xref: /freebsd/sys/geom/part/g_part_mbr.c (revision 0b3105a37d7adcadcb720112fed4dc4e8040be99)
1 /*-
2  * Copyright (c) 2007, 2008 Marcel Moolenaar
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  *
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 ``AS IS'' AND ANY EXPRESS OR
16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25  */
26 
27 #include <sys/cdefs.h>
28 __FBSDID("$FreeBSD$");
29 
30 #include <sys/param.h>
31 #include <sys/bio.h>
32 #include <sys/diskmbr.h>
33 #include <sys/endian.h>
34 #include <sys/kernel.h>
35 #include <sys/kobj.h>
36 #include <sys/limits.h>
37 #include <sys/lock.h>
38 #include <sys/malloc.h>
39 #include <sys/mutex.h>
40 #include <sys/queue.h>
41 #include <sys/sbuf.h>
42 #include <sys/systm.h>
43 #include <sys/sysctl.h>
44 #include <geom/geom.h>
45 #include <geom/geom_int.h>
46 #include <geom/part/g_part.h>
47 
48 #include "g_part_if.h"
49 
50 FEATURE(geom_part_mbr, "GEOM partitioning class for MBR support");
51 
52 SYSCTL_DECL(_kern_geom_part);
53 static SYSCTL_NODE(_kern_geom_part, OID_AUTO, mbr, CTLFLAG_RW, 0,
54     "GEOM_PART_MBR Master Boot Record");
55 
56 static u_int enforce_chs = 0;
57 SYSCTL_UINT(_kern_geom_part_mbr, OID_AUTO, enforce_chs,
58     CTLFLAG_RWTUN, &enforce_chs, 0, "Enforce alignment to CHS addressing");
59 
60 #define	MBRSIZE		512
61 
62 struct g_part_mbr_table {
63 	struct g_part_table	base;
64 	u_char		mbr[MBRSIZE];
65 };
66 
67 struct g_part_mbr_entry {
68 	struct g_part_entry	base;
69 	struct dos_partition ent;
70 };
71 
72 static int g_part_mbr_add(struct g_part_table *, struct g_part_entry *,
73     struct g_part_parms *);
74 static int g_part_mbr_bootcode(struct g_part_table *, struct g_part_parms *);
75 static int g_part_mbr_create(struct g_part_table *, struct g_part_parms *);
76 static int g_part_mbr_destroy(struct g_part_table *, struct g_part_parms *);
77 static void g_part_mbr_dumpconf(struct g_part_table *, struct g_part_entry *,
78     struct sbuf *, const char *);
79 static int g_part_mbr_dumpto(struct g_part_table *, struct g_part_entry *);
80 static int g_part_mbr_modify(struct g_part_table *, struct g_part_entry *,
81     struct g_part_parms *);
82 static const char *g_part_mbr_name(struct g_part_table *, struct g_part_entry *,
83     char *, size_t);
84 static int g_part_mbr_probe(struct g_part_table *, struct g_consumer *);
85 static int g_part_mbr_read(struct g_part_table *, struct g_consumer *);
86 static int g_part_mbr_setunset(struct g_part_table *, struct g_part_entry *,
87     const char *, unsigned int);
88 static const char *g_part_mbr_type(struct g_part_table *, struct g_part_entry *,
89     char *, size_t);
90 static int g_part_mbr_write(struct g_part_table *, struct g_consumer *);
91 static int g_part_mbr_resize(struct g_part_table *, struct g_part_entry *,
92     struct g_part_parms *);
93 
94 static kobj_method_t g_part_mbr_methods[] = {
95 	KOBJMETHOD(g_part_add,		g_part_mbr_add),
96 	KOBJMETHOD(g_part_bootcode,	g_part_mbr_bootcode),
97 	KOBJMETHOD(g_part_create,	g_part_mbr_create),
98 	KOBJMETHOD(g_part_destroy,	g_part_mbr_destroy),
99 	KOBJMETHOD(g_part_dumpconf,	g_part_mbr_dumpconf),
100 	KOBJMETHOD(g_part_dumpto,	g_part_mbr_dumpto),
101 	KOBJMETHOD(g_part_modify,	g_part_mbr_modify),
102 	KOBJMETHOD(g_part_resize,	g_part_mbr_resize),
103 	KOBJMETHOD(g_part_name,		g_part_mbr_name),
104 	KOBJMETHOD(g_part_probe,	g_part_mbr_probe),
105 	KOBJMETHOD(g_part_read,		g_part_mbr_read),
106 	KOBJMETHOD(g_part_setunset,	g_part_mbr_setunset),
107 	KOBJMETHOD(g_part_type,		g_part_mbr_type),
108 	KOBJMETHOD(g_part_write,	g_part_mbr_write),
109 	{ 0, 0 }
110 };
111 
112 static struct g_part_scheme g_part_mbr_scheme = {
113 	"MBR",
114 	g_part_mbr_methods,
115 	sizeof(struct g_part_mbr_table),
116 	.gps_entrysz = sizeof(struct g_part_mbr_entry),
117 	.gps_minent = NDOSPART,
118 	.gps_maxent = NDOSPART,
119 	.gps_bootcodesz = MBRSIZE,
120 };
121 G_PART_SCHEME_DECLARE(g_part_mbr);
122 
123 static struct g_part_mbr_alias {
124 	u_char		typ;
125 	int		alias;
126 } mbr_alias_match[] = {
127 	{ DOSPTYP_386BSD,	G_PART_ALIAS_FREEBSD },
128 	{ DOSPTYP_EXT,		G_PART_ALIAS_EBR },
129 	{ DOSPTYP_NTFS,		G_PART_ALIAS_MS_NTFS },
130 	{ DOSPTYP_FAT16,	G_PART_ALIAS_MS_FAT16 },
131 	{ DOSPTYP_FAT32,	G_PART_ALIAS_MS_FAT32 },
132 	{ DOSPTYP_EXTLBA,	G_PART_ALIAS_EBR },
133 	{ DOSPTYP_LDM,		G_PART_ALIAS_MS_LDM_DATA },
134 	{ DOSPTYP_LINSWP,	G_PART_ALIAS_LINUX_SWAP },
135 	{ DOSPTYP_LINUX,	G_PART_ALIAS_LINUX_DATA },
136 	{ DOSPTYP_LINLVM,	G_PART_ALIAS_LINUX_LVM },
137 	{ DOSPTYP_LINRAID,	G_PART_ALIAS_LINUX_RAID },
138 	{ DOSPTYP_PPCBOOT,	G_PART_ALIAS_PREP_BOOT },
139 	{ DOSPTYP_VMFS,		G_PART_ALIAS_VMFS },
140 	{ DOSPTYP_VMKDIAG,	G_PART_ALIAS_VMKDIAG },
141 	{ DOSPTYP_APPLE_UFS,	G_PART_ALIAS_APPLE_UFS },
142 	{ DOSPTYP_APPLE_BOOT,	G_PART_ALIAS_APPLE_BOOT },
143 	{ DOSPTYP_HFS,		G_PART_ALIAS_APPLE_HFS },
144 };
145 
146 static int
147 mbr_parse_type(const char *type, u_char *dp_typ)
148 {
149 	const char *alias;
150 	char *endp;
151 	long lt;
152 	int i;
153 
154 	if (type[0] == '!') {
155 		lt = strtol(type + 1, &endp, 0);
156 		if (type[1] == '\0' || *endp != '\0' || lt <= 0 || lt >= 256)
157 			return (EINVAL);
158 		*dp_typ = (u_char)lt;
159 		return (0);
160 	}
161 	for (i = 0;
162 	    i < sizeof(mbr_alias_match) / sizeof(mbr_alias_match[0]); i++) {
163 		alias = g_part_alias_name(mbr_alias_match[i].alias);
164 		if (strcasecmp(type, alias) == 0) {
165 			*dp_typ = mbr_alias_match[i].typ;
166 			return (0);
167 		}
168 	}
169 	return (EINVAL);
170 }
171 
172 static int
173 mbr_probe_bpb(u_char *bpb)
174 {
175 	uint16_t secsz;
176 	uint8_t clstsz;
177 
178 #define PO2(x)	((x & (x - 1)) == 0)
179 	secsz = le16dec(bpb);
180 	if (secsz < 512 || secsz > 4096 || !PO2(secsz))
181 		return (0);
182 	clstsz = bpb[2];
183 	if (clstsz < 1 || clstsz > 128 || !PO2(clstsz))
184 		return (0);
185 #undef PO2
186 
187 	return (1);
188 }
189 
190 static void
191 mbr_set_chs(struct g_part_table *table, uint32_t lba, u_char *cylp, u_char *hdp,
192     u_char *secp)
193 {
194 	uint32_t cyl, hd, sec;
195 
196 	sec = lba % table->gpt_sectors + 1;
197 	lba /= table->gpt_sectors;
198 	hd = lba % table->gpt_heads;
199 	lba /= table->gpt_heads;
200 	cyl = lba;
201 	if (cyl > 1023)
202 		sec = hd = cyl = ~0;
203 
204 	*cylp = cyl & 0xff;
205 	*hdp = hd & 0xff;
206 	*secp = (sec & 0x3f) | ((cyl >> 2) & 0xc0);
207 }
208 
209 static int
210 mbr_align(struct g_part_table *basetable, uint32_t *start, uint32_t *size)
211 {
212 	uint32_t sectors;
213 
214 	if (enforce_chs == 0)
215 		return (0);
216 	sectors = basetable->gpt_sectors;
217 	if (*size < sectors)
218 		return (EINVAL);
219 	if (start != NULL && (*start % sectors)) {
220 		*size += (*start % sectors) - sectors;
221 		*start -= (*start % sectors) - sectors;
222 	}
223 	if (*size % sectors)
224 		*size -= (*size % sectors);
225 	if (*size < sectors)
226 		return (EINVAL);
227 	return (0);
228 }
229 
230 static int
231 g_part_mbr_add(struct g_part_table *basetable, struct g_part_entry *baseentry,
232     struct g_part_parms *gpp)
233 {
234 	struct g_part_mbr_entry *entry;
235 	uint32_t start, size;
236 
237 	if (gpp->gpp_parms & G_PART_PARM_LABEL)
238 		return (EINVAL);
239 
240 	entry = (struct g_part_mbr_entry *)baseentry;
241 	start = gpp->gpp_start;
242 	size = gpp->gpp_size;
243 	if (mbr_align(basetable, &start, &size) != 0)
244 		return (EINVAL);
245 	if (baseentry->gpe_deleted)
246 		bzero(&entry->ent, sizeof(entry->ent));
247 
248 	KASSERT(baseentry->gpe_start <= start, ("%s", __func__));
249 	KASSERT(baseentry->gpe_end >= start + size - 1, ("%s", __func__));
250 	baseentry->gpe_start = start;
251 	baseentry->gpe_end = start + size - 1;
252 	entry->ent.dp_start = start;
253 	entry->ent.dp_size = size;
254 	mbr_set_chs(basetable, baseentry->gpe_start, &entry->ent.dp_scyl,
255 	    &entry->ent.dp_shd, &entry->ent.dp_ssect);
256 	mbr_set_chs(basetable, baseentry->gpe_end, &entry->ent.dp_ecyl,
257 	    &entry->ent.dp_ehd, &entry->ent.dp_esect);
258 	return (mbr_parse_type(gpp->gpp_type, &entry->ent.dp_typ));
259 }
260 
261 static int
262 g_part_mbr_bootcode(struct g_part_table *basetable, struct g_part_parms *gpp)
263 {
264 	struct g_part_mbr_table *table;
265 	uint32_t dsn;
266 
267 	if (gpp->gpp_codesize != MBRSIZE)
268 		return (ENODEV);
269 
270 	table = (struct g_part_mbr_table *)basetable;
271 	dsn = *(uint32_t *)(table->mbr + DOSDSNOFF);
272 	bcopy(gpp->gpp_codeptr, table->mbr, DOSPARTOFF);
273 	if (dsn != 0)
274 		*(uint32_t *)(table->mbr + DOSDSNOFF) = dsn;
275 	return (0);
276 }
277 
278 static int
279 g_part_mbr_create(struct g_part_table *basetable, struct g_part_parms *gpp)
280 {
281 	struct g_provider *pp;
282 	struct g_part_mbr_table *table;
283 
284 	pp = gpp->gpp_provider;
285 	if (pp->sectorsize < MBRSIZE)
286 		return (ENOSPC);
287 
288 	basetable->gpt_first = basetable->gpt_sectors;
289 	basetable->gpt_last = MIN(pp->mediasize / pp->sectorsize,
290 	    UINT32_MAX) - 1;
291 
292 	table = (struct g_part_mbr_table *)basetable;
293 	le16enc(table->mbr + DOSMAGICOFFSET, DOSMAGIC);
294 	return (0);
295 }
296 
297 static int
298 g_part_mbr_destroy(struct g_part_table *basetable, struct g_part_parms *gpp)
299 {
300 
301 	/* Wipe the first sector to clear the partitioning. */
302 	basetable->gpt_smhead |= 1;
303 	return (0);
304 }
305 
306 static void
307 g_part_mbr_dumpconf(struct g_part_table *table, struct g_part_entry *baseentry,
308     struct sbuf *sb, const char *indent)
309 {
310 	struct g_part_mbr_entry *entry;
311 
312 	entry = (struct g_part_mbr_entry *)baseentry;
313 	if (indent == NULL) {
314 		/* conftxt: libdisk compatibility */
315 		sbuf_printf(sb, " xs MBR xt %u", entry->ent.dp_typ);
316 	} else if (entry != NULL) {
317 		/* confxml: partition entry information */
318 		sbuf_printf(sb, "%s<rawtype>%u</rawtype>\n", indent,
319 		    entry->ent.dp_typ);
320 		if (entry->ent.dp_flag & 0x80)
321 			sbuf_printf(sb, "%s<attrib>active</attrib>\n", indent);
322 	} else {
323 		/* confxml: scheme information */
324 	}
325 }
326 
327 static int
328 g_part_mbr_dumpto(struct g_part_table *table, struct g_part_entry *baseentry)
329 {
330 	struct g_part_mbr_entry *entry;
331 
332 	/* Allow dumping to a FreeBSD partition or Linux swap partition only. */
333 	entry = (struct g_part_mbr_entry *)baseentry;
334 	return ((entry->ent.dp_typ == DOSPTYP_386BSD ||
335 	    entry->ent.dp_typ == DOSPTYP_LINSWP) ? 1 : 0);
336 }
337 
338 static int
339 g_part_mbr_modify(struct g_part_table *basetable,
340     struct g_part_entry *baseentry, struct g_part_parms *gpp)
341 {
342 	struct g_part_mbr_entry *entry;
343 
344 	if (gpp->gpp_parms & G_PART_PARM_LABEL)
345 		return (EINVAL);
346 
347 	entry = (struct g_part_mbr_entry *)baseentry;
348 	if (gpp->gpp_parms & G_PART_PARM_TYPE)
349 		return (mbr_parse_type(gpp->gpp_type, &entry->ent.dp_typ));
350 	return (0);
351 }
352 
353 static int
354 g_part_mbr_resize(struct g_part_table *basetable,
355     struct g_part_entry *baseentry, struct g_part_parms *gpp)
356 {
357 	struct g_part_mbr_entry *entry;
358 	struct g_provider *pp;
359 	uint32_t size;
360 
361 	if (baseentry == NULL) {
362 		pp = LIST_FIRST(&basetable->gpt_gp->consumer)->provider;
363 		basetable->gpt_last = MIN(pp->mediasize / pp->sectorsize,
364 		    UINT32_MAX) - 1;
365 		return (0);
366 	}
367 	size = gpp->gpp_size;
368 	if (mbr_align(basetable, NULL, &size) != 0)
369 		return (EINVAL);
370 	/* XXX: prevent unexpected shrinking. */
371 	pp = baseentry->gpe_pp;
372 	if ((g_debugflags & 0x10) == 0 && size < gpp->gpp_size &&
373 	    pp->mediasize / pp->sectorsize > size)
374 		return (EBUSY);
375 	entry = (struct g_part_mbr_entry *)baseentry;
376 	baseentry->gpe_end = baseentry->gpe_start + size - 1;
377 	entry->ent.dp_size = size;
378 	mbr_set_chs(basetable, baseentry->gpe_end, &entry->ent.dp_ecyl,
379 	    &entry->ent.dp_ehd, &entry->ent.dp_esect);
380 	return (0);
381 }
382 
383 static const char *
384 g_part_mbr_name(struct g_part_table *table, struct g_part_entry *baseentry,
385     char *buf, size_t bufsz)
386 {
387 
388 	snprintf(buf, bufsz, "s%d", baseentry->gpe_index);
389 	return (buf);
390 }
391 
392 static int
393 g_part_mbr_probe(struct g_part_table *table, struct g_consumer *cp)
394 {
395 	char psn[8];
396 	struct g_provider *pp;
397 	u_char *buf, *p;
398 	int error, index, res, sum;
399 	uint16_t magic;
400 
401 	pp = cp->provider;
402 
403 	/* Sanity-check the provider. */
404 	if (pp->sectorsize < MBRSIZE || pp->mediasize < pp->sectorsize)
405 		return (ENOSPC);
406 	if (pp->sectorsize > 4096)
407 		return (ENXIO);
408 
409 	/* We don't nest under an MBR (see EBR instead). */
410 	error = g_getattr("PART::scheme", cp, &psn);
411 	if (error == 0 && strcmp(psn, g_part_mbr_scheme.name) == 0)
412 		return (ELOOP);
413 
414 	/* Check that there's a MBR. */
415 	buf = g_read_data(cp, 0L, pp->sectorsize, &error);
416 	if (buf == NULL)
417 		return (error);
418 
419 	/* We goto out on mismatch. */
420 	res = ENXIO;
421 
422 	magic = le16dec(buf + DOSMAGICOFFSET);
423 	if (magic != DOSMAGIC)
424 		goto out;
425 
426 	for (index = 0; index < NDOSPART; index++) {
427 		p = buf + DOSPARTOFF + index * DOSPARTSIZE;
428 		if (p[0] != 0 && p[0] != 0x80)
429 			goto out;
430 	}
431 
432 	/*
433 	 * If the partition table does not consist of all zeroes,
434 	 * assume we have a MBR. If it's all zeroes, we could have
435 	 * a boot sector. For example, a boot sector that doesn't
436 	 * have boot code -- common on non-i386 hardware. In that
437 	 * case we check if we have a possible BPB. If so, then we
438 	 * assume we have a boot sector instead.
439 	 */
440 	sum = 0;
441 	for (index = 0; index < NDOSPART * DOSPARTSIZE; index++)
442 		sum += buf[DOSPARTOFF + index];
443 	if (sum != 0 || !mbr_probe_bpb(buf + 0x0b))
444 		res = G_PART_PROBE_PRI_NORM;
445 
446  out:
447 	g_free(buf);
448 	return (res);
449 }
450 
451 static int
452 g_part_mbr_read(struct g_part_table *basetable, struct g_consumer *cp)
453 {
454 	struct dos_partition ent;
455 	struct g_provider *pp;
456 	struct g_part_mbr_table *table;
457 	struct g_part_mbr_entry *entry;
458 	u_char *buf, *p;
459 	off_t chs, msize, first;
460 	u_int sectors, heads;
461 	int error, index;
462 
463 	pp = cp->provider;
464 	table = (struct g_part_mbr_table *)basetable;
465 	first = basetable->gpt_sectors;
466 	msize = MIN(pp->mediasize / pp->sectorsize, UINT32_MAX);
467 
468 	buf = g_read_data(cp, 0L, pp->sectorsize, &error);
469 	if (buf == NULL)
470 		return (error);
471 
472 	bcopy(buf, table->mbr, sizeof(table->mbr));
473 	for (index = NDOSPART - 1; index >= 0; index--) {
474 		p = buf + DOSPARTOFF + index * DOSPARTSIZE;
475 		ent.dp_flag = p[0];
476 		ent.dp_shd = p[1];
477 		ent.dp_ssect = p[2];
478 		ent.dp_scyl = p[3];
479 		ent.dp_typ = p[4];
480 		ent.dp_ehd = p[5];
481 		ent.dp_esect = p[6];
482 		ent.dp_ecyl = p[7];
483 		ent.dp_start = le32dec(p + 8);
484 		ent.dp_size = le32dec(p + 12);
485 		if (ent.dp_typ == 0 || ent.dp_typ == DOSPTYP_PMBR)
486 			continue;
487 		if (ent.dp_start == 0 || ent.dp_size == 0)
488 			continue;
489 		sectors = ent.dp_esect & 0x3f;
490 		if (sectors > basetable->gpt_sectors &&
491 		    !basetable->gpt_fixgeom) {
492 			g_part_geometry_heads(msize, sectors, &chs, &heads);
493 			if (chs != 0) {
494 				basetable->gpt_sectors = sectors;
495 				basetable->gpt_heads = heads;
496 			}
497 		}
498 		if (ent.dp_start < first)
499 			first = ent.dp_start;
500 		entry = (struct g_part_mbr_entry *)g_part_new_entry(basetable,
501 		    index + 1, ent.dp_start, ent.dp_start + ent.dp_size - 1);
502 		entry->ent = ent;
503 	}
504 
505 	basetable->gpt_entries = NDOSPART;
506 	basetable->gpt_first = basetable->gpt_sectors;
507 	basetable->gpt_last = msize - 1;
508 
509 	if (first < basetable->gpt_first)
510 		basetable->gpt_first = 1;
511 
512 	g_free(buf);
513 	return (0);
514 }
515 
516 static int
517 g_part_mbr_setunset(struct g_part_table *table, struct g_part_entry *baseentry,
518     const char *attrib, unsigned int set)
519 {
520 	struct g_part_entry *iter;
521 	struct g_part_mbr_entry *entry;
522 	int changed;
523 
524 	if (baseentry == NULL)
525 		return (ENODEV);
526 	if (strcasecmp(attrib, "active") != 0)
527 		return (EINVAL);
528 
529 	/* Only one entry can have the active attribute. */
530 	LIST_FOREACH(iter, &table->gpt_entry, gpe_entry) {
531 		if (iter->gpe_deleted)
532 			continue;
533 		changed = 0;
534 		entry = (struct g_part_mbr_entry *)iter;
535 		if (iter == baseentry) {
536 			if (set && (entry->ent.dp_flag & 0x80) == 0) {
537 				entry->ent.dp_flag |= 0x80;
538 				changed = 1;
539 			} else if (!set && (entry->ent.dp_flag & 0x80)) {
540 				entry->ent.dp_flag &= ~0x80;
541 				changed = 1;
542 			}
543 		} else {
544 			if (set && (entry->ent.dp_flag & 0x80)) {
545 				entry->ent.dp_flag &= ~0x80;
546 				changed = 1;
547 			}
548 		}
549 		if (changed && !iter->gpe_created)
550 			iter->gpe_modified = 1;
551 	}
552 	return (0);
553 }
554 
555 static const char *
556 g_part_mbr_type(struct g_part_table *basetable, struct g_part_entry *baseentry,
557     char *buf, size_t bufsz)
558 {
559 	struct g_part_mbr_entry *entry;
560 	int i;
561 
562 	entry = (struct g_part_mbr_entry *)baseentry;
563 	for (i = 0;
564 	    i < sizeof(mbr_alias_match) / sizeof(mbr_alias_match[0]); i++) {
565 		if (mbr_alias_match[i].typ == entry->ent.dp_typ)
566 			return (g_part_alias_name(mbr_alias_match[i].alias));
567 	}
568 	snprintf(buf, bufsz, "!%d", entry->ent.dp_typ);
569 	return (buf);
570 }
571 
572 static int
573 g_part_mbr_write(struct g_part_table *basetable, struct g_consumer *cp)
574 {
575 	struct g_part_entry *baseentry;
576 	struct g_part_mbr_entry *entry;
577 	struct g_part_mbr_table *table;
578 	u_char *p;
579 	int error, index;
580 
581 	table = (struct g_part_mbr_table *)basetable;
582 	baseentry = LIST_FIRST(&basetable->gpt_entry);
583 	for (index = 1; index <= basetable->gpt_entries; index++) {
584 		p = table->mbr + DOSPARTOFF + (index - 1) * DOSPARTSIZE;
585 		entry = (baseentry != NULL && index == baseentry->gpe_index)
586 		    ? (struct g_part_mbr_entry *)baseentry : NULL;
587 		if (entry != NULL && !baseentry->gpe_deleted) {
588 			p[0] = entry->ent.dp_flag;
589 			p[1] = entry->ent.dp_shd;
590 			p[2] = entry->ent.dp_ssect;
591 			p[3] = entry->ent.dp_scyl;
592 			p[4] = entry->ent.dp_typ;
593 			p[5] = entry->ent.dp_ehd;
594 			p[6] = entry->ent.dp_esect;
595 			p[7] = entry->ent.dp_ecyl;
596 			le32enc(p + 8, entry->ent.dp_start);
597 			le32enc(p + 12, entry->ent.dp_size);
598 		} else
599 			bzero(p, DOSPARTSIZE);
600 
601 		if (entry != NULL)
602 			baseentry = LIST_NEXT(baseentry, gpe_entry);
603 	}
604 
605 	error = g_write_data(cp, 0, table->mbr, cp->provider->sectorsize);
606 	return (error);
607 }
608