nfs4_fl_calc_j_index
j = nfs4_fl_calc_j_index(lseg, offset);
j = nfs4_fl_calc_j_index(lseg, offset);
j = nfs4_fl_calc_j_index(lseg, req_offset(req));
u32 nfs4_fl_calc_j_index(struct pnfs_layout_segment *lseg, loff_t offset);