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

[Kip Macy]

Let me say in advance that this is not an invitation to discuss the
technical merits of xen. This is purely a request to discuss how one
would structure the tree were one to import it into CVS.

Hypothetically speaking, if one were to import Xen support into CVS
what would be the best way to go about it?

There are a number of choices when doing it as a sub-arch:
  - A separate directory for i386 and amd64
      - sys/xen-i386
      - sys/xen-amd64
 - A shared directory as most of the bits will be shared:
      - sys/xen          - common bits
      - sys/xen/i386   - i386 specific bits
      - sys/xen/amd64 - amd64 specific bits

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


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.


 -Kip