Add a “skip_dsn” option to g_part's bootcode verb to prevent g_part_mbr

from setting the volume serial number.  This unbreaks older boot blocks
that don't support serial numbers, and allows boot0cfg to set the serial
number itself if requested by the user.

Submitted by:	lev@, yuripv@
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D17386

2 files changed, 12 insertions, 1 deletions

diff --git a/lib/geom/part/geom_part.c b/lib/geom/part/geom_part.c
index 29c066c4714f..b21ebf7ef8d8 100644
--- a/lib/geom/part/geom_part.c
+++ b/lib/geom/part/geom_part.c
@@ -72,6 +72,7 @@ volatile sig_atomic_t undo_restore;
 #define	GPART_PARAM_BOOTCODE	"bootcode"
 #define	GPART_PARAM_INDEX	"index"
 #define	GPART_PARAM_PARTCODE	"partcode"
+#define	GPART_PARAM_SKIP_DSN	"skip_dsn"
 
 static struct gclass *find_class(struct gmesh *, const char *);
 static struct ggeom * find_geom(struct gclass *, const char *);
@@ -115,8 +116,9 @@ struct g_command PUBSYM(class_commands)[] = {
 		{ 'p', GPART_PARAM_PARTCODE, G_VAL_OPTIONAL, G_TYPE_STRING },
 		{ 'i', GPART_PARAM_INDEX, G_VAL_OPTIONAL, G_TYPE_NUMBER },
 		{ 'f', "flags", GPART_FLAGS, G_TYPE_STRING },
+		{ 'N', GPART_PARAM_SKIP_DSN, NULL, G_TYPE_BOOL },
 		G_OPT_SENTINEL },
-	    "[-b bootcode] [-p partcode -i index] [-f flags] geom"
+	    "[-N] [-b bootcode] [-p partcode -i index] [-f flags] geom"
 	},
 	{ "commit", 0, gpart_issue, G_NULL_OPTS,
 	    "geom"
diff --git a/lib/geom/part/gpart.8 b/lib/geom/part/gpart.8
index 76177892ceb1..80ea0a317d3a 100644
--- a/lib/geom/part/gpart.8
+++ b/lib/geom/part/gpart.8
@@ -49,6 +49,7 @@
 .\" ==== BOOTCODE ====
 .Nm
 .Cm bootcode
+.Op Fl N
 .Op Fl b Ar bootcode
 .Op Fl p Ar partcode Fl i Ar index
 .Op Fl f Ar flags
@@ -214,6 +215,14 @@ The
 .Cm bootcode
 command accepts these options:
 .Bl -tag -width 10n
+.It Fl N
+Don't preserve the Volume Serial Number for MBR.
+MBR bootcode contains Volume Serial Number by default, and
+.Nm
+tries to preserve it when installing new bootstrap code.
+This option allows to skip the preservation to help with some versions of
+.Xr boot0 8
+that don't support Volume Serial Number.
 .It Fl b Ar bootcode
 Embed bootstrap code from the file
 .Ar bootcode