SCSI programming

Hello,
I am trying to communicate with a tape drive using ioctl and SCSI_IOCTL_SEND_COMMAND as ioctl(fd, SCSI_IOCTL_SEND_COMMAND, buffer);

I read that the buffer should be of the form :

Code:

struct sdata {
    unsigned int inlen;     [i] Length of data written to device
    unsigned int outlen;    [i] Length of data read from device
    unsigned char cmd[x];   [i] SCSI command (6 <= x <= 16)
                            [o] Data read from device starts here
                            [o] On error, sense buffer starts here
    unsigned char wdata[y]; [i] Data written to device starts here
   };

There may be commands only read data from the device and dont write or vice versa. Also some commands may read and write data. To what value can I set outlen so that it will cover all the 3 conditons?


Thanks

HI guys,
I need some help here.
Is it possible to write a generic function to support all SCSI commands?

Thanks....