Re: [PATCH] xen: core dom0 support

[Gerd Hoffmann <kraxel@redhat.com>]

Ingo Molnar wrote:
>>> In three years time, will we regret having merged this?
>> Its a pretty minor amount of extra stuff on top of what's been 
>> added over the last 3 years, so I don't think it's going to 
>> tip the scales on its own.  I wouldn't be comfortable in 
>> trying to merge something that's very intrusive.
> 
> Hm, how can the same code that you call "massive out-of-tree 
> patches which doesn't make anyone happy" in an out of tree 
> context suddenly become non-intrusive "minor amount of extra 
> stuff" in an upstream context?

The current, out-of-tree xen kernel stuff is based on 2.6.18.  That
predates pv_ops and is quite intrusive stuff, with alot of cut+paste
programming and dirty hacks.

Alot has happened in x86 land since 2.6.18.  Being one of the x86 arch
maintainers you should know that very well.  Most notably:

  * pv_ops.  Point of adding these is to allow virtualization-friendly
    kernels *without* being intrusive as hell.
  * x86 arch merge, followed up by tons of cleanups and code
    reorganizations.  These changes also make it easier to merge xen
    support in a non-intrusive manner.

Also the xen support code in the linux kernel itself is basically a
rewrite from scratch, it hasn't much in common with the 2.6.18 code base.

> I wish the upstream kernel was able to do such magic, but i'm 
> afraid it is not.

It's no magic, it's alot of hard work.

cheers,
  Gerd