[Libosinfo] Resources inheritance for OSes, I need some help/feedback!

[Daniel P. Berrangé]

On Tue, Nov 13, 2018 at 10:10:17AM +0100, Fabiano Fidêncio wrote:
> People,
> 
> I'm working on making OsinfoResources inherited for OSes that derives-
> from/clones another OSes. The inheritance, IMO, should work like:
> - os1 has:
>   <resources arch="all">
>     <minimum>
>       <cpu>1000000000</cpu>
>       <ram>1073741824</ram>
>     </minimum>
>   </resources>
> 
> - os2, which inherits the values from os1, has:
>   <resources arch="all">
>     <minimum>
>       <n-cpus>2</n-cpus>
>     </minimum>
>   </resources>

I wonder about making inheritance explicit, eg for os2, have

   <resources arch="all" inherit="yes">
     <minimum>
       <n-cpus>2</n-cpus>
     </minimum>
   </resources>

the benefit of this is that....  [1]

> - When calling osinfo_resources_get_cpu(os2), I'd expect to get:
> 1000000000.
> 
> 
> In order to achieve so, we'll need a few more changes in the way
> resources are added to OSes:
> - Do *not* have duplicated resources for the same OS;
>   - This can be easily done in osinfo_os_add_*_resources() + tests to
> catch this situation;
> - Do *not* have more than one resources with the same arch for the same
> OS;
>   - Although this can be easily done  in osinfo_os_add_*_resources() as
> well, I'd go only for tests to catch this situation;

These points look tangential to inheritance to me. Or to put it another
way, shouldn't we ensure uniqueness regardless of whether we have
inheritance or not.


> - Have a way to specify that a resource field shouldn't be inherited;
>   - Here I can basically see two different approaches, and my personal
> preference would be the former:
>     - A specific value to be set to the field that will just be checked
> when merging the resources' content when doing the inheritance
> (suggestions are welcome and remember we can't use -1);
>     - Add an extra attribute to the elements and have a new structure
> (similar to DeviceLinks) and play with it in the same way I proposed
> for removed devices*.

[1]...you solve this problem more attractively IMHO.

Regards,
Daniel
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