So here's the use case: lowerdir is an NFS mounted root filesystem (shared by a bunch of nodes). upperdir is a tmpfs RAM disk to allow for writes to happen. This works great with the caveat being I cannot make 'live' changes to the root filesystem, which poses the problem. Any access to a changed file causes a 'Stale file handle' error. With some experimenting, I've discovered that remounting the overlay filesystem (mount -o remount / /) registers any changes that have been made to the lower NFS filesystem. In addition, dumping cache (via /proc/sys/vm/drop_caches) also makes the stale file handle errors go away and reads pass through to the lower dir and correctly show changes. I'd like to make this use case feasible by allowing changes to the NFS lowerdir to work more or less transparently. It seems like if the overlay did not do any caching at all, all reads would fall through to either the upperdir ram disk or the NFS lower, which is precisely what I want. So, let me pose this somewhat naive question: Would it be possible to simply disable any cacheing performed by the overlay to force all reads to go to either the tmpfs upper or the (VFS-cached) NFS lower? Would this be enough to accomplish my goal of being able to change the lowerdir of an active overlayfs? -JE
