servers/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 <string.h>
  13 #include <minix/com.h>
  14 #include <minix/u64.h>
  15 #include "buf.h"
  16 #include "inode.h"
  17 #include "const.h"
  18
  19
  20 /*===========================================================================*
  21  *                              alloc_bit                                    *
  22  *===========================================================================*/
  23 PUBLIC bit_t alloc_bit(void)
  24 {
  25 /* Allocate a bit from a bit map and return its bit number. */
  26   bitchunk_t *wptr, *wlim;
  27   bit_t b;
  28   int i, bcount;
  29
  30   bcount = FS_BITMAP_CHUNKS(NR_INODES); /* Inode map has this many chunks. */
  31   wlim = &inodemap[bcount]; /* Point to last chunk in inodemap. */
  32
  33   for (wptr = &inodemap[0]; wptr < wlim; wptr++) {
  34         /* Does this word contain a free bit? */
  35         if (*wptr == (bitchunk_t) ~0) continue; /* No. Go to next word */
  36
  37         /* Find and allocate the free bit. */
  38         for (i = 0; (*wptr & (1 << i)) != 0; ++i) {}
  39
  40         /* Get inode number */
  41         b = (wptr - &inodemap[0]) * FS_BITCHUNK_BITS + i;
  42
  43         /* Don't allocate bits beyond end of map. */
  44         if (b >= NR_INODES) break;
  45
  46         /* Allocate and return bit number. */
  47         *wptr |= 1 << i;
  48
  49         /* Mark server 'busy' */
  50         busy++;
  51         return(b);
  52   }
  53
  54   return(NO_BIT);                       /* no bit could be allocated */
  55 }
  56
  57
  58 /*===========================================================================*
  59  *                              free_bit                                     *
  60  *===========================================================================*/
  61 PUBLIC void free_bit(bit_returned)
  62 bit_t bit_returned;             /* number of bit to insert into the inode map*/
  63 {
  64   bitchunk_t *k, mask;
  65   bit_t bit;
  66   unsigned word;
  67
  68   /* Get word offset and bit within offset */
  69   word = bit_returned / FS_BITCHUNK_BITS;
  70   bit = bit_returned % FS_BITCHUNK_BITS;
  71
  72   /* Unset bit */
  73   k = &inodemap[word];
  74   mask = 1 << bit;
  75   *k &= ~mask;
  76
  77   busy--; /* One inode less in use. */
  78 }
  79
  80