From: Martin Str|mberg <ams AT ludd DOT luth DOT se>
Message-Id: <199909221647.SAA27177@father.ludd.luth.se>
Subject: Re: FAT32 detection
To: djgpp-workers AT delorie DOT com (DJGPP-WORKERS)
Date: Wed, 22 Sep 1999 18:47:42 +0200 (MET DST)
In-Reply-To: <Pine.SUN.3.91.990921145316.19568B-100000@is> from Eli Zaretskii at "Sep 21, 99 02:53:40 pm"
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According to Eli Zaretskii:
> I don't remember, it was a long time ago.  Perhaps you could post an
> augmented source, and I will then test.

Ok, here it is.


Right,

							MartinS
/*
 * File getfatsz.c.
 *
 * Copyright (C) 1999 Martin Str<94>mberg <ams AT ludd DOT luth DOT se>.
 *
 * This software may be used freely so long as this copyright notice is
 * left intact. There is no warranty on this software.
 *
 * FAT size algorithm according to "Hardware White Paper, FAT: General
 * Overwiew of On-Disk Format" version 1.02, May 5, 1999, Microsoft
 * Corporation. Downloadable from <http://www.microsoft.com/hwdev/>.
 *
 */

#include <dpmi.h>
#include <go32.h>
#include <errno.h>
#include <sys/farptr.h>
#include <stdio.h>
#include <dos.h>
#include <errno.h>
#include <go32.h>
#include <dpmi.h>
#include <libc/dosio.h>
#include <sys/farptr.h>

/* Returns: -1 == error; 0 == result_str filled in. */
int
_get_fs_type( const int drive /* drive number (1=A:). */
            , char *const result_str  /* String to put result in. At least 9 cha
rs long. */
             )
{
  int n;
  __dpmi_regs r;

  /* Check DOZE version and return -1 if too low. */
  if( ( _get_dos_version(1) >> 8) < 4 )
  {
    errno = ENOSYS;
    return( -1 );
  }

  /* Call INT21, ax==0x6900 i.e. Get Disk Serial Number (sic!). */
  r.x.ax = 0x6900;
  r.h.bl = drive;
  r.h.bh = 0;
  r.x.ds = __tb >> 4;
  r.x.dx = __tb & 0x0f;
  __dpmi_int(0x21, &r);
  if( (r.x.flags & 1) == 0 )
  {
    /* Get the file system type. */
    for(n = 0; n < 8; n++)
    {
      result_str[n] = _farpeekb( _dos_ds, __tb + 0x11 + n);
    }
    result_str[8] = 0;

    /* Remove terminating spaces. */
    for(n = 7; n && result_str[n] == ' '; n-- )
    {
      result_str[n] = 0;
    }

    return( 0 );
  }

  errno = __doserr_to_errno(r.x.ax);
  return( -1 );

}

/* Returns number of bits in FAT; 0 == FAT of unknown size; -1 == error. */
int
_get_fat_size( const int drive /* drive number (1=A:). */
              )
{
  __dpmi_regs r = {{0}};
  int size;
  unsigned long bytes_per_sector, sectors_per_cluster, reserved_sectors;
  unsigned long number_of_fats, root_entries, fat16_size, fat32_size;
  unsigned long total16_sectors, total32_sectors;
  unsigned long root_sectors, fat_size, total_sectors, data_sectors;
  unsigned long number_of_clusters;

  r.x.ax = 0x440d;
  r.h.bl = drive;
  r.h.ch = 0x48; /* First we try a FAT32 disk drive. */
  r.h.cl = 0x60;
  r.x.ds = r.x.si = __tb >>4;
  r.x.dx = r.x.di = __tb & 0x0f;

  __dpmi_int(0x21, &r);
  if( r.x.flags & 0x01 )
  {
    /* Hmmpf! That didn't work; fall back to disk drive. */
    r.x.ax = 0x440d;
    r.h.bl = drive;
    r.h.ch = 0x08; /* Disk drive. */
    r.h.cl = 0x60;
    r.x.ds = r.x.si = __tb >>4;
    r.x.dx = r.x.di = __tb & 0x0f;

    __dpmi_int(0x21, &r);
    if( r.x.flags & 0x01 )
    {
      errno = ENOSYS;
      return(-1);
    }
  }

  bytes_per_sector = _farpeekw(_dos_ds, __tb+7+11-11);
  sectors_per_cluster = _farpeekb(_dos_ds, __tb+7+13-11);
  reserved_sectors = _farpeekw(_dos_ds, __tb+7+14-11);
  number_of_fats = _farpeekb(_dos_ds, __tb+7+16-11);
  root_entries = _farpeekw(_dos_ds, __tb+7+17-11);
  fat16_size = _farpeekw(_dos_ds, __tb+7+22-11);
  fat32_size = _farpeekl(_dos_ds, __tb+7+36-11);
  total16_sectors = _farpeekw(_dos_ds, __tb+7+19-11);
  total32_sectors = _farpeekl(_dos_ds, __tb+7+32-11);

  /* Check sectors_per_cluster, which might be zero. */
  if( sectors_per_cluster == 0 )
  {
    errno = ENOSYS;
    return( -1 );
  }

  /* Do the calculations. */
  root_sectors = ( (root_entries * 32)
                 + (bytes_per_sector - 1)
                   ) / bytes_per_sector;
  fat_size = fat16_size ? fat16_size : fat32_size;
  total_sectors = total16_sectors ? total16_sectors : total32_sectors;
  data_sectors = total_sectors - reserved_sectors - number_of_fats*fat_size
    - root_sectors;
  number_of_clusters = data_sectors / sectors_per_cluster;
  if( number_of_clusters < 4085 )
  {
    size = 12;
  }
  else if( number_of_clusters < 65525 )
  {
    /* The algorithm misdetects NTFS as FAT16, so lets check if it's NTFS. */
    char tmp[9];
    if( !_get_fs_type( drive, tmp ) && tmp[0] == 'N' && tmp[1] == 'T' )
    {
      errno = ENOSYS;
      return( -1 );
    }
    size = 16;
  }
  else
  {
    size = 32;
  }

#if 0
  fprintf(stderr, "bytes_per_sector = %ld.\n", bytes_per_sector);
  fprintf(stderr, "sectors_per_cluster = %ld.\n", sectors_per_cluster);
  fprintf(stderr, "reserved_sectors = %ld.\n", reserved_sectors);
  fprintf(stderr, "number_of_fats = %ld.\n", number_of_fats);
  fprintf(stderr, "root_entries = %ld.\n", root_entries);
  fprintf(stderr, "fat16_size = %ld.\n", fat16_size);
  fprintf(stderr, "fat32_size = %ld.\n", fat32_size);
  fprintf(stderr, "total16_sectors = %ld.\n", total16_sectors);
  fprintf(stderr, "total32_sectors = %ld.\n", total32_sectors);
  fprintf(stderr, "root_sectors = %ld.\n", root_sectors);
  fprintf(stderr, "data_sectors = %ld.\n", data_sectors);
  fprintf(stderr, "number_of_clusters = %ld.\n", number_of_clusters);
#endif

  return( size );

}

#if 1
int main(int argc, char *argv[])
{
  int ret;

  if( argc == 2
   && 'A' <= argv[1][0]
   && argv[1][0] <= 'Z' )
  {

    ret = _get_fat_size(argv[1][0] - 'A' + 1);
    fprintf(stderr, "_get_fat_size returned %d.\n", ret);

    return(0);
  }
  else
  {
    fprintf(stderr, "%s: run like this '%s C'.\n", argv[0], argv[0]);

    return(1);
  }

}
#endif