iSCSI: default values

[Black_David@emc.com]

Default values may be difficult to define for text keys added after
the first stable version of the spec.  The problem is that an
originator who does not send a text key cannot distinguish between:

- a responder who understands the key and implements the default AND
- a responder who does not understand the key and does something
	acceptable under a version of the spec prior to introduction
	of the key.

This whole notion of omitting a key being equivalent to sending
it with its default value strikes me as potentially problematic.
I would have thought that omitting a text key was equivalent to
"Don't Care" with the default values being "RECOMMENDED" rather
than "MANDATORY".  This leads to the following rule, which I think
should go in regardless:

- An implementation whose operational correctness and/or performance
	depends on the value of a text key MUST explicitly negotiate
	that key.

This is somewhat like the old adage about voting - those who do not
vote should not complain about the results, and leads to more robust
negotiation exchanges because mismatched assumptions about defaults
get exposed.

I realize this yields additional messages in some cases, but would
suggest that the additional negotiation robustness is an offsetting
benefit.

Comments?
--David
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David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
+1 (508) 435-1000 x75140     FAX: +1 (508) 497-8500
black_david@emc.com       Mobile: +1 (978) 394-7754
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