minix/fs/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 contains some
   4  * related routines, but the cache is now in libminixfs.
   5  */
   6
   7 #include "fs.h"
   8 #include <minix/u64.h>
   9 #include <minix/bdev.h>
  10 #include <sys/param.h>
  11 #include <stdlib.h>
  12 #include <assert.h>
  13 #include <minix/libminixfs.h>
  14 #include <math.h>
  15 #include "buf.h"
  16 #include "super.h"
  17 #include "inode.h"
  18
  19 /*===========================================================================*
  20  *                              get_block                                    *
  21  *===========================================================================*/
  22 struct buf *get_block(dev_t dev, block_t block, int how)
  23 {
  24 /* Wrapper routine for lmfs_get_block(). This MFS implementation does not deal
  25  * well with block read errors pretty much anywhere. To prevent corruption due
  26  * to unchecked error conditions, we panic upon an I/O failure here.
  27  */
  28   struct buf *bp;
  29   int r;
  30
  31   if ((r = lmfs_get_block(&bp, dev, block, how)) != OK && r != ENOENT)
  32         panic("MFS: error getting block (%llu,%u): %d", dev, block, r);
  33
  34   assert(r == OK || how == PEEK);
  35
  36   return (r == OK) ? bp : NULL;
  37 }
  38
  39 /*===========================================================================*
  40  *                              alloc_zone                                   *
  41  *===========================================================================*/
  42 zone_t alloc_zone(
  43   dev_t dev,                    /* device where zone wanted */
  44   zone_t z                      /* try to allocate new zone near this one */
  45 )
  46 {
  47 /* Allocate a new zone on the indicated device and return its number. */
  48
  49   bit_t b, bit;
  50   struct super_block *sp;
  51   static int print_oos_msg = 1;
  52
  53   /* Note that the routine alloc_bit() returns 1 for the lowest possible
  54    * zone, which corresponds to sp->s_firstdatazone.  To convert a value
  55    * between the bit number, 'b', used by alloc_bit() and the zone number, 'z',
  56    * stored in the inode, use the formula:
  57    *     z = b + sp->s_firstdatazone - 1
  58    * Alloc_bit() never returns 0, since this is used for NO_BIT (failure).
  59    */
  60   sp = &superblock;
  61
  62   /* If z is 0, skip initial part of the map known to be fully in use. */
  63   if (z == sp->s_firstdatazone) {
  64         bit = sp->s_zsearch;
  65   } else {
  66         bit = (bit_t) (z - (sp->s_firstdatazone - 1));
  67   }
  68   b = alloc_bit(sp, ZMAP, bit);
  69   if (b == NO_BIT) {
  70         err_code = ENOSPC;
  71         if (print_oos_msg)
  72                 printf("No space on device %d/%d\n", major(sp->s_dev),
  73                         minor(sp->s_dev));
  74         print_oos_msg = 0;      /* Don't repeat message */
  75         return(NO_ZONE);
  76   }
  77   print_oos_msg = 1;
  78   if (z == sp->s_firstdatazone) sp->s_zsearch = b;      /* for next time */
  79   return( (zone_t) (sp->s_firstdatazone - 1) + (zone_t) b);
  80 }
  81
  82 /*===========================================================================*
  83  *                              free_zone                                    *
  84  *===========================================================================*/
  85 void free_zone(
  86   dev_t dev,                            /* device where zone located */
  87   zone_t numb                           /* zone to be returned */
  88 )
  89 {
  90 /* Return a zone. */
  91
  92   register struct super_block *sp;
  93   bit_t bit;
  94
  95   /* Locate the appropriate super_block and return bit. */
  96   sp = &superblock;
  97   if (numb < sp->s_firstdatazone || numb >= sp->s_zones) return;
  98   bit = (bit_t) (numb - (zone_t) (sp->s_firstdatazone - 1));
  99   free_bit(sp, ZMAP, bit);
 100   if (bit < sp->s_zsearch) sp->s_zsearch = bit;
 101
 102   /* Also tell libminixfs, so that 1) if it has a block for this bit, it can
 103    * mark it as clean, thus reducing useless writes, and 2) it can tell VM that
 104    * any previous inode association is to be broken for this block, so that the
 105    * block will not be mapped in erroneously later on.
 106    */
 107   assert(sp->s_log_zone_size == 0); /* otherwise we need a loop here.. */
 108   lmfs_free_block(dev, (block_t)numb);
 109 }