Re: Christmas list for the kernel

Rob Landley
2005-11-24T04:17:38Z

On Tuesday 22 November 2005 16:11, Bill Davidsen wrote:
> Serious question, when/if xen is in the kernel, is there a reason for
> UML? If so, why would I use UML instead of xen, and where?

Xen requires support in the host kernel. UML (skas0 mode) does not.

I have a build system that uses UML as a better fakeroot. I can't use qemu
for this because I want to boot borrowing the hosts's filesystem (so the
build doesn't need a huge binary blob of precompiled stuff to start
doing ./configure;make;make install with... At that point I might as well
just distribute the final binaries and be done with it).

I don't want the thing to require root access, yet the build needs to drop a
symlink into /, wants to mknod, chown, chroot, and perform --bind and --move
mounts.

Fakeroot wouldn't be sufficient because there's no guarantee the host system
is running a 2.6 kernel (no --bind or --move mounts) and worse, I'm building
uClibc against the most recent Mazur headers I can find which means the
resulting uClibc may not run on an older kernel (even running against a
sufficiently old 2.6 kernel means segfaults due to missing features the new
headers describe).

I find UML a very convenient way to get a virtual environment borrowing
resources from the host without having to set up the host. This means I can
deploy it to relatively unknown systems, without requiring somebody with root
access on those systems to replace the kernel and reboot, which generally
isn't an option.

Rob