linux-kernel - Re: A proposal

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Date:	Fri, 04 Aug 2006 18:29:14 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andrew Morton <akpm@...l.org>
Cc:	jeremy@...source.com, greg@...ah.com, zach@...are.com,
	linux-kernel@...r.kernel.org, torvalds@...l.org, hch@...radead.org,
	jlo@...are.com, xen-devel@...ts.xensource.com, simon@...source.com,
	ian.pratt@...source.com, jeremy@...p.org
Subject: Re: A proposal - binary

On Fri, 2006-08-04 at 00:21 -0700, Andrew Morton wrote:
> On Fri, 04 Aug 2006 17:04:59 +1000
> Rusty Russell <rusty@...tcorp.com.au> wrote:
> 
> > On Thu, 2006-08-03 at 22:53 -0700, Andrew Morton wrote:
> > > VMI is being proposed as an appropriate way to connect Linux to Xen.  If
> > > that is true then no other glue is needed.
> > 
> > Sorry, this is wrong.
> 
> It's actually 100% correct.

Err, yes.  I actually misrepresented VMI: the native implementation is
inline (ie. no blob is required for native).  Bad Rusty.

> > > > Yes, we could force native and Xen to work via VMI, but the result would
> > > > be less clear, less maintainable, and gratuitously different from
> > > > elsewhere in the kernel.
> > > 
> > > I suspect others would disagree with that.  We're at the stage of needing
> > > to see code to settle this.
> > 
> > Wrong again.
> 
> I was referring to the VMI-for-Xen code.

I know.  And I repeat, we don't have to see that part, to know that the
result is less clear, less maintainable and gratuitously different from
elsewhere in the kernel than the paravirt_ops approach.  We've seen
paravirt and the VMI parts of this already.

> >  We've *seen* the code for VMI, and fairly hairy.
> 
> I probably slept through that discussion - I don't recall that things were
> that bad.   Do you recall the Subject: or date?

Read the patches which Zach sent back in March, particularly:

[RFC, PATCH 3/24] i386 Vmi interface definition
[RFC, PATCH 4/24] i386 Vmi inline implementation
[RFC, PATCH 5/24] i386 Vmi code patching

If you want to hack on x86 arch code, you'd need to understand these.

Then to see the paravirt patches go to http://ozlabs.org/~rusty/paravirt
and look at the approximately-equivalent paravirt_ops patches:

	008-paravirt-structure.patch
	009-binary-patch.patch

There's nothing in those paravirt_ops patches which will surprise any
kernel hacker.  That's my entire point: maintainable, unsurprising,
clear.

Rusty.
-- 
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