9954 loader: always set media size from partition.

[unleashed.git] / usr / src / boot / sys / boot / i386 / libi386 / biosdisk.c

/*
 * 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>

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

#include <sys/disk.h>
#include <sys/limits.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"

#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_MODEEDD      (BD_MODEEDD1 | BD_MODEEDD3)
#define BD_MODEMASK     0x0003
#define BD_FLOPPY       0x0004
#define BD_NO_MEDIA     0x0008
        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)->dd.d_unit])
#define BD_RD           0
#define BD_WR           1

static void bd_io_workaround(struct disk_devdesc *dev);

static int bd_io(struct disk_devdesc *, daddr_t, int, caddr_t, int);
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 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 int bd_ioctl(struct open_file *f, u_long cmd, void *data);
static int bd_print(int verbose);

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

/*
 * 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);
}

/*
 * Return EDD version or 0 if EDD is not supported on this drive.
 */
static int
bd_check_extensions(int unit)
{
        /* Determine if we can use EDD with this device. */
        v86.ctl = V86_FLAGS;
        v86.addr = 0x13;
        v86.eax = 0x4100;
        v86.edx = unit;
        v86.ebx = 0x55aa;
        v86int();

        if (V86_CY(v86.efl) ||                  /* carry set */
            (v86.ebx & 0xffff) != 0xaa55)       /* signature */
                return (0);

        /* extended disk access functions (AH=42h-44h,47h,48h) supported */
        if ((v86.ecx & EDD_INTERFACE_FIXED_DISK) == 0)
                return (0);

        return ((v86.eax >> 8) & 0xff);
}

static void
bd_reset_disk(int unit)
{
        /* reset disk */
        v86.ctl = V86_FLAGS;
        v86.addr = 0x13;
        v86.eax = 0;
        v86.edx = unit;
        v86int();
}

/*
 * Read CHS info. Return 0 on success, error otherwise.
 */
static int
bd_get_diskinfo_std(struct bdinfo *bd)
{
        bzero(&v86, sizeof (v86));
        v86.ctl = V86_FLAGS;
        v86.addr = 0x13;
        v86.eax = 0x800;
        v86.edx = bd->bd_unit;
        v86int();

        if (V86_CY(v86.efl) && ((v86.eax & 0xff00) != 0))
                return ((v86.eax & 0xff00) >> 8);

        /* return custom error on absurd sector number */
        if ((v86.ecx & 0x3f) == 0)
                return (0x60);

        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;
        bd->bd_sectors = (uint64_t)bd->bd_cyl * bd->bd_hds * bd->bd_sec;

        return (0);
}

/*
 * Read EDD info. Return 0 on success, error otherwise.
 */
static int
bd_get_diskinfo_ext(struct bdinfo *bd)
{
        struct edd_params params;
        uint64_t total;

        /* Get disk params */
        bzero(&params, sizeof (params));
        params.len = sizeof (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) && ((v86.eax & 0xff00) != 0))
                return ((v86.eax & 0xff00) >> 8);

        /*
         * Sector size must be a multiple of 512 bytes.
         * An alternate test would be to check power of 2,
         * powerof2(params.sector_size).
         * 4K is largest read buffer we can use at this time.
         */
        if (params.sector_size >= 512 &&
            params.sector_size <= 4096 &&
            (params.sector_size % BIOSDISK_SECSIZE) == 0)
                bd->bd_sectorsize = params.sector_size;

        bd->bd_cyl = params.cylinders;
        bd->bd_hds = params.heads;
        bd->bd_sec = params.sectors_per_track;

        if (params.sectors != 0) {
                total = params.sectors;
        } else {
                total = (uint64_t)params.cylinders *
                    params.heads * params.sectors_per_track;
        }
        bd->bd_sectors = total;

        return (0);
}

/*
 * Try to detect a device supported by the legacy int13 BIOS
 */
static int
bd_int13probe(struct bdinfo *bd)
{
        int edd;
        int ret;

        bd->bd_flags &= ~BD_NO_MEDIA;

        edd = bd_check_extensions(bd->bd_unit);
        if (edd == 0)
                bd->bd_flags |= BD_MODEINT13;
        else if (edd < 0x30)
                bd->bd_flags |= BD_MODEEDD1;
        else
                bd->bd_flags |= BD_MODEEDD3;

        /* Default sector size */
        bd->bd_sectorsize = BIOSDISK_SECSIZE;

        /*
         * Test if the floppy device is present, so we can avoid receiving
         * bogus information from bd_get_diskinfo_std().
         */
        if (bd->bd_unit < 0x80) {
                /* reset disk */
                bd_reset_disk(bd->bd_unit);

                /* Get disk type */
                v86.ctl = V86_FLAGS;
                v86.addr = 0x13;
                v86.eax = 0x1500;
                v86.edx = bd->bd_unit;
                v86int();
                if (V86_CY(v86.efl) || (v86.eax & 0x300) == 0)
                        return (0);
        }

        ret = 1;
        if (edd != 0)
                ret = bd_get_diskinfo_ext(bd);
        if (ret != 0 || bd->bd_sectors == 0)
                ret = bd_get_diskinfo_std(bd);

        if (ret != 0 && bd->bd_unit < 0x80) {
                /* Set defaults for 1.44 floppy */
                bd->bd_cyl = 80;
                bd->bd_hds = 2;
                bd->bd_sec = 18;
                bd->bd_type = 4;
                bd->bd_sectors = 2880;
                /* Since we are there, there most likely is no media */
                bd->bd_flags |= BD_NO_MEDIA;
                ret = 0;
        }

        if (ret != 0) {
                if (bd->bd_sectors != 0 && edd != 0) {
                        bd->bd_sec = 63;
                        bd->bd_hds = 255;
                        bd->bd_cyl =
                            (bd->bd_sectors + bd->bd_sec * bd->bd_hds - 1) /
                            bd->bd_sec * bd->bd_hds;
                } else {
                        printf("Can not get information about %s unit %#x\n",
                            biosdisk.dv_name, bd->bd_unit);
                        return (0);
                }
        }

        if (bd->bd_sec == 0)
                bd->bd_sec = 63;
        if (bd->bd_hds == 0)
                bd->bd_hds = 255;

        if (bd->bd_sectors == 0)
                bd->bd_sectors = (uint64_t)bd->bd_cyl * bd->bd_hds * bd->bd_sec;

        DEBUG("unit 0x%x geometry %d/%d/%d", bd->bd_unit, bd->bd_cyl,
            bd->bd_hds, bd->bd_sec);

        return (1);
}

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

        if (nbdinfo == 0)
                return (0);

        printf("%s devices:", biosdisk.dv_name);
        if ((ret = pager_output("\n")) != 0)
                return (ret);

        for (i = 0; i < nbdinfo; i++) {
                snprintf(line, sizeof (line),
                    "    disk%d:   BIOS drive %c (%s%ju X %u):\n", i,
                    (bdinfo[i].bd_unit < 0x80) ? ('A' + bdinfo[i].bd_unit):
                    ('C' + bdinfo[i].bd_unit - 0x80),
                    (bdinfo[i].bd_flags & BD_NO_MEDIA) == BD_NO_MEDIA ?
                    "no media, " : "",
                    (uintmax_t)bdinfo[i].bd_sectors,
                    bdinfo[i].bd_sectorsize);
                if ((ret = pager_output(line)) != 0)
                        break;

                if ((bdinfo[i].bd_flags & BD_NO_MEDIA) == BD_NO_MEDIA)
                        continue;

                dev.dd.d_dev = &biosdisk;
                dev.dd.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) == 0) {
                        snprintf(line, sizeof (line), "    disk%d", i);
                        ret = disk_print(&dev, line, verbose);
                        disk_close(&dev);
                        if (ret != 0)
                                break;
                }
        }
        return (ret);
}

/*
 * Read disk size from partition.
 * This is needed to work around buggy BIOS systems returning
 * wrong (truncated) disk media size.
 * During bd_probe() we tested if the multiplication of bd_sectors
 * would overflow so it should be safe to perform here.
 */
static uint64_t
bd_disk_get_sectors(struct disk_devdesc *dev)
{
        struct disk_devdesc disk;
        uint64_t size;

        disk.dd.d_dev = dev->dd.d_dev;
        disk.dd.d_unit = dev->dd.d_unit;
        disk.d_slice = -1;
        disk.d_partition = -1;
        disk.d_offset = 0;

        size = BD(dev).bd_sectors * BD(dev).bd_sectorsize;
        if (disk_open(&disk, size, BD(dev).bd_sectorsize) == 0) {
                (void) disk_ioctl(&disk, DIOCGMEDIASIZE, &size);
                disk_close(&disk);
        }
        return (size / BD(dev).bd_sectorsize);
}

/*
 * 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;
        int rc;

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

        if (dev->dd.d_unit < 0 || dev->dd.d_unit >= nbdinfo)
                return (EIO);

        if ((BD(dev).bd_flags & BD_NO_MEDIA) == BD_NO_MEDIA) {
                if (!bd_int13probe(&BD(dev)))
                        return (EIO);
                if ((BD(dev).bd_flags & BD_NO_MEDIA) == BD_NO_MEDIA)
                        return (EIO);
        }
        if (BD(dev).bd_bcache == NULL)
            BD(dev).bd_bcache = bcache_allocate();

        if (BD(dev).bd_open == 0)
                BD(dev).bd_sectors = bd_disk_get_sectors(dev);
        BD(dev).bd_open++;

        rc = disk_open(dev, BD(dev).bd_sectors * BD(dev).bd_sectorsize,
            BD(dev).bd_sectorsize);
        if (rc != 0) {
                BD(dev).bd_open--;
                if (BD(dev).bd_open == 0) {
                        bcache_free(BD(dev).bd_bcache);
                        BD(dev).bd_bcache = NULL;
                }
        }
        return (rc);
}

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;
        int rc;

        dev = (struct disk_devdesc *)f->f_devdata;

        rc = disk_ioctl(dev, cmd, data);
        if (rc != ENOTTY)
                return (rc);

        switch (cmd) {
        case DIOCGSECTORSIZE:
                *(uint32_t *)data = BD(dev).bd_sectorsize;
                break;
        case DIOCGMEDIASIZE:
                *(uint64_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 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, size,
            buf, rsize));
}

static int
bd_realstrategy(void *devdata, int rw, daddr_t dblk, size_t size,
    char *buf, size_t *rsize)
{
        struct disk_devdesc *dev = (struct disk_devdesc *)devdata;
        uint64_t disk_blocks, offset;
        size_t blks, blkoff, bsize, rest;
        caddr_t bbuf;
        int rc;

        if ((BD(dev).bd_flags & BD_NO_MEDIA) == BD_NO_MEDIA)
                return (EIO);

        /*
         * First make sure the IO size is a multiple of 512 bytes. While we do
         * process partial reads below, the strategy mechanism is built
         * assuming IO is a multiple of 512B blocks. If the request is not
         * a multiple of 512B blocks, it has to be some sort of bug.
         */
        if (size == 0 || (size % BIOSDISK_SECSIZE) != 0) {
                printf("bd_strategy: %d bytes I/O not multiple of %d\n",
                    size, BIOSDISK_SECSIZE);
                return (EIO);
        }

        DEBUG("open_disk %p", dev);

        offset = dblk * BIOSDISK_SECSIZE;
        dblk = offset / BD(dev).bd_sectorsize;
        blkoff = offset % BD(dev).bd_sectorsize;

        /*
         * Check the value of the size argument. We do have quite small
         * heap (64MB), but we do not know good upper limit, so we check against
         * INT_MAX here. This will also protect us against possible overflows
         * while translating block count to bytes.
         */
        if (size > INT_MAX) {
                DEBUG("too large I/O: %zu bytes", size);
                return (EIO);
        }

        blks = size / BD(dev).bd_sectorsize;
        if (blks == 0 || (size % BD(dev).bd_sectorsize) != 0)
                blks++;

        if (dblk > dblk + blks)
                return (EIO);

        if (rsize)
                *rsize = 0;

        /*
         * Get disk blocks, this value is either for whole disk or for
         * partition.
         */
        if (disk_ioctl(dev, DIOCGMEDIASIZE, &disk_blocks) == 0) {
                /* DIOCGMEDIASIZE does return bytes. */
                disk_blocks /= BD(dev).bd_sectorsize;
        } else {
                /* We should not get here. Just try to survive. */
                disk_blocks = BD(dev).bd_sectors - dev->d_offset;
        }

        /* Validate source block address. */
        if (dblk < dev->d_offset || dblk >= dev->d_offset + disk_blocks)
                return (EIO);

        /*
         * Truncate if we are crossing disk or partition end.
         */
        if (dblk + blks >= dev->d_offset + disk_blocks) {
                blks = dev->d_offset + disk_blocks - dblk;
                size = blks * BD(dev).bd_sectorsize;
                DEBUG("short I/O %d", blks);
        }

        if (V86_IO_BUFFER_SIZE / BD(dev).bd_sectorsize == 0)
                panic("BUG: Real mode buffer is too small\n");

        bbuf = PTOV(V86_IO_BUFFER);
        rest = size;

        while (blks > 0) {
                int x = min(blks, V86_IO_BUFFER_SIZE / BD(dev).bd_sectorsize);

                switch (rw & F_MASK) {
                case F_READ:
                        DEBUG("read %d from %lld to %p", x, dblk, buf);
                        bsize = BD(dev).bd_sectorsize * x - blkoff;
                        if (rest < bsize)
                                bsize = rest;

                        if ((rc = bd_io(dev, dblk, x, bbuf, BD_RD)) != 0)
                                return (EIO);

                        bcopy(bbuf + blkoff, buf, bsize);
                        break;
                case F_WRITE :
                        DEBUG("write %d from %lld to %p", x, dblk, buf);
                        if (blkoff != 0) {
                                /*
                                 * We got offset to sector, read 1 sector to
                                 * bbuf.
                                 */
                                x = 1;
                                bsize = BD(dev).bd_sectorsize - blkoff;
                                bsize = min(bsize, rest);
                                rc = bd_io(dev, dblk, x, bbuf, BD_RD);
                        } else if (rest < BD(dev).bd_sectorsize) {
                                /*
                                 * The remaining block is not full
                                 * sector. Read 1 sector to bbuf.
                                 */
                                x = 1;
                                bsize = rest;
                                rc = bd_io(dev, dblk, x, bbuf, BD_RD);
                        } else {
                                /* We can write full sector(s). */
                                bsize = BD(dev).bd_sectorsize * x;
                        }
                        /*
                         * Put your Data In, Put your Data out,
                         * Put your Data In, and shake it all about
                         */
                        bcopy(buf, bbuf + blkoff, bsize);
                        if ((rc = bd_io(dev, dblk, x, bbuf, BD_WR)) != 0)
                                return (EIO);

                        break;
                default:
                        /* DO NOTHING */
                        return (EROFS);
                }

                blkoff = 0;
                buf += bsize;
                rest -= bsize;
                blks -= x;
                dblk += x;
        }

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

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;
        /* Should we Write with verify ?? 0x4302 ? */
        if (dowrite == BD_WR)
                v86.eax = 0x4300;
        else
                v86.eax = 0x4200;
        v86.edx = BD(dev).bd_unit;
        v86.ds = VTOPSEG(&packet);
        v86.esi = VTOPOFF(&packet);
        v86int();
        if (V86_CY(v86.efl))
                return (v86.eax >> 8);
        return (0);
}

static int
bd_chs_io(struct disk_devdesc *dev, daddr_t dblk, int blks, caddr_t dest,
    int dowrite)
{
        uint32_t 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 == BD_WR)
                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();
        if (V86_CY(v86.efl))
                return (v86.eax >> 8);
        return (0);
}

static void
bd_io_workaround(struct disk_devdesc *dev)
{
        uint8_t buf[8 * 1024];

        bd_edd_io(dev, 0xffffffff, 1, (caddr_t)buf, BD_RD);
}

static int
bd_io(struct disk_devdesc *dev, daddr_t dblk, int blks, caddr_t dest,
    int dowrite)
{
        int result, retry;

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

        /*
         * Workaround for a problem with some HP ProLiant BIOS failing to work
         * out the boot disk after installation. hrs and kuriyama discovered
         * this problem with an HP ProLiant DL320e Gen 8 with a 3TB HDD, and
         * discovered that an int13h call seems to cause a buffer overrun in
         * the bios. The problem is alleviated by doing an extra read before
         * the buggy read. It is not immediately known whether other models
         * are similarly affected.
         * Loop retrying the operation a couple of times.  The BIOS
         * may also retry.
         */
        if (dowrite == BD_RD && dblk >= 0x100000000)
                bd_io_workaround(dev);
        for (retry = 0; retry < 3; retry++) {
                if (BD(dev).bd_flags & BD_MODEEDD)
                        result = bd_edd_io(dev, dblk, blks, dest, dowrite);
                else
                        result = bd_chs_io(dev, dblk, blks, dest, dowrite);

                if (result == 0) {
                        if (BD(dev).bd_flags & BD_NO_MEDIA)
                                BD(dev).bd_flags &= ~BD_NO_MEDIA;
                        break;
                }

                bd_reset_disk(BD(dev).bd_unit);

                /*
                 * Error codes:
                 * 20h  controller failure
                 * 31h  no media in drive (IBM/MS INT 13 extensions)
                 * 80h  no media in drive, VMWare (Fusion)
                 * There is no reason to repeat the IO with errors above.
                 */
                if (result == 0x20 || result == 0x31 || result == 0x80) {
                        BD(dev).bd_flags |= BD_NO_MEDIA;
                        break;
                }
        }

        if (result != 0 && (BD(dev).bd_flags & BD_NO_MEDIA) == 0) {
                if (dowrite == BD_WR) {
                        printf("%s%d: Write %d sector(s) from %p (0x%x) "
                            "to %lld: 0x%x\n", dev->dd.d_dev->dv_name,
                            dev->dd.d_unit, blks, dest, VTOP(dest), dblk,
                            result);
                } else {
                        printf("%s%d: Read %d sector(s) from %lld to %p "
                            "(0x%x): 0x%x\n", dev->dd.d_dev->dv_name,
                            dev->dd.d_unit, blks, dblk, dest, VTOP(dest),
                            result);
                }
        }

        return (result);
}

/*
 * 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.
 */
uint32_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->dd.d_unit);
        DEBUG("unit %d BIOS device %d", dev->dd.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) != 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->dd.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);
}