REVA on CephFS

<!--HTML-->CephFS is a distributed file system based on the popular storage system Ceph. This filesystem is a scalable system with POSIX features that makes it a compelling candidate for a Sync&Share backend. Sync&Share applications have a lot of users interacting with them, doing constant I/O tasks. Therefore, the need for a filesystem that can handle this I/O load is necessary. Even if the performance part is important, Sync & Share applications have a lot of features that improve the QoL of the system, for example, ACLs, file versions, fast file discovery for synchronisation and so on. We present a proof of concept module of CephFS on REVA, to evaluate whether this filesystem can fully support a Sync & Share application or not. This module is currently implemented using a local filesystem module, where the operations are performed on a file path using the tools that the Linux OSes provide. The CephFS module of REVA currently supports recursive mtime propagation for the fast detection of the files that changed. It also provides file versions based on snapshots, with the current limitation that the file versions are fixed based on a time difference rather than I/O based. Other features such as ACLs, or using a CephFS client instead of an OS interface are not present, but can easily be implemented. This proof of concept shows promising results and we firmly believe that with some minor changes it can support a Sync & Share application.