Fix extended attributes handling for VSS snapshots

internal/fs/ea_windows.go

@@ -8,6 +8,7 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"strings"
 	"syscall"
 	"unsafe"
 
@@ -298,3 +299,20 @@ func PathSupportsExtendedAttributes(path string) (supported bool, err error) {
 	supported = (fileSystemFlags & windows.FILE_SUPPORTS_EXTENDED_ATTRIBUTES) != 0
 	return supported, nil
 }
+
+// GetVolumePathName returns the volume path name for the given path.
+func GetVolumePathName(path string) (volumeName string, err error) {
+	utf16Path, err := windows.UTF16PtrFromString(path)
+	if err != nil {
+		return "", err
+	}
+	// Get the volume path (e.g., "D:")
+	var volumePath [windows.MAX_PATH + 1]uint16
+	err = windows.GetVolumePathName(utf16Path, &volumePath[0], windows.MAX_PATH+1)
+	if err != nil {
+		return "", err
+	}
+	// Trim any trailing backslashes
+	volumeName = strings.TrimRight(windows.UTF16ToString(volumePath[:]), "\\")
+	return volumeName, nil
+}

internal/restic/node_windows.go

@@ -407,40 +407,74 @@ func (node *Node) fillGenericAttributes(path string, fi os.FileInfo, stat *statT
 // checkAndStoreEASupport checks if the volume of the path supports extended attributes and stores the result in a map
 // If the result is already in the map, it returns the result from the map.
 func checkAndStoreEASupport(path string) (isEASupportedVolume bool, err error) {
-	// Check if it's an extended length path
-	if strings.HasPrefix(path, uncPathPrefix) {
-		// Convert \\?\UNC\ extended path to standard path to get the volume name correctly
-		path = `\\` + path[len(uncPathPrefix):]
-	} else if strings.HasPrefix(path, extendedPathPrefix) {
-		//Extended length path prefix needs to be trimmed to get the volume name correctly
-		path = path[len(extendedPathPrefix):]
-	} else if strings.HasPrefix(path, globalRootPrefix) {
-		// EAs are not supported for \\?\GLOBALROOT i.e. VSS snapshots
-		return false, nil
-	} else {
-		// Use the absolute path
-		path, err = filepath.Abs(path)
-		if err != nil {
-			return false, fmt.Errorf("failed to get absolute path: %w", err)
-		}
-	}
-	volumeName := filepath.VolumeName(path)
-	if volumeName == "" {
-		return false, nil
-	}
-	eaSupportedValue, exists := eaSupportedVolumesMap.Load(volumeName)
-	if exists {
-		return eaSupportedValue.(bool), nil
+	var volumeName string
+	volumeName, err = prepareVolumeName(path)
+	if err != nil {
+		return false, err
 	}
 
-	// Add backslash to the volume name to ensure it is a valid path
-	isEASupportedVolume, err = fs.PathSupportsExtendedAttributes(volumeName + `\`)
-	if err == nil {
-		eaSupportedVolumesMap.Store(volumeName, isEASupportedVolume)
+	if volumeName != "" {
+		// First check if the manually prepared volume name is already in the map
+		eaSupportedValue, exists := eaSupportedVolumesMap.Load(volumeName)
+		if exists {
+			return eaSupportedValue.(bool), nil
+		}
+		// If not found, check if EA is supported with manually prepared volume name
+		isEASupportedVolume, err = fs.PathSupportsExtendedAttributes(volumeName + `\`)
+		if err != nil {
+			return false, err
+		}
 	}
+	// If an entry is not found, get the actual volume name using the GetVolumePathName function
+	volumeNameActual, err := fs.GetVolumePathName(path)
+	if err != nil {
+		return false, err
+	}
+	if volumeNameActual != volumeName {
+		// If the actual volume name is different, check cache for the actual volume name
+		eaSupportedValue, exists := eaSupportedVolumesMap.Load(volumeNameActual)
+		if exists {
+			return eaSupportedValue.(bool), nil
+		}
+		// If the actual volume name is different and is not in the map, again check if the new volume supports extended attributes with the actual volume name
+		isEASupportedVolume, err = fs.PathSupportsExtendedAttributes(volumeNameActual + `\`)
+		if err != nil {
+			return false, err
+		}
+	}
+	eaSupportedVolumesMap.Store(volumeNameActual, isEASupportedVolume)
 	return isEASupportedVolume, err
 }
 
+// prepareVolumeName prepares the volume name for different cases in Windows
+func prepareVolumeName(path string) (volumeName string, err error) {
+	// Check if it's an extended length path
+	if strings.HasPrefix(path, globalRootPrefix) {
+		// Extract the VSS snapshot volume name eg. `\\?\GLOBALROOT\Device\HarddiskVolumeShadowCopyXX`
+		if parts := strings.SplitN(path, `\`, 7); len(parts) >= 6 {
+			volumeName = strings.Join(parts[:6], `\`)
+		} else {
+			volumeName = filepath.VolumeName(path)
+		}
+	} else {
+		if strings.HasPrefix(path, uncPathPrefix) {
+			// Convert \\?\UNC\ extended path to standard path to get the volume name correctly
+			path = `\\` + path[len(uncPathPrefix):]
+		} else if strings.HasPrefix(path, extendedPathPrefix) {
+			//Extended length path prefix needs to be trimmed to get the volume name correctly
+			path = path[len(extendedPathPrefix):]
+		} else {
+			// Use the absolute path
+			path, err = filepath.Abs(path)
+			if err != nil {
+				return "", fmt.Errorf("failed to get absolute path: %w", err)
+			}
+		}
+		volumeName = filepath.VolumeName(path)
+	}
+	return volumeName, nil
+}
+
 // windowsAttrsToGenericAttributes converts the WindowsAttributes to a generic attributes map using reflection
 func WindowsAttrsToGenericAttributes(windowsAttributes WindowsAttributes) (attrs map[GenericAttributeType]json.RawMessage, err error) {
 	// Get the value of the WindowsAttributes