fuse/nodefs: don't crash if trying to rename nonexistent entry.

This could happen to unionfs with ClientInodes set, and manipulations
that skipped the backing store.  Added a test.

fuse/nodefs/fsops.go

@@ -304,6 +304,9 @@ func (c *rawBridge) Rename(input *fuse.RenameIn, oldName string, newName string)
 	oldParent := c.toInode(input.NodeId)
 
 	child := oldParent.GetChild(oldName)
+	if child == nil {
+		return fuse.ENOENT
+	}
 	if child.mountPoint != nil {
 		return fuse.EBUSY
 	}

fuse/pathfs/pathfs.go

@@ -567,8 +567,9 @@ func (n *pathInode) findChild(fi *fuse.Attr, name string, fullPath string) (out
 		out = n.createChild(fi.IsDir())
 		out.clientInode = fi.Ino
 		n.addChild(name, out)
+	} else {
+		// should add 'out' as a child to n ?
 	}
-
 	return out
 }
 

unionfs/unionfs_test.go

@@ -88,6 +88,7 @@ func setupUfs(t *testing.T) (workdir string, cleanup func()) {
 		EntryTimeout:    entryTtl / 2,
 		AttrTimeout:     entryTtl / 2,
 		NegativeTimeout: entryTtl / 2,
+		PortableInodes:  true,
 	}
 
 	pathfs := pathfs.NewPathNodeFs(ufs,
@@ -1491,3 +1492,30 @@ func TestUnionFsCheckHiddenFiles(t *testing.T) {
 		t.Fatal("unexpected names", names)
 	}
 }
+
+func TestUnionFSBarf(t *testing.T) {
+	wd, clean := setupUfs(t)
+	defer clean()
+
+	if err := os.Mkdir(wd+"/mnt/dir", 0755); err != nil {
+		t.Fatalf("os.Mkdir: %v", err)
+	}
+	if err := os.Mkdir(wd+"/mnt/dir2", 0755); err != nil {
+		t.Fatalf("os.Mkdir: %v", err)
+	}
+	if err := ioutil.WriteFile(wd+"/rw/dir/file", []byte("bla"), 0644); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+	if _, err := os.Lstat(wd+"/mnt/dir/file"); err != nil {
+		t.Fatalf("Lstat: %v", err)
+	}
+	if err := os.Rename(wd+"/rw/dir/file", wd+"/rw/file"); err != nil {
+		t.Fatalf("os.Rename: %v", err)
+	}
+
+	err := os.Rename(wd+"/mnt/file", wd+"/mnt/dir2/file")
+	if fuse.ToStatus(err) != fuse.ENOENT {
+		// TODO - this should just succeed?
+		t.Fatalf("os.Rename: %v", err)
+	}
+}