/* blocks.c: routines to read and write blocks from a file. */
/* Copyright (C) 2007  Edoardo S. Biagioni

 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.

 * this program is free.  You are welcome to use it if you are
 * my student or if you find it useful, but there are no guarantees
 * it will do what you want.
 */


#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include "p6.h"

/* only open the file once */
static int fd = -1;
static int devsize = 0;

/* returns the device size (in blocks) if the operation is successful,
 * and -1 otherwise */
int dev_open ()
{
  struct stat st;

  if (fd < 0) {
    fd = open ("simulated_device", O_RDWR);
    if (fd < 0) {
      perror ("open");
      return -1;
    }
    if (fstat (fd, &st) < 0) {
      perror ("fstat");
      return -1;
    }
    devsize = st.st_size / BLOCKSIZE;
  }
  return devsize;
}

/* returns 0 if the operation is successful, and -1 otherwise */
int read_block (int block_num, char * block)
{
  if (block_num >= devsize) {
    printf ("block number requested %d, maximum %d", block_num, devsize - 1);
    return -1;
  }
  if (lseek (fd, block_num * BLOCKSIZE, SEEK_SET) < 0) {
    perror ("lseek");
    return -1;
  }
  if (read (fd, block, BLOCKSIZE) != BLOCKSIZE) {
    perror ("read");
    return -1;
  }
  return 0;
}

/* returns 0 if the operation is successful, and -1 otherwise */
int write_block (int block_num, char * block)
{
  if (block_num >= devsize) {
    printf ("block number requested %d, maximum %d", block_num, devsize - 1);
    return -1;
  }
  if (lseek (fd, block_num * BLOCKSIZE, SEEK_SET) < 0) {
    perror ("lseek");
    return -1;
  }
  if (write (fd, block, BLOCKSIZE) != BLOCKSIZE) {
    perror ("write");
    return -1;
  }
  if (fsync (fd) < 0)
    perror ("fsync");		/* but return success anyway */
  return 0;
}