Can't cancel reading on stdin with Luv

[haesbaert]

utop #   Eio_main.run @@ fun env ->
  let stdin = Eio.Stdenv.stdin env in
  let () =
    Eio.Fiber.first
      (fun () -> Eio.Flow.single_read stdin (Cstruct.create 1) |> ignore)
      (fun () -> Eio.traceln "second fiber done")
  in
  Eio.traceln "foo finished";;
+second fiber done

The same works with uring.

[talex5]

Hmm. We do call cancel, but Luv returns EBUSY (only logged at debug level).

I guess cancelling File.read isn't supported. We could make stdin be a Stream instead.

[talex5]

The works on the eio_posix backend that replaced eio_luv.