APPLIED: [PATCH] cgroup namespaces: add a 'nsroot=' mountinfo field

[Serge Hallyn]

Quoting Tim Gardner (tim.gardner at canonical.com):
> Applied anyway, but what are the odds that this'll break a user space
> regular expression ?

It's possible, although my xenial vms booted fine with it.  I would have
preferred to add this to the list of 'optional' fields before the -,
but there was not a hook for that.  As it is, elements in the options
field can be controllers if they are preceded by 'name=' or if they
are kernel controllers (listed in /proc/cgroups).  If userspace wants
every field element that it doesn't recognize to be a controller it could
be a problem.  As of now though the list of non-controller keywords I
regularly see includes rw, xattr (?), clone_children, release_agent=.