allow to install and boot the OpenBSD A6 partition and disklabel in an

extended DOS partition.  the concept of extended partitions is very
simple, it is just another mbr at the partition offset (well, the
standard "EBR" is a linked list with a few limitations, but this diff
works with both variants).

this diff has been in the snapshots for a while.

with input from weingart@ and krw@
ok deraadt@

1 files changed, 15 insertions, 7 deletions

diff --git a/sys/kern/subr_disk.c b/sys/kern/subr_disk.c
index e3d80ae69ff..186ff615e10 100644
--- a/sys/kern/subr_disk.c
+++ b/sys/kern/subr_disk.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: subr_disk.c,v 1.78 2008/06/12 06:58:39 deraadt Exp $	*/
+/*	$OpenBSD: subr_disk.c,v 1.79 2008/06/25 15:26:43 reyk Exp $	*/
 /*	$NetBSD: subr_disk.c,v 1.17 1996/03/16 23:17:08 christos Exp $	*/
 
 /*
@@ -409,7 +409,7 @@ readdoslabel(struct buf *bp, void (*strat)(struct buf *),
 
 		bcopy(bp->b_data + DOSPARTOFF, dp, sizeof(dp));
 
-		if (ourpart == -1 && part_blkno == DOSBBSECTOR) {
+		if (ourpart == -1) {
 			/* Search for our MBR partition */
 			for (dp2=dp, i=0; i < NDOSPART && ourpart == -1;
 			    i++, dp2++)
@@ -454,11 +454,6 @@ donot:
 				continue;
 			if (letoh32(dp2->dp_size) == 0)
 				continue;
-			if (letoh32(dp2->dp_start))
-				DL_SETPOFFSET(pp,
-				    letoh32(dp2->dp_start) + part_blkno);
-
-			DL_SETPSIZE(pp, letoh32(dp2->dp_size));
 
 			switch (dp2->dp_typ) {
 			case DOSPTYP_UNUSED:
@@ -499,6 +494,19 @@ donot:
 				n++;
 				break;
 			}
+
+			/*
+			 * There is no need to set the offset/size when
+			 * wandering; it would also invalidate the
+			 * disklabel checksum.
+			 */
+			if (wander)
+				continue;
+
+			if (letoh32(dp2->dp_start))
+				DL_SETPOFFSET(pp,
+				    letoh32(dp2->dp_start) + part_blkno);
+			DL_SETPSIZE(pp, letoh32(dp2->dp_size));
 		}
 	}
 	lp->d_npartitions = MAXPARTITIONS;