We recently saw the release of much awaited Android 4.1 Jelly Bean upgrade for Samsung Galaxy S2. Also, Android is known for its openness and ability to modify and customize it deeply which is powered by independent developers. So, to help the guys, people at Samsung have published the open source Kernel Source Code of the update.
Samsung has a history of quickly open sourcing the kernel code after its official launch and by these, it keeps successfully trying to play nice with the developer community. Normally users can get the update through OTA or Kies.
Also, although this may not mean such a big thing to every one but ROM developers know the importance of this. ROM devs can get the Kernel source code for Samsung Galaxy S2 Android 4.1.2 Jelly Bean(I9100XXLSD firmware) by visiting opensource.samsung.com.