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That being the case, it might be prudent to define distinct SCSI op-codes for transfer-in ATA passthrough commands and transfer-out ATA passthrough commands.
Yes please.
That, apart from being consistent with the definition of existing SCSI opcodes, frees up another bit in the CDB to use for some other purpose.
This is precisely the solution that appears buried, for example, in the LGPL open source code that in effect documents much of Iomega RRD firmware at http://iomrrdtools.sourceforge.net/
Pat LaVarre
P.S. More ack ack ack from me:
There is no SCSI opcode that sometimes does a transfer-in, and sometimes does a transfer-out, depending on other information.
No old standard op, aye.
Nonetheless, all SCSI HBA driver
interfaces provide in a "wrapper" of some sort, and indication of the
direction of the data transfer, even though that information is already
evident in the op-code. Why? Because the HBA doesn't want to be burdened
with parsing the CDB itself.
Yes.
The very same concept is at play here - with respect to the embedded ATA
command. Only in this case, the SCSI command itself is the "wrapper" for
the embedded ATA command, and so the SCSI CDB should contain an
indication of the transfer direction.
Now - to be fully consistent with existing SCSI models, we recognize that the SCSI/ATA passthrough CDB has a SCSI op-code. All SCSI op-codes defined so far indicate a transfer direction as part of the opcode (if there is a transfer at all).
Yes, all old standard ops.
