Fix getting cgroup pids

pkg/kubelet/cm/util/cgroups_linux.go

@@ -0,0 +1,76 @@
+/*
+Copyright 2016 The Kubernetes 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 util
+
+import (
+	"path/filepath"
+
+	libcontainercgroups "github.com/opencontainers/runc/libcontainer/cgroups"
+	libcontainerutils "github.com/opencontainers/runc/libcontainer/utils"
+)
+
+// Forked from opencontainers/runc/libcontainer/cgroup/fs.Manager.GetPids()
+func GetPids(cgroupPath string) ([]int, error) {
+	dir, err := getCgroupPath(cgroupPath)
+	if err != nil {
+		return nil, err
+	}
+	return libcontainercgroups.GetPids(dir)
+}
+
+// getCgroupPath gets the file path to the "devices" subsystem of the desired cgroup.
+// cgroupPath is the path in the cgroup hierarchy.
+func getCgroupPath(cgroupPath string) (string, error) {
+	cgroupPath = libcontainerutils.CleanPath(cgroupPath)
+
+	mnt, root, err := libcontainercgroups.FindCgroupMountpointAndRoot("devices")
+	// If we didn't mount the subsystem, there is no point we make the path.
+	if err != nil {
+		return "", err
+	}
+
+	// If the cgroup name/path is absolute do not look relative to the cgroup of the init process.
+	if filepath.IsAbs(cgroupPath) {
+		// Sometimes subsystems can be mounted togethger as 'cpu,cpuacct'.
+		return filepath.Join(root, mnt, cgroupPath), nil
+	}
+
+	parentPath, err := getCgroupParentPath(mnt, root)
+	if err != nil {
+		return "", err
+	}
+
+	return filepath.Join(parentPath, cgroupPath), nil
+}
+
+// getCgroupParentPath gets the parent filepath to this cgroup, for resolving relative cgroup paths.
+func getCgroupParentPath(mountpoint, root string) (string, error) {
+	// Use GetThisCgroupDir instead of GetInitCgroupDir, because the creating
+	// process could in container and shared pid namespace with host, and
+	// /proc/1/cgroup could point to whole other world of cgroups.
+	initPath, err := libcontainercgroups.GetThisCgroupDir("devices")
+	if err != nil {
+		return "", err
+	}
+	// This is needed for nested containers, because in /proc/self/cgroup we
+	// see paths from host, which don't exist in container.
+	relDir, err := filepath.Rel(root, initPath)
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(mountpoint, relDir), nil
+}