servers/pfs/buffer.c

   1 #include "fs.h"
   2 #include "buf.h"
   3 #include "inode.h"
   4 #include <sys/types.h>
   5 #include <stdlib.h>
   6 #include <alloca.h>
   7 #include <string.h>
   8
   9
  10 /*===========================================================================*
  11  *                              buf_pool                                     *
  12  *===========================================================================*/
  13 PUBLIC void buf_pool(void)
  14 {
  15 /* Initialize the buffer pool. */
  16
  17   front = NIL_BUF;
  18   rear = NIL_BUF;
  19 }
  20
  21
  22
  23 /*===========================================================================*
  24  *                              get_block                                    *
  25  *===========================================================================*/
  26 PUBLIC struct buf *get_block(dev, inum)
  27 Dev_t dev;
  28 ino_t inum;
  29 {
  30   struct buf *bp;
  31
  32   bp = front;
  33   while(bp != NIL_BUF) {
  34         if (bp->b_dev == dev && bp->b_num == inum) {
  35                 bp->b_count++;
  36                 return(bp);
  37         }
  38         bp = bp->b_next;
  39   }
  40
  41   /* Buffer was not found. Try to allocate a new one */
  42   return new_block(dev, inum);
  43 }
  44
  45
  46 /*===========================================================================*
  47  *                              new_block                                    *
  48  *===========================================================================*/
  49 PUBLIC struct buf *new_block(dev, inum)
  50 Dev_t dev;
  51 ino_t inum;
  52 {
  53 /* Allocate a new buffer and add it to the double linked buffer list */
  54   struct buf *bp;
  55
  56   bp = malloc(sizeof(struct buf));
  57   if (bp == NULL) {
  58         err_code = ENOSPC;
  59         return(NIL_BUF);
  60   }
  61   bp->b_num = inum;
  62   bp->b_dev = dev;
  63   bp->b_bytes = 0;
  64   bp->b_count = 1;
  65   memset(bp->b_data, 0 , PIPE_BUF);
  66
  67   /* Add at the end of the buffer */
  68   if (front == NIL_BUF) {       /* Empty list? */
  69         front = bp;
  70         bp->b_prev = NIL_BUF;
  71   } else {
  72         rear->b_next = bp;
  73         bp->b_prev = rear;
  74   }
  75   bp->b_next = NIL_BUF;
  76   rear = bp;
  77
  78   return(bp);
  79 }
  80
  81
  82 /*===========================================================================*
  83  *                              put_block                                    *
  84  *===========================================================================*/
  85 PUBLIC void put_block(dev, inum)
  86 dev_t dev;
  87 ino_t inum;
  88 {
  89   struct buf *bp;
  90
  91   bp = get_block(dev, inum);
  92   if (bp == NIL_BUF) return; /* We didn't find the block. Nothing to put. */
  93
  94   bp->b_count--;        /* Compensate for above 'get_block'. */
  95   if (--bp->b_count > 0) return;
  96
  97   /* Cut bp out of the loop */
  98   if (bp->b_prev == NIL_BUF)
  99         front = bp->b_next;
 100   else
 101         bp->b_prev->b_next = bp->b_next;
 102
 103   if (bp->b_next == NIL_BUF)
 104         rear = bp->b_prev;
 105   else
 106         bp->b_next->b_prev = bp->b_prev;
 107
 108   /* Buffer administration is done. Now it's safe to free up bp. */
 109   free(bp);
 110 }
 111
 112