drvread
if (drvread(dskp, secbuf, hdrlba, 1)) {
if (drvread(dskp, secbuf, slba, 1)) {
int drvread(struct dsk *dskp, void *buf, daddr_t lba, unsigned nblk);
return (drvread(&dsk, buffer, cdb2devb(blkno),