Slashdot Mirror
Linux Gains Two New Virtualization Solutions
An anonymous reader writes "The upcoming 2.6.23 kernel has gained two new virtualization solutions. According to KernelTrap, both Xen and lguest have been merged into the mainline kernel. These two virtualization solutions join the already merged KVM, offering Linux multiple ways to run multiple virtual machines each running their own OS."
Each of Xen, KVM, lguest, and UML can be considered virtualization products but they are all vastly different. Below I describe each of these products in relation to their inclusion to the Linux kernel.
Xen - the Linux kernel supports code allowing it to be run as a guest underneath the Xen kernel, all through software. Linux's support for Xen does not make Linux a virtualization platform, only a GUEST for the Xen kernel which sits at Ring-0. (though a "dom0" Linux system can interact intimately with the Xen kernel, it actually sits at Ring-1). I should note that the Xen kernel also supports hardware virtualized domains, though this is unrelated to the patches to Linux.
KVM - the Linux kernel supports virtualization of guests through hardware extensions, this requires supported hardware. Linux becomes the Ring-0 kernel.
lguest - (my understanding is) an unmodified Linux kernel can act as a hyper-supervisor through loading Linux kernels as modules. Linux sits as both Ring-0 (supervisor) and Ring-1 (guests). This is experimental with limited features and only supports Linux guests.
UML - the Linux kernel becomes a userspace program. This allows Linux to run as an executable application/program. With UML, Linux can be compiled for a Linux or Microsoft Windows target. The executing OS sits at Ring-0 and the UML program sits at Ring-1. This has the advantage of requiring no modifications to the host OS and is very portable (you could email an entire Linux system to a friend without requiring anything installed to their system), but the disadvantage of poor performance.
From a high-level, the products UML, Xen, and lguest are actually very similar in function. They act as architectures to which Linux can be compiled in order to make it a guest OS of another Ring-0 kernel. These architectures provide the targets of a kernel module (lguest), a userspace program (UML), or a xen-domU guest (Xen). On the other hand, KML is the only patch that is intended to add support to Linux to act as a Ring-0 kernel on behalf of guest systems -- and even then, KML can be viewed more as a hardware driver for the processor extensions.
These aren't even close to the same solution. KVM provides hardware-assisted virtualization, with Linux as the hypervisor. Lguest provides linux-in-linux paravirtualization (no hardware support), and is extremely lightweight (5000 lines of code, total), but lacks many advanced features. Xen provides both paravirtualization and full virtualization, runs under a custom hypervisor intended to run multiple different OSes (Linux, Solaris, Windows, etc.) simultaneously, and has a plethora of sophisticated features, such as live migration (and all the maintenance headache of the correspondingly huge codebase).
They each fill very different niches, so there are very good reasons for having all 3 in the kernel.
There's no failure quite as dissatisfying as a complete and total solution to the wrong problem.
You mean Lguest? FTA:
Lguest doesn't do full virtualization: it only runs a Linux kernel with lguest support.
So the answer is no, Lguest does not run Windows. Xen runs Windows, but only if you have a VT-capable processor. Like Lguest, Xen can run Linux without a VT-capable processor.