mount: use direct_io to avoid OS page cache

fix https://github.com/chrislusf/seaweedfs/issues/1752

weed/filesys/file.go

@@ -91,6 +91,9 @@ func (file *File) Getxattr(ctx context.Context, req *fuse.GetxattrRequest, resp
 func (file *File) Open(ctx context.Context, req *fuse.OpenRequest, resp *fuse.OpenResponse) (fs.Handle, error) {
 
 	glog.V(4).Infof("file %v open %+v", file.fullpath(), req)
+	if USE_DIRECT_IO {
+		resp.Flags |= fuse.OpenDirectIO
+	}
 
 	handle := file.wfs.AcquireHandle(file, req.Uid, req.Gid)
 

weed/filesys/file_darwin.go

@@ -0,0 +1,8 @@
+//+build darwin
+
+package filesys
+
+const (
+	USE_DIRECT_IO = false
+)
+

weed/filesys/file_other.go

@@ -0,0 +1,7 @@
+//+build !darwin
+
+package filesys
+
+const (
+	USE_DIRECT_IO = true
+)

weed/filesys/filehandle.go

@@ -90,8 +90,9 @@ func (fh *FileHandle) Read(ctx context.Context, req *fuse.ReadRequest, resp *fus
 		glog.Warningf("%s FileHandle Read %d: [%d,%d) size %d totalRead %d", fh.f.fullpath(), fh.handle, req.Offset, req.Offset+int64(req.Size), req.Size, totalRead)
 		totalRead = min(int64(len(buff)), totalRead)
 	}
-	// resp.Data = buff[:totalRead]
-	resp.Data = buff
+	if err == nil {
+		resp.Data = buff[:totalRead]
+	}
 
 	return err
 }