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

Hello, Serge.

On Mon, Mar 28, 2016 at 08:12:03PM -0500, Serge E. Hallyn wrote:

Quoting Serge E. Hallyn (serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org):

quoted

One practical problem I've found with cgroup namespaces is that there
is no way to disambiguate between a cgroupfs mount which was done in
a cgroup namespace, and a bind mount of a cgroupfs directory.  So
whether I do

unshare --cgroup -- bash -c "mount -t cgroup -o freezer f /mnt; cat /proc/self/mountinfo"

or whether I just

mount --bind /sys/fs/cgroup/freezer/$(awk -F: '/freezer/ { print $3 }' /proc/self/cgroup) /mnt

'mount root' field (field 3) in /proc/self/mountinfo will show the
same thing, the result of awk -F: '/freezer/ { print $3 }' /proc/self/cgroup.

This patch adds a 'nsroot=' field to cgroup mountinfo entries, so that
userspace can distinguish a mount made in a cgroup namespace from a bind
mount from a cgroup subdirectory.

no rush on the patch itself, I don't mind if i have to rewrite it from
scratch, but I'd like to get the patch into docker/libcontainer using it,
so can we decide on whether the syntax as shown here is ok?

Yeah, I think the syntax is fine.

Thanks.

-- 
tejun