How to implement a Linux Cloud Storage sync with placeholder files

On Windows, Microsoft offers their Cloud Filter API (parts of which are implemented in the Windows Kernel as the CldFlt Windows Cloud Files Mini Filter Driver), which provides for an interface for cloud storage integration with features similar to Microsoft's OneDrive. AFAIK, Linux doesn't offer anything quite like that (StackOverflow ). One of the most useful features of the Cloud Filter API are the placeholder files, which allow the local file system to display files that will be downloaded from the cloud storage on access. This is a huge usability improvement over having to select specific folders to fully sync and download. It also enables space saving by removing unused files from local storage. Are there any cloud storage clients on Linux that implement such a feature and if so, how do they do that? To be clear, I am not looking for a specific piece of software, but I would like to understand how such a mechanism is implemented on Linux. Using libfuse might be an option, but it seems less than ideal, since it would require hiding the actual local storage folder from the user and serving a full 'fake' filesystem instead. (What if the daemon isn't running? Can the user access the locally stored files, or see the placeholders and be notified that the daemon is down?)