From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by dpdk.org (Postfix) with ESMTP id 04E5537B3 for ; Mon, 10 Oct 2016 05:02:43 +0200 (CEST) Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga101.jf.intel.com with ESMTP; 09 Oct 2016 20:02:42 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.31,470,1473145200"; d="scan'208";a="17944192" Received: from yliu-dev.sh.intel.com (HELO yliu-dev) ([10.239.67.162]) by orsmga005.jf.intel.com with ESMTP; 09 Oct 2016 20:02:41 -0700 Date: Mon, 10 Oct 2016 11:03:33 +0800 From: Yuanhan Liu To: "Michael S. Tsirkin" Cc: Stephen Hemminger , Maxime Coquelin , dev@dpdk.org, qemu-devel@nongnu.org Message-ID: <20161010030333.GU1597@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> <20160926221112-mutt-send-email-mst@kernel.org> <20160927031158.GA25823@yliu-dev.sh.intel.com> <20160927224935-mutt-send-email-mst@kernel.org> <20160928022848.GE1597@yliu-dev.sh.intel.com> <20161010014900-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161010014900-mutt-send-email-mst@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Subject: Re: [dpdk-dev] [PATCH 1/2] vhost: enable any layout feature X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 10 Oct 2016 03:02:44 -0000 On Mon, Oct 10, 2016 at 02:20:22AM +0300, Michael S. Tsirkin wrote: > On Wed, Sep 28, 2016 at 10:28:48AM +0800, Yuanhan Liu wrote: > > On Tue, Sep 27, 2016 at 10:56:40PM +0300, Michael S. Tsirkin wrote: > > > On Tue, Sep 27, 2016 at 11:11:58AM +0800, Yuanhan Liu 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. > > > > > > > > Maybe, we could unset ANY_LAYOUT when VERSION_1 is _negotiated_? > > > > > > > > The unset after negotiation I proposed turned out it won't work: the > > > > feature is already negotiated; unsetting it only in vhost side doesn't > > > > change anything. Besides, it may break the migration as Michael stated > > > > below. > > > > > > I think the reverse. Teach vhost user that for future machine types > > > only VERSION_1 implies ANY_LAYOUT. > > So I guess at this point, we can teach vhost-user in qemu > that version 1 implies any_layout but only for machine types > qemu 2.8 and up. It sets a bad precedent but oh well. It should work. --yliu