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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.01.19 at 17:37, <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. 
> Reading the vm_event version from an actual vm_event is also out of the 
> question, because in order to be able to receive the first vm_event we 
> have to set the ring buffer up, and that requires knowledge of the size 
> of the vm_event. So a run-time mechanism for querying the vm_event 
> version is needed.
> 
> We just thought that this was the most flexible place to add it.

How about a new XEN_DOMCTL_VM_EVENT_GET_VERSION?

Jan



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