not very great docs indeed.. the issue is the log_msg (nice that it doesn't report it).. use something like this instead:

    my $log_msg_handler = sub {
        my $stringptr = shift;
        $$stringptr = "testing mkdir";
        return 1;
    };
    $svn->log_msg($log_msg_handler);

That should do the trick -- hopefully this prevents someone pulling out their hair.