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