Re: [Xen-devel] [PATCH 07/29] docs: libxl migration stream specification

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 11/09/14 12:03, Ian Campbell wrote:
> On Thu, 2014-09-11 at 11:56 +0100, Andrew Cooper wrote:
>>>> +            bit 1: Legacy Format. If set, this stream was created by
>>>> +                                  the legacy conversion tool.
>>> Are such streams otherwise distinguishable from a stream which was
>>> created directly? Should anything care about this?
>>>
>>> I fear this is going to be used to paper over shortcomings in the
>>> conversion tool somehow, but I suppose I'll see later in the series.
>> My concern here was regarding the d_config.  A legacy converted stream
>> cannot possibly contain a domain_json blob, so must have a d_config
>> passed by the caller.  Admittedly, this did pre-date realising that
>> libxl currently allows the caller to blindly overwrite the config
>> anyway, and this needs to continue for compatibility reasons.
>>
>> However, knowing that a stream has been converted is a key debugging
>> detail, even if this flag serves no other purpose from libxl's point of
>> view.
> Would it be worth saying so e.g. "This flag is for debugging purposes
> only, toolstacks should not modify their behaviour based on this flag"?

If it turns out that way, then absolutely.

>
> Or could you do away with this bit and use version==1 to indicate this
> (since version==1 doesn't actually get used by a real legacy stream)
>
>

I don't like this, concepually. The stream version is 2, as that states
that "this stream conforms to v2 of the spec", which describes the
framing etc.  (The problem needing to be solved is that there was no
older libxl stream where there should have been.)

~Andrew

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