fusefrontend: Handle PlaintextNames mode in Unlink

In PlaintextNames mode the "gocryptfs.longname." prefix does not have any
special meaning. We should not attempt to delete any .name files.

Partially fixes https://github.com/rfjakob/gocryptfs/issues/174

internal/fusefrontend/fs.go

@@ -388,7 +388,7 @@ func (fs *FS) Unlink(path string, context *fuse.Context) (code fuse.Status) {
 	}
 
 	cName := filepath.Base(cPath)
-	if nametransform.IsLongContent(cName) {
+	if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
 		var dirfd *os.File
 		dirfd, err = os.Open(filepath.Dir(cPath))
 		if err != nil {

tests/matrix/matrix_test.go

@@ -794,4 +794,21 @@ func TestMkfifo(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	err = os.Remove(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+// Make sure the Symlink call works with paths starting with "gocryptfs.longname."
+func TestSymlink(t *testing.T) {
+	path := test_helpers.DefaultPlainDir + "/gocryptfs.longname.XXX"
+	err := syscall.Symlink("target", path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = os.Remove(path)
+	if err != nil {
+		t.Fatal(err)
+	}
 }