Since a long time, I've tried using NFS v4 for the nfsroot. This did not worked since FAI uses overlayfs for making the read-only nfsroot writeable. Therefore FAI force a NFS v3 mount for the nfsroot which works nicely.
But now it's possible to use NFSv4. I put some effort in debugging the setup, and asked the overlayfs maintainers for help. It's a complicated mixture of NFS and acl support (POSIX and nfs4 acl) and what overlayfs expects from the filesystems in respect to certain xattr. There may be an improvement inside overlayfs in the future. But currently we can use NFS v4 for the FAI nfsroot with a very simple change. Just disable acl for the exported filesystem on the FAI server which holds /srv/fai/nfsroot. More is described here: http://fai-project.org/fai-guide/#_a_id_nfsv4_a_how_to_use_nfs_v4_with_the_nfsroot -- regards Thomas
