reflink help ambiguity

(10:21:39 AM) killermist: I was just noticing that the text for "--reflink" in "cp --help" (the explanation at the bottom) is a little ambiguous.
(10:22:23 AM) killermist: "When --reflink[=always] is specified, perform a lightweight copy, where the data blocks are copied only when modified.  If this is not possible the copy fails, or if --reflink=auto is specified, fall back to a standard copy."
(10:25:48 AM) killermist: The "if this is not possible" part is a little troubling.  Does that mean "if reflink=always, but creating reflinks are not possible, then the copy will fail"?
(10:26:20 AM) cwillu: that's how I'd interpret it
(10:27:28 AM) killermist: Additionally "if --reflink=auto is specified, fall back to a standard copy." could look like it is standing as its own thought, implying that --reflink=auto won't really try to create reflinks.
(10:28:38 AM) killermist: I'm sure that isn't the intended conclusion the user is supposed to come to, but the way that passage is worded can be confusing.
(10:29:01 AM) brilthor left the room (quit: Read error: Operation timed out).
(10:29:11 AM) cwillu: the comma is a clue :p
(10:29:25 AM) cwillu: (the one that you changed to a period)
(10:30:29 AM) killermist: But the part before the comma is talking about conditions of --reflink=always.  And you wouldn't use --reflink=always AND --reflink=auto in the same command.
(10:31:49 AM) ***cwillu shrugs
(10:33:52 AM) killermist: A more clear wording might be:  When --reflink[=always] is specified, perform a lightweight copy, where the data blocks are copied only when modified.  If this is not possible the copy fails.  If --reflink=auto is used, a lightweight copy will be created if possible, and fall back to a standard copy if it is not possible.