RE: Data in SCSI Response or SCSI Data

[Matthew Jacob <mjacob@feral.com>]

> Matt, I see your point in software implementation.  May be this is a good
> time to introduce the concept of "Good Status" flag bit.  In fact, 99.99%
> of iSCSI reads should be completed without error.  For the normal
> completions, all we need to is a flag bit in the data packet message
> header indicating "Everything is OK. This SCSI read is now completed
> normally."  If this flag bit is not set, there will be a status packet
> with sense data following.  In the hardware implementation, after
> transferring data packet into the buffer, if this flag bit is set, we
> interrupt the microcode which post the Request Block (RB) completion
> interrupt to the device driver.  If the bit is not set, the hardware does
> nothing after data transfer.  The status packet arrived later will be
> passed to the microcode that, in turn, generates a proper RB completion
> interrupt to pass the error information to the device driver.

Sounds good to me. If it makes the h/w easier- great. Although full status
isn't that much extra, I could see that h/w for it would be harder.

I'd like to point out that the software state machine in target mode for this
kind of stuff isn't entirely trivial either. If you have a layered system (as
you probably would) you still might have to set "Send Status with Data" state
at the upper end and check completion later to see whether it was actually
sent. But the performance differential (in the non-IPS case) makes it worth
the effort.

-matt