BYTE_OFF_T
#define secbyt(s) ((BYTE_OFF_T)(s) << SSHIFT)
#define blkbyt(fs, b) ((BYTE_OFF_T)(b) << (fs)->bshift)
static int ioread(DOS_FS *, BYTE_OFF_T, void *, u_int);
ioread(DOS_FS *fs, BYTE_OFF_T offset, void *buf, u_int nbyte)