text: /*-
   * Copyright (c) 1998 Michael Smith <msmith@freebsd.org>
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   * $FreeBSD: src/sys/boot/i386/libi386/biosdisk.c,v 1.45 2004/09/21 06:46:44 wes Exp $
   */
  
  /*
   * BIOS disk device handling.
   * 
   * Ideas and algorithms from:
   *
   * - NetBSD libi386/biosdisk.c
   * - FreeBSD biosboot/disk.c
   *
   */
  
  #include <stand.h>
  
  #include <sys/disklabel32.h>
  #include <sys/disklabel64.h>
  #include <sys/diskmbr.h>
  #include <sys/dtype.h>
  #include <machine/bootinfo.h>
  
  #include <stdarg.h>
  
  #include <bootstrap.h>
  #include <btxv86.h>
  #include "libi386.h"
  
  #define BIOS_NUMDRIVES		0x475
  #define BIOSDISK_SECSIZE	512
  #define BUFSIZE			(4 * BIOSDISK_SECSIZE)
  #define	MAXBDDEV		MAXDEV
  
  #define DT_ATAPI		0x10		/* disk type for ATAPI floppies */
  #define WDMAJOR			0		/* major numbers for devices we frontend for */
  #define WFDMAJOR		1
  #define FDMAJOR			2
  #define DAMAJOR			4
  
  #ifdef DISK_DEBUG
  # define DEBUG(fmt, args...)	printf("%s: " fmt "\n" , __func__ , ## args)
  #else
  # define DEBUG(fmt, args...)
  #endif
  
  struct open_disk {
      int			od_dkunit;		/* disk unit number */
      int			od_unit;		/* BIOS unit number */
      int			od_cyl;			/* BIOS geometry */
      int			od_hds;
      int			od_sec;
      int			od_boff;		/* block offset from beginning of BIOS disk */
      int			od_flags;
  #define BD_MODEINT13		0x0000
  #define BD_MODEEDD1		0x0001
  #define BD_MODEEDD3		0x0002
  #define BD_MODEMASK		0x0003
  #define BD_FLOPPY		0x0004
  #define BD_LABELOK		0x0008
  #define BD_PARTTABOK		0x0010
      union {
  	struct disklabel32		od_disklabel;
  	struct disklabel64		od_disklabel64;
      };
      int				od_nslices;	/* slice count */
      struct dos_partition	od_slicetab[NEXTDOSPART];
  };
  
  /*
   * List of BIOS devices, translation from disk unit number to
   * BIOS unit number.
   */
  static struct bdinfo
  {
      int		bd_unit;		/* BIOS unit number */
      int		bd_flags;
      int		bd_type;		/* BIOS 'drive type' (floppy only) */
  } bdinfo [MAXBDDEV];
  static int nbdinfo = 0;
  
  static int	bd_getgeom(struct open_disk *od);
  static int	bd_read(struct open_disk *od, daddr_t dblk, int blks,
  		    caddr_t dest);
  static int	bd_write(struct open_disk *od, daddr_t dblk, int blks,
  		    caddr_t dest);
  
  static int	bd_int13probe(struct bdinfo *bd);
  
  static void	bd_printslice(struct open_disk *od, struct dos_partition *dp,
  		    char *prefix, int verbose);
  static void	bd_printbsdslice(struct open_disk *od, daddr_t offset,
  		    char *prefix, int verbose);
  
  static int	bd_init(void);
  static int	bd_strategy(void *devdata, int flag, daddr_t dblk,
  		    size_t size, char *buf, size_t *rsize);
  static int	bd_realstrategy(void *devdata, int flag, daddr_t dblk,
  		    size_t size, char *buf, size_t *rsize);
  static int	bd_open(struct open_file *f, ...);
  static int	bd_close(struct open_file *f);
  static void	bd_print(int verbose);
  
  /*
   * Max number of sectors to bounce-buffer if the request crosses a 64k boundary
   */
  #define BOUNCEBUF_SIZE	8192
  #define BOUNCEBUF_SECTS	(BOUNCEBUF_SIZE / BIOSDISK_SECSIZE)
  
  struct devsw biosdisk = {
      "disk", 
      DEVT_DISK, 
      bd_init,
      bd_strategy, 
      bd_open, 
      bd_close, 
      noioctl,
      bd_print,
      NULL
  };
  
  static int	bd_opendisk(struct open_disk **odp, struct i386_devdesc *dev);
  static void	bd_closedisk(struct open_disk *od);
  static int	bd_bestslice(struct open_disk *od);
  static void	bd_chainextended(struct open_disk *od, u_int32_t base,
  					u_int32_t offset);
  
  static caddr_t	bounce_base;
  
  /*
   * Translate between BIOS device numbers and our private unit numbers.
   */
  int
  bd_bios2unit(int biosdev)
  {
      int		i;
      
      DEBUG("looking for bios device 0x%x", biosdev);
      for (i = 0; i < nbdinfo; i++) {
  	DEBUG("bd unit %d is BIOS device 0x%x", i, bdinfo[i].bd_unit);
  	if (bdinfo[i].bd_unit == biosdev)
  	    return(i);
      }
      return(-1);
  }
  
  int
  bd_unit2bios(int unit)
  {
      if ((unit >= 0) && (unit < nbdinfo))
  	return(bdinfo[unit].bd_unit);
      return(-1);
  }
  
  /*    
   * Quiz the BIOS for disk devices, save a little info about them.
   */
  static int
  bd_init(void) 
  {
      int	base, unit, nfd = 0;
  
      if (bounce_base == NULL)
  	bounce_base = malloc(BOUNCEBUF_SIZE * 2);
  
      /* sequence 0, 0x80 */
      for (base = 0; base <= 0x80; base += 0x80) {
  	for (unit = base; (nbdinfo < MAXBDDEV); unit++) {
  	    /* check the BIOS equipment list for number of fixed disks */
  	    if((base == 0x80) &&
  	       (nfd >= *(unsigned char *)PTOV(BIOS_NUMDRIVES)))
  	        break;
  
  	    bdinfo[nbdinfo].bd_unit = unit;
  	    bdinfo[nbdinfo].bd_flags = (unit < 0x80) ? BD_FLOPPY : 0;
  
  	    if (!bd_int13probe(&bdinfo[nbdinfo]))
  		break;
  
  	    /* XXX we need "disk aliases" to make this simpler */
  	    printf("BIOS drive %c: is disk%d\n", 
  		   (unit < 0x80) ? ('A' + unit) : ('C' + unit - 0x80), nbdinfo);
  	    nbdinfo++;
  	    if (base == 0x80)
  	        nfd++;
  	}
      }
      return(0);
  }
  
  /*
   * Try to detect a device supported by the legacy int13 BIOS
   */
  static int
  bd_int13probe(struct bdinfo *bd)
  {
      v86.ctl = V86_FLAGS;
      v86.addr = 0x13;
      v86.eax = 0x800;
      v86.edx = bd->bd_unit;
      v86int();
      
      if (!(v86.efl & 0x1) &&				/* carry clear */
  	((v86.edx & 0xff) > ((unsigned)bd->bd_unit & 0x7f))) {	/* unit # OK */
  
  	/*
  	 * Ignore devices with an absurd sector size.
  	 */
  	if ((v86.ecx & 0x3f) == 0) {
  		DEBUG("Invalid geometry for unit %d", bd->bd_unit);
  		return(0);
  	}
  	bd->bd_flags |= BD_MODEINT13;
  	bd->bd_type = v86.ebx & 0xff;
  
  	/* Determine if we can use EDD with this device. */
  	v86.ctl = V86_FLAGS;
  	v86.addr = 0x13;
  	v86.eax = 0x4100;
  	v86.edx = bd->bd_unit;
  	v86.ebx = 0x55aa;
  	v86int();
  	if (!(v86.efl & 0x1) &&				/* carry clear */
  	    ((v86.ebx & 0xffff) == 0xaa55) &&		/* signature */
  	    (v86.ecx & 0x1)) {				/* packets mode ok */
  	    bd->bd_flags |= BD_MODEEDD1;
  	    if((v86.eax & 0xff00) > 0x300)
  	        bd->bd_flags |= BD_MODEEDD3;
  	}
  	return(1);
      }
      return(0);
  }
  
  /*
   * Print information about disks
   */
  static void
  bd_print(int verbose)
  {
      int				i, j;
      char			line[80];
      struct i386_devdesc		dev;
      struct open_disk		*od;
      struct dos_partition	*dptr;
      
      for (i = 0; i < nbdinfo; i++) {
  	sprintf(line, "    disk%d:   BIOS drive %c:\n", i, 
  		(bdinfo[i].bd_unit < 0x80) ? ('A' + bdinfo[i].bd_unit) : ('C' + bdinfo[i].bd_unit - 0x80));
  	pager_output(line);
  
  	/* try to open the whole disk */
  	dev.d_kind.biosdisk.unit = i;
  	dev.d_kind.biosdisk.slice = -1;
  	dev.d_kind.biosdisk.partition = -1;
  	
  	if (!bd_opendisk(&od, &dev)) {
  
  	    /* Do we have a partition table? */
  	    if (od->od_flags & BD_PARTTABOK) {
  		dptr = &od->od_slicetab[0];
  
  		/* Check for a "dedicated" disk */
  		if (((dptr[3].dp_typ == DOSPTYP_386BSD) ||
  			(dptr[3].dp_typ == DOSPTYP_NETBSD)) &&
  		    (dptr[3].dp_start == 0) &&
  		    (dptr[3].dp_size == 50000)) {
  		    sprintf(line, "      disk%d", i);
  		    bd_printbsdslice(od, 0, line, verbose);
  		} else {
  		    for (j = 0; j < od->od_nslices; j++) {
  		        sprintf(line, "      disk%ds%d", i, j + 1);
  			bd_printslice(od, &dptr[j], line, verbose);
                      }
                  }
  	    }
  	    bd_closedisk(od);
  	}
      }
  }
  
  /*
   * Print information about slices on a disk.  For the size calculations we
   * assume a 512 byte sector.
   */
  static void
  bd_printslice(struct open_disk *od, struct dos_partition *dp, char *prefix,
  	int verbose)
  {
  	char line[80];
  
  	switch (dp->dp_typ) {
  	case DOSPTYP_386BSD:
  	case DOSPTYP_NETBSD:
  	/* XXX: possibly add types 0 and 1, as in subr_disk, for gpt magic */
  		bd_printbsdslice(od, (daddr_t)dp->dp_start, prefix, verbose);
  		return;
  	case DOSPTYP_LINSWP:
  		if (verbose)
  			sprintf(line, "%s: Linux swap %.6dMB (%d - %d)\n",
  			    prefix, dp->dp_size / 2048,
  			    dp->dp_start, dp->dp_start + dp->dp_size);
  		else
  			sprintf(line, "%s: Linux swap\n", prefix);
  		break;
  	case DOSPTYP_LINUX:
  		/*
  		 * XXX
  		 * read the superblock to confirm this is an ext2fs partition?
  		 */
  		if (verbose)
  			sprintf(line, "%s: ext2fs  %.6dMB (%d - %d)\n", prefix,
  			    dp->dp_size / 2048, dp->dp_start,
  			    dp->dp_start + dp->dp_size);
  		else
  			sprintf(line, "%s: ext2fs\n", prefix);
  		break;
  	case 0x00:				/* unused partition */
  	case DOSPTYP_EXT:
  		return;
  	case 0x01:
  		if (verbose)
  			sprintf(line, "%s: FAT-12  %.6dMB (%d - %d)\n", prefix,
  			    dp->dp_size / 2048, dp->dp_start,
  			    dp->dp_start + dp->dp_size);
  		else
  			sprintf(line, "%s: FAT-12\n", prefix);
  		break;
  	case 0x04:
  	case 0x06:
  	case 0x0e:
  		if (verbose)
  			sprintf(line, "%s: FAT-16  %.6dMB (%d - %d)\n", prefix,
  			    dp->dp_size / 2048, dp->dp_start,
  			    dp->dp_start + dp->dp_size);
  		else
  			sprintf(line, "%s: FAT-16\n", prefix);
  		break;
  	case 0x0b:
  	case 0x0c:
  		if (verbose)
  			sprintf(line, "%s: FAT-32  %.6dMB (%d - %d)\n", prefix,
  			    dp->dp_size / 2048, dp->dp_start,
  			    dp->dp_start + dp->dp_size);
  		else
  			sprintf(line, "%s: FAT-32\n", prefix);
  		break;
  	default:
  		if (verbose)
  			sprintf(line, "%s: Unknown fs: 0x%x  %.6dMB (%d - %d)\n",
  			    prefix, dp->dp_typ, dp->dp_size / 2048,
  			    dp->dp_start, dp->dp_start + dp->dp_size);
  		else
  			sprintf(line, "%s: Unknown fs: 0x%x\n", prefix,
  			    dp->dp_typ);
  	}
  	pager_output(line);
  }
  
  static void
  print_partition(u_int8_t fstype, unsigned long long offset,
  		unsigned long long size, int i, int od_flags,
  		char *prefix, int verbose, int type)
  {
  	char	line[80];
  
  	/*
  	 * For each partition, make sure we know what type of fs it is.  If
  	 * not, then skip it.  However, since floppies often have bogus
  	 * fstypes, print the 'a' partition on a floppy even if it is marked
  	 * unused.
  	 */
  	if ((fstype == FS_SWAP) ||
  	    (fstype == FS_VINUM) ||
  	    (fstype == FS_HAMMER) ||
  	    (fstype == FS_HAMMER2) ||
  	    (fstype == FS_BSDFFS) ||
  	    (fstype == FS_ZFS) ||
  	    (fstype == FS_JFS2) ||
  	    ((fstype == FS_UNUSED) &&
  	     (od_flags & BD_FLOPPY) && (i == 0))) {
  
  		/* Only print out statistics in verbose mode */
  		if (verbose) {
  			sprintf(line, "%c %s%c: %s  %.6lluMB (%llu - %llu)\n",
  			    /* prefix disks that can be used to load modules with '*' */
  			    ((fstype == FS_BSDFFS) || (fstype == FS_UNUSED) ||
  			    (fstype == FS_VINUM)) ? '*' : ' ',
  			    prefix, 'a' + i,
  			    (fstype == FS_SWAP) ? "swap" :
  			    (fstype == FS_VINUM) ? "vinum" :
  			    (fstype == FS_HAMMER) ? "HAMMER" :
  			    (fstype == FS_HAMMER2) ? "HAMMER2" :
  			    (fstype == FS_JFS2) ? "JFS2" :
  			    (fstype == FS_ZFS) ? "ZFS" :
  			    (fstype == FS_BSDFFS) ? "FFS" :
  			    "(unknown)",
  			    (type==32)?(size / 2048):(size/1024/1024),
  			    offset,
  			    offset + size);
  		} else {
  			sprintf(line, "%c %s%c: %s\n",
  			    /* prefix disks that can be used to load modules with '*' */
  			    ((fstype == FS_BSDFFS) || (fstype == FS_UNUSED) ||
  			    (fstype == FS_VINUM)) ? '*' : ' ',
  			    prefix, 'a' + i,
  			    (fstype == FS_SWAP) ? "swap" :
  			    (fstype == FS_VINUM) ? "vinum" :
  			    (fstype == FS_HAMMER) ? "HAMMER" :
  			    (fstype == FS_HAMMER2) ? "HAMMER2" :
  			    (fstype == FS_JFS2) ? "JFS2" :
  			    (fstype == FS_ZFS) ? "ZFS" :
  			    (fstype == FS_BSDFFS) ? "FFS" :
  			    "(unknown)");
  		}
  
  		pager_output(line);
  	}
  }
  
  /*
   * Print out each valid partition in the disklabel of a FreeBSD slice.
   * For size calculations, we assume a 512 byte sector size.
   */
  static void
  bd_printbsdslice(struct open_disk *od, daddr_t offset, char *prefix,
      int verbose)
  {
  	char		line[80];
  	char		buf[BIOSDISK_SECSIZE*2];
  	struct disklabel32	*lp = NULL;
  	struct disklabel64	*lp64 = NULL;
  	int			i;
  
  	/* read disklabel */
  	if (bd_read(od, offset + LABELSECTOR32, 1, buf))
  		return;
  	lp =(struct disklabel32 *)(&buf[0]);
  	if (lp->d_magic != DISKMAGIC32) {
  		if (bd_read(od, offset, 2, buf))
  			return;
  
  		lp64 =(struct disklabel64 *)(&buf[0]);
  		if (lp64->d_magic != DISKMAGIC64) {
  			sprintf(line, "%s: bad disklabel\n", prefix);
  			pager_output(line);
  			return;
  		}
  		lp = NULL; /* PARANOID */
  	}
  	if (lp64) {
  		/* We got ourselves a disklabel64 here */
  		for (i = 0; i < lp64->d_npartitions; i++) {
  			if (lp64->d_partitions[i].p_bsize == 0)
  				continue;
  
  			print_partition(lp64->d_partitions[i].p_fstype,
  					lp64->d_partitions[i].p_boffset,
  					lp64->d_partitions[i].p_bsize,
  					i, od->od_flags, prefix, verbose, 64);
  		}
  	} else if (lp) {
  		/* Print partitions */
  		for (i = 0; i < lp->d_npartitions; i++) {
  			print_partition(lp->d_partitions[i].p_fstype,
  					lp->d_partitions[i].p_offset,
  					lp->d_partitions[i].p_size,
  					i, od->od_flags, prefix, verbose, 32);
  		}
  	}
  }
  
  
  /*
   * Attempt to open the disk described by (dev) for use by (f).
   *
   * Note that the philosophy here is "give them exactly what
   * they ask for".  This is necessary because being too "smart"
   * about what the user might want leads to complications.
   * (eg. given no slice or partition value, with a disk that is
   *  sliced - are they after the first BSD slice, or the DOS
   *  slice before it?)
   */
  static int 
  bd_open(struct open_file *f, ...)
  {
      va_list			ap;
      struct i386_devdesc		*dev;
      struct open_disk		*od;
      int				error;
  
      va_start(ap, f);
      dev = va_arg(ap, struct i386_devdesc *);
      va_end(ap);
      if ((error = bd_opendisk(&od, dev)))
  	return(error);
      
      /*
       * Save our context
       */
      ((struct i386_devdesc *)(f->f_devdata))->d_kind.biosdisk.data = od;
      DEBUG("open_disk %p, partition at 0x%x", od, od->od_boff);
      return(0);
  }
  
  static int
  bd_opendisk(struct open_disk **odp, struct i386_devdesc *dev)
  {
      struct dos_partition	*dptr;
      struct disklabel32		*lp;
      struct disklabel64		*lp64;
      struct open_disk		*od;
      int				sector, slice, i;
      int				error;
      static char			buf[BUFSIZE];
  
      if (dev->d_kind.biosdisk.unit >= nbdinfo) {
  	DEBUG("attempt to open nonexistent disk");
  	return(ENXIO);
      }
      
      od = (struct open_disk *)malloc(sizeof(struct open_disk));
      if (!od) {
  	DEBUG("no memory");
  	return (ENOMEM);
      }
  
      /* Look up BIOS unit number, intialise open_disk structure */
      od->od_dkunit = dev->d_kind.biosdisk.unit;
      od->od_unit = bdinfo[od->od_dkunit].bd_unit;
      od->od_flags = bdinfo[od->od_dkunit].bd_flags;
      od->od_boff = 0;
      od->od_nslices = 0;
      error = 0;
      DEBUG("open '%s', unit 0x%x slice %d partition %c",
  	     i386_fmtdev(dev), dev->d_kind.biosdisk.unit, 
  	     dev->d_kind.biosdisk.slice, dev->d_kind.biosdisk.partition + 'a');
  
      /* Get geometry for this open (removable device may have changed) */
      if (bd_getgeom(od)) {
  	DEBUG("can't get geometry");
  	error = ENXIO;
  	goto out;
      }
  
      /*
       * Following calculations attempt to determine the correct value
       * for d->od_boff by looking for the slice and partition specified,
       * or searching for reasonable defaults.
       */
  
      /*
       * Find the slice in the DOS slice table.
       */
      if (bd_read(od, 0, 1, buf)) {
  	DEBUG("error reading MBR");
  	error = EIO;
  	goto out;
      }
  
      /* 
       * Check the slice table magic.
       */
      if (((u_char)buf[0x1fe] != 0x55) || ((u_char)buf[0x1ff] != 0xaa)) {
  	/* If a slice number was explicitly supplied, this is an error */
  	if (dev->d_kind.biosdisk.slice > 0) {
  	    DEBUG("no slice table/MBR (no magic)");
  	    error = ENOENT;
  	    goto out;
  	}
  	sector = 0;
  	goto unsliced;		/* may be a floppy */
      }
  
      /*
       * copy the partition table, then pick up any extended partitions.  The
       * base partition table always has four entries, even if some of them
       * represented extended partitions.  However, any additional sub-extended
       * partitions will be silently recursed and not included in the slice
       * table.
       */
      bcopy(buf + DOSPARTOFF, &od->od_slicetab,
        sizeof(struct dos_partition) * NDOSPART);
      od->od_nslices = NDOSPART;
  
      dptr = &od->od_slicetab[0];
      for (i = 0; i < NDOSPART; i++, dptr++) {
  	if ((dptr->dp_typ == DOSPTYP_EXT) || (dptr->dp_typ == DOSPTYP_EXTLBA))
  	    bd_chainextended(od, dptr->dp_start, 0); /* 1st offset is zero */
      }
      od->od_flags |= BD_PARTTABOK;
      dptr = &od->od_slicetab[0];
  
      /*
       * Overflow entries are not loaded into memory but we still keep
       * track of the count.  Fix it up now.
       */
      if (od->od_nslices > NEXTDOSPART)
  	od->od_nslices = NEXTDOSPART;
  
      /* 
       * Is this a request for the whole disk? 
       */
      if (dev->d_kind.biosdisk.slice == -1) {
  	sector = 0;
  	goto unsliced;
      }
  
      /*
       * if a slice number was supplied but not found, this is an error.
       */
      if (dev->d_kind.biosdisk.slice > 0) {
          slice = dev->d_kind.biosdisk.slice - 1;
          if (slice >= od->od_nslices) {
              DEBUG("slice %d not found", slice);
  	    error = ENOENT;
  	    goto out;
          }
      }
  
      /*
       * Check for the historically bogus MBR found on true dedicated disks
       */
      if ((dptr[3].dp_typ == DOSPTYP_386BSD) &&
        (dptr[3].dp_start == 0) &&
        (dptr[3].dp_size == 50000)) {
          sector = 0;
          goto unsliced;
      }
  
      /* Try to auto-detect the best slice; this should always give a slice number */
      if (dev->d_kind.biosdisk.slice == 0) {
  	slice = bd_bestslice(od);
          if (slice == -1) {
  	    error = ENOENT;
              goto out;
          }
          dev->d_kind.biosdisk.slice = slice;
      }
  
      dptr = &od->od_slicetab[0];
      /*
       * Accept the supplied slice number unequivocally (we may be looking
       * at a DOS partition).
       */
      dptr += (dev->d_kind.biosdisk.slice - 1);	/* we number 1-4, offsets are 0-3 */
      sector = dptr->dp_start;
      DEBUG("slice entry %d at %d, %d sectors", dev->d_kind.biosdisk.slice - 1, sector, dptr->dp_size);
  
      /*
       * If we are looking at a BSD slice, and the partition is < 0, assume the 'a' partition
       */
      if ((dptr->dp_typ == DOSPTYP_386BSD) && (dev->d_kind.biosdisk.partition < 0))
  	dev->d_kind.biosdisk.partition = 0;
  
  unsliced:
      /* 
       * Now we have the slice offset, look for the partition in the disklabel if we have
       * a partition to start with.
       *
       * XXX we might want to check the label checksum.
       */
      if (dev->d_kind.biosdisk.partition < 0) {
  	od->od_boff = sector;		/* no partition, must be after the slice */
  	DEBUG("opening raw slice");
      } else {
  	
  	if (bd_read(od, sector + LABELSECTOR32, 1, buf)) {
  	    DEBUG("error reading disklabel");
  	    error = EIO;
  	    goto out;
  	}
  	DEBUG("copy %d bytes of label from %p to %p", sizeof(struct disklabel32), buf + LABELOFFSET32, &od->od_disklabel);
  	bcopy(buf + LABELOFFSET32, &od->od_disklabel, sizeof(struct disklabel32));
  	lp = &od->od_disklabel;
  
  	if (lp->d_magic == DISKMAGIC32) {
  	    od->od_flags |= BD_LABELOK;
  
  	    if (dev->d_kind.biosdisk.partition >= lp->d_npartitions) {
  		DEBUG("partition '%c' exceeds partitions in table (a-'%c')",
  		      'a' + dev->d_kind.biosdisk.partition, 'a' + lp->d_npartitions);
  		error = EPART;
  		goto out;
  
  	    }
  
  #ifdef DISK_DEBUG
  	    /* Complain if the partition is unused unless this is a floppy. */
  	    if ((lp->d_partitions[dev->d_kind.biosdisk.partition].p_fstype == FS_UNUSED) &&
  		!(od->od_flags & BD_FLOPPY))
  		DEBUG("warning, partition marked as unused");
  #endif
  	    
  	    od->od_boff = 
  		    lp->d_partitions[dev->d_kind.biosdisk.partition].p_offset -
  		    lp->d_partitions[RAW_PART].p_offset +
  		    sector;
  
  	    goto out;
  	}
  
  	/* else maybe DISKLABEL64? */
  
  	if (bd_read(od, sector, (sizeof(od->od_disklabel64) + 511) / 512, buf)) {
  	    DEBUG("error reading disklabel");
  	    error = EIO;
  	    goto out;
  	}
  	DEBUG("copy %d bytes of label from %p to %p", sizeof(od->od_disklabel64), buf, &od->od_disklabel64);
  	bcopy(buf, &od->od_disklabel64, sizeof(od->od_disklabel64));
  	lp64 = &od->od_disklabel64;
  
  	if (lp64->d_magic == DISKMAGIC64) {
  	    od->od_flags |= BD_LABELOK;
  
  	    if (dev->d_kind.biosdisk.partition >= lp64->d_npartitions ||
  		lp64->d_partitions[dev->d_kind.biosdisk.partition].p_bsize == 0) {
  		DEBUG("partition '%c' exceeds partitions in table (a-'%c')",
  		      'a' + dev->d_kind.biosdisk.partition, 'a' + lp64->d_npartitions);
  		error = EPART;
  		goto out;
  
  	    }
  
  	    od->od_boff = 
  		    lp64->d_partitions[dev->d_kind.biosdisk.partition].p_boffset / 512 +
  		    sector;
  
  	    DEBUG("disklabel64 slice at %d", od->od_boff);
  
  	} else {
  	    DEBUG("no disklabel");
  	    error = ENOENT;
  	}
      }
  
   out:
      if (error) {
  	free(od);
      } else {
  	*odp = od;	/* return the open disk */
      }
      return(error);
  }
  
  
  static void
  bd_chainextended(struct open_disk *od, u_int32_t base, u_int32_t offset)
  {
          char   buf[BIOSDISK_SECSIZE];
          struct dos_partition *dp1, *dp2;
  	int i;
  
  	if (bd_read(od, (daddr_t)(base + offset), 1, buf)) {
                  printf("\nerror reading extended partition table");
  		return;
  	}
  
  	/*
  	 * dp1 points to the first record in the on-disk XPT,
  	 * dp2 points to the next entry in the in-memory parition table.
  	 *
  	 * NOTE: dp2 may be out of bounds if od_nslices >= NEXTDOSPART.
  	 *
  	 * NOTE: unlike the extended partitions in our primary dos partition
  	 * table, we do not record recursed extended partitions themselves 
  	 * in our in-memory partition table.
  	 *
  	 * NOTE: recording within our in-memory table must be breadth first
  	 * ot match what the kernel does.  Thus, two passes are required.
  	 *
  	 * NOTE: partitioning programs which support extended partitions seem
  	 * to always use the first entry for the user partition and the
  	 * second entry to chain, and also appear to disallow more then one
  	 * extended partition at each level.  Nevertheless we make our code
  	 * somewhat more generic (and the same as the kernel's own slice
  	 * scan).
  	 */
  	dp1 = (struct dos_partition *)(&buf[DOSPARTOFF]);
  	dp2 = &od->od_slicetab[od->od_nslices];
  
  	for (i = 0; i < NDOSPART; ++i, ++dp1) {
  		if (dp1->dp_scyl == 0 && dp1->dp_shd == 0 &&
  		    dp1->dp_ssect == 0 && dp1->dp_start == 0 && 
  		    dp1->dp_size == 0) {
  			continue;
  		}
  		if ((dp1->dp_typ == DOSPTYP_EXT) || 
  		    (dp1->dp_typ == DOSPTYP_EXTLBA)) {
  			/*
  			 * breadth first traversal, must skip in the 
  			 * first pass
  			 */
  			continue;
  		}
  
  		/*
  		 * Only load up the in-memory data if we haven't overflowed
  		 * our in-memory array.
  		 */
  		if (od->od_nslices < NEXTDOSPART) {
  			dp2->dp_typ = dp1->dp_typ;
  			dp2->dp_start = base + offset + dp1->dp_start;
  			dp2->dp_size = dp1->dp_size;
  		}
  		++od->od_nslices;
  		++dp2;
  	}
  
  	/*
  	 * Pass 2 - handle extended partitions.  Note that the extended
  	 * slice itself is not stored in the slice array when we recurse,
  	 * but any 'original' top-level extended slices are.  This is to
  	 * match what the kernel does.
  	 */
  	dp1 -= NDOSPART;
  	for (i = 0; i < NDOSPART; ++i, ++dp1) {
  		if (dp1->dp_scyl == 0 && dp1->dp_shd == 0 &&
  		    dp1->dp_ssect == 0 && dp1->dp_start == 0 && 
  		    dp1->dp_size == 0) {
  			continue;
  		}
  		if ((dp1->dp_typ == DOSPTYP_EXT) || 
  		    (dp1->dp_typ == DOSPTYP_EXTLBA))
  			bd_chainextended(od, base, dp1->dp_start);
  	}
  }
  
  /*
   * Search for a slice with the following preferences:
   *
   * 1: Active FreeBSD slice
   * 2: Non-active FreeBSD slice
   * 3: Active Linux slice
   * 4: non-active Linux slice
   * 5: Active FAT/FAT32 slice
   * 6: non-active FAT/FAT32 slice
   */
  #define PREF_RAWDISK	0
  #define PREF_FBSD_ACT	1
  #define PREF_FBSD	2
  #define PREF_LINUX_ACT	3
  #define PREF_LINUX	4
  #define PREF_DOS_ACT	5
  #define PREF_DOS	6
  #define PREF_NONE	7
  
  /*
   * slicelimit is in the range 0 .. NDOSPART
   */
  static int
  bd_bestslice(struct open_disk *od)
  {
  	struct dos_partition *dp;
  	int pref, preflevel;
  	int i, prefslice;
  	
  	prefslice = 0;
  	preflevel = PREF_NONE;
  
  	dp = &od->od_slicetab[0];
  	for (i = 0; i < od->od_nslices; i++, dp++) {
  		switch (dp->dp_typ) {
  		case DOSPTYP_386BSD:		/* FreeBSD */
  			pref = dp->dp_flag & 0x80 ? PREF_FBSD_ACT : PREF_FBSD;
  			break;
  
  		case DOSPTYP_LINUX:
  			pref = dp->dp_flag & 0x80 ? PREF_LINUX_ACT : PREF_LINUX;
  			break;
      
  		case 0x01:		/* DOS/Windows */
  		case 0x04:
  		case 0x06:
  		case 0x0b:
  		case 0x0c:
  		case 0x0e:
  			pref = dp->dp_flag & 0x80 ? PREF_DOS_ACT : PREF_DOS;
  			break;
  
  		default:
  		        pref = PREF_NONE;
  		}
  		if (pref < preflevel) {
  			preflevel = pref;
  			prefslice = i + 1;
  		}
  	}
  	return (prefslice);
  }
   
  static int 
  bd_close(struct open_file *f)
  {
      struct open_disk	*od = (struct open_disk *)(((struct i386_devdesc *)(f->f_devdata))->d_kind.biosdisk.data);
  
      bd_closedisk(od);
      return(0);
  }
  
  static void
  bd_closedisk(struct open_disk *od)
  {
      DEBUG("open_disk %p", od);
  #if 0
      /* XXX is this required? (especially if disk already open...) */
      if (od->od_flags & BD_FLOPPY)
  	delay(3000000);
  #endif
      free(od);
  }
  
  static int 
  bd_strategy(void *devdata, int rw, daddr_t dblk, size_t size, char *buf, size_t *rsize)
  {
      struct bcache_devdata	bcd;
      struct open_disk	*od = (struct open_disk *)(((struct i386_devdesc *)devdata)->d_kind.biosdisk.data);
  
      bcd.dv_strategy = bd_realstrategy;
      bcd.dv_devdata = devdata;
      return(bcache_strategy(&bcd, od->od_unit, rw, dblk+od->od_boff, size, buf, rsize));
  }
  
  static int 
  bd_realstrategy(void *devdata, int rw, daddr_t dblk, size_t size, char *buf, size_t *rsize)
  {
      struct open_disk	*od = (struct open_disk *)(((struct i386_devdesc *)devdata)->d_kind.biosdisk.data);
      int			blks;
  #ifdef BD_SUPPORT_FRAGS
      char		fragbuf[BIOSDISK_SECSIZE];
      size_t		fragsize;
  
      fragsize = size % BIOSDISK_SECSIZE;
  #else
      if (size % BIOSDISK_SECSIZE)
  	panic("bd_strategy: %d bytes I/O not multiple of block size", size);
  #endif
  
      DEBUG("open_disk %p", od);
  
      switch(rw){
      case F_READ:
  	blks = size / BIOSDISK_SECSIZE;
  	DEBUG("read %d from %d to %p", blks, dblk, buf);
  
  	if (rsize)
  	    *rsize = 0;
  	if (blks && bd_read(od, dblk, blks, buf)) {
  	    DEBUG("read error");
  	    return (EIO);
  	}
  #ifdef BD_SUPPORT_FRAGS
  	DEBUG("bd_strategy: frag read %d from %d+%d to %p", 
  	     fragsize, dblk, blks, buf + (blks * BIOSDISK_SECSIZE));
  	if (fragsize && bd_read(od, dblk + blks, 1, fragsize)) {
  	    DEBUG("frag read error");
  	    return(EIO);
  	}
  	bcopy(fragbuf, buf + (blks * BIOSDISK_SECSIZE), fragsize);
  #endif
  	if (rsize)
  	    *rsize = size;
  	return (0);
      case F_WRITE :
  	blks = size / BIOSDISK_SECSIZE;
  	DEBUG("write %d from %d to %p", blks, dblk, buf);
  
  	if (rsize)
  	    *rsize = 0;
  	if (blks && bd_write(od, dblk, blks, buf)) {
  	    DEBUG("write error");
  	    return (EIO);
  	}
  #ifdef BD_SUPPORT_FRAGS
  	if(fragsize) {
  	    DEBUG("Attempted to write a frag");
  	    return (EIO);
  	}
  #endif
  	if (rsize)
  	    *rsize = size;
  	return (0);
      default:
  	break; /* DO NOTHING */
      }
      return EROFS;
  }
  
  static int
  bd_read(struct open_disk *od, daddr_t dblk, int blks, caddr_t dest)
  {
      u_int	x, bpc, cyl, hd, sec, result, resid, retry, maxfer;
      caddr_t	p, xp, bbuf, breg;
      
      /* Just in case some idiot actually tries to read -1 blocks... */
      if (blks < 0)
  	return (-1);
  
      bpc = (od->od_sec * od->od_hds);		/* blocks per cylinder */
      resid = blks;
      p = dest;
  
      /*
       * Always bounce.  Our buffer is probably not segment-addressable.
       */
      if (1) {
  
  	/* 
  	 * There is a 64k physical boundary somewhere in the destination
  	 * buffer, so we have to arrange a suitable bounce buffer.  Allocate
  	 * a buffer twice as large as we need to.  Use the bottom half unless
  	 * there is a break there, in which case we use the top half.
  	 */
  	bbuf = bounce_base;
  	x = min(BOUNCEBUF_SECTS, (unsigned)blks);
  
  	if (((u_int32_t)VTOP(bbuf) & 0xffff8000) ==
  	    ((u_int32_t)VTOP(bbuf + x * BIOSDISK_SECSIZE - 1) & 0xffff8000)) {
  	    breg = bbuf;
  	} else {
  	    breg = bbuf + x * BIOSDISK_SECSIZE;
  	}
  	maxfer = x;		/* limit transfers to bounce region size */
      } else {
  	breg = bbuf = NULL;
  	maxfer = 0;
      }
      
      while (resid > 0) {
  	x = dblk;
  	cyl = x / bpc;			/* block # / blocks per cylinder */
  	x %= bpc;			/* block offset into cylinder */
  	hd = x / od->od_sec;		/* offset / blocks per track */
  	sec = x % od->od_sec;		/* offset into track */
  
  	/* play it safe and don't cross track boundaries (XXX this is probably unnecessary) */
  	x = szmin(od->od_sec - sec, resid);
  	if (maxfer > 0)
  	    x = min(x, maxfer);		/* fit bounce buffer */
  
  	/* where do we transfer to? */
  	xp = (bbuf == NULL ? p : breg);
  
  	/* correct sector number for 1-based BIOS numbering */
  	sec++;
  
  	/*
  	 * Loop retrying the operation a couple of times.  The BIOS may also
  	 * retry.
  	 */
  	for (retry = 0; retry < 3; retry++) {
  	    /*
  	     * If retrying, reset the drive.
  	     */
  	    if (retry > 0) {
  		v86.ctl = V86_FLAGS;
  		v86.addr = 0x13;
  		v86.eax = 0;
  		v86.edx = od->od_unit;
  		v86int();
  	    }
  	    
  	    /*
  	     * Always use EDD if the disk supports it, otherwise fall back
  	     * to CHS mode (returning an error if the cylinder number is
  	     * too large).
  	     */
  	    if (od->od_flags & BD_MODEEDD1) {
  		static unsigned short packet[8];
  
  		packet[0] = 0x10;
  		packet[1] = x;
  		packet[2] = VTOPOFF(xp);
  		packet[3] = VTOPSEG(xp);
  		packet[4] = dblk & 0xffff;
  		packet[5] = dblk >> 16;
  		packet[6] = 0;
  		packet[7] = 0;
  		v86.ctl = V86_FLAGS;
  		v86.addr = 0x13;
  		v86.eax = 0x4200;
  		v86.edx = od->od_unit;
  		v86.ds = VTOPSEG(packet);
  		v86.esi = VTOPOFF(packet);
  		v86int();
  		result = (v86.efl & 0x1);
  		if (result == 0)
  		    break;
  	    } else if (cyl < 1024) {
  	        /* Use normal CHS addressing */
  	        v86.ctl = V86_FLAGS;
  		v86.addr = 0x13;
  		v86.eax = 0x200 | x;
  		v86.ecx = ((cyl & 0xff) << 8) | ((cyl & 0x300) >> 2) | sec;
  		v86.edx = (hd << 8) | od->od_unit;
  		v86.es = VTOPSEG(xp);
  		v86.ebx = VTOPOFF(xp);
  		v86int();
  		result = (v86.efl & 0x1);
  		if (result == 0)
  		    break;
  	    } else {
  		result = 1;
  		break;
  	    }
  	}
  	
  	DEBUG("%u sectors from %u/%u/%d to %p (0x%x) %s",
  	      x, cyl, hd, sec - 1, p, VTOP(p), result ? "failed" : "ok");
  	/* BUG here, cannot use v86 in printf because putchar uses it too */
  	DEBUG("ax = 0x%04x cx = 0x%04x dx = 0x%04x status 0x%x", 
  	      0x200 | x,
  	      ((cyl & 0xff) << 8) | ((cyl & 0x300) >> 2) | sec,
  	      (hd << 8) | od->od_unit,
  	      (v86.eax >> 8) & 0xff);
  	if (result)
  	    return(-1);
  	if (bbuf != NULL)
  	    bcopy(breg, p, x * BIOSDISK_SECSIZE);
  	p += (x * BIOSDISK_SECSIZE);
  	dblk += x;
  	resid -= x;
      }
  	
  /*    hexdump(dest, (blks * BIOSDISK_SECSIZE)); */
      return(0);
  }
  
  
  static int
  bd_write(struct open_disk *od, daddr_t dblk, int blks, caddr_t dest)
  {
      u_int	x, bpc, cyl, hd, sec, result, resid, retry, maxfer;
      caddr_t	p, xp, bbuf, breg;
      
      /* Just in case some idiot actually tries to read -1 blocks... */
      if (blks < 0)
  	return (-1);
  
      bpc = (od->od_sec * od->od_hds);		/* blocks per cylinder */
      resid = blks;
      p = dest;
  
      /*
       * Always bounce.  Our buffer is probably not segment-addressable.
       */
      if (1) {
  	/* 
  	 * There is a 64k physical boundary somewhere in the destination
  	 * buffer, so we have to arrange a suitable bounce buffer.  Allocate
  	 * a buffer twice as large as we need to.  Use the bottom half
  	 * unless there is a break there, in which case we use the top half.
  	 */
  	bbuf = bounce_base;
  	x = min(BOUNCEBUF_SECTS, (unsigned)blks);
  
  	if (((u_int32_t)VTOP(bbuf) & 0xffff0000) ==
  	    ((u_int32_t)VTOP(bbuf + x * BIOSDISK_SECSIZE - 1) & 0xffff0000)) {
  	    breg = bbuf;
  	} else {
  	    breg = bbuf + x * BIOSDISK_SECSIZE;
  	}
  	maxfer = x;		/* limit transfers to bounce region size */
      } else {
  	breg = bbuf = NULL;
  	maxfer = 0;
      }
  
      while (resid > 0) {
  	x = dblk;
  	cyl = x / bpc;			/* block # / blocks per cylinder */
  	x %= bpc;			/* block offset into cylinder */
  	hd = x / od->od_sec;		/* offset / blocks per track */
  	sec = x % od->od_sec;		/* offset into track */
  
  	/* play it safe and don't cross track boundaries (XXX this is probably unnecessary) */
  	x = szmin(od->od_sec - sec, resid);
  	if (maxfer > 0)
  	    x = szmin(x, maxfer);		/* fit bounce buffer */
  
  	/* where do we transfer to? */
  	xp = (bbuf == NULL ? p : breg);
  
  	/* correct sector number for 1-based BIOS numbering */
  	sec++;
  
  
  	/* Put your Data In, Put your Data out,
  	   Put your Data In, and shake it all about 
  	*/
  	if (bbuf != NULL)
  	    bcopy(p, breg, x * BIOSDISK_SECSIZE);
  	p += (x * BIOSDISK_SECSIZE);
  	dblk += x;
  	resid -= x;
  
  	/*
  	 * Loop retrying the operation a couple of times.  The BIOS may also
  	 * retry.
  	 */
  	for (retry = 0; retry < 3; retry++) {
  	    /*
  	     * If retrying, reset the drive.
  	     */
  	    if (retry > 0) {
  		v86.ctl = V86_FLAGS;
  		v86.addr = 0x13;
  		v86.eax = 0;
  		v86.edx = od->od_unit;
  		v86int();
  	    }
  
  	    /*
  	     * Always use EDD if the disk supports it, otherwise fall back
  	     * to CHS mode (returning an error if the cylinder number is
  	     * too large).
  	     */
  	    if (od->od_flags & BD_MODEEDD1) {
  		static unsigned short packet[8];
  
  		packet[0] = 0x10;
  		packet[1] = x;
  		packet[2] = VTOPOFF(xp);
  		packet[3] = VTOPSEG(xp);
  		packet[4] = dblk & 0xffff;
  		packet[5] = dblk >> 16;
  		packet[6] = 0;
  		packet[7] = 0;
  		v86.ctl = V86_FLAGS;
  		v86.addr = 0x13;
  		    /* Should we Write with verify ?? 0x4302 ? */
  		v86.eax = 0x4300;
  		v86.edx = od->od_unit;
  		v86.ds = VTOPSEG(packet);
  		v86.esi = VTOPOFF(packet);
  		v86int();
  		result = (v86.efl & 0x1);
  		if (result == 0)
  		    break;
  	    } else if (cyl < 1024) {
  	        /* Use normal CHS addressing */
  	        v86.ctl = V86_FLAGS;
  		v86.addr = 0x13;
  		v86.eax = 0x300 | x;
  		v86.ecx = ((cyl & 0xff) << 8) | ((cyl & 0x300) >> 2) | sec;
  		v86.edx = (hd << 8) | od->od_unit;
  		v86.es = VTOPSEG(xp);
  		v86.ebx = VTOPOFF(xp);
  		v86int();
  		result = (v86.efl & 0x1);
  		if (result == 0)
  		    break;
  	    } else {
  		result = 1;
  		break;
  	    }
  	}
  	
   	DEBUG("%u sectors from %u/%u/%d to %p (0x%x) %s", x, cyl, hd, sec - 1, p, VTOP(p), result ? "failed" : "ok");
  	/* BUG here, cannot use v86 in printf because putchar uses it too */
  	DEBUG("ax = 0x%04x cx = 0x%04x dx = 0x%04x status 0x%x", 
  	      0x200 | x, ((cyl & 0xff) << 8) | ((cyl & 0x300) >> 2) | sec, (hd << 8) | od->od_unit, (v86.eax >> 8) & 0xff);
  	if (result)
  	    return(-1);
      }
  	
      /* hexdump(dest, (blks * BIOSDISK_SECSIZE)); */
      return(0);
  }
  static int
  bd_getgeom(struct open_disk *od)
  {
  
      v86.ctl = V86_FLAGS;
      v86.addr = 0x13;
      v86.eax = 0x800;
      v86.edx = od->od_unit;
      v86int();
  
      if ((v86.efl & 0x1) ||				/* carry set */
  	((v86.edx & 0xff) <= (unsigned)(od->od_unit & 0x7f)))	/* unit # bad */
  	return(1);
      
      /* convert max cyl # -> # of cylinders */
      od->od_cyl = ((v86.ecx & 0xc0) << 2) + ((v86.ecx & 0xff00) >> 8) + 1;
      /* convert max head # -> # of heads */
      od->od_hds = ((v86.edx & 0xff00) >> 8) + 1;
      od->od_sec = v86.ecx & 0x3f;
  
      DEBUG("unit 0x%x geometry %d/%d/%d", od->od_unit, od->od_cyl, od->od_hds, od->od_sec);
      return(0);
  }
  
  /*
   * Return the BIOS geometry of a given "fixed drive" in a format
   * suitable for the legacy bootinfo structure.  Since the kernel is
   * expecting raw int 0x13/0x8 values for N_BIOS_GEOM drives, we
   * prefer to get the information directly, rather than rely on being
   * able to put it together from information already maintained for
   * different purposes and for a probably different number of drives.
   *
   * For valid drives, the geometry is expected in the format (31..0)
   * "000000cc cccccccc hhhhhhhh 00ssssss"; and invalid drives are
   * indicated by returning the geometry of a "1.2M" PC-format floppy
   * disk.  And, incidentally, what is returned is not the geometry as
   * such but the highest valid cylinder, head, and sector numbers.
   */
  u_int32_t
  bd_getbigeom(int bunit)
  {
  
      v86.ctl = V86_FLAGS;
      v86.addr = 0x13;
      v86.eax = 0x800;
      v86.edx = 0x80 + bunit;
      v86int();
      if (v86.efl & 0x1)
  	return 0x4f010f;
      return ((v86.ecx & 0xc0) << 18) | ((v86.ecx & 0xff00) << 8) |
  	   (v86.edx & 0xff00) | (v86.ecx & 0x3f);
  }
  
  /*
   * Return a suitable cdev_t value for (dev).
   *
   * In the case where it looks like (dev) is a SCSI disk, we allow the number of
   * IDE disks to be specified in $num_ide_disks.  There should be a Better Way.
   */
  int
  bd_getdev(struct i386_devdesc *dev)
  {
      struct open_disk		*od;
      int				biosdev;
      int 			major;
      int				rootdev;
      char			*nip, *cp;
      int				unitofs = 0, i, unit;
  
      biosdev = bd_unit2bios(dev->d_kind.biosdisk.unit);
      DEBUG("unit %d BIOS device %d", dev->d_kind.biosdisk.unit, biosdev);
      if (biosdev == -1)				/* not a BIOS device */
  	return(-1);
      if (bd_opendisk(&od, dev) != 0)		/* oops, not a viable device */
  	return(-1);
  
      if (biosdev < 0x80) {
  	/* floppy (or emulated floppy) or ATAPI device */
  	if (bdinfo[dev->d_kind.biosdisk.unit].bd_type == DT_ATAPI) {
  	    /* is an ATAPI disk */
  	    major = WFDMAJOR;
  	} else {
  	    /* is a floppy disk */
  	    major = FDMAJOR;
  	}
      } else {
  	/* harddisk */
  	if ((od->od_flags & BD_LABELOK) && (od->od_disklabel.d_type == DTYPE_SCSI)) {
  	    /* label OK, disk labelled as SCSI */
  	    major = DAMAJOR;
  	    /* check for unit number correction hint, now deprecated */
  	    if ((nip = getenv("num_ide_disks")) != NULL) {
  		i = strtol(nip, &cp, 0);
  		/* check for parse error */
  		if ((cp != nip) && (*cp == 0))
  		    unitofs = i;
  	    }
  	} else {
  	    /* assume an IDE disk */
  	    major = WDMAJOR;
  	}
      }
      /* default root disk unit number */
      unit = (biosdev & 0x7f) - unitofs;
  
      /* XXX a better kludge to set the root disk unit number */
      if ((nip = getenv("root_disk_unit")) != NULL) {
  	i = strtol(nip, &cp, 0);
  	/* check for parse error */
  	if ((cp != nip) && (*cp == 0))
  	    unit = i;
      }
  
      rootdev = MAKEBOOTDEV(major,
  			  (dev->d_kind.biosdisk.slice + 1) >> 4, 	/* XXX slices may be wrong here */
  			  (dev->d_kind.biosdisk.slice + 1) & 0xf, 
  			  unit,
  			  dev->d_kind.biosdisk.partition);
      DEBUG("dev is 0x%x\n", rootdev);
      return(rootdev);
  }
  