bt_bad
for (bt = badmap.bt_bad; bt - badmap.bt_bad < NDKBAD; bt++) {
for (bt = badmap.bt_bad; bt - badmap.bt_bad < NDKBAD; bt++)
struct bt_bad *bt;
badmap.bt_bad[i].bt_cyl = -1;
badmap.bt_bad[i].bt_trksec = -1;
} bt_bad[NDKBAD];