iSCSI : Reject PDU Concerns.

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

Ref : Section 2.19 (Reject PDU), Section 5.5 (Digest Errors)

Issue :
=====
1) Reject PDU must return an Initiator Task Tag in the Reject PDU
header, which provides the initiator sufficient context to lookup the
outbound exchange that was transmitted.

2) An error_byte field should be considered for inclusion in the Reject
PDU which contains the byte offset of the errant byte[or word] in the
received header/payload that caused the target to send a Reject response
to the command.

This is a simple solution that provides for quick fault isolation and
root cause of the reason for the reject. This also rids the Reject PDU
of any detailed elaboration of reason codes meant to allow root cause of
the reason for the reject.

3) The Reject PDU should only be used for " Format Error" since the
Reject mechanism  is a per-task error recovery to deal with header
format problems.
"Digest Error" handling is too complex dealing with too many situations.
Digest error recovery should be simplified to a connection level error
recovery which involves Logout or connection close/re-start.

The current digest recovery is a ping-pong as follows :
- Target sends REJECT
- Initiator on seeing REJECT with "Digest Error" sends Logout
- Target sends Logout response.
(the spec is not clear on who drives the connection close. does the
initiator close the connection on receiving logout response, or does the
target close connection and send logout reponse on another connection
??).

The above procedure is quite convoluted and the followinf simplification
should be considered :
- On a digest error, target sends Logout, indicating appropriate reason
code.
- Target follows up the Logout with a TCP connection close.

4) There is no value add in expecting a logout response on a logout
which is intended to close a connection and is sent on the same
connection. The logout can be followed up with a connection close.

Regards,
Santosh




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