I have an upcoming application for some UML hosts, so I blew the cobwebs off the Debian packages over the last week and had a bit of a fiddle.
So if you want to run a UML guest, you really want to have the Seperate Kernel Address Space patch in the kernel of the host running the guests. As I track Sarge, and currently run a bog standard Sarge 2.6.8 kernel, I wanted to be able to just patch SKAS into it. I didn't want to deviate drastically.
So first cab off the rank was hacking kernel-patch-skas so that it would patch a 2.6.8 kernel. This was relatively easy, I just had to retrofit the 126.96.36.199 patch, which was already in there. I took out the hunk that patched the top level Makefile, and it applied perfectly to both a clean 2.6.8 kernel source, and a 2.6.8 source with kernel-patch-debian-2.6.8 applied. It built, I'm running it on my test box.
This is where the fun starts. At present, this patches 2.4.26 or 188.8.131.52. I naturally wanted to have it work with everything in Sarge, so I added 2.6.8 to the mix, with the same patch as 2.6.8. This applied fine to the 2.6.8 sources.
This is where the fun stops.
As it currently stands, this package is just a bit of glue between the kernel-source package and the kernel-patch package. It also introduces a few patches of its own, which I haven't been able to figure out yet. With some slight modifications to this package, I had it build-depending on kernel-source-2.6.8 and my new and improved kernel-patch-uml and had all the patches applying. Building was a different story.
I've temporarily given up on trying to get UML to work with everything in Sarge. Apparently there are some security issues with anything older than 2.6.9, so I've turned by attention to Sid for the time being. I believe 2.6.11 has all the UML patches merged in, so I've gutted user-mode-linux to just essentially build-depend on kernel-source-2.6.11 and not apply any patches at all, and build with ARCH=um. That's currently building, so we'll see what sort of a mess that leaves me with.
I NMUed kernel-patch-skas this morning, don't know if the release team will accept it into Sarge or not, given it is frozen, but if they do, at least you will be able to build a UML hostable kernel from Sarge. Building a guest will be a different story, unfortunately.
Matt Zimmerman replied to my NMU asking me if I'd like to adopt the UML packages. I probably will, given I'll be having a bit to do with it again. Unfortunately I have no kernel fu whatsoever, so if I hit problems, I'm going to be stuck between a rock and a hard place.