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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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