af01bda509
The "bdev" library provides basic primitives for file systems to talk to block device drivers, hiding the details of the underlying protocol and interaction model. This version of libbdev is rather basic. It is planned to support the following features in the long run: - asynchronous requests and replies; - recovery support for underlying block drivers; - retrying of failed I/O requests. The commit also changes our block-based file systems (mfs, ext2, isofs) to make use of libbdev.
116 lines
3.2 KiB
C
116 lines
3.2 KiB
C
/* The file system maintains a buffer cache to reduce the number of disk
|
|
* accesses needed. Whenever a read or write to the disk is done, a check is
|
|
* first made to see if the block is in the cache. This file manages the
|
|
* cache.
|
|
*
|
|
* The entry points into this file are:
|
|
* get_block: request to fetch a block for reading or writing from cache
|
|
* put_block: return a block previously requested with get_block
|
|
*
|
|
* Private functions:
|
|
* read_block: read physically the block
|
|
*/
|
|
|
|
#include "inc.h"
|
|
#include <minix/com.h>
|
|
#include <minix/u64.h>
|
|
#include <minix/bdev.h>
|
|
#include "buf.h"
|
|
|
|
FORWARD _PROTOTYPE(int read_block, (struct buf *));
|
|
|
|
PUBLIC struct buf *bp_to_pickup = buf; /* This is a pointer to the next node in the
|
|
* buffer cache to pick up*/
|
|
|
|
|
|
/*===========================================================================*
|
|
* get_block *
|
|
*===========================================================================*/
|
|
PUBLIC struct buf *get_block(block)
|
|
register block_t block; /* which block is wanted? */
|
|
{
|
|
register struct buf *bp, *free_bp;
|
|
|
|
free_bp = NULL;
|
|
|
|
/* Find if the block is already loaded */
|
|
for (bp = &buf[0]; bp < &buf[NR_BUFS]; bp++)
|
|
if (bp->b_blocknr == block) {
|
|
/* Block found. Increment count and return it */
|
|
bp->b_count++;
|
|
return bp;
|
|
} else
|
|
if (bp == bp_to_pickup) {
|
|
if (bp->b_count == 0)
|
|
free_bp = bp;
|
|
else /* Increment the node to pickup */
|
|
if (bp_to_pickup < &buf[NR_BUFS] - 1)
|
|
bp_to_pickup++;
|
|
else
|
|
bp_to_pickup = buf;
|
|
}
|
|
|
|
if (free_bp == NULL &&
|
|
bp_to_pickup == buf &&
|
|
bp_to_pickup->b_count == 0)
|
|
free_bp = bp_to_pickup;
|
|
|
|
if (free_bp != NULL) {
|
|
/* Set fields of data structure */
|
|
free_bp->b_blocknr = block;
|
|
if (read_block(free_bp) != OK) return NULL;
|
|
free_bp->b_count = 1;
|
|
|
|
if (bp_to_pickup < &buf[NR_BUFS] - 1)
|
|
bp_to_pickup++;
|
|
else
|
|
bp_to_pickup = buf;
|
|
|
|
return free_bp;
|
|
} else {
|
|
/* No free blocks. Return NULL */
|
|
return NULL;
|
|
}
|
|
}
|
|
|
|
/*===========================================================================*
|
|
* put_block *
|
|
*===========================================================================*/
|
|
PUBLIC void put_block(bp)
|
|
register struct buf *bp; /* pointer to the buffer to be released */
|
|
{
|
|
if (bp == NULL) return; /* it is easier to check here than in caller */
|
|
|
|
bp->b_count--; /* there is one use fewer now */
|
|
}
|
|
|
|
/*===========================================================================*
|
|
* read_block *
|
|
*===========================================================================*/
|
|
PRIVATE int read_block(bp)
|
|
register struct buf *bp; /* buffer pointer */
|
|
{
|
|
int r;
|
|
u64_t pos;
|
|
int block_size;
|
|
|
|
block_size = v_pri.logical_block_size_l; /* The block size is indicated by
|
|
* the superblock */
|
|
|
|
|
|
pos = mul64u(bp->b_blocknr, block_size); /* get absolute position */
|
|
r = bdev_read(fs_dev, pos, bp->b_data, block_size, BDEV_NOFLAGS);
|
|
if (r != block_size) {
|
|
if (r >= 0) r = END_OF_FILE;
|
|
if (r != END_OF_FILE)
|
|
printf("ISOFS(%d) I/O error on device %d/%d, block %u\n",
|
|
SELF_E, (fs_dev>>MAJOR)&BYTE, (fs_dev>>MINOR)&BYTE,
|
|
bp->b_blocknr);
|
|
|
|
rdwt_err = r;
|
|
return EINVAL;
|
|
}
|
|
|
|
return OK;
|
|
}
|