Make it possible to override config options from command line

Implement new '--options' command line flag that can be used to specify
config options from command line. Options specified via this command
line flag will override those read from the config file. The same format
as in the config file must be used, that is, the flag value must be
valid YAML or JSON.

README.md

@@ -39,6 +39,7 @@ node-feature-discovery.
   Usage:
   node-feature-discovery [--no-publish] [--sources=<sources>] [--label-whitelist=<pattern>]
      [--oneshot | --sleep-interval=<seconds>] [--config=<path>]
+     [--options=<config>]
   node-feature-discovery -h | --help
   node-feature-discovery --version
 
@@ -47,6 +48,11 @@ node-feature-discovery.
   --version                   Output version and exit.
   --config=<path>             Config file to use.
                               [Default: /etc/kubernetes/node-feature-discovery/node-feature-discovery.conf]
+  --options=<config>          Specify config options from command line. Config
+                              options are specified in the same format as in the
+                              config file (i.e. json or yaml). These options
+                              will override settings read from the config file.
+                              [Default: ]
   --sources=<sources>         Comma separated list of feature sources.
                               [Default: cpuid,iommu,memory,network,pstate,rdt,selinux,storage]
   --no-publish                Do not publish discovered features to the
@@ -224,18 +230,25 @@ For example, if some node is tainted NoSchedule or fails to start a job for some
 
 [![asciicast](https://asciinema.org/a/11wir751y89617oemwnsgli4a.png)](https://asciinema.org/a/11wir751y89617oemwnsgli4a)
 
-### Configuration file
+### Configuration options
 
 NFD supports a configuration file. The default location is
 `/etc/kubernetes/node-feature-discovery/node-feature-discovery.conf`
 ,but, this can be changed by
 specifying the`--config` command line flag. The file is read inside the Docker
 image. Thus, Volumes and VolumeMounts are needed, or, a custom Docker image
-must be built in order to specify your settings.
+must be built in order to specify your settings via a configuration file.
 The (empty) [example config](https://github.com/kubernetes-incubator/node-feature-discovery/blob/master/node-feature-discovery.conf.example)
 is available in the NFD Docker image, which can be used as base in custom-built
 images.
 
+Configuration options can also be specified via the `--options` command line
+flag, in which case no mounts need to be used. The same format as in the config
+file must be used, i.e. YAML or JSON.
+
+Configuration options specified from the command line will override those read
+from the config file.
+
 ## Building from source
 
 Download the source code.

main.go

@@ -88,6 +88,7 @@ type Args struct {
 	labelWhiteList string
 	configFile     string
 	noPublish      bool
+	options        string
 	oneshot        bool
 	sleepInterval  time.Duration
 	sources        []string
@@ -108,6 +109,12 @@ func main() {
 		stderrLogger.Printf("Failed to read config file: %v", err)
 	}
 
+	// Parse config overrides from command line
+	err = yaml.Unmarshal([]byte(args.options), &config)
+	if err != nil {
+		stderrLogger.Printf("Failed to parse --options: %v", err)
+	}
+
 	// Configure the parameters for feature discovery.
 	enabledSources, labelWhiteList, err := configureParameters(args.sources, args.labelWhiteList)
 	if err != nil {
@@ -147,6 +154,7 @@ func argsParse(argv []string) (args Args) {
   Usage:
   %s [--no-publish] [--sources=<sources>] [--label-whitelist=<pattern>]
      [--oneshot | --sleep-interval=<seconds>] [--config=<path>]
+     [--options=<config>]
   %s -h | --help
   %s --version
 
@@ -155,6 +163,11 @@ func argsParse(argv []string) (args Args) {
   --version                   Output version and exit.
   --config=<path>             Config file to use.
                               [Default: /etc/kubernetes/node-feature-discovery/node-feature-discovery.conf]
+  --options=<config>          Specify config options from command line. Config
+                              options are specified in the same format as in the
+                              config file (i.e. json or yaml). These options
+                              will override settings read from the config file.
+                              [Default: ]
   --sources=<sources>         Comma separated list of feature sources.
                               [Default: cpuid,iommu,memory,network,pstate,rdt,selinux,storage]
   --no-publish                Do not publish discovered features to the
@@ -178,6 +191,7 @@ func argsParse(argv []string) (args Args) {
 	var err error
 	args.configFile = arguments["--config"].(string)
 	args.noPublish = arguments["--no-publish"].(bool)
+	args.options = arguments["--options"].(string)
 	args.sources = strings.Split(arguments["--sources"].(string), ",")
 	args.labelWhiteList = arguments["--label-whitelist"].(string)
 	args.oneshot = arguments["--oneshot"].(bool)
@@ -202,6 +216,7 @@ func configParse(filepath string) error {
 		return err
 	}
 
+	// Read config file
 	err = yaml.Unmarshal(data, &config)
 	if err != nil {
 		return err