Should Xen be a sub-arch or a build option?

[Ivan Voras]

Kip Macy wrote:

> It could, in principle, also be done as a build option. I'm not sure
> how well it would mesh with the existing build tools as there are a
> number of files that I would not want to compile in (e.g. code that
> talked directly to the BIOS) that is normally built by default. In
> that case I would structure it:
> 
>       - sys/i386/xen     - xen specific bits for i386
>       - sys/amd64/xen - xen specific bits for amd64

I can only speak as an end-user: could it be done so that the
Xen-enabled kernel is bootable on a normal non-virtualized machine? In
this case it would be ideal if it's implemented as a build option, so
people can share kernels across the machines. If not, then it certainly
looks like a separate architecture.

> There is also a question of where the drivers should be put. I propose
> that they would be put under sys/dev/xen, so you would have e.g.
> sys/dev/xen/xennet, sys/dev/xen/xenblk etc.

In the above case (build option), this looks reasonable.