backup: convert reject funcs to use FS interface

Depending on parameters the paths in a snapshot do not directly
correspond to real paths on the filesystem. Therefore, reject funcs must
use the FS interface to work correctly.

internal/fs/fs_local.go

@@ -46,6 +46,12 @@ func (fs Local) Lstat(name string) (os.FileInfo, error) {
 	return os.Lstat(fixpath(name))
 }
 
+// DeviceID extracts the DeviceID from the given FileInfo. If the fs does
+// not support a DeviceID, it returns an error instead
+func (fs Local) DeviceID(fi os.FileInfo) (deviceID uint64, err error) {
+	return DeviceID(fi)
+}
+
 // Join joins any number of path elements into a single path, adding a
 // Separator if necessary. Join calls Clean on the result; in particular, all
 // empty strings are ignored. On Windows, the result is a UNC path if and only

internal/fs/fs_reader.go

@@ -122,6 +122,10 @@ func (fs *Reader) Lstat(name string) (os.FileInfo, error) {
 	return nil, pathError("lstat", name, os.ErrNotExist)
 }
 
+func (fs *Reader) DeviceID(_ os.FileInfo) (deviceID uint64, err error) {
+	return 0, errors.New("Device IDs are not supported")
+}
+
 // Join joins any number of path elements into a single path, adding a
 // Separator if necessary. Join calls Clean on the result; in particular, all
 // empty strings are ignored. On Windows, the result is a UNC path if and only

internal/fs/interface.go

@@ -10,6 +10,7 @@ type FS interface {
 	OpenFile(name string, flag int, perm os.FileMode) (File, error)
 	Stat(name string) (os.FileInfo, error)
 	Lstat(name string) (os.FileInfo, error)
+	DeviceID(fi os.FileInfo) (deviceID uint64, err error)
 
 	Join(elem ...string) string
 	Separator() string