ESA result on minix file system balloc.c

esa_balloc.c.xml

  <file path="/Volumes/HappyPecanDisk/repos/minix-src/servers/ext2/balloc.c"> 
    <content> 
      <text><![CDATA[/* This files manages blocks allocation and deallocation.
 *
 * The entry points into this file are:
 *   discard_preallocated_blocks: Discard preallocated blocks.
 *   alloc_block: somebody wants to allocate a block; find one.
 *   free_block:  indicate that a block is available for new allocation.
 *
 * Created:
 *   June 2010 (Evgeniy Ivanov)
 */

#include "fs.h"
#include <string.h>
#include <stdlib.h>
#include <minix/com.h>
#include <minix/u64.h>
#include "buf.h"
#include "inode.h"
#include "super.h"
#include "const.h"


static block_t alloc_block_bit(struct super_block *sp, block_t origin,
  struct inode *rip);

/*===========================================================================*
 *                      discard_preallocated_blocks                          *
 *===========================================================================*/
void discard_preallocated_blocks(struct inode *rip)
{
/* When called for rip, discard (free) blocks preallocated for rip,
 * otherwise discard all preallocated blocks.
 * Normally it should be called in following situations:
 * 1. File is closed.
 * 2. File is truncated.
 * 3. Non-sequential write.
 * 4. inode is "unloaded" from the memory.
 * 5. No free blocks left (discard all preallocated blocks).
 */
  int i;

  if (rip) {
  rip->i_prealloc_count = rip->i_prealloc_index = 0;
  for (i = 0; i < EXT2_PREALLOC_BLOCKS; i++) {
    if (rip->i_prealloc_blocks[i] != NO_BLOCK) {
      free_block(rip->i_sp, rip->i_prealloc_blocks[i]);
      rip->i_prealloc_blocks[i] = NO_BLOCK;
    }
  }
  return;
  }

  /* Discard all allocated blocks.
   * Probably there are just few blocks on the disc, so forbid preallocation.*/
  for(rip = &inode[0]; rip < &inode[NR_INODES]; rip++) {
  rip->i_prealloc_count = rip->i_prealloc_index = 0;
  rip->i_preallocation = 0; /* forbid preallocation */
  for (i = 0; i < EXT2_PREALLOC_BLOCKS; i++) {
    if (rip->i_prealloc_blocks[i] != NO_BLOCK) {
      free_block(rip->i_sp, rip->i_prealloc_blocks[i]);
      rip->i_prealloc_blocks[i] = NO_BLOCK;
    }
  }
  }
}


/*===========================================================================*
 *                              alloc_block                                  *
 *===========================================================================*/
block_t alloc_block(struct inode *rip, block_t block)
{
/* Allocate a block for inode. If block is provided, then use it as a goal:
 * try to allocate this block or his neghbors.
 * If block is not provided then goal is group, where inode lives.
 */
  block_t goal;
  block_t b;
  struct super_block *sp = rip->i_sp;

  if (sp->s_rd_only)
  panic("can't alloc block on read-only filesys.");

  /* Check for free blocks. First time discard preallocation,
   * next time return NO_BLOCK
   */
  if (!opt.use_reserved_blocks &&
      sp->s_free_blocks_count <= sp->s_r_blocks_count) {
  discard_preallocated_blocks(NULL);
  } else if (sp->s_free_blocks_count <= EXT2_PREALLOC_BLOCKS) {
  discard_preallocated_blocks(NULL);
  }

  if (!opt.use_reserved_blocks &&
      sp->s_free_blocks_count <= sp->s_r_blocks_count) {
  return(NO_BLOCK);
  } else if (sp->s_free_blocks_count == 0) {
  return(NO_BLOCK);
  }

  if (block != NO_BLOCK) {
  goal = block;
  if (rip->i_preallocation && rip->i_prealloc_count > 0) {
    /* check if goal is preallocated */
    b = rip->i_prealloc_blocks[rip->i_prealloc_index];
    if (block == b || (block + 1) == b) {
      /* use preallocated block */
      rip->i_prealloc_blocks[rip->i_prealloc_index] = NO_BLOCK;
      rip->i_prealloc_count--;
      rip->i_prealloc_index++;
      if (rip->i_prealloc_index >= EXT2_PREALLOC_BLOCKS) {
        rip->i_prealloc_index = 0;
        ASSERT(rip->i_prealloc_count == 0);
      }
      rip->i_bsearch = b;
      return b;
    } else {
      /* probably non-sequential write operation,
       * disable preallocation for this inode.
       */
      rip->i_preallocation = 0;
      discard_preallocated_blocks(rip);
    }
  }
  } else {
    int group = (rip->i_num - 1) / sp->s_inodes_per_group;
    goal = sp->s_blocks_per_group*group + sp->s_first_data_block;
  }

  if (rip->i_preallocation && rip->i_prealloc_count) {
  ext2_debug("There're preallocated blocks, but they're\
      neither used or freed!");
  }

  b = alloc_block_bit(sp, goal, rip);

  if (b != NO_BLOCK)
  rip->i_bsearch = b;

  return b;
}


static void check_block_number(block_t block, struct super_block *sp,
  struct group_desc *gd);

/*===========================================================================*
 *                              alloc_block_bit                              *
 *===========================================================================*/
static block_t alloc_block_bit(sp, goal, rip)
struct super_block *sp;   /* the filesystem to allocate from */
block_t goal;     /* try to allocate near this block */
struct inode *rip;    /* used for preallocation */
{
  block_t block = NO_BLOCK; /* allocated block */
  int word;     /* word in block bitmap */
  bit_t bit = -1;
  int group;
  char update_bsearch = FALSE;
  int i;

  if (goal >= sp->s_blocks_count ||
      (goal < sp->s_first_data_block && goal != 0)) {
  goal = sp->s_bsearch;
  }

  if (goal <= sp->s_bsearch) {
  /* No reason to search in a place with no free blocks */
  goal = sp->s_bsearch;
  update_bsearch = TRUE;
  }

  /* Figure out where to start the bit search. */
  word = ((goal - sp->s_first_data_block) % sp->s_blocks_per_group)
      / FS_BITCHUNK_BITS;

  /* Try to allocate block at any group starting from the goal's group.
   * First time goal's group is checked from the word=goal, after all
   * groups checked, it's checked again from word=0, that's why "i <=".
   */
  group = (goal - sp->s_first_data_block) / sp->s_blocks_per_group;
  for (i = 0; i <= sp->s_groups_count; i++, group++) {
  struct buf *bp;
  struct group_desc *gd;

  if (group >= sp->s_groups_count)
    group = 0;

  gd = get_group_desc(group);
  if (gd == NULL)
    panic("can't get group_desc to alloc block");

  if (gd->free_blocks_count == 0) {
    word = 0;
    continue;
  }

  bp = get_block(sp->s_dev, gd->block_bitmap, NORMAL);

  if (rip->i_preallocation &&
      gd->free_blocks_count >= (EXT2_PREALLOC_BLOCKS * 4) ) {
    /* Try to preallocate blocks */
    if (rip->i_prealloc_count != 0) {
      /* kind of glitch... */
      discard_preallocated_blocks(rip);
      ext2_debug("warning, discarding previously preallocated\
            blocks! It had to be done by another code.");
    }
    ASSERT(rip->i_prealloc_count == 0);
    /* we preallocate bytes only */
    ASSERT(EXT2_PREALLOC_BLOCKS == sizeof(char)*CHAR_BIT);

    bit = setbyte(b_bitmap(bp), sp->s_blocks_per_group);
    if (bit != -1) {
      block = bit + sp->s_first_data_block +
          group * sp->s_blocks_per_group;
      check_block_number(block, sp, gd);

      /* We preallocate a byte starting from block.
       * First preallocated block will be returned as
       * normally allocated block.
       */
      for (i = 1; i < EXT2_PREALLOC_BLOCKS; i++) {
        check_block_number(block + i, sp, gd);
        rip->i_prealloc_blocks[i-1] = block + i;
      }
      rip->i_prealloc_index = 0;
      rip->i_prealloc_count = EXT2_PREALLOC_BLOCKS - 1;

      lmfs_markdirty(bp);
      put_block(bp, MAP_BLOCK);

      gd->free_blocks_count -= EXT2_PREALLOC_BLOCKS;
      sp->s_free_blocks_count -= EXT2_PREALLOC_BLOCKS;
      lmfs_blockschange(sp->s_dev, -EXT2_PREALLOC_BLOCKS);
      group_descriptors_dirty = 1;
      return block;
    }
  }

        bit = setbit(b_bitmap(bp), sp->s_blocks_per_group, word);
  if (bit == -1) {
    if (word == 0) {
      panic("ext2: allocator failed to allocate a bit in bitmap\
        with free bits.");
    } else {
      word = 0;
      continue;
    }
  }

  block = sp->s_first_data_block + group * sp->s_blocks_per_group + bit;
  check_block_number(block, sp, gd);

  lmfs_markdirty(bp);
  put_block(bp, MAP_BLOCK);

  gd->free_blocks_count--;
  sp->s_free_blocks_count--;
  lmfs_blockschange(sp->s_dev, -1);
  group_descriptors_dirty = 1;

  if (update_bsearch && block != -1 && block != NO_BLOCK) {
    /* We searched from the beginning, update bsearch. */
    sp->s_bsearch = block;
  }

  return block;
  }

  return block;
}


/*===========================================================================*
 *                        free_block                                       *
 *===========================================================================*/
void free_block(struct super_block *sp, bit_t bit_returned)
{
/* Return a block by turning off its bitmap bit. */
  int group;    /* group number of bit_returned */
  int bit;    /* bit_returned number within its group */
  struct buf *bp;
  struct group_desc *gd;

  if (sp->s_rd_only)
  panic("can't free bit on read-only filesys.");

  if (bit_returned >= sp->s_blocks_count ||
      bit_returned < sp->s_first_data_block)
  panic("trying to free block %d beyond blocks scope.",
    bit_returned);

  /* At first search group, to which bit_returned belongs to
   * and figure out in what word bit is stored.
   */
  group = (bit_returned - sp->s_first_data_block) / sp->s_blocks_per_group;
  bit = (bit_returned - sp->s_first_data_block) % sp->s_blocks_per_group;

  gd = get_group_desc(group);
  if (gd == NULL)
  panic("can't get group_desc to alloc block");

  /* We might be buggy (No way! :P), so check if we deallocate
   * data block, but not control (system) block.
   * This should never happen.
   */
  if (bit_returned == gd->inode_bitmap || bit_returned == gd->block_bitmap
      || (bit_returned >= gd->inode_table
          && bit_returned < (gd->inode_table + sp->s_itb_per_group))) {
  ext2_debug("ext2: freeing non-data block %d\n", bit_returned);
  panic("trying to deallocate \
    system/control block, hardly poke author.");
  }

  bp = get_block(sp->s_dev, gd->block_bitmap, NORMAL);

  if (unsetbit(b_bitmap(bp), bit))
  panic("Tried to free unused block", bit_returned);

  lmfs_markdirty(bp);
  put_block(bp, MAP_BLOCK);

  gd->free_blocks_count++;
  sp->s_free_blocks_count++;
  lmfs_blockschange(sp->s_dev, 1);

  group_descriptors_dirty = 1;

  if (bit_returned < sp->s_bsearch)
  sp->s_bsearch = bit_returned;
}


static void check_block_number(block_t block, struct super_block *sp,
        struct group_desc *gd)
{

  /* Check if we allocated a data block, but not control (system) block.
   * Only major bug can cause us to allocate wrong block. If it happens,
   * we panic (and don't bloat filesystem's bitmap).
   */
  if (block == gd->inode_bitmap || block == gd->block_bitmap ||
      (block >= gd->inode_table
       && block < (gd->inode_table + sp->s_itb_per_group))) {
  ext2_debug("ext2: allocating non-data block %d\n", block);
  panic("ext2: block allocator tryed to return \
    system/control block, poke author.\n");
  }

  if (block >= sp->s_blocks_count) {
  panic("ext2: allocator returned blocknum greater, than \
      total number of blocks.\n");
  }
}]]></text>  
      <tokens> 
      </tokens>  
      <concepts>
        <concept id="1991219" weight="0.35588833689689636">JFFS2</concept>
        <concept id="437471" weight="0.41070467233657837">Block Island</concept>
        <concept id="1103580" weight="0.3325919806957245">Cinder block</concept>
        <concept id="572854" weight="0.39552876353263855">H&amp;R Block</concept>
        <concept id="512614" weight="0.3742939829826355">USS Block Island (CVE-106)</concept>
        <concept id="631107" weight="0.34605568647384644">City Block</concept>
        <concept id="1716537" weight="0.3287249803543091">Gauge blocks</concept>
        <concept id="981057" weight="0.34063366055488586">Minix file system</concept>
        <concept id="55347" weight="0.3387579321861267">Hierarchical File System</concept>
        <concept id="1251844" weight="0.37822970747947693">The Block (Sydney)</concept>
      </concepts>
    </content>  
    <comment> 
      <text><![CDATA[/*===========================================================================*
 *                      discard_preallocated_blocks                          *
/* When called for rip, discard (free) blocks preallocated for rip,
 * otherwise discard all preallocated blocks.
 * Normally it should be called in following situations:
 * 1. File is closed.
 * 2. File is truncated.
 * 3. Non-sequential write.
 * 4. inode is "unloaded" from the memory.
 * 5. No free blocks left (discard all preallocated blocks).
 */
  /* Discard all allocated blocks.
   * Probably there are just few blocks on the disc, so forbid preallocation.*/
/*===========================================================================*
 *                              alloc_block                                  *
/* Allocate a block for inode. If block is provided, then use it as a goal:
 * try to allocate this block or his neghbors.
 * If block is not provided then goal is group, where inode lives.
 */
  /* Check for free blocks. First time discard preallocation,
   * next time return NO_BLOCK
   */
    /* check if goal is preallocated */
      /* use preallocated block */
      /* probably non-sequential write operation,
       * disable preallocation for this inode.
       */
/*===========================================================================*
 *                              alloc_block_bit                              *
  /* No reason to search in a place with no free blocks */
  /* Figure out where to start the bit search. */
  /* Try to allocate block at any group starting from the goal's group.
   * First time goal's group is checked from the word=goal, after all
   * groups checked, it's checked again from word=0, that's why "i <=".
   */
    /* Try to preallocate blocks */
      /* kind of glitch... */
    /* we preallocate bytes only */
      /* We preallocate a byte starting from block.
       * First preallocated block will be returned as
       * normally allocated block.
       */
    /* We searched from the beginning, update bsearch. */
/*===========================================================================*
 *                        free_block                                       *
/* Return a block by turning off its bitmap bit. */
  /* At first search group, to which bit_returned belongs to
   * and figure out in what word bit is stored.
   */
  /* We might be buggy (No way! :P), so check if we deallocate
   * data block, but not control (system) block.
   * This should never happen.
   */
  /* Check if we allocated a data block, but not control (system) block.
   * Only major bug can cause us to allocate wrong block. If it happens,
   * we panic (and don't bloat filesystem's bitmap).
   */]]></text>  
      <tokens> 
      </tokens>  
      <concepts>
        <concept id="1991219" weight="0.11820138990879059">JFFS2</concept>
        <concept id="311193" weight="0.1060536727309227">Paging</concept>
        <concept id="437471" weight="0.12390121817588806">Block Island</concept>
        <concept id="572854" weight="0.11681419610977173">H&amp;R Block</concept>
        <concept id="512614" weight="0.11059369146823883">USS Block Island (CVE-106)</concept>
        <concept id="927752" weight="0.11466237902641296">HFS Plus</concept>
        <concept id="981057" weight="0.11578171700239182">Minix file system</concept>
        <concept id="55347" weight="0.12457172572612762">Hierarchical File System</concept>
        <concept id="329777" weight="0.12344598770141602">Fragmentation</concept>
        <concept id="1251844" weight="0.11170514672994614">The Block (Sydney)</concept>
      </concepts>
    </comment>  
    <sourceCode> 
      <text><![CDATA[#include "fs.h"
#include <string.h>
#include <stdlib.h>
#include <minix/com.h>
#include <minix/u64.h>
#include "buf.h"
#include "inode.h"
#include "super.h"
#include "const.h"
static block_t alloc_block_bit(struct super_block *sp, block_t origin,
  struct inode *rip);
void discard_preallocated_blocks(struct inode *rip)
{
  int i;
  if (rip) {
  rip->i_prealloc_count = rip->i_prealloc_index = 0;
  for (i = 0; i < EXT2_PREALLOC_BLOCKS; i++) {
    if (rip->i_prealloc_blocks[i] != NO_BLOCK) {
      free_block(rip->i_sp, rip->i_prealloc_blocks[i]);
      rip->i_prealloc_blocks[i] = NO_BLOCK;
    }
  }
  return;
  }
  for(rip = &inode[0]; rip < &inode[NR_INODES]; rip++) {
  rip->i_prealloc_count = rip->i_prealloc_index = 0;
  rip->i_preallocation = 0; /* forbid preallocation */
  for (i = 0; i < EXT2_PREALLOC_BLOCKS; i++) {
    if (rip->i_prealloc_blocks[i] != NO_BLOCK) {
      free_block(rip->i_sp, rip->i_prealloc_blocks[i]);
      rip->i_prealloc_blocks[i] = NO_BLOCK;
    }
  }
  }
}
block_t alloc_block(struct inode *rip, block_t block)
{
  block_t goal;
  block_t b;
  struct super_block *sp = rip->i_sp;
  if (sp->s_rd_only)
  panic("can't alloc block on read-only filesys.");
  if (!opt.use_reserved_blocks &&
      sp->s_free_blocks_count <= sp->s_r_blocks_count) {
  discard_preallocated_blocks(NULL);
  } else if (sp->s_free_blocks_count <= EXT2_PREALLOC_BLOCKS) {
  discard_preallocated_blocks(NULL);
  }
  if (!opt.use_reserved_blocks &&
      sp->s_free_blocks_count <= sp->s_r_blocks_count) {
  return(NO_BLOCK);
  } else if (sp->s_free_blocks_count == 0) {
  return(NO_BLOCK);
  }
  if (block != NO_BLOCK) {
  goal = block;
  if (rip->i_preallocation && rip->i_prealloc_count > 0) {
    b = rip->i_prealloc_blocks[rip->i_prealloc_index];
    if (block == b || (block + 1) == b) {
      rip->i_prealloc_blocks[rip->i_prealloc_index] = NO_BLOCK;
      rip->i_prealloc_count--;
      rip->i_prealloc_index++;
      if (rip->i_prealloc_index >= EXT2_PREALLOC_BLOCKS) {
        rip->i_prealloc_index = 0;
        ASSERT(rip->i_prealloc_count == 0);
      }
      rip->i_bsearch = b;
      return b;
    } else {
      rip->i_preallocation = 0;
      discard_preallocated_blocks(rip);
    }
  }
  } else {
    int group = (rip->i_num - 1) / sp->s_inodes_per_group;
    goal = sp->s_blocks_per_group*group + sp->s_first_data_block;
  }
  if (rip->i_preallocation && rip->i_prealloc_count) {
  ext2_debug("There're preallocated blocks, but they're\
      neither used or freed!");
  }
  b = alloc_block_bit(sp, goal, rip);
  if (b != NO_BLOCK)
  rip->i_bsearch = b;
  return b;
}
static void check_block_number(block_t block, struct super_block *sp,
  struct group_desc *gd);
static block_t alloc_block_bit(sp, goal, rip)
struct super_block *sp;   /* the filesystem to allocate from */
block_t goal;     /* try to allocate near this block */
struct inode *rip;    /* used for preallocation */
{
  block_t block = NO_BLOCK; /* allocated block */
  int word;     /* word in block bitmap */
  bit_t bit = -1;
  int group;
  char update_bsearch = FALSE;
  int i;
  if (goal >= sp->s_blocks_count ||
      (goal < sp->s_first_data_block && goal != 0)) {
  goal = sp->s_bsearch;
  }
  if (goal <= sp->s_bsearch) {
  goal = sp->s_bsearch;
  update_bsearch = TRUE;
  }
  word = ((goal - sp->s_first_data_block) % sp->s_blocks_per_group)
      / FS_BITCHUNK_BITS;
  group = (goal - sp->s_first_data_block) / sp->s_blocks_per_group;
  for (i = 0; i <= sp->s_groups_count; i++, group++) {
  struct buf *bp;
  struct group_desc *gd;
  if (group >= sp->s_groups_count)
    group = 0;
  gd = get_group_desc(group);
  if (gd == NULL)
    panic("can't get group_desc to alloc block");
  if (gd->free_blocks_count == 0) {
    word = 0;
    continue;
  }
  bp = get_block(sp->s_dev, gd->block_bitmap, NORMAL);
  if (rip->i_preallocation &&
      gd->free_blocks_count >= (EXT2_PREALLOC_BLOCKS * 4) ) {
    if (rip->i_prealloc_count != 0) {
      discard_preallocated_blocks(rip);
      ext2_debug("warning, discarding previously preallocated\
            blocks! It had to be done by another code.");
    }
    ASSERT(rip->i_prealloc_count == 0);
    ASSERT(EXT2_PREALLOC_BLOCKS == sizeof(char)*CHAR_BIT);
    bit = setbyte(b_bitmap(bp), sp->s_blocks_per_group);
    if (bit != -1) {
      block = bit + sp->s_first_data_block +
          group * sp->s_blocks_per_group;
      check_block_number(block, sp, gd);
      for (i = 1; i < EXT2_PREALLOC_BLOCKS; i++) {
        check_block_number(block + i, sp, gd);
        rip->i_prealloc_blocks[i-1] = block + i;
      }
      rip->i_prealloc_index = 0;
      rip->i_prealloc_count = EXT2_PREALLOC_BLOCKS - 1;
      lmfs_markdirty(bp);
      put_block(bp, MAP_BLOCK);
      gd->free_blocks_count -= EXT2_PREALLOC_BLOCKS;
      sp->s_free_blocks_count -= EXT2_PREALLOC_BLOCKS;
      lmfs_blockschange(sp->s_dev, -EXT2_PREALLOC_BLOCKS);
      group_descriptors_dirty = 1;
      return block;
    }
  }
        bit = setbit(b_bitmap(bp), sp->s_blocks_per_group, word);
  if (bit == -1) {
    if (word == 0) {
      panic("ext2: allocator failed to allocate a bit in bitmap\
        with free bits.");
    } else {
      word = 0;
      continue;
    }
  }
  block = sp->s_first_data_block + group * sp->s_blocks_per_group + bit;
  check_block_number(block, sp, gd);
  lmfs_markdirty(bp);
  put_block(bp, MAP_BLOCK);
  gd->free_blocks_count--;
  sp->s_free_blocks_count--;
  lmfs_blockschange(sp->s_dev, -1);
  group_descriptors_dirty = 1;
  if (update_bsearch && block != -1 && block != NO_BLOCK) {
    sp->s_bsearch = block;
  }
  return block;
  }
  return block;
}
void free_block(struct super_block *sp, bit_t bit_returned)
{
  int group;    /* group number of bit_returned */
  int bit;    /* bit_returned number within its group */
  struct buf *bp;
  struct group_desc *gd;
  if (sp->s_rd_only)
  panic("can't free bit on read-only filesys.");
  if (bit_returned >= sp->s_blocks_count ||
      bit_returned < sp->s_first_data_block)
  panic("trying to free block %d beyond blocks scope.",
    bit_returned);
  group = (bit_returned - sp->s_first_data_block) / sp->s_blocks_per_group;
  bit = (bit_returned - sp->s_first_data_block) % sp->s_blocks_per_group;
  gd = get_group_desc(group);
  if (gd == NULL)
  panic("can't get group_desc to alloc block");
  if (bit_returned == gd->inode_bitmap || bit_returned == gd->block_bitmap
      || (bit_returned >= gd->inode_table
          && bit_returned < (gd->inode_table + sp->s_itb_per_group))) {
  ext2_debug("ext2: freeing non-data block %d\n", bit_returned);
  panic("trying to deallocate \
    system/control block, hardly poke author.");
  }
  bp = get_block(sp->s_dev, gd->block_bitmap, NORMAL);
  if (unsetbit(b_bitmap(bp), bit))
  panic("Tried to free unused block", bit_returned);
  lmfs_markdirty(bp);
  put_block(bp, MAP_BLOCK);
  gd->free_blocks_count++;
  sp->s_free_blocks_count++;
  lmfs_blockschange(sp->s_dev, 1);
  group_descriptors_dirty = 1;
  if (bit_returned < sp->s_bsearch)
  sp->s_bsearch = bit_returned;
}
static void check_block_number(block_t block, struct super_block *sp,
        struct group_desc *gd)
{
  if (block == gd->inode_bitmap || block == gd->block_bitmap ||
      (block >= gd->inode_table
       && block < (gd->inode_table + sp->s_itb_per_group))) {
  ext2_debug("ext2: allocating non-data block %d\n", block);
  panic("ext2: block allocator tryed to return \
    system/control block, poke author.\n");
  }
  if (block >= sp->s_blocks_count) {
  panic("ext2: allocator returned blocknum greater, than \
      total number of blocks.\n");
  }
}]]></text>  
      <tokens> 
       
      </tokens>  
      <concepts>
        <concept id="1991219" weight="0.46036943793296814">JFFS2</concept>
        <concept id="437471" weight="0.5421051979064941">Block Island</concept>
        <concept id="1103580" weight="0.4406166672706604">Cinder block</concept>
        <concept id="572854" weight="0.5239951014518738">H&amp;R Block</concept>
        <concept id="512614" weight="0.49463191628456116">USS Block Island (CVE-106)</concept>
        <concept id="631107" weight="0.45932334661483765">City Block</concept>
        <concept id="1716537" weight="0.4348750114440918">Gauge blocks</concept>
        <concept id="981057" weight="0.44125351309776306">Minix file system</concept>
        <concept id="55347" weight="0.4211011826992035">Hierarchical File System</concept>
        <concept id="1251844" weight="0.5010773539543152">The Block (Sydney)</concept>
      </concepts>
    </sourceCode> 
  </file>  

TFIDF result of heading description

minix-src/servers/ext2/balloc.c": {
    "allocation": 0.09877671746236895,
    "blocks": 0.09087790472300472,
    "block": 0.07298637936941421,
    "discard": 0.06827943992945525,
    "free_block": 0.06827943992945525
  }

1. http://en.wikipedia.org/wiki/Allocation

In computers:
Delayed allocation
Block allocation map
File allocation table
IP address allocation
Memory allocation, see memory management
C++ allocators
No-write allocation (cache)
Register allocation

1. http://en.wikipedia.org/wiki/Blocks
   Technology[edit]

Block (data storage), the practice of storing electronic data in equally-sized units
Block (Internet), technical measures to restrict users' access to certain internet resources
Block (programming), a group of declarations and statements treated as a unit
Block (telecommunications), a unit of data transmission
Block-level element in the HTML markup language
Block Number (aircraft), a method of differentiating between groups of aircraft of the same type that have minor modifications
Blocks (C language extension), an extension to the C programming language designed to support parallel programming
Boom Blox, a 2008 video game for the Wii console from EA, previously known as Blocks
Block elements, a class of Box-drawing characters
Unicode block, a named range of codepoints in Unicode

1. http://en.wikipedia.org/wiki/Special:Search/Free_block
   no result.