[yifanlu]

It's done! Well, sort of. It's done, but untested. I'm going to release the first alpha, but here are the current limitations:

-ONLY supports upgrading Kindle 2 US 2.5.8 to 3.1 using a Kindle 3 3G 3.1 (All conditions version, model, etc must be met)
However, you can easily change the code to support other versions/models, but I want to concentrate on getting one thing right at a time. I made sure no model/version specific code exists, so you can rename stuff to produce other packages, but if you are knowledged enough to do this, I don't need to give directions.
-Slow. It WILL take 2 hours. Luckly, you don't have to stare at it. Just keep it charged.
-You need 900MB of free space on the Kindle 2.
-You need 1.2GB of free space on the Kindle 3.
-Make sure to back up your Kindle 2!!!

DO NOT PROCEED UNLESS YOU KNOW HOW TO RECOVER! I TRY TO MAKE IT BRICK PROOF, BUT IT IS UNTESTED

To use:
1) Copy "update_k2_2.5.8_prepare_kindle.bin" to your Kindle 2 US. It must be version 2.5.8 (555370010)
2) Run the updater. The updater will create a rootfs image and a backup recovery package (for restoring beck to 2.5.8). It will also flash the patched recovery kernel for running unsigned recovery packages. This will take around 45 minutes to complete (the compression takes the most time).
3) After the updater completes, connect the kindle 2 to the computer and open up the folder "output" on the usb drive. You'll find two files: update_restore-k2-os.bin and rootfs.img. Keep update_restore-k2-os.bin safe, as you need that to restore 2.5.8.
4) Copy rootfs.img from the Kindle 2's output folder and "update_k3g_3.1_create_updater.bin" from the download to the root of the Kindle 3's usb partition.
5) Run the update. This will take about an hour. Do NOT interrupt!
6) After that completes, connect your Kindle 3 back to your computer and you'll find "update_k2-os.bin" and "tts-files.tar" in the output folder.
7) Copy those two files to the root of the Kindle 2 (you can delete the output folder from Kindle 2)
8) Restart your kindle 2 and it'll update.

NOTES:
-Check the log files in the output folder to see what steps completed (if it fails)
-The kindle will display progress and error messages on the lower right hand corner of the screen.
-If you do not want to flash the recovery kernel because you flashed it before (recovery kernel is REQUIRED for upgrading), create a file named "NO_KERNEL" on the root of the USB partition.
-If you want to skip file checks, create a file named "NO_VALIDITY_CHECKS" on the root of the USB partition to bypass the md5 checks.