nri: add experimental NRI plugin.

Add a common NRI 'service' plugin. It takes care of relaying
requests and respones to and from NRI (external NRI plugins)
and the high-level containerd namespace-independent logic of
applying NRI container adjustments and updates to actual CRI
and other containers.

The namespace-dependent details of the necessary container
manipulation operations are to be implemented by namespace-
specific adaptations. This NRI plugin defines the API which
such adaptations need to implement.

Signed-off-by: Krisztian Litkey <krisztian.litkey@intel.com>

pkg/nri/sandbox_linux.go

@@ -0,0 +1,38 @@
+//go:build linux
+// +build linux
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package nri
+
+import (
+	nri "github.com/containerd/nri/pkg/adaptation"
+)
+
+func podSandboxToNRI(pod PodSandbox) *nri.PodSandbox {
+	nriPod := commonPodSandboxToNRI(pod)
+	lnxPod := pod.GetLinuxPodSandbox()
+	nriPod.Linux = &nri.LinuxPodSandbox{
+		Namespaces:   lnxPod.GetLinuxNamespaces(),
+		PodOverhead:  lnxPod.GetPodLinuxOverhead(),
+		PodResources: lnxPod.GetPodLinuxResources(),
+		CgroupParent: lnxPod.GetCgroupParent(),
+		CgroupsPath:  lnxPod.GetCgroupsPath(),
+		Resources:    lnxPod.GetLinuxResources(),
+	}
+	return nriPod
+}