I feel like this is a slap in Jeff's face, since i thought that UML will be developed as the first choice in virtualizations techniques.
Yup, just like the inclusion of reiserfs in the kernel is a slap in the face to ext3. Obviously they did it just to be insulting, didn't you read Linus's "I'm a bastard" speech?
No, i don't know that speech. In addition i like reiserfs, so i'm perhaps the wrong person to discuss that with. The next thing on the horizon is reiser4 - perhaps with the "files as directory" feature - what ever that means, but i guess i won't like it.
So what is it all about? When should somebody chose Xen, and when should somebody chose UML? and how will UML and Xen compete?
You know, ever since the release of the BSD source code in 1992 totally derailed that "Linux" project people were playing with back then, this kind of question has become vitally important. The release of any remotely similar project obviously can immediately halt all development of established projects that developers have sunk years of effort into, and they immediately start porting over things like the COW mounts and hostfs and honeypot procfs, and rewrite all the existing tutorials and retrain everybody overnight to work on the new as yet untested thingy that hasn't been particularly debugged yet.
So you critisize, that they don't concentrate forces on UML? I Agree.
With the integration of UML into the Linux-Kernel i thought, that it would speed up development of UML and make it more stable. Intead, the people still break the UML-stuff regularly and Jeff and Blaisorblade must provide patches again :-(
Especially in a case like this, where Xen actually competes with VMWare rather than UML. Obviously, UML is doomed. What with Xen requiring a modified host kernel to provide its virtualization environment whereas UML uses the process abstraction to virtualize it: I mean, who's going to use _processes_ in five years, will future kernels even bother to support them? Sure, UML not only runs on an unmodified Linux kernel (even running a 2.6 UML on a 2.2 host kernel), and even an effort underway to get it running on windows (who knows why, but a MacOS X host can only be a matter of time), but that just means maybe it can scrape on some tiny niches once it's driven off Linux by this new "Adeos" thing... Er, I mean "Plex86"... Um... "Xen", that's it. And obviously its original use as a Linux development tool letting you do things like create a filesystem driver and mount an instance of it without destablizing your host kernel, or run bits of the kernel under normal userspace debugging tools... Well, we're well rid of that, aren't we? And being to swap kernel memory to backing store just like a regular application, that was obviously a bad idea from day one...
VMWare, Xen and UML are different techniques. As far as i know, UML doesn't use processes as the virtualization environment when running in SKAS mode. It runs a new kernel within a different address space - afaik, this is more like VMWare and Xen. But due to haveing a relatively normal hostsystem, there are the advantages you mentioned.
You also forgot some things: Xen doesn't support NPTL too
Why was the question interesting again?
What's the future of Xen and UML? Will Xen grow bigger than UML? Which is Linus's favourite? UML or Xen?
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