Originally Posted by Graiden05
Actually there is one way to bring it back to JB. At least in tf300 kernel sources this function just disabled. So if uncomment line 913 in file drivers/usb/gadget/android.c "&mass_storage_function," and compile kernel with this change it will be possible to mount some partition as mass storage through usb cable with following commands (/dev/block/mmcblk1p1 - external microSD)
Maybe it's important to note that mounting the same partition from Android and via USB at the same time *will* lead to severe data corruption. But it could be a nice feature for the recovery or the pre-init shell.
Edit: just mounted my /data partition on my PC from the pre-init shell in my kernel (-that8, unreleased) and made a backup of installed apps and data - works great, thanks @Graiden05
for finding out how to do it. So it works if Android is not running (I didn't try to write yet, but that should work too), and of course you need a Linux PC to mount an ext4 filesystem. And remember that this accesses the block device directly, so it is possible to corrupt the filesystem.