Public bug reported:
[ note - this is a version of the patch I just sent to lkml ported to
our xenial tree. It's needed for things like docker and lxc to
be certain of which cgroup tasks file is their own in certain nesting
situations. We currently work around it by blindly assuming that
there are no legacy container managers running on cgroup-ns-enabled
kernels ]
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.
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Serge Hallyn (serge-hallyn)
Status: Fix Committed
** Affects: linux (Ubuntu Xenial)
Importance: Undecided
Assignee: Serge Hallyn (serge-hallyn)
Status: Fix Committed
** Also affects: linux (Ubuntu Xenial)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Xenial)
Status: New => Fix Committed
** Changed in: linux (Ubuntu Xenial)
Assignee: (unassigned) => Serge Hallyn (serge-hallyn)
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https://bugs.launchpad.net/bugs/1560489
Title:
cgroup namespaces: add a 'nsroot=' mountinfo field
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