From d42cbdf611cca8042c5431e4aef297ce5d2cd122 Mon Sep 17 00:00:00 2001
From: tsutsui <tsutsui@NetBSD.org>
Date: Tue, 7 Feb 2012 14:14:45 +0000
Subject: [PATCH] Explicitly zap possible Ext2fs magic leftover to prevent
 kernel vfs_mountroot() and bootloaders from mis-recognizing the newfs(8)'ed
 file system as still Ext2fs.

The problem is reported and the fix is tested by Frank Wille
on current-users@.  Also approved by releng.
---
 sbin/newfs/mkfs.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/sbin/newfs/mkfs.c b/sbin/newfs/mkfs.c
index 6d75decee4d9..0449288ba2f2 100644
--- a/sbin/newfs/mkfs.c
+++ b/sbin/newfs/mkfs.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: mkfs.c,v 1.110 2011/08/25 16:17:58 joerg Exp $	*/
+/*	$NetBSD: mkfs.c,v 1.111 2012/02/07 14:14:45 tsutsui Exp $	*/
 
 /*
  * Copyright (c) 1980, 1989, 1993
@@ -73,7 +73,7 @@
 #if 0
 static char sccsid[] = "@(#)mkfs.c	8.11 (Berkeley) 5/3/95";
 #else
-__RCSID("$NetBSD: mkfs.c,v 1.110 2011/08/25 16:17:58 joerg Exp $");
+__RCSID("$NetBSD: mkfs.c,v 1.111 2012/02/07 14:14:45 tsutsui Exp $");
 #endif
 #endif /* not lint */
 
@@ -152,6 +152,8 @@ union {
 	((sblock.fs_magic == FS_UFS1_MAGIC) ? \
 	(dp)->dp1.di_##field : (dp)->dp2.di_##field)
 
+#define EXT2FS_SBOFF	1024	/* XXX: SBOFF in <ufs/ext2fs/ext2fs.h> */
+
 char *iobuf;
 int iobufsize;			/* size to end of 2nd inode block */
 int iobuf_memsize;		/* Actual buffer size */
@@ -615,6 +617,12 @@ mkfs(const char *fsys, int fi, int fo,
 			for (sz = SBLOCKSIZE; sz <= 0x10000; sz <<= 1)
 				zap_old_sblock(roundup(sblkoff, sz));
 		}
+		/*
+		 * Also zap possible Ext2fs magic leftover to prevent
+		 * kernel vfs_mountroot() and bootloaders from mis-recognizing
+		 * this file system as Ext2fs.
+		 */
+		zap_old_sblock(EXT2FS_SBOFF);
 
 		if (isappleufs) {
 			struct appleufslabel appleufs;