Apparently `F_SETLKW` is special (this code is all from online examples, I'm not intimately familiar with file locking).

From the manpage:

> F_SETLKW
> 
> This command is the same as F_SETLK except that if a shared
> or exclusive lock is blocked by other locks, the process
> waits until the request can be satisfied.  If a signal that
> is to be caught is received while fcntl is waiting for a
> region, the fcntl will be interrupted if the signal handler
> has not specified the SA_RESTART (see sigaction(2)).

Which means that this should probably handle `EINTR`, but rustdoc usage does not currently generate any signals.