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Re: [Xen-devel] [PATCH 0/6] [VERY RFC] Migration Stream v2



On 04/15/2014 11:35 AM, Ian Jackson wrote:
David Vrabel writes ("Re: [Xen-devel] [PATCH 0/6] [VERY RFC] Migration Stream 
v2"):
On 14/04/14 18:49, George Dunlap wrote:
What did you imagine might constitute an "Optional" record?

This was something Ian Jackson asked for and it seems like a useful
capabilitity to have for future use.  Not sure what it might be used for
yet.

Right.

Long experience with protocol design has taught me that protocols
should almost always have both an extensibility mechanism which is
ignored by ignorant receivers, and one which causes ignorant receivers
to abort.

I don't know yet what we might use it for.  However, we should test
that it works (ie is ignored by) the receiver (or it will be useless).

Yes, this is the main concern. 2 billion record types should be plenty for the "required" field, so the 2 billion allocated for "optional" shouldn't be a big loss. :-) The main risk would be if something which is, in fact, required for proper operation on the far side is marked "optional". I guess as long as we have an "ignore everything optional" test case we should be OK.

 -George

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