Add support for feature flags

This change adds a features config that allows
individual features to be toggled at a global level. Each feature can (by default)
be controlled by an environment variable.

The GDS, MOFED, NVSWITCH, and GDRCOPY features are examples of such features.

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

internal/config/config.go

@@ -63,6 +63,9 @@ type Config struct {
 	NVIDIACTKConfig                  CTKConfig          `toml:"nvidia-ctk"`
 	NVIDIAContainerRuntimeConfig     RuntimeConfig      `toml:"nvidia-container-runtime"`
 	NVIDIAContainerRuntimeHookConfig RuntimeHookConfig  `toml:"nvidia-container-runtime-hook"`
+
+	// Features allows for finer control over optional features.
+	Features features `toml:"features,omitempty"`
 }
 
 // GetConfigFilePath returns the path to the config file for the configured system

internal/config/features.go

@@ -0,0 +1,85 @@
+/**
+# Copyright 2024 NVIDIA CORPORATION
+#
+# 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 config
+
+type featureName string
+
+const (
+	FeatureGDS      = featureName("gds")
+	FeatureMOFED    = featureName("mofed")
+	FeatureNVSWITCH = featureName("nvswitch")
+	FeatureGDRCopy  = featureName("gdrcopy")
+)
+
+// features specifies a set of named features.
+type features struct {
+	GDS      *feature `toml:"gds,omitempty"`
+	MOFED    *feature `toml:"mofed,omitempty"`
+	NVSWITCH *feature `toml:"nvswitch,omitempty"`
+	GDRCopy  *feature `toml:"gdrcopy,omitempty"`
+}
+
+type feature bool
+
+// IsEnabled checks whether a specified named feature is enabled.
+// An optional list of environments to check for feature-specific environment
+// variables can also be supplied.
+func (fs features) IsEnabled(n featureName, in ...getenver) bool {
+	featureEnvvars := map[featureName]string{
+		FeatureGDS:      "NVIDIA_GDS",
+		FeatureMOFED:    "NVIDIA_MOFED",
+		FeatureNVSWITCH: "NVIDIA_NVSWITCH",
+		FeatureGDRCopy:  "NVIDIA_GDRCOPY",
+	}
+
+	envvar := featureEnvvars[n]
+	switch n {
+	case FeatureGDS:
+		return fs.GDS.isEnabled(envvar, in...)
+	case FeatureMOFED:
+		return fs.MOFED.isEnabled(envvar, in...)
+	case FeatureNVSWITCH:
+		return fs.NVSWITCH.isEnabled(envvar, in...)
+	case FeatureGDRCopy:
+		return fs.GDRCopy.isEnabled(envvar, in...)
+	default:
+		return false
+	}
+}
+
+// isEnabled checks whether a feature is enabled.
+// If the enabled value is explicitly set, this is returned, otherwise the
+// associated envvar is checked in the specified getenver for the string "enabled"
+// A CUDA container / image can be passed here.
+func (f *feature) isEnabled(envvar string, ins ...getenver) bool {
+	if f != nil {
+		return bool(*f)
+	}
+	if envvar == "" {
+		return false
+	}
+	for _, in := range ins {
+		if in.Getenv(envvar) == "enabled" {
+			return true
+		}
+	}
+	return false
+}
+
+type getenver interface {
+	Getenv(string) string
+}