i386/libi386/biosdisk.c

	biosdisk.c revision 199767f8919635c4928607450d9e0abb932109ce
/*-
 * Copyright (c) 1998 Michael Smith <msmith@freebsd.org>
 * Copyright (c) 2012 Andrey V. Elsukov <ae@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.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

/*
 * BIOS disk device handling.
 *
 * Ideas and algorithms from:
 *
 * - NetBSD libi386/biosdisk.c
 * - FreeBSD biosboot/disk.c
 *
 */

#include <sys/disk.h>
#include <stand.h>
#include <machine/bootinfo.h>
#include <stdarg.h>

#include <bootstrap.h>
#include <btxv86.h>
#include <edd.h>
#include "disk.h"
#include "libi386.h"

CTASSERT(sizeof(struct i386_devdesc) >= sizeof(struct disk_devdesc));

#define BIOS_NUMDRIVES      0x475
#define BIOSDISK_SECSIZE    512
#define BUFSIZE         (1 * BIOSDISK_SECSIZE)

#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

/*
 * List of BIOS devices, translation from disk unit number to
 * BIOS unit number.
 */
static struct bdinfo
{
    int     bd_unit;    /* BIOS unit number */
    int     bd_cyl;     /* BIOS geometry */
    int     bd_hds;
    int     bd_sec;
    int     bd_flags;
#define BD_MODEINT13    0x0000
#define BD_MODEEDD1 0x0001
#define BD_MODEEDD3 0x0002
#define BD_MODEMASK 0x0003
#define BD_FLOPPY   0x0004
    int     bd_type;    /* BIOS 'drive type' (floppy only) */
    uint16_t    bd_sectorsize;  /* Sector size */
    uint64_t    bd_sectors; /* Disk size */
    int     bd_open;    /* reference counter */
    void        *bd_bcache; /* buffer cache data */
} bdinfo [MAXBDDEV];
static int nbdinfo = 0;

#define BD(dev)     (bdinfo[(dev)->d_unit])

static int bd_read(struct disk_devdesc *dev, daddr_t dblk, int blks,
    caddr_t dest);
static int bd_write(struct disk_devdesc *dev, daddr_t dblk, int blks,
    caddr_t dest);
static int bd_int13probe(struct bdinfo *bd);

static int bd_init(void);
static int bd_strategy(void *devdata, int flag, daddr_t dblk, size_t offset,
    size_t size, char *buf, size_t *rsize);
static int bd_realstrategy(void *devdata, int flag, daddr_t dblk, size_t offset,
    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 int bd_ioctl(struct open_file *f, u_long cmd, void *data);
static int bd_print(int verbose);
static void bd_cleanup(void);

struct devsw biosdisk = {
    "disk",
    DEVT_DISK,
    bd_init,
    bd_strategy,
    bd_open,
    bd_close,
    bd_ioctl,
    bd_print,
    bd_cleanup
};

/*
 * 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;

    /* sequence 0, 0x80 */
    for (base = 0; base <= 0x80; base += 0x80) {
        for (unit = base; (nbdinfo < MAXBDDEV); unit++) {
#ifndef VIRTUALBOX
            /*
             * Check the BIOS equipment list for number
             * of fixed disks.
             */
            if(base == 0x80 &&
                (nfd >= *(unsigned char *)PTOV(BIOS_NUMDRIVES)))
                break;
#endif
            bdinfo[nbdinfo].bd_open = 0;
            bdinfo[nbdinfo].bd_bcache = NULL;
            bdinfo[nbdinfo].bd_unit = unit;
            bdinfo[nbdinfo].bd_flags = unit < 0x80 ? BD_FLOPPY: 0;
            if (!bd_int13probe(&bdinfo[nbdinfo]))
                break;

#ifndef BOOT2
            /* 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);
#endif
            nbdinfo++;
            if (base == 0x80)
                nfd++;
        }
    }
    bcache_add_dev(nbdinfo);
    return(0);
}

static void
bd_cleanup(void)
{

    disk_cleanup(&biosdisk);
}

/*
 * Try to detect a device supported by the legacy int13 BIOS
 */
static int
bd_int13probe(struct bdinfo *bd)
{
    struct edd_params params;
    int ret = 1;    /* assume success */

    v86.ctl = V86_FLAGS;
    v86.addr = 0x13;
    v86.eax = 0x800;
    v86.edx = bd->bd_unit;
    v86int();

    /* Don't error out if we get bad sector number, try EDD as well */
    if (V86_CY(v86.efl) ||  /* carry set */
        (v86.edx & 0xff) <= (unsigned)(bd->bd_unit & 0x7f)) /* unit # bad */
        return (0); /* skip device */

    if ((v86.ecx & 0x3f) == 0)  /* absurd sector number */
        ret = 0;    /* set error */

    /* Convert max cyl # -> # of cylinders */
    bd->bd_cyl = ((v86.ecx & 0xc0) << 2) + ((v86.ecx & 0xff00) >> 8) + 1;
    /* Convert max head # -> # of heads */
    bd->bd_hds = ((v86.edx & 0xff00) >> 8) + 1;
    bd->bd_sec = v86.ecx & 0x3f;
    bd->bd_type = v86.ebx & 0xff;
    bd->bd_flags |= BD_MODEINT13;

    /* Calculate sectors count from the geometry */
    bd->bd_sectors = bd->bd_cyl * bd->bd_hds * bd->bd_sec;
    bd->bd_sectorsize = BIOSDISK_SECSIZE;
    DEBUG("unit 0x%x geometry %d/%d/%d", bd->bd_unit, bd->bd_cyl,
        bd->bd_hds, bd->bd_sec);

    /* 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_CY(v86.efl) ||  /* carry set */
        (v86.ebx & 0xffff) != 0xaa55 || /* signature */
        (v86.ecx & EDD_INTERFACE_FIXED_DISK) == 0)
        return (ret);   /* return code from int13 AH=08 */

    /* EDD supported */
    bd->bd_flags |= BD_MODEEDD1;
    if ((v86.eax & 0xff00) >= 0x3000)
        bd->bd_flags |= BD_MODEEDD3;
    /* Get disk params */
    params.len = sizeof(struct edd_params);
    v86.ctl = V86_FLAGS;
    v86.addr = 0x13;
    v86.eax = 0x4800;
    v86.edx = bd->bd_unit;
    v86.ds = VTOPSEG(&params);
    v86.esi = VTOPOFF(&params);
    v86int();
    if (!V86_CY(v86.efl)) {
        uint64_t total;

        if (params.sectors != 0)
            bd->bd_sectors = params.sectors;

        total = (uint64_t)params.cylinders *
            params.heads * params.sectors_per_track;
        if (bd->bd_sectors < total)
            bd->bd_sectors = total;

        bd->bd_sectorsize = params.sector_size;
        ret = 1;
    }
    DEBUG("unit 0x%x flags %x, sectors %llu, sectorsize %u",
        bd->bd_unit, bd->bd_flags, bd->bd_sectors, bd->bd_sectorsize);
    return (ret);
}

/*
 * Print information about disks
 */
static int
bd_print(int verbose)
{
    static char line[80];
    struct disk_devdesc dev;
    int i, ret = 0;

    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));
        ret = pager_output(line);
        if (ret != 0)
            return (ret);

        dev.d_dev = &biosdisk;
        dev.d_unit = i;
        dev.d_slice = -1;
        dev.d_partition = -1;
        if (disk_open(&dev,
            bdinfo[i].bd_sectorsize * bdinfo[i].bd_sectors,
            bdinfo[i].bd_sectorsize,
            (bdinfo[i].bd_flags & BD_FLOPPY) ?
            DISK_F_NOCACHE: 0) == 0) {
            sprintf(line, "    disk%d", i);
            ret = disk_print(&dev, line, verbose);
            disk_close(&dev);
            if (ret != 0)
                return (ret);
        }
    }
    return (ret);
}

/*
 * 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, ...)
{
    struct disk_devdesc *dev;
    va_list ap;

    va_start(ap, f);
    dev = va_arg(ap, struct disk_devdesc *);
    va_end(ap);

    if (dev->d_unit < 0 || dev->d_unit >= nbdinfo)
        return (EIO);
    BD(dev).bd_open++;
    if (BD(dev).bd_bcache == NULL)
        BD(dev).bd_bcache = bcache_allocate();
    return (disk_open(dev, BD(dev).bd_sectors * BD(dev).bd_sectorsize,
        BD(dev).bd_sectorsize, (BD(dev).bd_flags & BD_FLOPPY) ?
        DISK_F_NOCACHE: 0));
}

static int
bd_close(struct open_file *f)
{
    struct disk_devdesc *dev;

    dev = (struct disk_devdesc *)f->f_devdata;
    BD(dev).bd_open--;
    if (BD(dev).bd_open == 0) {
        bcache_free(BD(dev).bd_bcache);
        BD(dev).bd_bcache = NULL;
    }
    return (disk_close(dev));
}

static int
bd_ioctl(struct open_file *f, u_long cmd, void *data)
{
    struct disk_devdesc *dev;

    dev = (struct disk_devdesc *)f->f_devdata;
    switch (cmd) {
    case DIOCGSECTORSIZE:
        *(u_int *)data = BD(dev).bd_sectorsize;
        break;
    case DIOCGMEDIASIZE:
        *(off_t *)data = BD(dev).bd_sectors * BD(dev).bd_sectorsize;
        break;
    default:
        return (ENOTTY);
    }
    return (0);
}

static int
bd_strategy(void *devdata, int rw, daddr_t dblk, size_t offset, size_t size,
    char *buf, size_t *rsize)
{
    struct bcache_devdata bcd;
    struct disk_devdesc *dev;

    dev = (struct disk_devdesc *)devdata;
    bcd.dv_strategy = bd_realstrategy;
    bcd.dv_devdata = devdata;
    bcd.dv_cache = BD(dev).bd_bcache;

    return (bcache_strategy(&bcd, rw, dblk + dev->d_offset, offset, size,
        buf, rsize));
}

static int
bd_realstrategy(void *devdata, int rw, daddr_t dblk, size_t offset, size_t size,
    char *buf, size_t *rsize)
{
    struct disk_devdesc *dev = (struct disk_devdesc *)devdata;
    int         blks, remaining;
#ifdef BD_SUPPORT_FRAGS /* XXX: sector size */
    char        fragbuf[BIOSDISK_SECSIZE];
    size_t      fragsize;

    fragsize = size % BIOSDISK_SECSIZE;
#else
    if (size % BD(dev).bd_sectorsize)
    panic("bd_strategy: %d bytes I/O not multiple of block size", size);
#endif

    DEBUG("open_disk %p", dev);
    blks = size / BD(dev).bd_sectorsize;
    if (rsize)
    *rsize = 0;

    /*
     * Perform partial read to prevent read-ahead crossing
     * the end of disk - or any 32 bit aliases of the end.
     * Signed arithmetic is used to handle wrap-around cases
     * like we do for TCP sequence numbers.
     */
    remaining = (int)(BD(dev).bd_sectors - dblk);   /* truncate */
    if (remaining > 0 && remaining < blks) {
    blks = remaining;
    size = blks * BD(dev).bd_sectorsize;
    DEBUG("short read %d", blks);
    }

    switch(rw){
    case F_READ:
    DEBUG("read %d from %lld to %p", blks, dblk, buf);

    if (blks && bd_read(dev, dblk, blks, buf)) {
        DEBUG("read error");
        return (EIO);
    }
#ifdef BD_SUPPORT_FRAGS /* XXX: sector size */
    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
    break;
    case F_WRITE :
    DEBUG("write %d from %d to %p", blks, dblk, buf);

    if (blks && bd_write(dev, dblk, blks, buf)) {
        DEBUG("write error");
        return (EIO);
    }
#ifdef BD_SUPPORT_FRAGS
    if(fragsize) {
        DEBUG("Attempted to write a frag");
        return (EIO);
    }
#endif
    break;
    default:
    /* DO NOTHING */
    return (EROFS);
    }

    if (rsize)
    *rsize = size;
    return (0);
}

/* Max number of sectors to bounce-buffer if the request crosses a 64k boundary */
#define FLOPPY_BOUNCEBUF    18

static int
bd_edd_io(struct disk_devdesc *dev, daddr_t dblk, int blks, caddr_t dest,
    int dowrite)
{
    static struct edd_packet packet;

    packet.len = sizeof(struct edd_packet);
    packet.count = blks;
    packet.off = VTOPOFF(dest);
    packet.seg = VTOPSEG(dest);
    packet.lba = dblk;
    v86.ctl = V86_FLAGS;
    v86.addr = 0x13;
    if (dowrite)
    /* Should we Write with verify ?? 0x4302 ? */
    v86.eax = 0x4300;
    else
    v86.eax = 0x4200;
    v86.edx = BD(dev).bd_unit;
    v86.ds = VTOPSEG(&packet);
    v86.esi = VTOPOFF(&packet);
    v86int();
    return (V86_CY(v86.efl));
}

static int
bd_chs_io(struct disk_devdesc *dev, daddr_t dblk, int blks, caddr_t dest,
    int dowrite)
{
    u_int   x, bpc, cyl, hd, sec;

    bpc = BD(dev).bd_sec * BD(dev).bd_hds;  /* blocks per cylinder */
    x = dblk;
    cyl = x / bpc;          /* block # / blocks per cylinder */
    x %= bpc;               /* block offset into cylinder */
    hd = x / BD(dev).bd_sec;        /* offset / blocks per track */
    sec = x % BD(dev).bd_sec;       /* offset into track */

    /* correct sector number for 1-based BIOS numbering */
    sec++;

    if (cyl > 1023)
    /* CHS doesn't support cylinders > 1023. */
    return (1);

    v86.ctl = V86_FLAGS;
    v86.addr = 0x13;
    if (dowrite)
    v86.eax = 0x300 | blks;
    else
    v86.eax = 0x200 | blks;
    v86.ecx = ((cyl & 0xff) << 8) | ((cyl & 0x300) >> 2) | sec;
    v86.edx = (hd << 8) | BD(dev).bd_unit;
    v86.es = VTOPSEG(dest);
    v86.ebx = VTOPOFF(dest);
    v86int();
    return (V86_CY(v86.efl));
}

static int
bd_io(struct disk_devdesc *dev, daddr_t dblk, int blks, caddr_t dest, int dowrite)
{
    u_int   x, sec, result, resid, retry, maxfer;
    caddr_t p, xp, bbuf, breg;

    /* Just in case some idiot actually tries to read/write -1 blocks... */
    if (blks < 0)
    return (-1);

    resid = blks;
    p = dest;

    /* Decide whether we have to bounce */
    if (VTOP(dest) >> 20 != 0 || (BD(dev).bd_unit < 0x80 &&
    (VTOP(dest) >> 16) != (VTOP(dest +
    blks * BD(dev).bd_sectorsize) >> 16))) {

    /*
     * There is a 64k physical boundary somewhere in the
     * destination buffer, or the destination buffer is above
     * first 1MB of physical memory 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.
     */
    x = min(FLOPPY_BOUNCEBUF, (unsigned)blks);
    bbuf = alloca(x * 2 * BD(dev).bd_sectorsize);
    if (((u_int32_t)VTOP(bbuf) & 0xffff0000) ==
        ((u_int32_t)VTOP(bbuf + x * BD(dev).bd_sectorsize) & 0xffff0000)) {
        breg = bbuf;
    } else {
        breg = bbuf + x * BD(dev).bd_sectorsize;
    }
    maxfer = x;     /* limit transfers to bounce region size */
    } else {
    breg = bbuf = NULL;
    maxfer = 0;
    }

    while (resid > 0) {
    /*
     * Play it safe and don't cross track boundaries.
     * (XXX this is probably unnecessary)
     */
    sec = dblk % BD(dev).bd_sec;    /* offset into track */
    x = min(BD(dev).bd_sec - sec, resid);
    if (maxfer > 0)
        x = min(x, maxfer);     /* fit bounce buffer */

    /* where do we transfer to? */
    xp = bbuf == NULL ? p : breg;

    /*
     * Put your Data In, Put your Data out,
     * Put your Data In, and shake it all about
     */
    if (dowrite && bbuf != NULL)
        bcopy(p, breg, x * BD(dev).bd_sectorsize);

    /*
     * 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 = BD(dev).bd_unit;
        v86int();
        }

        if (BD(dev).bd_flags & BD_MODEEDD1)
        result = bd_edd_io(dev, dblk, x, xp, dowrite);
        else
        result = bd_chs_io(dev, dblk, x, xp, dowrite);
        if (result == 0)
        break;
    }

    if (dowrite)
        DEBUG("Write %d sector(s) from %p (0x%x) to %lld %s", x,
        p, VTOP(p), dblk, result ? "failed" : "ok");
    else
        DEBUG("Read %d sector(s) from %lld to %p (0x%x) %s", x,
        dblk, p, VTOP(p), result ? "failed" : "ok");
    if (result) {
        return(-1);
    }
    if (!dowrite && bbuf != NULL)
        bcopy(breg, p, x * BD(dev).bd_sectorsize);
    p += (x * BD(dev).bd_sectorsize);
    dblk += x;
    resid -= x;
    }

/*    hexdump(dest, (blks * BD(dev).bd_sectorsize)); */
    return(0);
}

static int
bd_read(struct disk_devdesc *dev, daddr_t dblk, int blks, caddr_t dest)
{

    return (bd_io(dev, dblk, blks, dest, 0));
}

static int
bd_write(struct disk_devdesc *dev, daddr_t dblk, int blks, caddr_t dest)
{

    return (bd_io(dev, dblk, blks, dest, 1));
}

/*
 * 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_CY(v86.efl))
    return 0x4f010f;
    return ((v86.ecx & 0xc0) << 18) | ((v86.ecx & 0xff00) << 8) |
       (v86.edx & 0xff00) | (v86.ecx & 0x3f);
}

/*
 * Return a suitable dev_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 *d)
{
    struct disk_devdesc     *dev;
    int             biosdev;
    int             major;
    int             rootdev;
    char            *nip, *cp;
    int             i, unit;

    dev = (struct disk_devdesc *)d;
    biosdev = bd_unit2bios(dev->d_unit);
    DEBUG("unit %d BIOS device %d", dev->d_unit, biosdev);
    if (biosdev == -1)              /* not a BIOS device */
    return(-1);
    if (disk_open(dev, BD(dev).bd_sectors * BD(dev).bd_sectorsize,
    BD(dev).bd_sectorsize,(BD(dev).bd_flags & BD_FLOPPY) ?
    DISK_F_NOCACHE: 0) != 0)        /* oops, not a viable device */
        return (-1);
    else
    disk_close(dev);

    if (biosdev < 0x80) {
    /* floppy (or emulated floppy) or ATAPI device */
    if (bdinfo[dev->d_unit].bd_type == DT_ATAPI) {
        /* is an ATAPI disk */
        major = WFDMAJOR;
    } else {
        /* is a floppy disk */
        major = FDMAJOR;
    }
    } else {
        /* assume an IDE disk */
        major = WDMAJOR;
    }
    /* default root disk unit number */
    unit = biosdev & 0x7f;

    /* 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_slice + 1, unit, dev->d_partition);
    DEBUG("dev is 0x%x\n", rootdev);
    return(rootdev);
}