MdpMinorShift
mdev = MKDEV(mdp_major, args->minor << MdpMinorShift);
shift = partitioned ? MdpMinorShift : 0;
rdev0->preferred_minor << MdpMinorShift);
unit = MINOR(dev) >> MdpMinorShift;
unit &= ~((1 << MdpMinorShift) - 1);
new->md_minor = MINOR(unit) >> MdpMinorShift;