rkt: Refactor version check with api-service.

Also mocked systemd interfaces for testing purpose.

pkg/kubelet/rkt/systemd.go

@@ -0,0 +1,103 @@
+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+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 rkt
+
+import (
+	"fmt"
+	"os/exec"
+	"strconv"
+	"strings"
+
+	"github.com/coreos/go-systemd/dbus"
+)
+
+// systemdVersion is a type wraps the int to implement kubecontainer.Version interface.
+type systemdVersion int
+
+func (s systemdVersion) String() string {
+	return fmt.Sprintf("%d", s)
+}
+
+func (s systemdVersion) Compare(other string) (int, error) {
+	v, err := strconv.Atoi(other)
+	if err != nil {
+		return -1, err
+	}
+	if int(s) < v {
+		return -1, nil
+	} else if int(s) > v {
+		return 1, nil
+	}
+	return 0, nil
+}
+
+// systemdInterface is an abstraction of the go-systemd/dbus to make
+// it mockable for testing.
+// TODO(yifan): Eventually we should move these functionalities to:
+// 1. a package for launching/stopping rkt pods.
+// 2. rkt api-service interface for listing pods.
+// See https://github.com/coreos/rkt/issues/1769.
+type systemdInterface interface {
+	// Version returns the version of the systemd.
+	Version() (systemdVersion, error)
+	// ListUnits lists all the loaded units.
+	ListUnits() ([]dbus.UnitStatus, error)
+	// StopUnits stops the unit with the given name.
+	StopUnit(name, mode string) (string, error)
+	// StopUnits restarts the unit with the given name.
+	RestartUnit(name, mode string) (string, error)
+	// Reload is equivalent to 'systemctl daemon-reload'.
+	Reload() error
+}
+
+// systemd implements the systemdInterface using dbus and systemctl.
+// All the functions other then Version() are already implemented by go-systemd/dbus.
+type systemd struct {
+	*dbus.Conn
+}
+
+// newSystemd creates a systemd object that implements systemdInterface.
+func newSystemd() (*systemd, error) {
+	dbusConn, err := dbus.New()
+	if err != nil {
+		return nil, err
+	}
+	return &systemd{dbusConn}, nil
+}
+
+// Version returns the version of the systemd.
+func (s *systemd) Version() (systemdVersion, error) {
+	output, err := exec.Command("systemctl", "--version").Output()
+	if err != nil {
+		return -1, err
+	}
+	// Example output of 'systemctl --version':
+	//
+	// systemd 215
+	// +PAM +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ -SECCOMP -APPARMOR
+	//
+	lines := strings.Split(string(output), "\n")
+	tuples := strings.Split(lines[0], " ")
+	if len(tuples) != 2 {
+		return -1, fmt.Errorf("rkt: Failed to parse version %v", lines)
+	}
+	result, err := strconv.Atoi(string(tuples[1]))
+	if err != nil {
+		return -1, err
+	}
+	return systemdVersion(result), nil
+}