[Bro] log_file variable in ftp.bro

[Cliff]

Hi all,
    I redefined the log_file variable in myself bro script as follwoing:
============================================
# $Id: myftp.bro,v1.0 2004/09/23 Cliff $
@load mt
redef root_servers={192.168.0.2};
redef interfaces="eth0";
redef restrict_filters={["net"]="net 192.168.10"};

#redefine log file in ftp.bro
redef log_file=open_log_file("comex");
=======================================

the log_file is defined in ftp.bro on line 54 as following:
...............
global log_file = open_log_file("ftp") &redef;
..........................

But I run bro ,the output is as following:

[root at oradata bro-pub-0.8a87]# ./bro myftp
policy/myftp.bro, line 11 (log_file): error, "redef" used but not previously defined

I don't understand the reason,who can help me?


Thanks,
Cliff