Read disk model and serial from udev data or sysfs on Linux

It reads model and serial data directly from files instead of using
`udevadm` command. This way obtaining the disk serial number doesn't
depend on command execution, and can be also possible even if udev or
udevadm are not available.

disk/disk_linux.go

@@ -3,10 +3,11 @@
 package disk
 
 import (
+	"bufio"
+	"bytes"
 	"context"
 	"fmt"
 	"io/ioutil"
-	"os/exec"
 	"path/filepath"
 	"strconv"
 	"strings"
@@ -385,26 +386,33 @@ func GetDiskSerialNumber(name string) string {
 }
 
 func GetDiskSerialNumberWithContext(ctx context.Context, name string) string {
-	n := fmt.Sprintf("--name=%s", name)
-	udevadm, err := exec.LookPath("/sbin/udevadm")
+	var stat unix.Stat_t
+	err := unix.Stat(name, &stat)
 	if err != nil {
 		return ""
 	}
+	major := unix.Major(stat.Rdev)
+	minor := unix.Minor(stat.Rdev)
 
-	out, err := invoke.CommandWithContext(ctx, udevadm, "info", "--query=property", n)
-
-	// does not return error, just an empty string
-	if err != nil {
-		return ""
-	}
-	lines := strings.Split(string(out), "\n")
-	for _, line := range lines {
-		values := strings.Split(line, "=")
-		if len(values) < 2 || values[0] != "ID_SERIAL" {
-			// only get ID_SERIAL, not ID_SERIAL_SHORT
-			continue
+	// Try to get the serial from udev data
+	udevDataPath := fmt.Sprintf("/run/udev/data/b%d:%d", major, minor)
+	if udevdata, err := ioutil.ReadFile(udevDataPath); err == nil {
+		scanner := bufio.NewScanner(bytes.NewReader(udevdata))
+		for scanner.Scan() {
+			values := strings.Split(scanner.Text(), "=")
+			if len(values) == 2 && values[0] == "E:ID_SERIAL" {
+				return values[1]
+			}
 		}
-		return values[1]
+	}
+
+	// Try to get the serial from sysfs, look at the disk device (minor 0) directly
+	// because if it is a partition it is not going to contain any device information
+	devicePath := fmt.Sprintf("/sys/dev/block/%d:0/device", major)
+	model, _ := ioutil.ReadFile(filepath.Join(devicePath, "model"))
+	serial, _ := ioutil.ReadFile(filepath.Join(devicePath, "serial"))
+	if len(model) > 0 && len(serial) > 0 {
+		return fmt.Sprintf("%s_%s", string(model), string(serial))
 	}
 	return ""
 }