Re: [Xen-devel] [RFC PATCH 6/6] xc_version: add vm_event interface version

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Tue, Jan 8, 2019 at 9:39 AM Razvan Cojocaru
<rcojocaru@xxxxxxxxxxxxxxx> wrote:
>
> On 1/8/19 6:27 PM, Jan Beulich wrote:
> >>>> On 19.12.18 at 19:52, <ppircalabu@xxxxxxxxxxxxxxx> wrote:
> >> Signed-off-by: Petre Pircalabu <ppircalabu@xxxxxxxxxxxxxxx>
> >
> > An empty description is not helpful. The immediate question is: Why?
> > We don't do this for other interface versions. I'm unconvinced a
> > special purpose piece of information like this one belongs into the
> > rather generic version hypercall.
>
> For an introspection application meant to be deployed on several Xen
> versions without recompiling, it is important to be able to decide at
> runtime what size and layout the vm_event struct has.
>
> Currently this can somewhat be done by associating the current version
> with the vm_event version, but that is not ideal for obvious reasons.

We do exactly that in LibVMI and it works fine - care to elaborate
what problem you have with doing that? There is a 1:1 match between
any stable Xen version and a vm_event interface version. I don't think
we will ever have a situation where we bump the vm_event interface
version but not the Xen release version.

Tamas

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