pick
dictAppendWord(dp, "pick", pick, FW_DEFAULT);
int pick = cs->sc_pick;
if (bn < cs->sc_blk[pick] - range ||
bn > cs->sc_blk[pick] + range
cs->sc_pick = pick = 1 - pick;
cs->sc_blk[pick] = bn + btodb(rcount);
g_io_request(cbp[pick], cbp[pick]->bio_from);