linux-kernel - Re: [PATCH 2/2] x86: replace BIO_VMERGE_BOUNDARY with BIOVEC_PHYS

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Date:	Mon, 27 Oct 2008 10:41:11 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	jeremy@...p.org, linux-kernel@...r.kernel.org, mingo@...e.hu
Subject: Re: [PATCH 2/2] x86: replace BIO_VMERGE_BOUNDARY with BIOVEC_PHYS_MERGEABLE

On Mon, Oct 27 2008, FUJITA Tomonori wrote:
> On Mon, 27 Oct 2008 20:18:44 +1100
> Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> 
> > FUJITA Tomonori wrote:
> > > I'm not familiar with what Xen does but why can't Xen just override
> > > BIOVEC_PHYS_MERGEABLE?
> > >
> > > Why does Xen need to hook BIOVEC_PHYS_MERGEABLE to the iommu_bio_merge
> > > parameter (as this patch does)? BIOVEC_PHYS_MERGEABLE and the
> > > iommu_bio_merge parameter are not related at all.
> > >   
> > 
> > No, it doesn't.  It was convenient to reuse that mechanism, but I can 
> > easily re-add something else (which would be more or less identical).
> 
> I still don't see how Xen needs something like the virtual merge
> (sounds that overriding BIOVEC_PHYS_MERGEABLE perfectly works for Xen)
> or why Xen needs a new boot parameter for it. The virtual merge just
> defines how IOMMUs should work.

Pretty much baffles me as well, xen should just need to do

#define BIOVEC_PHYS_MERGEABLE(vec1, vec2)       0

and that should be it.

-- 
Jens Axboe

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