Re: [Xen-devel] linux/arch/xen/i386 or linux/arch/i386/xen

[Chris Wright <chrisw@xxxxxxxx>]

* Magenheimer, Dan (HP Labs Fort Collins) (dan.magenheimer@xxxxxx) wrote:
> Um, one other minor semantic issue.  The semantics of
> using mach-xxx may be inappropriate.  If my understanding
> is correct, two mach-xxx's cannot both be built, e.g. one
> cannot build a kernel which supports (for i386) both
> mach-es7000 and mach-voyager.

Yes, I had thought about this.  It's not clear to me it's problematic yet.
In many cases, it's exactly the bits that would become irrelevant that
are in the sub-arch (irq, smpboot, timers, etc.), whereas the generic
arch code would be sufficient running xenlinux on one of the sub-arches.

> There have been various discussions on this list about
> "transparent paravirtualization", i.e. the ability for
> a paravirtualized kernel to run both as a guest of Xen
> and on bare metal.  This is definitely an objective of
> Xen/ia64.  Nobody has tried it for Xen/x86, but if it
> can be done, I'm sure commercial companies and distros
> would be eager to utilize it (one less set of bits to
> support).

Hmm, this would be interesting/problematic.  Hadn't considered that
part.

> In many ways, a "xen" subdirectory is much more like
> a "pci" or "math-emu" subdirectory, than a subarch.
> For example, mach-es7000 and xen may need to co-exist
> in the same kernel.
> 
> So, mach-xen may be a poor choice.  A subtle distinction
> perhaps but when dealing with Linux kernel developers,
> purity of thinking may avoid future patch submission
> arguments.

The primary goal is to avoid code duplication to keep maintenance sane.
Clean way to do that is what really matters.

> So I'd vote for:
> 
> xen arch code in              arch/$(ARCH)/xen/

that's effectively sub-arch

> xen generic code in           drivers/xen/core/

yup (although no need for core/ subdir)

> xen arch includes in          include/asm-$(ARCH)/xen/

again, effectively sub-arch

> xen generic includes in               include/asm-xen/

or just include/xen

> though I realize this is not a democracy :-)

heh ;-)

thanks,
-chris

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