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'.
1

tsmsrvi and tsmsrvj (nfs client and server) both run Ubuntu 20.04 with
btrfs-progs v5.4.1 

On Ubuntu 18.04 this setup works without errors:

root@mutter:/backup/rsync# grep tandem /etc/exports 
/backup/rsync/tandem            176.9.135.138(rw,async,no_subtree_check,no_root_squash)

root@mutter:/backup/rsync# btrfs subvolume list /backup/rsync | grep tandem
ID 257 gen 62652 top level 5 path tandem
ID 5898 gen 62284 top level 257 path tandem/.snapshot/2021-03-01_0300.rsync
ID 5906 gen 62284 top level 257 path tandem/.snapshot/2021-03-02_0300.rsync
ID 5914 gen 62284 top level 257 path tandem/.snapshot/2021-03-03_0300.rsync
ID 5924 gen 62284 top level 257 path tandem/.snapshot/2021-03-04_0300.rsync
ID 5932 gen 62284 top level 257 path tandem/.snapshot/2021-03-05_0300.rsync
ID 5941 gen 62284 top level 257 path tandem/.snapshot/2021-03-06_0300.rsync
ID 5950 gen 62284 top level 257 path tandem/.snapshot/2021-03-07_0300.rsync
ID 5962 gen 62413 top level 257 path tandem/.snapshot/2021-03-08_0300.rsync
ID 5970 gen 62522 top level 257 path tandem/.snapshot/2021-03-09_0300.rsync
ID 5978 gen 62626 top level 257 path tandem/.snapshot/2021-03-10_0300.rsync

root@mutter:/backup/rsync# btrfs version
btrfs-progs v4.15.1

root@tandem:/backup# mount | grep backup
mutter:/backup/rsync/tandem on /backup type nfs (ro,relatime,vers=3,rsize=1048576,wsize=1048576,namlen=255,soft,proto=tcp,timeo=600,retrans=1,sec=sys,mountaddr=176.9.68.251,mountvers=3,mountport=52943,mountproto=tcp,local_lock=none,addr=176.9.68.251)

root@tandem:/backup# ls -l .snapshot/
total 0
drwxr-xr-x 1 root root 392 Mar  1 03:00 2021-03-01_0300.rsync
drwxr-xr-x 1 root root 392 Mar  2 03:00 2021-03-02_0300.rsync
drwxr-xr-x 1 root root 392 Mar  3 03:00 2021-03-03_0300.rsync
drwxr-xr-x 1 root root 392 Mar  4 03:00 2021-03-04_0300.rsync
drwxr-xr-x 1 root root 392 Mar  5 03:00 2021-03-05_0300.rsync
drwxr-xr-x 1 root root 392 Mar  6 03:00 2021-03-06_0300.rsync
drwxr-xr-x 1 root root 392 Mar  7 03:00 2021-03-07_0300.rsync
drwxr-xr-x 1 root root 392 Mar  8 03:00 2021-03-08_0300.rsync
drwxr-xr-x 1 root root 392 Mar  9 03:00 2021-03-09_0300.rsync
drwxr-xr-x 1 root root 392 Mar 10 03:00 2021-03-10_0300.rsync

So, it is an issue with the newer btrfs version on Ubuntu 20.04? 


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