It would be helpful to know which path is being dumped and ideally what led to the dumpage. Given where the warning is emitted right now in the code, it's not obvious to me how to add that detail to the message, but it's pretty unfriendly right now. I guess we could add a constructor parameter to an FdSink that tells it some human-meaningful representation of the thing being written to it?

cc @edolstra @shlevy