Subject: [Ips] Retiring unexpected PDUs

From: Mike Ko <[email-masked]>
Date: Mon, 20 Jun 2005 16:48:29 -0700

Mallikarjun and I have an offline discussion on immediate commands and how 
they should be retired.  In iSCSI, an immediate command can be rejected 
for out of resource conditions at the target.  But the Reject PDU may not 
get sent if the limit imposed by MaxOutstandingUnexpectedPDUs declared by 
the initiator is reached at the target.  To avoid the situation where the 
credit consumed by the immediate command is lost forever, the following 
rule to retire outstanding PDUs in the unexpected category (where the 
immediate flag is set) is proposed to be incorporated in iSER:

"An oustanding PDU in this category is retired as follows.  If the CmdSN 
of the PDU sent by the intiator in this category is x, the PDU is 
outstanding until the initiator sends a non-immediate control-type PDU on 
the same connection with CmdSN = y (where y is at least x) and the target 
responds with a control-type PDU on any connection where ExpCmdSN is at 
least y+1."

This rule is the same as the one previously used for retiring 
unidirectional NOP-Outs.  It is now the only rule for retiring all 
unexpected PDUs where the immediate flag is set and replaces all other 
rules.  Please comment if you find a problem with this approach.

Mike

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