add writeback test

Signed-off-by: jiefenghuang <[email protected]>

fuse/test/writeback_test.go

@@ -0,0 +1,91 @@
+//go:build linux
+// +build linux
+
+// Copyright 2024 the Go-FUSE Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+	"github.com/hanwen/go-fuse/v2/fuse/nodefs"
+	"github.com/hanwen/go-fuse/v2/internal/testutil"
+)
+
+type writebackFS struct {
+	nodefs.Node
+	writeCnt int
+}
+
+func newWritebackFS() *writebackFS {
+	return &writebackFS{
+		Node: nodefs.NewDefaultNode(),
+	}
+}
+
+func (fs *writebackFS) Open(flags uint32, context *fuse.Context) (file nodefs.File, code fuse.Status) {
+	return nil, fuse.OK
+}
+
+func (fs *writebackFS) Write(file nodefs.File, data []byte, off int64, context *fuse.Context) (written uint32, code fuse.Status) {
+	fs.writeCnt++
+	return uint32(len(data)), fuse.OK
+}
+
+func TestWriteback(t *testing.T) {
+	dir := t.TempDir()
+
+	root := nodefs.NewDefaultNode()
+	opts := nodefs.NewOptions()
+	opts.Debug = testutil.VerboseTest()
+
+	mountOpts := &fuse.MountOptions{
+		EnableWriteback: true,
+	}
+	if opts != nil && opts.Debug {
+		mountOpts.Debug = opts.Debug
+	}
+
+	srv, _, err := nodefs.Mount(dir, root, mountOpts, opts)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	fileName := "writeback.txt"
+	node := newWritebackFS()
+	root.Inode().NewChild(fileName, false, node)
+
+	go srv.Serve()
+	if err := srv.WaitMount(); err != nil {
+		t.Fatal("WaitMount", err)
+	}
+	defer func() {
+		err := srv.Unmount()
+		if err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	path := filepath.Join(dir, fileName)
+	f, err := os.OpenFile(path, os.O_WRONLY, 0644)
+	if err != nil {
+		t.Fatalf("OpenFile %s: %v", path, err)
+	}
+	defer f.Close()
+
+	cnt := 10
+	for i := 0; i < cnt; i++ {
+		if _, err = f.Write([]byte("1")); err != nil {
+			t.Fatalf("Write: %v", err)
+		}
+	}
+
+	if node.writeCnt >= cnt {
+		t.Fatalf("write count: got %d; want < %d", node.writeCnt, cnt)
+	}
+}