linux-kernel - Re: [PATCH v2] xen/block: Correctly define structures in public headers on ARM32 and ARM64

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Message-ID: <20131203180139.GG3734@phenom.dumpdata.com>
Date:	Tue, 3 Dec 2013 13:01:39 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	Julien Grall <julien.grall@...aro.org>,
	xen-devel@...ts.xenproject.org, patches@...aro.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Roger Pau Monne <roger.pau@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>
Subject: Re: [PATCH v2] xen/block: Correctly define structures in public
 headers on ARM32 and ARM64

On Tue, Dec 03, 2013 at 05:10:50PM +0000, David Vrabel wrote:
> On 03/12/13 15:40, Julien Grall wrote:
> > On ARM (32 bits and 64 bits), the double-word is 8-bytes aligned. This will
> > result on different structure from Xen and Linux repositories.
> > 
> > As Linux is using __packed__ attribute, it must have a 4-bytes padding before
> > each "id" field.
> > 
> > This change breaks guest block support with older kernel. IMHO, it's acceptable
> > because Xen on ARM is still on Tech Preview and the hypercall ABI is not yet
> > freezed.
> > 
> > Only one architecture (x86_32) doesn't have 64-bit ABI for the block interface.
> > Don't add padding if Linux is compiled for this architecture.
> 
> I'm now satisfied that this is the right thing to do.
> 
> Acked-by: David Vrabel <david.vrabel@...rix.com>

Before we go any further, I need testing confirmation that with this patch
can still run on x86 hardware the following combinations:

 32-bit guest on 64-bit dom0
 64-bit guest on 32-bit dom0

and with an 3.12 dom0

B/c I am not seeing that mentioned anywhere and I think that is creating
confusion with folks thinking it would break the x86-world (which it shouldn't).

> 
> David
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