Populate Block count in GetAttr result.

This fixes 'du'.

Fixes #159.

zipfs/memtree.go

@@ -114,6 +114,7 @@ func (n *memNode) GetAttr(out *fuse.Attr, file nodefs.File, context *fuse.Contex
 		return fuse.OK
 	}
 	n.file.Stat(out)
+	out.Blocks = (out.Size + 511) / 512
 	return fuse.OK
 }
 

zipfs/zipfs_test.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"syscall"
 	"testing"
 	"time"
 
@@ -72,6 +73,10 @@ func TestZipFs(t *testing.T) {
 	if fi.Mode() != 0664 {
 		t.Fatalf("File mode 0%o != 0664", fi.Mode())
 	}
+	if st := fi.Sys().(*syscall.Stat_t); st.Blocks != 1 {
+		t.Errorf("got block count %d, want 1", st.Blocks)
+	}
+
 	mtime, err := time.Parse(time.RFC3339, "2011-02-22T12:56:12Z")
 	if err != nil {
 		panic(err)