From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:47778)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stephen@networkplumber.org>) id 1boyMO-00039z-Jz
	for qemu-devel@nongnu.org; Tue, 27 Sep 2016 15:48:13 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <stephen@networkplumber.org>) id 1boyMK-0004hM-M8
	for qemu-devel@nongnu.org; Tue, 27 Sep 2016 15:48:12 -0400
Received: from mail-pa0-x22d.google.com ([2607:f8b0:400e:c03::22d]:34973)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stephen@networkplumber.org>) id 1boyMK-0004fI-Dc
	for qemu-devel@nongnu.org; Tue, 27 Sep 2016 15:48:08 -0400
Received: by mail-pa0-x22d.google.com with SMTP id oz2so8586729pac.2
	for <qemu-devel@nongnu.org>; Tue, 27 Sep 2016 12:48:07 -0700 (PDT)
Date: Tue, 27 Sep 2016 12:48:18 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
Message-ID: <20160927124818.3a37c7c1@xeon-e3>
In-Reply-To: <20160927031158.GA25823@yliu-dev.sh.intel.com>
References: <1474872056-24665-1-git-send-email-yuanhan.liu@linux.intel.com>
	<1474872056-24665-2-git-send-email-yuanhan.liu@linux.intel.com>
	<CAOaVG17N_giiwPwWg-=8eHCCTGOcLHPxJBUxrx04YhLp2EjCdw@mail.gmail.com>
	<20160926221112-mutt-send-email-mst@kernel.org>
	<20160927031158.GA25823@yliu-dev.sh.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 1/2] vhost: enable any layout feature
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: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, Maxime Coquelin <maxime.coquelin@redhat.com>, dev@dpdk.org, qemu-devel@nongnu.org

On Tue, 27 Sep 2016 11:11:58 +0800
Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote:

> On Mon, Sep 26, 2016 at 10:24:55PM +0300, Michael S. Tsirkin wrote:
> > On Mon, Sep 26, 2016 at 11:01:58AM -0700, Stephen Hemminger wrote:  
> > > I assume that if using Version 1 that the bit will be ignored  
> 
> Yes, but I will just quote what you just said: what if the guest
> virtio device is a legacy device? I also gave my reasons in another
> email why I consistently set this flag:
> 
>   - we have to return all features we support to the guest.
>   
>     We don't know the guest is a modern or legacy device. That means
>     we should claim we support both: VERSION_1 and ANY_LAYOUT.
>   
>     Assume guest is a legacy device and we just set VERSION_1 (the current
>     case), ANY_LAYOUT will never be negotiated.
>   
>   - I'm following the way Linux kernel takes: it also set both features.

Agreed, just do what the Linux kernel does.