Compiling tun.ko for Android - OpenVPN

I have a Xoom, and a Galaxy S, and need to be able to compile my own tun.ko for the kernel version I have. As you all know, if the kernel version of the module you are trying to insert isn't the same, it won't insert, and will give you errors like:


<3>[95175.874872] tun: version magic '2.6.36.4-athm1-OV-launchpad-1.2.2+ SMP preempt mod_unload ARMv7 ' should be '2.6.36.3-gc2bee64 SMP preempt mod_unload ARMv7 '

in dmesg. We need to compile the module for the right version of the kernel

1. Download the Kernel source - normally from http://android.git.kernel.org/. The Xoom can be found at http://android.git.kernel.org/kernel/tegra.git, and the Galaxy S can be found at http://android.git.kernel.org/kernel/samsung.git. Use
   
   $ pwd
      /scratch/xoom
   $ git clone http://android.git.kernel.org/kernel/tegra.git to clone the Xoom kernel source
2. Copy your old kernel config from your device
   
   $ pwd
      /scratch/xoom
   $ adb pull /proc/config.gz
   $ gunzip config.gz
   $ mv config.gz tegra
3. Download an ARM crosscompiler from http://www.codesourcery.com/sgpp/lite/arm/portal/release1293
4. Untar the crosscompiler, and add the binary directory to the path
   
   $ pwd
      /scratch/gnu-eabi
   $ tar -jxvf arm-2010q1-202-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2
   $ export PATH=$PATH:/scratch/gnu-eabi/arm-2010q1/bin
5. Prepare the kernel for compilation
   $ cd /scratch/xoom/tegra
   $ vi scripts/setlocalversion
   
      Find the following lines
          # If only the short version is requested, don't bother
          # running further git commands
          if $short; then
             echo "+"
             return
          fi
   
      Change the line - echo "+" to echo ""
   
   $ ARCH=arm make menuconfig
   
      Go to General setup->Local version - append to kernel release. Make the value of this "-gc2bee64", without the quotes
      Exit, and say Y to saving changes
   $ Edit the file .config, and check for the value CONFIG_TUN
      If there is not a line CONFIG_TUN=m, create it. Save and exit the file
6. Compile the modules only
   $ ARCH=arm make modules SUBDIRS=drivers/net
7. If all goes well, there will now be a file tun.ko in drivers/net. Copy it to your device using adb, and place it in /system/lib/modules (create the directory if necessary). To check the version of the module, type "strings drivers/net/tun.ko". It will show you the version of the module.

You now have to install OpenVPN on your device. Grab the OpenVPN Installer and OpenVPN Settings app from the Market, and install. Install OpenVPN to /system/xbin. Then install BusyBox to /system/xbin (or /sbin if you have run out of room) using the Busybox Installer (from the market)

With the latest versions of Android (or if you have push rules in your config), you have to get a newer version of the openvpn binary than what comes with the OpenVPN Installer. So grab http://github.com/downloads/fries/android-external-openvpn/openvpn-static-2.1.1.bz2 and extract it over the top of /system/xbin/openvpn

With that above version of openvpn, it goes looking for ifconfig and route in particular locations. It looks for them in /system/xbin/bb/ifconfig and /system/xbin/bb/route. So

$ mkdir /system/xbin/bb
$ ln -s /system/xbin/busybox /system/xbin/bb/route

$ ln -s /system/xbin/busybox /system/xbin/bb/ifconfig

And that should be that!