I solved the "trust-loop" bug with this help: http://itsfoss.com/mount-iphone-ipad-ios-7-ubuntu-13-10/
But after my ipad is successfully mounted, I found out there is only one device detected but it's just some digital files there, like DCIM etc.
I can't find the Documents on iPad device which contain apps folders.
I want to transfer files to the apps in my iPad. What should i do?