xref: /freebsd/stand/i386/libi386/biosdisk.c (revision e9ac41698b2f322d55ccf9da50a3596edb2c1800)
1 /*-
2  * Copyright (c) 1998 Michael Smith <msmith@freebsd.org>
3  * Copyright (c) 2012 Andrey V. Elsukov <ae@FreeBSD.org>
4  * All rights reserved.
5  *
6  * Redistribution and use in source and binary forms, with or without
7  * modification, are permitted provided that the following conditions
8  * are met:
9  * 1. Redistributions of source code must retain the above copyright
10  *    notice, this list of conditions and the following disclaimer.
11  * 2. Redistributions in binary form must reproduce the above copyright
12  *    notice, this list of conditions and the following disclaimer in the
13  *    documentation and/or other materials provided with the distribution.
14  *
15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25  * SUCH DAMAGE.
26  */
27 
28 /*
29  * BIOS disk device handling.
30  *
31  * Ideas and algorithms from:
32  *
33  * - NetBSD libi386/biosdisk.c
34  * - FreeBSD biosboot/disk.c
35  *
36  */
37 
38 #include <sys/disk.h>
39 #include <sys/limits.h>
40 #include <sys/queue.h>
41 #include <stand.h>
42 #include <machine/bootinfo.h>
43 #include <stdarg.h>
44 #include <stdbool.h>
45 
46 #include <bootstrap.h>
47 #include <btxv86.h>
48 #include <edd.h>
49 #include "disk.h"
50 #include "libi386.h"
51 
52 #define	BIOS_NUMDRIVES		0x475
53 #define	BIOSDISK_SECSIZE	512
54 #define	BUFSIZE			(1 * BIOSDISK_SECSIZE)
55 
56 #define	DT_ATAPI	0x10	/* disk type for ATAPI floppies */
57 #define	WDMAJOR		0	/* major numbers for devices we frontend for */
58 #define	WFDMAJOR	1
59 #define	FDMAJOR		2
60 #define	DAMAJOR		4
61 #define	ACDMAJOR	117
62 #define	CDMAJOR		15
63 
64 /*
65  * INT13 commands
66  */
67 #define	CMD_RESET	0x0000
68 #define	CMD_READ_CHS	0x0200
69 #define	CMD_WRITE_CHS	0x0300
70 #define	CMD_READ_PARAM	0x0800
71 #define	CMD_DRIVE_TYPE	0x1500
72 #define	CMD_CHECK_EDD	0x4100
73 #define	CMD_READ_LBA	0x4200
74 #define	CMD_WRITE_LBA	0x4300
75 #define	CMD_EXT_PARAM	0x4800
76 #define	CMD_CD_GET_STATUS 0x4b01
77 
78 #define	DISK_BIOS	0x13
79 
80 #ifdef DISK_DEBUG
81 #define	DPRINTF(fmt, args...)	printf("%s: " fmt "\n", __func__, ## args)
82 #else
83 #define	DPRINTF(fmt, args...)	((void)0)
84 #endif
85 
86 struct specification_packet {
87 	uint8_t		sp_size;
88 	uint8_t		sp_bootmedia;
89 	uint8_t		sp_drive;
90 	uint8_t		sp_controller;
91 	uint32_t	sp_lba;
92 	uint16_t	sp_devicespec;
93 	uint16_t	sp_buffersegment;
94 	uint16_t	sp_loadsegment;
95 	uint16_t	sp_sectorcount;
96 	uint16_t	sp_cylsec;
97 	uint8_t		sp_head;
98 	uint8_t		sp_dummy[16];	/* Avoid memory corruption */
99 };
100 
101 /*
102  * List of BIOS devices, translation from disk unit number to
103  * BIOS unit number.
104  */
105 typedef struct bdinfo
106 {
107 	STAILQ_ENTRY(bdinfo)	bd_link;	/* link in device list */
108 	int		bd_unit;	/* BIOS unit number */
109 	int		bd_cyl;		/* BIOS geometry */
110 	int		bd_hds;
111 	int		bd_sec;
112 	int		bd_flags;
113 #define	BD_MODEINT13	0x0000
114 #define	BD_MODEEDD1	0x0001
115 #define	BD_MODEEDD3	0x0002
116 #define	BD_MODEEDD	(BD_MODEEDD1 | BD_MODEEDD3)
117 #define	BD_MODEMASK	0x0003
118 #define	BD_FLOPPY	0x0004
119 #define	BD_CDROM	0x0008
120 #define	BD_NO_MEDIA	0x0010
121 	int		bd_type;	/* BIOS 'drive type' (floppy only) */
122 	uint16_t	bd_sectorsize;	/* Sector size */
123 	uint64_t	bd_sectors;	/* Disk size */
124 	int		bd_open;	/* reference counter */
125 	void		*bd_bcache;	/* buffer cache data */
126 } bdinfo_t;
127 
128 #define	BD_RD		0
129 #define	BD_WR		1
130 
131 typedef STAILQ_HEAD(bdinfo_list, bdinfo) bdinfo_list_t;
132 static bdinfo_list_t fdinfo = STAILQ_HEAD_INITIALIZER(fdinfo);
133 static bdinfo_list_t cdinfo = STAILQ_HEAD_INITIALIZER(cdinfo);
134 static bdinfo_list_t hdinfo = STAILQ_HEAD_INITIALIZER(hdinfo);
135 
136 static void bd_io_workaround(bdinfo_t *);
137 static int bd_io(struct disk_devdesc *, bdinfo_t *, daddr_t, int, caddr_t, int);
138 static bool bd_int13probe(bdinfo_t *);
139 
140 static int bd_init(void);
141 static int cd_init(void);
142 static int fd_init(void);
143 static int bd_strategy(void *devdata, int flag, daddr_t dblk, size_t size,
144     char *buf, size_t *rsize);
145 static int bd_realstrategy(void *devdata, int flag, daddr_t dblk, size_t size,
146     char *buf, size_t *rsize);
147 static int bd_open(struct open_file *f, ...);
148 static int bd_close(struct open_file *f);
149 static int bd_ioctl(struct open_file *f, u_long cmd, void *data);
150 static int bd_print(int verbose);
151 static int cd_print(int verbose);
152 static int fd_print(int verbose);
153 static void bd_reset_disk(int);
154 static int bd_get_diskinfo_std(struct bdinfo *);
155 
156 struct devsw biosfd = {
157 	.dv_name = "fd",
158 	.dv_type = DEVT_FD,
159 	.dv_init = fd_init,
160 	.dv_strategy = bd_strategy,
161 	.dv_open = bd_open,
162 	.dv_close = bd_close,
163 	.dv_ioctl = bd_ioctl,
164 	.dv_print = fd_print,
165 	.dv_cleanup = nullsys,
166 };
167 
168 struct devsw bioscd = {
169 	.dv_name = "cd",
170 	.dv_type = DEVT_CD,
171 	.dv_init = cd_init,
172 	.dv_strategy = bd_strategy,
173 	.dv_open = bd_open,
174 	.dv_close = bd_close,
175 	.dv_ioctl = bd_ioctl,
176 	.dv_print = cd_print,
177 	.dv_cleanup = nullsys,
178 };
179 
180 struct devsw bioshd = {
181 	.dv_name = "disk",
182 	.dv_type = DEVT_DISK,
183 	.dv_init = bd_init,
184 	.dv_strategy = bd_strategy,
185 	.dv_open = bd_open,
186 	.dv_close = bd_close,
187 	.dv_ioctl = bd_ioctl,
188 	.dv_print = bd_print,
189 	.dv_cleanup = nullsys,
190 	.dv_fmtdev = disk_fmtdev,
191 	.dv_parsedev = disk_parsedev,
192 };
193 
194 static bdinfo_list_t *
195 bd_get_bdinfo_list(struct devsw *dev)
196 {
197 	if (dev->dv_type == DEVT_DISK)
198 		return (&hdinfo);
199 	if (dev->dv_type == DEVT_CD)
200 		return (&cdinfo);
201 	if (dev->dv_type == DEVT_FD)
202 		return (&fdinfo);
203 	return (NULL);
204 }
205 
206 /* XXX this gets called way way too often, investigate */
207 static bdinfo_t *
208 bd_get_bdinfo(struct devdesc *dev)
209 {
210 	bdinfo_list_t *bdi;
211 	bdinfo_t *bd = NULL;
212 	int unit;
213 
214 	bdi = bd_get_bdinfo_list(dev->d_dev);
215 	if (bdi == NULL)
216 		return (bd);
217 
218 	unit = 0;
219 	STAILQ_FOREACH(bd, bdi, bd_link) {
220 		if (unit == dev->d_unit)
221 			return (bd);
222 		unit++;
223 	}
224 	return (bd);
225 }
226 
227 /*
228  * Translate between BIOS device numbers and our private unit numbers.
229  */
230 int
231 bd_bios2unit(int biosdev)
232 {
233 	bdinfo_list_t *bdi[] = { &fdinfo, &cdinfo, &hdinfo, NULL };
234 	bdinfo_t *bd;
235 	int i, unit;
236 
237 	DPRINTF("looking for bios device 0x%x", biosdev);
238 	for (i = 0; bdi[i] != NULL; i++) {
239 		unit = 0;
240 		STAILQ_FOREACH(bd, bdi[i], bd_link) {
241 			if (bd->bd_unit == biosdev) {
242 				DPRINTF("bd unit %d is BIOS device 0x%x", unit,
243 				    bd->bd_unit);
244 				return (unit);
245 			}
246 			unit++;
247 		}
248 	}
249 	return (-1);
250 }
251 
252 int
253 bd_unit2bios(struct i386_devdesc *dev)
254 {
255 	bdinfo_list_t *bdi;
256 	bdinfo_t *bd;
257 	int unit;
258 
259 	bdi = bd_get_bdinfo_list(dev->dd.d_dev);
260 	if (bdi == NULL)
261 		return (-1);
262 
263 	unit = 0;
264 	STAILQ_FOREACH(bd, bdi, bd_link) {
265 		if (unit == dev->dd.d_unit)
266 			return (bd->bd_unit);
267 		unit++;
268 	}
269 	return (-1);
270 }
271 
272 /*
273  * Use INT13 AH=15 - Read Drive Type.
274  */
275 static int
276 fd_count(void)
277 {
278 	int drive;
279 
280 	for (drive = 0; drive < MAXBDDEV; drive++) {
281 		bd_reset_disk(drive);
282 
283 		v86.ctl = V86_FLAGS;
284 		v86.addr = DISK_BIOS;
285 		v86.eax = CMD_DRIVE_TYPE;
286 		v86.edx = drive;
287 		v86int();
288 
289 		if (V86_CY(v86.efl))
290 			break;
291 
292 		if ((v86.eax & 0x300) == 0)
293 			break;
294 	}
295 
296 	return (drive);
297 }
298 
299 /*
300  * Quiz the BIOS for disk devices, save a little info about them.
301  */
302 static int
303 fd_init(void)
304 {
305 	int unit, numfd;
306 	bdinfo_t *bd;
307 
308 	numfd = fd_count();
309 	for (unit = 0; unit < numfd; unit++) {
310 		if ((bd = calloc(1, sizeof(*bd))) == NULL)
311 			break;
312 
313 		bd->bd_sectorsize = BIOSDISK_SECSIZE;
314 		bd->bd_flags = BD_FLOPPY;
315 		bd->bd_unit = unit;
316 
317 		/* Use std diskinfo for floppy drive */
318 		if (bd_get_diskinfo_std(bd) != 0) {
319 			free(bd);
320 			break;
321 		}
322 		if (bd->bd_sectors == 0)
323 			bd->bd_flags |= BD_NO_MEDIA;
324 
325 		printf("BIOS drive %c: is %s%d\n", ('A' + unit),
326 		    biosfd.dv_name, unit);
327 
328 		STAILQ_INSERT_TAIL(&fdinfo, bd, bd_link);
329 	}
330 
331 	bcache_add_dev(unit);
332 	return (0);
333 }
334 
335 static int
336 bd_init(void)
337 {
338 	int base, unit;
339 	bdinfo_t *bd;
340 
341 	TSENTER();
342 
343 	base = 0x80;
344 	for (unit = 0; unit < *(unsigned char *)PTOV(BIOS_NUMDRIVES); unit++) {
345 		/*
346 		 * Check the BIOS equipment list for number of fixed disks.
347 		 */
348 		if ((bd = calloc(1, sizeof(*bd))) == NULL)
349 			break;
350 		bd->bd_unit = base + unit;
351 		if (!bd_int13probe(bd)) {
352 			free(bd);
353 			break;
354 		}
355 
356 		printf("BIOS drive %c: is %s%d\n", ('C' + unit),
357 		    bioshd.dv_name, unit);
358 
359 		STAILQ_INSERT_TAIL(&hdinfo, bd, bd_link);
360 	}
361 	bcache_add_dev(unit);
362 	TSEXIT();
363 	return (0);
364 }
365 
366 /*
367  * We can't quiz, we have to be told what device to use, so this function
368  * doesn't do anything.  Instead, the loader calls bc_add() with the BIOS
369  * device number to add.
370  */
371 static int
372 cd_init(void)
373 {
374 
375 	return (0);
376 }
377 
378 /*
379  * Information from bootable CD-ROM.
380  */
381 static int
382 bd_get_diskinfo_cd(struct bdinfo *bd)
383 {
384 	struct specification_packet bc_sp;
385 	int ret = -1;
386 
387 	(void) memset(&bc_sp, 0, sizeof (bc_sp));
388 	/* Set sp_size as per specification. */
389 	bc_sp.sp_size = sizeof (bc_sp) - sizeof (bc_sp.sp_dummy);
390 
391         v86.ctl = V86_FLAGS;
392         v86.addr = DISK_BIOS;
393         v86.eax = CMD_CD_GET_STATUS;
394         v86.edx = bd->bd_unit;
395         v86.ds = VTOPSEG(&bc_sp);
396         v86.esi = VTOPOFF(&bc_sp);
397         v86int();
398 
399 	if ((v86.eax & 0xff00) == 0 &&
400 	    bc_sp.sp_drive == bd->bd_unit) {
401 		bd->bd_cyl = ((bc_sp.sp_cylsec & 0xc0) << 2) +
402 		    ((bc_sp.sp_cylsec & 0xff00) >> 8) + 1;
403 		bd->bd_sec = bc_sp.sp_cylsec & 0x3f;
404 		bd->bd_hds = bc_sp.sp_head + 1;
405 		bd->bd_sectors = (uint64_t)bd->bd_cyl * bd->bd_hds * bd->bd_sec;
406 
407 		if (bc_sp.sp_bootmedia & 0x0F) {
408 			/* Floppy or hard-disk emulation */
409 			bd->bd_sectorsize = BIOSDISK_SECSIZE;
410 			return (-1);
411 		} else {
412 			bd->bd_sectorsize = 2048;
413 			bd->bd_flags = BD_MODEEDD | BD_CDROM;
414 			ret = 0;
415 		}
416 	}
417 
418 	/*
419 	 * If this is the boot_drive, default to non-emulation bootable CD-ROM.
420 	 */
421 	if (ret != 0 && bd->bd_unit >= 0x88) {
422 		bd->bd_cyl = 0;
423 		bd->bd_hds = 1;
424 		bd->bd_sec = 15;
425 		bd->bd_sectorsize = 2048;
426 		bd->bd_flags = BD_MODEEDD | BD_CDROM;
427 		bd->bd_sectors = 0;
428 		ret = 0;
429 	}
430 
431 	/*
432 	 * Note we can not use bd_get_diskinfo_ext() nor bd_get_diskinfo_std()
433 	 * here - some systems do get hung with those.
434 	 */
435 	/*
436 	 * Still no size? use 7.961GB. The size does not really matter
437 	 * as long as it is reasonably large to make our reads to pass
438 	 * the sector count check.
439 	 */
440 	if (bd->bd_sectors == 0)
441 		bd->bd_sectors = 4173824;
442 
443 	return (ret);
444 }
445 
446 int
447 bc_add(int biosdev)
448 {
449 	bdinfo_t *bd;
450 	int nbcinfo = 0;
451 
452 	if (!STAILQ_EMPTY(&cdinfo))
453                 return (-1);
454 
455 	if ((bd = calloc(1, sizeof(*bd))) == NULL)
456 		return (-1);
457 
458 	bd->bd_unit = biosdev;
459 	if (bd_get_diskinfo_cd(bd) < 0) {
460 		free(bd);
461 		return (-1);
462 	}
463 
464 	STAILQ_INSERT_TAIL(&cdinfo, bd, bd_link);
465         printf("BIOS CD is cd%d\n", nbcinfo);
466         nbcinfo++;
467         bcache_add_dev(nbcinfo);        /* register cd device in bcache */
468         return(0);
469 }
470 
471 /*
472  * Return EDD version or 0 if EDD is not supported on this drive.
473  */
474 static int
475 bd_check_extensions(int unit)
476 {
477 	/* do not use ext calls for floppy devices */
478 	if (unit < 0x80)
479 		return (0);
480 
481 	/* Determine if we can use EDD with this device. */
482 	v86.ctl = V86_FLAGS;
483 	v86.addr = DISK_BIOS;
484 	v86.eax = CMD_CHECK_EDD;
485 	v86.edx = unit;
486 	v86.ebx = EDD_QUERY_MAGIC;
487 	v86int();
488 
489 	if (V86_CY(v86.efl) ||			/* carry set */
490 	    (v86.ebx & 0xffff) != EDD_INSTALLED) /* signature */
491 		return (0);
492 
493 	/* extended disk access functions (AH=42h-44h,47h,48h) supported */
494 	if ((v86.ecx & EDD_INTERFACE_FIXED_DISK) == 0)
495 		return (0);
496 
497 	return ((v86.eax >> 8) & 0xff);
498 }
499 
500 static void
501 bd_reset_disk(int unit)
502 {
503 	/* reset disk */
504 	v86.ctl = V86_FLAGS;
505 	v86.addr = DISK_BIOS;
506 	v86.eax = CMD_RESET;
507 	v86.edx = unit;
508 	v86int();
509 }
510 
511 /*
512  * Read CHS info. Return 0 on success, error otherwise.
513  */
514 static int
515 bd_get_diskinfo_std(struct bdinfo *bd)
516 {
517 	bzero(&v86, sizeof(v86));
518 	v86.ctl = V86_FLAGS;
519 	v86.addr = DISK_BIOS;
520 	v86.eax = CMD_READ_PARAM;
521 	v86.edx = bd->bd_unit;
522 	v86int();
523 
524 	if (V86_CY(v86.efl) && ((v86.eax & 0xff00) != 0))
525 		return ((v86.eax & 0xff00) >> 8);
526 
527 	/* return custom error on absurd sector number */
528 	if ((v86.ecx & 0x3f) == 0)
529 		return (0x60);
530 
531 	bd->bd_cyl = ((v86.ecx & 0xc0) << 2) + ((v86.ecx & 0xff00) >> 8) + 1;
532 	/* Convert max head # -> # of heads */
533 	bd->bd_hds = ((v86.edx & 0xff00) >> 8) + 1;
534 	bd->bd_sec = v86.ecx & 0x3f;
535 	bd->bd_type = v86.ebx;
536 	bd->bd_sectors = (uint64_t)bd->bd_cyl * bd->bd_hds * bd->bd_sec;
537 
538 	return (0);
539 }
540 
541 /*
542  * Read EDD info. Return 0 on success, error otherwise.
543  *
544  * Avoid stack corruption on some systems by adding extra bytes to
545  * params block.
546  */
547 static int
548 bd_get_diskinfo_ext(struct bdinfo *bd)
549 {
550 	struct disk_params {
551 		struct edd_params head;
552 		struct edd_device_path_v3 device_path;
553 		uint8_t dummy[16];
554 	} __packed dparams;
555 	struct edd_params *params;
556 	uint64_t total;
557 
558 	params = &dparams.head;
559 
560 	/* Get disk params */
561 	bzero(&dparams, sizeof(dparams));
562 	params->len = sizeof(struct edd_params_v3);
563 	v86.ctl = V86_FLAGS;
564 	v86.addr = DISK_BIOS;
565 	v86.eax = CMD_EXT_PARAM;
566 	v86.edx = bd->bd_unit;
567 	v86.ds = VTOPSEG(&dparams);
568 	v86.esi = VTOPOFF(&dparams);
569 	v86int();
570 
571 	if (V86_CY(v86.efl) && ((v86.eax & 0xff00) != 0))
572 		return ((v86.eax & 0xff00) >> 8);
573 
574 	/*
575 	 * Sector size must be a multiple of 512 bytes.
576 	 * An alternate test would be to check power of 2,
577 	 * powerof2(params.sector_size).
578 	 * 16K is largest read buffer we can use at this time.
579 	 */
580 	if (params->sector_size >= 512 &&
581 	    params->sector_size <= 16384 &&
582 	    (params->sector_size % BIOSDISK_SECSIZE) == 0)
583 		bd->bd_sectorsize = params->sector_size;
584 
585 	bd->bd_cyl = params->cylinders;
586 	bd->bd_hds = params->heads;
587 	bd->bd_sec = params->sectors_per_track;
588 
589 	if (params->sectors != 0) {
590 		total = params->sectors;
591 	} else {
592 		total = (uint64_t)params->cylinders *
593 		    params->heads * params->sectors_per_track;
594 	}
595 	bd->bd_sectors = total;
596 
597 	return (0);
598 }
599 
600 /*
601  * Try to detect a device supported by the legacy int13 BIOS
602  */
603 static bool
604 bd_int13probe(bdinfo_t *bd)
605 {
606 	int edd, ret;
607 
608 	bd->bd_flags &= ~BD_NO_MEDIA;
609 
610 	if ((bd->bd_flags & BD_CDROM) != 0) {
611 		return (bd_get_diskinfo_cd(bd) == 0);
612 	}
613 
614 	edd = bd_check_extensions(bd->bd_unit);
615 	if (edd == 0)
616 		bd->bd_flags |= BD_MODEINT13;
617 	else if (edd < 0x30)
618 		bd->bd_flags |= BD_MODEEDD1;
619 	else
620 		bd->bd_flags |= BD_MODEEDD3;
621 
622 	/* Default sector size */
623 	if (bd->bd_sectorsize == 0)
624 		bd->bd_sectorsize = BIOSDISK_SECSIZE;
625 
626 	/*
627 	 * Test if the floppy device is present, so we can avoid receiving
628 	 * bogus information from bd_get_diskinfo_std().
629 	 */
630 	if (bd->bd_unit < 0x80) {
631 		/* reset disk */
632 		bd_reset_disk(bd->bd_unit);
633 
634 		/* Get disk type */
635 		v86.ctl = V86_FLAGS;
636 		v86.addr = DISK_BIOS;
637 		v86.eax = CMD_DRIVE_TYPE;
638 		v86.edx = bd->bd_unit;
639 		v86int();
640 		if (V86_CY(v86.efl) || (v86.eax & 0x300) == 0)
641 			return (false);
642 	}
643 
644 	ret = 1;
645 	if (edd != 0)
646 		ret = bd_get_diskinfo_ext(bd);
647 	if (ret != 0 || bd->bd_sectors == 0)
648 		ret = bd_get_diskinfo_std(bd);
649 
650 	if (ret != 0 && bd->bd_unit < 0x80) {
651 		/* Set defaults for 1.44 floppy */
652 		bd->bd_cyl = 80;
653 		bd->bd_hds = 2;
654 		bd->bd_sec = 18;
655 		bd->bd_sectors = 2880;
656 		/* Since we are there, there most likely is no media */
657 		bd->bd_flags |= BD_NO_MEDIA;
658 		ret = 0;
659 	}
660 
661 	if (ret != 0) {
662 		if (bd->bd_sectors != 0 && edd != 0) {
663 			bd->bd_sec = 63;
664 			bd->bd_hds = 255;
665 			bd->bd_cyl =
666 			    (bd->bd_sectors + bd->bd_sec * bd->bd_hds - 1) /
667 			    bd->bd_sec * bd->bd_hds;
668 		} else {
669 			const char *dv_name;
670 
671 			if ((bd->bd_flags & BD_FLOPPY) != 0)
672 				dv_name = biosfd.dv_name;
673 			else
674 				dv_name = bioshd.dv_name;
675 
676 			printf("Can not get information about %s unit %#x\n",
677 			    dv_name, bd->bd_unit);
678 			return (false);
679 		}
680 	}
681 
682 	if (bd->bd_sec == 0)
683 		bd->bd_sec = 63;
684 	if (bd->bd_hds == 0)
685 		bd->bd_hds = 255;
686 
687 	if (bd->bd_sectors == 0)
688 		bd->bd_sectors = (uint64_t)bd->bd_cyl * bd->bd_hds * bd->bd_sec;
689 
690 	DPRINTF("unit 0x%x geometry %d/%d/%d\n", bd->bd_unit, bd->bd_cyl,
691 	    bd->bd_hds, bd->bd_sec);
692 
693 	return (true);
694 }
695 
696 static int
697 bd_count(bdinfo_list_t *bdi)
698 {
699 	bdinfo_t *bd;
700 	int i;
701 
702 	i = 0;
703 	STAILQ_FOREACH(bd, bdi, bd_link)
704 		i++;
705 	return (i);
706 }
707 
708 /*
709  * Print information about disks
710  */
711 static int
712 bd_print_common(struct devsw *dev, bdinfo_list_t *bdi, int verbose)
713 {
714 	char line[80];
715 	struct disk_devdesc devd;
716 	bdinfo_t *bd;
717 	int i, ret = 0;
718 	char drive;
719 
720 	if (STAILQ_EMPTY(bdi))
721 		return (0);
722 
723 	printf("%s devices:", dev->dv_name);
724 	if ((ret = pager_output("\n")) != 0)
725 		return (ret);
726 
727 	i = -1;
728 	STAILQ_FOREACH(bd, bdi, bd_link) {
729 		i++;
730 
731 		switch (dev->dv_type) {
732 		case DEVT_FD:
733 			drive = 'A';
734 			break;
735 		case DEVT_CD:
736 			drive = 'C' + bd_count(&hdinfo);
737 			break;
738 		default:
739 			drive = 'C';
740 			break;
741 		}
742 
743 		snprintf(line, sizeof(line),
744 		    "    %s%d:   BIOS drive %c (%s%ju X %u):\n",
745 		    dev->dv_name, i, drive + i,
746 		    (bd->bd_flags & BD_NO_MEDIA) == BD_NO_MEDIA ?
747 		    "no media, " : "",
748 		    (uintmax_t)bd->bd_sectors,
749 		    bd->bd_sectorsize);
750 		if ((ret = pager_output(line)) != 0)
751 			break;
752 
753 		if ((bd->bd_flags & BD_NO_MEDIA) == BD_NO_MEDIA)
754 			continue;
755 
756 		if (dev->dv_type != DEVT_DISK)
757 			continue;
758 
759 		devd.dd.d_dev = dev;
760 		devd.dd.d_unit = i;
761 		devd.d_slice = D_SLICENONE;
762 		devd.d_partition = D_PARTNONE;
763 		if (disk_open(&devd,
764 		    bd->bd_sectorsize * bd->bd_sectors,
765 		    bd->bd_sectorsize) == 0) {
766 			snprintf(line, sizeof(line), "    %s%d",
767 			    dev->dv_name, i);
768 			ret = disk_print(&devd, line, verbose);
769 			disk_close(&devd);
770 			if (ret != 0)
771 				break;
772 		}
773 	}
774 	return (ret);
775 }
776 
777 static int
778 fd_print(int verbose)
779 {
780 	return (bd_print_common(&biosfd, &fdinfo, verbose));
781 }
782 
783 static int
784 bd_print(int verbose)
785 {
786 	return (bd_print_common(&bioshd, &hdinfo, verbose));
787 }
788 
789 static int
790 cd_print(int verbose)
791 {
792 	return (bd_print_common(&bioscd, &cdinfo, verbose));
793 }
794 
795 /*
796  * Read disk size from partition.
797  * This is needed to work around buggy BIOS systems returning
798  * wrong (truncated) disk media size.
799  * During bd_probe() we tested if the multiplication of bd_sectors
800  * would overflow so it should be safe to perform here.
801  */
802 static uint64_t
803 bd_disk_get_sectors(struct disk_devdesc *dev)
804 {
805 	bdinfo_t *bd;
806 	struct disk_devdesc disk;
807 	uint64_t size;
808 
809 	bd = bd_get_bdinfo(&dev->dd);
810 	if (bd == NULL)
811 		return (0);
812 
813 	disk.dd.d_dev = dev->dd.d_dev;
814 	disk.dd.d_unit = dev->dd.d_unit;
815 	disk.d_slice = D_SLICENONE;
816 	disk.d_partition = D_PARTNONE;
817 	disk.d_offset = 0;
818 
819 	size = bd->bd_sectors * bd->bd_sectorsize;
820 	if (disk_open(&disk, size, bd->bd_sectorsize) == 0) {
821 		(void) disk_ioctl(&disk, DIOCGMEDIASIZE, &size);
822 		disk_close(&disk);
823 	}
824 	return (size / bd->bd_sectorsize);
825 }
826 
827 /*
828  * Attempt to open the disk described by (dev) for use by (f).
829  *
830  * Note that the philosophy here is "give them exactly what
831  * they ask for".  This is necessary because being too "smart"
832  * about what the user might want leads to complications.
833  * (eg. given no slice or partition value, with a disk that is
834  *  sliced - are they after the first BSD slice, or the DOS
835  *  slice before it?)
836  */
837 static int
838 bd_open(struct open_file *f, ...)
839 {
840 	bdinfo_t *bd;
841 	struct disk_devdesc *dev;
842 	va_list ap;
843 	int rc;
844 
845 	TSENTER();
846 
847 	va_start(ap, f);
848 	dev = va_arg(ap, struct disk_devdesc *);
849 	va_end(ap);
850 
851 	bd = bd_get_bdinfo(&dev->dd);
852 	if (bd == NULL)
853 		return (EIO);
854 
855 	if ((bd->bd_flags & BD_NO_MEDIA) == BD_NO_MEDIA) {
856 		if (!bd_int13probe(bd))
857 			return (EIO);
858 		if ((bd->bd_flags & BD_NO_MEDIA) == BD_NO_MEDIA)
859 			return (EIO);
860 	}
861 	if (bd->bd_bcache == NULL)
862 	    bd->bd_bcache = bcache_allocate();
863 
864 	if (bd->bd_open == 0)
865 		bd->bd_sectors = bd_disk_get_sectors(dev);
866 	bd->bd_open++;
867 
868 	rc = 0;
869 	if (dev->dd.d_dev->dv_type == DEVT_DISK) {
870 		rc = disk_open(dev, bd->bd_sectors * bd->bd_sectorsize,
871 		    bd->bd_sectorsize);
872 		if (rc != 0) {
873 			bd->bd_open--;
874 			if (bd->bd_open == 0) {
875 				bcache_free(bd->bd_bcache);
876 				bd->bd_bcache = NULL;
877 			}
878 		}
879 	}
880 	TSEXIT();
881 	return (rc);
882 }
883 
884 static int
885 bd_close(struct open_file *f)
886 {
887 	struct disk_devdesc *dev;
888 	bdinfo_t *bd;
889 	int rc = 0;
890 
891 	dev = (struct disk_devdesc *)f->f_devdata;
892 	bd = bd_get_bdinfo(&dev->dd);
893 	if (bd == NULL)
894 		return (EIO);
895 
896 	bd->bd_open--;
897 	if (bd->bd_open == 0) {
898 	    bcache_free(bd->bd_bcache);
899 	    bd->bd_bcache = NULL;
900 	}
901 	if (dev->dd.d_dev->dv_type == DEVT_DISK)
902 		rc = disk_close(dev);
903 	return (rc);
904 }
905 
906 static int
907 bd_ioctl(struct open_file *f, u_long cmd, void *data)
908 {
909 	bdinfo_t *bd;
910 	struct disk_devdesc *dev;
911 	int rc;
912 
913 	dev = (struct disk_devdesc *)f->f_devdata;
914 	bd = bd_get_bdinfo(&dev->dd);
915 	if (bd == NULL)
916 		return (EIO);
917 
918 	if (dev->dd.d_dev->dv_type == DEVT_DISK) {
919 		rc = disk_ioctl(dev, cmd, data);
920 		if (rc != ENOTTY)
921 			return (rc);
922 	}
923 
924 	switch (cmd) {
925 	case DIOCGSECTORSIZE:
926 		*(uint32_t *)data = bd->bd_sectorsize;
927 		break;
928 	case DIOCGMEDIASIZE:
929 		*(uint64_t *)data = bd->bd_sectors * bd->bd_sectorsize;
930 		break;
931 	default:
932 		return (ENOTTY);
933 	}
934 	return (0);
935 }
936 
937 static int
938 bd_strategy(void *devdata, int rw, daddr_t dblk, size_t size,
939     char *buf, size_t *rsize)
940 {
941 	bdinfo_t *bd;
942 	struct bcache_devdata bcd;
943 	struct disk_devdesc *dev;
944 	daddr_t offset;
945 
946 	dev = (struct disk_devdesc *)devdata;
947 	bd = bd_get_bdinfo(&dev->dd);
948 	if (bd == NULL)
949 		return (EINVAL);
950 
951 	bcd.dv_strategy = bd_realstrategy;
952 	bcd.dv_devdata = devdata;
953 	bcd.dv_cache = bd->bd_bcache;
954 
955 	offset = 0;
956 	if (dev->dd.d_dev->dv_type == DEVT_DISK) {
957 
958 		offset = dev->d_offset * bd->bd_sectorsize;
959 		offset /= BIOSDISK_SECSIZE;
960 	}
961 	return (bcache_strategy(&bcd, rw, dblk + offset, size,
962 	    buf, rsize));
963 }
964 
965 static int
966 bd_realstrategy(void *devdata, int rw, daddr_t dblk, size_t size,
967     char *buf, size_t *rsize)
968 {
969 	struct disk_devdesc *dev = (struct disk_devdesc *)devdata;
970 	bdinfo_t *bd;
971 	uint64_t disk_blocks, offset, d_offset;
972 	size_t blks, blkoff, bsize, bio_size, rest;
973 	caddr_t bbuf = NULL;
974 	int rc;
975 
976 	bd = bd_get_bdinfo(&dev->dd);
977 	if (bd == NULL || (bd->bd_flags & BD_NO_MEDIA) == BD_NO_MEDIA)
978 		return (EIO);
979 
980 	/*
981 	 * First make sure the IO size is a multiple of 512 bytes. While we do
982 	 * process partial reads below, the strategy mechanism is built
983 	 * assuming IO is a multiple of 512B blocks. If the request is not
984 	 * a multiple of 512B blocks, it has to be some sort of bug.
985 	 */
986 	if (size == 0 || (size % BIOSDISK_SECSIZE) != 0) {
987 		printf("bd_strategy: %d bytes I/O not multiple of %d\n",
988 		    size, BIOSDISK_SECSIZE);
989 		return (EIO);
990 	}
991 
992 	DPRINTF("open_disk %p", dev);
993 
994 	offset = dblk * BIOSDISK_SECSIZE;
995 	dblk = offset / bd->bd_sectorsize;
996 	blkoff = offset % bd->bd_sectorsize;
997 
998 	/*
999 	 * Check the value of the size argument. We do have quite small
1000 	 * heap (64MB), but we do not know good upper limit, so we check against
1001 	 * INT_MAX here. This will also protect us against possible overflows
1002 	 * while translating block count to bytes.
1003 	 */
1004 	if (size > INT_MAX) {
1005 		DPRINTF("too large I/O: %zu bytes", size);
1006 		return (EIO);
1007 	}
1008 
1009 	blks = size / bd->bd_sectorsize;
1010 	if (blks == 0 || (size % bd->bd_sectorsize) != 0)
1011 		blks++;
1012 
1013 	if (dblk > dblk + blks)
1014 		return (EIO);
1015 
1016 	if (rsize)
1017 		*rsize = 0;
1018 
1019 	/*
1020 	 * Get disk blocks, this value is either for whole disk or for
1021 	 * partition.
1022 	 */
1023 	d_offset = 0;
1024 	disk_blocks = 0;
1025 	if (dev->dd.d_dev->dv_type == DEVT_DISK) {
1026 		if (disk_ioctl(dev, DIOCGMEDIASIZE, &disk_blocks) == 0) {
1027 			/* DIOCGMEDIASIZE does return bytes. */
1028 			disk_blocks /= bd->bd_sectorsize;
1029 		}
1030 		d_offset = dev->d_offset;
1031 	}
1032 	if (disk_blocks == 0)
1033 		disk_blocks = bd->bd_sectors * (bd->bd_sectorsize /
1034 		    BIOSDISK_SECSIZE) - d_offset;
1035 
1036 	/* Validate source block address. */
1037 	if (dblk < d_offset || dblk >= d_offset + disk_blocks)
1038 		return (EIO);
1039 
1040 	/*
1041 	 * Truncate if we are crossing disk or partition end.
1042 	 */
1043 	if (dblk + blks >= d_offset + disk_blocks) {
1044 		blks = d_offset + disk_blocks - dblk;
1045 		size = blks * bd->bd_sectorsize;
1046 		DPRINTF("short I/O %d", blks);
1047 	}
1048 
1049 	bio_size = min(BIO_BUFFER_SIZE, size);
1050 	while (bio_size > bd->bd_sectorsize) {
1051 		bbuf = bio_alloc(bio_size);
1052 		if (bbuf != NULL)
1053 			break;
1054 		bio_size -= bd->bd_sectorsize;
1055 	}
1056 	if (bbuf == NULL) {
1057 		bio_size = V86_IO_BUFFER_SIZE;
1058 		if (bio_size / bd->bd_sectorsize == 0)
1059 			panic("BUG: Real mode buffer is too small");
1060 
1061 		/* Use alternate 4k buffer */
1062 		bbuf = PTOV(V86_IO_BUFFER);
1063 	}
1064 	rest = size;
1065 	rc = 0;
1066 	while (blks > 0) {
1067 		int x = min(blks, bio_size / bd->bd_sectorsize);
1068 
1069 		switch (rw & F_MASK) {
1070 		case F_READ:
1071 			DPRINTF("read %d from %lld to %p", x, dblk, buf);
1072 			bsize = bd->bd_sectorsize * x - blkoff;
1073 			if (rest < bsize)
1074 				bsize = rest;
1075 
1076 			if ((rc = bd_io(dev, bd, dblk, x, bbuf, BD_RD)) != 0) {
1077 				rc = EIO;
1078 				goto error;
1079 			}
1080 
1081 			bcopy(bbuf + blkoff, buf, bsize);
1082 			break;
1083 		case F_WRITE :
1084 			DPRINTF("write %d from %lld to %p", x, dblk, buf);
1085 			if (blkoff != 0) {
1086 				/*
1087 				 * We got offset to sector, read 1 sector to
1088 				 * bbuf.
1089 				 */
1090 				x = 1;
1091 				bsize = bd->bd_sectorsize - blkoff;
1092 				bsize = min(bsize, rest);
1093 				rc = bd_io(dev, bd, dblk, x, bbuf, BD_RD);
1094 			} else if (rest < bd->bd_sectorsize) {
1095 				/*
1096 				 * The remaining block is not full
1097 				 * sector. Read 1 sector to bbuf.
1098 				 */
1099 				x = 1;
1100 				bsize = rest;
1101 				rc = bd_io(dev, bd, dblk, x, bbuf, BD_RD);
1102 			} else {
1103 				/* We can write full sector(s). */
1104 				bsize = bd->bd_sectorsize * x;
1105 			}
1106 			/*
1107 			 * Put your Data In, Put your Data out,
1108 			 * Put your Data In, and shake it all about
1109 			 */
1110 			bcopy(buf, bbuf + blkoff, bsize);
1111 			if ((rc = bd_io(dev, bd, dblk, x, bbuf, BD_WR)) != 0) {
1112 				rc = EIO;
1113 				goto error;
1114 			}
1115 
1116 			break;
1117 		default:
1118 			/* DO NOTHING */
1119 			rc = EROFS;
1120 			goto error;
1121 		}
1122 
1123 		blkoff = 0;
1124 		buf += bsize;
1125 		rest -= bsize;
1126 		blks -= x;
1127 		dblk += x;
1128 	}
1129 
1130 	if (rsize != NULL)
1131 		*rsize = size;
1132 error:
1133 	if (bbuf != PTOV(V86_IO_BUFFER))
1134 		bio_free(bbuf, bio_size);
1135 	return (rc);
1136 }
1137 
1138 static int
1139 bd_edd_io(bdinfo_t *bd, daddr_t dblk, int blks, caddr_t dest,
1140     int dowrite)
1141 {
1142 	static struct edd_packet packet;
1143 
1144 	TSENTER();
1145 
1146 	packet.len = sizeof(struct edd_packet);
1147 	packet.count = blks;
1148 	packet.off = VTOPOFF(dest);
1149 	packet.seg = VTOPSEG(dest);
1150 	packet.lba = dblk;
1151 	v86.ctl = V86_FLAGS;
1152 	v86.addr = DISK_BIOS;
1153 	if (dowrite == BD_WR)
1154 		v86.eax = CMD_WRITE_LBA; /* maybe Write with verify 0x4302? */
1155 	else
1156 		v86.eax = CMD_READ_LBA;
1157 	v86.edx = bd->bd_unit;
1158 	v86.ds = VTOPSEG(&packet);
1159 	v86.esi = VTOPOFF(&packet);
1160 	v86int();
1161 	if (V86_CY(v86.efl))
1162 		return (v86.eax >> 8);
1163 
1164 	TSEXIT();
1165 	return (0);
1166 }
1167 
1168 static int
1169 bd_chs_io(bdinfo_t *bd, daddr_t dblk, int blks, caddr_t dest,
1170     int dowrite)
1171 {
1172 	uint32_t x, bpc, cyl, hd, sec;
1173 
1174 	TSENTER();
1175 
1176 	bpc = bd->bd_sec * bd->bd_hds;	/* blocks per cylinder */
1177 	x = dblk;
1178 	cyl = x / bpc;			/* block # / blocks per cylinder */
1179 	x %= bpc;				/* block offset into cylinder */
1180 	hd = x / bd->bd_sec;		/* offset / blocks per track */
1181 	sec = x % bd->bd_sec;		/* offset into track */
1182 
1183 	/* correct sector number for 1-based BIOS numbering */
1184 	sec++;
1185 
1186 	if (cyl > 1023) {
1187 		/* CHS doesn't support cylinders > 1023. */
1188 		return (1);
1189 	}
1190 
1191 	v86.ctl = V86_FLAGS;
1192 	v86.addr = DISK_BIOS;
1193 	if (dowrite == BD_WR)
1194 		v86.eax = CMD_WRITE_CHS | blks;
1195 	else
1196 		v86.eax = CMD_READ_CHS | blks;
1197 	v86.ecx = ((cyl & 0xff) << 8) | ((cyl & 0x300) >> 2) | sec;
1198 	v86.edx = (hd << 8) | bd->bd_unit;
1199 	v86.es = VTOPSEG(dest);
1200 	v86.ebx = VTOPOFF(dest);
1201 	v86int();
1202 	if (V86_CY(v86.efl))
1203 		return (v86.eax >> 8);
1204 	TSEXIT();
1205 	return (0);
1206 }
1207 
1208 static void
1209 bd_io_workaround(bdinfo_t *bd)
1210 {
1211 	uint8_t buf[8 * 1024];
1212 
1213 	bd_edd_io(bd, 0xffffffff, 1, (caddr_t)buf, BD_RD);
1214 }
1215 
1216 static int
1217 bd_io(struct disk_devdesc *dev, bdinfo_t *bd, daddr_t dblk, int blks,
1218     caddr_t dest, int dowrite)
1219 {
1220 	int result, retry;
1221 
1222 	TSENTER();
1223 
1224 	/* Just in case some idiot actually tries to read/write -1 blocks... */
1225 	if (blks < 0)
1226 		return (-1);
1227 
1228 	/*
1229 	 * Workaround for a problem with some HP ProLiant BIOS failing to work
1230 	 * out the boot disk after installation. hrs and kuriyama discovered
1231 	 * this problem with an HP ProLiant DL320e Gen 8 with a 3TB HDD, and
1232 	 * discovered that an int13h call seems to cause a buffer overrun in
1233 	 * the bios. The problem is alleviated by doing an extra read before
1234 	 * the buggy read. It is not immediately known whether other models
1235 	 * are similarly affected.
1236 	 * Loop retrying the operation a couple of times.  The BIOS
1237 	 * may also retry.
1238 	 */
1239 	if (dowrite == BD_RD && dblk >= 0x100000000)
1240 		bd_io_workaround(bd);
1241 	for (retry = 0; retry < 3; retry++) {
1242 		if (bd->bd_flags & BD_MODEEDD)
1243 			result = bd_edd_io(bd, dblk, blks, dest, dowrite);
1244 		else
1245 			result = bd_chs_io(bd, dblk, blks, dest, dowrite);
1246 
1247 		if (result == 0) {
1248 			if (bd->bd_flags & BD_NO_MEDIA)
1249 				bd->bd_flags &= ~BD_NO_MEDIA;
1250 			break;
1251 		}
1252 
1253 		bd_reset_disk(bd->bd_unit);
1254 
1255 		/*
1256 		 * Error codes:
1257 		 * 20h	controller failure
1258 		 * 31h	no media in drive (IBM/MS INT 13 extensions)
1259 		 * 80h	no media in drive, VMWare (Fusion)
1260 		 * There is no reason to repeat the IO with errors above.
1261 		 */
1262 		if (result == 0x20 || result == 0x31 || result == 0x80) {
1263 			bd->bd_flags |= BD_NO_MEDIA;
1264 			break;
1265 		}
1266 	}
1267 
1268 	if (result != 0 && (bd->bd_flags & BD_NO_MEDIA) == 0) {
1269 		if (dowrite == BD_WR) {
1270 			printf("%s%d: Write %d sector(s) from %p (0x%x) "
1271 			    "to %lld: 0x%x\n", dev->dd.d_dev->dv_name,
1272 			    dev->dd.d_unit, blks, dest, VTOP(dest), dblk,
1273 			    result);
1274 		} else {
1275 			printf("%s%d: Read %d sector(s) from %lld to %p "
1276 			    "(0x%x): 0x%x\n", dev->dd.d_dev->dv_name,
1277 			    dev->dd.d_unit, blks, dblk, dest, VTOP(dest),
1278 			    result);
1279 		}
1280 	}
1281 
1282 	TSEXIT();
1283 
1284 	return (result);
1285 }
1286 
1287 /*
1288  * Return a suitable dev_t value for (dev).
1289  *
1290  * In the case where it looks like (dev) is a SCSI disk, we allow the number of
1291  * IDE disks to be specified in $num_ide_disks.  There should be a Better Way.
1292  */
1293 int
1294 bd_getdev(struct i386_devdesc *d)
1295 {
1296 	struct disk_devdesc *dev;
1297 	bdinfo_t *bd;
1298 	int	biosdev;
1299 	int	major;
1300 	int	rootdev;
1301 	char	*nip, *cp;
1302 	int	i, unit, slice, partition;
1303 
1304 	/* XXX: Assume partition 'a'. */
1305 	slice = 0;
1306 	partition = 0;
1307 
1308 	dev = (struct disk_devdesc *)d;
1309 	bd = bd_get_bdinfo(&dev->dd);
1310 	if (bd == NULL)
1311 		return (-1);
1312 
1313 	biosdev = bd_unit2bios(d);
1314 	DPRINTF("unit %d BIOS device %d", dev->dd.d_unit, biosdev);
1315 	if (biosdev == -1)			/* not a BIOS device */
1316 		return (-1);
1317 
1318 	if (dev->dd.d_dev->dv_type == DEVT_DISK) {
1319 		if (disk_open(dev, bd->bd_sectors * bd->bd_sectorsize,
1320 		    bd->bd_sectorsize) != 0)	/* oops, not a viable device */
1321 			return (-1);
1322 		else
1323 			disk_close(dev);
1324 		slice = dev->d_slice + 1;
1325 		partition = dev->d_partition;
1326 	}
1327 
1328 	if (biosdev < 0x80) {
1329 		/* floppy (or emulated floppy) or ATAPI device */
1330 		if (bd->bd_type == DT_ATAPI) {
1331 			/* is an ATAPI disk */
1332 			major = WFDMAJOR;
1333 		} else {
1334 			/* is a floppy disk */
1335 			major = FDMAJOR;
1336 		}
1337 	} else {
1338 		/* assume an IDE disk */
1339 		major = WDMAJOR;
1340 	}
1341 	/* default root disk unit number */
1342 	unit = biosdev & 0x7f;
1343 
1344 	if (dev->dd.d_dev->dv_type == DEVT_CD) {
1345 		/*
1346 		 * XXX: Need to examine device spec here to figure out if
1347 		 * SCSI or ATAPI.  No idea on how to figure out device number.
1348 		 * All we can really pass to the kernel is what bus and device
1349 		 * on which bus we were booted from, which dev_t isn't well
1350 		 * suited to since those number don't match to unit numbers
1351 		 * very well.  We may just need to engage in a hack where
1352 		 * we pass -C to the boot args if we are the boot device.
1353 		 */
1354 		major = ACDMAJOR;
1355 		unit = 0;       /* XXX */
1356 	}
1357 
1358 	/* XXX a better kludge to set the root disk unit number */
1359 	if ((nip = getenv("root_disk_unit")) != NULL) {
1360 		i = strtol(nip, &cp, 0);
1361 		/* check for parse error */
1362 		if ((cp != nip) && (*cp == 0))
1363 			unit = i;
1364 	}
1365 
1366 	rootdev = MAKEBOOTDEV(major, slice, unit, partition);
1367 	DPRINTF("dev is 0x%x\n", rootdev);
1368 	return (rootdev);
1369 }
1370