fs: Split out ClearCache from File

src/restic/fs/file.go

@@ -12,7 +12,4 @@ type File interface {
 	io.Closer
 
 	Stat() (os.FileInfo, error)
-
-	// ClearCache removes the file's content from the OS cache.
-	ClearCache() error
 }

src/restic/fs/file_all.go

@@ -6,15 +6,10 @@ import "os"
 
 // Open opens a file for reading.
 func Open(name string) (File, error) {
-	f, err := os.OpenFile(name, os.O_RDONLY, 0)
-	return osFile{File: f}, err
+	return os.OpenFile(name, os.O_RDONLY, 0)
 }
 
-// osFile wraps an *os.File and adds a no-op ClearCache() method.
-type osFile struct {
-	*os.File
-}
-
-func (osFile) ClearCache() error {
+// ClearCache syncs and then removes the file's content from the OS cache.
+func ClearCache(f File) error {
 	return nil
 }

src/restic/fs/file_linux.go

@@ -58,12 +58,17 @@ func (f *nonCachingFile) Read(p []byte) (int, error) {
 	return n, err
 }
 
-func (f *nonCachingFile) ClearCache() error {
-	err := f.File.Sync()
+// ClearCache syncs and then removes the file's content from the OS cache.
+func ClearCache(file File) error {
+	f, ok := file.(*os.File)
+	if !ok {
+		panic("ClearCache called for file not *os.File")
+	}
 
+	err := f.Sync()
 	if err != nil {
 		return err
 	}
 
-	return unix.Fadvise(int(f.File.Fd()), 0, 0, _POSIX_FADV_DONTNEED)
+	return unix.Fadvise(int(f.Fd()), 0, 0, _POSIX_FADV_DONTNEED)
 }