open Lwt

let other ic =
  lwt blah = Lwt_io.read ~count:8 ic in
  return ()

let load fn =
  Lwt_io.with_file
    ~flags:Unix.( [O_CREAT;O_WRONLY (* <- here's the bug *) ;O_TRUNC ] )
    ~perm:0o644
    ~mode:Lwt_io.input
    fn
    (fun ic ->
       lwt s = other ic in
       wrap (fun () -> return 1234))

let main () = load Sys.argv.(1)

let _ =
  Lwt_main.run (main ())

(* Compile with:

 ocamlfind ocamlc -c -g -syntax camlp4o -package lwt -package lwt.syntax -thread -ppopt -lwt-debug -o bar.cmo bar.ml && ocamlfind ocamlc -linkpkg -g -syntax camlp4o -package lwt -package lwt.unix -package lwt.syntax -thread -ppopt -lwt-debug bar.cmo -o bar

$ OCAMLRUNPARAM=b ./bar fofo
Fatal error: exception Unix.Unix_error(3, "read", "")
Raised at file "src/core/lwt.ml", line 782, characters 22-23
Called from file "src/unix/lwt_main.ml", line 34, characters 8-18
Called from file "bar.ml", line 20, characters 2-24

*)