When samsung releases new phones, we can benefit from the support for the new phones by extracting all the new features, because some of the new phones are somewhat similar to our spica (such as is the case with i5800/i5801).
The problem with that is, when you find a new rom from, say samsung-firmares.com
You can't just flash the new phones rom to the spica and take files from a live spica. So when you open tar file for the rom, you discover the .rfs file format..
Because the spica uses the same "Robust File System" samsung proprietary filesystem, and of course has the drivers for that, we can just mount the image to a folder.
Open a new adb shell session.
Then we just need to set up a loop device like this:
And then mount the .rfs file to a folder:
mknod /dev/loop0 b 7 0
mount /sdcard/system.rfs /somefolder