Quoting Tech World
Linus Torvalds has released the 2.6.20 Linux kernel, introducing two separate implementations of virtualization, among other features.
Virtualization has become a hot topic over the past year, and players such as VMware Inc. and XenSource Inc. have been angling to get their code included directly in the Linux kernel. However, developers have been reluctant to include a significant amount of code that would tie into a single vendor's technology.
To get around that, Kernel 2.6.20 includes an implementation of paravirtualization that can work with different hypervisors, Torvalds said. Paravirtualization allows different virtual machines to run very efficiently, but needs either modification of the guest operating system or support at the hardware level.
Xen is an open-source example of paravirtualization, and VMware ESX Server and Parallels Workstation also use the technique. The implementation in the new kernel supports i386 hardware.
The kernel also includes a relatively new technology called KVM (Kernel-based Virtual Machine), a full-virtualization system developed by Qumranet, an Israel-based start-up. KVM requires the hardware-based virtualization support found in newer processors from Advanced Micro Devices Inc. and Intel Corp.
KVM consists of two pieces of open-source software, the user module and the kernel module, kvm.ko, which has been included in Linux 2.6.20.
The technique of "full virtualization" simulates enough hardware to allow unmodified guest operating systems as guests. This technique is used by KVM, as well as VMware Workstation, VMware Server and Parallels Desktop, among others.
Other additions include support for relocatable x86 kernels and a debugging feature called fault injection.
Torvalds said that despite the addition of virtualization and other new features, there were few basic changes to the kernel.
"I tried rather hard to make 2.6.20 largely a 'stabilization release,'" Torvalds wrote to the kernel development mailing list. "Unlike a lot of kernels lately, there aren't really any big fundamental changes to some core infrastructure area, and while we always have bugs, I really am hoping that we fixed many more than we introduced."
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