I get a lengthy error while trying to compile the shiftfs module for kernel 5.16.
I am using the shiftfs file from the jammy ubuntu kernel repo:
https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy/log/fs/shiftfs.c?h=master-next
I can provide the log if necessary, but I am quite sure you can reproduce.
The kernel team should be taking care of this and a ported version should show up.
I’m running a testing version of 5.15 with shiftfs, so they have that work about ready to rollout (if they didn’t push it yet after my validation yesterday).
master-next seems to have it now: ~ubuntu-kernel/ubuntu/+source/linux/+git/jammy - [no description]
Related question - on Ubuntu 22.04 LTS with ext4 fs will LXD 5.0 use Idmapped mounts directly?
LXD will use idmapped mounts on any filesystem which supports it, so yeah, ext4 on 22.04 will use idmapped mounts.
Ok thx for the info.
Could you maybe elaborate on the potential regressions that are mentioned in the commit?
No idea what this refers to as filesystem namespace isn’t something that exists 
Maybe it’s about interaction with the VFS idmapped feature and mount namespaces?
Definitely a question for @brauner
shiftfs shouldn’t be mounted on top of idmapped mounts and idmapped mounts shouldn’t be mounted on top of shiftfs. That’s just asking for a lot of trouble. Shiftfs should check whether it’s on an idmapped mount just like I patched overlayfs and refuse to work on top of it.