Tweak code to make it clear that MBR_init() uses just the boot code and

partition 0 information from the default MBR.

loongson and macppc provide partition 0 information but no boot code.

amd64, i386, landisk provide boot code but no partition 0 information.

Other arch's get by w/o a default MBR (a.k.a. /usr/mdec/mbr).

No functional change.

diff --git a/sbin/fdisk/mbr.c b/sbin/fdisk/mbr.c
index b14863d..3793e6a 100644 (file)
--- a/sbin/fdisk/mbr.c
+++ b/sbin/fdisk/mbr.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: mbr.c,v 1.101 2021/09/26 13:13:16 krw Exp $   */
+/*     $OpenBSD: mbr.c,v 1.102 2021/10/29 18:38:19 krw Exp $   */
 
 /*
  * Copyright (c) 1997 Tobias Weingartner
@@ -41,6 +41,7 @@ void          dos_mbr_to_mbr(const struct dos_mbr *, const uint64_t,
 void
 MBR_init(struct mbr *mbr)
 {
+       struct dos_partition    dp;
        uint64_t                adj;
        daddr_t                 daddr;
 
@@ -56,19 +57,13 @@ MBR_init(struct mbr *mbr)
                return;
        }
 
-       dos_mbr_to_mbr(&default_dmbr, 0, 0, mbr);
+       memset(mbr, 0, sizeof(*mbr));
+       memcpy(mbr->mbr_code, default_dmbr.dmbr_boot, sizeof(mbr->mbr_code));
+       memcpy(&dp, &default_dmbr.dmbr_parts[0], sizeof(dp));
+       PRT_parse(&dp, 0, 0, &mbr->mbr_prt[0]);
 
-       /*
-        * XXX Do *NOT* zap all MBR parts! Some archs still read default mbr
-        * from disk! Just mark them inactive until -b goodness spreads
-        * further.
-        */
-
-       mbr->mbr_prt[0].prt_flag = 0;
-       mbr->mbr_prt[1].prt_flag = 0;
-       mbr->mbr_prt[2].prt_flag = 0;
-
-       mbr->mbr_prt[3].prt_flag = DOSACTIVE;
+       if (mbr->mbr_prt[0].prt_flag != DOSACTIVE)
+               mbr->mbr_prt[3].prt_flag = DOSACTIVE;
        mbr->mbr_signature = DOSMBR_SIGNATURE;
 
        /* Use whole disk. Reserve first track, or first cyl, if possible. */