fuse/pathfs: fix LookupKnownChildren I/O errors

There was a thinko in PathFS.Lookup: if GetAttr returns OK, we did not
copy the attribute if there was a known child with that name. This
lead returning status OK, with a zeroed out Attr structure. The 0 mode
would sometimes lead to I/O errors, as files without type are not
allowed.

Fixes #239

fuse/pathfs/pathfs.go

@@ -545,14 +545,15 @@ func (n *pathInode) Lookup(out *fuse.Attr, name string, context *fuse.Context) (
 	fullPath := filepath.Join(n.GetPath(), name)
 	fi, code := n.fs.GetAttr(fullPath, context)
 	node := n.Inode().GetChild(name)
-
 	if node != nil && (!code.Ok() || node.IsDir() != fi.IsDir()) {
 		n.Inode().RmChild(name)
 		node = nil
 	}
 
-	if code.Ok() && node == nil {
-		node = n.findChild(fi, name, fullPath).Inode()
+	if code.Ok() {
+		if node == nil {
+			node = n.findChild(fi, name, fullPath).Inode()
+		}
 		*out = *fi
 	}
 

fuse/test/loopback_test.go

@@ -933,3 +933,26 @@ func TestChgrp(t *testing.T) {
 		t.Errorf("Chown failed: %v", err)
 	}
 }
+
+func TestLookupKnownChildrenAttrCopied(t *testing.T) {
+	tc := NewTestCase(t)
+	defer tc.Cleanup()
+
+	if err := ioutil.WriteFile(tc.mountFile, []byte("hello"), 0644); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	fi, err := os.Lstat(tc.mountFile)
+	if err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+	mode := fi.Mode()
+	time.Sleep(2 * testTtl)
+
+	if fi, err = os.Lstat(tc.mountFile); err != nil {
+		t.Fatalf("Lstat: %v", err)
+	} else if fi.Mode() != mode {
+		t.Fatalf("got mode %o, want %o", fi.Mode(), mode)
+	}
+
+}