Make the kernel feature source configurable

Adding two config options:
- kernel config file to read
- kconfig options that are detected

README.md

@@ -172,16 +172,17 @@ such as restricting discovered features with the --label-whitelist option._
 
 ### Kernel Features
 
-| Feature | Attribute   | Description                                          |
-| ------- | ----------- | ---------------------------------------------------- |
-| config  | NO_HZ       | Kernel config option is enabled
-| <br>    | NO_HZ_FULL  |
-| <br>    | NO_HZ_IDLE  |
-| <br>    | PREEMPT     |
-| 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')
+| Feature | Attribute           | Description                                  |
+| ------- | ------------------- | -------------------------------------------- |
+| config  | &lt;option name&gt; | Kernel config option is enabled (set 'y' or 'm').<br> Default options are `NO_HZ`, `NO_HZ_IDLE`, `NO_HZ_FULL` and `PREEMPT`
+| 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')
+
+Kernel config file to use, and, the set of config options to be detected are
+configurable.
+See [configuration options](#configuration-options) for more information.
 
 ### Local (User-specific Features)
 
@@ -381,7 +382,7 @@ Configuration options specified from the command line will override those read
 from the config file.
 
 Currently, the only available configuration options are related to the
-[PCI feature source](#pci-features).
+[PCI](#pci-features) and [Kernel](#kernel-features) feature sources.
 
 ## Building from source
 

main.go

@@ -60,7 +60,8 @@ var (
 // Global config
 type NFDConfig struct {
 	Sources struct {
-		Pci *pci.NFDConfig `json:"pci,omitempty"`
+		Kernel *kernel.NFDConfig `json:"kernel,omitempty"`
+		Pci    *pci.NFDConfig    `json:"pci,omitempty"`
 	} `json:"sources,omitempty"`
 }
 
@@ -223,6 +224,7 @@ func argsParse(argv []string) (args Args) {
 
 // Parse configuration options
 func configParse(filepath string, overrides string) error {
+	config.Sources.Kernel = &kernel.Config
 	config.Sources.Pci = &pci.Config
 
 	data, err := ioutil.ReadFile(filepath)

main_test.go

@@ -205,6 +205,9 @@ func TestConfigParse(t *testing.T) {
 		defer os.Remove(f.Name())
 		So(err, ShouldBeNil)
 		f.WriteString(`sources:
+  kernel:
+    configOpts:
+      - "DMI"
   pci:
     deviceClassWhitelist:
       - "ff"`)
@@ -215,6 +218,7 @@ func TestConfigParse(t *testing.T) {
 
 			Convey("Should return error", func() {
 				So(err, ShouldBeNil)
+				So(config.Sources.Kernel.ConfigOpts, ShouldResemble, []string{"DMI"})
 				So(config.Sources.Pci.DeviceClassWhitelist, ShouldResemble, []string{"ff"})
 			})
 		})

node-feature-discovery.conf.example

@@ -1,4 +1,10 @@
 #sources:
+#  kernel:
+#    kconfigFile: "/path/to/kconfig"
+#    configOpts:
+#      - "NO_HZ"
+#      - "X86"
+#      - "DMI"
 #  pci:
 #    deviceClassWhitelist:
 #      - "0200"

source/kernel/kernel.go

@@ -28,16 +28,24 @@ import (
 	"github.com/kubernetes-incubator/node-feature-discovery/source"
 )
 
-// Default kconfig flags
-var defaultKconfigFlags = [...]string{
-	"NO_HZ",
-	"NO_HZ_IDLE",
-	"NO_HZ_FULL",
-	"PREEMPT",
+// Configuration file options
+type NFDConfig struct {
+	KconfigFile string
+	ConfigOpts  []string `json:"configOpts,omitempty"`
 }
 
 var logger = log.New(os.Stderr, "", log.LstdFlags)
 
+var Config = NFDConfig{
+	KconfigFile: "",
+	ConfigOpts: []string{
+		"NO_HZ",
+		"NO_HZ_IDLE",
+		"NO_HZ_FULL",
+		"PREEMPT",
+	},
+}
+
 // Implement FeatureSource interface
 type Source struct{}
 
@@ -63,9 +71,9 @@ func (s Source) Discover() (source.Features, error) {
 	}
 
 	// Check flags
-	for _, flag := range defaultKconfigFlags {
-		if _, ok := kconfig[flag]; ok {
-			features["config."+flag] = true
+	for _, opt := range Config.ConfigOpts {
+		if _, ok := kconfig[opt]; ok {
+			features["config."+opt] = true
 		}
 	}
 
@@ -121,11 +129,22 @@ func readKconfigGzip(filename string) ([]byte, error) {
 func parseKconfig() (map[string]bool, error) {
 	kconfig := map[string]bool{}
 	raw := []byte(nil)
+	err := error(nil)
 
-	// First, try to read from /proc as this is the most reliable source
-	raw, err := readKconfigGzip("/proc/config.gz")
-	if err != nil {
-		logger.Printf("ERROR: Failed to read /proc/config.gz: %s", err)
+	// First, try kconfig specified in the config file
+	if len(Config.KconfigFile) > 0 {
+		raw, err = ioutil.ReadFile(Config.KconfigFile)
+		if err != nil {
+			logger.Printf("ERROR: Failed to read kernel config from %s: %s", Config.KconfigFile, err)
+		}
+	}
+
+	// Then, try to read from /proc
+	if raw == nil {
+		raw, err = readKconfigGzip("/proc/config.gz")
+		if err != nil {
+			logger.Printf("Failed to read /proc/config.gz: %s", err)
+		}
 	}
 
 	// Last, try to read from /boot/