Arch Linux

foowtf

Member

Registered: 2015-08-12

Posts: 4

overlay fs: NFS as a lowerdir

I want to mount an overlay fs with a read-only NFS as lowerdir and an ext4 fs as upperdir/workdir.
I am using the Arch Linux stock kernel and have about the following folder hierarchy:

|- ro <- NFS is mounted here
|--|- folder
|- rw <- ext4 is mounted here
|--|- root
|--|- work
|- merged <- overlay is mounted here

When I mount with

# mount -t overlay overlay -o lowerdir=/ro,upperdir=/rw/root,workdir=/rw/work /merged

then I can successfully execute

# touch /merged/file

However, open(2)s and mkdir(2)s on lower levels fail with ‘Operation not supported’:

# touch /merged/folder/file
# mkdir /merged/folder/folder

This seems to be the same problem the person here has: http://www.gossamer-threads.com/lists/l … el/2529909

The NFS share options are (ro,no_root_squash,async). I also tested this setup with a tmpfs as lowerdir and it works as expected. NFS as lowerdir was declared functional in the thread here: https://www.mail-archive.com/linux-unio … 00364.html , but the linked post in particular does not demonstrate accesses to subdirectories.

So does this work in general? What must I do differently?