wdc_e6_header_t
const wdc_e6_header_t *header;
wdc_e6_read(npa, req, 0, buf, sizeof (wdc_e6_header_t));
if (len < sizeof (wdc_e6_header_t)) {
wdc_e6_write(ofd, buf, sizeof (wdc_e6_header_t));
off = sizeof (wdc_e6_header_t);
CTASSERT((sizeof (wdc_e6_header_t) % 4) == 0);
CTASSERT(sizeof (wdc_e6_header_t) == 8);