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

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Date:	Tue, 03 Dec 2013 11:11:59 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Ian Campbell" <Ian.Campbell@...rix.com>,
	"Roger Pau Monne" <roger.pau@...rix.com>
Cc:	"David Vrabel" <david.vrabel@...rix.com>,
	"Stefano Stabellini" <stefano.stabellini@...citrix.com>,
	"Julien Grall" <julien.grall@...aro.org>,
	<xen-devel@...ts.xenproject.org>,
	"BorisOstrovsky" <boris.ostrovsky@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH RFC] xen-block: correctly define
 structures in public headers

>>> On 03.12.13 at 12:05, Ian Campbell <Ian.Campbell@...rix.com> wrote:
> On Tue, 2013-12-03 at 11:57 +0100, Roger Pau Monne wrote:
>> Using __packed__ on the public interface is not correct, this
>> structures should be compiled using the native ABI, and __packed__
>> should only be used in the backend counterpart of those structures
>> (which needs to handle different ABIs).
>> 
>> This was even worse in the ARM case, where the Linux kernel was
>> incorrectly using the X86_32 protocol ABI. This patch fixes it, but
>> also breaks compatibility, so an ARM DomU kernel compiled with
>> this patch will fail to communicate with PV disk devices unless the
>> Dom0 also has this patch.
> 
> This is acceptable IMHO, the ARM ABI is clearly defined and previous
> kernels were simply buggy. The fact that front and backend were
> equivalently buggy and so it happened to work is not an excuse.

But afaics the change is not just to the ARM form of the ABI,
but to x86 (32- and 64-bit) too. And that clearly must not be
altered.

Jan

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