minix/fs/pfs/super.c

   1 /* This file manages the super block table and the related data structures,
   2  * namely, the bit maps that keep track of which zones and which inodes are
   3  * allocated and which are free.  When a new inode or zone is needed, the
   4  * appropriate bit map is searched for a free entry.
   5  *
   6  * The entry points into this file are
   7  *   alloc_bit:       somebody wants to allocate a zone or inode; find one
   8  *   free_bit:        indicate that a zone or inode is available for allocation
   9  */
  10
  11 #include "fs.h"
  12 #include "buf.h"
  13 #include "inode.h"
  14 #include "const.h"
  15
  16
  17 /*===========================================================================*
  18  *                              alloc_bit                                    *
  19  *===========================================================================*/
  20 bit_t alloc_bit(void)
  21 {
  22 /* Allocate a bit from a bit map and return its bit number. */
  23   bitchunk_t *wptr, *wlim;
  24   bit_t b;
  25   unsigned int i, bcount;
  26
  27   bcount = FS_BITMAP_CHUNKS(PFS_NR_INODES); /* Inode map has this many chunks. */
  28   wlim = &inodemap[bcount]; /* Point to last chunk in inodemap. */
  29
  30   for (wptr = &inodemap[0]; wptr < wlim; wptr++) {
  31         /* Does this word contain a free bit? */
  32         if (*wptr == (bitchunk_t) ~0) continue; /* No. Go to next word */
  33
  34         /* Find and allocate the free bit. */
  35         for (i = 0; (*wptr & (1 << i)) != 0; ++i) {}
  36
  37         /* Get inode number */
  38         b = (bit_t) ((wptr - &inodemap[0]) * FS_BITCHUNK_BITS + i);
  39
  40         /* Don't allocate bits beyond end of map. */
  41         if (b >= PFS_NR_INODES) break;
  42
  43         /* Allocate and return bit number. */
  44         *wptr |= 1 << i;
  45
  46         /* Mark server 'busy' */
  47         busy++;
  48         return(b);
  49   }
  50
  51   return(NO_BIT);                       /* no bit could be allocated */
  52 }
  53
  54
  55 /*===========================================================================*
  56  *                              free_bit                                     *
  57  *===========================================================================*/
  58 void free_bit(bit_returned)
  59 bit_t bit_returned;             /* number of bit to insert into the inode map*/
  60 {
  61   bitchunk_t *k, mask;
  62   bit_t bit;
  63   unsigned word;
  64
  65   /* Get word offset and bit within offset */
  66   word = (unsigned) (bit_returned / (bit_t) FS_BITCHUNK_BITS);
  67   bit = bit_returned % (bit_t) FS_BITCHUNK_BITS;
  68
  69   /* Unset bit */
  70   k = &inodemap[word];
  71   mask = (unsigned) 1 << bit;
  72   *k &= ~mask;
  73
  74   busy--; /* One inode less in use. */
  75 }