minix/servers/pfs/buffer.c
2009-12-20 20:41:50 +00:00

112 lines
2.5 KiB
C

#include "fs.h"
#include "buf.h"
#include "inode.h"
#include <sys/types.h>
#include <stdlib.h>
#include <alloca.h>
#include <string.h>
/*===========================================================================*
* buf_pool *
*===========================================================================*/
PUBLIC void buf_pool(void)
{
/* Initialize the buffer pool. */
front = NIL_BUF;
rear = NIL_BUF;
}
/*===========================================================================*
* get_block *
*===========================================================================*/
PUBLIC struct buf *get_block(dev, inum)
Dev_t dev;
ino_t inum;
{
struct buf *bp;
bp = front;
while(bp != NIL_BUF) {
if (bp->b_dev == dev && bp->b_num == inum) {
bp->b_count++;
return(bp);
}
bp = bp->b_next;
}
/* Buffer was not found. Try to allocate a new one */
return new_block(dev, inum);
}
/*===========================================================================*
* new_block *
*===========================================================================*/
PUBLIC struct buf *new_block(dev, inum)
Dev_t dev;
ino_t inum;
{
/* Allocate a new buffer and add it to the double linked buffer list */
struct buf *bp;
bp = malloc(sizeof(struct buf));
if (bp == NULL) {
err_code = ENOSPC;
return(NIL_BUF);
}
bp->b_num = inum;
bp->b_dev = dev;
bp->b_bytes = 0;
bp->b_count = 1;
memset(bp->b_data, 0 , PIPE_BUF);
/* Add at the end of the buffer */
if (front == NIL_BUF) { /* Empty list? */
front = bp;
bp->b_prev = NIL_BUF;
} else {
rear->b_next = bp;
bp->b_prev = rear;
}
bp->b_next = NIL_BUF;
rear = bp;
return(bp);
}
/*===========================================================================*
* put_block *
*===========================================================================*/
PUBLIC void put_block(dev, inum)
dev_t dev;
ino_t inum;
{
struct buf *bp;
bp = get_block(dev, inum);
if (bp == NIL_BUF) return; /* We didn't find the block. Nothing to put. */
bp->b_count--; /* Compensate for above 'get_block'. */
if (--bp->b_count > 0) return;
/* Cut bp out of the loop */
if (bp->b_prev == NIL_BUF)
front = bp->b_next;
else
bp->b_prev->b_next = bp->b_next;
if (bp->b_next == NIL_BUF)
rear = bp->b_prev;
else
bp->b_next->b_prev = bp->b_prev;
/* Buffer administration is done. Now it's safe to free up bp. */
free(bp);
}