"This is a formal announcement of Lguest64," Steven Rostedt said in an email posted to the Linux Kernel mailing list. He explained:

"Most are aware of the little puppies (lguest32, or simply lguest, or in some circles "rustyvisor"). But this time the puppies ate a bit too much. No more lean and mean puppies, now we got big fat lazy ones. Running on the hardware that's too lazy to do full virtualization. Yes, lguest now runs on x86_64!"

Steven went on to caution that lguest64 is still a new code base, "lguest64 is still going through a bit of growth pains, but its getting better. It's to a point that we are not that afraid to bring it to the dog show." The list of items left to do include getting SMP working for both the host and the guest, matching Rusty Russel's lguest32 feature set, and greatly optimizing the performance of the code. Steven noted that the goal is to ultimately get the 64-bit version of lguest merged into the mainline kernel.

Some entertaining lguest documentation discussed in an earlier story was merged into the mainline kernel with the commit message, "the netfilter code had very good documentation: the Netfilter Hacking HOWTO. Noone ever read it. So this time I'm trying something different, using a bit of Knuthiness." Both Netfliter and lguest, as well as the documentation for both, were written by Rusty Russell. He describes the lguest driver as, "a simple hypervisor for Linux on Linux. Unlike kvm it doesn't need VT/SVM hardware. Unlike Xen it's simply 'modprobe and go'. Unlike both, it's 5000 lines and self-contained."

Downloading the 2.6.23-rc2 kernel and looking in the "drivers/lguest/" directory I found a simple README that kicks off an interesting documentation process, beginning, "welcome, friend reader, to lguest." It goes on to note, "I can't think of many 5000-line projects which offer both such capability and glimpses of future potential; it is an exciting time to be delving into the source!" At the end of the included README is a hint as to how to find the rest of the documentation, which is embedded inline within all the lguest files. Read on to begin the exploration into lguest and its documentation.

"Lguest is an adventure, with you, the reader, as Hero," began some documentation for lguest recently submitted by Rusty Russell. The documentation continued, "but be warned; this is an arduous journey of several hours or more! And as we know, all true Heroes are driven by a Noble Goal. Thus I offer a Beer (or equivalent) to anyone I meet who has completed this documentation. So get comfortable and keep your wits about you (both quick and humorous). Along your way to the Noble Goal, you will also gain masterly insight into lguest, and hypervisors and x86 virtualization in general."

Andrew Morton noted that he would consider the documentation patches for inclusion in the 2.6.23 kernel, to which Rusty replied, "indeed, no code changes, and I feel strongly that it should go into 2.6.23 because it's *fun*. And (as often complained) there's not enough poetry in the kernel." Linus Torvalds quipped, "there's a reason for that," going on to rhyme, "there once was a lad from Braidwood, with a wife and a hatred for FUD, he hacked kernels for fun, couldn't get them to run, but he always felt that he should." He added, "so when you say 'there's not enough poetry', next time you'll know why. You *really* don't want want poetry." This led to numerous additional poetic submissions about which Rusty noted, "there was a poetic infection, which distorted the kernel's direction, the code got no time, as they all tried to rhyme, and it shipped needing lots of correction."

As expected, Linus Torvalds released the 2.6.23-rc1 kernel two weeks after the release of 2.6.22, ending the merge window, "and it has a *ton* of changes as usual for the merge window, way too much for me to be able to post even just the shortlog or diffstat on the mailing list". He noted, "I personally like how 'sendfile' is now totally gone internally, and the kernel now ends up doing all that with splice insted. Good riddance, although we'll obvously end up supporting the old user level interfaces for a long time." Linus went on to summarize the other changes:

"Lots of architecture updates (for just about all of them - x86[-64], arm, alpha, mips, ia64, powerpc, s390, sh, sparc, um..), lots of driver updates (again, all over - usb, net, dvb, ide, sata, scsi, isdn, infiniband, firewire, i2c, you name it).

"Filesystems, VM, networking, ACPI, it's all there. And virtualization all over the place (kvm, lguest, Xen).

"Notable new things might be the merge of the cfs scheduler, and the UIO driver infrastructure might interest some people."

Rusty Russell's lguest was recently merged into the upcoming 2.6.23 Linux kernel. The merge comment describes the project, "lguest is a simple hypervisor for Linux on Linux. Unlike kvm it doesn't need VT/SVM hardware. Unlike Xen it's simply 'modprobe and go'. Unlike both, it's 5000 lines and self-contained." The comment goes on to note:

"Performance is ok, but not great (-30% on kernel compile). But given its hackability, I expect this to improve, along with the paravirt_ops code which it supplies a complete example for. There's also a 64-bit version being worked on and other craziness.

"But most of all, lguest is awesome fun! Too much of the kernel is a big ball of hair. lguest is simple enough to dive into and hack, plus has some warts which scream 'fork me!'."

Andrew Morton [interview] sent out the latest lguest patches for review, noting that he intends to merge the code into the mainline kernel, "some concern was expressed over the lguest review status, so I shall send the patches out again for people to review, to test, to make observations about the author's personal appearance, etc. I'll plan on sending these patches off to Linus in a week's time, assuming all goes well." The project's FAQ notes, "lguest is designed to be simple to use and modify, with the aim of keeping the codebase small. Currently it's around 5000 lines including userspace utility, whereas kvm is over 10 times that size, and Xen is around 10 times bigger again (of course, both have far more features)."

The lguest patches are written and maintained by Rusty Russell [interview] who also authored Rusty's Remarkably Unreliable Guide to Lguest, the project's documentation. The guide explains, "lguest is designed to be a minimal hypervisor for the Linux kernel, for Linux developers and users to experiment with virtualization with the minimum of complexity. Nonetheless, it should have sufficient features to make it useful for specific tasks, and, of course, you are encouraged to fork and enhance it." In the FAQ, lguest is compared to kvm [story], "kvm requires hardware virtualization support (most recent Intel and AMD chips have it), but it can run almost any Operating System (since it does full virtualization. It also has 64-bit support. Lguest doesn't do full virtualization: it only runs a Linux kernel with lguest support." The FAQ also compares lguest to Xen, "Xen is similar, in that it doesn't need hardware virtualization support (although it can use it), but Xen supports an extensive range of features such as PAE (ie. lots of memory), SMP guests, 64-bit. You have to boot your kernel under the Xen hypervisor; you can't simply modprobe when you want to create a guest."

Avi Kivity is the lead developer and maintainer of the Kernel-based Virtual Machine project, better known as kvm. The project was started in mid-2006, and has been part of the Linux kernel since the 2.6.20 release in February of 2007. kvm is a full virtualization system for x86-based Linux hosts, allowing users to run isolated x86 guest operating systems in virtual machines.