Turns out that when documentation says, very explicitly, that on error it will return the standard error value ENOBUFS, what it means is that it might return -ENOBUFS, or maybe -EINVAL. So, basically, not what the documentation says. Great, that'd have been nice to know earlier, perhaps even before i had to look into the source code to find out. So, guess there's a report and/or pr to make on Jack2 for this thing that has been a thing for over a decade at this point.