Re: iSCSI: ordered command delivery at the target

[Luben Tuikov <luben@splentec.com>]

Julian Satran wrote:
> 
> Luben,
> 
> Amir is right. The text says explicitly that CmdSN has no significance whatsoever after delivery
> to SCSI (when the task is instantiated).
> ITT is the only means to identify safely a task. As for the difficulty of search for the ITT -
> that is all a question of implementation prowess
> (i.e., it should not e as difficult as you make it sound).

Julian,

I'm talking about Data-Out PDU's. CmdSN is NOT advanced
for Data-Out PDU's, only _copied_ from the original task/command.

A task CANNOT be delivered to the device server
without all data being available at the target,
being the case that there could be a huge
network (Ethernet) latency. Once all data has
arrived, then the task is delivered to the
device server (LL SCSI) and CmdSN becomes irrelevant.

Furthermore, CmdSN is NOT advanced on sending
Data-Out pdu's -- it is just copied there
from the original task/command.

The whole point of this is making
inserting into the ``incoming'' priority
queue ordered.

When the task is moved into a ``pending for more data'' queue,
this would naturally make the Data-out PDUs immediate
PDUs, as they should be. When Data-Outs arrive at the
target, CmdSN has advanced by at least k*** since the task has been
just _received_, and any ``older'' Data-Out PDUs (carrying the same CmdSN)
will go to the front of the ``incoming'' queue and be seen immediately.

*** If k = 0, then the task is still in the ``incoming'' queue
and the Data-Out is sorted right after it -- same effect.

Furthermore, the target will NOT allow CmdSN wrapping
for an outstanding task (one for which data is being delivered, I->T,
in order to be sent to the device server (SCSI), _only_ after which
CmdSN becomes irrelevant, but this means that all data was
delivered....).

Do you see it?

-- 
Luben
P.S. CmdSN wrapping MUST not depend on the choice of
maximum data segment. The suggestion I posted preserves
this reservation.