Skip EA processing for volumes that do not support EA

internal/fs/ea_windows.go

@@ -53,6 +53,15 @@ var (
 	errInvalidEaBuffer = errors.New("invalid extended attribute buffer")
 	errEaNameTooLarge  = errors.New("extended attribute name too large")
 	errEaValueTooLarge = errors.New("extended attribute value too large")
+
+	kernel32dll = syscall.NewLazyDLL("kernel32.dll")
+
+	procGetVolumeInformationW = kernel32dll.NewProc("GetVolumeInformationW")
+)
+
+const (
+	// fileSupportsExtendedAttributes is a bitmask that indicates whether the file system supports extended attributes.
+	fileSupportsExtendedAttributes = 0x00000004
 )
 
 // ExtendedAttribute represents a single Windows EA.
@@ -283,3 +292,34 @@ func setFileEA(handle windows.Handle, iosb *ioStatusBlock, buf *uint8, bufLen ui
 	status = ntStatus(r0)
 	return
 }
+
+// PathSupportsExtendedAttributes returns true if the path supports extended attributes.
+func PathSupportsExtendedAttributes(path string) (bool, error) {
+	var (
+		volumeName      [syscall.MAX_PATH + 1]uint16
+		fsName          [syscall.MAX_PATH + 1]uint16
+		volumeSerial    uint32
+		maxComponentLen uint32
+		fileSystemFlags uint32
+	)
+	utf16Path, err := windows.UTF16PtrFromString(path)
+	if err != nil {
+		return false, err
+	}
+	ret, _, err := procGetVolumeInformationW.Call(
+		uintptr(unsafe.Pointer(utf16Path)),
+		uintptr(unsafe.Pointer(&volumeName[0])),
+		uintptr(len(volumeName)),
+		uintptr(unsafe.Pointer(&volumeSerial)),
+		uintptr(unsafe.Pointer(&maxComponentLen)),
+		uintptr(unsafe.Pointer(&fileSystemFlags)),
+		uintptr(unsafe.Pointer(&fsName[0])),
+		uintptr(len(fsName)),
+	)
+	if ret == 0 {
+		return false, err
+	}
+
+	supportsEAs := (fileSystemFlags & fileSupportsExtendedAttributes) != 0
+	return supportsEAs, nil
+}

internal/restic/node_windows.go

@@ -32,6 +32,9 @@ var (
 	modAdvapi32     = syscall.NewLazyDLL("advapi32.dll")
 	procEncryptFile = modAdvapi32.NewProc("EncryptFileW")
 	procDecryptFile = modAdvapi32.NewProc("DecryptFileW")
+
+	// eaUnsupportedVolumesMap is a map of volumes that do not support extended attributes.
+	eaUnsupportedVolumesMap = map[string]bool{}
 )
 
 // mknod is not supported on Windows.
@@ -358,7 +361,20 @@ func (node *Node) fillGenericAttributes(path string, fi os.FileInfo, stat *statT
 		// Also do not allow processing of extended attributes for ADS.
 		return false, nil
 	}
-	if !strings.HasSuffix(filepath.Clean(path), `\`) {
+	if strings.HasSuffix(filepath.Clean(path), `\`) {
+		// This path is a volume
+		supportsEAs, err := fs.PathSupportsExtendedAttributes(path)
+		if err != nil {
+			return false, err
+		}
+		if supportsEAs {
+			delete(eaUnsupportedVolumesMap, filepath.VolumeName(path))
+		} else {
+			// Add the volume to the map of volumes that do not support extended attributes.
+			eaUnsupportedVolumesMap[filepath.VolumeName(path)] = true
+		}
+		return supportsEAs, nil
+	} else {
 		// Do not process file attributes and created time for windows directories like
 		// C:, D:
 		// Filepath.Clean(path) ends with '\' for Windows root drives only.
@@ -375,8 +391,8 @@ func (node *Node) fillGenericAttributes(path string, fi os.FileInfo, stat *statT
 			FileAttributes:     &stat.FileAttributes,
 			SecurityDescriptor: sd,
 		})
+		return !eaUnsupportedVolumesMap[filepath.VolumeName(path)], err
 	}
-	return true, err
 }
 
 // windowsAttrsToGenericAttributes converts the WindowsAttributes to a generic attributes map using reflection