I understand your point. But it will add some complexity to the code.

Before trying to make it work for non-unified hierarchy cases, I would
like to get a clearer idea.
What do you expect to be mounted when you run:
  container:/ # mount -t cgroup none /sys/fs/cgroup/
from inside the container?

Note that cgroup-namespace wont be able to change the way cgroups are
mounted .. i.e., if say cpu and cpuacct subsystems are mounted
together at a single mount-point, then we cannot mount them any other
way (inside a container or outside). This restriction exists today and
cgroup-namespaces won't change that.

So, If on the host we have:
root@adityakali-vm2:/sys/fs/cgroup# cat /proc/mounts | grep cgroup
tmpfs /sys/fs/cgroup tmpfs rw,relatime 0 0
cgroup /sys/fs/cgroup/cpu cgroup rw,relatime,cpuset,cpu,cpuacct 0 0
cgroup /sys/fs/cgroup/mem cgroup rw,relatime,memory,hugetlb 0 0
cgroup /sys/fs/cgroup/rest cgroup
rw,relatime,devices,freezer,net_cls,blkio,perf_event,net_prio 0 0

And inside the container we want each subsystem to be on its own
mount-point, then it will fail. Do you think even then its useful to
support virtualizing paths for non-unified hierarchies?

Thanks,


On Mon, Jan 5, 2015 at 4:17 PM, Richard Weinberger [off-list ref] wrote:

Am 06.01.2015 um 01:10 schrieb Aditya Kali:

quoted

Since the old/default behavior is on its way out, I didn't invest time
in fixing that. Also, some of the properties that make
cgroup-namespace simpler are only provided by unified hierarchy (for
example: a single root-cgroup per container).

Does the new sane cgroupfs behavior even have a single real world user?
I always thought it isn't stable yet.

Linux distros currently use systemd v210. They don't dare to use a newer one.
Even *if* systemd would support the sane sane cgroupfs behavior in the most recent
version it will take 1-2 years until it would hit a recent distro.

So please support also the old and nasty behavior such that one day we can run current
systemd distros in Linux containers.

Thanks,
//richard

-- 
Aditya