servers/mfs/cache.c

   1 /* The file system maintains a buffer cache to reduce the number of disk
   2  * accesses needed.  Whenever a read or write to the disk is done, a check is
   3  * first made to see if the block is in the cache.  This file manages the
   4  * cache.
   5  *
   6  * The entry points into this file are:
   7  *   get_block:   request to fetch a block for reading or writing from cache
   8  *   put_block:   return a block previously requested with get_block
   9  *   alloc_zone:  allocate a new zone (to increase the length of a file)
  10  *   free_zone:   release a zone (when a file is removed)
  11  *   invalidate:  remove all the cache blocks on some device
  12  *
  13  * Private functions:
  14  *   read_block:    read or write a block from the disk itself
  15  */
  16
  17 #include "fs.h"
  18 #include <minix/u64.h>
  19 #include <minix/bdev.h>
  20 #include <sys/param.h>
  21 #include <stdlib.h>
  22 #include <assert.h>
  23 #include <minix/libminixfs.h>
  24 #include <math.h>
  25 #include "buf.h"
  26 #include "super.h"
  27 #include "inode.h"
  28
  29 /*===========================================================================*
  30  *                              alloc_zone                                   *
  31  *===========================================================================*/
  32 zone_t alloc_zone(
  33   dev_t dev,                    /* device where zone wanted */
  34   zone_t z                      /* try to allocate new zone near this one */
  35 )
  36 {
  37 /* Allocate a new zone on the indicated device and return its number. */
  38
  39   bit_t b, bit;
  40   struct super_block *sp;
  41   static int print_oos_msg = 1;
  42
  43   /* Note that the routine alloc_bit() returns 1 for the lowest possible
  44    * zone, which corresponds to sp->s_firstdatazone.  To convert a value
  45    * between the bit number, 'b', used by alloc_bit() and the zone number, 'z',
  46    * stored in the inode, use the formula:
  47    *     z = b + sp->s_firstdatazone - 1
  48    * Alloc_bit() never returns 0, since this is used for NO_BIT (failure).
  49    */
  50   sp = get_super(dev);
  51
  52   /* If z is 0, skip initial part of the map known to be fully in use. */
  53   if (z == sp->s_firstdatazone) {
  54         bit = sp->s_zsearch;
  55   } else {
  56         bit = (bit_t) (z - (sp->s_firstdatazone - 1));
  57   }
  58   b = alloc_bit(sp, ZMAP, bit);
  59   if (b == NO_BIT) {
  60         err_code = ENOSPC;
  61         if (print_oos_msg)
  62                 printf("No space on device %d/%d\n", major(sp->s_dev),
  63                         minor(sp->s_dev));
  64         print_oos_msg = 0;      /* Don't repeat message */
  65         return(NO_ZONE);
  66   }
  67   print_oos_msg = 1;
  68   if (z == sp->s_firstdatazone) sp->s_zsearch = b;      /* for next time */
  69   return( (zone_t) (sp->s_firstdatazone - 1) + (zone_t) b);
  70 }
  71
  72 /*===========================================================================*
  73  *                              free_zone                                    *
  74  *===========================================================================*/
  75 void free_zone(
  76   dev_t dev,                            /* device where zone located */
  77   zone_t numb                           /* zone to be returned */
  78 )
  79 {
  80 /* Return a zone. */
  81
  82   register struct super_block *sp;
  83   bit_t bit;
  84
  85   /* Locate the appropriate super_block and return bit. */
  86   sp = get_super(dev);
  87   if (numb < sp->s_firstdatazone || numb >= sp->s_zones) return;
  88   bit = (bit_t) (numb - (zone_t) (sp->s_firstdatazone - 1));
  89   free_bit(sp, ZMAP, bit);
  90   if (bit < sp->s_zsearch) sp->s_zsearch = bit;
  91 }
  92
  93