On Fri, 03 Sep 2021, Frank Filz wrote:

quoted

On Thu, 2 Sept 2021 at 09:18, Christoph Hellwig [off-list ref] wrote:

quoted

quoted

 Your attitude seems to be that this is a btrfs problem and must be
fixed in btrfs.

Yes.

st_ino space issues affect overlayfs as well.   The two problems are
not the same, but do share some characteristics.  And this limitation will likely
come up again in the future.

I suspect the long term solution would involve introducing new userspace API
(variable length inode numbers) and deprecating st_ino.
E.g. make stat return an error if the inode number doesn't fit into st_ino and add
a statx extension to return the full number.  But this would be a long process...

But then what do we do where fileid in NFS is only 64 bits?

Hence my suggestion that user-space should move to using the filehandle.

Two file handles being different doesn't guarantee that the two objects
are different, but the problems caused by incorrectly assuming two
things are different are much less than the problems caused by
incorrectly assuming two things are the same.

The solution of giving each subvol a separate fsid is the only real
solution to enlarging the NFS fileid space, however that has downsides
on the client side.

And this doesn't help overlayfs...  

NeilBrown