SM_OFFSET_BITS
(offset >= (1ULL << SM_OFFSET_BITS) ||
#define SM_OFFSET_DECODE(x) BF64_DECODE(x, 16, SM_OFFSET_BITS)
#define SM_OFFSET_ENCODE(x) BF64_ENCODE(x, 16, SM_OFFSET_BITS)
uint64_t shift = vd->vdev_ashift + SM_OFFSET_BITS;