From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57504) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e5LAR-00007E-2k for qemu-devel@nongnu.org; Thu, 19 Oct 2017 20:28:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1e5LAN-0007b1-Un for qemu-devel@nongnu.org; Thu, 19 Oct 2017 20:28:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43426) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1e5LAN-0007aV-Pj for qemu-devel@nongnu.org; Thu, 19 Oct 2017 20:27:59 -0400 Date: Fri, 20 Oct 2017 03:27:55 +0300 From: "Michael S. Tsirkin" Message-ID: <20171020032138-mutt-send-email-mst@kernel.org> References: <1508390650-19115-1-git-send-email-changpeng.liu@intel.com> <1508390650-19115-2-git-send-email-changpeng.liu@intel.com> <20171019183638-mutt-send-email-mst@kernel.org> <42aa8736-bc23-d66d-27de-dbaf83ea2f99@redhat.com> <20171019204305-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Changpeng Liu , qemu-devel@nongnu.org, stefanha@gmail.com, marcandre.lureau@redhat.com, felipe@nutanix.com, james.r.harris@intel.com On Thu, Oct 19, 2017 at 11:04:48PM +0200, Paolo Bonzini wrote: > On 19/10/2017 19:43, Michael S. Tsirkin wrote: > > On Thu, Oct 19, 2017 at 05:43:18PM +0200, Paolo Bonzini wrote: > >> On 19/10/2017 17:39, Michael S. Tsirkin wrote: > >>>> Add VHOST_USER_GET_CONFIG/VHOST_USER_SET_CONFIG messages which can be > >>>> used for live migration of vhost user devices, also vhost user devices > >>>> can benefit from the messages to get/set virtio config space from/to the > >>>> I/O target. For the purpose to support virtio config space change, > >>>> VHOST_USER_SET_CONFIG_FD message is added as the event notifier > >>>> in case virtio config space change in the I/O target. > >>>> > >>>> Signed-off-by: Changpeng Liu > >>> I don't much like it that config is getting passed through. > >>> > >>> IMO this makes managing things harder not easier. > >>> > >>> How about specific messages about specific parts of > >>> config space that you want to get from the backend? > >> > >> In the case of virtio-blk that would be all of it. Do you have a case > >> in mind where some part of the configuration space is owned by QEMU? > >> > >> Paolo > > > > Yes. seg_max > > The seg_max limit is established by whoever reads buffers from the vring > and passes them down to the lower layer. For vhost-blk that's the > device server, not QEMU. > > Paolo Good point. How about num_queues though? Also why is there SET_CONFIG? Does not look like blk uses it. And I wonder how do we do it for other devices. E.g. for net there's a bit in the middle of the config field that deals with migration. -- MST