secbyt
#define blkoff(fs, b) (secbyt((fs)->lsndta) + blkbyt(fs, (b) - LOCLUS))
secbyt(f->fs->lsndir)) + off,
fs->bsize = secbyt(fs->spc);
sc = (secbyt(fs->spf) << 1) / (fs->fatsz >> 2) - 1;
err = ioread(fs, secbyt(fs->lsnfat) + fatoff(fs->fatsz, *c), buf,
secbyt(nsec), buf, &rsize);