linux-kernel - Re: [Xen-devel] [PATCH RFC] xen-block: correctly define structures in public headers

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Message-ID: <alpine.DEB.2.02.1312041058130.7093@kaball.uk.xensource.com>
Date:	Wed, 4 Dec 2013 11:03:50 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Ian Campbell <Ian.Campbell@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Julien Grall <julien.grall@...aro.org>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Roger Pau Monne <roger.pau@...rix.com>
Subject: Re: [Xen-devel] [PATCH RFC] xen-block: correctly define structures
 in public headers

On Tue, 3 Dec 2013, Konrad Rzeszutek Wilk wrote:
> > > If Konrad and Boris agree that breaking the kernel's ABI in this way is
> > > acceptable in this specific case, I'll defer to them.
> > 
> > My opinion as Xen on ARM hypervisor maintainer is that this is the right
> > thing to do in this case.
> 
> Heh. If somebody can guarantee me that (by testing the right variants and
> mentioning this in the git commit) that this does not break x86, then
> I am fine.
> 
> And by 'break x86' I mean that this combination works:
>  32-bit domU on 64-bit dom0
>  64-bit domU on 32-bit dom0
> 
> And perhaps also the obvious:
>  64-bit domU on 64-bit dom0
>  32-bit domU on 32-bit dom0
> 
> Since the xen-blkback has its own version of the structs there is no
> need to change change newer and older version of it.
> 
> As long as that works I am OK sticking it in.
> 
> I think from the ARM perspective it is still in 'experimental' phase
> so anything goes to make it work under ARM.

To be honest I am unhappy about this, but I don't want to clutter even
more a code path already plagued by an ifdef infestation.

Even if the ARM port is experimental, I would prefer to retain
compatibility if it was possible to do so with a couple of lines fix.
Otherwise I would rather break ABI compatibility than introducing
another half a dozen ifdefs.
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