@Systems Engineer Thank you for your reply and the API. I don't know if fskit can solve my scenario (sorry I don't figure out the detail of fskit, can you add example code to demonstrate how these API work together?) I've two idea and want to see if user space file system can achieve it. The first one is I want to develop an app which can mount cloud storage (AWS S3 etc) on my macOS as file system directory, user can save data to the directory, and I can use end to end encrypt to protect user data then save it to cloud storage. The second one is I want filesystem has ability to quick revert file/folder to history version (like git, docker layer filesystem or APFS snapshot, but APFS snapshot is the whole volume). with this ability, my app can batch process media like audio/video with multi steps, if something is not what I want, I can quick revert to history version.