Mention that FICLONE, FICLONERANGE, and FIDEDUPERANGE all require
both files to reside on the same filesystem.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Document the FIDEDUPERANGE ioctl, formerly known as
BTRFS_IOC_EXTENT_SAME.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>