Remove (or reduce) dependency on runc libcontainer dependency

[thaJeztah]

The runc maintainers have indicated that the libcontainer package is not intended for external consumption, and because of that has an "unstable" API.

We should reduce our use of this dependency.

• libcontainer/cgroups Use the container/cgroups package (https://github.com/containerd/cgroups) instead of libcontainer/cgroups (where possible), e.g. see Fix setting swaplimit=true without checking memory.swap.max #42071 (comment).
  • identify what functionality is provided by libcontainer/cgroups that is not provided by containerd/cgroups
• libcontainer/configs
  • device parts we need have moved into libcontainer/devices: vendor: github.com/opencontainers/runc v1.0.0-rc95 #42143
  • still used by libcontainer/cgroups
• libcontainer/devices used for oci.Device, oci.DevicesFromPath(). Need to look what's needed (and if this can be replaced with code from containerd; oci.DeviceFromPath() switch to use containerd implementation #43055
• libcontainer/userns
  • used by libcontainer/cgroups
• libcontainer/nsenter is not used, but vendored because it has c code
• libcontainer/user Is still needed; perhaps this package should live elsewhere (also used by containerd); migrate to github.com/moby/sys/user #46711

[AkihiroSuda]

libcontainer/user Is still needed; perhaps this package should live elsewhere (also used by containerd)

Can we move this to moby/sys?

cc @kolyshkin

[thaJeztah]

It looks like the only remaining part is now libcontainer/cgroups (but that brings in libcontainer/userns and libcontainer/configs, libcontainer/devices. The only uses are in daemon: withCgroups(), and for these utilities;

GetInitCgroup and GetOwnCgroup

moby/daemon/oci_linux.go

Lines 902 to 906 in 84ba255

	initPath, err := cgroups.GetInitCgroup("cpu")
	if err != nil {
	return errors.Wrap(err, "unable to init CPU RT controller")
	}
	_, err = cgroups.GetOwnCgroup("cpu")

FindCgroupMountpointAndRoot:

moby/daemon/oci_linux.go

Line 919 in 84ba255

mnt, root, err := cgroups.FindCgroupMountpointAndRoot("", "cpu")