Re: [Xen-devel] [PATCH v2] kexec: implement STATUS hypercall to check if image is loaded

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Fri, Jan 13, 2017 at 06:19:28AM -0700, Jan Beulich wrote:
> >>> On 13.01.17 at 13:49, <daniel.kiper@xxxxxxxxxx> wrote:
> > On Fri, Jan 13, 2017 at 05:35:35AM -0700, Jan Beulich wrote:
> >> >>> On 13.01.17 at 13:14, <daniel.kiper@xxxxxxxxxx> wrote:
> >> > Jan, so, __XEN_LATEST_INTERFACE_VERSION__ is used only for Xen internal 
> >> > purposes
> >> > (eg. for xl build, etc.) and should not be used as a reference point 
> >> > externally,
> >> > e.g. in kexec-tools?
> >>
> >> It's certainly meant for external consumption (see my original reply
> >> to Eric), but if at all possible you should not use it for (build time,
> >> obviously) feature detection.
> >
> > So, AIUI, __XEN_LATEST_INTERFACE_VERSION__ should be used when e.g. 
> > structure
> > layout passed to a given hypercall changes and it is not possible to detect
> > such change in other way. Right?
>
> No, structure _layout_ must not change (other than in tools only
> interfaces). But structure field naming occasionally changes. While
> that retains binary compatibility, source code requires changes in
> such a case, and that's what the symbol is meant to help with.

Thanks, make sense.

Daniel

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