Expose opt-in features in toolkit-container

This change enables opt-in (off-by-default) features to be opted into.
These features can be toggled by name by specifying the (repeated)
--opt-in-feature command line argument or as a comma-separated list
in the NVIDIA_CONTAINER_TOOLKIT_OPT_IN_FEATURES environment variable.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

tools/container/toolkit/toolkit.go

@@ -81,6 +81,8 @@ type options struct {
 	acceptNVIDIAVisibleDevicesAsVolumeMounts   bool
 
 	ignoreErrors bool
+
+	optInFeatures cli.StringSlice
 }
 
 func main() {
@@ -250,6 +252,12 @@ func main() {
 			Destination: &opts.createDeviceNodes,
 			EnvVars:     []string{"CREATE_DEVICE_NODES"},
 		},
+		&cli.StringSliceFlag{
+			Name:        "opt-in-feature",
+			Hidden:      true,
+			Destination: &opts.optInFeatures,
+			EnvVars:     []string{"NVIDIA_CONTAINER_TOOLKIT_OPT_IN_FEATURES"},
+		},
 	}
 
 	// Update the subcommand flags with the common subcommand flags
@@ -518,6 +526,10 @@ func installToolkitConfig(c *cli.Context, toolkitConfigPath string, nvidiaContai
 		"nvidia-container-runtime.runtimes":                      opts.ContainerRuntimeRuntimes,
 		"nvidia-container-cli.debug":                             opts.ContainerCLIDebug,
 	}
+	for _, feature := range opts.optInFeatures.Value() {
+		optionalConfigValues["features."+feature] = true
+	}
+
 	for key, value := range optionalConfigValues {
 		if !c.IsSet(key) {
 			log.Infof("Skipping unset option: %v", key)