Document basic operations for V1, V2 and system cases

[c3d]

In the context of kata containers, I am trying to figure out how to write code that works both for legacy and unified mode. I did not find any good example of that, and I was wondering if it is documented anywhere. If not, maybe it would be nice to update the readme and other examples with code for both cases?

Also, am I correct in understanding that the module does not presently abstract away resources in the two cases, i.e. you need to use Resources for unified and LinuxResources for legacy? Is the plan that everything will switch to Resources over time, or will that dichotomy persist?

Assuming the two interfaces will coexist in the near future, is there any function that converts from one to the other?

(I will try to answer my own questions here, but I would appreciate if someone more knowledgeable with the project can provide some guidance, notably with respect to future intent).

[c3d]

Possibly related is that when @sameo pulled a more recent version in kata containers PR #2332, this seems to have introduced a regression in the systemd case.

From a discussion with @fgiudici:

The cgroups creation complying with the systemd cgroups management has been dropped. See kata code. What we need seems to be to create the cgroups as explained here.

@fgiudici will provide more details once he's done analyzing the problem.