This is a trivial patch that adds support for copy_file_range for cifs. This uses the copy_file_range interface which cifs.ko supports. Note that cloner.c uses an ioctl() for copying an entire file. This is an older interface from before cifs.ko added proper copy_file_range support but both interfaces eventually end up in the same codepaths and use the same SMB2 commands on the wire. Could argue that we could/should use copy_file_range() for the whole file case as well but there is no harm leaving it as-is using the older interface.
