Re: [Xen-devel] RFC: QEMU bumping memory limit and domain restore

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-06-02 at 15:08 +0100, Wei Liu wrote:
[...]
> > So here is a proof of concept patch to record and honour that value
> > during migration.  A new field is added in IDL. Note that we don't
> > provide xl level config option for it and mandate it to be default value
> > during domain creation. This is to prevent libxl user from using it to
> > avoid unforeseen repercussions.
> [...]
> > This field is mandated to be default value during guest creation to
> > avoid unforeseen repercussions. It's only honour when restoring a guest.

IMHO this means that the libxl API/IDL is the wrong place for this
value. Only user and/or application serviceable parts belong in the API.

So while I agree that this value need to be communicated across a
migration, the JSON blob is not the right mechanism for doing so. IOW if
you go down this general path I think you need a new
field/record/whatever in the migration protocol at some layer or other
(if not libxc then at the libxl layer).

To my mind this "actual state" vs "user configured state" is more akin
to the sorts of things which is in the hypervisor save blob or something
like that (nb: This is not a suggestion that it should go there).

IIRC Don also outlined another case, which is
    xl create -p
    xl migrate
    xl unpause

Which might need more thought if any bumping can happen after the
migrate i.e. on unpause?



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