On Mon, 16 Aug 2021, kreijack@inwind.it wrote:

On 8/15/21 9:35 PM, Roman Mamedov wrote:

quoted

On Sun, 15 Aug 2021 09:39:08 +0200
Goffredo Baroncelli [off-list ref] wrote:

quoted

I am sure that it was discussed already but I was unable to find any track
of this discussion. But if the problem is the collision between the inode
number of different subvolume in the nfd export, is it simpler if the export
is truncated to the subvolume boundary ? It would be more coherent with the
current behavior of vfs+nfsd.

See this bugreport thread which started it all:
https://www.spinics.net/lists/linux-btrfs/msg111172.html

In there the reporting user replied that it is strongly not feasible for them
to export each individual snapshot.

Thanks for pointing that.

However looking at the 'exports' man page, it seems that NFS has already an
option to cover these cases: 'crossmnt'.

If NFSd detects a "child" filesystem (i.e. a filesystem mounted inside an already
exported one) and the "parent" filesystem is marked as 'crossmnt',  the client mount
the parent AND the child filesystem with two separate mounts, so there is not problem of inode collision.

As you acknowledged, you haven't read the whole back-story.  Maybe you
should.

https://lore.kernel.org/linux-nfs/20210613115313.BC59.409509F4@e16-tech.com/ (local)
https://lore.kernel.org/linux-nfs/162848123483.25823.15844774651164477866.stgit@noble.brown/ (local)
https://lore.kernel.org/linux-btrfs/162742539595.32498.13687924366155737575.stgit@noble.brown/ (local)

The flow of conversation does sometimes jump between threads.

I'm very happy to respond you questions after you've absorbed all that.

NeilBrown