iSCSI: R2T/ABORT_TASK interaction

["Pittman, Joseph" <Joseph.Pittman@netapp.com>]

Can anyone describe the required behavior of an initiator under
the following condition?  This may be a basic SCSI-3 question
rather than iSCSI specific; if so, I apologize, but still ask
for guidance.

Suppose an initiator submits a SCSI Command PDU containing a large
SCSI write operation (where large means >= FirstBurstSize).
Before the initiator receives an R2T for the first (or next)
chunk of the data, the initiator decides to abort the task with
an ABORT_TASK (or other) Task Management PDU.

In the meantime, the target has prepared its buffers and submits
the R2T.  The R2T and the ABORT_TASK PDUs 'cross paths':

  Time     Initiator                          Target
    |
  0 |      SCSI_CMD ---------\
    |                         \-------------->
    |
    |      ABORT_TASK ------\
    |                        \   /------------- R2T
    |                         \ /
    |                          X------------->
    |                         /
    |                <-------/
  T |
    V

At time T, the target has received an ABORT_TASK for the SCSI
command, but has already sent an R2T.  The initiator has
just received an R2T for a SCSI task which it is trying to
abort.  The target has not yet sent a response to the ABORT_TASK
task management command.

The question is this: what are the responsibilities of the
initiator and target at this point?

- Is the initiator required or expected to respond to the
  R2T, perhaps with a zero-length DATA_OUT PDU?

- Is the target expected to wait for the initiator to respond
  before aborting the task?  Or is the initiator allowed (or
  required) to go ahead and abort the task and send the task
  management response, without waiting for any DATA_OUT, then
  silently discard any R2T it might receive later?


Thanks in advance for any help.
--
Joe Pittman
jpittman@netapp.com