servers/iso9660fs/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  *
  10  * Private functions:
  11  *   read_block:  read physically the block
  12  */
  13
  14 #include "inc.h"
  15 #include <minix/com.h>
  16 #include <minix/u64.h>
  17 #include "buf.h"
  18
  19 FORWARD _PROTOTYPE(int read_block, (struct buf *));
  20
  21 PUBLIC struct buf *bp_to_pickup = buf; /* This is a pointer to the next node in the
  22                                           * buffer cache to pick up*/
  23
  24
  25 /*===========================================================================*
  26  *                              get_block                                    *
  27  *===========================================================================*/
  28 PUBLIC struct buf *get_block(block)
  29 register block_t block;         /* which block is wanted? */
  30 {
  31   int b;
  32   register struct buf *bp, *free_bp;
  33
  34   free_bp = NIL_BUF;
  35
  36   /* Find if the block is already loaded */
  37   for (bp = &buf[0]; bp < &buf[NR_BUFS]; bp++)
  38     if (bp->b_blocknr == block) {
  39       /* Block found. Increment count and return it  */
  40       bp->b_count++;
  41       return bp;
  42     } else
  43       if (bp == bp_to_pickup) {
  44         if (bp->b_count == 0)
  45           free_bp = bp;
  46         else                    /* Increment the node to pickup */
  47           if (bp_to_pickup < &buf[NR_BUFS] - 1)
  48             bp_to_pickup++;
  49           else
  50             bp_to_pickup = buf;
  51       }
  52
  53   if (free_bp == NIL_BUF &&
  54       bp_to_pickup == buf &&
  55       bp_to_pickup->b_count == 0)
  56     free_bp = bp_to_pickup;
  57
  58   if (free_bp != NIL_BUF) {
  59     /* Set fields of data structure */
  60     free_bp->b_blocknr = block;
  61     if (read_block(free_bp) != OK) return NIL_BUF;
  62     free_bp->b_count = 1;
  63
  64     if (bp_to_pickup < &buf[NR_BUFS] - 1)
  65       bp_to_pickup++;
  66     else
  67       bp_to_pickup = buf;
  68
  69     return free_bp;
  70   } else {
  71     /* No free blocks. Return NIL_BUF */
  72     return NIL_BUF;
  73   }
  74 }
  75
  76 /*===========================================================================*
  77  *                              put_block                                    *
  78  *===========================================================================*/
  79 PUBLIC void put_block(bp)
  80 register struct buf *bp;        /* pointer to the buffer to be released */
  81 {
  82   if (bp == NIL_BUF) return;    /* it is easier to check here than in caller */
  83
  84   bp->b_count--;                /* there is one use fewer now */
  85 }
  86
  87 /*===========================================================================*
  88  *                              read_block                                   *
  89  *===========================================================================*/
  90 PRIVATE int read_block(bp)
  91 register struct buf *bp;        /* buffer pointer */
  92 {
  93   int r, op;
  94   u64_t pos;
  95   int block_size;
  96
  97   block_size = v_pri.logical_block_size_l; /* The block size is indicated by
  98                                             * the superblock */
  99
 100
 101   pos = mul64u(bp->b_blocknr, block_size); /* get absolute position */
 102   op = MFS_DEV_READ;            /* flag to read */
 103   r = block_dev_io(op, fs_dev, SELF_E, bp->b_data, pos, block_size, 0);
 104   if (r != block_size) {
 105     if (r >= 0) r = END_OF_FILE;
 106     if (r != END_OF_FILE)
 107       printf("ISOFS(%d) I/O error on device %d/%d, block %ld\n",
 108              SELF_E, (fs_dev>>MAJOR)&BYTE, (fs_dev>>MINOR)&BYTE,
 109              bp->b_blocknr);
 110
 111     rdwt_err = r;
 112     return EINVAL;
 113   }
 114
 115   return OK;
 116 }