feat: add -read flag to print current META config to stdout

README.md

@@ -1,6 +1,6 @@
-# Talos metadata writer tool
+# Talos metadata tool
 
-Tool for writing network metadata in the Talos META partition.
+Tool for reading and writing network metadata in the Talos META partition.
 
 Doc: https://docs.siderolabs.com/talos/v1.13/platform-specific-installations/bare-metal-platforms/metal-network-configuration
 
@@ -12,6 +12,9 @@ GOOS=linux GOARCH=amd64 go build -o talos-meta-tool .
 
 Usage:
 ```bash
+# read current config
+talos-meta-tool -device /dev/sda -read
+
 # write config from file
 talos-meta-tool -device /dev/sda -config config.yaml
 

main.go

@@ -89,6 +89,18 @@ func writeConfig(dev interface{ io.ReaderAt; io.WriterAt }, configData []byte) e
 	return nil
 }
 
+func readConfig(dev io.ReaderAt) ([]byte, error) {
+	adv, err := talos.NewADV(io.NewSectionReader(dev, 0, int64(talos.Size)))
+	if err != nil {
+		return nil, fmt.Errorf("loading ADV: %w", err)
+	}
+	data, ok := adv.ReadTagBytes(FixedTag)
+	if !ok {
+		return nil, fmt.Errorf("tag %#x not found", FixedTag)
+	}
+	return data, nil
+}
+
 func loadConfig(path, envVar string, b64 bool) ([]byte, error) {
 	if envVar != "" {
 		val, ok := os.LookupEnv(envVar)
@@ -119,18 +131,23 @@ func loadConfig(path, envVar string, b64 bool) ([]byte, error) {
 
 func main() {
 	devicePath := flag.String("device", "", "Path to the disk device (e.g., /dev/sda)")
+	read := flag.Bool("read", false, "Read and print the current configuration from the META partition")
 	configPath := flag.String("config", "", "Path to the configuration file (e.g., config.yaml)")
 	configEnv := flag.String("config-env", "", "Name of the environment variable containing the configuration")
 	configEnvBase64 := flag.Bool("config-env-base64", false, "Decode the -config-env value as base64 before use")
 	skipValidation := flag.Bool("skip-validation", false, "Skip schema validation of the configuration file")
 	flag.Parse()
 
 	if *devicePath == "" {
-		fmt.Fprintln(os.Stderr, "Usage: talos-meta-tool -device <disk-device> (-config <file> | -config-env <VAR> [-config-env-base64])")
+		fmt.Fprintln(os.Stderr, "Usage: talos-meta-tool -device <disk-device> (-read | -config <file> | -config-env <VAR> [-config-env-base64])")
 		os.Exit(1)
 	}
-	if *configPath == "" && *configEnv == "" {
-		fmt.Fprintln(os.Stderr, "Usage: talos-meta-tool -device <disk-device> (-config <file> | -config-env <VAR> [-config-env-base64])")
+	if !*read && *configPath == "" && *configEnv == "" {
+		fmt.Fprintln(os.Stderr, "Usage: talos-meta-tool -device <disk-device> (-read | -config <file> | -config-env <VAR> [-config-env-base64])")
+		os.Exit(1)
+	}
+	if *read && (*configPath != "" || *configEnv != "") {
+		fmt.Fprintln(os.Stderr, "Error: -read is mutually exclusive with -config and -config-env")
 		os.Exit(1)
 	}
 	if *configPath != "" && *configEnv != "" {
@@ -142,7 +159,12 @@ func main() {
 		os.Exit(1)
 	}
 
-	device, err := os.OpenFile(*devicePath, os.O_RDWR, 0)
+	openMode := os.O_RDWR
+	if *read {
+		openMode = os.O_RDONLY
+	}
+
+	device, err := os.OpenFile(*devicePath, openMode, 0)
 	if err != nil {
 		log.Fatalf("Error opening device: %v", err)
 	}
@@ -153,6 +175,15 @@ func main() {
 		log.Fatalf("Error: %v", err)
 	}
 
+	if *read {
+		data, err := readConfig(meta)
+		if err != nil {
+			log.Fatalf("Error reading config: %v", err)
+		}
+		fmt.Print(string(data))
+		return
+	}
+
 	configData, err := loadConfig(*configPath, *configEnv, *configEnvBase64)
 	if err != nil {
 		log.Fatalf("loading configuration: %v", err)

main_test.go

@@ -390,3 +390,36 @@ func TestWriteConfigFullDisk(t *testing.T) {
 		t.Fatalf("tag value: got %q, want %q", got, payload)
 	}
 }
+
+func TestReadConfigRoundTrip(t *testing.T) {
+	f := newTestFile(t)
+
+	payload := []byte("key: value\n")
+
+	if err := writeConfig(f, payload); err != nil {
+		t.Fatalf("writeConfig: %v", err)
+	}
+
+	got, err := readConfig(f)
+	if err != nil {
+		t.Fatalf("readConfig: %v", err)
+	}
+
+	if !bytes.Equal(got, payload) {
+		t.Fatalf("readConfig: got %q, want %q", got, payload)
+	}
+}
+
+func TestReadConfigEmpty(t *testing.T) {
+	f := newTestFile(t)
+
+	if _, err := readConfig(f); err == nil {
+		t.Fatal("expected error reading from empty ADV, got nil")
+	}
+}
+
+func TestReadConfigBadDevice(t *testing.T) {
+	if _, err := readConfig(errDevice{}); err == nil {
+		t.Fatal("expected error for bad device, got nil")
+	}
+}