reflink support and Samba running over XFS

[Christoph Hellwig]

On Wed, Nov 09, 2022 at 11:30:55PM +0100, David Disseldorp via samba-technical wrote:
> I think it's doable too :-). As indicated in my other mail, I think
> FICLONERANGE will need to be used for FSCTL_DUP_EXTENTS_TO_FILE instead
> of copy_file_range().
> I'm not sure how to best handle FILE_SUPPORTS_BLOCK_REFCOUNTING -
> ideally we'd set it for Btrfs and XFS(reflink=1) backed shares only.
> Another option might be to advertise FILE_SUPPORTS_BLOCK_REFCOUNTING and
> then propagate errors up to the client if FICLONERANGE fails for
> FSCTL_DUP_EXTENTS_TO_FILE. Client copy fallback would work, but the
> extra request overhead would be ugly.

We could probably add a bit to struct statx if that is helpful for
samba.