Bcachefs lead developer Kent Overstreet posted ap atch series today enabling use of the OverlayFS file-system in cojunction with an underlying file-system supporting case-folding for case insensitive files/folders/

With this patch series to support case-folded file-systems, it's wired up through for Bcachefs for its case insensitive support. Kent commented on the [1]patch series :

"This series allows overlayfs and casefolding to safely be used on the same filesystem by providing exclusion to ensure that overlayfs never has to deal with casefolded directories.

Currently, overlayfs can't be used _at all_ if a filesystem even supports casefolding, which is really nasty for users.

Components:

- filesystem has to track, for each directory, "does any _descendent_ have casefolding enabled"

- new inode flag to pass this to VFS layer

- new dcache methods for providing refs for overlayfs, and filesystem methods for safely clearing this flag

- new superblock flag for indicating to overlayfs & dcache "filesystem supports casefolding, it's safe to use provided new dcache methods are used""

The OverlayFS union mount file-system is commonly used for live Linux images, IoT/embedded devices, and similar purposes.



[1] https://lore.kernel.org/lkml/20250520051600.1903319-1-kent.overstreet@linux.dev/