Pass Nsenter to NsenterMounter and NsenterWriter

So Nsenter is initialized only once and with the right parameters.

cmd/kubelet/app/BUILD

@@ -110,6 +110,7 @@ go_library(
         "//pkg/util/io:go_default_library",
         "//pkg/util/mount:go_default_library",
         "//pkg/util/node:go_default_library",
+        "//pkg/util/nsenter:go_default_library",
         "//pkg/util/oom:go_default_library",
         "//pkg/util/rlimit:go_default_library",
         "//pkg/version:go_default_library",
@@ -170,6 +171,7 @@ go_library(
         "//vendor/k8s.io/client-go/tools/record:go_default_library",
         "//vendor/k8s.io/client-go/util/cert:go_default_library",
         "//vendor/k8s.io/client-go/util/certificate:go_default_library",
+        "//vendor/k8s.io/utils/exec:go_default_library",
     ] + select({
         "@io_bazel_rules_go//go/platform:linux": [
             "//vendor/golang.org/x/exp/inotify:go_default_library",

cmd/kubelet/app/server.go

@@ -91,10 +91,12 @@ import (
 	kubeio "k8s.io/kubernetes/pkg/util/io"
 	"k8s.io/kubernetes/pkg/util/mount"
 	nodeutil "k8s.io/kubernetes/pkg/util/node"
+	"k8s.io/kubernetes/pkg/util/nsenter"
 	"k8s.io/kubernetes/pkg/util/oom"
 	"k8s.io/kubernetes/pkg/util/rlimit"
 	"k8s.io/kubernetes/pkg/version"
 	"k8s.io/kubernetes/pkg/version/verflag"
+	"k8s.io/utils/exec"
 )
 
 const (
@@ -360,11 +362,12 @@ func UnsecuredDependencies(s *options.KubeletServer) (*kubelet.Dependencies, err
 	var writer kubeio.Writer = &kubeio.StdWriter{}
 	if s.Containerized {
 		glog.V(2).Info("Running kubelet in containerized mode")
-		mounter, err = mount.NewNsenterMounter(s.RootDirectory)
+		ne, err := nsenter.NewNsenter(nsenter.DefaultHostRootFsPath, exec.New())
 		if err != nil {
 			return nil, err
 		}
-		writer = &kubeio.NsenterWriter{}
+		mounter = mount.NewNsenterMounter(s.RootDirectory, ne)
+		writer = kubeio.NewNsenterWriter(ne)
 	}
 
 	var dockerClientConfig *dockershim.ClientConfig

pkg/util/io/writer.go

@@ -50,18 +50,24 @@ func (writer *StdWriter) WriteFile(filename string, data []byte, perm os.FileMod
 // it will not see the mounted device in its own namespace. To work around this
 // limitation one has to first enter hosts namespace (by using 'nsenter') and
 // only then write data.
-type NsenterWriter struct{}
+type NsenterWriter struct {
+	ne *nsenter.Nsenter
+}
+
+// NewNsenterWriter creates a new Writer that allows writing data to file using
+// nsenter command.
+func NewNsenterWriter(ne *nsenter.Nsenter) *NsenterWriter {
+	return &NsenterWriter{
+		ne: ne,
+	}
+}
 
 // WriteFile calls 'nsenter cat - > <the file>' and 'nsenter chmod' to create a
 // file on the host.
 func (writer *NsenterWriter) WriteFile(filename string, data []byte, perm os.FileMode) error {
-	ne, err := nsenter.NewNsenter()
-	if err != nil {
-		return err
-	}
 	echoArgs := []string{"-c", fmt.Sprintf("cat > %s", filename)}
 	glog.V(5).Infof("nsenter: write data to file %s by nsenter", filename)
-	command := ne.Exec("sh", echoArgs)
+	command := writer.ne.Exec("sh", echoArgs)
 	command.SetStdin(bytes.NewBuffer(data))
 	outputBytes, err := command.CombinedOutput()
 	if err != nil {
@@ -71,7 +77,7 @@ func (writer *NsenterWriter) WriteFile(filename string, data []byte, perm os.Fil
 
 	chmodArgs := []string{fmt.Sprintf("%o", perm), filename}
 	glog.V(5).Infof("nsenter: change permissions of file %s to %s", filename, chmodArgs[0])
-	outputBytes, err = ne.Exec("chmod", chmodArgs).CombinedOutput()
+	outputBytes, err = writer.ne.Exec("chmod", chmodArgs).CombinedOutput()
 	if err != nil {
 		glog.Errorf("Output from chmod command: %v", string(outputBytes))
 		return err

pkg/util/mount/BUILD

@@ -71,6 +71,18 @@ go_library(
         "//vendor/github.com/golang/glog:go_default_library",
         "//vendor/k8s.io/utils/exec:go_default_library",
     ] + select({
+        "@io_bazel_rules_go//go/platform:android": [
+            "//pkg/util/nsenter:go_default_library",
+        ],
+        "@io_bazel_rules_go//go/platform:darwin": [
+            "//pkg/util/nsenter:go_default_library",
+        ],
+        "@io_bazel_rules_go//go/platform:dragonfly": [
+            "//pkg/util/nsenter:go_default_library",
+        ],
+        "@io_bazel_rules_go//go/platform:freebsd": [
+            "//pkg/util/nsenter:go_default_library",
+        ],
         "@io_bazel_rules_go//go/platform:linux": [
             "//pkg/util/file:go_default_library",
             "//pkg/util/io:go_default_library",
@@ -78,8 +90,24 @@ go_library(
             "//vendor/golang.org/x/sys/unix:go_default_library",
             "//vendor/k8s.io/apimachinery/pkg/util/sets:go_default_library",
         ],
+        "@io_bazel_rules_go//go/platform:nacl": [
+            "//pkg/util/nsenter:go_default_library",
+        ],
+        "@io_bazel_rules_go//go/platform:netbsd": [
+            "//pkg/util/nsenter:go_default_library",
+        ],
+        "@io_bazel_rules_go//go/platform:openbsd": [
+            "//pkg/util/nsenter:go_default_library",
+        ],
+        "@io_bazel_rules_go//go/platform:plan9": [
+            "//pkg/util/nsenter:go_default_library",
+        ],
+        "@io_bazel_rules_go//go/platform:solaris": [
+            "//pkg/util/nsenter:go_default_library",
+        ],
         "@io_bazel_rules_go//go/platform:windows": [
             "//pkg/util/file:go_default_library",
+            "//pkg/util/nsenter:go_default_library",
         ],
         "//conditions:default": [],
     }),

pkg/util/mount/nsenter_mount.go

@@ -48,15 +48,11 @@ type NsenterMounter struct {
 }
 
 // NewNsenterMounter creates a new mounter for kubelet that runs as a container.
-// rootDir is location of /var/lib/kubelet directory (in case it's not on the
+func NewNsenterMounter(rootDir string, ne *nsenter.Nsenter) *NsenterMounter {
-// default place). This directory must be available in the container
+	return &NsenterMounter{
-// on the same place as it's on the host.
+		rootDir: rootDir,
-func NewNsenterMounter(rootDir string) (*NsenterMounter, error) {
+		ne:      ne,
-	ne, err := nsenter.NewNsenter()
-	if err != nil {
-		return nil, err
 	}
-	return &NsenterMounter{ne: ne}, nil
 }
 
 // NsenterMounter implements mount.Interface

pkg/util/mount/nsenter_mount_unsupported.go

@@ -21,12 +21,14 @@ package mount
 import (
 	"errors"
 	"os"
+
+	"k8s.io/kubernetes/pkg/util/nsenter"
 )
 
 type NsenterMounter struct{}
 
-func NewNsenterMounter(rootDir string) (*NsenterMounter, error) {
+func NewNsenterMounter(rootDir string, ne *nsenter.Nsenter) *NsenterMounter {
-	return &NsenterMounter{}, nil
+	return &NsenterMounter{}
 }
 
 var _ = Interface(&NsenterMounter{})