Retire the DIOCGMBR ioctl before anybody starts to use it.

sys/geom/geom_mbr.c

@@ -242,11 +242,6 @@ g_mbr_start(struct bio *bp)
 	gio = (struct g_ioctl *)bp->bio_data;
 
 	switch (gio->cmd) {
-	case DIOCGMBR:
-		/* Return a copy of the disklabel to userland. */
-		bcopy(mp->sec0, gio->data, 512);
-		g_io_deliver(bp, 0);
-		return (1);
 	case DIOCSMBR:
 		/*
 		 * These we cannot do without the topology lock and some

sys/sys/diskmbr.h

@@ -69,7 +69,6 @@ CTASSERT(sizeof (struct dos_partition) == 16);
 #define	DPSECT(s) ((s) & 0x3f)		/* isolate relevant bits of sector */
 #define	DPCYL(c, s) ((c) + (((s) & 0xc0)<<2)) /* and those that are cylinder */
 
-#define DIOCGMBR 	_IOR('M', 128, u_char[512])
 #define DIOCSMBR 	_IOW('M', 129, u_char[512])