On Wed 2021-03-10 (08:46), Ulli Horlacher wrote:
> When I try to access a btrfs filesystem via nfs, I get the error:
> root@tsmsrvi:~# mount tsmsrvj:/data/fex /nfs/tsmsrvj/fex
> root@tsmsrvi:~# time find /nfs/tsmsrvj/fex | wc -l
> find: File system loop detected; '/nfs/tsmsrvj/fex/spool' is part of the same 
> file system loop as '/nfs/tsmsrvj/fex'.

It is even worse:

root@tsmsrvj:# grep localhost /etc/exports
/data/fex       localhost(rw,async,no_subtree_check,no_root_squash)

root@tsmsrvj:# mount localhost:/data/fex /nfs/localhost/fex

root@tsmsrvj:# du -s /data/fex
64282240        /data/fex

root@tsmsrvj:# du -s /nfs/localhost/fex
du: WARNING: Circular directory structure.
This almost certainly means that you have a corrupted file system.
The following directory is part of the cycle:

0       /nfs/localhost/fex

root@tsmsrvj:# btrfs subvolume list /data
ID 257 gen 42 top level 5 path fex
ID 270 gen 42 top level 257 path fex/spool
ID 271 gen 21 top level 270 path fex/spool/.snapshot/2021-03-07_1453.test
ID 272 gen 23 top level 270 path fex/spool/.snapshot/2021-03-07_1531.test
ID 273 gen 25 top level 270 path fex/spool/.snapshot/2021-03-07_1532.test
ID 274 gen 27 top level 270 path fex/spool/.snapshot/2021-03-07_1718.test

root@tsmsrvj:# uname -a
Linux tsmsrvj 5.4.0-66-generic #74-Ubuntu SMP Wed Jan 27 22:54:38 UTC 2021 
x86_64 x86_64 x86_64 GNU/Linux

root@tsmsrvj:# btrfs version
btrfs-progs v5.4.1

root@tsmsrvj:# dpkg -l | grep nfs-
ii  nfs-common                             1:1.3.4-2.5ubuntu3.3              
amd64        NFS support files common to client and server
ii  nfs-kernel-server                      1:1.3.4-2.5ubuntu3.3              
amd64        support for NFS kernel server

The same bug appears if nfs server and client are different hosts or the
client is an older Ubuntu 18.04 system.

Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlac...@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/

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