I think the right interface for this should be a "fold" over open file
descriptors:

    open Unix

    let descr_of_int n = (Obj.magic (n : int) : file_descr)

    let valid_descr fd =
      try ignore (fstat fd); true
      with Unix_error (EBADF, "fstat", _) -> false

    let fold_open_fds f init =
      let f' x s =
	let fd = descr_of_int (int_of_string s) in
	if valid_descr fd then f x fd else x
      in
      Array.fold_left f' init (Sys.readdir "/proc/self/fd")

Note that the readdir itself opens a file descriptor, which is
included in the result but then closed. So there's a little extra
complexity to filter it out so that the caller's function doesn't get
applied to a bad descriptor.

-- 
Eric Cooper             e c c @ c m u . e d u