From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1KQ78M-0007m1-Uu
	for qemu-devel@nongnu.org; Mon, 04 Aug 2008 16:58:27 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1KQ78L-0007iw-1g
	for qemu-devel@nongnu.org; Mon, 04 Aug 2008 16:58:26 -0400
Received: from [199.232.76.173] (port=38259 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1KQ78K-0007it-VB
	for qemu-devel@nongnu.org; Mon, 04 Aug 2008 16:58:24 -0400
Received: from py-out-1112.google.com ([64.233.166.181]:52269)
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <blauwirbel@gmail.com>) id 1KQ78K-0005jD-NB
	for qemu-devel@nongnu.org; Mon, 04 Aug 2008 16:58:24 -0400
Received: by py-out-1112.google.com with SMTP id p76so1178663pyb.10
	for <qemu-devel@nongnu.org>; Mon, 04 Aug 2008 13:58:24 -0700 (PDT)
Message-ID: <f43fc5580808041358m45ac50a8g950f5a36639d0a28@mail.gmail.com>
Date: Mon, 4 Aug 2008 23:58:23 +0300
From: "Blue Swirl" <blauwirbel@gmail.com>
Subject: Re: [Qemu-devel] [PATCH 5/7] xen: add block device backend driver.
In-Reply-To: <48975D9A.7070109@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
References: <1217865045-10722-1-git-send-email-kraxel@redhat.com>
	<1217865045-10722-6-git-send-email-kraxel@redhat.com>
	<f43fc5580808041026t49c8962fhe6ef926608e3db6c@mail.gmail.com>
	<48975D9A.7070109@redhat.com>
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: xen-devel@lists.xensource.com, qemu-devel@nongnu.org

On 8/4/08, Gerd Hoffmann <kraxel@redhat.com> wrote:
> Blue Swirl wrote:
>  > On 8/4/08, Gerd Hoffmann <kraxel@redhat.com> wrote:
>  >>  +/* i386 protocol version */
>  >>  +#pragma pack(push, 4)
>  >
>  > What's wrong with __attribute__(__aligned__)?
>
>
> That one is tricky because we must be binary compatible with xen.  And
>  the block driver protocol has a small design flaw:  It has a 64bit value
>   which is not aligned on a 64bit border.  This leads to different struct
>  layouts on i386 and x86_64 due to different alignment rules.  Unless you
>  force them into something else, like we do in that header file to deal
>  with it.  Which is needed to run 32bit guests on 64bit hosts.

Isn't this internal Xen protocol, so hopefully next version of Xen
could use more efficient structures?

>  > Would I need to add
>  > Sparc32 and Sparc64 versions some day?
>
>
> Not sure whenever the same 32/64bit ABI issue exists on sparc.  If so,
>  the code handling this on x86 should work for sparc too.

Well, I'd rather define a new, more architecturally neutral structure.