cgroupsv2 adjustments proposal

[x7upLime]

This proof of concept and related talks helped me getting a grasp about container internals, to then be able to solve some other related issues.. and in a really entertaining way also.
Really fine material, thank you :)

As for now, I'm not able to compile main.go,
the main issue being a "no such file" when talking about pids.max
Just learned about cgroups and if I'm not wrong the reason is that the example was built for cgroupsv1
and the linux distro I'm running (as the major ones are) is using cgroupsv2 by default,
so I'd like to propose the changes I made to make it work.
It didn't took much to catch up with cgroups and differences between version,
it was an instructive activity actually.. but for the one that is in a hurry...

[kyzyc]

same with you, cannot create file /sys/fs/cgroup/pids/liz/pids.max even as root user.

[netskink]

Take a look at the comments I added to x7uplime's pull request. I mounted the sysfs file system, but didn't find the file system writable.