fix: handle dangling symlink in config-manager updateSymlink

cmd/config-manager/main.go

@@ -17,6 +17,7 @@
 package main
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -398,29 +399,18 @@ func updateSymlink(config string, f *Flags) (bool, error) {
 		src = filepath.Join(f.ConfigFileSrcdir, config)
 	}
 
-	exists, err := fileExists(f.ConfigFileDst)
-	if err != nil {
-		return false, fmt.Errorf("error checking if file '%s' exists: %v", f.ConfigFileDst, err)
-	}
-	if exists {
-		srcRealpath, err := filepath.EvalSymlinks(src)
-		if err != nil {
-			return false, fmt.Errorf("error evaluating realpath of '%v': %v", src, err)
-		}
-
-		dstRealpath, err := filepath.EvalSymlinks(f.ConfigFileDst)
-		if err != nil {
-			return false, fmt.Errorf("error evaluating realpath of '%v': %v", f.ConfigFileDst, err)
-		}
-
-		if srcRealpath == dstRealpath {
+	current, err := os.Readlink(f.ConfigFileDst)
+	if err == nil {
+		if current == src {
 			return false, nil
 		}
+	} else if !os.IsNotExist(err) && !errors.Is(err, syscall.EINVAL) {
+		return false, fmt.Errorf("error reading symlink '%s': %v", f.ConfigFileDst, err)
+	}
 
-		err = os.Remove(f.ConfigFileDst)
-		if err != nil {
-			return false, fmt.Errorf("error removing existing config: %v", err)
-		}
+	err = os.Remove(f.ConfigFileDst)
+	if err != nil && !os.IsNotExist(err) {
+		return false, fmt.Errorf("error removing existing config: %v", err)
 	}
 
 	err = os.Symlink(src, f.ConfigFileDst)
@@ -463,17 +453,6 @@ func findPidToSignal(f *Flags) (int, error) {
 	return -1, fmt.Errorf("no process found")
 }
 
-func fileExists(filename string) (bool, error) {
-	info, err := os.Stat(filename)
-	if os.IsNotExist(err) {
-		return false, nil
-	}
-	if err != nil {
-		return false, err
-	}
-	return !info.IsDir(), nil
-}
-
 func getConfigFileNameMap(f *Flags) (map[string]bool, error) {
 	files, err := os.ReadDir(f.ConfigFileSrcdir)
 	if err != nil {

cmd/config-manager/main_test.go

@@ -0,0 +1,67 @@
+/**
+# Copyright (c) NVIDIA CORPORATION.  All rights reserved.
+#
+# 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 main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func newTestFlags(srcdir, dst string) *Flags {
+	return &Flags{
+		ConfigFileSrcdir: srcdir,
+		ConfigFileDst:    dst,
+	}
+}
+
+func TestUpdateSymlinkDanglingDestination(t *testing.T) {
+	srcdir := t.TempDir()
+	dst := filepath.Join(t.TempDir(), "config.yaml")
+	f := newTestFlags(srcdir, dst)
+
+	testCases := []struct {
+		description string
+		config      string
+		wantChanged bool
+	}{
+		{
+			description: "create dangling symlink",
+			config:      "missing-config",
+			wantChanged: true,
+		},
+		{
+			description: "dangling symlink already pointing at config is a no operation",
+			config:      "missing-config",
+			wantChanged: false,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.description, func(t *testing.T) {
+			changed, err := updateSymlink(tc.config, f)
+			require.NoError(t, err)
+			require.Equal(t, tc.wantChanged, changed)
+		})
+	}
+
+	link, err := os.Readlink(dst)
+	require.NoError(t, err)
+	require.Equal(t, filepath.Join(srcdir, "missing-config"), link)
+}