reflink support and Samba running over XFS

[Jeremy Allison]

On Mon, Nov 07, 2022 at 06:45:38PM -0600, Steve French wrote:
>I noticed that reflink (FSCTL_DUPLICATE_EXTENTS) is not supported on
>Samba when run over XFS but is with the vfs_btrfs.
>
>I can do reflink locally on the XFS mount point, but not remotely
>unless it is BTRFS (or to Windows eg. when the share is on REFS).
>
>Any idea if there is a way to enable reflink (FSCTL_DUPLICATE_EXTENT)
>support for Samba when not running on btrfs (e.g. on xfs)?
>
>duplicate extents is needed for various Linux client features
>(especially various fallocate operations)

This is implemented in vfs_btrfs.c via:

ret = ioctl(fsp_get_io_fd(dest_fsp), BTRFS_IOC_CLONE_RANGE, &cr_args);

what ioctls are used for this in XFS ?

We'd need a VFS module that implements them for XFS.