XFS_IEXT_LENGTH_MASK
uint32_t rec_len = rec->hi & XFS_IEXT_LENGTH_MASK;
ASSERT((irec->br_blockcount & ~XFS_IEXT_LENGTH_MASK) == 0);
rec->hi = irec->br_blockcount & XFS_IEXT_LENGTH_MASK;
irec->br_blockcount = rec->hi & XFS_IEXT_LENGTH_MASK;