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

[gnn at freebsd.org]

At Sun, 21 Oct 2007 20:56:35 -0700,
Kip Macy wrote:
> 
> 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
> 

If most of the bits will be shared, then lets share them, that is, use
the second proposal.  I couldn't find a good example in the tree for a
precedent, though the powerpc might come close, with its powermac and
powerpc sub-directories.

> 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.

Yes, this makes sense too.

Thanks,
George