/* vdev.c - for 415.340 and 415.341 Assignment 2
   Provides the virtual device layer.
   Written by Robert Sheehan - 27/07/96
   */

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

#define NUMBLOCKS 64		/* a very small device */
#define BLOCKSIZE 256		/* small block size */

int vdev;			/* file descriptor for the virtual file system */

/*------------------------------------------------------------*/

void sysErrMsg(const char *message)
/* Shows the error message and quits. */
{
  extern int errno, sys_nerr;
  
  fprintf(stderr, "System error: %d - ", errno);
  if (errno > 0 && errno < sys_nerr)
    perror(message);
  else
    fprintf(stderr, "%s\n", message);
  exit(1);
}

/*------------------------------------------------------------*/

void vdev_init()
/* Initialises the virtual device.
   If the device doesn't exist it is created. */
{
  struct stat vdevStat;
  char blankblock[BLOCKSIZE];
  int block;
  
  if ((vdev = open("vdev", O_RDWR | O_CREAT, 0600)) == -1)
    sysErrMsg("Can't open the \"vdev\".");
  if (fstat(vdev, &vdevStat) == -1)
    sysErrMsg("Can't stat the \"vdev\".");
  if (vdevStat.st_size == 0){
    printf("\"vdev\" is empty.\n");
    memset(blankblock, 0, BLOCKSIZE);
    for (block = 0; block < NUMBLOCKS; block++)
      if (write(vdev, blankblock, BLOCKSIZE) < BLOCKSIZE)
	sysErrMsg("Writing the \"vdev\".");  
  }
}

/*------------------------------------------------------------*/
  
int vdev_blockread(const int blocknum, void *blockbuf)
/* Reads "blocknum" from the vdev and returns the data in "blockbuf".
   Possible errors are in vdev.h */
{
  if (blocknum < 0 || blocknum >= NUMBLOCKS)
    return VDBADBLOCK; 
  /* should really check "blockbuf" as well */
  if (lseek(vdev, blocknum * BLOCKSIZE, SEEK_SET) == -1)
    return VDBADDEV;
  if (read(vdev, blockbuf, BLOCKSIZE) != BLOCKSIZE)
    return VDBADDEV;
  return VDOK;
}

/*------------------------------------------------------------*/

int vdev_blockwrite(const int blocknum, const void *blockbuf)
/* Writes the contents of "blockbuf" into "blocknum" on the vdev.
   Possible errors are in vdev.h */
{
  if (blocknum < 0 || blocknum >= NUMBLOCKS)
    return VDBADBLOCK; 
  /* should really check "blockbuf" as well */
  if (lseek(vdev, blocknum * BLOCKSIZE, SEEK_SET) == -1)
    return VDBADDEV;
  if (write(vdev, blockbuf, BLOCKSIZE) != BLOCKSIZE)
    return VDBADDEV;
  return VDOK;
}

/*------------------------------------------------------------*/

int vdev_numblocks()
/* Returns the number of blocks on the vdev. */
{
  return NUMBLOCKS;
}

/*------------------------------------------------------------*/

int vdev_blocksize()
/* Returns the number of blocks on the vdev. */
{
  return BLOCKSIZE;
}