To support overlayfs [1], a filesystem must meet a number of requirements (checked by the overlayfs driver at runtime):

• Support RENAME_WHITEOUT and RENAME_EXCHANGE [2]
• Do not implement a custom d_compare() method

Optionally, the filesystem may implement the following for performance improvements:

• O_TMPFILE support
• reflinks

We should implement the minimum features required to support Lustre as both an upper and lower layer on overlayfs. This can provide significant acceleration to container workloads (like podman) otherwise would have to use fuse-overlayfs to give containers a read/write view of host filesystems.

[1] https://www.kernel.org/doc/html/latest/filesystems/overlayfs.html

[2] https://www.man7.org/linux/man-pages/man2/rename.2.html