driveio
int driveio(struct drive *, char *, size_t, off_t, buf_cmd_t);
#define read_drive(a, b, c, d) driveio (a, b, c, d, BUF_CMD_READ)
#define write_drive(a, b, c, d) driveio (a, b, c, d, BUF_CMD_WRITE)