biosdisk_read
if (biosdisk_read(d->dev, 0, 0, 18, 1, buf)) {
if (biosdisk_read(d->dev, cyl, head, sec, nsec, buf)) {
int biosdisk_read(int, int, int, int, int, void *);
return biosdisk_read(dev, blkaddr, buf, nblks);
int biosdisk_read(int dev, uint32_t blkaddr, void *buf, size_t nblks);