Add GetKernelVersion to ipvs.KernelHandler interface

ipvs `getProxyMode` test fails on mac as `utilipvs.GetRequiredIPVSMods`
try to reach `/proc/sys/kernel/osrelease` to find version of the running
linux kernel. Linux kernel version is used to determine the list of required
kernel modules for ipvs.

Logic to determine kernel version is moved to GetKernelVersion
method in LinuxKernelHandler which implements ipvs.KernelHandler.
Mock KernelHandler is used in the test cases.

Read and parse file is converted to go function instead of execing cut.

pkg/proxy/ipvs/proxier.go

@@ -19,8 +19,10 @@ package ipvs
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"net"
+	"os"
 	"regexp"
 	"strconv"
 	"strings"
@@ -28,13 +30,13 @@ import (
 	"sync/atomic"
 	"time"
 
-	"k8s.io/klog"
-
 	v1 "k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/types"
 	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/apimachinery/pkg/util/version"
 	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/client-go/tools/record"
+	"k8s.io/klog"
 	"k8s.io/kubernetes/pkg/proxy"
 	"k8s.io/kubernetes/pkg/proxy/healthcheck"
 	"k8s.io/kubernetes/pkg/proxy/metrics"
@@ -473,6 +475,7 @@ func newServiceInfo(port *v1.ServicePort, service *v1.Service, baseInfo *proxy.B
 // KernelHandler can handle the current installed kernel modules.
 type KernelHandler interface {
 	GetModules() ([]string, error)
+	GetKernelVersion() (string, error)
 }
 
 // LinuxKernelHandler implements KernelHandler interface.
@@ -490,11 +493,17 @@ func NewLinuxKernelHandler() *LinuxKernelHandler {
 // GetModules returns all installed kernel modules.
 func (handle *LinuxKernelHandler) GetModules() ([]string, error) {
 	// Check whether IPVS required kernel modules are built-in
-	kernelVersion, ipvsModules, err := utilipvs.GetKernelVersionAndIPVSMods(handle.executor)
+	kernelVersionStr, err := handle.GetKernelVersion()
 	if err != nil {
 		return nil, err
 	}
-	builtinModsFilePath := fmt.Sprintf("/lib/modules/%s/modules.builtin", kernelVersion)
+	kernelVersion, err := version.ParseGeneric(kernelVersionStr)
+	if err != nil {
+		return nil, fmt.Errorf("error parseing kernel version %q: %v", kernelVersionStr, err)
+	}
+	ipvsModules := utilipvs.GetRequiredIPVSModules(kernelVersion)
+
+	builtinModsFilePath := fmt.Sprintf("/lib/modules/%s/modules.builtin", kernelVersionStr)
 	b, err := ioutil.ReadFile(builtinModsFilePath)
 	if err != nil {
 		klog.Warningf("Failed to read file %s with error %v. You can ignore this message when kube-proxy is running inside container without mounting /lib/modules", builtinModsFilePath, err)
@@ -516,15 +525,49 @@ func (handle *LinuxKernelHandler) GetModules() ([]string, error) {
 	}
 
 	// Find out loaded kernel modules
-	out, err := handle.executor.Command("cut", "-f1", "-d", " ", "/proc/modules").CombinedOutput()
+	modulesFile, err := os.Open("/proc/modules")
 	if err != nil {
 		return nil, err
 	}
 
-	mods := strings.Split(string(out), "\n")
+	mods, err := getFirstColumn(modulesFile)
+	if err != nil {
+		return nil, fmt.Errorf("failed to find loaded kernel modules: %v", err)
+	}
+
 	return append(mods, bmods...), nil
 }
 
+// getFirstColumn reads all the content from r into memory and return a
+// slice which consists of the first word from each line.
+func getFirstColumn(r io.Reader) ([]string, error) {
+	b, err := ioutil.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+
+	lines := strings.Split(string(b), "\n")
+	words := make([]string, 0, len(lines))
+	for i := range lines {
+		fields := strings.Fields(lines[i])
+		if len(fields) > 0 {
+			words = append(words, fields[0])
+		}
+	}
+	return words, nil
+}
+
+// GetKernelVersion returns currently running kernel version.
+func (handle *LinuxKernelHandler) GetKernelVersion() (string, error) {
+	kernelVersionFile := "/proc/sys/kernel/osrelease"
+	fileContent, err := ioutil.ReadFile(kernelVersionFile)
+	if err != nil {
+		return "", fmt.Errorf("error reading osrelease file %q: %v", kernelVersionFile, err)
+	}
+
+	return strings.TrimSpace(string(fileContent)), nil
+}
+
 // CanUseIPVSProxier returns true if we can use the ipvs Proxier.
 // This is determined by checking if all the required kernel modules can be loaded. It may
 // return an error if it fails to get the kernel modules information without error, in which
@@ -534,12 +577,21 @@ func CanUseIPVSProxier(handle KernelHandler, ipsetver IPSetVersioner) (bool, err
 	if err != nil {
 		return false, fmt.Errorf("error getting installed ipvs required kernel modules: %v", err)
 	}
-	wantModules := sets.NewString()
 	loadModules := sets.NewString()
-	linuxKernelHandler := NewLinuxKernelHandler()
-	_, ipvsModules, _ := utilipvs.GetKernelVersionAndIPVSMods(linuxKernelHandler.executor)
-	wantModules.Insert(ipvsModules...)
 	loadModules.Insert(mods...)
+
+	kernelVersionStr, err := handle.GetKernelVersion()
+	if err != nil {
+		return false, fmt.Errorf("error determining kernel version to find required kernel modules for ipvs support: %v", err)
+	}
+	kernelVersion, err := version.ParseGeneric(kernelVersionStr)
+	if err != nil {
+		return false, fmt.Errorf("error parseing kernel version %q: %v", kernelVersionStr, err)
+	}
+	mods = utilipvs.GetRequiredIPVSModules(kernelVersion)
+	wantModules := sets.NewString()
+	wantModules.Insert(mods...)
+
 	modules := wantModules.Difference(loadModules).UnsortedList()
 	var missingMods []string
 	ConntrackiMissingCounter := 0