Re: [Xen-devel] [PATCH] arm/vm_event: get/set registers

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

On Jul 29, 2016 08:21, "Razvan Cojocaru" <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>
> On 07/29/2016 05:11 PM, Julien Grall wrote:
> > Which lead to my next question. For instance, we have an app A which is
> > built for Xen 4.N and they want to also support Xen 4.(N + 1) which will
> > set more registers and take advantage of it. How the app will
> > differentiate the 2 versions?
>
> We currenly have macros like VM_EVENT_INTERFACE_VERSION that can be
> incremented so that applications can know at compile-time which
> interface they get.
>
> At runtime, I suppose we could use code similar to what runs when "xl
> info" is called (which outputs xen_major, xen_minor and xen_extra, or
> the complete xen_version).
>
>

The vm_event interface version is included in all requests and responses so the user knows at runtime what it is running on. We enforce on the Xen side that the response matches the interface expected.

Tamas

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