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

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 2/12/19 8:13 PM, Tamas K Lengyel wrote:
> 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.

XenServer. Any given version of XenServer may or may not fit the matrix
you're talking about (because some patches are backported, some are not,
etc.). In which case it all becomes very complicated.


Thanks,
Razvan

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