Test and fix truncate on open file.

fuse/memnode.go

@@ -178,13 +178,17 @@ func (me *memNode) GetAttr(file File, context *Context) (fi *os.FileInfo, code S
 
 func (me *memNode) Truncate(file File, size uint64, context *Context) (code Status) {
 	if file != nil {
-		return file.Truncate(size)
+		code = file.Truncate(size)
+	} else {
+		err := os.Truncate(me.filename(), int64(size))
+		code = ToStatus(err)
 	}
-
-	me.info.Size = int64(size)
-	err := os.Truncate(me.filename(), int64(size))
-	me.info.Ctime_ns = time.Nanoseconds()
-	return ToStatus(err)
+	if code.Ok() {
+		me.info.Ctime_ns = time.Nanoseconds()
+		// TODO - should update mtime too?
+		me.info.Size = int64(size)
+	}
+	return code
 }
 
 func (me *memNode) Utimens(file File, atime uint64, mtime uint64, context *Context) (code Status) {

fuse/memnode_test.go

@@ -58,3 +58,21 @@ func TestMemNodeFs(t *testing.T) {
 		t.Fatalf("Readdir got %v, expected 1 file named 'test'", entries)
 	}
 }
+
+func TestMemNodeSetattr(t *testing.T) {
+	wd, _, clean := setupMemNodeTest(t)
+	defer clean()
+
+	f, err := os.OpenFile(wd+"/test", os.O_CREATE|os.O_WRONLY, 0644)
+	CheckSuccess(err)
+	defer f.Close()
+
+	err = f.Truncate(4096)
+	CheckSuccess(err)
+
+	fi, err := f.Stat()
+	CheckSuccess(err)
+	if fi.Size != 4096 {
+		t.Errorf("Size should be 4096 after Truncate: %d", fi.Size)
+	}
+}