Implement kernel version detection

Add a new 'kernel' feature source, detecting the kernel version. The
kernel version is split into multiple labels in order to make this more
usable in label selectors. Kernel version in the format X.Y.Z-patch will
be presented as
  node.alpha.kubernetes-incubator.io/nfd-kernel-version.full=X.Y.Z-patch
  node.alpha.kubernetes-incubator.io/nfd-kernel-version.major=X
  node.alpha.kubernetes-incubator.io/nfd-kernel-version.minor=Y
  node.alpha.kubernetes-incubator.io/nfd-kernel-version.revision=Z

The '.full' label will always be avaiable. The other labels if these
components can be parsed from the kernel version number.

README.md

@@ -54,7 +54,7 @@ node-feature-discovery.
                               will override settings read from the config file.
                               [Default: ]
   --sources=<sources>         Comma separated list of feature sources.
-                              [Default: cpuid,iommu,memory,network,pci,pstate,rdt,selinux,storage]
+                              [Default: cpuid,iommu,kernel,memory,network,pci,pstate,rdt,selinux,storage]
   --no-publish                Do not publish discovered features to the
                               cluster-local Kubernetes API server.
   --label-whitelist=<pattern> Regular expression to filter label names to
@@ -79,6 +79,7 @@ The current set of feature sources are the following:
 
 - [CPUID][cpuid] for x86/Arm64 CPU details
 - IOMMU
+- Kernel
 - Memory
 - Network
 - Pstate ([Intel P-State driver][intel-pstate])
@@ -114,6 +115,7 @@ the only label value published for features is the string `"true"`._
   "node.alpha.kubernetes-incubator.io/node-feature-discovery.version": "v0.3.0",
   "node.alpha.kubernetes-incubator.io/nfd-cpuid-<feature-name>": "true",
   "node.alpha.kubernetes-incubator.io/nfd-iommu-<feature-name>": "true",
+  "node.alpha.kubernetes-incubator.io/nfd-kernel-version.<version component>": "<version number>",
   "node.alpha.kubernetes-incubator.io/nfd-memory-<feature-name>": "true",
   "node.alpha.kubernetes-incubator.io/nfd-network-<feature-name>": "true",
   "node.alpha.kubernetes-incubator.io/nfd-pci-<device label>.present": "true",
@@ -165,6 +167,15 @@ such as restricting discovered features with the --label-whitelist option._
 | :------------: | :---------------------------------------------------------------------------------: |
 | enabled        | IOMMU is present and enabled in the kernel
 
+### Kernel Features
+
+| Feature | Attribute | Description                                            |
+| ------- | --------- | ------------------------------------------------------ |
+| version | full      | Full kernel version as reported by `/proc/sys/kernel/osrelease` (e.g. '4.5.6-7-g123abcde')
+| <br>    | major     | First component of the kernel version (e.g. '4')
+| <br>    | minor     | Second component of the kernel version (e.g. '5')
+| <br>    | revision  | Third component of the kernel version (e.g. '6')
+
 ### Memory Features
 
 | Feature name   | Description                                                                         |

main.go

@@ -15,6 +15,7 @@ import (
 	"github.com/kubernetes-incubator/node-feature-discovery/source/cpuid"
 	"github.com/kubernetes-incubator/node-feature-discovery/source/fake"
 	"github.com/kubernetes-incubator/node-feature-discovery/source/iommu"
+	"github.com/kubernetes-incubator/node-feature-discovery/source/kernel"
 	"github.com/kubernetes-incubator/node-feature-discovery/source/memory"
 	"github.com/kubernetes-incubator/node-feature-discovery/source/network"
 	"github.com/kubernetes-incubator/node-feature-discovery/source/panic_fake"
@@ -165,7 +166,7 @@ func argsParse(argv []string) (args Args) {
                               will override settings read from the config file.
                               [Default: ]
   --sources=<sources>         Comma separated list of feature sources.
-                              [Default: cpuid,iommu,memory,network,pci,pstate,rdt,selinux,storage]
+                              [Default: cpuid,iommu,kernel,memory,network,pci,pstate,rdt,selinux,storage]
   --no-publish                Do not publish discovered features to the
                               cluster-local Kubernetes API server.
   --label-whitelist=<pattern> Regular expression to filter label names to
@@ -243,6 +244,7 @@ func configureParameters(sourcesWhiteList []string, labelWhiteListStr string) (e
 		cpuid.Source{},
 		fake.Source{},
 		iommu.Source{},
+		kernel.Source{},
 		memory.Source{},
 		network.Source{},
 		panic_fake.Source{},

main_test.go

@@ -139,7 +139,7 @@ func TestArgsParse(t *testing.T) {
 				So(args.sleepInterval, ShouldEqual, 60*time.Second)
 				So(args.noPublish, ShouldBeTrue)
 				So(args.oneshot, ShouldBeTrue)
-				So(args.sources, ShouldResemble, []string{"cpuid", "iommu", "memory", "network", "pci", "pstate", "rdt", "selinux", "storage"})
+				So(args.sources, ShouldResemble, []string{"cpuid", "iommu", "kernel", "memory", "network", "pci", "pstate", "rdt", "selinux", "storage"})
 				So(len(args.labelWhiteList), ShouldEqual, 0)
 			})
 		})
@@ -161,7 +161,7 @@ func TestArgsParse(t *testing.T) {
 
 			Convey("args.labelWhiteList is set to appropriate value and args.sources is set to default value", func() {
 				So(args.noPublish, ShouldBeFalse)
-				So(args.sources, ShouldResemble, []string{"cpuid", "iommu", "memory", "network", "pci", "pstate", "rdt", "selinux", "storage"})
+				So(args.sources, ShouldResemble, []string{"cpuid", "iommu", "kernel", "memory", "network", "pci", "pstate", "rdt", "selinux", "storage"})
 				So(args.labelWhiteList, ShouldResemble, ".*rdt.*")
 			})
 		})

source/kernel/kernel.go

@@ -0,0 +1,72 @@
+/*
+Copyright 2018 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 kernel
+
+import (
+	"io/ioutil"
+	"regexp"
+	"strings"
+
+	"github.com/golang/glog"
+	"github.com/kubernetes-incubator/node-feature-discovery/source"
+)
+
+// Implement FeatureSource interface
+type Source struct{}
+
+func (s Source) Name() string { return "kernel" }
+
+func (s Source) Discover() (source.Features, error) {
+	features := source.Features{}
+
+	// Read kernel version
+	version, err := parseVersion()
+	if err != nil {
+		glog.Errorf("Failed to get kernel version: %v", err)
+	} else {
+		for key := range version {
+			features["version."+key] = version[key]
+		}
+	}
+	return features, nil
+}
+
+// Read and parse kernel version
+func parseVersion() (map[string]string, error) {
+	version := map[string]string{}
+
+	// Open file for reading
+	raw, err := ioutil.ReadFile("/proc/sys/kernel/osrelease")
+	if err != nil {
+		return nil, err
+	}
+
+	full := strings.TrimSpace(string(raw))
+	version["full"] = full
+
+	// Regexp for parsing version components
+	re := regexp.MustCompile(`^(?P<major>\d+)(\.(?P<minor>\d+))?(\.(?P<revision>\d+))?(-.*)?$`)
+	if m := re.FindStringSubmatch(full); m != nil {
+		for i, name := range re.SubexpNames() {
+			if i != 0 && name != "" {
+				version[name] = m[i]
+			}
+		}
+	}
+
+	return version, nil
+}