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

quoted

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 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?

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.

Frank