source: parametrise host directory paths

Specify and handle system paths we use for discovery in a unified way.

Dockerfile

@@ -14,7 +14,7 @@ COPY . /go/node-feature-discovery
 ARG NFD_VERSION
 
 RUN go install \
-  -ldflags "-s -w -X sigs.k8s.io/node-feature-discovery/pkg/version.version=$NFD_VERSION" \
+  -ldflags "-s -w -X sigs.k8s.io/node-feature-discovery/pkg/version.version=$NFD_VERSION -X sigs.k8s.io/node-feature-discovery/source.pathPrefix=/host-" \
   ./cmd/*
 RUN install -D -m644 nfd-worker.conf.example /etc/kubernetes/node-feature-discovery/nfd-worker.conf
 

source/config.go

@@ -0,0 +1,39 @@
+/*
+Copyright 2020 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 source
+
+import (
+	"path/filepath"
+)
+
+var (
+	pathPrefix = "/"
+	// BootPath is where the /boot directory of the system to be inspected is located
+	BootDir = HostDir(pathPrefix + "boot")
+	// EtcPath is where the /etc directory of the system to be inspected is located
+	EtcDir = HostDir(pathPrefix + "etc")
+	// SysfsPath is where the /sys directory of the system to be inspected is located
+	SysfsDir = HostDir(pathPrefix + "sys")
+)
+
+// HostDir is a helper for handling host system directories
+type HostDir string
+
+// Path returns a full path to a file under HostDir
+func (d HostDir) Path(elem ...string) string {
+	return filepath.Join(append([]string{string(d)}, elem...)...)
+}

source/kernel/kernel.go

@@ -167,7 +167,7 @@ func parseKconfig() (map[string]string, error) {
 			return nil, err
 		}
 		// Read kconfig
-		raw, err = ioutil.ReadFile("/host-boot/config-" + uname)
+		raw, err = ioutil.ReadFile(source.BootDir.Path("config-" + uname))
 		if err != nil {
 			return nil, err
 		}

source/kernel/selinux.go

@@ -19,11 +19,13 @@ package kernel
 import (
 	"fmt"
 	"io/ioutil"
+
+	"sigs.k8s.io/node-feature-discovery/source"
 )
 
 // Detect if selinux has been enabled in the kernel
 func SelinuxEnabled() (bool, error) {
-	status, err := ioutil.ReadFile("/host-sys/fs/selinux/enforce")
+	status, err := ioutil.ReadFile(source.SysfsDir.Path("fs/selinux/enforce"))
 	if err != nil {
 		return false, fmt.Errorf("Failed to detect the status of selinux, please check if the system supports selinux and make sure /sys on the host is mounted into the container: %s", err.Error())
 	}

source/system/system.go

@@ -66,7 +66,7 @@ func (s Source) Discover() (source.Features, error) {
 func parseOSRelease() (map[string]string, error) {
 	release := map[string]string{}
 
-	f, err := os.Open("/host-etc/os-release")
+	f, err := os.Open(source.EtcDir.Path("os-release"))
 	if err != nil {
 		return nil, err
 	}