Comment 3 for bug 1918599

I have reported the bug also on the btrfs mailing list.
They say, it is a bug of the nfs server, which get confused about btrfs snapshots.

As a consequence I cannot use (any more) btrfs on the Ubuntu 20.04 nfs server (Ubuntu 18.04 is ok):

root@tsmsrvj:~# mount | grep data
/dev/sdb1 on /data type btrfs (rw,relatime,space_cache,user_subvol_rm_allowed,subvolid=5,subvol=/)
localhost:/data/fex on /nfs/localhost/fex type nfs4 (rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=127.0.0.1,local_lock=none,addr=127.0.0.1)

root@tsmsrvj:~# ls -R /nfs/localhost/fex | wc
ls: /nfs/localhost/fex/spool: not listing already-listed directory