Add imex mode to CDI spec generation

This change adds a imex mode to CDI spec generation. This mode detected
generates CDI specifications for existing IMEX channels. By default these
devices have the fully qualified CDI device names:

nvidia.com/imex-channel=<ID>

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

pkg/nvcdi/lib-imex_test.go

@@ -0,0 +1,80 @@
+/**
+# 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 nvcdi
+
+import (
+	"bytes"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	testlog "github.com/sirupsen/logrus/hooks/test"
+	"github.com/stretchr/testify/require"
+
+	"github.com/NVIDIA/nvidia-container-toolkit/internal/test"
+)
+
+func TestImexMode(t *testing.T) {
+	t.Setenv("__NVCT_TESTING_DEVICES_ARE_FILES", "true")
+
+	logger, _ := testlog.NewNullLogger()
+
+	moduleRoot, err := test.GetModuleRoot()
+	require.NoError(t, err)
+	hostRoot := filepath.Join(moduleRoot, "testdata", "lookup", "rootfs-1")
+
+	expectedSpec := `---
+cdiVersion: 0.5.0
+containerEdits:
+  env:
+  - NVIDIA_VISIBLE_DEVICES=void
+devices:
+- containerEdits:
+    deviceNodes:
+    - hostPath: {{ .hostRoot }}/dev/nvidia-caps-imex-channels/channel0
+      path: /dev/nvidia-caps-imex-channels/channel0
+  name: "0"
+- containerEdits:
+    deviceNodes:
+    - hostPath: {{ .hostRoot }}/dev/nvidia-caps-imex-channels/channel1
+      path: /dev/nvidia-caps-imex-channels/channel1
+  name: "1"
+- containerEdits:
+    deviceNodes:
+    - hostPath: {{ .hostRoot }}/dev/nvidia-caps-imex-channels/channel2047
+      path: /dev/nvidia-caps-imex-channels/channel2047
+  name: "2047"
+kind: nvidia.com/imex-channel
+`
+	expectedSpec = strings.ReplaceAll(expectedSpec, "{{ .hostRoot }}", hostRoot)
+
+	lib, err := New(
+		WithLogger(logger),
+		WithMode(ModeImex),
+		WithDriverRoot(hostRoot),
+	)
+	require.NoError(t, err)
+
+	spec, err := lib.GetSpec()
+	require.NoError(t, err)
+
+	var b bytes.Buffer
+
+	_, err = spec.WriteTo(&b)
+	require.NoError(t, err)
+	require.Equal(t, expectedSpec, b.String())
+}