         return ext4_bg_num_gdb_meta(sb,group);
 666
 667 }
 668
 669 /*
 670  * This function returns the number of file system metadata clusters at
 671  * the beginning of a block group, including the reserved gdt blocks.
 672  */
 673 static unsigned ext4_num_base_meta_clusters(struct super_block *sb,
 674                                      ext4_group_t block_group)
 675 {
 676         struct ext4_sb_info *sbi = EXT4_SB(sb);
 677         unsigned num;
 678
 679         /* Check for superblock and gdt backups in this group */
 680         num = ext4_bg_has_super(sb, block_group);
 681
 682         if (!EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG) ||
 683             block_group < le32_to_cpu(sbi->s_es->s_first_meta_bg) *
 684                           sbi->s_desc_per_block) {
 685                 if (num) {
 686                         num += ext4_bg_num_gdb(sb, block_group);
 687                         num += le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
 688                 }
 689         } else { /* For META_BG_BLOCK_GROUPS */
 690                 num += ext4_bg_num_gdb(sb, block_group);
 691         }
 692         return EXT4_NUM_B2C(sbi, num);
 693 }
 694 /**
 695  *      ext4_inode_to_goal_block - return a hint for block allocation
 696  *      @inode: inode for block allocation
 697  *
 698  *      Return the ideal location to start allocating blocks for a
 699  *      newly created inode.
 700  */
 701 ext4_fsblk_t ext4_inode_to_goal_block(struct inode *inode)
 702 {
 703         struct ext4_inode_info *ei = EXT4_I(inode);
 704         ext4_group_t block_group;
 705         ext4_grpblk_t colour;
 706         int flex_size = ext4_flex_bg_size(EXT4_SB(inode->i_sb));
 707         ext4_fsblk_t bg_start;
 708         ext4_fsblk_t last_block;
 709
 710         block_group = ei->i_block_group;
 711         if (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) {
 712                 /*
 713                  * If there are at least EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME
 714                  * block groups per flexgroup, reserve the first block
 715                  * group for directories and special files.  Regular
 716                  * files will start at the second block group.  This
 717                  * tends to speed up directory access and improves
 718                  * fsck times.
 719                  */
 720                 block_group &= ~(flex_size-1);
 721                 if (S_ISREG(inode->i_mode))
 722                         block_group++;
 723         }
 724         bg_start = ext4_group_first_block_no(inode->i_sb, block_group);
 725         last_block = ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es) - 1;
 726
 727         /*
 728          * If we are doing delayed allocation, we don't need take
 729          * colour into account.
 730          */
 731         if (test_opt(inode->i_sb, DELALLOC))
 732                 return bg_start;
 733
 734         if (bg_start + EXT4_BLOCKS_PER_GROUP(inode->i_sb) <= last_block)
 735                 colour = (current->pid % 16) *
 736                         (EXT4_BLOCKS_PER_GROUP(inode->i_sb) / 16);
 737         else
 738                 colour = (current->pid % 16) * ((last_block - bg_start) / 16);
 739         return bg_start + colour;
 740 }
 741