Index: head/sys/geom/part/g_part_mbr.c
===================================================================
--- head/sys/geom/part/g_part_mbr.c	(revision 222209)
+++ head/sys/geom/part/g_part_mbr.c	(working copy)
@@ -194,38 +194,22 @@ g_part_mbr_add(struct g_part_table *basetable, str
 {
 	struct g_part_mbr_entry *entry;
 	struct g_part_mbr_table *table;
-	uint32_t start, size, sectors;
 
 	if (gpp->gpp_parms & G_PART_PARM_LABEL)
 		return (EINVAL);
 
-	sectors = basetable->gpt_sectors;
+	if (gpp->gpp_start > UINT_MAX || gpp->gpp_size > UINT_MAX)
+		return (EINVAL);
 
 	entry = (struct g_part_mbr_entry *)baseentry;
 	table = (struct g_part_mbr_table *)basetable;
-
-	start = gpp->gpp_start;
-	size = gpp->gpp_size;
-	if (size < sectors)
-		return (EINVAL);
-	if (start % sectors) {
-		size = size - sectors + (start % sectors);
-		start = start - (start % sectors) + sectors;
-	}
-	if (size % sectors)
-		size = size - (size % sectors);
-	if (size < sectors)
-		return (EINVAL);
-
 	if (baseentry->gpe_deleted)
 		bzero(&entry->ent, sizeof(entry->ent));
 
-	KASSERT(baseentry->gpe_start <= start, ("%s", __func__));
-	KASSERT(baseentry->gpe_end >= start + size - 1, ("%s", __func__));
-	baseentry->gpe_start = start;
-	baseentry->gpe_end = start + size - 1;
-	entry->ent.dp_start = start;
-	entry->ent.dp_size = size;
+	baseentry->gpe_start = gpp->gpp_start;
+	baseentry->gpe_end = gpp->gpp_start + gpp->gpp_size - 1;
+	entry->ent.dp_start = gpp->gpp_start;
+	entry->ent.dp_size = gpp->gpp_size;
 	mbr_set_chs(basetable, baseentry->gpe_start, &entry->ent.dp_scyl,
 	    &entry->ent.dp_shd, &entry->ent.dp_ssect);
 	mbr_set_chs(basetable, baseentry->gpe_end, &entry->ent.dp_ecyl,
@@ -254,17 +238,18 @@ g_part_mbr_create(struct g_part_table *basetable,
 	struct g_consumer *cp;
 	struct g_provider *pp;
 	struct g_part_mbr_table *table;
-	uint32_t msize;
 
 	pp = gpp->gpp_provider;
 	cp = LIST_FIRST(&pp->consumers);
 
 	if (pp->sectorsize < MBRSIZE)
 		return (ENOSPC);
+	if (pp->sectorsize > 4096)
+		return (EOPNOTSUPP);
 
-	msize = MIN(pp->mediasize / pp->sectorsize, UINT32_MAX);
-	basetable->gpt_first = basetable->gpt_sectors;
-	basetable->gpt_last = msize - (msize % basetable->gpt_sectors) - 1;
+	basetable->gpt_first = 1;
+	basetable->gpt_last = MIN(pp->mediasize / pp->sectorsize,
+	    2 * UINT32_MAX);
 
 	table = (struct g_part_mbr_table *)basetable;
 	le16enc(table->mbr + DOSMAGICOFFSET, DOSMAGIC);
@@ -331,21 +316,13 @@ g_part_mbr_resize(struct g_part_table *basetable,
     struct g_part_entry *baseentry, struct g_part_parms *gpp)
 {
 	struct g_part_mbr_entry *entry;
-	uint32_t size, sectors;
 
-	sectors = basetable->gpt_sectors;
-	size = gpp->gpp_size;
-
-	if (size < sectors)
+	if (gpp->gpp_size > UINT_MAX)
 		return (EINVAL);
-	if (size % sectors)
-		size = size - (size % sectors);
-	if (size < sectors)
-		return (EINVAL);
 
 	entry = (struct g_part_mbr_entry *)baseentry;
-	baseentry->gpe_end = baseentry->gpe_start + size - 1;
-	entry->ent.dp_size = size;
+	baseentry->gpe_end = baseentry->gpe_start + gpp->gpp_size - 1;
+	entry->ent.dp_size = gpp->gpp_size;
 	mbr_set_chs(basetable, baseentry->gpe_end, &entry->ent.dp_ecyl,
 	    &entry->ent.dp_ehd, &entry->ent.dp_esect);
 	return (0);
@@ -433,7 +410,7 @@ g_part_mbr_read(struct g_part_table *basetable, st
 
 	pp = cp->provider;
 	table = (struct g_part_mbr_table *)basetable;
-	msize = MIN(pp->mediasize / pp->sectorsize, UINT32_MAX);
+	msize = MIN(pp->mediasize / pp->sectorsize, 2 * UINT32_MAX);
 
 	buf = g_read_data(cp, 0L, pp->sectorsize, &error);
 	if (buf == NULL)
@@ -472,8 +449,8 @@ g_part_mbr_read(struct g_part_table *basetable, st
 	}
 
 	basetable->gpt_entries = NDOSPART;
-	basetable->gpt_first = basetable->gpt_sectors;
-	basetable->gpt_last = msize - (msize % basetable->gpt_sectors) - 1;
+	basetable->gpt_first = 1;
+	basetable->gpt_last = msize - 1;
 
 	g_free(buf);
 	return (0);