Quoting Alban Crequy (alban.crequy-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org):

Hi,

On 29 January 2016 at 09:54,  [off-list ref] wrote:

quoted

Hi,

following is a revised set of the CGroup Namespace patchset which Aditya
Kali has previously sent.  The code can also be found in the cgroupns.v10
branch of

https://git.kernel.org/cgit/linux/kernel/git/sergeh/linux-security.git/

To summarize the semantics:

1. CLONE_NEWCGROUP re-uses 0x02000000, which was previously CLONE_STOPPED

What's the best way for a userspace application to test at run-time
whether the kernel supports cgroup namespaces? Would you recommend to
test if the file /proc/self/ns/cgroup exists?

Yup.