add support for getting path to backend, where supported (#331)

Signed-off-by: Avi Deitcher <[email protected]>

Author: deitch

backend/file/file.go

@@ -12,10 +12,11 @@ import (
 
 type rawBackend struct {
 	storage  fs.File
+	path     string
 	readOnly bool
 }
 
-// Create a backend.Storage from provided fs.File
+// Create a backend.Storage from provided fs.File. Will not store any path.
 func New(f fs.File, readOnly bool) backend.Storage {
 	return rawBackend{
 		storage:  f,
@@ -49,6 +50,7 @@ func OpenFromPath(pathName string, readOnly bool) (backend.Storage, error) {
 	return rawBackend{
 		storage:  f,
 		readOnly: readOnly,
+		path:     pathName,
 	}, nil
 }
 
@@ -74,6 +76,7 @@ func CreateFromPath(pathName string, size int64) (backend.Storage, error) {
 	return rawBackend{
 		storage:  f,
 		readOnly: false,
+		path:     pathName,
 	}, nil
 }
 
@@ -125,3 +128,7 @@ func (f rawBackend) Seek(offset int64, whence int) (int64, error) {
 	}
 	return -1, backend.ErrNotSuitable
 }
+
+func (f rawBackend) Path() string {
+	return f.path
+}

backend/interface.go

@@ -30,4 +30,6 @@ type Storage interface {
 	Sys() (*os.File, error)
 	// file for read-write operations
 	Writable() (WritableFile, error)
+	// Path returns the path to the underlying storage, if any; returns empty string if not applicable
+	Path() string
 }

backend/substorage.go

@@ -10,13 +10,15 @@ type SubStorage struct {
 	underlying Storage
 	offset     int64
 	size       int64
+	path       string
 }
 
 func Sub(u Storage, offset, size int64) Storage {
 	return SubStorage{
 		underlying: u,
 		offset:     offset,
 		size:       size,
+		path:       u.Path(),
 	}
 }
 
@@ -76,6 +78,10 @@ func (s SubStorage) Writable() (WritableFile, error) {
 	}, nil
 }
 
+func (s SubStorage) Path() string {
+	return s.path
+}
+
 type subWritable struct {
 	underlying WritableFile
 	offset     int64