Due to some reason (tracing provider problem and some firewall features) I have to save all openwrt log to file on external drive (now to usb, in plans to hdd).
uci set system.@system.log_file='/mnt/sdb1/log/messages.log'
So it would be good idea to check in luci app if this parameter is not empty and if so call something like cat or tail system.@system.log_file instead of logread.