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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/* Buffered I/O functions. By cacheing the most recently used blocks,
* we can cut WAAY down on disk traffic...
*/
static int bio_fd = -1;
static int bio_counter = 0;
static int bio_blocksize = 0;
struct bio_buf {
int blkno;
int last_access;
int dirty;
char * data;
};
#define NBUFS 32
struct bio_buf buflist[NBUFS];
/* initialize the buffer cache. Blow away anything that may
* have been previously cached...
*/
void
binit(int fd, int blocksize)
{
int i;
bio_fd = fd;
bio_blocksize = blocksize;
for(i = 0; i < NBUFS; i++) {
buflist[i].blkno = 0;
if(buflist[i].data) {
free(buflist[i].data);
}
buflist[i].data = 0;
buflist[i].last_access = 0;
buflist[i].dirty = 0;
}
}
/* Flush out any dirty blocks */
void
bflush(void)
{
int i;
for(i = 0; i < NBUFS; i++) {
if(buflist[i].dirty) {
#ifdef BIO_DEBUG
printf("bflush: writing block %d\n", buflist[i].blkno);
#endif
lseek(bio_fd, buflist[i].blkno * bio_blocksize, 0);
write(bio_fd, buflist[i].data, bio_blocksize);
buflist[i].dirty = 0;
}
}
}
/* Read a block. */
void
bread(int blkno, void * blkbuf)
{
int i;
int lowcount;
int lowcount_buf;
/* First, see if the block is already in memory... */
for(i = 0; i < NBUFS; i++) {
if(buflist[i].blkno == blkno) {
/* Got it! Bump the access count and return. */
buflist[i].last_access = ++bio_counter;
#ifdef BIO_DEBUG
printf("bread: buffer hit on block %d\n", blkno);
#endif
memcpy(blkbuf, buflist[i].data, bio_blocksize);
return;
}
}
/* Not in memory; need to find a buffer and read it in. */
lowcount = buflist[0].last_access;
lowcount_buf = 0;
for(i = 1; i < NBUFS; i++) {
if(buflist[i].last_access < lowcount) {
lowcount = buflist[i].last_access;
lowcount_buf = i;
}
}
/* If the buffer is dirty, we need to write it out... */
if(buflist[lowcount_buf].dirty) {
#ifdef BIO_DEBUG
printf("bread: recycling dirty buffer %d for block %d\n",
lowcount_buf, buflist[lowcount_buf].blkno);
#endif
lseek(bio_fd, buflist[lowcount_buf].blkno * bio_blocksize, 0);
write(bio_fd, buflist[lowcount_buf].data, bio_blocksize);
buflist[lowcount_buf].dirty = 0;
}
#ifdef BIO_DEBUG
printf("bread: Using buffer %d for block %d\n", lowcount_buf, blkno);
#endif
buflist[lowcount_buf].blkno = blkno;
if(!buflist[lowcount_buf].data) {
buflist[lowcount_buf].data = (char *)malloc(bio_blocksize);
}
lseek(bio_fd, blkno * bio_blocksize, 0);
if(read(bio_fd,buflist[lowcount_buf].data,bio_blocksize)!=bio_blocksize) {
perror("bread: I/O error");
}
buflist[lowcount_buf].last_access = ++bio_counter;
memcpy(blkbuf, buflist[lowcount_buf].data, bio_blocksize);
}
/* Write a block */
void
bwrite(int blkno, void * blkbuf)
{
int i;
int lowcount;
int lowcount_buf;
/* First, see if the block is already in memory... */
for(i = 0; i < NBUFS; i++) {
if(buflist[i].blkno == blkno) {
/* Got it! Bump the access count and return. */
#ifdef BIO_DEBUG
printf("bwrite: buffer hit on block %d\n", blkno);
#endif
buflist[i].last_access = ++bio_counter;
memcpy(buflist[i].data, blkbuf, bio_blocksize);
buflist[i].dirty = 1;
return;
}
}
/* Not in memory; need to find a buffer and stuff it. */
lowcount = buflist[0].last_access;
lowcount_buf = 0;
for(i = 1; i < NBUFS; i++) {
if(buflist[i].last_access < lowcount) {
lowcount = buflist[i].last_access;
lowcount_buf = i;
}
}
/* If the buffer is dirty, we need to write it out... */
if(buflist[lowcount_buf].dirty) {
#ifdef BIO_DEBUG
printf("bwrite: recycling dirty buffer %d for block %d\n",
lowcount_buf, buflist[lowcount_buf].blkno);
#endif
lseek(bio_fd, buflist[lowcount_buf].blkno * bio_blocksize, 0);
write(bio_fd, buflist[lowcount_buf].data, bio_blocksize);
buflist[lowcount_buf].dirty = 0;
}
#ifdef BIO_DEBUG
printf("bwrite: Using buffer %d for block %d\n", lowcount_buf, blkno);
#endif
buflist[lowcount_buf].blkno = blkno;
if(!buflist[lowcount_buf].data) {
buflist[lowcount_buf].data = (char *)malloc(bio_blocksize);
}
buflist[lowcount_buf].last_access = ++bio_counter;
memcpy(buflist[lowcount_buf].data, blkbuf, bio_blocksize);
buflist[lowcount_buf].dirty = 1;
}
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