RE: aborting an out of sequence cmdSN

[Black_David@emc.com]

Sandeep,

> The "iSCSI cancel" proposal you describe below has been presented 
> once before.  If you recall, I was asking for a refCmdSN in the 
> TaskMgmt PDU.
> 
> The only difference between that and what you now describe below 
> is the addition of this concept of an "iSCSI service error" response.

Close enough - sorry for the lack of acknowledgement.  Of the four
options, (1) and (3) make the most sense to me.  Assuming that
we document the iSCSI-based effects of task management operations
(probably should do this not only for task abort, but also task set
abort and task set clear):

> (1) use connection allegiance for TASK MGMT PDU.

Ok, with the possible concern about something going wrong on
that connection.

> (2) reject all commands prior to cmdSN of TASK MGMT PDU.

I don't see anyone aside from Doug interested in this, so I consider
WG rough consensus to have rejected this approach.

> (3) cmdSN of original task is sent with TASK MGMT PDU and
>     target at the iSCSI layer keeps state.

The state's not a big deal - in essence the iSCSI target pretends it
received a NOP instead of the actual command if the abort arrives
ahead of the command.

> (4) iSCSI initiator retains state for deleted tasks to ensure
>     that R2T/Scsi Responses are appropriately handled.

Ugly, although errant R2Ts may show up if the abort/clear is
across connections.  With the iSCSI enhancements, the
initiator should be able to throw these away.

--David

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