Re: [Devel] Re: containers and cgroups mini-summit @ Linux Plumbers

[ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman)]

Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> writes:

>>>
>>> Another old issue is that unless I have missed something control groups
>>> are still broken for generic use in containers.  Does anyone care?
>>> Are there any plans on fixing this issue?
>>>
>
> What is "generic use in containers" ? I am using them alright, but not
> sure if this counts as generic or specific =)

The general container use case would be.

- Create a new mount namespace.
- Create fresh mounts of all of the control groups like I would do at
  boot, with no consideration to any other control group state.
- Start forking processes.

The expected semantics would be something like chroot for control
groups, where all of the control groups that are created by fresh mounts
are relative to whatever state the process of being in a control group
that the process that mounted them was in.

Last I looked the closest you could come to that was bind mounts, and
even with bind mounts you get into weird things where control groups are
bound into hierarchies and you may be running a distribution that wants
it's control groups bound into different hierarchies.

Last I looked this was just about a total disaster, and the only thing
that allowed systemd to run in containers was the fact that systemd did
not user controllers.

Eric