Re: [Xen-devel] [PATCH v3 01/24] xen: Extend DOMCTL createdomain to support arch configuration

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.02.15 at 16:15, <ian.campbell@xxxxxxxxxx> wrote:
> On Tue, 2015-01-13 at 14:25 +0000, Julien Grall wrote:
>>     This is a follow-up of 
> http://lists.xen.org/archives/html/xen-devel/2014-11/msg00522.html 
>> 
>>     TODO: What about migration? For now the configuration lives in internal
>>     libxl structure. We need a way to pass the domain configuration to the
>>     other end.
> 
> Things like the GIC version and number of SPIs would normally end up
> being encoded in the hvm save records, i.e. the blob which Xen provides
> to the toolstack to be included in the save stream. That would then be
> alongside the actual related interrupt architectural state etc (e.g.
> pending, active, masked etc).
> 
> That's problematic here because you can't pass that blob to the create
> function and the toolstack cannot really parse the blob to figure out
> the details to pass.
> 
> Looking back at msg00522.html it does seem like migration is a good
> motivation for doing it as a separate hypercall as you originally did,
> so initial create would be
>       DOMCTL_create
>       DOMCTL_set_the_variables
> and restore would be
>       DOMCTL_create
>       DOMCTL_restore_from_blob
> 
> In both cases this needn't preclude requiring the call to be made before
> unpause or that it is only called exactly once.
> 
> Write once HVM params would be another option here.
> 
> Jan, do you find any of that convincing as to the need for doing this
> outside the the create domctl? Based on msg00522 is seems you would
> prefer some HVM params over a new domctl?

Not really (HVM params are already being dealt with for migration
iirc, i.e. one wouldn't even need to think about that aspect), but
considering the other domctl-vs-HVM-param discussion we're having
I suppose at least Andrew might be of a different opinion. My main
reservation against domctl-s is (more there than here) that HVM
params scale better (there it's domain creation flag being defined,
of which we have only so many), along with said "built-in" migration.

But then again - if everyone else thinks domctl-s are the mechanism
to use (here and there), I don#t want to stand in the way...

Jan


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