From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id 88BF52BE5 for ; Thu, 2 Feb 2017 18:16:46 +0100 (CET) Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DE6AAC057FAD; Thu, 2 Feb 2017 17:16:46 +0000 (UTC) Received: from [10.36.117.234] (ovpn-117-234.ams2.redhat.com [10.36.117.234]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id v12HGevr014133 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Thu, 2 Feb 2017 12:16:42 -0500 To: "Michael S. Tsirkin" , Laine Stump References: <20170201094304.GA3232@redhat.com> <20170201114119.GE3232@redhat.com> <20170202150621.GQ2915@redhat.com> <20170202190811-mutt-send-email-mst@kernel.org> Cc: "Daniel P. Berrange" , "dev@openvswitch.org" , Yuanhan Liu , Flavio Leitner , "dev@dpdk.org" , Michal Privoznik , Ciara Loftus , Kevin Traynor , Daniele Di Proietto , "libvir-list@redhat.com" , mark.b.kavanagh@intel.com From: Maxime Coquelin Message-ID: <7637e2f5-5002-a39c-ad39-a814cdd33145@redhat.com> Date: Thu, 2 Feb 2017 18:16:39 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 MIME-Version: 1.0 In-Reply-To: <20170202190811-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Thu, 02 Feb 2017 17:16:46 +0000 (UTC) Subject: Re: [dpdk-dev] [libvirt] [RFC] Vhost-user backends cross-version migration support X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 02 Feb 2017 17:16:46 -0000 On 02/02/2017 06:09 PM, Michael S. Tsirkin wrote: > On Thu, Feb 02, 2017 at 11:47:57AM -0500, Laine Stump wrote: >> On 02/02/2017 10:06 AM, Daniel P. Berrange wrote: >>> On Thu, Feb 02, 2017 at 03:14:01PM +0100, Maxime Coquelin wrote: >>>> >>>> On 02/01/2017 12:41 PM, Daniel P. Berrange wrote: >>>>> It depends where / how in OVS it needs to be set. The only stuff libvirt >>>>> does with OVS is to run 'add-port' and 'del-port' commands via the ovs >>>>> cli tool. >> >> (aside note: the code that exec's ovs-vsctl was written back when there was >> no standardized API for performing such operations. libvirt would prefer to >> not exec external programs though, and I've heard that OVS may now have an >> official API of some sort for doing things like this (maybe via netlink or >> dbus or something?) If that's the case, can someone point me in the right >> direction?) >> >>>>> We pass through arguments from the port profile stored in the >>>>> XML config. >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> eg those things in get passed as cli args to the 'add-port' >>>>> command. Soo if add-port needs this new version string, then we'd need >>>>> to add the version to the openvswitch virtualport XML. >>>>> >>>>> If the version is provided to OVS in a different command, then it would >>>>> probably be outside scope of libvirt. >>>> I think it would make sense to be a parameter of the add-port command. >>>> But it would be for vhost-user related add-port command, I didn't find >>>> where/if this is managed in libvirt XML. >>> For vhost-user, libvirt does not have any interaction with OVS at >>> all. If the thing that's using the vhost-user UNIX socket, in turn >>> connects to OVS, that's outside scope of libvirt. IOW, for vhost-user >>> OVS it seems like that job is for Nova / os-vif to solve. >> >> This brings up another tangentially related question I came up against last >> night - qemu now has an option to report the host's MTU to the guest for >> virtio and vhost-user interfaces, and Michal Privoznik recently pushed >> patches to set the MTU sent to the guest via an explicit in >> libvirt's interface config: >> >> https://bugzilla.redhat.com/1408701 >> >> But it would be much nicer if libvirt could learn the MTU of [that stuff at >> the other end of the unix socket] without requiring intervention in >> libvirt's config. For example, I'm just now testing patches for tap-based >> interfaces (connecting to Linux host bridges or OVS switches) that query the >> current MTU of the bridge and report that to qemu; this eliminates the >> burden of configuring each interface of each guest individually (and >> changing that config in all those places if someone ever wants to change the >> MTU of the bridge). >> >> As Dan says, though, libvirt's only interaction in the case of vhost-user is >> with the unix socket. Is there any way to learn what is the appropriate MTU >> from OVS in these cases? Or must Nova (or ovirt or some poor user) set that >> up in the libvirt config for every single interface? > > We could add commands for all kind of queries to the vhost-user > protocol. libvirt would have to learn the vhost-user protocol though. > Interested? > I think it could be possible to query the MTU value from the OVS DB using its JSON RPC-like API, but this is something I haven't tried. I guess it would need to resolve the ovs interface from the vhost-user socket path. Can people familiar with OVS confirm this is something possible? Regards, Maxime