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SubjectRe: [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@hallyn.com):
> > 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

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