Re: cannot use btrfs for nfs server

[Forza <forza@tnonline.net>]

On 2021-07-19 14:06, Forza wrote:
> 
> 
> On 2021-07-13 09:37, Ulli Horlacher wrote:
>> On Mon 2021-07-12 (23:56), g.btrfs@cobb.uk.net wrote:
>>
>>>> root@tsmsrvj:/etc# du -Hs /nfs/localhost/snapshots
>>>> du: WARNING: Circular directory structure.
>>>> This almost certainly means that you have a corrupted file system.
>>>> NOTIFY YOUR SYSTEM MANAGER.
>>>> The following directory is part of the cycle:
>>>>    /nfs/localhost/snapshots/spool
>>>
>>> Sure. But it makes the useful operations work. du, find, ls -R, etc all
>>> work properly on /nfs/localhost/fex.
>>
>> Properly on /nfs/localhost/fex : yes
>> Properly on /nfs/localhost/snapshots : NO
>>
>> And the error messages are annoying!
>>
>> root@tsmsrvj:/etc# exportfs -v
>> /data/fex       
>> localhost.localdomain(rw,async,wdelay,crossmnt,no_root_squash,no_subtree_check,sec=sys,rw,secure,no_root_squash,no_all_squash) 
>>
>> /data/snapshots 
>> localhost.localdomain(rw,async,wdelay,crossmnt,no_root_squash,no_subtree_check,sec=sys,rw,secure,no_root_squash,no_all_squash) 
>>
>>
>> root@tsmsrvj:/etc# mount -o vers=3 localhost:/data/fex /nfs/localhost/fex
>> root@tsmsrvj:/etc# mount -o vers=3 localhost:/data/snapshots 
>> /nfs/localhost/snapshots
>> root@tsmsrvj:/etc# mount | grep localhost
>> localhost:/data/fex on /nfs/localhost/fex type nfs 
>> (rw,relatime,vers=3,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=127.0.0.1,mountvers=3,mountport=37961,mountproto=udp,local_lock=none,addr=127.0.0.1) 
>>
>> localhost:/data/snapshots on /nfs/localhost/snapshots type nfs 
>> (rw,relatime,vers=3,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=127.0.0.1,mountvers=3,mountport=37961,mountproto=udp,local_lock=none,addr=127.0.0.1) 
>>
>>
> 
> What kind of NFS server is this? Isn't UDP mounts legacy and not 
> normally used by default?
> 
> Can you switch to an nfs4 server and try again? I also still think you 
> should use fsid export option.
> 
> 
> 
I'm replying to myself here because I booted up a VM with Fedora 34 and 
tested a similar setup as Mr Horlacher's and can reproduce the errors.

Setup:
1) create a subvolume /mnt/rootvol/nfs
2) create some snapshots:
btrfs sub snap /mnt/rootvol/nfs /mnt/rootvol/nfs/.snapshots/nfs-1
btrfs sub snap /mnt/rootvol/nfs /mnt/rootvol/nfs/.snapshots/nfs-2

3) export as:
/mnt/rootvol/nfs/ *(fsid=1234,no_root_squash)

4) mount -o vers=4 localhost:/mnt/rootvol/nfs /media/nfs-mnt/
5) "du -sh /media/nfs-mnt" fails with
"WARNING: Circular directory structure."

6) "ls -alR /mnt/nfs-mnt" fails with
"not listing already-listed directory"

In addition I have tried with various export options such as crossmnt, 
nohide and subtree_check. They do not improve the situation.

Also the behaviour is the same with nfs3 as with nfs4.

Full outputs are available at https://paste.ee/p/pkHLh