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From: "Andrey V. Elsukov" <ae@FreeBSD.org>
Date: Mon, 27 Jun 2011 10:42:06 +0000 (UTC)
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Subject: svn commit: r223587 - in head/sys: geom/part sys
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Author: ae
Date: Mon Jun 27 10:42:06 2011
New Revision: 223587
URL: http://svn.freebsd.org/changeset/base/223587

Log:
  MS Windows NT+ uses 4 bytes at offset 0x1b8 in the MBR to identify
  disk drive. The boot0cfg(8) utility preserves these 4 bytes when is
  writing bootcode to keep a multiboot ability.
  Change gpart's bootcode method to keep DSN if it is not zero. Also
  do not allow writing bootcode with size not equal to MBRSIZE.
  
  PR:		kern/157819
  Tested by:	Eir Nym
  MFC after:	1 month

Modified:
  head/sys/geom/part/g_part_mbr.c
  head/sys/sys/diskmbr.h

Modified: head/sys/geom/part/g_part_mbr.c
==============================================================================
--- head/sys/geom/part/g_part_mbr.c	Mon Jun 27 09:15:41 2011	(r223586)
+++ head/sys/geom/part/g_part_mbr.c	Mon Jun 27 10:42:06 2011	(r223587)
@@ -237,14 +237,16 @@ static int
 g_part_mbr_bootcode(struct g_part_table *basetable, struct g_part_parms *gpp)
 {
 	struct g_part_mbr_table *table;
-	size_t codesz;
+	uint32_t dsn;
+
+	if (gpp->gpp_codesize != MBRSIZE)
+		return (ENODEV);
 
-	codesz = DOSPARTOFF;
 	table = (struct g_part_mbr_table *)basetable;
-	bzero(table->mbr, codesz);
-	codesz = MIN(codesz,  gpp->gpp_codesize);
-	if (codesz > 0)
-		bcopy(gpp->gpp_codeptr, table->mbr, codesz);
+	dsn = *(uint32_t *)(table->mbr + DOSDSNOFF);
+	bcopy(gpp->gpp_codeptr, table->mbr, DOSPARTOFF);
+	if (dsn != 0)
+		*(uint32_t *)(table->mbr + DOSDSNOFF) = dsn;
 	return (0);
 }
 

Modified: head/sys/sys/diskmbr.h
==============================================================================
--- head/sys/sys/diskmbr.h	Mon Jun 27 09:15:41 2011	(r223586)
+++ head/sys/sys/diskmbr.h	Mon Jun 27 10:42:06 2011	(r223587)
@@ -36,6 +36,7 @@
 #include <sys/ioccom.h>
 
 #define	DOSBBSECTOR	0	/* DOS boot block relative sector number */
+#define	DOSDSNOFF	440	/* WinNT/2K/XP Drive Serial Number offset */
 #define	DOSPARTOFF	446
 #define	DOSPARTSIZE	16
 #define	NDOSPART	4