VDB_FOLLOW
DNPRINTF(VDB_FOLLOW, "vndopen(%x, %x, %x, %p)\n", dev, flags, mode, p);
DNPRINTF(VDB_FOLLOW, "vndclose(%x, %x, %x, %p)\n", dev, flags, mode, p);
DNPRINTF(VDB_FOLLOW, "vndstrategy(%p): unit %d\n", bp, unit);
DNPRINTF(VDB_FOLLOW, "vndioctl(%x, %lx, %p, %x, %p): unit %d\n",
DNPRINTF(VDB_FOLLOW, "vndclear(%p): vp %p\n", sc, vp);