overlayfs and inotify limitation with 4.9 kernel

[madisongh]

I'm noting this here, since we use overlayfs in the demo distro.

There is a limitation with overlayfs in kernels older than 4.14 that filesystem notifications (e.g., for inotify, or systemd .path units) don't work reliably on files that reside in an overlay - if cached inodes get flushed to reclaim memory, any notifications registered against those inodes will stop working. This is particularly noticeable on smaller-memory systems.

There is a repo with later overlayfs implementations back-ported to 4.9 in this repo set up by one of the overlayfs maintainers. The patches are extensive, since the code was restructured quite a bit in 4.13, but they mostly apply cleanly (not completely, thanks to some Android patches we have).