Missing output when running mdx

[talex5]

In https://github.com/ocaml-multicore/eioio/blob/main/README.md#getting-started I use MDX with this example:

# #require "eunix";;

# let main stdenv =
    let src = Eio.Source.of_string "Hello, world!\n" in
    let dst = Eio.Stdenv.stdout stdenv in
    Eio.Sink.write dst ~src;;
val main : < stdout : Eio.Sink.t; .. > -> unit = <fun>

# Eunix.run main;;
- : unit = ()
# (* prints "Hello, world!" *)

However, it doesn't capture the output (I had to add it as a comment instead).

Interestingly, if I change the last command to

# print_endline "Wibble!"; Eunix.run main;;

then it shows the output as Hello, w, suggesting that it has tried to read the number of bytes that the print statement produced. Any idea what might cause that?

[talex5]

I guess it's because it redirects output to a file rather than a pipe, and ocaml-uring wrote to the file at offset zero (rather than using the current position). Fixed by ocaml-multicore/ocaml-uring#17.