On 30/01/2020 17:42, Durrant, Paul wrote:
>> -----Original Message-----
>> From: Ian Jackson <ian.jack...@citrix.com>
>> Sent: 30 January 2020 17:29
>> To: Durrant, Paul <pdurr...@amazon.co.uk>
>> Cc: xen-devel@lists.xenproject.org; Wei Liu <w...@xen.org>; Anthony Perard
>> <anthony.per...@citrix.com>
>> Subject: Re: [PATCH v4 7/7] xl: allow domid to be preserved on
>> save/restore or migrate
>>
>> Paul Durrant writes ("[PATCH v4 7/7] xl: allow domid to be preserved on
>> save/restore or migrate"):
>>> This patch adds a '-D' command line option to save and migrate to allow
>>> the domain id to be incorporated into the saved domain configuration and
>>> hence be preserved.
>> Thanks.
>>
>> In response to v3 6/6 I wrote:
>>
>> I wonder if this should be done more in libxl. Should this be a
>> domain property ? Wei, Anthony ?
>>
>> This question remains unanswered. I'm sorry that neither Wei nor
>> Anthony had a chance to answer yet...
>>
>> Paul, do you have a reason for doing it this way ? My inclination is
>> that think doing it at the libxl layer would make more sense. Do you
>> think that would be possible ?
>>
> I'm not sure how it would work at the libxl level as the domid is part of
> create_info and that it transferred by xl on migration. IIUC we'd need a new
> libxl save record to transfer it at that level, and then I'm not sure whether
> we'd hit an ordering problem as we'd have to dig that save record out before
> we could actually create the domain.
There is definitely an ordering problem.
I agree that it should logically be part of the libxl level of the
stream, but none of that is even parsed until after the domain has been
created on the destination side.
I have no idea how easy/difficult it would be to rearrange libxl to
start parsing the migration stream before creating the domain. I think
there will be a lot of code relying on the domid already being valid.
~Andrew
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