Paul Moore [off-list ref] writes:

As Eric, and others, have stated, the container concept is a userspace idea, 
not a kernel idea; the kernel only knows, and cares about, namespaces.  This 
is unlikely to change.

However, as Steve points out, there is precedence for the kernel to record 
userspace tokens for the sake of audit.  Personally I'm not a big fan of this 
in general, but I do recognize that it does satisfy a legitimate need.  Think 
of things like auid and the sessionid as necessary evils; audit is already 
chock full of evilness I doubt one more will doom us all to hell.

Moving forward, I'd like to see the following:

* Create a container ID token (unsigned 32-bit integer?), similar to 
auid/sessionid, that is set by userspace and carried by the kernel to be used 
in audit records.  I'd like to see some discussion on how we manage this, e.g. 
how do handle container ID inheritance, how do we handle nested containers 
(setting the containerid when it is already set), do we care if multiple 
different containers share the same namespace config, etc.?

Can we all live with this?  If not, please suggest some alternate ideas; 
simply shouting "IT'S ALL CRAP!" isn't helpful for anyone ... it may be true, 
but it doesn't help us solve the problem ;)

Without stopping and defining what someone means by container I think it
is pretty much nonsense.

Should every vsftp connection get a container every?  Every chrome tab?

At some of the connections per second numbers I have seen we might
exhaust a 32bit number in an hour or two.  Will any of that make sense
to someone reading the audit logs?

Without considerning that container creation is an unprivileged
operation I think it is pretty much nonsense.  Do I get to say I am any
container I want?  That would seem to invalidate the concept of
userspace setting a container id.

How does any of this interact with setns?  AKA entering a container?

I will go as far as looking at patches.  If someone comes up with
a mission statement about what they are actually trying to achieve and a
mechanism that actually achieves that, and that allows for containers to
nest we can talk about doing something like that.

But for right now I just hear proposals for things that make no sense
and can not possibly work.  Not least because it will require modifying
every program that creates a container and who knows how many of them
there are.  Especially since you don't need to be root.  Modifying
/usr/bin/unshare seems a little far out to me.

Eric