Re: iSCSI : Digest Error Problems & CmdSN/ExpCmdSN window issues

[Santosh Rao <santoshr@cup.hp.com>]

Matt,

(You may want to take another look at the thread.). Here's the details again :

> 3) The policy of "discard and restart" is also subject some race
> conditions in the CmdSN sliding window. At the time the digest error was
>
> detected at the initiator, the ExpCmdSN may not yet have acknowledged
> that
> command. This causes the initiator to restart the command with the same
> Initiator Task Tag, CmdSN and "retry" bit set.
>
> However, by the time the command gets to the target, the target may have
>
> updated its ExpCmdSN window having sent a later PDU which updated the
> ExpCmdSN. This results in the target discarding the received CmdSN since
>
> <js> at command restart you never really rely on the CmdSN. you will want
> to check
> the Initiator Task Tag and accept it in the above case. </js>

The draft states the following on this subject :

Section 5.1
=========
-    the initiator will reissue all outstanding commands with their
      original Initiator Task Tag and their original CmdRN if they
      are not acknowledged yet or a CmdRN of 0 (not-numbered) if they
      were acknowledged; the retry (X) flag in the command PDU will
      be set

Section 1.2.2.1
===========
- The target MUST silently ignore any command
   outside this range or duplicates within the range not flagged with
   the retry bit (the X bit in the opcode).

This, to me, means :
- ignore all commands outside the (ExpCmdSN, MaxCmdSN) range.
- ignore all duplicate commands within the range that are not flagged with the
retry
bit. << "duplicate" added this time >>

Can you please clarify the intent of the text ?



Matt Wakeley wrote:

> Santosh Rao wrote:
> > Alright (so the cut & paste did'nt work)  ;-}
> >
> > The issue under discussion is a retried command [and thereby, a duplicate
> > CmdSN] that is OUTSIDE the (ExpCmdSn, MaxCmdSN) range. That falls under the
> > first criteria.
>
> And the point is?  What am I missing?
>
> -Matt
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