From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:56879)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <paolo.bonzini@gmail.com>) id 1Wv0nb-0000DI-Ox
	for qemu-devel@nongnu.org; Thu, 12 Jun 2014 04:56:04 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <paolo.bonzini@gmail.com>) id 1Wv0nS-0003Ac-OL
	for qemu-devel@nongnu.org; Thu, 12 Jun 2014 04:55:55 -0400
Received: from mail-we0-x22f.google.com ([2a00:1450:400c:c03::22f]:60117)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <paolo.bonzini@gmail.com>) id 1Wv0nS-0003AW-Gk
	for qemu-devel@nongnu.org; Thu, 12 Jun 2014 04:55:46 -0400
Received: by mail-we0-f175.google.com with SMTP id k48so194728wev.6
	for <qemu-devel@nongnu.org>; Thu, 12 Jun 2014 01:55:45 -0700 (PDT)
Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
Message-ID: <53996B0E.4040808@redhat.com>
Date: Thu, 12 Jun 2014 10:55:42 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
MIME-Version: 1.0
References: <20140514154130.10746.1412.stgit@bahia.local>	<20140514154230.10746.56297.stgit@bahia.local>	<5384A8D2.8050104@redhat.com>
	<20140529111253.4ff55199@bahia.local>	<538708FA.4070309@redhat.com>
	<20140612094351.6295fd38@bahia.local>
In-Reply-To: <20140612094351.6295fd38@bahia.local>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH RFC 8/8] virtio: add endian-ambivalent
	support to VirtIODevice
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Greg Kurz <gkurz@linux.vnet.ibm.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, Anthony Liguori <aliguori@amazon.com>, Juan Quintela <quintela@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Alexander Graf <agraf@suse.de>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Amit Shah <amit.shah@redhat.com>, =?ISO-8859-1?Q?Andreas_F=E4rber?= <afaerber@suse.de>

Il 12/06/2014 09:43, Greg Kurz ha scritto:
> Since we know that 0 < max_nr_ports < 32,  is it acceptable to guess
> the correct endianness with a heuristic ?
>
> if (max_nr_ports > tswap32(s->config.max_nr_ports)) {
> 	max_nr_ports = bswap32(max_nr_ports);
> }
>
> if (max_nr_ports > tswap32(s->config.max_nr_ports)) {
> 	return -EINVAL;
> }

Yes, I guess it is acceptable.  So first you should fix the code to 
always serialize fields as big-endian, and then apply this little hack 
and virtio_tswap on top of the previous change.

Paolo